now if there is one kind of boat that tickles my fancy...

Discussion in 'Multihulls' started by dionysis, Jun 3, 2003.

  1. dionysis
    Joined: Jan 2003
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    dionysis Senior Member

    it's a proa, specifically a pacific proa.

    It is arguably the most efficient sailing machine of all.

    Here are the main entry points for those of you who are interested interested:

    The Proa File

    Review of proa alternatives

    Links site

    I am surprised there is so little discussion of such a marvelous sailing boat.

    I am working up a design, along the following lines:

    84 ft long, 6.5 ft in diameter sears-haack canoebody, reversible spade rudders at each end, single 50ft righting arm connecting a similar but very much smaller water ballasted hull to weather.

    Best sail configuration is cantilevered cat sail canted slightly to leeward, but balance becomes a challenge. Still working on it.

    I would be interested in what people think about proas. I believe they will become the boat of the future, especially for blue water racing.

    cheers, dionysis.
     
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  2. Stephen Ditmore
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    Stephen Ditmore Senior Member

    I share your enthusiasm, like what Joeseph Norwood has written on the subject, and like what I've seen from Kurt Hughes.
     
  3. dionysis
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    dionysis Senior Member

    thanks for the reply, Stephen

    Hi Stephen,

    The size of the boat is not of concern, but merely to see it it was feasable as a cruiser volume. Yes the idea is attractive, and I am certainly not the first to think about it. I like the idea of no ballast, minimum resistance, minimum material etc, but am trying to work out how a pcific proa can be made to tend to itself, just like a monohull does.

    Because (excuse my grammar) of a pacific proa's sensitivity to flying the windward hull, one needs to be at the sheet and tiller all the time - no good if you want to sleep!

    A possible solution is to cant the sail to leeward enough to alter the ratio of heeling/righting moments, and thereby induce the same kind of behaviour as a monohull when encountering a gust, vis. heeling and luffing up. Well that is the idea i am working on at the moment.

    If she can be made to sail by herself under all resonable conditions, just as monohulls do, then in my view the greatest obstacle has been surmounted.

    Cheers dionyis, and thanks for the reply.
     
  4. dirtybeard
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    dirtybeard Junior Member

    what makes proas efficient is not the boat hull, but rather a combination of the trade winds (less tacking), the asymetric nature of the primary hull, and the flopping rig.

    Turns out that in light airs or areas of congestion or variable winds, proa's are not that desirable.
     
  5. terhohalme
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    terhohalme BEng Boat Technology

  6. terhohalme
    Joined: Jun 2003
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    terhohalme BEng Boat Technology

    Here is Ping-Pong proa.
     

    Attached Files:

  7. dionysis
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    dionysis Senior Member

    yes, Terho and dirtybeard.

    Hi Terho and dirtybeard,

    I have seen your site Terho, and found it very helpfull. Your proa is of the 'Harry' kind. From the posts on the Yahoo multihull forum, there are many successful harry proa designs. I am sure your proa will be a success.

    I feel that there is marginal difference between a harry proa and a catamaran or half a trimaran. I may be wrong of course.

    I was intruiged with the pure pacific proa configuration due to its minimal loads on rig and ama, minimal sail area etc., but do agree with dirtybeard that a pacific proa does belong away from congested ports etc.

    It is a no compromise design for a vessel but as you have found, the more you incorporate practicalities into a pacific proa, the more it loses its distinct advantages, and becomes an atlantic type like yours.

    cheers, dionysis.
     
  8. dirtybeard
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    dirtybeard Junior Member

    sorry to diverge

    sorry to diverge,
    but I went through a proa phase and discovered that the sailing characteristics are greatly enhanced by trades. The shunting becomes wearisome in erratic airs such as we find in mountainous coastal areas like PNW. So though I fell in love with asymetry as a result of building the proa, I have had to move toward something different.

    Circumstance, age, and global economy now dictate a genuine interest in junks. Now because they can be produced as cheaply as a high end kayak, can be an effective live-aboard. There is a ready market for the beasts in parts north for reasonable money.

