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70' Cruising Proa....Big Red Yacht


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On 1/17/2021 at 5:00 AM, harryproa said:

Russ (and anyone else who cares to do so), bring on the harryproa comments.

I'd rather you went away. I don't see the benefit to you of an ongoing public, lie-strewn war and it's embarrassing to me. Without you, Rob I wouldn't get the hairy eyeball on these forums. I'm not selling proas and I don't lie. I'm also generally helpful on the forums and I see them as a great tool. You see them as a way to conquer the world with proas. Everything that you post, whether its about your boats or mine is meant to drive sales of plans of your boats. Or maybe its just some weird vindictive urge you have.

My one page of thoughts on Harryproas should be posted somewhere else. I just don't know where.

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This thread has gone the way I thought it would. Rob is going to bash it over the head with his vindictive form of logic, but for what purpose? He's quoting things that I didn't write, some that were

It's happened one time in 10K miles of sailing Jzerro and this was due to an abrupt wind shift under a rain shower in the Gulf while sailing to Cuba.  I dropped the jib, lowered both rudders and put t

I'd rather you went away. I don't see the benefit to you of an ongoing public, lie-strewn war and it's embarrassing to me. Without you, Rob I wouldn't get the hairy eyeball on these forums. I'm not se

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On 1/17/2021 at 5:00 AM, harryproa said:

Snip

There is no "hate in this camp".

this is true, there is no hate involved in robs trolling, it's just business

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Dan,
We designed a 16'ter and licensed construction to a German builder in China.  I built a prototype first and it worked ok,
 was a cool thrill for my 6 year old daughter and a couple of mates who were maybe 50 kgs total, soaking wet.   The German guy built a few, then disappeared.  The best way to build one would be Intelligent Infusion, but the cost of plans to cover this would be excessive.  A better bet if you are trying to convince yourself you are still young, would be an E25 and blow the socks off all the non foilers on the Harbour.  If it is for the grand kids, then scaling it down would be simple, and could use a windsurfer rig.
 
Pil,
I don't expect to convince you to try anything that has not been done many times before,  although basing your data on 'the overwhelming majority of boat owners and designers" you'd be sailing a monohull.     However, I am curious as to why you continually post that you don't get proas, but won't enter into a discussion of why.  Seems a waste of your time. 
 
As for you 'convincing me of the pound for pound  benefits of cats and tris", I have done more than enough miles in both, including a Sydney Hobart in Verbatim (12m tri) and several (5 since my first build) decades building, racing, capsizing, designing, delivering and living on cats to know that they can be  improved, particularly for cruising.  
 
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2 hours ago, DtM said:

Did Andrew Rogers finish the build of the E25 and what has happened to it if he did?

No idea, last I heard he was busy with a 60' cat.  The E25 is for him and his kid to sail, so it is not high priority, nor is he likely to sell it.  If he did, you would be #3 (that I know of) on the waiting list.  

If you want a project boat, I have to sell my Elementarry http://harryproa.com/?p=1753  by the middle of the year, prior to taking 3 years off to demonstrate the cargo proa through the Pacific.  Needs a paint job, rudders and rigs, and a new arm on the trailer.  Foam/carbon hulls, telescoping beams, una or schooner (or kite) rig.  

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1 hour ago, Zonker said:

The proa is not as fast as the AC boat. Its sail trim is suspect too.

More seriously why is it reefed so much? It does not appear to be very windy.

That is the (in)famous Aroha that (used to I suspect, given recent events) be raised every time I posted about Harrys.  The 12m Harryproa that broke a ring frame while sailing overloaded in a gale across the Tasman 15 years ago, but still completed the journey.  

It was then used as a day sailor for several years until the original owner died and last year was bought as a fixer upper.  Looks like that is now done.  I have emailed the owners for an update.  

Definitely not a match for the AC boats, but a great comparison of speed and size.    Looking at the white caps and the sheltered conditions, the wind would be 20 odd knots.  Not enough for a reef usually, but it is probably one of his first sails since the refit, so caution is required.  Or, maybe he had issues as it is sailing under a single sail at 11.43.

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9 minutes ago, KONeill said:

Jesus, $27k NZ is what? $20k US? I'd snap that up in a heartbeat if it was anywhere near me. Wow.

If it sells, it will be for less than the asking price.  There are reasons for that...  It looks beaten up and in need of work:

https://www.trademe.co.nz/a/motors/boats-marine/yachts/multihull/listing/2974613048

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5 minutes ago, KONeill said:

Of course it is for that price, but come on man.

You'd have to pay me that much to take it off your hands, and I'd haul it straight to the dump.  Nothing but a list of headaches, several owners unhappy with it.

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18 hours ago, ProaSailor said:

You'd have to pay me that much to take it off your hands, and I'd haul it straight to the dump.  Nothing but a list of headaches, several owners unhappy with it.

If that's all you can think of to do with all those parts I'm sad for you.

Look, if it's way overweight I'd just walk away. If there's a bunch of water in the core or any serious damage, walk away. Aside from that? He's asking $20k US, probably take, what? $15k? Come on.

I'd no doubt fiddle with it a bit. I've been fiddling with proa design for twenty years, I couldn't stop myself. I don't really like wheel steering, and I like the flipping rudders I have on my proa a lot. I'd put a pair of those on it with tillers and get rid of the wheels. Maybe a leeboard on the windward hull? Who knows. Have to sail it a bit to see.

But as a basic platform for not much money, come on. That's an amazing amount of boat there. From the HP web site the build looks like it was a decent setup.

I realize it's not your kind of boat, but man. As a cheap light cruiser, I'd snap that up. Then I'd probably be in Sidecar's DMs asking for details on what he did with his boat, kind of a similar configuration and it looks like it works pretty good :)

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42 minutes ago, KONeill said:

If that's all you can think of to do with all those parts I'm sad for you.

Look, if it's way overweight I'd just walk away. If there's a bunch of water in the core or any serious damage, walk away. Aside from that? He's asking $20k US, probably take, what? $15k? Come on.

I'd no doubt fiddle with it a bit. I've been fiddling with proa design for twenty years, I couldn't stop myself. I don't really like wheel steering, and I like the flipping rudders I have on my proa a lot. I'd put a pair of those on it with tillers and get rid of the wheels. Maybe a leeboard on the windward hull? Who knows. Have to sail it a bit to see.

But as a basic platform for not much money, come on. That's an amazing amount of boat there. From the HP web site the build looks like it was a decent setup.

I realize it's not your kind of boat, but man. As a cheap light cruiser, I'd snap that up. Then I'd probably be in Sidecar's DMs asking for details on what he did with his boat, kind of a similar configuration and it looks like it works pretty good :)

It saddens me that you consider this worth your money and effort.   But talk is cheap.
It is not at all "a similar configuration" to Sidecar, which is a Pacific proa.

Look at the videos as I did before making my comment:

https://www.youtube.com/watch?v=ROXdDKJbqkU

https://www.youtube.com/watch?v=hXSGfd2J9Q8

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I dunno, I can see the appeal but it sounds like a few owners have tried just what you describe and have given up after spending time and money on it, I really think the only way you'd ever make a harryproa work really well is to put a second mast on the windward hull and make it a biplane schooner, or run backstays out to the ama and use sidecar's or Robert Biegler's staysails.

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9 minutes ago, ProaSailor said:

It saddens me that you consider this worth your money and effort.   It is not at all "a similar configuration" to Sidecar, which is a Pacific proa.

