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      Abbreviated rules   07/28/2017

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Amati

bi-directional Proa

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This is from a hikack over on CA, if anyone's interested:

Look what I did! 

Some pics from the garage- I'm not sure I can fit better resolution and stay under the byte ceiling.   If the weather gets better and anyone's interested, I can drag her outside, rig her up, and take a few pics, ditto with descriptions-

 

IMG_0360.JPG

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Here's another, slightly different angle

14'LOA,  15 sq ft SA, ~ 50lbs

messing with the smaller spiral in extremis. Although she's a pacific Proa if I want to stand, if I want to sit, I'll have to redo the float and rigging to go frankenboat Atlantic/ small float for the rig only. She's tiny (looking for a windsurfer replacement vehicle)  and I'll know more next spring when the ice floes break up-

 

IMG_0359.JPG

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You are doing something wrong because those photos look more like thumbnails and are still upside down here. No way they could be near the bit size limit here. If I click them they don't resize either, still the same size. Looks like 324x244 pixels when I check.

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3 minutes ago, Rasputin22 said:

You are doing something wrong because those photos look more like thumbnails and are still upside down here. No way they could be near the bit size limit here. If I click them they don't resize either, still the same size. Looks like 324x244 pixels when I check.

When I get done walking the terrier I'll work on it/

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18 minutes ago, Amati said:

Here's another, slightly different angle

14'LOA,  15 sq ft SA, ~ 50lbs

messing with the smaller spiral in extremis. Although she's a pacific Proa if I want to stand, if I want to sit, I'll have to redo the float and rigging to go frankenboat Atlantic/ small float for the rig only. She's tiny (looking for a windsurfer replacement vehicle)  and I'll know more next spring when the ice floes break up-

 

IMG_0359.JPG

Very interesting! Did you mean 150 sq.ft rather than 15?   Good Luck! I'd love to see it rigged up......

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18 minutes ago, Doug Lord said:

Very interesting! Did you mean 150 sq.ft rather than 15?   Good Luck! I'd love to see it rigged up......

Sorry, posting while a walking a wild assed terrier, on leash!

55 sq ft just to get started-  I'm trying to think of a simple way to steer, so unimaginable sail power comes anon...

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Much better clarity and resolution and what did Groucho do to rotate 180? Ama looks a little short but it does have a high prismatic coeff so may be fine...

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19 minutes ago, Groucho Marx said:

FFS.

upsidedown copy.jpg

It's ok on my iPhone, but not downunder?  Thanks-

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Let's see if the laptop works better (the previous pics were ok on this one too <_<)

One Speer bidirectional leeboard in the middle, lets see what the order of the pics comes out as....

Edit, OK!  And upright here at least...

as of now, steering by changing the CE.  (It's a small sail, what could go wrong?)  I'll be using parriels (sp?) of some sort, so the boom stays attached to the mast while it slides (with any luck) effortlessly back and forth, and I can hold on to it with my hands.  In my rich fantasy life, when I'm sitting waaaaaaay out, flying the ama, I imagine controlling the boom with a loop from each end to me hands.   And yes, where am I going to put my feet?  Some sort of extension of the plank to leeward, methinks...

Ive tried to make the whole thing user friendly for falling off of at speed, so no bracing etc, except for the halyard going out to the ama.

The ama is solid balsa, which should make some modification of shape easy with the belt sander and some varnish.  I based it on some Italian floatplane floats from the Dawn of Aviation,  just as a place to start, and to keep the Prismatic (Yes!) close to 1.0.

Any other questions, fire away.  It is just a toy, but if it works, who knows- maybe its a sit down windsurfer.  That, and the sail rolls around the boom for easy storage! :D  Oh- and if I make the plank and ama detachable, everything should be light enough for an old guy like me (with massive amounts of sports injuries over the decades) to carry from the car to the agua and back- I'm hoping the next one will have parts (including the hull) weighing no more that 20lbs.... 

 

IMG_0366.jpg

IMG_0368.jpg

IMG_0369.jpg

IMG_0370.jpg

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Displacement and prismatic of main hull?  How far "forward" can you sit on the main hull before the bow deck is awash?

What is the displacement of that ama?  Will it hold your weight standing still?

Pacific proas in general don't carry much weight for their length.  The corollary is that they have the longest waterline for any given weight/cost, but that only becomes an advantage as boats get larger, with adequate displacement for the intended use.  Short proas are especially dicey - and this one is extremely short.

For comparison, here are some old sketches of 19' hulls intended to support two guys, comparing displacement at different prismatic coefficients: http://pacificproa.com/prismatic/

prismatic_62.gif

prismatic1.gif

sides_62_70.gif

Quote

Leaving the length, beam and draft (middle cross section) the same while allowing displacement to go up with prismatic coefficient (Cp); in this case, going from Cp=0.62 to Cp=0.70 gains 61 lbs. displacement (12.5%) at the waterline shown.

bows_62_70.gif

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1 hour ago, ProaSailor said:

Displacement and prismatic of main hull?  How far "forward" can you sit on the main hull before the bow deck is awash?

What is the displacement of that ama?  Will it hold your weight standing still?

Pacific proas in general don't carry much weight for their length.  The corollary is that they have the longest waterline for any given weight/cost, but that only becomes an advantage as boats get larger, with adequate displacement for the intended use.  Short proas are especially dicey - and this one is extremely short.

For comparison, here are some old sketches of 19' hulls intended to support two guys, comparing displacement at different prismatic coefficients: http://pacificproa.com/prismatic/

prismatic_62.gif

prismatic1.gif

sides_62_70.gif

bows_62_70.gif

.64 prismatic, and 250lb Displacement.  But only because of the flat rocker. I think I can go 1 1/2' either way without things getting dicey.  I intentionally kept the ends fine so I can use hip action while sitting, or foot weighting, for trim,  more like speed needles used to be like Windsurfing.  I also wanted the deck to come down easily for reboarding, like my prone paddle board (14' by 22"), so I can pretty much float back on. 

The ama will not support my weight- it's good for about 40 lbs displacement, which should be ok when I'm sitting on the windward gunwale, but just barely. The ama is small in the interests of weight, and to help in reboarding. If an ama is planing, It might help, but as you imply, this is where a Proa Might not be minimalist,  except in comparison to other multihulls.

On the other hand, what I'm coming to is if the configuration is conceptually Atlantic, but with me sitting on the long hull to windward, and the rig and a (hydro/bruce) foil are on the short hull to leeward, the dynamic changes dramatically, but steering, design, engineering, and balance become more, um,   ......interesting.

I'd like to see if the current approach works- my hunch is it might be pretty squirrelly- but it's ready to go, so I am refraining from cutting her up.  For a while, anyway.  She's not going to be an easy boat to sail, I don't think.

Messing around with her on the hard has made it really apparent how much leverage even a light ama like this has, so we'll see. :)

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18 hours ago, Amati said:

.64 prismatic, and 250lb Displacement.  But only because of the flat rocker. I think I can go 1 1/2' either way without things getting dicey.  I intentionally kept the ends fine so I can use hip action while sitting, or foot weighting, for trim,  more like speed needles used to be like Windsurfing.  I also wanted the deck to come down easily for reboarding, like my prone paddle board (14' by 22"), so I can pretty much float back on. 

The ama will not support my weight- it's good for about 40 lbs displacement, which should be ok when I'm sitting on the windward gunwale, but just barely. The ama is small in the interests of weight, and to help in reboarding. If an ama is planing, It might help, but as you imply, this is where a Proa Might not be minimalist,  except in comparison to other multihulls.

On the other hand, what I'm coming to is if the configuration is conceptually Atlantic, but with me sitting on the long hull to windward, and the rig and a (hydro/bruce) foil are on the short hull to leeward, the dynamic changes dramatically, but steering, design, engineering, and balance become more, um,   ......interesting.

I'd like to see if the current approach works- my hunch is it might be pretty squirrelly- but it's ready to go, so I am refraining from cutting her up.  For a while, anyway.  She's not going to be an easy boat to sail, I don't think.

