Re: [Paddlewise] ship wakes and such

Dave wrote;


>
> I've noticed that on the Columbia, also.  There is a *small* tour boat
(200-300
> tons?) which runs the stretch from Portland, OR to the mouth of the River
(ca.
> 150 km) that puts out more wake (sometimes) than large freighters.
Watched
> some friends get swamped over a shallow bar one day.  Pumped waves into
their
> open cockpits and just sunk 'em.  Funnier than hell!
>
> Maybe Winters understands this ... ?

Small ships operating at or near Froude number 0.40 can raise larger waves
than larger ships operating at well below 0.40. (0.40 = S/L 1.34 in feet
and knots). I prefer Froude number as it doesn't matter what dimensional
system I use I always get the same number.) Tugs do this since they seem to
operate at only two speeds -  very slow and wide open. :-)



Also cats seem to build up interference waves between the hulls. It seems to
me that this would increase resistance  but maybe I don't understand
everything I know about it. I have seen some cats throw huge waves way out
of proportion to their size and maybe it has to do with the boat operating
at an inefficient speed range.

Getting swamped on the shallow bar may have more to do with the depth than
anything else. Waves really start to pile up and become more vertical as the
water gets shallower than the critical depth and small waves get become
gnarly and steep.

Cheers,

J. Winters






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