Amati

bi-directional Proa

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This adapts an old favorite technique to the same 27' ama hull by adding a parametric radius in place of the hard chine at the midsection, then sweeping that curve along the sheer line.  Only a slight loss of displacement, less wetted surface, smoother transition between bottom and topsides.  Simple in CAD, harder to build.

p36_ama27_2017_Dec18a5.png.53afdb6e440365b3830ad9f3ea2482aa.pngp36_ama27_2017_Dec18a.png.6b502f3b486312cb1b9966f2c20a1640.pngp36_ama27_2017_Dec18a2.thumb.png.0dd77a27a46c7bc2d9d122bee327e119.pngp36_ama27_2017_Dec18a3.png.38cd1b29d3e4999e65ca46ca658bdfda.pngp36_ama27_2017_Dec18a4.png.bd99d36a2864d79cac949079af5aab82.png

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Might take a bit of fiddling with plywood shape, but with a 90 degree angle at the bottom (and the top, for that matter),  it wouldn't  be that weird to fold up a hull from the keel using square keel/'deck' timber (lighter than a solid epoxy fillet) - might use 'bow' overhang to make it easier- the shape ^ could be approximated, rounder (pointed oval) and a little skinnier?  Phil S. likes to point out that water likes a shape that doesn't shatter ply.  Go monocoque or use a horizontal web down the widest point of the beam that would double as structure and molding/bending point?  I wonder if molding inner butt joints would double as support for the aka's attachment points. Might do that modularly?  The bonus would be wave piercing 'bows' and would cleave up through a wave easily.  Might have to put all accommodations on the akas/safety pod, leaving hulls only for floatation and hydrodynamics, which would be very post modern.

Sounds too easy.  There must be massive problems in there somewhere....

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28 minutes ago, Amati said:

Might take a bit of fiddling with plywood shape, but with a 90 degree angle at the bottom (and the top, for that matter),  it wouldn't  be that weird to fold up a hull from the keel using square keel/'deck' timber (lighter than a solid epoxy fillet) - might use 'bow' overhang to make it easier- the shape ^ could be approximated, rounder (pointed oval) and a little skinnier?  Phil S. likes to point out that water likes a shape that doesn't shatter ply.  Go monocoque or use a horizontal web down the widest point of the beam that would double as structure and molding/bending point?  I wonder if molding inner butt joints would double as support for the aka's attachment points. Might do that modularly?  The bonus would be wave piercing 'bows' and would cleave up through a wave easily.  Might have to put all accommodations on the akas/safety pod, leaving hulls only for floatation and hydrodynamics, which would be very post modern.

Sounds too easy.  There must be massive problems in there somewhere....

I'm not following that description, sorry?  And not seeing any benefit from that ama at all.  Yesterday you said "Planing amas are da bomb....", yet you see benefit in wave piercing bows - is that a good combination?  What's wrong with a bidirectional sailing SUP, with no ama?  Steering to be settled, I guess...  Oh, center daggerboard and tilt mast forward to steer to leeward, aft to steer to windward - like a conventional windsurfer.

upsidedown copy.jpg

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28 minutes ago, ProaSailor said:

I'm not following that description, sorry?  And not seeing any benefit from that ama at all.  Yesterday you said "Planing amas are da bomb....", yet you see benefit in wave piercing bows - is that a good combination?  What's wrong with a bidirectional sailing SUP, with no ama?  Steering to be settled, I guess...  Oh, center daggerboard and tilt mast forward to steer to leeward, aft to steer to windward - like a conventional windsurfer.

upsidedown copy.jpg

No, just looking at your latest design.  I don't have anything against long, slim, wave piercing hulls- they are very cool.  With my latest opus, I'm following a different idea involving dynamic lift, that's all (totally rockerless flat bottom).  We have an L7, and I like her a lot.  Not getting rid of her.  When I was windsurfing, I had an 8' sinker and a D2.  Loved them both.   Although there has been some experimentation in windsurfing with longboard planing hulls with a wave piercing  bow.  Same with some SUP's.....

Here's an example I found in 30 seconds-

http://horizonsup.com/#construction

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48 minutes ago, ProaSailor said:

I'm not following that description, sorry?  And not seeing any benefit from that ama at all.  Yesterday you said "Planing amas are da bomb....", yet you see benefit in wave piercing bows - is that a good combination?  What's wrong with a bidirectional sailing SUP, with no ama?  Steering to be settled, I guess...  Oh, center daggerboard and tilt mast forward to steer to leeward, aft to steer to windward - like a conventional windsurfer.

upsidedown copy.jpg

I did a bidirectional no ama sailing canoe with a plank, and the problem was keeping her upright while shunting- she had a dipping lug rig.  I figured an Ama would help, and then one thing lead to another, and I wound up with ^.........:lol:

Here's a pic of the tippycanoe!

DSC02669.jpeg

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It's really hard for me to draw a proa as small as what you have in mind.  This is a 14' main hull and 12' ama, six feet beam overall:

Main hull: LOA: 14', L/B Ratio: 17, BOA: 9.9", Draft: 7.3", Disp: 235 lbs, Cp: 0.62, Awp: 8.5 sq ft, WS: 17.3 sq ft, Srf Area: 33.8 sq ft, Volume: 6.2 cubic feet (398 lbs), Srf/Vol Ratio: 5.4

Ama: LOA: 12', L/B Ratio: 18, BOA: 8", Draft: 6", Disp: 101 lbs, Cp: 0.63, Awp: 5.8 sq ft, WS: 10.8 sq ft, Srf Area: 24.5 sq ft, Volume: 3.6 cubic feet (231 lbs), Srf/Vol Ratio: 6.8

proa14_2017_Dec18a.thumb.png.45624aca5bb2344fe49c127e7608f377.png

See it magnified: http://forums.sailinganarchy.com/uploads/monthly_2017_12/proa14_2017_Dec18a.png.4efd13934f8026df71768acd448986ee.png

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12 hours ago, ProaSailor said:

It's really hard for me to draw a proa as small as what you have in mind.  This is a 14' main hull and 12' ama, six feet beam overall:

Main hull: LOA: 14', L/B Ratio: 17, BOA: 9.9", Draft: 7.3", Disp: 235 lbs, Cp: 0.62, Awp: 8.5 sq ft, WS: 17.3 sq ft, Srf Area: 33.8 sq ft, Volume: 6.2 cubic feet (398 lbs), Srf/Vol Ratio: 5.4

Ama: LOA: 12', L/B Ratio: 18, BOA: 8", Draft: 6", Disp: 101 lbs, Cp: 0.63, Awp: 5.8 sq ft, WS: 10.8 sq ft, Srf Area: 24.5 sq ft, Volume: 3.6 cubic feet (231 lbs), Srf/Vol Ratio: 6.8

proa14_2017_Dec18a.thumb.png.45624aca5bb2344fe49c127e7608f377.png

See it magnified: http://forums.sailinganarchy.com/uploads/monthly_2017_12/proa14_2017_Dec18a.png.4efd13934f8026df71768acd448986ee.png

You have to get sneaky when you do a small Proa-  the WS of my 14er is ~19sq ft, but the wave resistance tops out at 4 lbs, and starts to fall, where the resistance curve (at least in Vacanti land) of your typeform goes up to 28 lbs.  so this might explain why SUP’s are going flatter on the bottom (as well as for stability).  Gutelle points out that less draft gives less drag  than more draft and skinnier hulls, although in a nasty seaway, a softer ride is nice and easier on everything-  Geissler approach a good example there.  Add to this Moth low rider narrow hull design- which was pirogue-esque and volume heavy as well as fast, and that’s the gestation of my 14’ garage queen. 