Messing around with her on the hard has made it really apparent how much leverage even a light ama like this has, so we'll see. :)

Uh...  I'll try to put this as delicately as I can...  Does the 50 lb. weight of this boat need to be subtracted from the 250 lb. displacement to get the payload capacity?  Only 200 lbs.?  Where does that put the waterline?  SUP boards only 10' to 12' long can typically carry ~300 lbs. or more, right?

I don't understand how that 40 lb. displacement ama does you any practical good at all?  I think you'll be swimming frequently if you count on that.  Isn't this configuration pretty much the same as a windsurfer with no ama?

Gary Dierking's smallest proa Tarawa is 16': http://homepages.paradise.net.nz/garyd/tarawa.html

tarawa2.gif

harm2.jpg

Have fun.

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It puts the freeboard pretty fucking low!  (I'm 163lbs)  But compared to sinkers, it's a lot of displacement!  Swimming is a given, but we get 3-4 months of + 85 - 100 degrees, so, hey! My Waterman 14' prone dumps me more than what you are implying!

The ama gives but a moment of respite, which is better than a Div 2 board, in light air, and 2' cross chop......

On the other hand, she's an excellent proto to the next iteration.  Who thought a proa had to be really really big?

 

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11 hours ago, Amati said:

Who thought a proa had to be really really big?

I've always thought so.  The bigger they get, the more sense they make.  The 24' Bieker proa in the R2AK was a marvel of technical innovations and expertise with one major flaw - it was too small.  Except for a motor and dingy, they tried to carry most of the same load (crew, personal gear and provisions) that Kauri, Cimba and Jzerro do so well but with 12' less waterline.  Just my personal opinion, I don't speak for anyone else.

After early experiments, Russell's first proa was 30' long:

jzero78-cl.jpg.e5cfb67236a185cc1490e83a4b19bc84.jpg

wb-rb-caption.png.59ef898fdc64ccb0bf8190cb05dc0b84.pngwb-rb.thumb.jpg.d319e9659d3592351939e792746b76a3.jpg

Source: Wooden Boat magazine, issue #83 July/Aug 1988

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4 hours ago, ProaSailor said:

I've always thought so.  The bigger they get, the more sense they make.  The 24' Bieker proa in the R2AK was a marvel of technical innovations and expertise with one major flaw - it was too small.  Except for a motor and dingy, they tried to carry most of the same load (crew, personal gear and provisions) that Kauri, Cimba and Jzerro do so well but with 12' less waterline.  Just my personal opinion, I don't speak for anyone else.

After early experiments, Russell's first proa was 30' long:

jzero78-cl.jpg.e5cfb67236a185cc1490e83a4b19bc84.jpg

wb-rb-caption.png.59ef898fdc64ccb0bf8190cb05dc0b84.pngwb-rb.thumb.jpg.d319e9659d3592351939e792746b76a3.jpg

Source: Wooden Boat magazine, issue #83 July/Aug 1988

The bottom pic is why I’ve been fooling with a sliding seat on the plank- it would make weight responses quicker, but quick enough to get rid of the need for an ama with enough float for my weight?

always thought Russel’s 30’er (second pic up) was perfect...

still, when I see an RS Aero zipping around, I think ‘why not a small Proa?’

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Amati, an international canoe works quite well so there probably is scope for a small proa with similar performances. The only thing that would worry me is that the bow keeps digging in. Have you considered a way of trimming the boat longitudinally by moving your weight around?

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I cobbled together some bits of Rhino Grasshopper I had laying around to create this parametric "beach proa".  Hard chines, flat surfaces, not much time into it, not optimal in some ways (too short!), and about as "big" as I can make it in only 14' LOA.  Both hulls have an L/B ratio of 17:1, six feet apart on centerlines.

beachProa_2017_Nov20a.jpg.30a05a7fdd48d189f5445235a0f021e5.jpg

Main hull - LOA: 14', BOA: 9.88"
0" - Disp: 255 lbs., Cp: 0.62
6" - Disp: 532 lbs., Cp: 0.68 (PPI: 46 lbs.)

Ama - LOA: 12', BOA: 8.5"
0" - Disp: 167 lbs., Cp: 0.62
3" - Disp: 263 lbs., Cp: 0.65 (PPI: 32 lbs.)

beachProa_2017_Nov20a4.thumb.png.ec2d88febc2aa372f84bc7308e9044a5.png

beachProa_2017_Nov20a2.thumb.png.3f7c844760f7b038240b204d3e60b35d.png

Top view, hulls only two feet apart for easier comparison:

beachProa_2017_Nov20a3.thumb.png.76f058fb906bd0891b35c76618478221.png

These are the parameters:

beachProa_2017_Nov20a5.png.a0acaff1bfa64b3d9441548932c152a1.png

Two options are not shown:

  • number of bottom sections (4 on the ama, 5 on the main hull).
  • a switch between two deck styles, shown below on different hulls.

two_ama_decks.png

Cheers

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4 hours ago, ProaSailor said:

Main hull - LOA: 14', BOA: 9.88"
0" - Disp: 255 lbs., Cp: 0.62, , Draft: 7.7"
6" - Disp: 532 lbs., Cp: 0.68 (PPI: 46 lbs.)

By the way, those displacement numbers are for saltwater; in fresh water, displacement drops seven pounds from 255 lbs. to 248 lbs.

Bumping the LOA slider from 14' to sixteen feet gives these numbers (again, in saltwater):

Main hull - LOA: 16', BOA: 11.3"
0" - Disp: 359 lbs., Cp: 0.62, Draft: 8.4"
3" - Disp: 540 lbs., Cp: 0.66 (PPI: 60 lbs.)
6" - Disp: 721 lbs., Cp: 0.68 (PPI: 60 lbs.)

And at 19 feet:

Main hull - LOA: 19', BOA: 13.4"
0" - Disp: 562 lbs., Cp: 0.62, Draft: 9.4"
3" - Disp: 818 lbs., Cp: 0.66 (PPI: 85 lbs.)
6" - Disp: 1073 lbs., Cp: 0.68 (PPI: 85 lbs.)

In addition to other benefits, the longer main hulls can clearly support two guys flying the ama, even with reduced topsides height (reserve buoyancy).

This is the 19' main hull (green) with the 14' hull inside and the same 12' ama six feet to windward (just for comparison, not a proposal):

beachProa_2017_Nov20b.thumb.jpg.b9d8fe72d4990acff52ddd5ce9e0c8ae.jpg

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Small/short proas work well.  Heavy proas not so much.  The smallest I (85 kgs/190 lbs) have built/sailed is a 15.5' flat bottomed ply proa with windward hull a bit bigger than yours.  Worked a treat (about as quick as a Laser around the track)  until it capsized and the stayed, keel stepped mast (65mm/2.5" alloy tube) sheered off at the deck when it hit the water.

 Next smallest is a 16'ter i built for my 8 yr old daughter and a friend to sail.  

It had rudders and a windsurfer rig.  As you can see, crew weight was on the rear beam for best balance.    This became the protoype for a short harryproa production run in China.  

Due to all the rudders I have broken, I am also quite experienced at steering with weight shift and sail balance.  ;-)

Based on that experience, I think you are on the right track.    Sail it like a windsurfer and it will plane and overcome any displacement issues.   Sailing it sitting down will be too hard and slow to shift your weight for steering.    Maybe extend the deck to ww to widen your standing area if you want more rm, but i doubt you will until you get a bigger rig or serious breeze.    

Steering by moving the coe requires a fair bit of movement when you are too close to the wind or or on any off the wind course.     

A problem with bidirection jibs is the luff needs to be tight for upwind performance.  Imparts big compression loads in the mast and makes it tricky to move the boom to steer.  As well as moving the boom, you will have to adjust it's angle.  Not sure you will do this with only two lines.  

