Bolger Advanced Sharpie Proa, now with Videos.
Hi all!
I have been thinking of a way to build a cheap simple Proa for extended cruising with my family.
As i understand, multihulls needs higher CP than monohulls, and Proas need more dynamic lift to counteract the down-pushing forces of the sails?!
Has anybody tried a Advanced Sharpie - like Proa-Vaka?
I have been reading about Matt Laydens Paradox sailboat, Loose Moose 2 and other sharpie-type boats, and they seem to sail quite fast for monohulls. They cary a lot of weight and have a lot of usable space.
The big flat bottom will have a lot of dynamic lift.
Im building a small hull to test the concept. Its 116 cm long, 12 cm wide and has 5 cm rocker in the bottom and the sides.
The first hull is a Wharram Tiki - like hull. The middle one is the Advanced Sharpie - like.
And too the far right is a simplified Matt Layden Paradox.
The epoxi is mixed with barley-flour. I didnt have anything else at home at the moment. 😉
The barley-epoxy-porridge has set during the night.
Has anybody tried a Advanced Sharpie - like Proa-Vaka?
Bolger has. In the AYRS publication “catalyst” from a few years back there was a one-page description and photo of a 6 metre long proa designed by Bolger. She carried the AYRS/Bolger rig. Searching for a picture, I found a drawing right here on proafile: http://proafile.com/archive/article/phil_bolger_1927_2009
I am not sure you should copy the blunt ends ends of the Advanced Sharpie. Those blunt ends are usually out of the water. That’s why the Advanced Sharpie series are sometimes criticised for being noisy at anchor. If you want a monohull with a square cross section and same curvature for side and bottom panels, you really have no choice but to lift the bow out of the water. For such a monohull to be stable, the draft is usually 1/5 to 1/4 of the waterline beam. If the end is out of the water anyway, it can be blunt.
A multihull would typically have a draft of 1/2 the beam, or more, both because it doesn’t need the form stability from a wide hull and because it has less water plane area. That means a hull with equal curvature panels will carry its ends near to or in the water. Then a blunt end throws up lots of spray.
Bolger was interviewed on the Furled Sails podcast (http://www.furledsails.com). He mentions that rounding the chine with a radius of only 10cm took care of eddies and made it possible to have a totally flat bottom. He thought a boat designed along those lines would have problems, but when he saw it in actions it did fine. Bolger then applied the same principle to design the Dovekie. You could do the same by having a strip-planked constant radius rounded chine. Then you could have the flatter rocker on the hull bottom and higher prismatic coefficient of the Layden-inspired hull without the worries about eddies.
Regards
Robert Biegler
Hi Johannes. These are all worthwhile proa experiments, thanks for letting us know about them. Sharpies like Paradox are designed to heel and sail on a chine when close hauled, presenting a V shape to the waves and thus avoid pounding. Since a proa (or any multihull) heels very little in normal sailing, it will always be presenting the flat bottom to the waves and could lead to pounding. That said, the very long and slender hull will help mitigate that, and it is also true that Comm. Munroe’s 1898 flying proa was built flat bottom, sharpie-style, and was a brilliant success!
I am not sure you should copy the blunt ends ends of the Advanced Sharpie.
No, I’m not sure either, but i want to try it anyway. It makes the vaka bigger inside for a given length an width.
Those blunt ends are usually out of the water. That’s why the Advanced Sharpie series are sometimes criticised for being noisy at anchor.
The blunt ends will be about 4 inches out of the water in a fullsize vaka. Now they are about one half inch above the water.
Noise is maybe a problem. I will have to build it and see.
Sharpies like Paradox are designed to heel and sail on a chine when close hauled, presenting a V shape to the waves and thus avoid pounding.
I have built a Paradox-inspired Sharpie with chinerunners. Scale 10:1.
http://www.youtube.com/watch?v=yzOZdJdrZfs
http://www.youtube.com/watch?v=J6WILcwe5hk
It was watching it sail that inspired me to try a “advanced sharpie” Proa.
My primary interesst in this, is to see how a heavy, easily built sharpie proa would sail, specially compared to a “normal” Layden Paradox like sharpie. I dont need to sail at 17 knots in heavy seas. 10 knots with a 40-something foot sharpie-proa would do just fine.
It didnt heel that much, and still managed to sail to windwards quite good. I am very impressed with its sailing-abilities. I hope some of it caries over to the Proa. Its a fun test of some ideas. I will test-sail it in a couple of days. I will hopefulle be able to shoot some videos of it sailing. I will post them here if anyone wants to see them.
Thanks for intresting answers.
Johannes.
I hate writing in the English language, soo i tend to shorten everything down as much as possible.
I will try to explain my thoughts a little bit better.
My veiw on the Proa, is that its the most rationell multihull-configuration. Its the longest waterline-length possible from a given number of plywood sheets. Waterline-length gives seakeeping-ability.
Im not primarly into proas for their dazzling spead, but more because they handle big seas way better than the catamaran and tri. The diffent length hulls meet waves in a better maner than a tri och catamaran.
One big hull and one small hull is easier and cheaper to build than two equal-sized hulls. There is less stress on the crossbeams and all that. You all now what im talking about.
Soo, my thought is that dropping the spead-requirment should give a cheap and nice behaving sailboat. A heavy cruising proa, with lots of room and weight-carrying capacity. (for a multihull).
I know this is an unusual way of designing a proa, but i want to try it. I know multihulls should be as light as possible, but i think and hope, it not that critical. I hope a heavy proa will sail better than a monohull with the same weight and shorter waterline-lenght.