Look at the videos as I did before making my comment:

https://www.youtube.com/watch?v=ROXdDKJbqkU

https://www.youtube.com/watch?v=hXSGfd2J9Q8

Oh wait, Sidecar's not WTW, is it? Never mind.

I've seen the videos. It's someone sailing the boat the wrong way round, and getting there fine anyway. I don't think they're making the point you think they are.

A WTW proa doesn't seem like a doomed idea to me; it's just an Atlantic with the rig moved over. Newick made an Atlantic work, I think it's certainly possible to make a WTW proa with the rig on the lee hull work. You probably don't, we're not going to settle it here. And I'm not going to buy the boat, it's too far away. I was just shocked at the price.

Anyway, I'm done going on about it. Have a nice weekend, what's left of it.

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5 minutes ago, TwoBirds said:

I dunno, I can see the appeal but it sounds like a few owners have tried just what you describe and have given up after spending time and money on it, I really think the only way you'd ever make a harryproa work really well is to put a second mast on the windward hull and make it a biplane schooner, or run backstays out to the ama and use sidecar's or Robert Biegler's staysails.

I don't think either of those is necessary. I might consider a windward stay if the mast top is really flexing off; that's what my boat was doing. I had masts that were strong enough to not break but were way too flexible. I put a windward stay on them and it transformed the boat. But you can still let the boom go all the way forward if you're running downwind, so the safety aspect isn't affected.

I have no idea how much time or effort people have put into it, I'm just looking at it and thinking that it's not that radical a concept. It's like an Atlantic proa with the rig moved. There's no reason it can't work. Maybe the rudders are not great, I don't know. Maybe it doesn't have enough lateral surface in the water to go to windward well. Maybe the forestay sags, one balestron owner told me that he had a hell of a time with forestay tension.

You can fix all that stuff if you like fiddling with things and you don't give up. If it's not too heavy and it's not waterlogged I'd love it as a project.

But it's half a world away and I'm supposed to be grading :)

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Looking a he vids of Aroha; its not pushed at all - bu i seems like he water is coming high up on the bow of the ama -  and the main hull is very plumb in the water. Really struggle to se the genius here. 

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Here’s a 3 day delivery trip. Seems to sail... ok. 
Bit of a junk show on deck, but it’s only 20g. 

 

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5 minutes ago, Zonker said:

The lee hull has so little buoyancy and vertical depth. I can see in any sort of waves it would wave pierce so much that the beam would be banging into waves.

I can assure you, there is only one way to find out.

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What with all the confusion on pacific vs atlantic, weight to windward / buoyancy arrangements and so forth.  I suggest a symmetrical proa:  2 hulls the same, so it doesn't matter which ends up to windward.  We could then put the mast in between them, so it may be easily stayed.  So hulls and foils and rigs really only work well if they are going forwards, allows the front of them to be different to the back, as the front does different things to the back, so I suggest a different kind of shunt, where instead of putting the boat beam on, and swapping rig and boards around, we just turn the whole boat through the wind, and maybe just change sides ourself?

Crazy ideas i'm sure, just chucking it out there.

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7 hours ago, maxstaylock said:

What with all the confusion on pacific vs atlantic, weight to windward / buoyancy arrangements and so forth.  I suggest a symmetrical proa:  2 hulls the same, so it doesn't matter which ends up to windward.  We could then put the mast in between them, so it may be easily stayed.  So hulls and foils and rigs really only work well if they are going forwards, allows the front of them to be different to the back, as the front does different things to the back, so I suggest a different kind of shunt, where instead of putting the boat beam on, and swapping rig and boards around, we just turn the whole boat through the wind, and maybe just change sides ourself?

Crazy ideas i'm sure, just chucking it out there.

FIFY

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If one wants to compare apples and bananas, WTW proas seem quite limited to me. The weather hull is like a 2 times fully ballasted float of a pacific proa. It's quite easy to imagine the slamming and the beams suffering in a strong sea. Under-canvassed and on a flat sea, that might work.

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1 hour ago, triple jim said:

If one wants to compare apples and bananas, WTW proas seem quite limited to me. The weather hull is like a 2 times fully ballasted float of a pacific proa. It's quite easy to imagine the slamming and the beams suffering in a strong sea. Under-canvassed and on a flat sea, that might work.

actually weight to windward  works really well with an atlantic proa because the rigs COE  operates between the hulls much like a catamaran and the hulls have about the same hullspeed.

the problem with moving weight to windward in a pacific proa is that you get a lot of drag from the ama, it gets worse at speed because the hullspeed of the lee hull is higher than the the hullspeed of the short wide windward hull, it gets even worse when going DDW as the center of effort of the rig moves out to leeward.

Now you can balance that all out most of the time, the long leeward hull resists rounding up and the rudders could be setup so they constantly exert lift to keep the boat from rounding up, but not all the time, the problem I see with this hullform is that sometimes the main hull can't resist the tendency to round up, like at the crest of a wave where one or both ends of the leeward hull are sticking out of the front and back of the wave, maybe one or both rudders as well, right at a time when wave drag on the windward hull is at it's highest.

Strictly armchair sailing.

as Ryan says, there's only one way to know, which is why I'd like to hear from the people who sail the boats, not just from the guy who makes money off of them.

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Maxstaylock is on to something there. If however, one were to ask, "what is the most efficient approach for Sailing Anarchy?" the answer would clearly be to race America's Cup on proas. Then you would be able to combine all the proa arguments with the America's Cup arguments in one place.

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It would give the crew lots to do. You couldn't use symmetric foils so every shunt you'd have to raise one or two foils in the A direction and lower them in the B direction. Do the same for rudders. 

Then roll/unroll jib on either end. Better add running backstays to control mast bend. That's another crew member.

The union will love it.

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2 hours ago, TwoBirds said:

you can balance that all out most of the time, the long leeward hull resists rounding up and the rudders could be setup so they constantly exert lift to keep the boat from rounding up, but not all the time, the problem I see with this hullform is that sometimes the main hull can't resist the tendency to round up,

This..... But wait..... There’s more!

Fag packet, if you analyse the profile drawings, and crunch a few numbers, like, upwind SA/ Lateral Resistance Area, including all “working” foils at any given time,  you get:

Madness: 7.53, Jester 2: 9.20, Sidecar (now): 11.19, SeaCart 30: 12.15, Bucket List: 18.4. SeaCart 30 with Bucket List’s SA is 9.14. I have included some leeward ama immersion in the SeaCart numbers. Sidecar originally, without centreboard, was 12.95.

The average hull(s) LRA contribution to total LRA of all the others is 84%. Bucket List is 64%.

Hull depths. The average LWL/D of all the others is 25. Bucket List is 120. Sidecar is 32, which pulled the average up.

Rocker: All the others have significant rocker, of remarkably similar form, especially if you mirror the front half of the SeaCart. Ditto most Farrier designs. Bucket List has zero, with some token rocker at the ends.

So the rudders only “balance” approach means they work harder all the time and can/do stall out much more often. Especially at slow speeds, which happen every time you shunt. More centrally located rudders only make it worse.

On the water, I think Sidecar still needs a little more LR in some situations, and the numbers also suggest it. The ama contribution appears to be deficient and will be addressed next winter.

 

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7 hours ago, Sidecar said:

This..... But wait..... There’s more!

