Deep V continuous rocker proa. version 2.0
I keep on testing some of my ideas. This time it is a Wharram inspired deep V vaka with a circular continuous rocker from end to end.
Even though there was almost no wind today, I got really impressed. I can not say anything conclusive about speed yet, as the retreival line slowed the proa very much. I hope there is more wind tomorrow. It tracked very straight without any adjustments to the rudder or sail. It seems to behave very controlled and well damped in the few waves there was today (wake from motorboats).
Cheers,
Johannes
The vaka is 179 cm long, 17 cm wide, 17 cm high from the bottom of the keel to the peak of the ends. It is 11,5 cm high in the middle with about 7 cm freeboard when not loaded down.
The hull is very light. It is made of 4 mm plywood and some epoxy. It weights 0,95 kg. I will load it down some with some sand next time I sail it. I want to see how it will sail with some cargo. A cruising proa is never this light. I can never build a 64 foot vaka (this scaled 10X) that only weights 950 kgs.
Cheers,
Johannes
Wow Johannes
You have gone from one extreme to another, love the vaka. Would be great to see it in the same sort of wind of the barge proa.
I don’t think my sailing club would approve of me coming ashore with a fleet of optimists skewered on each bow.
Fantastic keep the developments coming
Tink
Hi Johannes,
This latest vaka is looking really promising. If the two profiles are made different to each other then you could build in asymmetry….
Don’t worry about spearing surrounding boats - saw off the ends a bit above the waterline, fit flat transoms fore and aft and mount rudders at each end.
With a deep draught amidships you might not need to worry about grounding the rudders ?
Would be great to see it in the same sort of wind of the barge proa.
I hope there is more wind tomorrow. I might take a trip out to the coast if the weather is right. I want to test this vaka properly in some real waves.
I don’t think my sailing club would approve of me coming ashore with a fleet of optimists skewered on each bow.
LOL!!!!
Thanks Tink!
Cheers,
Johannes
Don’t worry about spearing surrounding boats - saw off the ends a bit above the waterline, fit flat transoms fore and aft and mount rudders at each end.
I was only joking about skewering optimists, a result of my lack of control in tp03 and my very crowded club.
You must keep the bows, I will never own a J Class or even Skerry cruiser but could see myself in one of these.
Hope you get some good weather, it is getting windy here in the uk so you should get some soon.
Cheers
Tink
Looking realy nice, love it! somewhat inspired by the swedish “skärgårdskryssare” i guess? (:
/Garg
If I read this correctly, at the hull midpoint, the width is 170 mm and height is 115 mm, making the width about 150% of the height.
I find this interesting because one of the issues with many vee hulls is lack of displacement. I had been looking at hulls where the width was about 2/3 of the height and found that they did not have enough buoyancy (using design software).
Perhaps this wide configuration might increase displacement enough to make the hull shape more practical than a narrow vee hull.
The scitmar shaped hull is very striking.
This latest vaka is looking really promising. If the two profiles are made different to each other then you could build in asymmetry…
Thanks pr1066!
That is a simple way to create an asymmetric hull. I have to test it with a paper-model.
Don’t worry about spearing surrounding boats - saw off the ends a bit above the waterline
I think this is a bad idea. I believe many people see the overhangs as “wasted material and length” but it is actually an important part of the design.
The overhangs will damp pitching and other unwanted motion when the hull is sailing through waves.
At low speeds the waterline-length is short and the hull has a low wetted area and low skin-friction, but at higher speeds the hull will sink into its own wave-system and gain a lot of waterline-length and potential speed. The directional stability will increse at higher speeds to.
If I build a 24 foot deep-V proa I probably have to use flat transoms for and aft, to get a longer waterline-length and a greater displacement. That is a tradeoff though. I´m thinking about making it 32 foot with the full rocker and pointy ends instead.
somewhat inspired by the swedish “skärgårdskryssare” i guess?
Yes! The classic skerrycruiser and J-class boats are very beautifull and very much a source of inspiration.
If I read this correctly, at the hull midpoint, the width is 170 mm and height is 115 mm, making the width about 150% of the height.
You are reading this correctly.
I want a large angle “V” to gain both displacement and damping. A to narrow deep V hull will not resist pitching and other unwanted motions as well. I have become spoiled by the extreme damping properties of the barge-hulls, and I want some of that to carry over to the deep-V hull.
The scitmar shaped hull is very striking.
Thanks! I get a lot of attention wherever I try to sail the model. Much more soo than with the barge. People seem to appreciate this kind of timeless classic shape.
Thanks!
Cheers,
Johannes
I have tested this proa some more today. No pictures or videos.