I’ve wondered what the bottom of Jzero was like- never have seen a pic of her out of the water.

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Proa, if you joined the keel first, and only wet out the seam and then forced it into a shape jig you could torture it quite a bit.  I made several Greenough spoon kneeboards this way.  If you want rounded chines find a production hull section that meets your plug needs and strip plank the section you want and tie it in with the other parts.  Mathematics  usually doesn't consider planking stress, although maybe you have some FEA software that does.  I really enjoyed just bending stuff to see how it fits.  Did you know strip planking came from lobster trap scrap wood and long Maine winters?  Aloha, Guerdon.

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1 hour ago, guerdon said:

Proa, if you joined the keel first, and only wet out the seam and then forced it into a shape jig you could torture it quite a bit.  I made several Greenough spoon kneeboards this way.  If you want rounded chines find a production hull section that meets your plug needs and strip plank the section you want and tie it in with the other parts.  Mathematics  usually doesn't consider planking stress, although maybe you have some FEA software that does.  I really enjoyed just bending stuff to see how it fits.  Did you know strip planking came from lobster trap scrap wood and long Maine winters?  Aloha, Guerdon.

George had to be in there somewhere!  Why he's never scarfed up a MacArthur Grant is beyond me.  Met Greenough down in Santa Barbara on the beach when we were both much much younger.  He had one of his morphing spoons.  Cool to watch him play the waves.  Trying to remember if he had the metal skeg on that one, or if that was windsurfer only.....  

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1 hour ago, guerdon said:

Proa, if you joined the keel first, and only wet out the seam and then forced it into a shape jig you could torture it quite a bit.  I made several Greenough spoon kneeboards this way.  If you want rounded chines find a production hull section that meets your plug needs and strip plank the section you want and tie it in with the other parts.  Mathematics  usually doesn't consider planking stress, although maybe you have some FEA software that does.  I really enjoyed just bending stuff to see how it fits.  Did you know strip planking came from lobster trap scrap wood and long Maine winters?  Aloha, Guerdon.

George had to be in there somewhere!  Why he's never scarfed up a MacArthur Grant is beyond me.  Met Greenough down in Santa Barbara on the beach when we were both much much younger.  He had one of his morphing spoons.  Cool to watch him play the waves.  Trying to remember if he had the metal skeg on that one, or if that was windsurfer only.....  

lowrider moths:

http://www.bloodaxeboats.co.uk/moth.htm

more chine stuff

https://www.storerboatplans.com/design/chines-vs-round-bilge-is-there-evidence-of-superiority/

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On 11/16/2017 at 12:27 PM, Amati said:

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...

[...]  I'm hoping the next one will have parts (including the hull) weighing no more that 20lbs.... 

IMG_0370.jpg

Just so I have this straight...  On this ama, "sitting waaaaaaay out" means moving your body's center of gravity no more than ~12" to windward without sinking it?  You may want to move farther to balance the sail but unless you can move FAST back to the main hull, you'll sink the ama, right?  So knowing you might have to suddenly pull yourself back, how far to windward do you think you can move sitting down?  Then imagine how much more casual sailing would be if the ama supported your weight at rest?  Or at least allowed a 200 lb adult to sit out half way to the ama?

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1 hour ago, ProaSailor said:

Just so I have this straight...  On this ama, "sitting waaaaaaay out" means moving your body's center of gravity no more than ~12" to windward without sinking it?  You may want to move farther to balance the sail but unless you can move FAST back to the main hull, you'll sink the ama, right?  So knowing you might have to suddenly pull yourself back, how far to windward do you think you can move sitting down?  Then imagine how much more casual sailing would be if the ama supported your weight at rest?  Or at least allowed a 200 lb adult to sit out half way to the ama?

I picture the ama for shunting- the rest of the time flying it just above the water- this is a sit down Windsurfing vibe, which is what I would call serious fun- and adding a sliding seat, maybe

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Amati, the wave craft all had glass, then carbon fins.  The windsurfers had carbon, then  ss[passivated].  If you know anyone that wants spoons or windsurfers I have some.  They are amazing.  Aloha, Guerdon.

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9 hours ago, ProaSailor said:

I'm not drawing Jzerrohttp://pacificproa.com/brown/jzerro_haulout.html   "3250 lbs"

Interesting sling rig.

DSCN1193.JPG

 

4 hours ago, Amati said:

I picture the ama for shunting- the rest of the time flying it just above the water- this is a sit down Windsurfing vibe, which is what I would call serious fun- and adding a sliding seat, maybe

Wanting to sit down on a windsurfer is something I haven't heard of before but sounds like a wet kind of fun. Great if water is above 80 degrees!

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3 hours ago, Uncooperative Tom said:

Interesting sling rig.

DSCN1193.JPG

 

Wanting to sit down on a windsurfer is something I haven't heard of before but sounds like a wet kind of fun. Great if water is above 80 degrees!

Cross pollinate with an IC and you've got it!

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I think International Canoe Class sailors might say my 14er has a  training wheel-

http://www.intcanoe.org.uk/new/images/pdf/Sliding Seat/Sliding Seat Iss 4 Aug 07 small.pdf

Look at the bottom pic on pg 20 to get an idea of an una rigged IC...

Given that, the question might become ‘why have an Ama?’. A look at traditional proas might be thought of as showing a range of approaches from weight (balance) to flotation, with a wide range of strategies in between.  The IC dispenses with it altogether, and you could say just uses an aka to sit on.

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1 hour ago, Amati said:

I think International Canoe Class sailors might say my 14er has a  training wheel-

http://www.intcanoe.org.uk/new/images/pdf/Sliding Seat/Sliding Seat Iss 4 Aug 07 small.pdf

Look at the bottom pic on pg 20 (below) to get an idea of an una rigged IC...

Given that, the question might become ‘why have an Ama?’. A look at traditional proas might be thought of as showing a range of approaches from weight (balance) to flotation, with a wide range of strategies in between.  The IC dispenses with it altogether, and you could say just uses an aka to sit on.

Exciting.  And very wet.  Not my idea of fun.

5a3a99021f950_SlidingSeatIss4Aug07small.jpg.8f479adec0d326bf9703249a9a0968a4.jpg

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20 hours ago, guerdon said:

Amati, the wave craft all had glass, then carbon fins.  The windsurfers had carbon, then  ss[passivated].  If you know anyone that wants spoons or windsurfers I have some.  They are amazing.  Aloha, Guerdon.

I wish I could, but with a rebuilt shoulder.......