Fag packet, if you analyse the profile drawings, and crunch a few numbers, like, upwind SA/ Lateral Resistance Area, including all “working” foils at any given time,  you get:

Madness: 7.53, Jester 2: 9.20, Sidecar (now): 11.19, SeaCart 30: 12.15, Bucket List: 12.43. SeaCart 30 with Bucket List’s SA is 9.14. I have included some leeward ama immersion in the SeaCart numbers. Sidecar originally, without centreboard, was 12.95.

The average hull(s) LRA contribution to total LRA of all the others is 84%. Bucket List is 74%.

Hull depths. The average LWL/D of all the others is 25. Bucket List is 60. Sidecar is 32, which pulled the average up.

Rocker: All the others have significant rocker, of remarkably similar form, especially if you mirror the front half of the SeaCart. Ditto most Farrier designs. Bucket List has zero, with some token rocker at the ends.

So the rudders only “balance” approach means they work harder all the time and can/do stall out much more often. Especially at slow speeds, which happen every time you shunt. More centrally located rudders only make it worse.

On the water, I think Sidecar still needs a little more LR in some situations, and the numbers also suggest it. The ama contribution appears to be deficient and will be addressed next winter.

Apologies to Bucket List, I was crunching the numbers to add in hull windage, and found an error. Adjusted figures above are in bold italics.....The differences are now far less, but still significant.

Back to hull windage.....if you add above LWL hull(s) profile areas to the sail areas (because the rudders still have to deal with it)  the SA/LRA numbers become:

Madness: 9.76, Jester 2: 11.3, Sidecar (now): 13.93, SeaCart 30: 16.86, Bucket List: 16.65. SeaCart 30 with Bucket List’s SA is 13.74.

Windage numbers do not include beam and mast/rig windage, but they would be a significant extra in the case of the SeaCart and Bucket List. FWIW, SeaCart has more than double the hull(s) windage of Sidecar and the other small proas, excluding extra beam and sail/rig windage.

 

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10 hours ago, TwoBirds said:

actually weight to windward  works really well with an atlantic proa because the rigs COE  operates between the hulls much like a catamaran and the hulls have about the same hullspeed. 

the problem with moving weight to windward in a pacific proa is that you get a lot of drag from the ama, it gets worse at speed because the hullspeed of the lee hull is higher than the the hullspeed of the short wide windward hull, it gets even worse when going DDW as the center of effort of the rig moves out to leeward.

Now you can balance that all out most of the time, the long leeward hull resists rounding up and the rudders could be setup so they constantly exert lift to keep the boat from rounding up, but not all the time, the problem I see with this hullform is that sometimes the main hull can't resist the tendency to round up, like at the crest of a wave where one or both ends of the leeward hull are sticking out of the front and back of the wave, maybe one or both rudders as well, right at a time when wave drag on the windward hull is at it's highest.

Strictly armchair sailing.

as Ryan says, there's only one way to know, which is why I'd like to hear from the people who sail the boats, not just from the guy who makes money off of them.

My mistake as WTW proas can be Atlantic ! I was thinking of WTW pacific proas so and then we agree.

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2 hours ago, Sidecar said:

Apologies to Bucket List, I was crunching the numbers to add in hull windage, and found an error. Adjusted figures above are in bold italics.....The differences are now far less, but still significant.

Back to hull windage.....if you add above LWL hull(s) profile areas to the sail areas (because the rudders still have to deal with it)  the SA/LRA numbers become:

Madness: 9.76, Jester 2: 11.3, Sidecar (now): 13.93, SeaCart 30: 16.86, Bucket List: 16.65. SeaCart 30 with Bucket List’s SA is 13.74.

Windage numbers do not include beam and mast/rig windage, but they would be a significant extra in the case of the SeaCart and Bucket List. FWIW, SeaCart has more than double the hull(s) windage of Sidecar and the other small proas, excluding extra beam and sail/rig windage.

 

So - what happens in an upwind course with some tacks/shunts? Is it numbers for the SC30 on one hull? 

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4 hours ago, triple jim said:

My mistake as WTW proas can be Atlantic ! I was thinking of WTW pacific proas so and then we agree.

There is no such thing as a WTW Pacific proa.

The proa terms WTW (Weight To Windward) and WTL (Weight To Leeward) imply more than 50% displacement on one hull or the other, at rest.  It's the only thing that counts.  Length of hulls and location of sails or accommodation has nothing to do with it.

15 hours ago, TwoBirds said:

actually weight to windward  works really well with an atlantic proa because the rigs COE  operates between the hulls much like a catamaran and the hulls have about the same hullspeed.

Rig/sail placement has nothing to do with it.

Rig Placement and Heeling Load
by Tom Speer
http://pacificproa.com/rig_placement.html

rig_placement.gif.21a31b268153e9ee724ccdbc669070a0.gif
diagram by Joseph Oster based on diagram by Mal Smith

Hull length and shape does matter, which I guess is what you mean by "hull speed", though that term doesn't mean much with long narrow hulls.

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5 hours ago, SeaGul said:

So - what happens in an upwind course with some tacks/shunts? Is it numbers for the SC30 on one hull? 

No.

But the numbers would be roughly the same, because the LWL of both ama and Vaka are pretty much the same, and flying (and exposing) the main hull is roughly counteracted by a similar increased immersion (and decreased exposure) of the leeward ama.

The point was that there is a balance and leeway limit on what you can ask foils and particularly rudders to do. The SeaCart was only included as a global reference because we know it works well. It also is an approximate indicator of the extra windage associated with trimarans relative to similar sized proas. At speeds a lot faster than 4 KSB’s, it starts to count....

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1 hour ago, ProaSailor said:

Rig/sail placement has nothing to do with it.

It does in terms of balance.

A boat with a rig whose CE  is to windward of CR laterally will have inherent lee helm, and a boat with a rig whose CE is to leeward of it will have weather helm. A WTW proa has a lateral CR position 50% of c/c beam geometrically, and more in reality because of the extra drag of the short windward ama. A pacific Proa has a lateral CR closer to 20%., so less inherent weather helm as the rig CE in both cases is somewhere the leeward hull c/l.

Think of push steering a trailer. Push in the middle between the wheels, it goes straight, because the CR is in the middle. If the weather tyre is flat, or you push elsewhere?

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  • 4 weeks later...
On 2/15/2021 at 5:48 PM, SeaGul said:

Looking a he vids of Aroha; its not pushed at all - bu i seems like he water is coming high up on the bow of the ama -  and the main hull is very plumb in the water. Really struggle to se the genius here. 

Agreed.  The boat was designed to weigh 800 kgs, with 800 kgs payload.  It was sailed across the Tasman with approx 1,100 kgs of payload.   

According to the crane scales, it was 1,800 kgs before the current owner and his gear went aboard.  He is looking at what he can remove.    

Kevin,

I asked him if he would put Aroha in a container.  He replied he will see if it fits.  

Sidecar,

If you quote Bucket List ratios, could you please also quote the numbers they are based on.  Otherwise, the ratios are meaningless.  ta.

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12 hours ago, harryproa said:

The boat was designed to weigh 800 kgs, with 800 kgs payload.  It was sailed across the Tasman with approx 1,100 kgs of payload.   

According to the crane scales, it was 1,800 kgs before the current owner and his gear went aboard.  He is looking at what he can remove.  

So designed to weigh 800 kg but as-built 1800 kg? This may be a record...

Did you do a detailed weight estimate before hand? 800 kg seems incredibly light for a single 9m fat windward hull, much less adding the weight of the rig/leeward hull/beams/motor etc. etc.

