89er

JulianB

Super Anarchist
1,101
1,423
Sydney mostly
Here we go again.

This did not end well for you last time, but if you wish to be slammed again, so be it, your problem not mine.

#1, the reference to speed was purely in relation to the fact that a lot of long thin bowed boats are capable of quite extraordinary speeds and the inference was that whether the bow was a punt, a scow, or a long & thin, it did not seem detrimental to top end performance in sailing boats.

One could sight Wild Oat, Comanche, Itchy Ban, even Vesta Rocket.

But I chose 49er, 29er & Vivace, because they were more relevant.

#2, re top end speeds of 29ers.

Simple fact, 29er are capable of higher top end speed than 49er, they always have, and they always will.

If you now wish to dispute top end speed of a 49er, be my guess to slam you head against into the wall, (it’s always good when you stop) there are ample race recorder records to suggest that 49er can and do often achieve speeds in the hi 20 knts.     If you wish to dispute that, please do, I have better things to do than respond.   Suggest you start with Emmett late in the 2000’s.

WRT 29er.

Some time in the early 2000’s I got a very elated email from an American, saying he had broken the 30 knts barrier and he had ample proof to prove it, GPS, etc ete.    I congratulated him.

2005, I was at St Francis Yacht Cub, in a Protector, a few photo jornos, and one Janet Baxter who at the time was Pres of US Sailing.   It was the US 29er Worlds BTW, the sailor had come around a mark somewhere up off the GG, had gybed of StFYC and where heading for Alcatraz, some jurnos asked if we could format on some back markers in gold fleet, I remember it well as we formatted on Soren, a Norwegian team who where in about 15th at the time (they had stayed in my house a year earlier, so I knew them, Sister steering, Brother in the bow), now they were 15th, Silija Letiean (Finnish) who went on to win was gapping them, someone asked how fast we were going, every instrument in that boat was telling us we were doing hi 20’s (knts), and yes there was a universal comment of Bullshit, but it was more in awr than dis-belief.

Now I was driving and I did that and I was party to that and I knew they could be quick, but that was 1st hand and I was impressed.

Since then there have been about another 8 pretty well documented accounts of teams “joining the 30knt club”.   AND GOOD LUCK TO THEM.   They are kids having fun.    I am very well aware of one such sailor who over the last 2 months has tried to break into the club but missed out by only 0.5knts.     He was telling me this, to my face, I have little doubt he will get there.

And then there where the 2018-19 HK Worlds, a particularly breezy series, bruising to put it bluntly.

If the speed off the trackers out on the track where not enough, and again, I had heard this all before, it was impressive, but to then get back home, for any of you who know Middle Island in HK and the gutter between it and the mainland where the wind picked up another 20-25%, the kids had to sail through this and rather than being terrified, they where having a ball., most made it, some ended up in tears but the shrieks of joy and the smiles on these kids faces said it all, they were having a hoot, and I have rarely ever seen boats go quite so fast.

It is of no concern to me what you believe and what you wish to believe.   That’s your problem.

I know what the boats are capable of.

I am vey comfortable with my comments and have no real need to do any more.

                            jB

 
A

Amati

Guest
At the end of the day, that's roughly where I have my fin, but I can't see why that would reduce induced drag.

Love to hear the thinking on that, I get that you already commented you have not seen the data, but it would be interesting to see why someone thinks that?    Normally such things have a element of substance behind them, ofcourse Moths have anhedral which is therefore counter intuative even to me, and as I said before, what do I know, I have always just put my TE perpendicular to the keel line aft and worked around that.
FWIW, our 40’ cruising sled has a forward swept bulb keel initially inspired by Gutelle and dinghy class practice. David Vacanti was involved in the hydro. She’s not a racer, but based on feel, grip, smoothness, speed and height upwind, we’ve been happy, and she’s stable, never a twitch planing downwind.  Tiller driven.  ( On the other hand, Bob Perry, the designer, in his book ‘Perry on Yacht design’, written after Amati’s design, states he’s skeptical about forward sweep, so there you go….)