I'll spread the word around- cool stuff-

The only spoon I use right now outside of eating is a hickory 3 wood- :)

 
Baffing-Spoon-e1386041307588-600x600.jpg

Baffing Spoon

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Radial Chines vs. Sweep Chines

The Grasshopper hull model I've been working with is an expression of the "Prismatic Epiphany" page I posted sixteen years ago, where a single sheer curve determines the entire hull, since the bottom shape consists of semi-circles.  In this version, polygons were used instead to define "radial chines" like this main hull:

chines_2017_Dec20a3.png.4436d4a1db664094511156106101d269.pngchines_2017_Dec20a3s.thumb.png.039d44db0d01cc9d92c3084e04d3ae0f.png

There is an option to loft the radial chines to produce a semi-circular hull, like this - similar in shape and volume to the hard chine version:

chines_2017_Dec20a1.png.746dbdd84f84941127ed7b386b1a159d.png

 

The radius chine and sweep approach I posted the other day produces a very different set of hulls from the same mid-sections.  Skipping the radius/filet for a moment, here are sweep versions of the chine and round sections above:

chines_2017_Dec20a4.png.d6c8c041c9fe4cfb9c2a1c7f6de7ab03.pngchines_2017_Dec20a2.png.ce1ac53d3f54879fee472e852651cda1.pngchines_2017_Dec20a4s.thumb.png.b13fcddde2913fef22bd78d6ddeeb74c.pngchines_2017_Dec20a2s.thumb.png.92c2963668ebde222d35d2655efd6d24.png

Sweep using five chines instead of six, then using a radius/fillet of the same mid-section:

chines_2017_Dec20a6.png.316b80abb79062b8190525a89de97f2d.pngchines_2017_Dec20a5.png.85243c7dec81a8327ff6e0a71ac25243.pngchines_2017_Dec20a5s.thumb.png.22a31d86a4f3d93c43723f21d152f910.png

A twenty-four chine sweep, effectively strip planking, resulting in a shape very similar to the sweep round above.

chines_2017_Dec20a7.png.f83361d5a1cdcd51696fff40150ee1d4.png

These alternatives can affect displacement by well over 10%, in addition to other hydrostatic factors like prismatic, wetted surface, etc.

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Proa, will you please use your software to draw a 2 chine per side hull.  That is what I am building[Salamba].  As a hyper builder these long narrow hulls are a pain, but when they are done they show graceful power.

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1 hour ago, guerdon said:

Proa, will you please use your software to draw a 2 chine per side hull.  That is what I am building[Salamba].  As a hyper builder these long narrow hulls are a pain, but when they are done they show graceful power.

Radial chines or sheer?  Depending on how you count chines, I did one above - two chines on each side - radial chines:

chines_2017_Dec20c1.png.7cbf9dba65ed408d7cc43e0acb1c25ba.png

and sheer chines:

chines_2017_Dec20c2.png.c8cf922f07952f391a9da1e8e5e1b2a8.png

Or is this what you mean (looks like 3 chines per side to me)?  Radial chines:

chines_2017_Dec20c4.png.cb2224f44586fae4dfcdc186df9ff1aa.png

and sheer chines:

chines_2017_Dec20c3.png.e1446913ff36ebf186b92045717ff7cd.png

Even with a simple model like this, there is an extremely wide range of hull shapes possible, depending on parameter settings.

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3 hours ago, guerdon said:

Amati, have you tried riding a mat?  Paul Gross, 4th gear Flyer.

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Yep-  fun to try different air pressures, a pain to paddle out.  Never could decide if a mattress with a pillow was worth the effort.  Never could get the flop right...

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5 hours ago, ProaSailor said:

Radial Chines vs. Sweep Chines

Same images organized a little differently...

Six chines (flat bottom), radial on the left, sweep on the right:   (left and right will be top and bottom on narrow devices)

chines_2017_Dec20a3.pngchines_2017_Dec20a4.png

Six lofted chines (round), radial on the left, sweep on the right:   (left and right will be top and bottom on narrow devices)

chines_2017_Dec20a1.pngchines_2017_Dec20a2.png

Five chines, sweep on the left, filet and sweep on the right:   (left and right will be top and bottom on narrow devices)

chines_2017_Dec20a6.pngchines_2017_Dec20a5.png

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Proa, thanks, what I was looking for was a triplane hull.  Flat bottom panel, flat bevel bottom,vertical sides,and a flat deck.  Phil Bolger did many of them as power skiffs.  The Greenough edge boards have a flat bottom and then a rounded displacement hull for sides.  In effect the flat bottom act as a waterski to plane you out of displacement mode.  By having the beveled garboards you avoid pounding like a skiff, because the bottom is narrower.

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Amati, I was referring to the mats George rides, not the blow up toys [although I did consider one with a dragon front end just clear out the line up].

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11 hours ago, guerdon said:

Proa, thanks, what I was looking for was a triplane hull.  Flat bottom panel, flat bevel bottom,vertical sides,and a flat deck.  Phil Bolger did many of them as power skiffs.  The Greenough edge boards have a flat bottom and then a rounded displacement hull for sides.  In effect the flat bottom act as a waterski to plane you out of displacement mode.  By having the beveled garboards you avoid pounding like a skiff, because the bottom is narrower.

Half of a hexagon?  Radial or sweep chines?  Do you see the difference?  These hulls have identical mid-sections.

Before you assign me anymore tasks, I have one for you.  Do yourself a favor and learn how to copy/paste and post images on this forum?

chines_2017_Dec21a1.png.c551795f5acc9f5a640d6ffffb492292.pngchines_2017_Dec21a2.png.895d27c19323740b17572f33e623a199.pngchines_2017_Dec21a3.png.49912c85048977e6187fbcdf351bc0d3.pngchines_2017_Dec21a4.png.c7a08db720a3d9f3ee11dc51f4840535.png

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Proa, thank you, sorry for being a luddite.  Computer graphics has been been a sore point for me.  Do your recent hulls all have the same displacement, and other qualities[P.C.,M.C.S. ect.] ?  I appreciate your efforts.  Aloha, Guerdon.

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41 minutes ago, guerdon said:

Proa, thank you, sorry for being a luddite.  Computer graphics has been been a sore point for me.  Do your recent hulls all have the same displacement, and other qualities[P.C.,M.C.S. ect.] ?  I appreciate your efforts.  Aloha, Guerdon.

Posting images to a forum is not "computer graphics".  It's a fundamental communication skill.  You must have pictures of your boat projects?

I didn't bother to check hydrostatics on these two versions.  They are certainly different shapes so they have different displacements.  You already have plans for your boat so why should I bother?  I don't have critical dimensions from you like beam and draft anyway.  And you still haven't told me whether you have radial or sweep chines?

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Proa, I wasn't asking for you to work out my boat #s .  I already have them.  I was just interested in your hulls.  Thanks for your time and good luck to you.

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16 hours ago, guerdon said:

Amati, I was referring to the mats George rides, not the blow up toys [although I did consider one with a dragon front end just clear out the line up].

Yeah, George was riding surplus army mats or something, at least at first?  Did he ever make his own?   Couple of times I bought what I could find ^ (with pillows, no dragons.  Well, one yellow one had a seahorse,  which was as stupid as it sounds).  Getting beat on the head and neck by a pillow (or a seahorse!).  Pretty much everybody on the beach had to try it.  :lol: Ha! Ha!  Tried cutting off the pillows, but that created leaks.....

Edit- I did score an Army surplus short mat that looked sort of right- it worked ok- kind of like a pentamaran (?), but it tracked, at least.  

For a long time I conflated George with intellectual unobtainiaum.  

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Amati,  George is a curious fellow.  The difference between him and most folks is when he gets an idea he runs with it.  Go to Mat Matters on blog and see what is going on now.  Aloha, Guerdon.

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Hey Proa, thanks for all the cool sections.  I have another job for you...  Sorta kidding, but does the radial or sweep chine (post 230) plane sooner / better?  Just curious whether there are inexpensive CFD tools that can answer that.