    They can easily be built by a single person, are/can be flat bottomed, are easily handled, can be docked and rented as bed and breakfast. Can be beached. And are cheap to build.

    Especially if one has the will to fall and slice their own lumber. As it happens I am oldish and have no money to put toward the building of a boat. But, I have built myself a bandsaw mill and have the good fortune to live on timbered property. I have a number of planks and dimensional pieces made with a chainsaw mill but in my advancing age do not look forward to driving the chainsaw through fifty foot trees. So I built the sawmill. About 800 bucks into it and nearly done to the point of precision milling.
    Built my own guides. Learned a lot. Bought the bandsaw blade.

    Anyway, I can cut all the lumber necessary to build the junk. I plan to start advertising for sale when the hull is decked. The cedar mast is curing now.

    It will have a long center trunk on the flat bottom which will be the ballast area. This ballast will be long life batteries. No thru hull fittings. Lee boards as I have no patience building centerboard trunks. I love the space provided by leeboards. The junk will be multi stateroom and have 7 foot head room.
    Based on a phil bolger design.

    Anyway, being an old fart I need some more comforts than can be provided by the necessary lightness of a proa.. now I need hot meals and steady decks.
     
  9. tspeer
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    tspeer Senior Member

    This type of proa has been well developed and widely publicized by Rob Denney. See: http://www.harryproa.com/ .

    [​IMG]
    [​IMG]

    I agree that shunting is a pain, especially in light air - the last thing you want to do is come to a stop. But if one is going the proa route, I think this is the way to go.
     
  10. dionysis
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    dionysis Senior Member

    it's nice isn't it

    Yes Tom, it is a really nice design. Make it bigger so you can cruise in comfort. I like the aerodynamic styling.

    Another way to go that is successful, and perhaps the most viable compromise, is an alternating pacific- atlantic proa, that way you can tack.

    I still think though, that keeping the accomodation in the main hull is overall more efficient. That way you do not have to compromise aerodynamic efficiency.

    cheers, dionysis.
     
  11. dionysis
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    dionysis Senior Member

    junks

    dirtybeard,

    I have always had a soft spot for junks. They are simple and cheap to build as you say. In fact the available info on junks, is so user friendly, that you do not have to be a rocket scientist to design one. There is a successful precedent for all aspects of design.

    One of the nicest aspects is that you can construct and dismantle the rigging single handed, even on a big boat, and leeboards are great too.

    I worry about crawling off a lee shore in a breeze. They are not the most weatherly boats around. You got any worries about this aspect?

    cheers, dionysis.
     
  12. terhohalme
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    terhohalme BEng Boat Technology

    Well, the marginal is quite wide. Weight to wind proa is much lighter than catamaran or trimaran and has much more righting moment per displacement. So he can carry more sail area and be faster.

    There is one problem in pasific proa: flying ama is not acceptable for a cruising boat. Without flying ama pasific proa is slow (too low sail area wetted surface -ratio). Water ballast is just a non necessary add to displacement. In a light long and narrow hull you just can't avoid high wetted surface area and you need moderate sail area to keep the speed.

    What distinct advantages of pasific proa are lost in Ping-Pong (EQL7)? There still is: light displacement, low rigging loads, speed, smooth passage thrue the waves, no ballast, etc. Yes, true, I don't need a crew to shunt him. ;)

    I still won't be too strict in my opinion. If I liked to sail beach boat, it would positively be a basific proa.

    Terho
     

  13. dionysis
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    dionysis Senior Member

    My solution for the righting moment was to go wide; at least 0.6 times the overall length of proa. As far as water ballast is concerned, I had to have somewhere to put the fresh water, batteries etc.

    But anyway I take your point. The original design was not for high speed, but efficient cruising. I felt that making the float on the end of the ama, as small as posible, what I lost in righting moment i could gain in lack of windward wind resistance-parasitic drag.

    I am with you, I am open to a better way of doing things.

    thanks and cheers, dionysis.
     
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