Always liked your balsa 18- Amati is constructed using Steve Rander’s COVE method- e glas, strip planked cedar, e glas, klegecell, e glas, cedar, e glas, all in epoxy. Deck uses e glas, plywood, e glas, klegecell, e glas, plywood e glas 20 years later, still stiff.  

Nice project of yours!
 

 
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JulianB

Super Anarchist
1,101
1,423
Sydney mostly
Amati,  Moths (following in your footsteps) have proven that fwd sweep is not such a bit deal. Had a very interesting conversation WRT "to bulb or not to bulb" with Leon few days back. When I say no bulb, I'm talking lead in the fin rather than that in the bulb. 

If you assume that you are getting a endplate effect from the bulb, then my back of the envelope maths would suggest that you would have to increase the size of the fin and infact be at a greater disadvantage without the bulb than you would be with it.

Whole range of assumptions yad yad yad, but the reason I am saying this now, in reference to your fwd sweep is you fwd sweep to increase efficiency (as commented before by Sidecar) if you have a bulb (or a endplate) then KISS and just make it vertical or close to it.

Really appreciate your comments,  adds to the colour of the conversation.

      jB

BTW, given the developments in the ABSA, Leon and I will probably get small 70-80kg bulbs made.  One for him, one for me.

 

Taipan

New member
22
1
Aus
Hi Julian B,

Thank you for continuing to post and comment on the 89er progress. I've read your book (and Frank's) and it's still very insightful to follow and appreciate the thought and science that goes into developing a new boat.

A little off topic but i wondered if you have/or could express your thoughts on the RS Aero? Is the design right? The class seems to be building towards success with growing fleet numbers (something lacking in my region of fragmented classes). 

Kind regards

Dave

 
A

Amati

Guest
Amati,  Moths (following in your footsteps) have proven that fwd sweep is not such a bit deal. Had a very interesting conversation WRT "to bulb or not to bulb" with Leon few days back. When I say no bulb, I'm talking lead in the fin rather than that in the bulb. 

If you assume that you are getting a endplate effect from the bulb, then my back of the envelope maths would suggest that you would have to increase the size of the fin and infact be at a greater disadvantage without the bulb than you would be with it.

Whole range of assumptions yad yad yad, but the reason I am saying this now, in reference to your fwd sweep is you fwd sweep to increase efficiency (as commented before by Sidecar) if you have a bulb (or a endplate) then KISS and just make it vertical or close to it.

Really appreciate your comments,  adds to the colour of the conversation.

      jB

BTW, given the developments in the ABSA, Leon and I will probably get small 70-80kg bulbs made.  One for him, one for me.
Thanks!  Gutelle points out Delft studies that IIRR, sweep forward or aft, if kept between 10 degrees inclusive (5 either way) doesn’t mess up L/D much, so my insistence of forward sweep was for less tip vortex, and upwash that would clean up the hull/ fin join at lower speeds, and give some lift to the hull at higher speed / length ratios, and maybe damp squatting. Because of this, the hull is a deeper v in front of the fin, and flatter after.  The bulb has a stinger tale rather than a flat horizontal tale, which Vacanti described as a rough water shape.  The bulb is round, not squashed, I think partially because of the difference in tip vortex. (Laurie Davidson apparently didn’t like it, said it should have been flattened w/ a horizontal tail). Had a flat tail bulb on the U20, so I knew what that felt like, but the U20 was beamy, 20’ by 8’, where Amati is slender, 40’ by 10’, so different motions.  What I’ve noticed is that in lumpy water, Amati doesn’t get knocked to leeward of the lumps, which makes steering through the valleys different, and I think more precise, so different hull motions between the two hulls. Water Rat rudder helps too- never had a spin out.  Prismatic is low, for light wind sailing, ~ .53, but doesn’t seem to have a discernible hump, having at least a very clean release at all speeds.  In some ways I think this revolves around sailing style, and the design trade offs that flow from that, which for me were a direct benefit of the Bethwaite smaller spiral of, in this case a slender hull, which I think shows how flexible the concept is.  I guess surfboard/ windsurfer shapers would call it expression.  I do. 