Thread drift off:  Been lurking here, great thread.  

Amati:  We had some great army surplus matts that were the bomb.  Grab a water ski handle, roll it on the leading edge, lay down and "hit it", is a great way to get a kid a better ride than an innertube.  Could even cross the wake by leaning and dragging a foot.

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17 hours ago, Kenny Dumas said:

does the radial or sweep chine (post 230) plane sooner / better?  Just curious whether there are inexpensive CFD tools that can answer that.

I don't have any CFD or VPP software so can't say how these hulls compare with those tools.  As to planing a narrow hull (L/B ratio of 16+, for example), I don't know to what extent that ever happens?  Or whether a flat bottom is necessary or not?  I can say that sweep compared to radial (as I've used the terms here) results in a higher prismatic with rocker carried further forward, more displacement, more wetted surface.  Several changes can be made to compensate for more displacement.

Sweep surfaces are what I use in the original Grasshopper model (prior to the "Prismatic Epiphany" version created for this thread), where the mid-section curve isn't chined and can have flare instead of vertical topsides.  Another thing happens with sweep that is a surprising annoyance at first but can be used creatively.  The Rhino/Grasshopper 'Sweep' feature can use multiple station curves but if you give it just one, it effectively copies the curve to the other end of the rail but with a twist - literally.  Called "torsion", it's a property of mathematical curvature that causes the perpendicular frame at each point along a curve to be oriented like a banked roadway.  When the forward station isn't vertical, either from torsion or from direct parametric rotation (manual setting), the effect at the bow will be either flare or tumblehome (which causes a reverse bow).

Getting into the weeds of CAD, yet barely scratching the surface (so to speak) of possible ways to draw hull shapes.

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2 hours ago, ProaSailor said:

Sweep surfaces are what I use in the original Grasshopper model (prior to the "Prismatic Epiphany" version created for this thread), where the mid-section curve isn't chined and can have flare instead of vertical topsides.

From 2.5 years ago.  TLTV?

https://youtu.be/2ktrKMaLjus?t=4m25s

 

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5 hours ago, ProaSailor said:

I can say that sweep compared to radial (as I've used the terms here) results in a higher prismatic with rocker carried further forward, more displacement, more wetted surface.  Several changes can be made to compensate for more displacement.

One way is to eliminate the flat bottom, or zero deadrise angle, which adds a lot of volume.  Use a V-shaped keel at the mid-section from a five chine filet/radius sweep (main hull; ama uses a three chine filet/radius sweep).

The second is a one degree rotation of the sweep bow station, creating bow flare, rake and a slightly shorter waterline (main hull).

p36_ama27_2017_Dec22a5.thumb.png.3f47b2a1734de22095c4f070e4c66ee8.pngp36_ama27_2017_Dec22a3.png.be9416df30c5db82cbff77faad048b4d.pngp36_ama27_2017_Dec22a.thumb.png.922f224094a2f2ec8a1346a8622c8ea9.pngp36_ama27_2017_Dec22a2.png.41706e46b0dbda4cf6567dfce39e40a3.pngp36_ama27_2017_Dec22a4.thumb.png.9672d9afcf00ad61cd49f5b6ebb4ab2b.pngp36_ama27_2017_Dec22a6.thumb.png.75ed75b0ce09f0346613c9135d8ae93f.png

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13 hours ago, ProaSailor said:

One way is to eliminate the flat bottom, or zero deadrise angle, which adds a lot of volume.  Use a V-shaped keel at the mid-section from a five chine filet/radius sweep (main hull; ama uses a three chine filet/radius sweep).

Depending on how you look at it, eliminating the flat bottom (blue hull) requires an extra inch of draft (~300 lbs) to get the same displacement as the red hull using sweep round (zero deadrise angle).  There is so much volume in the flatter bottom (red hull) that more bow rake was used to match the blue hull's lower displacement.

Proa Main Hull - LOA: 36', L/B Ratio: 17, BOA: 25.4".

  • Blue: Draft: 16.7", Disp: 3042 lbs, Cp: 0.62, Awp: 52.9 sq ft, WS: 99.3 sq ft, Max section Area (Ax): 2.23
  • Red: Draft: 15.7", Disp: 3063 lbs, Cp: 0.61, Awp: 52.1 sq ft, WS: 98.5 sq ft, Max section Area (Ax): 2.28

p36_ama27_2017_Dec23a.png.a5b6a3095b432409c7c4a8f2b1f9592d.pngp36_ama27_2017_Dec23a3.png.72d922c3b9c7d3dd0204a13353cb9563.pngp36_ama27_2017_Dec23a2.thumb.png.0b12a244a3165dcf029789084aeb5c3f.png

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13 hours ago, guerdon said:

Proa, this is your best yet.  Looks like something Joe Quigg would have done.  Thanks, Guerdon.

Agreed!

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2 hours ago, ProaSailor said:

Depending on how you look at it, eliminating the flat bottom (blue hull) requires an extra inch of draft (~300 lbs) to get the same displacement as the red hull using sweep round (zero deadrise angle).  There is so much volume in the flatter bottom (red hull) that more bow rake was used to match the blue hull's lower displacement.

Proa Main Hull - LOA: 36', L/B Ratio: 17, BOA: 25.4".

  • Blue: Draft: 16.7", Disp: 3042 lbs, Cp: 0.62, Awp: 52.9 sq ft, WS: 99.3 sq ft, Max section Area (Ax): 2.23
  • Red: Draft: 15.7", Disp: 3063 lbs, Cp: 0.61, Awp: 52.1 sq ft, WS: 98.5 sq ft, Max section Area (Ax): 2.28

p36_ama27_2017_Dec23a.png.a5b6a3095b432409c7c4a8f2b1f9592d.pngp36_ama27_2017_Dec23a3.png.72d922c3b9c7d3dd0204a13353cb9563.pngp36_ama27_2017_Dec23a2.thumb.png.0b12a244a3165dcf029789084aeb5c3f.png

The nice thing about a flat bottomed hull in this context is more volume means a different, in some ways more efficient hull- I’m wondering if you have certain size parameters in mind for accommodations and storage?  Granted, I’m transfixed by flat bottom hulls right now, but for what it’s worth, with skinny hulls (l/b 12:1 to 18:1) I’ve done with flat bottoms have not pounded, and were easy to construct.  Also my wave making modeling (Vacanti) shows some advantages at higher speeds, although this could be an artifact of modeling assumptions-  I think somebody was posting somewhere about whether using supersonic flow modeling for higher Froud numbers was a good idea, but at worst I’ve found it a good approximation. If anybody’s  interested, I could post some of my hull hacks in 10 days or so.  

Herreschoff liked to point out that his aesthetic preference for skinny hulls was  offset by the better performance of chunkier hulls, and it may be that skinnier hulls give better performance in a high powered scenario (like a trimaran) but proas don’t operate in that arena, except in light airs, so 8:1 to 12:1 might be a better trade off, proas bring a lot lighter, and capable more dynamic lift, which is where a flat hull bottom with a higher L/B might be a bit better. It always astonishes me how much wave and friction resistance lower with even one inch of hull rise.  

I’ve wondered the L/B for Jzerro’s hulls were, if you’re lurking out there, Mr. Brown- they look a bit higher L/B than your first Jzerro (sp?), or is that flare talking?

