Bolger Advanced Sharpie Proa, now with Videos.
Hi Johannes
It is not bad when it cracks you just know you went too far. In the book of the Gougeon Brothers there is a table comparing thiknesses of plywoot for models in scale 1:10 with the thikness of plywood for the real boat. If it works in the model the correspondent size of plywood will work on the boat. They also found out by try and error.
Alexander
In the book of the Gougeon Brothers there is a table comparing thicknesses of plywood for models in scale 1:10 with the thickness of plywood for the real boat.
Thanks!!! I will look into that. If i build a large version of this barge/triloboat-proa i would probably use several layers of plywood. I want something like 1,5 - 2 inch thick bottom. It needs to be able to withstand regular groundings like a working scow. I want to be able to sail it up onto a beach, even if there is some rocks and other sharp stuff there. One should not have to be afraid to sail in very shallow waters when the weather permits (no large waves etc).
http://www.boatdesign.net/forums/sailboats/new-zealand-scow-28735.html#post292466
In post nr 11 in this thread about the working scows of New Zeeland, there is some very interesting stuff.
I post a picture of some interesting text. I have my ideas why the scow had the ability to beat of a lee shore in a heavy sea.
Johannes.
I have (finally) made some progress. I simplified the ama/vaka-connection with some 45 degree cutouts in the hull-side. They feel very firm and secure that way. I hope the aka is oriented the right way to take the expected loads. I think the loads should be mostly at a 45 degree angle up and back or up and frontwards. The shrouds and the wires going from the ends of the vaka to the opposite ends of the ama should take most of the horizontal and vertical loads.
I’m very curious of its sailing abilities.. Its effectively a very slender Puddle Duck Racer or Puddle Goose Racer with an outrigger. They have been sailing the Texas 200 and one PDR even competed in the 2012 Everglade Challenge, no small feat for an 8 feet sailing barge.
Johannes
This is what it looks like when ready to sail. I´m going to test-sail it in the next hour.
Contrary to what i have said before, i have to try side-hung rudder and centerboard. I really don´t like having them piercing the surface, as they are prone to suck air down and loosing some control. They create more drag and are much easily damaged. On the positive side, they are easier to build and repair.
I hope there will be a video or two soon.
Johannes.
I tested my barge proa. As usual it was cold in the water. I´m happy there was no ice.
I think it sails way better than it is supposed to. A box-barge without any leeboard or other foils should not be able to sail this good. It did about 45 - 50 degrees upwind but would probably be happier with even larger angle.
I think it moves smooth and very controlled, even though it has a lot of buoyancy out in the ends.
Its a very quick first try. I did not work much on sheeting the sails properly or anything like that. It was a fast 5 minutes sail, then i ran up to my car.
Johannes.
I think the little barge-proa handles the waves really good. The three pictures shows how it takes a breaking wave slamming right into the main hull. I would not like to try that with a normal monohull. It tracks very straight through the wave, even without a leebord or any active steering of any kind. The rudder is locked to an angle by a thick rubberband.
Johannes.
Watching you in that freezing water fills me with awe at your enthusiasm and commitment, Johannes!! 😊
I wonder how a chine runner would perform?
Great to see the stills, I did not pick that up so well on the video. Can you imagine being at full size with a wave like that! Just shows how good the concept is.
Generally I am not sure the modelling is that close to reality, the viscosity does not scale? The model experiences ‘thicker’ water and you do not see the same choppy conditions - what do you find?
That said, seeing how it breaks through a wave will give a huge amount of confidence, well worth making a model just for that.
A suggestion: get hold of a fishing rod with a light line, you will be able to reel her back with freezing your whatsits off!
Mark
Watching you in that freezing water fills me with awe at your enthusiasm and commitment, Johannes!! 😊
Thank you! I really enjoy building and testing my models. I think its a great way to learn much about the behavior of proas. It would be much slower and much more expensive to build a real full-sized proa, and try to rebuild it every time a get an idea. I hope my videos can be useful to other people wanting to build proas.
I wonder how a chine runner would perform?