 

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17 minutes ago, Zonker said:

So designed to weigh 800 kg but as-built 1800 kg? This may be a record...

Did you do a detailed weight estimate before hand? 800 kg seems incredibly light for a single 9m fat windward hull, much less adding the weight of the rig/12m leeward hull/beams/motor etc. etc.

 

Fixed.

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Yeah a F24 trimaran is 818 kg which was the closest I could figure out that has sort of similar accommodation. But a lot less boat overall.

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30 minutes ago, Zonker said:

Yeah a F24 trimaran is 818 kg which was the closest I could figure out that has sort of similar accommodation. But a lot less boat overall.

Sidecar 9.5 metres LOA ~970kg in OMR trim was home built in plank Paulownia (ie less glue, snots and bog), which is lighter than cedar, and I sweated blood keeping girths, weight and windage down whilst keeping accommodation volume up. Sidecar’s ama is tiny by comparison, but does have carbon spars...

And yes, I did a detailed weight estimate beforehand.

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On 12/29/2020 at 8:29 AM, TwoBirds said:

ever notice that if you were to chop about a third off the forward end of a crabclaw the remainder would essentially be a lug sail?

Sure have! I have seen this observation made elsewhere too.  its part of the reason I just had (2) 75sqft balanced lugs made for my raidboat proa build (yay schooner) Im beginning work on the hulls this week now that my garage has some oh-so-lovely space again. I see the lugs being easier to reef, shorter lighter spars, and plenty powerful and weatherly enough for me.   Ive seen LOTS of schemes to reef a lateen or crabclaw (1 spar or 2?)  but none seem to be the solution for me.

 Im really trying for freestanding masts, but the advantages I see dont seem to outweigh a comparatively smaller aluminum tube with 1/8" dyneema stays to the ama.  

 Im gunning for the Everglades Challenge in the next few years so well see.   I am reading with gusto here on the SA forum, boatdesign.net, etc about proas and sail rigs and the multitude of advantages and disadvantages.  Lots of passion, lots of experience, lots of successes and failures, lots interesting boats, and WAY too much animosity from history I clearly dont fully understand.  

For now Ill STFU and keep lurking to glean the best ideas I can find, build my boat, sail him to the point of crashing, and then the 180 proof will be in the pudding.  See yall on the Ft Desoto Beach sometime.

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On 3/15/2021 at 9:49 AM, Zonker said:

So designed to weigh 800 kg but as-built 1800 kg? This may be a record...

Designed to weigh 800, and carry a further 800.  Weighed 1,800 before the owner arrived for the weekend sail in the video.   No idea what it weighed when launched as I was not there and I don't think they used a crane.  The cover over the cockpit was not part of the original.  

On 3/15/2021 at 9:49 AM, Zonker said:

Did you do a detailed weight estimate before hand? 800 kg seems incredibly light for a single 9m fat windward hull, much less adding the weight of the rig/leeward hull/beams/motor etc. etc.

Of course.  And based on the other Harryproasbuilt at the time, it was comprehensive.  This 15m/50'ter was spot on at a tad over 2 tonnes. A cruising version, ready to cruise was 3 and a bit tonnes.   Shows what can be achieved when you run the design spiral down instead of up.  1096458594_Blinddatelaunchpic.jpg.454666ac4e3df1174fa70460c10583fd.jpg

To see what happens when you push the spiral hard:  https://www.facebook.com/Harryproa/?ref=page_internal for some actual weights and some estimates on the 24m/80' cargo proa.  

Or this home built (on an island north of the Arctic Circle) 20m/65'ter which is on target for well under 4 tonnes, ready to sail according to finished weights of the hulls and beams http://harryproa.com/?p=726 and a 220 line spreadsheet. 896625427_hjfljyg-3.png.afffb187181c9981a4b276e00c3aba25.png   Or this 60'ter, also home built, which weighed 4 tonnes at launch.

18m_melbourne-4-e1443362091414.thumb.jpg.79f3bc87b6a1c32577d9a86e5bf6952b.jpg

 

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did anyone else notice in the video of the HarryProa delivery voyage that the proa was being sailed in the weight to leeward style? As opposed to the intended weight to windward style. I mean the main hull (the fat hull) was being pushed slightly down as opposed to how Atlantic Proas are 'meant' to be sailed where the accommodation is to windward and acts as a counterweight

A similar flexible concept is used in Mozambique, where the shunting canoes, will often just tack if the weather is mild. I have also seen this on videos of canoes of Anuta Island, Solomon islands, where they are meant to shunt, but sometimes they cant be bothered and they tack if weather is mild, saves the complications of having to move the mast over to the new bow.

 

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  • 2 weeks later...

I have been looking into proas for several years now and don't necessarily lean one way or the other. I have exactly 0 investment in any perspective that has been posted here so far and hold nothing against anyone. Everyone is 110% entitled to their own opinion. Proas are and will always be niche boats. They have many compromises that make them unsuited for mass market production and to be honest, I prefer it that way. I think many of you do as well. I am not a poser, but I like to think that if I moor up in a marina in one, someone there will remember my boat and not just pass it over in their mind like they would with a Lagoon or a Bavaria. I have always like the oddities and will go out of my way to track them down, so obviously proas are very appealing to me.

With that out of the way I can actually present my thoughts and opinions. As has been previously stated there are advantages and disadvantages to both designs. The Harrys tend to be a bit more modern in their design language than others (although I must say that Sidecar is absolutely gorgeous with those big windows, clean lines, and those bows...) but still suffer from their UFO saucer-looking bridge deck saloons that look very out of place (especially on the old ones. shudders). 

I have some 3D design experience and access to software so I have begun the process of making preliminary renderings for my "dream proa" in SolidWorks. It will have a focus on cruising, but no excessively heavy luxuries (this is necessary especially in the windward hull as I will explain shortly) When completed it should be nearly 60' in length with a 35' or 40' windward hull. I plan to follow some of the Harry design language with a windward salon and cabins but with a few key differences. The wetted surfaces of the hulls will have length/beam ratios that are very similar. This will lead to a windward hull that is very narrow to compensate it will be flared quite aggressively just above the waterline to preserve interior volume to a certain degree. The hulls will have some shape and rocker to help keep my sanity intact. Plus, big flat bricks are ugly. Yes it will have a freestanding schooner rig, although likely with more traditional booms. I don't like wishbones very much. 

Windward Hull: This hull will host two very sparse transverse cabins separated two head compartments which would likely have composting toilets to save complexity and weight (plus I've had some very bad experiences with holding tanks). This is very similar to the C60 Harry. The windward hull will have a deep draft to help add some load capacity.

Saloon: This is planned to be also very similar in layout to the C60.  Haven't settled on a coachroof design yet but it will likely resemble the EX40.

Bridge Deck: This is where things start to get interesting. There will be no massive catamaran tender and I have no illusions about the layout of the Harry cockpit as it would be absolutely unlivable for me on an extended passage. I'll have to get back to you on this one when I do the bridge deck in SW. I plan to have the rest of the deck relatively open. The tender will be a traditional affair and will rest in a cradle on deck. It will be lifted over the lee hull and deposited in the water by one of the booms. Much of the tankage will be located on the leeward side of the bridge deck so as to reduce weight to windward.