 

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56 minutes ago, Amati said:

The nice thing about a flat bottomed hull in this context is more volume means a different, in some ways more efficient hull

"more efficient" in what sense?  Less draft, less wetted surface and waterplane areas, yes, but the differences in this case are small.  There are good reasons for wanting a "V" bottom instead of a flat bottom, even on a main hull.  It exposes a single keel timber down the middle, which is better if you want to slide it out on a ramp, or if you hit something, fixed or floating.  Some deadrise is also likely to produce a smoother ride in rough seas with less sudden vertical accelerations.  I'm not sure what an optimal deadrise angle is but an inch of draft (~6%) doesn't seem like much of a price to pay for the slimmer blue hull above, which has 22 degrees of deadrise at its mid-section.

1 hour ago, Amati said:

I’m wondering if you have certain size parameters in mind for accommodations and storage?

All my thoughts in that regard are in the 70' to 90' range.

1 hour ago, Amati said:

for what it’s worth, with skinny hulls (l/b 12:1 to 18:1) I’ve done with flat bottoms have not pounded, and were easy to construct.

Were you driving them at 18 knots?  In what conditions?  One doesn't generally fly a main hull, of course, but there may be times at sea, leaping off a wave, where a flat bottom may not be ideal.

jzerro-flying.jpg

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29 minutes ago, ProaSailor said:

"more efficient" in what sense?  Less draft, less wetted surface and waterplane areas, yes, but the differences in this case are small.  There are good reasons for wanting a "V" bottom instead of a flat bottom, even on a main hull.  It exposes a single keel timber down the middle, which is better if you want to slide it out on a ramp, or if you hit something, fixed or floating.  Some deadrise is also likely to produce a smoother ride in rough seas with less sudden vertical accelerations.  I'm not sure what an optimal deadrise angle is but an inch of draft (~6%) doesn't seem like much of a price to pay for the slimmer blue hull above, which has 22 degrees of deadrise at its mid-section.

All my thoughts in that regard are in the 70' to 90' range.

Were you driving them at 18 knots?  In what conditions?  One doesn't generally fly a main hull, of course, but there may be times at sea, leaping off a wave, where a flat bottom may not be ideal.

jzerro-flying.jpg

70-90’?  Yikes!

No flat then.

Although 12” foam on the bottom would be floatation.  

;)

soggy when wet- a gigantic surfboard!

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1 hour ago, Amati said:

70-90’?  Yikes!

This Grasshopper model at 85', with few changes so far... the blue hull above looks like this: BOA: 60" (5')

  • At Rest: Draft: 36", Disp: 36,000 lbs, crossbeam clearance: 4' 8"
  • Flying Ama: Draft: 44" (+8"), Disp: 49,000 lbs (not heavy for 85' - perfect for the Na Pali Coast in winter), crossbeam clearance: 4'

Could make it wider and heavier, reduce L/B from 17 to:

  • L/B: 16, BOA: 64", Disp: 40,300 lbs
  • L/B: 14, BOA: 73" (6'), Disp: 52,000 lbs
  • L/B: 12, BOA: 85" (7'), Disp: 69,500 lbs (see below)

p85_2017_Dec23a.png.ffb62ba9c978655bf8406c3c11504b00.png

Will need a bigger ama than 27'!p85_2017_Dec23a2.thumb.png.f48fe85682c84669c5869e488b516559.png

L/B: 12, BOA: 85" (7'), Disp: 69,500 lbs (below, w/ 27' ama for comparison only)  Half-angle of entry at bow is 16 degrees.p85_2017_Dec23a3.thumb.png.cca81f10ddb9a943547c5f8044f03414.png

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15 minutes ago, Amati said:

Proa here’s a linky to a post modern take on Fiji hull strategy- big chop, Cadillac ride

 

https://www.boatdesign.net/threads/catamaran-hull-design-question.32221/

Not sure what you're referring to?  I see this, which confirms my recollection of the flat rocker issue being settled more than fifty years ago (not good):

Quote

In the final analysis Mr. Robert B. Harris [in his book "Modern Sailing Catamarans"] concluded "At all times the abundance of wetted area due to her fine lines added greatly to the total resistance. The flat bottoms pounded going to windward, especially the weather hull when close to the surface. She was slow in tacking due to the long flat keel, and partially to the bottom chines. the chines also created eddies along her entire length when rolling, which added to the resistance."

naramatac-jpg.41995

 

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1 hour ago, ProaSailor said:

Not sure what you're referring to?  I see this, which confirms my recollection of the flat rocker issue being settled more than fifty years ago (not good):

 

Making a point about G cats- slicers, lots of rocker- look farther down  the thread -  

I’ll post a pic of the Fiji slicer in a week or so- the WS is not a huge deal, given the improved motion, which means the sails are more effective..

always had this fantasy about a slicer with a hingepoint in the middle or two hinge points at 25% & 75% (or at the aka points or so) so the hull articulated, no rudders required.  

Kind of grew as an idea from plank on edge raters with those huge rudders.....

B)

 

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8 hours ago, ProaSailor said:

Proa Main Hull - LOA: 36', L/B Ratio: 17, BOA: 25.4".

  • Blue: Draft: 16.7", Disp: 3042 lbs, Cp: 0.62, Awp: 52.9 sq ft, WS: 99.3 sq ft, Max section Area (Ax): 2.23

Deep-V Proa Main Hull - LOA: 36', L/B Ratio: 12, BOA: 36", Draft: 21", Disp: 3389 lbs (10% heavy), Cp: 0.59, Awp: 63.2 sq ft, WS: 104.6 sq ft, Max section Area (Ax): 2.79

p36_ama27_2017_Dec23b3.thumb.png.ec580bec1fdcc1c2f2d307d52dcd558b.pngp36_ama27_2017_Dec23b2.thumb.png.32d77db88c1a94580e8a97b52f557397.pngp36_ama27_2017_Dec23b.thumb.png.57e44f9766e337eda7e774794a292cd0.pngp36_ama27_2017_Dec23b4.thumb.png.8ca92af082287937501d70c7595959e5.png

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16 minutes ago, Amati said:

look farther down  the thread

I read the page but missed the point?  You could be more specific?  Quote it?  Poor turning with no rocker is what I remember being told when I asked about this.

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4 minutes ago, Amati said:

Here- http://www.formula16.net/f16-catamarans-boat-overview/g-cat/

google GCat catamaran images too.  Randy Smith liked them, and they had a good racing record, especially in rough water races....

OK, I didn't miss anything.  Saw all that, Googled images earlier.  Not that impressed.  I'm not tuned into small multihulls, other than Prindle 19s.

 

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19 minutes ago, ProaSailor said:

OK, I didn't miss anything.  Saw all that, Googled images earlier.  Not that impressed.  I'm not tuned into small multihulls, other than Prindle 19s.

 

Huh.

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Just so you guys know, I’m really trying to follow, cause the little proa is interesting, but, what’s going on now? Gcats? Pringle 16s? Huh?

maybe it’s just my east Asia jet lag. 

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1 hour ago, Raz'r said:

Just so you guys know, I’m really trying to follow, cause the little proa is interesting, but, what’s going on now? Gcats? Pringle 16s? Huh?

maybe it’s just my east Asia jet lag. 

I haven't left home in a long time and am having similar difficulty so it's not the jet lag.

But I don't want to discourage the meandering of the discussion.

