Can a Pacific Proa Benefit From Lifting Foils ?

Discussion in 'Multihulls' started by mcm, Feb 5, 2015.

  1. Doug Lord
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    Doug Lord Flight Ready

    Flying Boat

    After thinking about it a lot I think the best solution for flying the main hull would be:
    1) a midship main foil designed to carry as close as possible to 80+% of the load, and
    a.The foil would have a flap and wand. The wand needs more thought.
    b. The foil would have to rotate 180 degrees with every shunt AND it would have to automatically(as it rotates) set the main foil at a plus 2.5 degree angle of incidence.
    2) two retractable rudders +foil with only one used at a time. Adjustable angle of incidence but shouldn't have to adjust under sail.
    3) Crew MUST sit aft with each shunt.
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    This would probably work well with excellent pitch stability and altitude control but it seems too complex even for me. Just add another ama and you could have a flying tri esp. if you added UptiP foils to each ama. With the tri configuration everything is automatic requiring infrequent adjustment. Sorry, couldn't help myself.....
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  2. mcm
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    mcm Senior Member

    I haven't heard any better solution, and it sounds like it would work.

    When you say plus 2.5 degree angle of incidence, you mean the vertical axis part of the t-foil's angle to windward not the horizontal elevator of the t-foil's angle to the water-line,, right ?

    Not a problem, i go through the same back and forth arguments in my head all the time.

    But the thing about pacific proas is that the loads are lighter with only one ama to windward, and that load is shared by the heeling moment of wind and rig with the ama flying or nearly flying most of the time.

    The beams can be a lot lighter and the rig a lot smaller and still get alot of speed. Russel Brown's 'Jezerro' can make over 20knts and that's a cruiser without lifting foils.

    Not to mention a pacific proa is cheaper and easier to build,,, once you got the design down.

    The atlantic proa is an option; with the ama to leeward it's more like a tri.
    But then the ama is plowing through the water and needs a lot of buoyancy to maintain enough righting moment.
    That means the beams have to take heavy loads like a tri.
    And you still have to shunt; so you still have two rudders and any other foils would still have to possess either bi-directional symmetry or asymmetry that must rotate 180deg..
     
  3. Doug Lord
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    Doug Lord Flight Ready

    By 2.5 degree angle of incidence I mean that the lifting foil is angled up that much in reference to the static waterline(assuming it is parallel to the flight waterline). It wouldn't be a bad idea if, in addition to that for the lifting foil, that the leading edge of the daggerboard is angled forward at the bottom to help deal with ventilation-say 5-7 degrees. You would still keep the lifting foil at +2.5.
    The rudder hydrofoil would be set at zero degrees AOI.
     
  4. cavalier mk2
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    cavalier mk2 Senior Member

    I personally feel using the lighter beams possible for the Pacific is a mistake. That sort of construction leaves you open for catastrophic failure in a caught aback situation. As far as cost and complexity for the Atlantic and
    Pacific there isn't much difference. In fact a basic Newick with a cat schooner rig is less involved than Russell Brown's boats. For racing the Atlantic has more speed potential, All those record setting tris have done pretty well with the ama to leeward.
     
  5. Timothy
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    Timothy Senior Member

    Would not moving the lifting foil to leeward help? Some of those racing tris use canting rigs which if used on pacific proas can be designed to ease to leeward if caught aback. Catastrophe avoided? I think Doug has the right approach with the lift distribution and attack angles. I am just wondering if this can be accomplished with two simple conventional straight foils that can be pulled from one cnc cut half mould?
     
  6. Doug Lord
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    Doug Lord Flight Ready

    You could make a split mold less expensively than having it CNC cut(maybe) but as long as the mold halves allowed for the flap on the lifting foil and the pushrod tube on the vertical foil I think a single mold(2halves) could work well.
     
  7. rob denney
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    rob denney Senior Member

    Not really. Harrys have all possible weight, apart from rig and rudders in the windward hull, to maximise righting moment. This is the lightest, fastest configuration over a variety of wind strengths. Pacific proas have small, empty ww hulls with the crew sitting to lee. In smaller sizes they may move to windward. In larger sizes, they use water ballast. A foil to lift the crew sitting in the lee hull while adding water ballast to the windward hull for righting moment is an inefficient use of resources. To get to speeds fast enough to use foils to advantage, you will need as much rm as you can get.

    The rudders on harrys are big enough to not require daggerboards with all their drag, complexity and potential for damage in a collision. Large rudders also make shunting much easier, particularly at slow speeds.

    Bucket List https://www.youtube.com/watch?v=ttXu3pRTzs8 is not a dedicated race boat. It is a fast, simple, low cost boat for charter to people who want to race but do not have the time/money to spend on a complicated boat.

    It is great to see some experimentation happening. A couple of points that may help, based on my experience.

