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A good question. In fact, one hull is always more draggy than the other as soon as the buoyancy is shifted by the sail pressure - on every boat.That sounds good in theory. I wonder how it works out when both hulls produce different levels of drag force. Would boat try to turn towards more draggy hull and have to be compensated by slight rudder deflection?
Both correct in my experience. Thanks for mentioning them.I have never sailed a proa. But imagining sailing her upwind, both hulls entering the wave at the same time and moving together ... Compared to a cat with two hulls of equal length, each trying to impose its movement on the other, it looks for me like a much smoother ride, with much less stress on the structure and crew. Thinking this is a main advantage of a proa, I am curious if experienced proa sailors agree.
On the other hand - in light winds and low speeds when frictional drag dominates, the shorter luv hull produces LESS drag because its wetted surface is smaller in relation to displacement. As the wind and the speed are increasing, the weight is transferred more and more to the slender leeward hull, which causes less wave drag ... it looks very unusual and I don't know how it works in practice, but from a technical point of view this is a very elegant principle.
My experience with a 'conventional proa' in light winds is that overall minimal wetted surface dominates. The least amount of wetted surface occurs when as much displacement as possible is transferred to the lee hull where the added displacement is absorbed by a slight increase in draft which is smaller than the lessened area of the smaller windward hull, a squared/cubed relationship.On the other hand - in light winds and low speeds when frictional drag dominates, the shorter luv hull produces LESS drag because its wetted surface is smaller in relation to displacement. As the wind and the speed are increasing, the weight is transferred more and more to the slender leeward hull, which causes less wave drag ... it looks very unusual and I don't know how it works in practice, but from a technical point of view this is a very elegant principle.
You can tack a proa, but depending on the length of the small hull, need to be careful of a diagonal capsize, so light- moderate wind only.
To reef, the sheet is released and the sail weathercocks, regardless of point of sail. The reefs are then pulled in as per normal, but with none of the stress and highly loaded ropes involved when reefing a cat or tri while sailing. It is made even easier with the simple halyard lock (essentially a rope loop around the mast which 'catches' at each reef point). Trip the lock by slightly tensioning the halyard, it drops to the next reef point and the luff and leech lines are tensioned.
Crab claws are great, but not suitable for cruisers. Attached is a vid of me sailing one in the Marshalls. And another of a modern version of the boat which we taught the locals how to build. Notice the lack of use of the steering paddle in the second vid, the difference in payload and the logic of having crew to windward. Both sails are well over 20 years old, have had a hard life. Both boats sailed at similar speeds, but the traditional one was far more exciting.
I cannot think of a more difficult way to build a carbon mast than the one in the video. Ours are way simpler, and lighter.
This is a drawback of the ship's outboard on the tender. If you are doing a lot of motorsailing, it is not a good solution. On the cargo proa, I have a 6kw electric motor with a fairly big prop on the end of a steerable strut through the toybox. It can be used to move the boat in any direction. We are using this instead of the tender as it was a gift (in lieu of grant money owed to us) and because the tender was included in the design as a boat which could access shallower water than the mothership. This is not a problem, so we don't need the tender.That's a concern because with outboard motor it is not too difficult to get overpowered. Motorsailing and tacking with mainsail only is my go to solution if facing strong headwinds in channel too narrow to reliably tack upwind using sails alone. Although doing it with heavily reefed sails on proa probably would greatly reduce possibility of flipping it and water would be fairly calm.
Yeah. Sitting to leeward and pumping water ballast requires a mindset that I don't have.Great video. Modern proa is actually quite similar how you would sail normal catamaran of similar size by having crew sit on windward hull to counterbalance.
This is a drawback of the ship's outboard on the tender. If you are doing a lot of motorsailing, it is not a good solution.
The Hendon proa builder is almost 70, started 2 years ago and had to build a shed and a house before he could start. He has no helpers and is a perfectionist. I have no idea how that compares to the Dix builder, but I would be amazed if he was as quick. In his "End of 2021" video at least one hull is up and part covered in ply and he talks about local helpers, so closer to 4 than 3 years, I think. In his "reality" video he spent 3 weeks fairing the bow blocks and the chainplates. It will take him a lot longer to do the entire boat once it is glassed.
Whether you choose ply or infusion is up to you. But before you choose , try infusion. Spend a couple of hundred bucks on an E Bay pump and a starter kit from your local supplier. Or visit the 20m Harryproa builder in Norway and give him a hand for a couple of days.
I made the three planks that sit on the cross beams of QB with some XPS foam with a Gpet cap reinforced with uni top and bottom covered with 18 oz cloth. Infused one at a time it was a fairly easy learning experience. Need advice on infusion/vacuum line arrangement https://www.boatdesign.net/threads/need-advice-on-infusion-vacuum-line-arrangement.69702/I
That sounds like good idea. I know I would be extremely stressed if I had to infuse large parts with potential to waste weeks of set up time and thousands of euros in materials or introduce hidden weakness if I screw up something with vacuum setup. Maybe infusing something simple and cheap like homemade XPS foam paddle board would be good start.
Mulkari. What are the exact length and width dimensions of the plywood sheets you're thinking about using? Also, there have been some questions you've asked that haven't been answered thoroughly along with some statements you've made that haven't been explored. Are you still looking for feedback or have you finalized a plan?
I made the three planks that sit on the cross beams of QB with some XPS foam with a Gpet cap reinforced with uni top and bottom covered with 18 oz cloth. Infused one at a time it was a fairly easy learning experience. Need advice on infusion/vacuum line arrangement https://www.boatdesign.net/threads/need-advice-on-infusion-vacuum-line-arrangement.69702/
Plywood I plan to use is available in various sizes including sheets up to 4 m long. With 4 m sheet length there would be only 3 stitches on 15 m hull.
https://www.finieris.com/products/riga-shipply/
- 1220 / 1250 mm × 2440 / 2500 / 2745 / 2750 / 3000 / 3050 / 3340 / 3660 mm
- 1500 / 1525 mm × 2440 / 2500 / 2745 / 2750 / 3000 / 3050 / 3340 / 3660 mm
- 1830 / 1850 mm × 3050 / 3340 / 3660 / 3850 mm
- 2150 mm × 3050 / 3340 / 3850 / 4000 mm
- 2290 mm × 4000 mm
My design is still in progress, I'm also contemplating Harryproa, but if I decide on that I would start only after one of the C50 currently in progress is finished and test sailed in stormy conditions similar to what would be expected in North Atlantic. I also have to secure the build site, owner of the hangar I plan to rent space will be back in Latvia after few months, the place needs some cleanup from various junk and I need a guarantee that the place it will be available to me while the boat is built to a stage where it can be put in water. It would be no fun to have to relocate half built hulls and finish who knows where.
Possibility of dry spots freak me out. In carbon it is hard to see where it is infused properly and where it may not. It is absolutely critical for masts and beams. Having a hidden dry spot could easily lead to failure later.
Sorry disturbing this thread by trivialitys but that is simply not true. Neither the generality of the claim nor the generality of the "acceptance".It is generally accepted that multi mast rigs are poor performers to windward because of extra drag and bad air caused by mast and sail in front.