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The snow is on the ground, the Little Proa sleeps in the garage, the Wise Men of SA talk of Proas to pass the dark cold nights, and sailors travel afar, some from the east, bringing the gifts of interesting posts and differing hull strategies to sail the world’s seas with speed comfort, and style!  Or just fiddle around on local lakes...

 

 

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7 hours ago, Raz'r said:

Just so you guys know, I’m really trying to follow, cause the little proa is interesting, but, what’s going on now? Gcats? Pringle 16s? Huh?

maybe it’s just my east Asia jet lag. 

When I think of a beach proa (which is not that often), I think of a Prindle 19 with one or two people trapezed out on the rail and trucking hard.   A 6 meter proa similar to what I posted a month ago would be great: http://forums.sailinganarchy.com/index.php?/topic/194654-bi-directional-proa/&tab=comments#comment-6005543

Possibly as small as this pair of 16' hulls from three weeks ago: http://forums.sailinganarchy.com/index.php?/topic/194654-bi-directional-proa/&tab=comments#comment-6012963

A couple of possible 14' proas that might work for one person or two kids:

As to Amati's design with an ama that won't support my weight, I'm not interested.  Better off with a windsurfer/SUP approach.

My interest is in production of affordable boats, not building a one-off myself or even assembling a kit.  "ProaSailor", not "ProaBuilder".  ;)

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Proa, if you want it affordable i admire you, probably the loftiest goal in the pantheon of boatbuilders.  Me, I am a bottom feeder like Russell.

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L/B=17 vs. L/B=12

The "Prismatic Epiphany" method of creating a semicircular bottom shape (with optional hard chines from polygons instead of circles) is great for radial chines but has limits for the sweep method.  In particular, deadrise angle is limited to 45 degrees, 22.5 degrees and lesser fixed angles defined by polygons.  So I retrofitted another piece from old code, this "Deadrise Hull Shape Cross-section" tool that defines a NURBS curve from deadrise and flare parameters:

dr_curve.png

I wanted to explore L/B=12 hull shapes compared to the L/B=17 I've been using, and came up with this alternative for the 14' proa main hull from a week ago.  The stats again for that L/B=17 hull are as follows:

Quote

Main hull (purple below):
LOA: 14', L/B Ratio: 17, BOA: 9.9", Srf Area: 33.8 sq ft, Volume: 6.2 cubic feet (398 lbs), Srf/Vol Ratio: 5.4

  • Draft: 7.3", Disp: 235 lbs, Cp: 0.62, Awp: 8.5 sq ft, WS: 17.3 sq ft, Max section Area (Ax): 0.43
  • Draft: 10.3" (+3), Disp: 370 lbs, Cp: 0.65, Awp: 7.3 sq ft, WS: 25.2 sq ft, Max section Area (Ax): 0.63

Compare those numbers carefully to the L/B=12 hull, in light blue below:

Quote

Deep-V Proa Main hull (light blue below):
LOA: 14', L/B: 12, BOA: 14", Srf Area: 37.8 sq ft, Volume: 7.9 cubic feet (507 lbs), Srf/Vol Ratio: 4.8, Deadrise: 30 degrees, Half-angle of entry: 11.8

  • Draft: 7", Disp: 233 lbs, Cp: 0.59, Awp: 11.3 sq ft, WS: 16.9 sq ft, Max section Area (Ax): 0.46
  • Draft: 10" (+3), Disp: 414 lbs, Cp: 0.62, Awp: 11.4 sq ft, WS: 23.9 sq ft, Max section Area (Ax): 0.75

p14_main_2017_Dec25a.png.13d27ad1b0eaf2a30cbaba224dd16455.pngp14_main_2017_Dec25a2.thumb.png.1fd17e8512d0c371c0b6e2dc542fa2b7.pngp14_main_2017_Dec25a4.png.711f0fc08af312aedeccb0f0f8a50e43.pngp14_main_2017_Dec25a3.png.0544c6fb47e46fa31930a0c3cdd01807.pngp14_main_2017_Dec25a6.png.5d7c877cb84d7fa7a7831ecb88bd6ee0.pngp14_main_2017_Dec25a5.png.263f535121c27f0365755507bc9eb029.png

This is a proa for one (or two small people) that could be driven reasonably well using a conventional windsurfing rig, with a wishbone and leash to drop and retrieve it.

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4 hours ago, ProaSailor said:

p14_main_2017_Dec25a6.png.5d7c877cb84d7fa7a7831ecb88bd6ee0.pngp14_main_2017_Dec25a5.png.263f535121c27f0365755507bc9eb029.png

Deep-V Proa main hull L/B=12 fleet: Deadrise: 30 degrees     (no effort to optimize for each length...)

LOA: 14', BOA: 14", Draft: 7", Disp: 233 lbs  (+3":  lbs)
LOA: 16', BOA: 16", Draft: 9", Disp: 416 lbs  (+3": 654 lbs)
LOA: 19.7' (6 m), BOA: 19.7", Draft: 9", Disp: 559 lbs  (+3": 918 lbs)
LOA: 36', BOA: 36", Draft: 21", Disp: 4971 lbs  (+3": 6166 lbs)

proaFleet_mains_2017_Dec25a.thumb.png.635eca75b4a9f9d29ea62f72c933d682.pngproaFleet_mains_2017_Dec25a2.thumb.png.859a72632156d43adca65bb9781744ca.png

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1 hour ago, ProaSailor said:
6 hours ago, ProaSailor said:

p14_main_2017_Dec25a6.png.5d7c877cb84d7fa7a7831ecb88bd6ee0.pngp14_main_2017_Dec25a5.png.263f535121c27f0365755507bc9eb029.png

Deep-V Proa main hull L/B=12 fleet: Deadrise: 30 degrees     (no effort to optimize for each length...)

LOA: 14', BOA: 14", Draft: 7", Disp: 233 lbs  (+3": 414 lbs)
LOA: 16', BOA: 16", Draft: 9", Disp: 416 lbs  (+3": 654 lbs)
LOA: 19.7' (6 m), BOA: 19.7", Draft: 9", Disp: 559 lbs  (+3": 918 lbs)
LOA: 36', BOA: 36", Draft: 21", Disp: 4971 lbs  (+3": 6166 lbs)

proaFleet_mains_2017_Dec25a.thumb.png.635eca75b4a9f9d29ea62f72c933d682.pngproaFleet_mains_2017_Dec25a2.thumb.png.859a72632156d43adca65bb9781744ca.png

The 36' hull has a PPI of ~400 lbs so reducing it's draft an inch or two would bring displacement figures down to ~1000 lbs more than what I'm guessing for Jzerro?

proaFleet_mains_2017_Dec25a3.thumb.png.d6c7d303b862dcea9fa504d092f9b25f.pngproaFleet_mains_2017_Dec25a4.thumb.png.5d93668c65ddaccbcde27833ece301b4.pngproaFleet_mains_2017_Dec25a5.thumb.jpg.bc80bd173897b5694bae1bc914b65754.jpg

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42 minutes ago, ProaSailor said:

The 36' hull has a PPI of ~400 lbs so reducing it's draft an inch or two would bring displacement figures down to ~1000 lbs more than what I'm guessing for Jzerro?