    1)The least additional wetted surface approach for foils is to sleeve them onto the bottom of beam mounted rudders. The rudders are easily raked to adjust the angle of attack and set the front one with a higher aoa than the aft one, aiding stability and overcoming the lack of weight aft. Various sizes and shapes are easily made and installed for different wind strengths, etc. The foils can be raised in light air or for removing weeds. A break away mechanism for impact is easily included.
    2) Foil shapes: After experimenting with Tom's sections, I agree that a sharp edged section is a better proposition. We are using modified ogive sections for lifting foils (on kite proas, not sailing ones) and for bidirectional rudders. While they are not as efficient as other shapes, they are very easy to build. A smooth, fair surface is more important than an ultimate foil section. Once the system and foil size is sorted, then start playing with exotic shapes, flaps and wands.
    3) Rudders to leeward are a good idea, once the bugs are out. Otherwise, they are hard to get to to make adjustments. They will also make a mess of the hull if they kick up for any reason. Canted rudder/foil combinations will alter pitch as well as yaw when steering.
    4) Size your beams for caught aback loads. If you push the boat in conditions that will generate enough speed for the foils to work, you will be really pissed off if (when) you are caught aback and the rig falls on your head or the beams break.
    rob
     
  8. mcm
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    mcm Senior Member

    Thanks for your input Rob,
    but what about a wand adjusted t-foil on the ama that provides both downward and upward lift to increase and decrease RM as the wand adjusts to maintain pitch.

    Which edge should be the sharp edge,,, not the leading edge, but the trailing edge - right ? nor the bottom edge - right ?

    By the way Rob, ever try S2 glass/wood composite for masts instead of carbon fiber ?
    Less than half the price if one can get it stiff enough. Maybe an internal web of laminated fir could stiffen it up.
     
  9. mcm
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    mcm Senior Member

    Flying an ama to leeward takes a good sized foil compared to flying one to windward.

    Still, a atlantic's buoyant leeward float gives one a sense of confidence where as a good set of nerves is useful with a pacific proa.

    But of course Cheers is a beautiful boat, and Russell has a large poster of it in his shop where the two of us couldn't help but stand and admire the flowing lines. Russell even went so far as to say that those long graceful overhangs are useful around here to slide over the top of submerged timber.

    Good point, but not with a cat schooner, which, according to the guy that sailed Cheers across the atlantic, didn't point all that well.
     
  10. cavalier mk2
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    cavalier mk2 Senior Member

    Foil assist like the tris is the way to go imho, hence the set of bananas for the ama. Rigs have a lot of possibilities, no reason not to have what you want. A sloop could be a 30 knot boat.
    I'm with Russell on the overhangs in the PNW. They are staying on the Vagabond. Everything in the water up here makes me cringe when people talk about reliable foiling....
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    "Good point, but not with a cat schooner, which, according to the guy that sailed Cheers across the atlantic, didn't point all that well."

    Better watch the tendency to base modern performance on old results. I noticed the trend yesterday with the reference to Slingshot's waterballast. There is a huge difference today in say a battened square top mains catketch and the old rig they had on Cheers.
     
  12. mcm
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    mcm Senior Member

    Sounds interesting, and point taken, but do you have any links illustrating your point.
     
  13. cavalier mk2
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    cavalier mk2 Senior Member

    Check into that bastion of original thinking, unbound by convention and learning by rote, Gary. His Black Skimmer comes to mind, you can find it without too much effort on one of his threads.
     
  14. Timothy
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    Timothy Senior Member

    I guess you guys have all seen the Slatts 22 https://www.youtube.com/watch?v=tzPYbzbdOTg
     

  15. rob denney
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    rob denney Senior Member

    Better than pumping water ballast, but still pretty stupid to be sitting to leeward as foils are still drag. If the foil is overwhelmed and lifts out or gets weed/plastic on it, you are in trouble.

    For bidirectional foils, both. For one way foils, just the trailing edge, although ogives were the shape of choice for the early hydrofoils.

    Max stiffness and min weight are what you want for spars. Wood just adds weight, as does an internal web. Carbon is cheaper than S glass as you need more of it (and resin) than carbon.

    Yeah, but not much point in riding over the logs only to have them wipe out the rudders, daggerboards and foils! Plus you get more pitching and less waterline length, which is less speed. I prefer vertical bows with foam collision pads and angled bow bulkheads. And of course, kick up rudders and no daggerboards.

    Elementarry, my schooner rigger 25'ter would point as high and as fast as a top Tornado cat. Sleeved sails, longer hull, lighter weight, less windage all contributed. Cheers' masts were 150mm/6" square section, with no vangs and pinhead sails. No wonder it did not go upwind. It is a pity Vincent did not upgrade the rig when they restored it. It would be a real weapon if he had.
     
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