Anyway, I put my $$ where my brain was, for a hull untainted by any nods to a rating rule.  But she is an orphan.  Beguiling, to be sure, but an orphan nonetheless.  

Cheers!  Look forward to your progress!

ps- the Trrfetz plane (never can remember how to spell that) is definitely happier with a vertical trailing edge, but I’d point out that when an 18 is jumping out of the water, the daggerboard is effectively swept forward relative to. the air/water interface, which does help prevent ventilation of a surface piercing foil.  :)

 

 
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JulianB

Super Anarchist
1,101
1,423
Sydney mostly
Hi Julian B,

Thank you for continuing to post and comment on the 89er progress. I've read your book (and Frank's) and it's still very insightful to follow and appreciate the thought and science that goes into developing a new boat.

A little off topic but i wondered if you have/or could express your thoughts on the RS Aero? Is the design right? The class seems to be building towards success with growing fleet numbers (something lacking in my region of fragmented classes). 

Kind regards

Dave
David, they are very much my father's books. Sure, I was extraordinary lucky to have a strong connection with dad, and he and I became partners in crime.  Mum and I where very much the initial editors, we are about the only people who could read dad's hand writting.   But I can claim zero authorship and would not dare to claim it.

While on the subject of dad and his books, I certainly went of on my tangents, and he supported that, but I have strong views of how I assess various aspects of the sailing platform and those ideas are probably close to dad's but may not be the same.

        jB

 

JulianB

Super Anarchist
1,101
1,423
Sydney mostly
David, 2nd part of your email, there are enough "deck chair commodores" passing judgment on the 29er & 49er at present & you should have seen the shit flying around the SKUD, so I have a bit of a un-written rule which is to not sledge or even comment on any design, because at the end of the day it’s all about bums in boats, and better they be in boats than in a golf buggy or a bicycle or a ------!

What I can comment on are my views on the present status of single-handed sailing.

 If you look at the range of single-handers (monohulls) on the market at present, with exception of the Int Moth, maybe the Contender, Musto Skiff, and there is a RS in there also, they are basically hull speed boats.   Some bells and whistles with Spinnakers for downhill, but 99% of them get to HS and that’s it. (Talking about 75-80% of the time, going upwind.)

So what you end up with a range of boats, with a very definite “price point” and if you pay more, you get better design, better ergonomics, better materials and better race management (Associations, think ILCA).

RS are very clever, in that they try to bracket the whole “box and dice” and in many ways they do that, and from what I have seen of the Aero, which is mostly at boat-shows, and speaking with people who sail them (a coffee shop friend is a aficionado) it’s very much at the premium end of the range, that’s what you get and it dose that very well.

It will sell well, but you’re unlikely to get sailing schools or resort to buy it so the actual number of boats that they will sell is limited to the market they have embraced.

OK, enough of talking about existing boats.

The industry needs a breakthrough boat.

That boat will have potentially above average performance, in fact the possibility of hi-performance (and by hi-perf I mean it will break the HS nexus) is key.   99.99% expectation it will be built of Polyethylene [PE] (so Roto-moulded) or blow moulded (like the Bic) and there are 2-3 other things that it needs, but the above 2 are the biggy.

Most people turn their noses up at PE and RM but advances in chemistry is not confined to Carbon Fibre and Basalt, the sample of PE that I have on my desk is impressive and inevitable.

A 4m FRP boat (hull) simply is going to cost at retail say $5+k.   It’s very hard to do it any cheaper.

A PE boat (hull) at retail could cost less than ½, closer to ⅓ and if you want penetration and if you want to convert people who are presently doing something else to sailing, nothing but PE will delivery you a product at a price that will attract.