Here is the 36' main hull (L/B=12) two inches higher on its lines, Disp: 4179 lbs (808 lbs lighter!):

proaFleet_mains_2017_Dec25a6.thumb.jpg.0ad50b9bc87deeb45cea9b09baa358cc.jpg

There is a lot of optimization that can be done at each length.

That half-angle of entry I mentioned above of 11.8 degrees applies to all these hulls, though.

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On 12/24/2017 at 8:12 AM, ProaSailor said:

 I see this, which confirms my recollection of the flat rocker issue being settled more than fifty years ago (not good):In the final analysis Mr. Robert B. Harris [in his book "Modern Sailing Catamarans"] concluded "At all times the abundance of wetted area due to her fine lines added greatly to the total resistance. The flat bottoms pounded going to windward, especially the weather hull when close to the surface. She was slow in tacking due to the long flat keel, and partially to the bottom chines. the chines also created eddies along her entire length when rolling, which added to the resistance."

 

The "abundance of wetted surface" is due to the fineness of the hulls,  not the lack of rocker.  "Slow in tacking" is more a result of the lack of daggerboards, barn door rudders and the deep, narrow hulls rather than the lack of rocker.   

Harryproas have no rocker.  They perform well, as can be seen in the video at https://www.youtube.com/watch?v=8chR6DAFjGA&list=PL16877B8994035140     Despite the overly bluff bow shape, rudder drag (both changed in later designs) and small rig (no extras), the boat is sailing at windspeed in 10 and 15 knots.  Top recorded speed in flat water is 19 knots in about 20 knots of breeze.     This boat turns on a dime due to it's shallow draft and fore and aft rudders which are large enough to prevent leeway.

"Dynamic lift" from rocker is a peculiar concept.  if you look at rocker as a wing section (of low aspect ratio), all the 'lift' is downwards.   The same shape, rotated through 90 degees is approximately the shape for assymetric hulls which provide lift towards the curve (same as a wing).  Yet, when it is under the hull, the same shape is supposed to provide lift in the opposite direction?   

Rocker is required for tacking boats and combined with relatively fat mid sections reduces wetted surface at slow speeds, but is not a speed or lift generator.  As proas don't tack, rocker is an unnecessary (and slow) complication.

A flat bottom, with ski tip ends (or pitched bow up)  provides dynamic lift and at some speed, planes, which reduces drag even further. It is also way easier to build.

I do agree with Mr Harris about the chines.  The more of them there are the more eddys are generated, albeit smaller.   Not a problem with a decent leeway preventer in flat water as the water flows along them, but otherwise a definite brake.   Chines are also a lot of work for one offs (5 of them in a 16'ter is 150' of filleting and tabbing, which then needs to be faired) and unnecessary for moulded boats.   

Amati,

I think weight shift steering will be too slow on your boat, plus there is not enough range unless you are sitting on the lee hull, which will only happen in light air.  A solution might be to have the beam pivot around the mast with lines (maybe foot operated) to control the beam angle to the hull.  Loads are low, and if you had a series of foot holds, you could move in and out along the beam as well. This would be an easier option than raking the rig, although not as powerful for steering. 

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On 12/25/2017 at 9:58 AM, ProaSailor said:

In particular, deadrise angle is limited to 45 degrees, 22.5 degrees and lesser fixed angles defined by polygons.  So I retrofitted another piece from old code, this "Deadrise Hull Shape Cross-section" tool that defines a NURBS curve from deadrise and flare parameters

Looking at the NURBS curve surfaces in yesterday's "L/B=12 fleet", the relatively flat areas concerned me so I tried another option built in at the same time; radius chine (as before) but with parameter-specified deadrise angle.  The difference is very subtle.  Displacement and profiles are practically identical.  The section curves differ slightly in two areas that cancel each other in displacement.

NURBS curve/surface in blue, radius chine in yellow:

proaFleet_mains_2017_Dec26a2.png.d0beb740e3d1fd23b0fadff3e01b51da.png

NURBS curve/surface fleet on the left, radius chine 36' hull on the right:

proaFleet_mains_2017_Dec26a.thumb.jpg.1fb2c394159c93b8f6d8f9d1505b7da6.jpg

The radius chine might also be more amenable to "tortured ply" construction than a NURBS-based surface? 

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7 hours ago, harryproa said:

The "abundance of wetted surface" is due to the fineness of the hulls,  not the lack of rocker.  "Slow in tacking" is more a result of the lack of daggerboards, barn door rudders and the deep, narrow hulls rather than the lack of rocker.   

Harryproas have no rocker.  They perform well, as can be seen in the video at https://www.youtube.com/watch?v=8chR6DAFjGA&list=PL16877B8994035140     Despite the overly bluff bow shape, rudder drag (both changed in later designs) and small rig (no extras), the boat is sailing at windspeed in 10 and 15 knots.  Top recorded speed in flat water is 19 knots in about 20 knots of breeze.     This boat turns on a dime due to it's shallow draft and fore and aft rudders which are large enough to prevent leeway.

"Dynamic lift" from rocker is a peculiar concept.  if you look at rocker as a wing section (of low aspect ratio), all the 'lift' is downwards.   The same shape, rotated through 90 degees is approximately the shape for assymetric hulls which provide lift towards the curve (same as a wing).  Yet, when it is under the hull, the same shape is supposed to provide lift in the opposite direction?   

Rocker is required for tacking boats and combined with relatively fat mid sections reduces wetted surface at slow speeds, but is not a speed or lift generator.  As proas don't tack, rocker is an unnecessary (and slow) complication.

A flat bottom, with ski tip ends (or pitched bow up)  provides dynamic lift and at some speed, planes, which reduces drag even further. It is also way easier to build.

I do agree with Mr Harris about the chines.  The more of them there 

Amati,

I think weight shift steering will be too slow on your boat, plus there is not enough range unless you are sitting on the lee hull, which will only happen in light air.  A solution might be to have the beam pivot around the mast with lines (maybe foot operated) to control the beam angle to the hull.  Loads are low, and if you had a series of foot holds, you could move in and out along the beam as well. This would be an easier option than raking the rig, although not as powerful for steering. 

I’ve been going that same direction, but let me run this past you- and it revolves around how little a sail actually lifts a boat (based on Windsurfing experiments on weight differences with an inclined rig.

since even when the ama clears the water, it’s weight, and the sailors weight, shift mostly to the main hull, why not go Atlantic configuration (which is entering Denny Land), but with the smaller hull underneath the rig, to leeward, attached  to the main hull with 2 akas with basically a hinged parallelogram to move the rigs CoE, keeping my Speer bidirectional asymmetric foil on the main hull, and controlling the fore and aft movement with feet?  Since with sail, my rig weighs 10-13lbs, and I could control rake with a diagonal strut from the main hull, I could possibly change rake on the fly, and not have to hike out at all, and with any luck, fly the lee hull from what would be a in essence, a captive kite.  Kind of a bizzaro world mix between Denny & Smith, although drifting  (mildly) into SailRocket land.....

be kind of like playing classical organ:lol:

 

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37 minutes ago, Amati said:

I’ve been going that same direction, but let me run this past you- and it revolves around how little a sail actually lifts a boat (based on Windsurfing experiments on weight differences with an inclined rig.