I don´t think a chinerunner would do any good on a barge like this.
Dave Zeiger tried chinerunners on his small Triloboat, and found that he needed a leeboard to tack. They might make a small difference, but i have not tried it.
Great to see the stills, I did not pick that up so well on the video. Can you imagine being at full size with a wave like that! Just shows how good the concept is.
Thanks! I am very impressed by the way it handled the waves. I could not imagine a barge tacking upwind in breaking waves several times larger than the hull, - without a leeboard!
I know the effect of water-viscosity does not scale linear, but i think there is some correlation between how the model behaves and how a large 40 foot barge-proa would behave. I hope i never have to sail through 9 feet breaking waves 30 feet from a beach. I think models are quite accurate in their behavior in waves. I have been watching my videos in slow-motion over and over to get a feel for the way it moves.
A suggestion: get hold of a fishing rod with a light line, you will be able to reel her back with freezing your whatsits off!
I think i finally have to do that… I have been down with a cold since sailing my model. I´m a little concerned that the drag from the line will effect how it sails. I know that trailering a rope behind a real sailboat can help it steer better and usually slows the boat down a bit. I want to see how it sails without any help from outside.
Johannes.
If that would be a 40 foot proa, what would the wave-height be? The Vaka is 4 feet long, 4 inch wide and 4 inch high.
I estimate that to somewhere around 10 feet or so ???
I´m trying to get a feeling for this proa, and since its a quite odd looking barge-proa its a bit hard to compare it to any experience i have gained from other boats.
I would be very happy if someone with some proa-experience (rough weather) could say something about the pictures and videos.
I find it hard to draw any really useful conclusions, except that i think it sails way better than it should. If i compare this with the videos of Jzerro, i can see that the speed of my model is very low. That is something i expected, and its a trade-of i have to make to build a very simple hull that can carry a lot of weight.
I got a quite nasty cold when testing my model, so i have not been able to test it any more.
Johannes.
Thanks for keeping us updated with your ongoing experiments in “going where no proa has gone before”. From a design/build aspect, the box section is near perfect for ease of build and flexible layout, like a box car for the water. I’m very attracted to constant section hulls (in the center) for the reason that the design can be modular and it’s relatively simple to add or subtract length depending on the needs of the builder.
Also, this must finally be the perfect proa for SketchUp! 😉
I sailed my barge proa again. This time in some sheltered water. The wind was very uneven and strange, changing direction and strength all the time.
Its easy to see that the abrupt changes at the ends creates a lot of wake and resistance. A continuous rocker creates a lot less resistance and wake. My advanced sharpie proa is faster and sails smoother through the water. The large frontal area that pushes water aside creates a lot of lift to counter the pressure from the sail.
Its quite fast when the wind picks up, but i think it needs a slightly larger sail-area. I will try to sew a Wharram soft wingsail and a genoa or a jib out of spinnaker-cloth soon.
Thanks for keeping us updated with your ongoing experiments in “going where no proa has gone before”
I like testing things, and i don´t like “you can´t do it like that” so i tend to experiment a lot before decide on a design.
Johannes.
A picture to show the wake and the bow lifting slightly even though the pressure in the sail presses the bow down.
My next model will have an easier entry and exit.
Johannes.
Some thoughts.
BARGE
Does the barge form have any real advantage in a slim hull?
Why not form the bow in the ‘normal’ way? As the hull is so slim, it still can be parrallel sided over most of its length. Basically square profile sharpie with a flat centre section. No more difficut to make or loss of space.
ROCKER
Whilst those well rockered ends give lift at the front, they give drag at the back. If (with a sharpie) there is no rocker, there is no water flow over the chine (that is without any leeway). Otherwise the sharp edge gives turbulance. Also as rocker is added, so will hobby-horsing.
With no rocker there is far less dynamic lift. If the hull are slim enough to be wave piercing this is no problem.
If the boat heels to a large angle, the barge form offers a flat side, so lacking in lift, at a time when it would be desirable. No problem with a normal hull.
Cheers
Mark