Rockerless hulls respond to weight shift steering better than rockered hulls and are faster.  Flat bottom hulls plane better.  Multiple chines are hard work to build and won't plane, might be marginally better in sub planing conditions due to less wetted surface, but I doubt it on a boat like yours.

Assuming the mast needs the stay to windward, it will also need a backstay for downwind.  I would ditch them both and support it the same way you do a windsurfer rig.    

The other things I learnt on the little proas are that oar steering is hard work, rudders are a challenge and daggerboards a pain in the butt.    But for upwind performance on a sit down proa for any length of time, leeway resistance and rudders are a necessary evil.  

Your boat should be fun to sail, but I suspect it will not scale up very far if you want to do more than reach back and forth.  Look forward to hearing how it goes.  

 

5a138d0eef7c6_Plyproa.jpg.4be7488396342da5d2292a3860846e5a.jpg5a1396b7e7e46_harrietteinShanghai.JPG.17ce2e7b01baac22818545a38e8f83ff.JPG

 

 

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Looks like wet fun.  Check out Salamba,18' tri-plane proa, she the big sister of your design.  When I finish her I let you in on her performance.  Good luck to you.

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1 hour ago, guerdon said:

Check out Salamba,18' tri-plane proa

What is a "tri-plane proa"?  Where do we check out Salamba?  I see one on YouTube from 2008... too far away, blurry and jiggly to see any details.  I found some renderings that look remarkably similar to John Harris' Mbuli, a 20' proa?  CLC web site appears to be down at the moment, here is a pic of Squid ("a Mbuli class proa") from Gary Dierking's blog (2009):

Squid1.jpg

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Contact Jonathon Foucher, Marine Tech, in France.  She is like Mubuli, but much lighter @ 300lbs., and uses windsurfing masts for a Gibbons, rig.  Hopefully I will be able to sail her like a windsufer.  The try-plane hull is a Phil Bolger, boat concept.  This one uses George Greenoughs'  edge board chines for quicker planning.  Occume fun!

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4 hours ago, guerdon said:

She is like Mubuli, but much lighter @ 300lbs.

The CLC web site is back - 20', 450 lbs.: http://www.clcboats.com/shop/boats/wooden-sailboat-kits/proa/mbuli-pacific-proa-beach-cruiser-plans.html

Rael Dobkins says 100kg (220 lbs.) for his proa WHY NOT? so... it depends somewhat on how much "top hamper" one carries, eh?

 

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Deltro was indeed gorgeous.  Ply sheathed in carbon/kevlar, quite light, expensive sail, good gear, no expense spared by Peter, who was a pretty good sailor.  I sailed on the boat with Peter during the Proa Conference in 1997 (8?).  It was not a happy experience.  To get the boat to track upwind, I had to lie on the aft deck with my feet in the water, while Peter stood on the outrigger.  If I took my feet out of the water, the boat would luff up, the sail would flap and the mast fall down on Peter.   It tacked through about 110 degrees, partly due to this and partly to the crab claw sail.  Leeway was high as it had an assymetric hull, no foils.    Reaching was better, but I still had to sit on the stern and it was pretty slow to respond.  Shunting was reasonable due to the track on the lee side, the slow part was me shifting from end to end.

The Deltro  video on the pacificproa page  shows a 404 error, but if it is the one I am thinking of, it shows it sailing.  There is/was another one of it reaching back and forth through some reasonable surf which it handled well.   

 

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On 11/20/2017 at 10:03 AM, Panoramix said:

Amati, an international canoe works quite well so there probably is scope for a small proa with similar performances. The only thing that would worry me is that the bow keeps digging in. Have you considered a way of trimming the boat longitudinally by moving your weight around?

That is a huge problem, and why I have gone to a sub .5 prismatic with a flat bottom, in hopes that trim control becomes easier as foot pounds (to depress the ends of the hull from the plank) become less and less-  the smaller spiral.  The IC is a convenient starting point, and I keep bouncing back and forth between a DSS plank/foil or an ama, or some sort of fusion between the 2 concepts.  But as everybody who has messed with an IC knows, the forces are enormou$.

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On 11/20/2017 at 7:52 PM, harryproa said:

Small/short proas work well.  Heavy proas not so much.  The smallest I (85 kgs/190 lbs) have built/sailed is a 15.5' flat bottomed ply proa with windward hull a bit bigger than yours.  Worked a treat (about as quick as a Laser around the track)  until it capsized and the stayed, keel stepped mast (65mm/2.5" alloy tube) sheered off at the deck when it hit the water.

 Next smallest is a 16'ter i built for my 8 yr old daughter and a friend to sail.  

It had rudders and a windsurfer rig.  As you can see, crew weight was on the rear beam for best balance.    This became the protoype for a short harryproa production run in China.  

Due to all the rudders I have broken, I am also quite experienced at steering with weight shift and sail balance.  ;-)

Based on that experience, I think you are on the right track.    Sail it like a windsurfer and it will plane and overcome any displacement issues.   Sailing it sitting down will be too hard and slow to shift your weight for steering.    Maybe extend the deck to ww to widen your standing area if you want more rm, but i doubt you will until you get a bigger rig or serious breeze.    

Steering by moving the coe requires a fair bit of movement when you are too close to the wind or or on any off the wind course.     

A problem with bidirection jibs is the luff needs to be tight for upwind performance.  Imparts big compression loads in the mast and makes it tricky to move the boom to steer.  As well as moving the boom, you will have to adjust it's angle.  Not sure you will do this with only two lines.  

Rockerless hulls respond to weight shift steering better than rockered hulls and are faster.  Flat bottom hulls plane better.  Multiple chines are hard work to build and won't plane, might be marginally better in sub planing conditions due to less wetted surface, but I doubt it on a boat like yours.

Assuming the mast needs the stay to windward, it will also need a backstay for downwind.  I would ditch them both and support it the same way you do a windsurfer rig.    

The other things I learnt on the little proas are that oar steering is hard work, rudders are a challenge and daggerboards a pain in the butt.    But for upwind performance on a sit down proa for any length of time, leeway resistance and rudders are a necessary evil.  

Your boat should be fun to sail, but I suspect it will not scale up very far if you want to do more than reach back and forth.  Look forward to hearing how it goes.  

 

5a138d0eef7c6_Plyproa.jpg.4be7488396342da5d2292a3860846e5a.jpg5a1396b7e7e46_harrietteinShanghai.JPG.17ce2e7b01baac22818545a38e8f83ff.JPG

 

 

Modeling calculates weight shifting a rockerless hull as a bit draggy- is that your experience?  Or does no rudder drag make up for it?

For this exercise, I’m relying on Marchaj’s work on upwind flying sails that don’t deploy on a straight luff-  I’ve got a drifter on my 40’ that has a curved leading edge that goes upwind nicely.  Kitesurfers, sailplanes and the 787’s have curved leading edges, so it seems worth a shot......its only $$! :lol:

Edit-  how long does it take to fiddle around with the CoE of a Balestron (I think that’s the name of the top rig?) to get it right?

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I got to sail on the proa Toroa in Auckland and was very impressed. It had enough freeboard and volume to really rip in choppy water. The design of the outrigger hull showed me just how bad my outrigger hulls had all been. It was long enough to carry our weight easily and skinny enough to slice through the chop without throwing spray all over us. It was also quite beautiful even though it was just a four-panel plywood hull.

The crab claw rig was impressive too and it was my first experience with one. The boat seemed weatherly and very well balanced. One thing I didn't expect is that the flogging of the sail would really fling the lower spar (boom?) around.

Harmen's blog has some good photos of the boat, but I think there are more somewhere. I was looking for a good photo of the outrigger hull as it's worth a study.  http://harmenhielkema.blogspot.com

 

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1 hour ago, Russell Brown said:

I got to sail on the proa Toroa in Auckland and was very impressed. It had enough freeboard and volume to really rip in choppy water. The design of the outrigger hull showed me just how bad my outrigger hulls had all been. It was long enough to carry our weight easily and skinny enough to slice through the chop without throwing spray all over us. It was also quite beautiful even though it was just a four-panel plywood hull.