From memory when the Sunfish and Laser where release (different dates) they would have been the equivalent of about $4k in today terms (I think I remember the laser being $699 (CDN) and that would have been in 196---??? .   Windsurfer, Hobie where all the same.

The next thing is the next biggest market is the one just to the North of me, Asia.

You have to stop thinking British, or god forbid Nth America, and think Asian.

For that reason, I expect that the next revolution will be Asian!

 

JulianB

Super Anarchist
1,101
1,423
Sydney mostly
Thanks!  Gutelle points out Delft studies that IIRR, sweep forward or aft, if kept between 10 degrees inclusive (5 either way) doesn’t mess up L/D much, so my insistence of forward sweep was for less tip vortex, and upwash that would clean up the hull/ fin join at lower speeds, and give some lift to the hull at higher speed / length ratios, and maybe damp squatting. Because of this, the hull is a deeper v in front of the fin, and flatter after.  The bulb has a stinger tale rather than a flat horizontal tale, which Vacanti described as a rough water shape.  The bulb is round, not squashed, I think partially because of the difference in tip vortex. (Laurie Davidson apparently didn’t like it, said it should have been flattened w/ a horizontal tail). Had a flat tail bulb on the U20, so I knew what that felt like, but the U20 was beamy, 20’ by 8’, where Amati is slender, 40’ by 10’, so different motions.  What I’ve noticed is that in lumpy water, Amati doesn’t get knocked to leeward of the lumps, which makes steering through the valleys different, and I think more precise, so different hull motions between the two hulls. Water Rat rudder helps too- never had a spin out.  Prismatic is low, for light wind sailing, ~ .53, but doesn’t seem to have a discernible hump, having at least a very clean release at all speeds.  In some ways I think this revolves around sailing style, and the design trade offs that flow from that, which for me were a direct benefit of the Bethwaite smaller spiral of, in this case a slender hull, which I think shows how flexible the concept is.  I guess surfboard/ windsurfer shapers would call it expression.  I do. 

Anyway, I put my $$ where my brain was, for a hull untainted by any nods to a rating rule.  But she is an orphan.  Beguiling, to be sure, but an orphan nonetheless.  

Cheers!  Look forward to your progress!

ps- the Trrfetz plane (never can remember how to spell that) is definitely happier with a vertical trailing edge, but I’d point out that when an 18 is jumping out of the water, the daggerboard is effectively swept forward relative to. the air/water interface, which does help prevent ventilation of a surface piercing foil.  :)

 
Mate, I may need to re-read this a few times, but I promise to respond, thanks for the input!

AS I may have commented before I am NOT a Naval Architeck (can't even spell it) and Prixmatic Cof is one of those things I have never taken notice of!

            jB

 

Taipan

New member
22
1
Aus
David, 2nd part of your email, there are enough "deck chair commodores" passing judgment on the 29er & 49er at present & you should have seen the shit flying around the SKUD, so I have a bit of a un-written rule which is to not sledge or even comment on any design, because at the end of the day it’s all about bums in boats, and better they be in boats than in a golf buggy or a bicycle or a ------!

What I can comment on are my views on the present status of single-handed sailing.

 If you look at the range of single-handers (monohulls) on the market at present, with exception of the Int Moth, maybe the Contender, Musto Skiff, and there is a RS in there also, they are basically hull speed boats.   Some bells and whistles with Spinnakers for downhill, but 99% of them get to HS and that’s it. (Talking about 75-80% of the time, going upwind.)

So what you end up with a range of boats, with a very definite “price point” and if you pay more, you get better design, better ergonomics, better materials and better race management (Associations, think ILCA).

RS are very clever, in that they try to bracket the whole “box and dice” and in many ways they do that, and from what I have seen of the Aero, which is mostly at boat-shows, and speaking with people who sail them (a coffee shop friend is a aficionado) it’s very much at the premium end of the range, that’s what you get and it dose that very well.