since even when the ama clears the water, it’s weight, and the sailors weight, shift mostly to the main hull, why not go Atlantic configuration (which is entering Denny Land), but with the smaller hull underneath the rig, to leeward, attached  to the main hull with 2 akas with basically a hinged parallelogram to move the rigs CoE, keeping my Speer bidirectional asymmetric foil on the main hull, and controlling the fore and aft movement with feet?  Since with sail, my rig weighs 10-13lbs, and I could control rake with a diagonal strut from the main hull, I could possibly change rake on the fly, and not have to hike out at all, and with any luck, fly the lee hull from what would be a in essence, a captive kite.  Kind of a bizzaro world mix between Denny & Smith, although drifting  (mildly) into SailRocket land.....

be kind of like playing classical organ:lol:

 

While sitting on the large hull to windward that would not fly

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Amati, this is what i am trying to do with my Salamba Proa.  I loved water starting, and since I used to trade my art for sails I was used to being overpowered[I got all the (9.0 sails] this should be like that only 3 x bigger, and the wl beam is @10" .  I am using one mast for the windward stay/preventer, another for the hoist mast amidships, and two masts joined together with a CF boom for the "yardarm sail".  I got all the north CF masts at a yard sale so it seems appropriate.  I call the Stay/preventer the sky hook from my rock climbing days.  I have always wanted the tell someone to adjust the skyhook.  Now if I can only find something to call the Johnson rod.

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Proa main hull: LOA: 14', L/B: 12, BOA: 14", Deadrise: 30 degrees, Draft: 7", Disp: 238 lbs, Volume: 512 lbs, PPI: 60 lbs/inch

Proa ama hull: LOA: 12', L/B: 16, BOA: 9", Deadrise: 40 degrees, Draft: 7", Disp: 145 lbs, Volume: 291 lbs, PPI: 36 lbs/inch

p14_2017_Dec26a.png.e2df528d2e33be5e5deaa7eb1d5aa03d.pngp14_2017_Dec26a2.png.8a2ccd30e0020c44632b5d47b928e7cb.pngp14_2017_Dec26a3.thumb.png.1e854433692e8dd8ed326aec772215a1.pngp14_2017_Dec26a4.thumb.jpg.d907f4296d8eff1703384ed3fc405310.jpgp14_2017_Dec26a5.thumb.jpg.1e7f6cc07bbcf48e3e8044bfbd771c21.jpg

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38 minutes ago, NunBouy said:

Speaking of Proa’s 

this never gets old:

 

Well...  this thread title is "bi-directional Proa", which some of us consider to be redundant wording...  Vestas is cool but it's not bi-directional or even tacking, so it's not a proa or even a tacking outrigger.  I know there is a history of "one way proas" like Slingshot and Crossbow for speed records but still... these are purpose-built speed boats, not practical.

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Proa, you are right, still it's really wonderful when folks stick to their dreams.  I have gone faster on the water under power, but never this fast under sail.  When he get it aligned and it lights up it is magic for me.  Aloha, Guerdon.

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2 hours ago, NunBouy said:
  • Webster's Revised Unabridged Dictionary
    • n Proa (Naut) A sailing canoe of the Ladrone Islands and Malay Archipelago, having its lee side flat and its weather side like that of an ordinary boat. The ends are alike. The canoe is long and narrow, and is kept from overturning by a cigar-shaped log attached to a frame extending several feet to windward. It has been called the flying proa, and is the swiftest sailing craft known.
    • ***
Century Dictionary and Cyclopedia
    • n proa A kind of Malay vessel remarkable for swiftness, formerly much used by pirates in the Eastern Archipelago. Proas are found chiefly within the region of the trade-winds, to which by their construction they are peculiarly adapted; for, being formed with stem and stern equally sharp, they never require to be turned round in order to change their course, but sail equally well in either direction. The lee side is flat and in a straight line from stem to stern, and acts as a lee-board or center-board; but the weather side is rounded as in other vessels. This shape, with their small breadth, would render them very liable to heel over, were it not for the outrigger, which is used on either side or on both. The proa is fastened together with coir yarns, is extremely light, and carries an enormous triangular sail. Also called flying proa.
    • ***
Chambers's Twentieth Century Dictionary
    • n Proa prō′a a small and swift Malay sailing-vessel, with both ends equally sharp.

PROA defintion: A proa, also seen as (prau), (perahu), and (prahu), is a type of multihull sailboat. It is a vessel consisting of two unequal length parallel hulls. 

 

The Vestas Sail rocket is NOT a "bi-directional" Proa. I stand corrected. 

Apologies for interfering with the thread flow. 

Nons Needed, Nun

B)

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11 hours ago, ProaSailor said:

Well...  this thread title is "bi-directional Proa", which some of us consider to be redundant wording...  Vestas is cool but it's not bi-directional or even tacking, so it's not a proa or even a tacking outrigger.  I know there is a history of "one way proas" like Slingshot and Crossbow for speed records but still... these are purpose-built speed boats, not practical.

Paul's comment on that point was that Sailrocket could easily be designed to go other directions at the cost of speed. An angled wing pulling against an angled foil is the basic idea.

Going really fast is a practical purpose. It brings distant destinations within range, allows one to outrun weather, and is just fun, which is the real "practical purpose" of any boat that doesn't have a job.

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Tom, fun is work fulfilled.  Tilting foils are fun. Proa, designing foils is fun for me to watch your thinking.  It's cool to be able to be into such an obscure pastime.  Aloha, Guerdon.

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On 12/26/2017 at 2:37 PM, guerdon said:

Amati, this is what i am trying to do with my Salamba Proa.  I loved water starting, and since I used to trade my art for sails I was used to being overpowered[I got all the (9.0 sails] this should be like that only 3 x bigger, and the wl beam is @10" .  I am using one mast for the windward stay/preventer, another for the hoist mast amidships, and two masts joined together with a CF boom for the "yardarm sail".  I got all the north CF masts at a yard sale so it seems appropriate.  I call the Stay/preventer the sky hook from my rock climbing days.  I have always wanted the tell someone to adjust the skyhook.  Now if I can only find something to call the Johnson rod.

Cool! Can you adjust your sail  cant underway? With your hands? Your legs? Can you fly the lee hull with the sail with stability, or do you need to move  your weight around?  I image I’ll have to move my weight towards the ama if the sail’s upward lift is not controllable, which is non intuitive, to say the least...

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Amati, the hoisting mast can be tilted to windward by adjusting the skyhook to windward by hand.  I will have to move around to balance things out but it should be like a windsurfer with a giant sail.  The thing that has me excited is the flying aspect of using the sail as wing to lift the hull out of the water.  I remember chasing George on windsurfers.  The faster we would go would make us even faster.  The G32 used to do this in light winds or when we were riding ground swells.  I hope to figure this out to the extent that I can plane out this narrow hull.  This is a great time to play.  Aloha, Guerdon.

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12 hours ago, guerdon said:

Amati, the hoisting mast can be tilted to windward by adjusting the skyhook to windward by hand.  I will have to move around to balance things out but it should be like a windsurfer with a giant sail.  The thing that has me excited is the flying aspect of using the sail as wing to lift the hull out of the water.  I remember chasing George on windsurfers.  The faster we would go would make us even faster.  The G32 used to do this in light winds or when we were riding ground swells.  I hope to figure this out to the extent that I can plane out this narrow hull.  This is a great time to play.  Aloha, Guerdon.

Should be like the Speed needle boards back in the late 70’s early 80’s.  (?).   There wasn’t a lot of dynamic lift, but when it clicked in, the acceleration was relentless, but not head snapping.:)

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