A colleague from work followed me to a nice beach where we tested the proa without the retreival-cord. The beach is very shallow so it was easy to walk along the proa.
At first we had some problems getting it to sail straight. We had to remove the rudder and lift the sail to a more upright position. Suddenly the proa tracked straight and sailed quite fast in the calm winds. I added about 1,5 kg of sand in the bottom of the vaka so there was only 3 cm freeboard left and I could not see any marked drop of speed. Since the waterline-lenght increases and the windage decreases when loaded with some sand, the speed seems to stay roughly the same. I hope there is more wind tomorrow.
Cheers,
Johannes
Loving your development Johannes
Hope you get some good wind tomorrow, (here in the UK it is forecast too windy for my daughters first solo sail) I agree with your idea of keeping your aesthetic integrity, steering is a minor consideration. There are many alternatives to brake (oops sorry rudder) at the end of the hulls.
Keep it coming
Tink
Hi Johannes,
If the two profiles are made different to each other then you could build in asymmetry…
When planing Proud Mary this was one of my first ideas, and it worked very nicely in a cardboard model I made at the time. This was a beautiful shape.
It is a very appealing, clean, simple and easy design that I’d be keen to try if it didn’t demand so much draft.
Can’t wait to see where this takes you, I’ll keep my eye on this one!
Cheers!
I woke up early from the wind hissing in trees outside, so I drove down to the lake before breakfast to get some sailing done.
It is not easy to sail the proa, stand on a slippery rock slab - trying not to drop the cellphone or fall into the water and try to take a video of the boat at the same time. You have to excuse the poor quality of the video. Usually it is my oldest son or my wife holding the camera/cellphone.
The wind was so strong the proa wanted to flip over almost immediatly. I had to use the strong resistance to stalling of the crab claw sail, and let it out as much as possible. The proa seems fast, but not as fast as the barge-proa. When I weighted it down with some gravel it started behaving a lot better with much less pitching. I am spoiled by the barge-proa and its great damping and calm behaviour.
I am still impressed by the proa. I think it is doing a lot of things right. With some added weight it is calm and still fast. It is not as close-winded as the barge, but that might be due to the large sail and strong wind today. It is really good at keeping its bows above the surface, almost regardless of any abuse I throw at it.
Cheers,
Johannes
Johannes. I think your video proves it to not be a good design. All that pitching would kill the drive in the sail. One of the bonuses of a proa is the relatively long hull gives a very good pitch resistance, read Sven’s report on Pacific Bee.
Reading from real experience of sailing proas, very little rocker is required and is not beneficial, which was a suprise until I thought it over.
Cheers
Mark
Johannes. I think your video proves it to not be a good design. All that pitching would kill the drive in the sail.
I partly agree with you.
If you watch the “Deep V proa, windy morning” video where I have about half a kg of gravel in the bottom of the hull, you can see that it does pitch only slightly more then my red Barge-proa. When it is sailing empty in the other video it is very light, only 44% weight of the red barge-proa, and it pitches around much more. A much lighter and shorter hull (waterline-length) with a higher center of gravity will pitch more than a heavier and longer (waterline-length) hull with a lower center of gravity. When empty, the deep-V hull has a waterline-length of about 100 cm. The barge-proa has 128 cm, and with a lot of displacement very far out in the ends.
I don´t think it is fair to call it a failure based on an very unfair comparison. I don´t think less rocker would do much good in this case, since it is the long overhangs and wider V-shape that is resisting the pitching motion.
There are several ways to damp the resonant system a hull is. A perfectly round bowl with low weight and a high center of gravity and no appendages would have a very high Q (resonance tendency). If you add flare or a flat section or a protuding appendage which lower the resonant frequency or more mass or hard chines (chinerunners), you will damp the Q to a lower value. Hard chines, chinerunners, a full keel, a daggerboard, and asymmetry are all good ways to lower Q by turning unwanted motion into vortices.
It is not only Q that matters, but the resonant frequency has to be lower then the wave-period the hull encounters.
This deep-V hull has a larger overall length and I believe that contributes to the impression of more pitching motion than my barge-proa. Watch the videos side by side.
I do think it is beneficial to use a larger radius for the keel-line, an that means a longer hull or less draught or not as high ends as I use now, or all these combined.
I will sail it some more before I make up my mind about this hull, even though I am quite impressed. It is not perfect, but I have seen a lot worse. My green ASP does have more high frequence pitching between waves, that I am not at all pleased with. This deep-V has a softer more simple low harmonic motion than any of my flat bottom hulls.
Cheers,
Johannes