It will sell well, but you’re unlikely to get sailing schools or resort to buy it so the actual number of boats that they will sell is limited to the market they have embraced.

OK, enough of talking about existing boats.

The industry needs a breakthrough boat.

That boat will have potentially above average performance, in fact the possibility of hi-performance (and by hi-perf I mean it will break the HS nexus) is key.   99.99% expectation it will be built of Polyethylene [PE] (so Roto-moulded) or blow moulded (like the Bic) and there are 2-3 other things that it needs, but the above 2 are the biggy.

Most people turn their noses up at PE and RM but advances in chemistry is not confined to Carbon Fibre and Basalt, the sample of PE that I have on my desk is impressive and inevitable.

A 4m FRP boat (hull) simply is going to cost at retail say $5+k.   It’s very hard to do it any cheaper.

A PE boat (hull) at retail could cost less than ½, closer to ⅓ and if you want penetration and if you want to convert people who are presently doing something else to sailing, nothing but PE will delivery you a product at a price that will attract.

From memory when the Sunfish and Laser where release (different dates) they would have been the equivalent of about $4k in today terms (I think I remember the laser being $699 (CDN) and that would have been in 196---??? .   Windsurfer, Hobie where all the same.

The next thing is the next biggest market is the one just to the North of me, Asia.

You have to stop thinking British, or god forbid Nth America, and think Asian.

For that reason, I expect that the next revolution will be Asian!
Thank you, appreciate your thoughts.

 
A

Amati

Guest
David, 2nd part of your email, there are enough "deck chair commodores" passing judgment on the 29er & 49er at present & you should have seen the shit flying around the SKUD, so I have a bit of a un-written rule which is to not sledge or even comment on any design, because at the end of the day it’s all about bums in boats, and better they be in boats than in a golf buggy or a bicycle or a ------!

What I can comment on are my views on the present status of single-handed sailing.

 If you look at the range of single-handers (monohulls) on the market at present, with exception of the Int Moth, maybe the Contender, Musto Skiff, and there is a RS in there also, they are basically hull speed boats.   Some bells and whistles with Spinnakers for downhill, but 99% of them get to HS and that’s it. (Talking about 75-80% of the time, going upwind.)

So what you end up with a range of boats, with a very definite “price point” and if you pay more, you get better design, better ergonomics, better materials and better race management (Associations, think ILCA).

RS are very clever, in that they try to bracket the whole “box and dice” and in many ways they do that, and from what I have seen of the Aero, which is mostly at boat-shows, and speaking with people who sail them (a coffee shop friend is a aficionado) it’s very much at the premium end of the range, that’s what you get and it dose that very well.

It will sell well, but you’re unlikely to get sailing schools or resort to buy it so the actual number of boats that they will sell is limited to the market they have embraced.

OK, enough of talking about existing boats.

The industry needs a breakthrough boat.

That boat will have potentially above average performance, in fact the possibility of hi-performance (and by hi-perf I mean it will break the HS nexus) is key.   99.99% expectation it will be built of Polyethylene [PE] (so Roto-moulded) or blow moulded (like the Bic) and there are 2-3 other things that it needs, but the above 2 are the biggy.

Most people turn their noses up at PE and RM but advances in chemistry is not confined to Carbon Fibre and Basalt, the sample of PE that I have on my desk is impressive and inevitable.

A 4m FRP boat (hull) simply is going to cost at retail say $5+k.   It’s very hard to do it any cheaper.

A PE boat (hull) at retail could cost less than ½, closer to ⅓ and if you want penetration and if you want to convert people who are presently doing something else to sailing, nothing but PE will delivery you a product at a price that will attract.

From memory when the Sunfish and Laser where release (different dates) they would have been the equivalent of about $4k in today terms (I think I remember the laser being $699 (CDN) and that would have been in 196---??? .   Windsurfer, Hobie where all the same.

The next thing is the next biggest market is the one just to the North of me, Asia.