Lee Hull: This is planned to have far more accommodation than the C60 or any other Harry for that matter. It too will be flared aggressively, have a smaller raised cabin top with generous windows, and have two transverse cabins (or one plus a workshop/storage area) also separated by head compartments. These cabins might even have separate shower stalls if I can shoehorn them in. This is fundamentally a cruising boat that would likely be chartered as well so accommodation and comfort count here. To keep some more weight out of the windward hull, I plan for any tankage not located between the transverse bunks on the bridge deck to be located beneath the cabin sole here. These cabins can be fitted out a little nicer than those in the windward hull because the volume is here for it. 

Mechanical: There is a lot to unpack here and I will not get into it very much because I have not decided. I'd love some kick up rudders on the hull sides but those present their own challenges and don't look very nice. Trunk rudders or barrel rudders are the most likely options if I don't want to delve into bi-directional foils. Sudden changes in depth are an expected part of sailing and you should have done your homework better (coming from a long-time keelboat sailor who is used to having a 6 foot lead fin to deal with). I would still like them to be able to retract fully however. As mentioned the rig will be a free-standing schooner rig with proper booms if I can help it. As for auxiliary, I'd love a retractable propulsion unit but fear I'll be settling for an outboard on a sled. 

In conclusion, I have a lot of ideas and opinions, as do we all. Having decided on what I want, I have just begin the design process. I'll leave an early rendering of the hull shapes in SolidWorks here while I start on the superstructure. The render doesn't like to show depth very well so it kind of undersells the hull flare from this angle. 

Early Proa Hull Renders.PNG

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Interesting first post...

 

Welcome to the zoo.

 

Nothing you said seemed outrageously out of wack to me, but I am sure others will chime in...

Just 2 small comments:

  • you state several times that you do not want to put too much weight to windward: what do you expect the weight distribution to be between the big hull and the small hull?
  • Your 3D model makes to a large extend the small hull look like the baby of the big hull, which may be pleasing to the eye. Or maybe it is the 3D rendering that is fooling me. In any case, you should consider that you do not necessarily need the same keel line sweep between the 2 hulls. The big hull will always be firmly in the water, with always steady direction (proas don't tack or jibe with 90° change of direction), so a flatter keel line makes sense; it can also help (to some extend) reduce hobby-horsing. The small hull will need to have minimum drag at low speed and the ability to gently and gradually "go up and down". I do not mean lifting the hull out of the water; not fun for too long on a cruiser; but wave action and wind strength variations will make the windward hull lose some of its displacement and then go back down. If you do not want too much slamming onto the water, a more pronounced curved keel line makes sense...

 

My 2 cents.

 

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21 minutes ago, Laurent said:

Interesting first post...

 

Welcome to the zoo.

 

Nothing you said seemed outrageously out of wack to me, but I am sure others will chime in...

Just 2 small comments:

  • you state several times that you do not want to put too much weight to windward: what do you expect the weight distribution to be between the big hull and the small hull?
  • Your 3D model makes to a large extend the small hull look like the baby of the big hull, which may be pleasing to the eye. Or maybe it is the 3D rendering that is fooling me. In any case, you should consider that you do not necessarily need the same keel line sweep between the 2 hulls. The big hull will always be firmly in the water, with always steady direction (proas don't tack or jibe with 90° change of direction), so a flatter keel line makes sense; it can also help (to some extend) reduce hobby-horsing. The small hull will need to have minimum drag at low speed and the ability to gently and gradually "go up and down". I do not mean lifting the hull out of the water; not fun for too long on a cruiser; but wave action and wind strength variations will make the windward hull lose some of its displacement and then go back down. If you do not want too much slamming onto the water, a more pronounced curved keel line makes sense...

 

My 2 cents.

 

I appreciate the response Laurent and thanks for the welcome. Long-time spectator, first time actually participating. You make very valid points and I won't dispute them as I have very little in the way of actual yacht design experience. While the render does little to help the case, I am not a naval architect and so the underwater portion is not my forte. I don't usually pay it much attention when I dabble for fun and rest assured that if I ever go and actually follow through on anything at all, I will seek the assistance of a professional so that I don't become the topic of someone's argument against proas.

As for the weight, we will need to see how the saloon falls but I do expect the majority to fall in the longer leeward hull, especially with full tanks and provisions. Dry, it might fall closer to even distribution but I still expect it to favor the longer hull slightly. 

On the subject of a deeper keel line to windward, that might also help with my other problem which is that when I provide the windward hull with livable headroom (barely standing in the heads) the proportions are somewhat off and it starts looking like a shapeless brick again. Even an extra few inches would help this a lot and, since there will be no tankage or really anything beneath the cabin sole here, I can take full advantage of it. I have so little work into the hulls at this point (maybe an hour total to figure out all of the dimensions and then CAD them) that I can make radical changes and even start over without hesitation.

11 minutes ago, harryproa said:

Sounds feasible.  Anything I can help with let me know.  

There are a couple of Harrys being built in the PNW.  If you want to get in touch with them, and get feedback from another source, join the Harryproa chat group at https://groups.io/g/HarryProa/topics

I've taken a look around and might join the fun. Was unaware that there were any Harrys in my neck of the woods under construction so might have to look into that. The proa community is quite small, a fact of which we are all clearly aware, so having one so far from their home down south might be an opportunity.

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  • 2 weeks later...

Very cool design goals. 
I’ve seen a dink flying around 10 feet off the deck when the norther swung into the crappy anchorage right off the beach in Cabo. The boat was rolling side to since the waves preceded the wind. It was really spectacular watching the dink, lifted by a halyard, bounce from shroud to forestay. Premix is more interesting to clean up than straight gas, it turns out. But anyway, I’d lift the dink on davits or anything besides lifting it way up and over. 
 

I assume the leeward hull is flat on the leeward side, as the Polynesians figured out when Pyramids were young?  Sure would be cool to see someone simulate that. 

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Hello proa fellows! I am new to this forum, being more of a trimaran guy myself, but I just came across an unfinished, all parts complete, Harryproa 40 here in Maine, so I wanted to flag it here. Here's what I know per email from the owner: 

Thank you for your interest. I have attached two pictures of the trailer, and a link to 32 additional photos of the proa. 
 
 
This particular harryproa is unique in that it is the first ever commercially built harryproa. It was built by Mark Stephens in Australia and exported to Maine - all pieces in tact, but not painted or put together. It was built specifically for my father as a dream for his sailing school. Unfortunately, he passed away. We have neither the knowledge, nor the skill to see this beauty fulfill her potential. 
 
We have been in contact with the builder at harryproa that my father worked with to provide the most accurate details about the boat below.
 
The hulls are strip planked cedar. The beams, rudders and boom are timber and carbon. The mast is vac bagged carbon. I'm unsure of the sail set up, but we do have them, still wrapped. We can't remember if they were sent with the boat, or we had them made here. I know my father worked with a sailmaker for his other boats. If they were sent from Australia, they would have been made by Pierre Gal.
 
The windward hull has a throughway, since the boat was going to double as a water taxi with access from the windward side and a 50 hp outboard. The cut out is strongly beefed up. It could be left as is, or covered in. 
 
The lee hull is 40'. The other dimensions will be similar to those at Harry - HARRYPROA. 
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4 hours ago, JanetC Gougeon32 said:

I wonder how much it cost to build.. 

it’s kind of a shame. Kind of a cool boat, but it looks crude as hell from the interior photos. 

