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Kayak and Canoe Design Bulletin Board
Re: Design Water Line
Posted By: Andy Waddington In Response To: Re: Design Water Line *LINK* (Capn Jimbo)
Date: Monday, 22 January 2007, at 4:44 a.m.
: when comparing kayaks it's important that the DWL be adjusted so that the
: design displacement matches the target displacement, ie that both kayaks
: are designed to carry the very same displacement for purposes of comparing
: drag.It depends on why you are comparing kayaks. But the implicit purpose in this
statement is that you want to know how the drag differs for different kayaks
being paddled on the same trip by the same paddler. To make that comparison,
you would want a waterline for drag calculations that reflected exactly the
same load. That doesn't have to be the design waterline, but, as Nick says,
the word "design" merely indicates a somewhat arbitrary displacement that the
designer chose to reflect what he or she intended to be "typical" usage by
the sort of sized paddler for whom the boat was designed.If you are using Kayak Foundry, the calculations are done for what it calls
the design waterline, but you can change the displacement as needed to make
two different designs carry the same load for comparisons. If you are
comparing two different boats, then strictly speaking, the displacements
should differ if the boat masses differ - only the paddler and cargo mass
should be held constant. However, similar boats have similar weights and
the odd kilo or two won't make much difference.It's unfortunate that none of these design tools seems to incorporate any
code which shows up differences in performance in anything other than
completely flat, static water. I don't know about you, but I rarely paddle
in conditions like those, and it's generally how boats cope in wind and
waves which make me prefer one over another.Andy
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Kayak and Canoe Design Bulletin Board is maintained by Nick Schade - Guillemot Kayaks with WebBBS 5.12.
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