You have to stop thinking British, or god forbid Nth America, and think Asian.

For that reason, I expect that the next revolution will be Asian!
I wonder if Starboard is a leading edge indicator there?  

 
A

Amati

Guest
Sorry, don't get the Starboard infrence, can you expand??
Gladly-

here’s a link to their website.  High tech company, wondering out loud if they are leading an Asian future for sailing- based in Thailand.  

I’ll post it in a minute- technical problems

 

JulianB

Super Anarchist
1,101
1,423
Sydney mostly
That Starboard!  I was on a conference call with them month or so ago, part of greening the sport.  They are also part of the i-Foiler from memory.

Small side note is that the original name of Bethwaite Design was Starboard Products, registered in 1965. It was changed in 2001 because that's what people called us.

     Foaming my hull, come back to you tomorrow.

          jB

 

JulianB

Super Anarchist
1,101
1,423
Sydney mostly
Thanks!  Gutelle points out Delft studies that IIRR, sweep forward or aft, if kept between 10 degrees inclusive (5 either way) doesn’t mess up L/D much, so my insistence of forward sweep was for less tip vortex, and upwash that would clean up the hull/ fin join at lower speeds, and give some lift to the hull at higher speed / length ratios, and maybe damp squatting. Because of this, the hull is a deeper v in front of the fin, and flatter after.  The bulb has a stinger tale rather than a flat horizontal tale, which Vacanti described as a rough water shape.  The bulb is round, not squashed, I think partially because of the difference in tip vortex. (Laurie Davidson apparently didn’t like it, said it should have been flattened w/ a horizontal tail). Had a flat tail bulb on the U20, so I knew what that felt like, but the U20 was beamy, 20’ by 8’, where Amati is slender, 40’ by 10’, so different motions.  What I’ve noticed is that in lumpy water, Amati doesn’t get knocked to leeward of the lumps, which makes steering through the valleys different, and I think more precise, so different hull motions between the two hulls. Water Rat rudder helps too- never had a spin out.  Prismatic is low, for light wind sailing, ~ .53, but doesn’t seem to have a discernible hump, having at least a very clean release at all speeds.  In some ways I think this revolves around sailing style, and the design trade offs that flow from that, which for me were a direct benefit of the Bethwaite smaller spiral of, in this case a slender hull, which I think shows how flexible the concept is.  I guess surfboard/ windsurfer shapers would call it expression.  I do. 

Anyway, I put my $$ where my brain was, for a hull untainted by any nods to a rating rule.  But she is an orphan.  Beguiling, to be sure, but an orphan nonetheless.  

Cheers!  Look forward to your progress!

ps- the Trrfetz plane (never can remember how to spell that) is definitely happier with a vertical trailing edge, but I’d point out that when an 18 is jumping out of the water, the daggerboard is effectively swept forward relative to. the air/water interface, which does help prevent ventilation of a surface piercing foil.  :)

 
Amati, I owe you a response, agree with everything you said, but I would have said it was +/- 7° but we are spliting hairs.

Sorry Prismatic my eys glaze over, some one will have to explain to me why this has a bearing on SportsBoat design???

And I am also with you, putting my money where my mouth/brain is, I probably won't be a orphan, but just think about what Herreshoff had to go through or even more so (but hidden away in NZ) what Archie Logan did, just imagine if he had remained in Scotland, fortune favors the bold.   (I just should have done it years ago)

(it's spelt) Trefftz plane, need to take that on notice.

I also have been taken to task over Froud numbers.   All I care about is the angle that the water is split at nominal water lever by the bow, front say 5-7% of LWL.   I call it Froud, I'm being told I can't!   Good luck.

And I am also being told my 89er will surely plane up wind.