Johannes.
I took two pictures of the end of the hull. I put a piece of wood where the waterline will be.
I dont think slapping or pounding will be much of a problem. The hull is around one inch wide where the waterline will be.
Soo, my thought is that dropping the speed-requirment should give a cheap and nice behaving sailboat. A heavy cruising proa, with lots of room and weight-carrying capacity. (for a multihull).
I’ve often wondered about that as well. I look at relatively slender, double-ended monohull designs like sharpies or folkboats, and why not keep the general proportions but remove the heavy weighted keel and use an ama instead? It won’t be as fast as Banque Populaire, but so what?
I was re-reading Design for Fast Sailing by Edmond Bruce and Harry Morss (AYRS 82) and Bruce’s opinion was that a hull length to WL beam ratio of 8:1 was a good all around performer for a cruising multihull, and even wider was advisable in lower wind ranges. This would give a 5’ beam WL for a 40’ hull, which is quite enough beam for a comfortable interior and good load carrying ability.
I’ll be following your experiments with much interest!
I’ll be following your experiments with much interest!
Thank you! I hope this will give some results. Even my girlfriend thinks this could be a good idea. She has had to put up with a lot of tinkering with boats of all different kinds.
I need to write something about the rudders i hope to use on this boat - if i ever get to build a large one.
It will be cassette-rudders attached to a protruding piece of the leeward hullside in the end of the hull.
With cassette-rudders it will be very easy to adjust CLR by just sliding more or less of the rudder down into the water. The rudders will kick up if they hit something. They are easy to build and easy to repair.
In calm seas both rudders will be in their cassetts,but only the rear one down into the water. As the wind and waves picks up, one has to pull the forwar rudder higher and higher. If waves start slaming into the bow one just detach the rudder, place it on deck (remember that the bow is over a feet wide, and easy to move around on) and tie it down. The rudder-cassette fold flat against the blunt bow, and is similary tied down. All this is probably best done before a violent gale, but not impossible during a gale.
This kind of rudder should be easy to build, easy to maintain. Cheap and generaly foolprof. I like tied rudders, because they don’t relay on expensive stainless, they are easy to inspect and repair.
First video of several i made today. The water was really really cold, so i start to studder and have a hard time speaking. The water is cold up here in sweden this time of the year.
I only have one rudder, so i can only sail it in one direction. Its meant to be a shunting proa, but i just wanted to see it sail. The same goes for the sail. Its just a first test. Now that i know how it performs i will take the time to build it properly.
Johannes.
First test of Advanced Sharpie Proa
Video 2/6. A short presentation with a short clip of sailing. Better sailing-videos soon.
Even more pros sailing, part 2
Im very impressed by this simple sharpie-proa. Its sails way better than i thought it would.
40 degres to windward. I say 30 - 35 degres in the video but i don’t belive it now when i watch the videos on my computer.
I loaded it with wet sand to se how it would perform. It still sails quite ok. The speed goes down a bit - as expected. Thats a 10:1 scale of a 40 feet proa, sailing with 3,6 kgs weight - 3,6 ton if it were fullsized.
I’ve been playing with a Bolger box keel for a lot of the same reasons. Lately I’ve been going back and forth between a dorie hull and a vertical sided bolger style hull. the advantages to the dorie are a flatter run on the keel for more longitudinal stability. it also widens above the waterline for more interior room where it’s needed. If you make the bottom curvature max the sides on the bolger style, you end up with quite a bit more rocker. not necessarily and advantage on a shunter.
I’ve been playing with waterlines @ 23ft x 2 ft.
As to rudders, Gary D has the coolest one yet right here on his Blog.
http://1.bp.blogspot.com/-tUvNpOhvVzg/T1ADtOFxM_I/AAAAAAAAA8E/9q91EsVyoC8/s1600/rudd2.JPG
I think this is where I’ll end up for rudders, whatever the hull style.
Tom
As to rudders, Gary D has the coolest one yet right here on his Blog.
It was that kind of rudder i meant, but i am placing them on the ends of the hull, not on the sides. That way i can fold them flat against the blunt end of the hull and protect them from slamming waves in harsh conditions.
I want to have the rudders as far aft as possible, as it gives better steering and better control.
I’ve been playing with a Bolger box keel for a lot of the same reasons. Lately I’ve been going back and forth between a dorie hull and a vertical sided bolger style hull. the advantages to the dorie are a flatter run on the keel for more longitudinal stability
That is true, but i dont want to use any centerboard, keel or anything else protruding from the bottom of the vaka. I want to be able to sail in very shallow water. I dont think hobbyhorsing will be much of a problem, even with all that rocker i have on my model. I dont mind blunt ends. Sharp chines are very rolldamping. And the very full ends vill damp rolling and hobbyhorsing motion too. The boxy and square - ended hull behaves like a longer hull in many ways.
Johannes.
I can see that some people read this thread, and i hope someone will say something about all this. I hope i can start a intresting discussion about square and shallow draft hulls and proas.
I think there is a lot of merit to shallow draft proas and square hulls. They are easy and cheap to build. The sharp chines are rolldamping, and as seen in the videos i made yeasterday, makes them go to windward realy well. I think it sails very good. Way better than expected. I want to build a 40 - 50 foot proa along these lines.
Me and my family wants to circumnavigte the globe in a couple of years, and a proa seems to be the best kind of boat for that. Fast and weatherly. Easy motion and very little heeling.
Please comment on the videos and this kind of proa-hulls.
Johannes.