I don't know if these photos are still on Harmen's blog - couldn't find them just now.

sc00021cdb.jpg

sc00021cdb-ama.jpg.945b79c9fc2cd02a44c43d6aaeca590c.jpgP1030905.jpg.5ac775c2b4df14b7338bad855584cc24.jpg

sc00022bef.jpg

 

I changed a few Grasshopper parameters and got this; needs more work.  A closer (deeper forward?) rendition requires adding a keel curve parameter or two to the model:

Ama - LOA: 16'BOA: 12", L/B ratio: 16:1, almost fully submerged Disp. as shown below: 313 lbs., Cp: 0.68

beachProaAma_2017_Nov25a.png.089cdd8a56149af41953d6e3554b154a.png

beachProaAma_2017_Nov25a2.jpg.12c599e3513df5752ba40f16c7bd9a4e.jpg

beachProaAma_2017_Nov25a3.thumb.png.f9a156ed3104644a51420c1ea60fcf05.png

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5 hours ago, ProaSailor said:

I changed a few Grasshopper parameters and got this; needs more work.  A closer (deeper forward?) rendition requires adding a keel curve parameter or two to the model:

Ama - LOA: 16'BOA: 12", L/B ratio: 16:1, almost fully submerged Disp. as shown below: 313 lbs., Cp: 0.68

Instead of charging off and adding an explicit keel rocker curve to this model (rocker is derived by other means), I measured the ama above from 0" to 8" increased draft.

Proa hull: LOA: 16', BOA: 12", L/B ratio: 16:1
Disp. 0":  25 lbs, Cp: 0.58, LWL: 10.6'
Disp. 1":  50 lbs, Cp: 0.59, LWL: 11.8'
Disp. 2":  85 lbs, Cp: 0.60, LWL: 12.7'
Disp. 3": 132 lbs, Cp: 0.61, LWL: 13.5'
Disp. 4": 185 lbs, Cp: 0.63, LWL: 14.1'
Disp. 5": 235 lbs, Cp: 0.65, LWL: 14.6'
Disp. 6": 274 lbs, Cp: 0.67, LWL: 15.0'
Disp. 7": 302 lbs, Cp: 0.68, LWL: 15.4'
Disp. 8": 315 lbs, Cp: 0.68, LWL: 15.7'

I'm not sure I want a deeper forefoot on the rocker since prismatic already gets high fast.  The best way I can see to increase displacement (volume) within L/B dimensions is vertical topsides.  Just one more pair of surfaces to build, keeps the deep-V bottom, which makes sense on the ama.  A pair of these sixteen-foot hulls would make a decent proa for two, or use this 16' hull as the ama for a longer, taller main hull with more chines and flat bottom.

Proa ama hull as before in Top View: LOA: 16', BOA: 12", L/B ratio: 16:1 with vertical 5" topsides added.

Disp.  at 0" immersion: 252 lbs, Cp: 0.61, LWL: 15.4'  (mid-range displacement)

beachProaAma_2017_Nov25c2.png.3f4a7ed347dad5e26c224bed502b5abc.png

Disp. at 10": 524 lbs, Cp: 0.68, LWL: 16.0'
beachProaAma_2017_Nov25c.png.9e60fb4e5191745fdc80e47f16c7dc6a.png

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1 hour ago, ProaSailor said:

Proa ama hull as before in Top View: LOA: 16', BOA: 12", L/B ratio: 16:1 with vertical 5" topsides added.

Disp.  at 0" immersion: 252 lbs (each hull), Cp: 0.61, LWL: 15.4'  (mid-range displacement)

Matched pair of same 16' proa hulls, six feet apart, ~504 lbs. total displacement at 0" immersion shown below, ~524 lbs. maximum on each hull (deck awash!), reserve buoyancy from bow knuckle above waterline and 5" vertical topsides.

beachProaAma_two16s_2017_Nov25c.thumb.jpg.4d586e57c90f087c9b273314576d779e.jpg

beachProaAma_two16s_2017_Nov25c2.thumb.jpg.81acf543216e4ef7886d4c926a26b176.jpg

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40 minutes ago, ProaSailor said:
1 hour ago, ProaSailor said:

Proa ama hull as before in Top View: LOA: 16', BOA: 12", L/B ratio: 16:1 with vertical 5" topsides added.

Disp.  at 0" immersion: 252 lbs (each hull), Cp: 0.61, LWL: 15.4'  (mid-range displacement)

Matched pair of same 16' proa hulls, six feet apart, ~504 lbs. total displacement at 0" immersion shown below, ~524 lbs. maximum on each hull (deck awash!), reserve buoyancy from bow knuckle above waterline and 5" vertical topsides.

beachProaAma_two16s_2017_Nov25c3.thumb.png.538076a3d9c7c90ca1dc91e5f1a0aa1e.png

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9 hours ago, Amati said:

Modeling calculates weight shifting a rockerless hull as a bit draggy- is that your experience?  Or does no rudder drag make up for it?

For this exercise, I’m relying on Marchaj’s work on upwind flying sails that don’t deploy on a straight luff-  I’ve got a drifter on my 40’ that has a curved leading edge that goes upwind nicely.  Kitesurfers, sailplanes and the 787’s have curved leading edges, so it seems worth a shot......its only $$! :lol:

Edit-  how long does it take to fiddle around with the CoE of a Balestron (I think that’s the name of the top rig?) to get it right?

Rockerless hulls are not draggy.  All else being equal, they are less draggy at high speed, more at very low speeds.  If the boat is light enough, you need less weight shift to move the clr than with a rockered hull. Plus it will have a higher top speed, is much easier to build and in your case, will plane easier.      It is good to remove rudder drag, but you still need leeway resistance and an assymetric hull will not supply this for serious upwind work.    Combining the rudder and the leeway resister is least work, weight and wetted surface.  And makes the boat a lot more responsive to steer.

Curved leading edges are ok on solid foils (kites, gliders and aeroplanes), not so much on soft sails.  Sagging forestays are not fast.    But,  everything is worth a try,   I look forward to seeing the results.   Money on a small boat is not as big deal as time is.

Balestron balancing is easy enough.  With a square head or roachy main, you ease the leech pressure until it is balanced.   If you want it to be fully efficient, you put up with increased sheet load, which is still much lower than conventional rigs.  To get fully efficient and balanced, you need to work with your sailmaker.  My advice is always to put the onus for the balance on the sailmaker, and not to pay the last installment until the rig is as specified.  It is best to err on the side of caution.  It is a funny feeling flying a hull and pushing on the mainsheet to ease it.  ;-)

 

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15 hours ago, ProaSailor said:

Proa ama hull as before in Top View: LOA: 16', BOA: 12", L/B ratio: 16:1 with vertical 5" topsides added.

Disp.  at 0" immersion: 252 lbs, Cp: 0.61, LWL: 15.4'  (mid-range displacement)

Disp. at 10  5" immersion: 524 lbs, Cp: 0.68, LWL: 16.0'

Correcting a minor transcribing/frame of reference error: the deck awash displacement of 524 lbs (on the right, below) is five inches deeper than the middle condition (below) of 252 lbs and seven inches deeper than the image on the left (below), where the chine is at the waterline with displacement at 134 lbs and Cp is 0.59.  So PPI is ~50 to 56 lbs.

beachProaAma_2017_Nov26c2.thumb.png.fee56d032190c62e5892fd553c9f2013.png

beachProaAma_2017_Nov26c.thumb.png.27a23c60be764f45a68813aeef3e18de.png

For a main hull instead of an ama, where a rounder shape and flat bottom work better, displacement of this 16' hull goes up ~70 lbs at all depths, with no other changes (though it's easy to make the vertical topsides taller too, of course).  204 lbs on the left, 597 lbs on the right below:

beachProaAma_2017_Nov26c3.png.63123c4dfcabee79e073d91f10b01bfa.png

Scaled up to six meters (19.7') works very well.  So does 24', 30' 36', etc.