OK, if I am sailing at 89° to the wind, then technically I'm upwind and yes I can probably get it planning especially as I suspect that my AWA will never get aft of the beam unless I am running dead into a mark, but my definition of planning up wind, used to be WS, which was you can acheive a great VMG to windward by doing so, and under that definition, I think not!

~~~~~~~~~~~~~~~~~~~~~~~

image.png

Prior to glassing the plug (with polyester to get a vacuum seal) I took the oppotunity to pre-fit the foam, by screwing into the plug, yes brutal, but the polyester/CSM/cloth/gelcaot will cover all ills.

I resorted to a 9" angle grinder and torture board fair the plug, pulling staples out so I could use a plane did more damage to the plug than was warrented (and was very time consuming) so if your going to replicate what I have done, turn the pressure up on the staple gun so they go well down into the MDF.

Took maybe 8hrs of toil, but its pretty good.

So in this process you make the hi spots with a pencil, use the 9" to grind them off, then do a rudimentray fair with the torture board, mark where its been in contact by scribbling with a pencil, 9" and grind it off, and repeat as many times as it takes to come down to say +/-1mm.

You get good at keeping the 9" moving so it dose not dig, and yes you get covered in dust, so wear a resporator!

With any luck, by the end of Monday the plug will be glassed, by the end of Tuesday, it will be gelcoated (Wednesday is beer can racing) Thursday will be final prep, then early Friday, got 2 helpers coming up and the plan is to get the Unies down, the innner layer of basalt and the P80, 10mm and 20mm core all sucked down.

Saturday 27th got the 7 Islands race, so Stanno, if your at Hunter Hill you can bring me out a beer.

Monday 6th, clean up, and a pretty serious fairing job, that may continue into Tuesday.

But by Thursday or Friday we should have the 3.5mm P115 core and outer skin sucked on.

Mid december we should be up-right.

 
A

Amati

Guest
Amati, I owe you a response, agree with everything you said, but I would have said it was +/- 7° but we are spliting hairs.

Sorry Prismatic my eys glaze over, some one will have to explain to me why this has a bearing on SportsBoat design???

And I am also with you, putting my money where my mouth/brain is, I probably won't be a orphan, but just think about what Herreshoff had to go through or even more so (but hidden away in NZ) what Archie Logan did, just imagine if he had remained in Scotland, fortune favors the bold.   (I just should have done it years ago)

(it's spelt) Trefftz plane, need to take that on notice.

I also have been taken to task over Froud numbers.   All I care about is the angle that the water is split at nominal water lever by the bow, front say 5-7% of LWL.   I call it Froud, I'm being told I can't!   Good luck.

And I am also being told my 89er will surely plane up wind.

OK, if I am sailing at 89° to the wind, then technically I'm upwind and yes I can probably get it planning especially as I suspect that my AWA will never get aft of the beam unless I am running dead into a mark, but my definition of planning up wind, used to be WS, which was you can acheive a great VMG to windward by doing so, and under that definition, I think not!

~~~~~~~~~~~~~~~~~~~~~~~

View attachment 475143

Prior to glassing the plug (with polyester to get a vacuum seal) I took the oppotunity to pre-fit the foam, by screwing into the plug, yes brutal, but the polyester/CSM/cloth/gelcaot will cover all ills.

I resorted to a 9" angle grinder and torture board fair the plug, pulling staples out so I could use a plane did more damage to the plug than was warrented (and was very time consuming) so if your going to replicate what I have done, turn the pressure up on the staple gun so they go well down into the MDF.

Took maybe 8hrs of toil, but its pretty good.

So in this process you make the hi spots with a pencil, use the 9" to grind them off, then do a rudimentray fair with the torture board, mark where its been in contact by scribbling with a pencil, 9" and grind it off, and repeat as many times as it takes to come down to say +/-1mm.

You get good at keeping the 9" moving so it dose not dig, and yes you get covered in dust, so wear a resporator!

With any luck, by the end of Monday the plug will be glassed, by the end of Tuesday, it will be gelcoated (Wednesday is beer can racing) Thursday will be final prep, then early Friday, got 2 helpers coming up and the plan is to get the Unies down, the innner layer of basalt and the P80, 10mm and 20mm core all sucked down.

