Re: [Paddlewise] paddlefloat photo

Michael Daly wrote:
> 
> From: "Robert Livingston & Pam Martin" <bearboat2_at_attbi.com>

> > The second is that the rear bulkhead wraps around the paddler so that the
> > kayak retains an air pocket on each side of his/her thighs (a continuation
> > of the rear compartment) - Dare we say built-in "sponson"?
> 
> This can provide additional bouyancy to prevent sinking, but it will not contribute
> to stability.  The water on the outside of the hull doesn't know what's inside the
> hull.  Adding a sponson to the _outside_ of a hull can make a difference.
>
Having water on the inside of the hull can decrease stability since this
water is free to slosh around from side to side and affect the balance
of the boat.  Interior sponsons can markedly decrease the ability of
this water to move from side to side and therefore they can aid in the
boat's stability when the cockpit is flooded.  Imagine a boat that just
has a narrow channel down the centerline that can flood with water with
the rest of the space fully occupied by the paddler and interior
air-filled sponsons.  In that case, the water in the cockpit is
constrained to stay in that channel and will actually aid the boat's
stability by acting as a weighted keel (albeit not as effective as that
on a sailboat since it has a much shorter lever arm). 
OTOH, without the sponsons on the sides, the water is free to flow to
the low side of the boat.  Any initial tip to port then results in the
water shifting to the port side and helping to tip the boat further in
that direction - clearly reducing the boat's stability.
It's impractical to make a boat with interior sponsons that are as
effective at controlling water movement as in this hypothetical case,
but to the extent that they keep interior water from sloshing to the
sides of the boat they will certainly aid the stability relative to a
boat of the same shape that lacks internal sponsons.  

> 
> I thought we've been over this before?  And the conclusion every time is the same:
> flooding a kayak is a bad thing.

I didn't think that was the topic of conversation. Matt proposed that
boats with high initial stability are most affected by flooding while
those with low initial stability are least affected.  I agree with
Robert/Pam that there can be designs that have high initial stability
but are also affected relatively little by flooding.  One such design is
a rather wide boat that still has a narrow cockpit with the remaining
space on the sides occupied by air-filled internal sponsons. This
doesn't mean they aren't affected at all and certainly doesn't disagree
with the premise that flooding the cockpit 'is a bad thing.' Nor BTW, am
I suggesting that such a design is superior to others - only that it
does not follow the hypothesis proposed by Matt.

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