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Nothing final or sacred about any of the parameters I'm using to shape this Rhino Grasshopper model.  Just sketches...

Double-ended Proa Hull - LOA: 6 meters (19.7 feet), L/B ratio: 16 to 1, BOA: 14.78", 12" vertical topsides.

=== Multi chine, flat bottom main hull ===
Disp. at 0" (chine at waterline): 389 lbs, Cp: 0.62, LWL: 17.6'
Disp. at 2": 575 lbs, Cp: 0.62, LWL: 19'
Disp. at 7": 1049 lbs, Cp: 0.65, LWL: 19.7'

=== Deep V, one chine ama ===
Disp. at 0" (chine at waterline): 256 lbs, Cp: 0.60, LWL: 17.7'
Disp. at 2": 438 lbs, Cp: 0.61, LWL: 19'
Disp. at 7": 912 lbs, Cp: 0.66, LWL: 19.7'

beachProa-6m_2017_Nov26a.thumb.png.a0da3374c301a0f32893cb976215a3a6.png

 

 

Below: six meter (19.7') multi-chine main hull with a 16' single chine deep-V ama, eight feet BOA both hulls, lightly loaded, 575 lbs on main hull, 134 lbs on the ama, 709 lbs total.

beachProa-6m_2017_Nov26a2.thumb.jpg.b78d544efe2ee954ad4a986f3c432a83.jpg

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On 11/25/2017 at 3:57 PM, Amati said:

That is a huge problem, and why I have gone to a sub .5 prismatic with a flat bottom, in hopes that trim control becomes easier as foot pounds (to depress the ends of the hull from the plank) become less and less-  the smaller spiral.  The IC is a convenient starting point, and I keep bouncing back and forth between a DSS plank/foil or an ama, or some sort of fusion between the 2 concepts.  But as everybody who has messed with an IC knows, the forces are enormou$.

Mmh, I am not entirely sure about this low prismatic coefficient being good for pitch stability, it might be easier in a static condition (no wind) to control pitch but on the other hand, when it is windy, a relatively small pitching moment from the rig will make the boat pitch a lot. That's one fo the reason why the mini have fuller and fuller ends, newer boats with a lot of volume in the ends can push harder than the older ones that will dig their bow in sooner.

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Surfboard longboard longitudinally symmetrical gun is the answer then? , but that approach has its own light air problems, and they tend to get heavy in sit down mode.  

But planing? :wub:

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Same hull model at 30' (9.1m), L/B: 16 - Things get serious!  Approaching 2,000 lbs (900 kg) total displacement, including ~500 lbs on an ama.

Proa30_2017_Nov26a.thumb.png.df495dd2c65098810af06e37c0ce69c5.png

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16 hours ago, Amati said:

Surfboard longboard longitudinally symmetrical gun is the answer then? , but that approach has its own light air problems, and they tend to get heavy in sit down mode.  

But planing? :wub:

Proas tend to have quite a lot of freeboard. May be that's the best answer? You accept some digging but make sure that your boat self convert to a submarine. More of a question for the proa experts than a statement.

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28 minutes ago, Panoramix said:

Proas tend to have quite a lot of freeboard. May be that's the best answer? You accept some digging but make sure that your boat self convert to a submarine. More of a question for the proa experts than a statement.

More structure = more weight, but maybe weight is a proa’s friend?  

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59 minutes ago, Panoramix said:

Proas tend to have quite a lot of freeboard. May be that's the best answer? You accept some digging but make sure that your boat self convert to a submarine. More of a question for the proa experts than a statement.

That makes sense to me.  The load is temporary due to weight shift (lifting the windward ama) or burying a bow, so build up.  A few inches of vertical with established waterplane (PPI) is buoyancy without flare.  Less drama, more wave piercing.  Big waves are gonna roll, let them go bye!

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On the other hand, the only difference between these three 16' ama hulls is the L/B ratio.  All have a high prismatic (Cp = 0.69).  How much displacement do you want in a 16' ama?

  1. L/B: 12, Disp: 529 lbs (234 kg).
  2. L/B: 13.6, Disp: 436 lbs (198 kg).
  3. L/B: 16, Disp: 341 lbs (155 kg).

harmen-style_amas.thumb.png.797042a1c113f5e0282695a1ec2cc49d.png

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2 hours ago, Amati said:

More structure = more weight, but maybe weight is a proa’s friend?  

Can weight ever be your friend? May be when in your keel but for a proa probably not as you enter into the negative spiral more weight - > more load -> heavier structure -> more weight etc... IMHO Newick and Walter Greene perfectly understood this and their boats were amongst the quickest at the time despite being rather small.

As usual, the best answer is probably a compromise, enough but as little freeboard as needed to avoid completely burying the bow.

I still think that your hull is nice but if it was mine I would make sure that the helm can physically move its weight aft. After all it's a beach boat, not a cruising boat, so a bit of acrobatic work is part of the fun (and I mean it as I own a hobie cat 16 which will send into orbit around the mast anyone fool enough to stay forward on a reach).

 

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A bit tongue in cheek (me^), but I’m beginning to think proas are inherently heavier than monohulls (think high performance monos and windsurfers) .  As long as you brought up Alter’s freeboards:

 

48481139-9036-44A1-8ACF-16A2E32674F4.jpeg

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3 hours ago, ProaSailor said:

L/B: 16, Disp: 341 lbs (155 kg).

Adding four inch topsides (thickness?) to the narrowest of those ama variations (L/B:16) substantially increases their reserve buoyancy, from 341 lbs to ~600+ lbs (273 kg):

beachProaAma_2017_Nov27c2.png.1a431f9e0c94e3ea5973303cfea106e1.png

And "working load" of ~474 lbs (215 kg).

beachProaAma_2017_Nov27c.png.403f1247542efd60d426a92219787058.png

beachProaAma_2017_Nov27c3.png.4d15441eb7245a55faa75ed67fb5233a.png

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1 hour ago, ProaSailor said:

Adding four inch topsides (thickness?) to the narrowest of those ama variations (L/B:16) substantially increases their reserve buoyancy, from 341 lbs to ~600+ lbs (273 kg):

beachProaAma_2017_Nov27c3.png.4d15441eb7245a55faa75ed67fb5233a.png

All three are LOA: 16' , L/B: 16, BOA: 12". same single chine deep-V bottoms.  Two have 4" topsides, two have inverted-V decks, one has "lofted" deck (on left).

beachProaAma_2017_Nov27c4.thumb.jpg.62f90cee97092b13e9fefad8b178a97d.jpg

Curvature.  Red is flatish, blue more curvature, esp. the "lofted" curved deck (in middle below, on left above):

beachProaAma_2017_Nov27c6.png.c04c86b072728b3e7969aa3d4115b7da.png

beachProaAma_2017_Nov27c5.jpg.89c31292f3d38e8e96dafab0178d4e85.jpg

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Main hull to leeward (left), multi-chine, LOA: 30' (914 cm) , BOA: 22.5" (57 cm), Disp: 2188 lbs (992 kg), LWL: 28.8'.
Ama to windward (right), deep-V, LOA: 22.5' (686 cm), BOA: 16.88" (43 cm), Disp: 671 lbs (304 kg), LWL: 21.67'.

TOTAL Displacement, both hulls at waterlines shown: 2859 lbs (1296 kg)

ProaAma22.5_2017_Nov27a.thumb.jpg.2e1aaeead4a0c1624951f7404ce8ab7f.jpg

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33 minutes ago, ProaSailor said:

Main hull to leeward (left), multi-chine, LOA: 30' (914 cm) , BOA: 22.5" (57 cm), Disp: 2188 lbs (992 kg), LWL: 28.8'.
Ama to windward (right), deep-V, LOA: 22.5' (686 cm), BOA: 16.88" (43 cm), Disp: 671 lbs (304 kg), LWL: 21.67'.