Saturday 27th got the 7 Islands race, so Stanno, if your at Hunter Hill you can bring me out a beer.

Monday 6th, clean up, and a pretty serious fairing job, that may continue into Tuesday.

But by Thursday or Friday we should have the 3.5mm P115 core and outer skin sucked on.

Mid december we should be up-right.
Thanks for the reply Julian, you’re busy and I appreciate it. FWIW, personally, I look at prismatic as part of the structural poetics of sailboat design- for example, immersed wetted surface and pressure recovery in really light air. If the crew can’t run around on a boat and change the shape of the immersed wetted surface I think prismatic matters, although many decades ago an older wise head told me that if you throw supersonic flow characteristics into design modeling, low prismatic could be made to work at higher speed/lengths, if you’re light enough. He was a Boeing fluid flow tech fellow who was hired by an AC team.  He had a thick & delicious German accent, we were drinking a great Chardonnay, and a lot of the conversation was about the AC team actually doing something with his design input. (Like when they got desperate.) He did have fun with that.  He also had an unlimited glider in his garage that he designed, built, and flew himself.  Neat! 

I really need to accept that Trefftz wasn’t Welsh. :p

There are so many pursuits that are intrinsically worth doing- Herreschoff, Logan etc etc at the very least had a lot of intense fun thinking their thoughts.  

Have fun sculpting!  The artist at work.
 

 

Sidecar

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Sorry Prismatic my eys glaze over, some one will have to explain to me why this has a bearing on SportsBoat design??
It doesn’t.

Because the majority of the displacement is taken up with dynamic crew weight which can be shifted around to change trim to suit conditions. Your 89’er is a big dinghy, the keel bulb is mostly there for the ride, and only really useful to help bring it back from (near) capsize, and to make sure the boat won’t tip over when left alone on a mooring or pontoon. FWIW, By eye and fag  packet, I reckon your 89’er has a Cp of ~ 0.52, which is pretty low anyhow.

Back in the day, on yachts where most of the weight was “fixed” in the boat, and absolute flat water top speeds were pretty much limited to 1.34*LWL^0.5, Cp might have been important. With the advent of advanced materials, much lighter “fixed” weights and design, those days are pretty well gone.

@Amati FWIW: Even current fat little Dudley Dix designs have Cp’s of ~ 0.54.

 
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Amati

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It doesn’t.

Because the majority of the displacement is taken up with dynamic crew weight which can be shifted around to change trim to suit conditions. Your 89’er is a big dinghy, the keel bulb is mostly there for the ride, and only really useful to help bring it back from (near) capsize, and helps to make sure the boat won’t tip over when left alone on a mooring. FWIW, By eye and fag  packet, I reckon your 89’er has a Cp of ~ 0.52, which is pretty low anyhow.

Back in the day, on yachts where most of the weight was fixed in the boat, and absolute top speeds were pretty much limited to 1.34*LWL^0.5, Cp might have been important. With the advent of advanced materials and design, those days are pretty well gone.

@Amati FWIW: Even current fat little Dudley Dix designs have Cp’s of ~ 0.54.
Yup.  But 20 years ago people were warning me .53 was daft for a 40er. :eek:  

It’s more than nice that Dudley includes all that info, isn’t it?  Even SA to WS!  Dudley!  Yay!  

 
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Amati

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^^^^ This.

Forward sweep has been tried many times on aircraft because theoretically it is more efficient for a given wing area, you are effectively preventing span wise flow because of the large fuselage/hull end plate. It also theoretically makes the wing and whatever it is attached to more manoeuvrable, but it tends to be more unstable and subject to structural flutter. Anhedral wings can have a similar effect.

And as previously mentioned, Moths have some forward sweep to prevent/minimise ventilation down the leading edge.

Sweep at large angles, can also help with longitudinal stability.

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This is my favorite

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