Rowing Skiff Design Tango 17 vs. Heritage 18

Discussion in 'Boat Design' started by SailorDon, Oct 23, 2016.

  1. Squidly-Diddly
    Joined: Sep 2007
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    Location: SF bay

    Squidly-Diddly Senior Member

    I'm not seeing too much hobby-horsing, mostly the hull slows greatly on your return stroke due to your body weight moving aft.

    I think you could get 200lbs on rack with a couple tricks, but still a PIA to get to water, etc.

  2. Dolfiman
    Joined: Aug 2017
    Posts: 929
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    Location: NICE (France)

    Dolfiman Senior Member

    I participated here below on a similar thread but for a tandem canoe, about the comparison of a Freedom 17 and a Cirrus 18, for which I did 2 numerical boats and a tentative Velocity Prediction Program VPP to compare their performance. For the example very similar to yours, on flat sea and no head wind, the net propulsion power requested for the C18 at 4,5 mph is 48 W, at 5 mph it is 70W, so 46% more. Reliability of such speed and net power prediction is all about the estimation of the residuary drag component, the other two components (friction, aero) being estimated with good reliability with usual formulations, providing of course that you know the wetted surface in the exact displacement condition. For the residuary drag, I use a formulation derived from the Delft model series as reported in « Principles of Yacht Design » Edition 2 (2000) by Larson & Eliasson , using 4 design ratios : Bw/Tc, Lw/D^1/3, Cp, LCB. The key point of such prediction tool is not at such the accuracy of the speed prediction in absolute, but its correct response to the modification of such or such parameter, in other words its capacity to discriminate two designs, I hope that using this PYD formulation contributes to that relevance.
    Documents with more details and sources are in quote #58 (with my explanations in quote #56) :
    Canoe length, efficiency and speed
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