TOTAL Displacement, both hulls at waterlines shown: 2859 lbs (1296 kg)

ProaAma22.5_2017_Nov27a.thumb.jpg.2e1aaeead4a0c1624951f7404ce8ab7f.jpg

ProaAma22.5_2017_Nov27a2.thumb.jpg.ff5f53a86338424c095c4abdfd462f5e.jpg

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Proa main hull rotated five degrees to windward at rest, multi-chine, LOA: 30' (914 cm) , BOA: 22.5" (57 cm), L/B: 16:

  • Disp: 2188 lbs (992 kg) at Draft: 15" (38 cm), LWL: 28.8' (878 cm).
  • Disp: 2850 lbs (1293 kg) at Draft: 18" (46 cm), LWL: 30' (914 cm).

Proa30_2017_Nov28a.png.08c45f4809db364ea42a1ce793fdb6ab.png

Proa30_2017_Nov28a2.png.15f8aa56c105f082aa876b172082d6a2.png

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Same proa main hull model rotated five degrees to windward at rest, multi-chine.
LOA: 6 meters (19.685'), BOA: 14.76" (37.5 cm), L/B: 16, Cp: 0.62.

  • Disp: 717 lbs (325 kg) at Draft: 11.17" (28.4 cm), LWL: 18.7' (570 cm)
  • Disp: 1002 lbs (454 kg) at Draft: 14.17" (36 cm), LWL: 19.685' (6 m)

Proa6m_2017_Nov28a.png.f45d75d6b43acf62b301cd64666f95ed.png

Proa6m_2017_Nov28a2.thumb.png.317fe4478156833ca156452164b57571.png

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On 11/27/2017 at 6:13 PM, Amati said:

A bit tongue in cheek (me^), but I’m beginning to think proas are inherently heavier than monohulls (think high performance monos and windsurfers) .  As long as you brought up Alter’s freeboards:

 

48481139-9036-44A1-8ACF-16A2E32674F4.jpeg

You got me. Cp seems quite high on this one.

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The plan outline looks gun-ish to me.  I know- the cross section is round, but the ama doesn’t look light- solid?  Kind of a floating keel?

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Racing, sails de-powered  waiting for the start, Admirality Islands maybe, Manus ?

DSC_9873.thumb.jpg.264754b63d83d3ade5f55238f028f686.jpg

Racing hard, the trailing edge spar has gone to base of the mast:

DSC_9262.thumb.jpg.9877ccb88a6db0e27278dff6aeb7f180.jpg

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There must be some reason the spars are on the weather side of the mast, but I don't get it.  Distorts sail shape and makes harder to depower I would think.  What am I missing?

Also, they seem to use high density amas, less cross sectional area / drag for the weight I guess.  More interested in righting moment than buoyancy eh?

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4.7 meter = 15.42'.  Hate to promote this mis-use of the word proa, but construction method and size is relevant here:

3D printed rudder!

 

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On 11/28/2017 at 8:05 AM, ProaSailor said:

Same proa main hull model rotated five degrees to windward at rest, multi-chine.
LOA: 6 meters (19.685'), BOA: 14.76" (37.5 cm), L/B: 16, Cp: 0.62.

  • Disp: 717 lbs (325 kg) at Draft: 11.17" (28.4 cm), LWL: 18.7' (570 cm)
  • Disp: 1002 lbs (454 kg) at Draft: 14.17" (36 cm), LWL: 19.685' (6 m)

Proa6m_2017_Nov28a.png.f45d75d6b43acf62b301cd64666f95ed.png

Proa6m_2017_Nov28a2.thumb.png.317fe4478156833ca156452164b57571.png

Does your modeling give you some idea of surface sq feet?

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8 hours ago, Kenny Dumas said:

There must be some reason the spars are on the weather side of the mast, but I don't get it.  Distorts sail shape and makes harder to depower I would think.  What am I missing?

Also, they seem to use high density amas, less cross sectional area / drag for the weight I guess.  More interested in righting moment than buoyancy eh?

The only reason I see for the spars on the weather side is to help with better sail twist and camber. It looks very strange to me too, but all the photographs I've found, old and new, are like this.

Solid wood amas are the norm for traditional outriggers. Usually the wood chosen would be of not so hight density. Less work to do is also a bonus with this choice.

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11 hours ago, Amati said:

Does your modeling give you some idea of surface sq feet?

Six meter (19.7') proa hull, multi-chine, L/B: 16, BOA: 14.76" (37.5 cm)

  • Draft of 11" (28 cm) , Disp.: 717 lbs (325 kg), Waterplane area (Awp): 17.6 sq ft (1.64 sq m), Waterplane ratio (Cwp): 0.77, Wetted Surface: 35.5 sq ft (3.3 sq m), Cp: 0.62
  • Draft of 14" (35.6 cm), Disp.: 1001 lbs (454 kg), Waterplane area (Awp): 17.76 sq ft (1.65 sq m), Waterplane ratio (Cwp): 0.73, Wetted Surface: 45.3 sq ft (4.2 sq m), Cp: 0.62

Proa6m_2017_Dec1a.png.b7b0a9c8a36e72477ee6c6a547fb25b8.png

Proa6m_2017_Dec1a2.thumb.png.532c4160ff496de2e7bb9f538668a2fa.png

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2 hours ago, ProaSailor said:

Six meter (19.7') proa hull, multi-chine, L/B: 16, BOA: 14.76" (37.5 cm)

  • Draft of 11" (28 cm) , Disp.: 717 lbs (325 kg), Waterplane area (Awp): 17.6 sq ft (1.64 sq m), Waterplane ratio (Cwp): 0.77, Wetted Surface: 35.5 sq ft (3.3 sq m), Cp: 0.62
  • Draft of 14" (35.6 cm), Disp.: 1001 lbs (454 kg), Waterplane area (Awp): 17.76 sq ft (1.65 sq m), Waterplane ratio (Cwp): 0.73, Wetted Surface: 45.3 sq ft (4.2 sq m), Cp: 0.62

Proa6m_2017_Dec1a.png.b7b0a9c8a36e72477ee6c6a547fb25b8.png

Proa6m_2017_Dec1a2.thumb.png.532c4160ff496de2e7bb9f538668a2fa.png

LOA: 14' (427 cm), multi-chine proa hull, L/B: 16, BOA: 10.5" (26.7 cm)

  • Draft: 9" (22.9 cm) , Disp.: 300 lbs (136 kg), Waterplane area (Awp): 8.9 sq ft (0.83 sq m), Waterplane ratio (Cwp): 0.77, Wetted Surface: 19.6 sq ft (1.82 sq m), Cp: 0.62
  • Draft: 12" (30 cm), Disp.: 444 lbs (201 kg), Waterplane area (Awp): 8.98 sq ft (0.83 sq m), Waterplane ratio (Cwp): 0.73, Wetted Surface: 26.56 sq ft (2.47 sq m), Cp: 0.62

LOA: 16' (488 cm), multi-chine proa hull, L/B: 16, BOA: 12" (30.5 cm)

  • Draft: 9.7" (24.6 cm) , Disp.: 421 lbs (191 kg), Waterplane area (Awp): 11.6 sq ft (1.0 sq m), Waterplane ratio (Cwp): 0.77, Wetted Surface: 24.7 sq ft (2.3 sq m), Cp: 0.62
  • Draft: 12.7" (32.25 cm), Disp.: 608 lbs (276 kg), Waterplane area (Awp): 11.73 sq ft (1.01 sq m), Waterplane ratio (Cwp): 0.73, Wetted Surface: 32.6 sq ft (3.0 sq m), Cp: 0.62

All three hulls side by side: 6 meters (19.7'), 16' and 14'.  Only model length is changed, no other parameters.  At minimum draft/displacement values noted above:Proa6m_2017_Dec1b2.thumb.jpg.20c44e6bf4bd5203c0e0ed49405faa69.jpg

More heavily loaded to +3" displacement values noted above:Proa6m_2017_Dec1b.thumb.jpg.f8713de43b29cd8e21784e9f47e288e0.jpg

Proa6m_2017_Dec1b3.thumb.png.2883057236003bcc5e2e0a334ec8942a.png

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There is an unintended curiosity about this model...  Been meaning to "fix it" but want to note its effects before it goes away (if it goes away - maybe add a switch?).