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I feel I need to rant a bit and this seems like just as good a place as any...
I'm annoyed by hull designs with the whole "reverse bow" going that are super fat at deck level: this means the hull shape is NOT meant to have a reverse bow and means there's a blunt downward facing barn door that will plow through waves. That's just dumb! Just make it a "normal" bow that comes to a "point" from the waterline to the deck for F's sakes!

/Rant.

I guess Proas don't need to tack so can get away without much rocker but I do wonder how much speed you would lose when doing direction changes with a shape with no rocker at all like this...

There's a weird mix of nice looking stuff and super crude bits that can't be helping with the resale value. Looks rough overall but looks like a hell of a lot of boat for the $$$ and could be quite cozy with a bit of "detailing"

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4 hours ago, Airwick said:

I'm annoyed by hull designs with the whole "reverse bow" going that are super fat at deck level: this means the hull shape is NOT meant to have a reverse bow and means there's a blunt downward facing barn door that will plow through waves.

Additionally the designer/ creator of the fat upper bow has thrown away most of the benefits of a reverse bow, ie reduced windage/improved airflow at foredeck level, reduced forward sectional girths for less (high level) weight in the ends and for lower overall CG.

4 hours ago, Airwick said:

I guess Proas don't need to tack so can get away without much rocker but I do wonder how much speed you would lose when doing direction changes with a shape with no rocker at all like this...

Proas need to “tack” as much as any other kind of boat, they still have to turn through at least ~ 90 degrees, but do it a different way. So ease of direction change (and rocker) is just as important as in any other boat. And, unlike other boats, they have to do most of it from a standing start, with no way on.

I added bow skegs on Sidecar early on aiming to get additional directional stability and balance, which at the end of the day was insufficient and it was a pig to change direction.... you should have seen the wake coming off the bow when bearing away..... The skegs are gone now. Moving the reversible rudders to near the bows did the trick and under motor in calm conditions,  using both rudders, I can spin/turn Sidecar full circle around the ama.

66441665-7BCD-40B4-92FD-F68524240873.jpeg

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11 hours ago, Sidecar said:

Proas need to “tack” as much as any other kind of boat

I guess what I meant is that it's less critical to be able to carry speed while turning as it will not cause you to "miss" a tack if it's a high drag maneuver. You will just be a slower as you turn back upwind after a shunt so less rocker will hurt performance but not your ability to perform the change in direction.

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Turning a proa slower up into the new wind is still lost ground and time getting back up to speed, which isn’t guaranteed to be regained by being theoretically slightly faster overall with less rocker. Even offshore or around the world.

If you look at the overlays I provided upthread, Sidecar on another proa (Jester), a tri and a cat,  they all have remarkably similar rockers. None are dead flat. 

3E7D648F-CDDA-4435-B7D8-18E87CCD85CB.jpeg

EFFA30A9-916D-4792-8A6F-FFA18F2BB319.jpeg

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5 hours ago, Airwick said:

I guess what I meant is that it's less critical to be able to carry speed while turning as it will not cause you to "miss" a tack if it's a high drag maneuver. You will just be a slower as you turn back upwind after a shunt so less rocker will hurt performance but not your ability to perform the change in direction.

I don’t think I’d argue with Sidecar. He’s easily the most rational proa guy here. He’s got a cool boat, and actually admits when design ideas failed. 

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2 hours ago, Monkey said:

don’t think I’d argue with Sidecar.

Not arguing... Just clarifying what i meant. A traditional sailboat that develops too much drag when turning can end up being completely unable to tack.

A proa in the same situation will always be able to complete the shunt regardless of how inefficient the process is. That's one of the big advantages of proas, you can take as long as you need to shunt and even have a coffee break in the middle if you want and you'll always be able to complete the process so the consequences of lack of rocker aren't quite as serious.

Obviously from a performance perspective you want to be able to steer without too much drag and my comment was that the hull shape looked pretty bad for this and I was just preemptively acknowledging that it was maybe slightly less critical on a proa.

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Rocker is not just for turning, it also reduces wetted surface area for a given displacement. This is particularly important for fine hulls as friction resistance increasingly dominates wave resistance.

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5 hours ago, Airwick said:

A proa in the same situation will always be able to complete the shunt regardless of how inefficient the process is. That's one of the big advantages of proas, you can take as long as you need to shunt and even have a coffee break in the middle if you want and you'll always be able to complete the process so the consequences of lack of rocker aren't quite as serious.

These very long flat hulls - to shunt them must be a nightmare; at almost no speed you have to turn a 60ft flat hull  that will brake in both enda and have no boyancy in the middle ti pivot around. And you are not always mid ocean - even proas can get in a situation that they need to make good progress upwind. And then the slamming in waves - even a slightly flatter part of the bow of a 36ft cat got problems with that. The designer of my tri stated that the biggest forces on the beams was the slamming of the ama in seas - and they are pretty slim and rounded - and not flat. 

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7 hours ago, hump101 said:

Rocker is not just for turning, it also reduces wetted surface area for a given displacement. This is particularly important for fine hulls as friction resistance increasingly dominates wave resistance.

100 percent correct... For fine hulls, the surface friction resistance is often greater than the wave making resistance for any given speed.

Increased rocker also means more headroom and lower CG for the same freeboard/windage. And when flying a hull, when that hull splashes down, the more rocker, the softer the bang.

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Monsieur Hump101

17 hours ago, hump101 said:

Rocker is not just for turning, it also reduces wetted surface area for a given displacement. This is particularly important for fine hulls as friction resistance increasingly dominates wave resistance.

Is there some sort of formula that dictates a minimal rocker per length ?

Or in this case ;  how much for a 60'er ?

Thanks.

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There is no set formula for rocker. Zero rocker for a given Displ and LWL will give a high Cp (prismatic coefficient). Most boats seem to have a Cp of ~ 0.55. Anything over 0.6 is pretty high. FWIW, Sidecar is  0.53.

In general terms, the lower the Cp, the less WSA drag and the higher the wave drag. The higher the Cp, the higher the WSA drag and lower the wave drag.

Assume a Cp (say 0.55) multiply it by LWL (say metres) and then divide the result into Displ (m3) and you will get a midship section area in m2 to achieve the chosen Cp.

You then have to design the midsection shape to achieve that area. Wide and shallow or deep and narrow. Or somewhere in between. You decide. That will give you the hull depth at the midsection, and the basic parameter for rocker. Wide and shallow will need more reliance on foils for lateral resistance and balance, deep and narrow, less so. If you check the underwater girth of several options, you will get a better idea of how much WSA you are likely to end up with.. Any deviation from a semi circle is extra, but a little more, may give other more desirable benefits. Deep V is the worst of all in terms of WSA.

When you have designed the hull sufficiently, you can check to see the Cp achieved. Fuller sections and/or extra curvature in the rocker towards the ends can still increase the Cp above what you were aiming for, so it can take a few iterations to get what you want.

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17 hours ago, peterbike said:

Monsieur Hump101

Is there some sort of formula that dictates a minimal rocker per length ?

Or in this case ;  how much for a 60'er ?

Thanks.

Sidecar has answered this quite comprehensively, so I won't duplicate too much.

Basically, do the maths on your hull. Set up a spreadsheet that will calculate displaced volume and waterplane area and wetted surface area, etc., based on sections along the hull, then vary the hull sections along the length and see the result. It is very sensitive for long, slender hulls, because bow sections (so both ends of a proa) tend to be relatively fine so don't contribute much to displacement but without rocker they do contribute significantly to wetted surface area.

