Re: [Paddlewise] Rollability Hypothosis

Nick wrote;

> I have been having some discussions about kayak "rollability". The common
> idea is a kayak will be hard to roll if it is stable upside-down. This
> makes sense initially, but then again most people can get most of the way
> up in a roll. The hard part is getting all the way. If inverted stability
> was the most important thing, getting from upside-down to the point where
> you can breath would be the hardest part.
>
> I thought that maybe the slope of the stability curve at 90 and 270
degrees
> would be a better indication of how easy a boat is to roll. A lower slope
> indicating and easier boat to roll, i.e. the effort required to change the
> angle fo the boat would be less.
>

A few thoughts:

Lower stability when upside should make rolling easier particularly when you
factor in the righting moment of the life jacket/paddler. I would suspect
that the deck shape along the sheer impacts as well since the boat rolls
rather rapidly. A rounded sheer such as Nick uses on some of his boats
should roll more easily than a more angular sheer (such as I  use on some of
my boats). The narrower the boat the easier it seems to roll in both
directions - up and down.

One could calculate the rolling resistance of the shape and merge that with
the upside down stability. Seems like a lot of work when taking a boat out
and rolling it tells whether you find it easy or difficult to roll. Of
course, none of this applies to owners of wide kayaks who consider rolling
something "other" people do and people like myself who has done it and can't
imagine why anyone would want to do it more than once. :-)


Cheers,

John Winters
Redwing Designs
Web site address http://home.ican.net/~735769

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