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Thread: Satyr Canoe / Punt prototype

  1. #36
    Join Date
    May 2015
    Location
    Port Elizabeth, South Africa
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    164

    Default Re: Satyr Canoe / Punt prototype

    A sailing design? I would be very interested to know what it was. The Hobie Monocat and the Seamite were one-piece hulls but still cats as far as the water was concerned. Some of the old scow Moth hulls had a concave bow but the concavity was not allowed to extend very far aft.
    This hull shape that I am experimenting with does have a rather slender waterplane area from about 15deg heel with a fine entry and wider flat aft sections. It has a lot of wetted area when flat. I am looking forward to finding out just how much (or little) power is required to get it to plane. This is my first venture into hull design and my grasp of the principles is still only at "rule-of-thumb" level, i.e. not very academic. My guess would be that it should perform well at 10-12deg heel when it has shed a good deal of wetted area but not an inch of waterline length.

    I did some flow simulations a while ago to compare this hull with the original Duck Punt. I was not able to simulate a free surface, so the results would only really be applicable to low speed where wave-making is not a big factor. It is nevertheless quite obvious what the effect is on the bow pressure when aligning the bow with the track through the water - 8 degrees as the case was here. I wanted to test the inherent ability of each hull to resist leeway. The satyr hull created 70% more lift with no extra drag to show for it. Heel was at 15deg.



  2. #37
    Join Date
    Jan 2004
    Location
    Norwich,United Kingdom
    Posts
    4,776

    Default Re: Satyr Canoe / Punt prototype

    I am impressed to see a CFD plot on this forum-more please!The scow Moths referenced above had limited hollow because the class rules stipulated that a tight string stretched across the hull should be no more than 75mm from the surface at any point.Without this limitation its quite possible that catamarans might have infiltrated the class.

  3. #38
    Join Date
    Feb 2006
    Location
    Pennsylvania
    Posts
    7,622

    Default Re: Satyr Canoe / Punt prototype

    The scow Moths referenced above had limited hollow because the class rules stipulated that a tight string stretched across the hull should be no more than 75mm from the surface at any point.Without this limitation its quite possible that catamarans might have infiltrated the class.
    I do believe there was a similar history in the scow classes.
    -Dave

  4. #39
    Join Date
    May 2015
    Location
    Port Elizabeth, South Africa
    Posts
    164

    Default Re: Satyr Canoe / Punt prototype

    Quote Originally Posted by John Meachen View Post
    I am impressed to see a CFD plot on this forum-more please!The scow Moths referenced above had limited hollow because the class rules stipulated that a tight string stretched across the hull should be no more than 75mm from the surface at any point.Without this limitation its quite possible that catamarans might have infiltrated the class.
    I often wonder what exactly the rule-makers wanted to achieve, preserve or prevent by rules like that. IC10 canoe rules have something similar. If a cat-hull of similar beam would perform better, why prevent it? The Italian Diecipiedi (Ten Foot) Class has none of that, and the beam limits even suit trimarans. Yet some races are still won by monohulls. Go figure.

    As I mentioned earlier, this hull shape was driven by the aerodynamic interaction between hull and rig. One of the design objectives was to improve on the Duck Punt's ability to point. I want to achieve this without any increase in heeling moment so it precludes going to a higher aspect, taller sail. One solution would be to bring the sail down flush with the deck to eliminate the foot vortex. This would immediately lower the center of effort and also improve the Lift/Drag ratio. Or so I thought. Simulations showed that it was nearly impossible to maintain attached flow over the foot of the sail. The culprit turned out to be a separation bubble just to the lee of a plumb or raked stem. By curving the stem back into the wave-piercing shape, the flow instead forms a horizontal vortex extending down the side of the hull. This seems to have solved the problem.




  5. #40
    Join Date
    May 2015
    Location
    Port Elizabeth, South Africa
    Posts
    164

    Default Re: Satyr Canoe / Punt prototype

    2hp Yamaha test fit. Not a high priority but I want to keep my options open for the future while I plan the internal layout.

    The height of the bulkhead is 2" less than the transom height specified in the outboard's manual. Does a well-mounted motor require the same mounting height? (I will most likely consider using a close-fitting plug around the shaft to reduce the amount of free water surface in the well).


  6. #41
    Join Date
    Sep 2010
    Location
    UK
    Posts
    818

    Default Re: Satyr Canoe / Punt prototype

    So nice to see an interesting and innovative build. Can't wait to see how this turns out.

  7. #42
    Join Date
    May 2015
    Location
    Port Elizabeth, South Africa
    Posts
    164

    Default Re: Satyr Canoe / Punt prototype

    Internal bracing is finally sufficient to manhandle the hull without the decks on and it was time to get a better look at the bottom. I specifically wanted to look at the rocker before adding any further internal floor stiffners.

    A mis-measurement (not taking scarf overlap into account) led to a post-box sized slot at the base of the inverted-V. Just as well, because the area required some surgery to get a smoother transition (larger radius) where the panels meet. Since this will be an area subject to a good deal of pounding, I decided to try my hand at building with strips of white ash, same thickness as the ply (4mm).

    The boxy hull shape flipped on its side made for easy access to the work area from either side.










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