There is a slider labeled "Bow Rel Height" which is now an absolute value in the Rhino/GH model's units.  This value is not proportional to length so didn't change and all three of these hulls have the same heights related to sheer, chines, bow knuckle and rocker.  Didn't really mean to do that and perhaps its not best, though it is interesting.  If "Bow Rel Height" were proportional to LOA or BOA, side view scaling (in Z) would be different - probably more as expected?

Proa6m_2017_Dec1b4.png.45538d6891408e2f51c51cad61ec8d0c.png

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15 hours ago, semelis said:

The only reason I see for the spars on the weather side is to help with better sail twist and camber. It looks very strange to me too, but all the photographs I've found, old and new, are like this.

 

Maybe it's easier to get "luff tension"?  Without high strength materials (blue tarp) the sail would stretch / bag too much and be slow to weather or on a tight reach?  A distorted flat sail is better than a baggy smooth sail?  And crab claws / latteen rigs have  a spar for the luff so are set to leeward?

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Probably. The original design worked with a sail made of pandanus leafs, standard material there.

They kept it when cotton sails arrived, while in other parts of Melanesia  and Polynesia did switch to sprit sails or other western rigging.

They are still at it with the blue tarp, so I guess it does work well enough.

 

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3 hours ago, ProaSailor said:

LOA: 14' (427 cm), multi-chine proa hull, L/B: 16, BOA: 10.5" (26.7 cm)

  • Draft: 9" (22.9 cm) , Disp.: 300 lbs (136 kg), Waterplane area (Awp): 8.9 sq ft (0.83 sq m), Waterplane ratio (Cwp): 0.77, Wetted Surface: 19.6 sq ft (1.82 sq m), Cp: 0.62
  • Draft: 12" (30 cm), Disp.: 444 lbs (201 kg), Waterplane area (Awp): 8.98 sq ft (0.83 sq m), Waterplane ratio (Cwp): 0.73, Wetted Surface: 26.56 sq ft (2.47 sq m), Cp: 0.62

LOA: 16' (488 cm), multi-chine proa hull, L/B: 16, BOA: 12" (30.5 cm)

  • Draft: 9.7" (24.6 cm) , Disp.: 421 lbs (191 kg), Waterplane area (Awp): 11.6 sq ft (1.0 sq m), Waterplane ratio (Cwp): 0.77, Wetted Surface: 24.7 sq ft (2.3 sq m), Cp: 0.62
  • Draft: 12.7" (32.25 cm), Disp.: 608 lbs (276 kg), Waterplane area (Awp): 11.73 sq ft (1.01 sq m), Waterplane ratio (Cwp): 0.73, Wetted Surface: 32.6 sq ft (3.0 sq m), Cp: 0.62

All three hulls side by side: 6 meters (19.7'), 16' and 14'.  Only model length is changed, no other parameters.  At minimum draft/displacement values noted above:Proa6m_2017_Dec1b2.thumb.jpg.20c44e6bf4bd5203c0e0ed49405faa69.jpg

More heavily loaded to +3" displacement values noted above:Proa6m_2017_Dec1b.thumb.jpg.f8713de43b29cd8e21784e9f47e288e0.jpg

Proa6m_2017_Dec1b3.thumb.png.2883057236003bcc5e2e0a334ec8942a.png

Take the WS of, say, the last iteration, and double it (as a guess) to get total surface area (so the last one would be ~65sq ft , divided by a 4 by 8 of marine ply, ~ 2 sheets, and if you’re using 6mm, which is about 22lbs/sheet, so without  interior structural stuff, glueing, sheathing, or paint = 44lbs, so add them, you’re up to ~70 lbs? / hull (go with 9mm and it gets up to >100lbs), then add everything else, is this close to what you’re assuming?

One of the reasons I’ve gone with low freeboard is weight saving a by paring the hull.  Which is not optimum, granted...

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2 hours ago, ProaSailor said:

There is an unintended curiosity about this model...  Been meaning to "fix it" but want to note its effects before it goes away (if it goes away - maybe add a switch?).

There is a slider labeled "Bow Rel Height" which is now an absolute value in the Rhino/GH model's units.  This value is not proportional to length so didn't change and all three of these hulls have the same heights related to sheer, chines, bow knuckle and rocker.  Didn't really mean to do that and perhaps its not best, though it is interesting.  If "Bow Rel Height" were proportional to LOA or BOA, side view scaling (in Z) would be different - probably more as expected?

Proa6m_2017_Dec1b4.png.45538d6891408e2f51c51cad61ec8d0c.png

Added a switch to make bow height relative (proportional) to length.  Keeps things in expected 3-D scale, the shorter hulls sit lower, gain a little displacement, less absolute sheer which distorted with length.  The new fleet is on the right:

Proa6m_2017_Dec1c.thumb.jpg.a3f19bcd21ddcdb782398e4526b370eb.jpg

LOA: 14', multi-chine proa hull, L/B: 16, BOA: 10.5"

  • Draft: 9", Disp.: 314 lbs, Waterplane area (Awp): 8.98 sq ft, Waterplane ratio (Cwp): 0.74, Wetted Surface: 20.65 sq ft, Cp: 0.62
  • Draft: 12", Disp.: 458 lbs, Waterplane area (Awp): 8.98 sq ft, Waterplane ratio (Cwp): 0.73, Wetted Surface: 27.68 sq ft, Cp: 0.62

LOA: 16', multi-chine proa hull, L/B: 16, BOA: 12" (30.5 cm)

  • Draft: 9.7", Disp.: 432 lbs, Waterplane area (Awp): 11.7 sq ft, Waterplane ratio (Cwp): 0.75, Wetted Surface: 25.5 sq ft, Cp: 0.62
  • Draft: 12.7", Disp.: 621 lbs, Waterplane area (Awp): 11.73 sq ft, Waterplane ratio (Cwp): 0.73, Wetted Surface: 33.5 sq ft, Cp: 0.62
36 minutes ago, Amati said:

Do take the WS of day the last one, and double it to get total surface area (so the last one would be ~65sq f, divided by a 4 by 8 of marine ply, ~ 2 sheets, and at you’re using 6mm, which is about 22lbs/sheet, so without  interior structural stuff, glueing, sheathing, or paint = 44lbs, so you’re up to ~70 lbs? / hull (go with 9mm and it gets up to >100lbs), then add everything else, is this close to what you’re assuming?

One of the reasons I’ve gone with low freeboard is weight saving a by paring the hull.  Which is not optimum, granted...

Yes, that is close to what I'm assuming, if I understand  you correctly.  I don't know weights of plywood anymore.  These multi-chine hulls might be best for main hulls and the single-chine deep-V better for the amas?

 I think a lot of work is required to build a boat so why not make it worthwhile?  If it can't carry what an old Hobie cat can then why bother?  Two or three big people with some gear is ~700 lbs payload not including the hulls and rig.  That is very heavy on 14', more manageable at 16' and easy at six meters (19.7'), with displacement to spare.

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[sails hijack, last. You can look at how low the freeboard is, too :)  , not intended for off-shore I would say. ] 

Sail material progression, I find interesting that the pandanus  leaf one has rounded tips, even if it does not get to be elliptical :

Neuguinea_waga1.jpg.e791417a15f37e8e84751572412a19f8.jpg

It says "pandanus" in the photograph, but I think it's not, cotton maybe.

5a21b908b00d8_Ninigosailingcanoes0002.jpg.6f8c484c38720a30c70b799c106868e9.jpg

Blue tarp, showing the effect of the sail leaning on the mast.