There are sages that will tell you that the only criterion that matters for hull resistance in fine hulls is length/displacement ratio. This hypothesis is supported by comprehensive tank testing of geo-similar hull forms, which of course will give this result since the form of the CP curve is just scaled between geosim hulls. In practice the variation in longitudinal volume distribution has a significant effect on resistance, and as Sidecar noted, the local form at each station that dictates the ratio of the wetted surface area to the section area is critical.

Of course, hull design needs to consider not just hull resistance, but also seakeeping and motions, pitch, roll and yaw resistance, etc., and most requirements contradict each other, hence the wonderful art of compromise is paramount. Rob has chosen to eliminate rocker, and as has been pointed out here, this leads to high yaw resistance and high wetted surface area, which may not be desirable for manoeuvering or speed, but he also achieves higher pitch stiffness, which is desirable to resist rig forces and is particularly difficult in proa hulls, so it is just a different set of compromises. The harryproa concept will tend to be speed-limited by the relatively short and full windward hull, which also will not provide much pitch stiffness, and will induce a yaw moment that needs to be resisted, so the properties of the leeward hull should be viewed with this in mind, and the result for the combination of the two is what matters.

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22 hours ago, Sidecar said:

Assume a Cp (say 0.55)

Multi hulls usually have quite a bit higher Cp - around 0.62-0.65. Mono sailboats are happier around 0.55

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1 hour ago, Zonker said:

Multi hulls usually have quite a bit higher Cp - around 0.62-0.65. Mono sailboats are happier around 0.55

Perhaps it is because of the generally wider sterns and the need for lots of displacement and accommodation over limited LWL condo multis? Eg see Stowaway 8.5 thread.

Maybe canoe sterns make the difference. The Gougeon 32 comes in at Cp 0.58, Sidecar is 0.53 for both hulls.  The MOD 70’s main hulls imaged upthread don’t look >0.6. Nor do Farrier amas.

Sidecar 2 would have more rocker and hence probably a lower Cp..... and certainly the ama would have the same rocker depth as the main hull, over a shorter LWL, so lower again.

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There is no magic "correct" Cp. Just an optimum Cp for a given speed. So you optimize the boat to more easily move in light airs (lower speeds) but sacrifice top speed.

There is no way I can look at a hull and guess the Cp. I am better at guessing Cb (block coefficient). I'd say this one is about 0.96.

image.png.9913c1f644ae55a06833bc541d479835.png

 

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10 hours ago, Sidecar said:

@hump101

Apologies for jumping in.... I didn’t notice that the question was addressed to you.

None required - that's what forums are for...

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On 5/20/2021 at 3:23 AM, ALL@SEA said:

Some history:

The owner was a 60+ year old power boater who thought it would be fun to build and sail a boat.  Chose a Harryproa because they made sense to an elderly non sailor, would be quick and low cost to build and were different.  He bought a set of 15m/50' cedar strip Harry plans and used them (and a lot of phone calls and emails) as a reference for the infused flat panel plastic honeycomb/fibreglass/epoxy hulls, in hull rudders and standard at the time rig.  He made it longer, enlarged the windward hull and installed a 60 hp outboard.   I gave no idea what it cost to build, but it would have been less than $50,000 for materials and, from memory, 2 years work.  He has since added a lot of equipment. 

He could not decide what to do with the bows where the flat panels met, so made them blunt and slightly raked.   He enjoyed watching the spray coming off them at speed, took a bit of convincing to sharpen them up.  He'd be flattered to hear that someone thought they were designed, amused that the design is  "incorrect".    

Rick Willoughby (designer of sundry world record human powered boats, propellor, electric motor and hydrodynamics guru and very smart bloke) took a shine to the boat and helped optimise it with VPP's which they tested and confirmed.  Consequently, it is probably the most analysed (and validated) proa ever built.  Between Rick and the owner, they removed the in-hull rudders after the boat washed ashore and bent them and installed non standard centreboard and smaller in hull rudders, worked on the ballestron rig and fitted 2 electric motors with a diesel gen set.  They had a lot of fun both sailing and playing with it.  

The owner reckons he is now too old to make the effort to go sailing, so is selling it.   It's a bargain for anyone prepared to sail outside the conventional box, but as it is in Melbourne, Australia, shipping elsewhere would cost as much as the boat (still a cheap 60'ter) and visiting and sailing it away will be difficult for at least 12 months due to COVID restrictions in Aus.  

Rick wrote often about the boat on the Harryproa chat group.  https://groups.io/g/HarryProa/topics  along with discussions on rocker, rudders, rigs and boards in a far more rigorous (and polite) fashion than on this site.   Some of his comments:

On the boat generally: "The basic structure has stood the test of time and has proven to be low maintenance.  The new diesel is superb but largely untested apart from regular starts and some limited motoring. The drive batteries are still holding up well and the chargers and panels are all in good order.  The solar panels could be better secured. "

Some others, based on his theoretical and practical Harryproa experience. 

"The standard HP design (2 large rudders, no other water foils) operating a single aft rudder has near perfect sailing efficiency.  The lee helm required to balance the natural weather helm negates leeway.  No one-way boat achieves that unless they have a steerable keel or cambered leeboard."  

"I am an advocate of a narrow flat bottom with some rocker (ski tips) in the ends to provide dynamic lift.  It has potential to reduce hull drag by around 20% on a lightweight boat compared with the round section."

"In moderate winds and feeling lazy, we have often just sheeted from the leading end of the boom and sailed with just the jib.  It is surprising how well the HP sails with a little jib.  In 10kts of wind we do 6 to 7kts with just the jib."

"At high speed, the water drag on the windward hull is reduced as it unloads while sail drive is then aligned with lee hull drag.  If anything it still has slight weather helm as the top of the rig moves further leeward with the list.   One multi-hull sailor who had a sail on the 18m proa used the term long-legged in describing the boat.  I believe that is a good term; a 60ft long, 2ft wide knife.  It sails very easily in the range 12 to 15kts.  It can carry full sail to just over 20kts and speed is impressive despite the large cabin. "

An example of  'the most analysed (and validated) proa' comment:  

"The listed drag components for the 18m proa are derived for the condition of sailing at 50 degrees to apparent wind with windspeed of 15kts.  Drag balances drive at 9.9kts for calm sea state.  The apparent wind is 23 kts and 30 degrees to boat course.  The total lateral force is 5179N.  All forces listed are in Newtons and in line with direction of boat travel:
LW Hull 838
Rig 402
WW Hull 566
Lee Board 348
Frontal Windage 388 (slightly off centre toward the windward hull; mast included in rig drag)
Front Rudder 28
Back Rudder 25
 
So the windward hull drag and boat frontal windage is being offset by rudder drag of just 53N.  The cambered board is completely balancing the lateral forces so the hulls are going where pointed."
 
"At higher windspeed the windward hull unloads even more.  One way boats with uncambered board/s will have at least 4 degrees of leeway which will be affecting their VMG plus there is extra hull drag involved in forcing the hull sideways through the water. "
 
There is much more on the chat group for those interested in the theory and practice of modern proas.

