59703Beachcat #589 & free flooding keel (was Re: Water Ballasted Chebacco)
- Feb 6, 2009I missed that.
Charles' posted there was info about Big Tortoise in "Instant
Boatbuilding with Dynamite Payson". I browsed on to Catfish, a
Chebacco spin-off, and, blow me down, in the first short paragraph
Payson describes the self-righting and light trailering gained from
the free flooding keel under this design. I mean - it's the first
thing he jumps in at to describe!
PB&F have described aspects of the high and wide decks of Beachcat
that make for ease of mind in potential knock-down sailing
conditions. They mention the good ability of the salient keel in
thinner water than the centreboard of the upgrade plans can handle.
PCB seems to prefer the salient keel on Beachcat for himself, but to
my knowledge they have never elaborated on the benefits of the keel
being free flooding. Never published on this design aspect - I
thought it solid. This free-flooding/slow-draining is what adds so
much to Micro, supplemental to the lead ballast, in self-righting
immediately following a knockdown all the way to a beam ends attitude
where the keel is lifted above the water and before the internal
water has had time to drain out. The cross section of Beachcat
probably means that the flooded keel begins to lift above the water
and have a righting effect at more intermediate angles of heel than
on Micro, and keeps righting moment fairly positive as heeling
progresses for some arc beyond 90deg.
In a certain published vignette, that although un-named could only
have featured cruising aboard an original Catfish, a prominent Aussie
designer/builder didn't mention the designed benefits of freely
flooding the Catfish keel. Has Mr Payson got his wires crossed?
--- In email@example.com, "mcdennyw" <dwolfe@...> wrote:
> I modelled the full keel 246# lead ballast design
> version) and the RM is right in between the no ballast and water
> ballast designs. At 20 degrees the 246# lead gives RM of 1393 ft-
> lbs. No ballast RM is 1041, water ballast RM is 1883.
> The vertical CG of the water ballasted boat is 2.5" lower than the
> one with lead ballast. The lead is lower but only half the weight.:
> > Denny,
> > that sounds all to be good. Great.
> > I wonder how much different are the figures for the lead
> > keel version. They'd cost a little extra in the 246lbs to
> > and another 6 inches of draft. I wonder if that lead ballast keel
> > might add a bit more than the 500lbs internal water ballast to
> > initial stability, but then not to final stability?
> > Graeme
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