5a21b9219a356_Ninigo-254.jpg.7ea0de9b8f85c02adffd57b044834d17.jpg

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1 hour ago, semelis said:

[sails hijack, last. You can look at how low the freeboard is, too :)  , not intended for off-shore I would say. ] 

Sail material progression, I find interesting that the pandanus  leaf one has rounded tips, even if it does not get to be elliptical :

Neuguinea_waga1.jpg.e791417a15f37e8e84751572412a19f8.jpg

It says "pandanus" in the photograph, but I think it's not, cotton maybe.

5a21b908b00d8_Ninigosailingcanoes0002.jpg.6f8c484c38720a30c70b799c106868e9.jpg

Blue tarp, showing the effect of the sail leaning on the mast.

5a21b9219a356_Ninigo-254.jpg.7ea0de9b8f85c02adffd57b044834d17.jpg

Pandanus ~ thick membrane sails?  Has a better hand?

heres my sailmaker’s stab at it- at my prodding/

 

5AB9A372-EE67-427C-8C1E-7AE1EA40815D.jpeg

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On 11/30/2017 at 11:35 AM, Kenny Dumas said:

There must be some reason the spars are on the weather side of the mast, but I don't get it.  Distorts sail shape and makes harder to depower I would think.  What am I missing?

Also, they seem to use high density amas, less cross sectional area / drag for the weight I guess.  More interested in righting moment than buoyancy eh?

That’s my thought- it does minimize the the thrill of the deathroll, especially if you don’t have to fully commit.....

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22 hours ago, ProaSailor said:

I think a lot of work is required to build a boat so why not make it worthwhile?  If it can't carry what an old Hobie cat can then why bother?  Two or three big people with some gear is ~700 lbs payload not including the hulls and rig.  That is very heavy on 14', more manageable at 16' and easy at six meters (19.7'), with displacement to spare.

While bigger is still better, a minimum size small proa for me could be two 16' hulls like these, where the ama supports two big guys and the main hull can handle three+.  Beam for both hulls together is eight feet.:

Main hull - LOA:16', multi-chine, L/B: 16, BOA: 12"
Draft 9.7", 448 lbs, Cp: 0.64, Awp: 12.1, WS: 26 sq ft
+6", 837 lbs, Cp: 0.68, Awp: 12.1, WS: 42.1 sq ft

Ama - LOA:16', single-chine, deep-V, L/B: 16, BOA: 12"
Draft 9", 287 lbs, Cp: 0.62, Awp: 11.5, WS: 20.5 sq ft
+3", 446 lbs, Cp: 0.66, Awp: 6.5, WS: 31.5 sq ft

Stills from animations, above and below:

Proa16_2017_Dec2a2.png.d672eaf4f2808ed772a80e4fdeb271ee.png

Proa16_2017_Dec2a.png.7865b492e538e38e1a96a0f3f6e14c09.png

Proa16_2017_Dec2a3.png.b2dfaf831f239415a2b9259ab9e7dc06.png

Proa16_2017_Dec2a4.png.d2e358429553718f85a75eafe0d8691b.png

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Amati, your sail maker needs to study the classics:

O1_0175.jpg.769283ee66b43fcfb6f31a686c11dedd.jpg

Most of the small (and not that small) traditional outriggers (shunting proas as well as tacking ones) have a leeward platform, or extension of the platform, to compensate with crew weight there the low buoyancy of the ama when needed.

Fijian druas, or kalias as they are known in Tonga or Samoa, have 2 real hulls, the smaller to windward, but those were quite big boats.

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1 hour ago, semelis said:

Amati, your sail maker needs to study the classics:

O1_0175.jpg.769283ee66b43fcfb6f31a686c11dedd.jpg

Most of the small (and not that small) traditional outriggers (shunting proas as well as tacking ones) have a leeward platform, or extension of the platform, to compensate with crew weight there the low buoyancy of the ama when needed.

Fijian druas, or kalias as they are known in Tonga or Samoa, have 2 real hulls, the smaller to windward, but those were quite big boats.

Great drawing!  Shows the mast base stepped to windward on the forward beam.  Moved to either end, no doubt.

And yeah, the windward ama in the old canoes was often literally a carved log, heavy with neutral or minimum reserve buoyancy, easily sinkable - requires more active balancing by moving bodies or getting wet.

By the way, surface area on the pair of 16' proa hulls mentioned above is 41 sq ft plus 64 sq ft = 105 square feet total surface (skin) area for both hulls for ~800 lbs  displacement.

Kayaks and canoes with size and displacement similar to the ama are often built for ~50 lbs or less.
http://www.selway-fisher.com/Opcan16.htm

Wren Particulars

LOA			15'10"	4.83m
Beam			33"	0.84m
Hull Mid Depth		12 1/2"	0.32m
Approx. Dry Weight	45lbs	20kg
Approx. Capacity	750lbs	340kg

Hull Shape		Narrow flat bottom plank plus 2 planks per side
Construction Method	Stitch and tape
Plywood Requirements	3 sheets of 4,5 or 6mm
Guidance Use		General purpose with 2 adults
Drawing/Design Package	2 x A1 drawings + 8 x A4 instruction sheets

Wrenp5.jpg

Twenty years ago, Ted Warren launched Tiny Dancer, a 21' proa that weighed 100 lbs "assembled boat and spars". 

td2-l.jpgtd3-l.jpg

 

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2 hours ago, semelis said:

Amati, your sail maker needs to study the classics:

O1_0175.jpg.769283ee66b43fcfb6f31a686c11dedd.jpg

Most of the small (and not that small) traditional outriggers (shunting proas as well as tacking ones) have a leeward platform, or extension of the platform, to compensate with crew weight there the low buoyancy of the ama when needed.

Fijian druas, or kalias as they are known in Tonga or Samoa, have 2 real hulls, the smaller to windward, but those were quite big boats.

We considered that, so we upped the cloth weight (kind of like the Stradivarius AC tri initially did with the black sail) The top spar is too centered in the pic for designed twist. I moved it.

I wanted the mast on the leeward rail so I had somewhere to sit in light airs, also so the mast weight to leeward would allow me to sit to windward a bit more comfortably in light airs. I had a leeward extension of the plank, but sawed it off  in the interest of weight.  Dumb. 

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1 hour ago, Amati said:

I wanted the mast on the leeward rail so I had somewhere to sit in light airs

You accepted an un-stayed mast right from the beginning?  Does that become a limiting factor in carrying sail when the hulls get sorted out?

Here are six guys sailing a Hawaiian canoe with a safety ama.  Big canoe.

smaller canoe:

One more:

 

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19 minutes ago, ProaSailor said:

You accepted an un-stayed mast right from the beginning?  Does that become a limiting factor in carrying sail when the hulls get sorted out?

Here are six guys sailing a Hawaiian canoe with a safety ama.  Big canoe.

smaller canoe:

 

An unstayed mast was the center of the design:

ease of rigging 

better when backed

doesn’t get in the way of a dipping lug (which is what the rig is)

less to get snagged on when crashing and burning

I like unstayed masts- I have 3 unstayed masts (2 of which I had designed and built for me)  and I wanted to use one I had

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1 hour ago, Amati said:

We considered that, so we upped the cloth weight (kind of like the Stradivarius AC tri initially did with the black sail) The top spar is too centered in the pic for designed twist. I moved it.

I wanted the mast on the leeward rail so I had somewhere to sit in light airs, also so the mast weight to leeward would allow me to sit to windward a bit more comfortably in light airs. I had a leeward extension of the plank, but sawed it off  in the interest of weight.  Dumb. 

I guess that the battens were necessary with the pandanus sail, maybe not so much with modern materials.

The right twist in a sail with that aspect ratio must be tricky. 

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13 minutes ago, semelis said:

I guess that the battens were necessary with the pandanus sail, maybe not so much with modern materials.

The right twist in a sail with that aspect ratio must be tricky. 

Lower AR is easier, but washout has its rewards....B)

In light airs, this ^ rig is amazing, although it is fiddly....

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