Re rocker:  Early Harryproas had rocker, I found they tended to 'rock' onto the front section at speed and sail bow down, the same as most proas at the time.  Without rocker, it doesn't happen.  Current boats have ski tip bows (ie the front section of the hull kicks up),  which keeps them level, with the enhanced lift promoting planing and possibly sailing over submerged objects.  The rockerless hulls have been analysed and found to be about 5% more draggy than an optimised hull in flat water.  40N out of the total 2,600N of drag on the analysis above.  ie 1.5%.   More than offset by the speed (and comfort) gains from reduced pitching.   The higher prismatic (the cargo proa Cp is 0.82, other Harrys and the Melbourne boat a bit less) also results in higher top speed and more buoyancy forward, without adding the windage and weight of a higher bow.   I learnt about this the fun way on the original Elementarry which could be sailed hard downwind with the top of the bow just submerged.  Sheet off and it would rise, sheet on and over the front you would go.  

When comparing hulls with trimarans, the proa lee hull behaves more like the tri outrigger.  Faster tri outriggers have near zero outrigger rocker and are much flatter than the main hulls.

All of which is mostly academic on cruising proas.  We 'use a ruler for the keel line' (and several other lines) because it makes it easier, quicker and cheaper to build.  Which is why the Melbourne proa got built and 2 old age pensioners can easily handle and sail it in the high teens.  The Harryproa philosophy considers this to be more important than convention and, to some extent, looks.  The cargo proa extends this philosophy (and the 2 x OAPS building it!) towards it's limits.     

Rudders: 2 large rudders mounted fore and aft, with no stalling daggerboard, skegs or other appendages make turning shallow rockerless hulls easy.   With a schooner rig, it is even easier.  Good crew can luff, shunt and be back sailing upwind with no lost distance downwind.   Upwind, the aft rudder is locked to offset the drag and windage of the ww hull and the front one steers.  Small movements give large and rapid course changes, far more so than stern hung rudders.      Off the wind, the front rudder is raised to optimise the balance, the aft one partly raised and used for steering.  Crews not in a hurry leave both rudders down and steer with either or both.   

For self steering, the front one is raised for balance.  Straightlining for long periods with the helm tied is easy.  The cargo proa will not have an autopilot.  

Pointing both rudders in the same direction crabs the boat to windward; handy for motoring off 'lee shore jetties' and clearing obstacles, but unless the helmsperson is more skilled than me, results in lousy vmg.  

Windward hull limiting performance:  In my experience, (20+ years of proa experimenting), as long as it is kept narrow (less than 1:10 B:L), does not exceed it's designed weight and does not have a daggerboard in it, the effect on performance is negligible.  Elementarry with a 4m/13' windward hull would match a 6m/20' Tornado cat, the harryproa cruisers have no trouble sailing at windspeed under main and jib.   Tornados, with their equal hulls, gain less than 10% speed with one hull flying.  Important for racing, hardly noticable while cruising.  

Theory on these items is great, but unless it is backed up with experience of all the variations under discussion, it is easy to travel down unproductive rabbit holes, when there are more relevant areas to focus on.    The Melbourne proa and Rick's analysis and validation are great examples of where the effort can be gainfully spent.  

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On 5/23/2021 at 3:26 AM, harryproa said:

Theory on these items is great, but unless it is backed up with experience of all the variations under discussion, it is easy to travel down unproductive rabbit holes,

Just so funny that you would say that. You still haven't proven that your boats sail worth a damm.  

Has one ever placed in a race? Do they sail upwind well? Do they steer downwind in waves? Do they cross oceans? are they cheap and easy to build? Is there resale value?

There's still no proof that any of these things are possible in a Harry proa. Still no testimony from a single owner who is racing or cruising on one of your boats. There's lots of expert talk and some flashy images, but does that make a successful boat? How can you talk the way you do?

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On 5/23/2021 at 12:00 PM, Zonker said:

There is no magic "correct" Cp. Just an optimum Cp for a given speed. So you optimize the boat to more easily move in light airs (lower speeds) but sacrifice top speed.

There is no way I can look at a hull and guess the Cp. I am better at guessing Cb (block coefficient). I'd say this one is about 0.96.

image.png.9913c1f644ae55a06833bc541d479835.png

 

Agree there is no magic “correct” Cp.

Regarding the MOD 70 images..... the clues are the amount of rocker on the front two thirds of the main hull, zero forefoot, the almost canoe stern and the fairly narrow deep V ish appearance of the cross sections.

Out of curiosity, I found enough MOD 70 info which I could overlay trace and develop sections and fag packet numbers.

MOD 70 Cp: 0.55. Block Coefficient (Cbl) is 0.40.

FWIW, Sidecar Cbl  is also 0.40.....

Without a stern and a profile shot, I wouldn’t even try to guess the Cp or Cbl of your example.

 

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It's a Great Lakes Laker. They are made to fit in locks where maximum length and beam is constrained. So they evolved to be bricks with slightly pointed ends.  Lloyds Register scantling rules for bulk carriers has a computer scantling program. It's max Cb allowed is something like 0.92 and these exceed them. I worked on one with a Cb of 0.985.  That is so close to a brick it isn't funny.

They don't cross oceans so the scantlings are a bit scary if you are used to ocean going freighters.

With regard to MOD 70 - I figure that except in very light winds, the main hull is flying. When wind is light and the main hull is in the water you're not going very fast (by MOD 70 standards). This might explain the low Cp.

image.png.c68e557350cede0397b38076a0caa773.png

 

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There is notably less rocker and no doubt higher Cp on the MOD 70 amas, which do the work at high speeds, with main hull flying, and the nearly 800mm deep main hull and comparatively “extreme” main hull rocker could also be a a way to soften main hull “landings”, reduce windage whilst maintaining headroom below, provide additional lateral resistance at slower speeds, and make it easier to tack/steer which helps to keep rudder size(s) down for less drag.

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Interesting discussion.  Something to discuss:   When I look at a rockered hull, I see a Hobie 16 or early Rudy Choy hull on it's side.  These hulls are flat(ish) on the lee side and curved on the windward side.  They generate sufficient lift to almost negate the need for daggerboards.    Turn them on their side and from  the side they look like a rockered hull.  Move them through the water and the 'lift' pulls them down.    On rockerless hulls (that trim bow up) the hull shape is causing it to lift in the opposite direction.
 
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8 hours ago, harryproa said:

Turn them on their side and from  the side they look like a rockered hull.  Move them through the water and the 'lift' pulls them down.

Doesn't the lift come from the fluid flowing on both sides of the asymmetrical foil? So if you throw in a free surface between 2 fluids it changes things a lot no?
There's also a big difference between the outline (silhouette) of a hull and the actual 3D shape so the 3D shape of a rockered hull with a rounded cross section is nothing like a Hobie hull on its side so I don't really see how this is relevant...


 

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On 5/30/2021 at 8:48 PM, harryproa said:

Turn them on their side and from  the side they look like a rockered hull.  Move them through the water and the 'lift' pulls them down.

The “lift” comes from the asymmetry in the vertical plane, with fluid passing along both sides of the section, not the horizontal one with fluid passing under only one side.

If the suggestion is that rocker causes hulls to be “sucked” into the water, then all water skiers, surfers and windsurfers, for starters, should all submarine? The fastest ones are “sinkers”, which barely support their own weight, let alone being capable of resisting any downward force.

The more you push water under a hull, rather than shove it aside, the more dynamic uplift, not down lift is created. Useful even at HP boat speeds.

Sidecar has rocker and flat bottoms on both hulls. When I motor in flat calm conditions, as the speed increases above four knots, you can see the ama starting to rise, not sink.

As for Randy Smyth’s “Sizzor”......

14A8C214-D75F-4B5A-91F9-561C0EF5324C.jpeg

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