Proa question...

[Anau]

Why do I see some proa with daggerboards and some without? What facilitates the lateral resistance for those that don't have one?

[frosh]

Hi Anau, Hobie cat hulls are quite asymmetric when viewed from the bows. This is also the principle of providing lateral resistance on all the ancient and some modern proas. Daggerboards, one at each end ( around 20% in from the ends actually) serve a dual function of lateral resistance and also tracking and directional balance. On correctly deploying the 2 daggerboards, steering is done by moving crew weight fore and aft, as there is no conventional rudder fitted. It is a bit complex, but you can find quite a lot about it on the web.

Rob Denney has designed a couple of proas using rotating retractable twin foils that provide all the lateral resistance for the boat as well as steering. Further ,they are able to use "collective" which means that both foils can be turned the same direction to eliminate leeway.This is similar in effect to the twin foil system used in CBTF monohulls.
As I remember it the foils are set up like daggerboards in rotating cylinders.
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C Class version by Rob Denney
Address:http://www.sailinganarchy.com/forums...=post&id=17099

[Anau]

Originally Posted by frosh

Hi Anau, Hobie cat hulls are quite asymmetric when viewed from the bows. This is also the principle of providing lateral resistance on all the ancient and some modern proas. Daggerboards, one at each end ( around 20% in from the ends actually) serve a dual function of lateral resistance and also tracking and directional balance. On correctly deploying the 2 daggerboards, steering is done by moving crew weight fore and aft, as there is no conventional rudder fitted. It is a bit complex, but you can find quite a lot about it on the web.

Hmm, I'm afraid to ask just how they calculate how much asymmetry to put in the hull.

So for those people who do use a steering oar, do they deploy only one of the dagger boards at a time? After a long time, I'm finally think of switching over my plans to a proa but I'm not sure how difficult they are to build. Thanks.

[frosh]

Hi Anau, Quite a lot of asymmetry like a Hobie 16 hull is appropriate. I have shown in the following web site some plans by a naval architect on his version of hull shape which is more symmetrical than the Hobie.
http://www.wingo.com/proa/index.html
As far as using a steering oar I have indicated some photos of an oar in use,
http://homepages.paradise.net.nz/garyd/tarawa.html
I personally don't like the idea much as it can be heavily loaded up but most proas using them have no daggerboard at all. Also after shunting you have to remove the oar and take it the opposite end of the main hull and re-install it.
There is a lot involved in designing a proa that will sail reasonably well, and I would be very wary until you understand the mechanics extremely well.
Lastly I will indicate a web site showing a boat with 2 dagger boards, no rudder, and no steering oar.
Good luck. http://www.clcboats.com/boats/pacificproa.php

[Anau]

Thanks, I've seen some of Gary Dierking's other boats, I may end up purchasing one of his plans. There's one called Wa'apa that's symmetrically constructed from 3 panels and I noticed that his design has one leeboard placed at the middle of the ama.

[frosh]

Hi Anau, good move to buy a Gary Dierking plan and go with that. For the small outlay you avoid the strong possibility of building a self designed flop.
With respect to you, design of a fairly unconventional craft is tricky. Now you have to decide which of about 4 versions you prefer!

[Anau]

Actually, I've had my eye on the T2 for a while now. I think if I were to build a proa, it would be that one because the design is just so beautiful. The only thing I'm not really sure about is strip plank construction. The hull doesnt't have any complex bends so I don't think it would be too difficult for a beginner. Also I'm wondering if the planks can be made of plywood.

[nero]

You will have no problems stripping up this boat. Plywood is a bad choice. Foam strips would not be very expensive. Y'all have cypress in TX. It smells bad at times, but it works well to strip with. (quarter sawn strips only) Swamp ash would work also. or Sassafrass.

[frosh]

Hi Anau, T2 is a great choice, much prettier than Wa'apa and no hassle of daggerboard or leeboard. The hull (vaka) will provide the lateral resistance although you wont point as high a modern yacht. I love the Gibbons Rig, as it reminds me of the highly efficient hang-glider sail, although the lateen is more traditional. I say, go for it! Build a boat you will be truly proud of.

[Anau]

Alright, well as soon as I find a source for some planks, I'll go ahead and order the plans. Thanks for all your help

Edit: Just out of curiosity, how come plywood wouldn't work?

[nero]

Strip planking relies on the wood to give the hull strength in the fore and aft direction. Half the would grain in plywood is running in the wrong direction to provide this strength. There is a laminated lumber used in building houses. I think it is too heavy for boat building.

[frosh]

Hi Anau, now that you are thinking strip planking, look at a variety of Cedar, being light and strong. Best to get them professionally sawn up with the edges shaped as " Bead and Cove". Ignore this last bit of advice if you are a very experienced woodworker with a good work shop and can rip up and shape large planks of timber yourself.

[Anau]

^unfortunately, that's not true. I wonder if I could get a general home improvement store to cut out the strips for me. I emailed Gary and he said you could use 1x6's to make them.

Just found today that my previous post in this thread about Rob Denney's proa's using twin foils with collective "steering" is incorrect. Apparently, he mentioned the twin foils in connection with two different proas but tested them on a small version and has concluded that they do no work and that collective does not work. The other thread with Rob's comments is under "Sailboats" in this forum.