... If conventional boats with heavy, weighted keels,
particularly those of heavy construction, had enough positive flotation
to keep the boat afloat, there would be little room left in the cabin.


Bull****.


Maxprop wrote:
You are correct, but I'd be interested to see the volume of flotation
material needed to compensate for that displacement of water. *The volume
of flotation material required to offset a given volume of water is not
necessarily same.*

I'm not sure what you mean, here.


... Lear Siegler, the builder of O'Day boats, published a
lengthy report some years ago about why larger boats don't have positive
flotation. It was written from an engineering point of view and made sense
to me at the time, albeit I'm no engineer. Their point was essentially what
Jim C was claiming--loss of interior volume in a marketplace demanding more
and more interior space.

Whoa... "marketplace" and "Engineering" are usually two
viewpoints in conflict.

From an engineering standpoint, there is less than no
reason at all why *any* boat shouldn't have positive
flotation. Just fill it all up with foam.

From a more practical standpoint of a useful cruising boat,
then you (as I believe you were driving at above) all you
need is a flotation volume equal to the difference between
the boat's volume of material and the immersed volume needed
to float that weight. I've worked out such figures for a
couple of production boats and the answer is that the volume
of the seat & berth cushions is pretty close to enough. Of
course, you need a safety margin, and that volume needs to
be both *secure* and also distributed in such a way that the
boat floats in it's proper attitude (ie not bow pointed
down, or leaned over 45 degrees) & has some stability.



... They even explored the concept of flotation that
could be inflated in crisis, but cited cost and space requirements for even
this more compact system.

There have been two such systems on the market, both went
out of business. People won't pay enough for such a
system... from a viewpoint of market analysis, a failure.
From a viewpoint of somebody who wants as much safety as
practical, and cares less about costs, it's a total success.

People buy cheap stuff. Why do think Wal-Mart does so well?


... So I'm not quite sure Jim is wrong.

From a marketing standpoint, sure. MacGregor can only
afford to offer positive floation because it's partially
installed anyway by their building method... and their foam
is the cheap stuff.



... Can you
provide some documentation to the contrary, beyond just your opinion?


Umm, show me a boat that doesn't float to start with, and
I'll show you one that probably can't have positive flotation.





Positive flotation probably wouldn't be offered by manufacturers
voluntarily.

It already is, by several. Sadler & Etap spring to mind.



... It would most likely be the result of a government requirement
(there's that nanny state again, Doug), and it would have to be applied to
all boats, regardless of design.

Show me where I suggested that it be mandated that all boats
be required to have positive flotation.


So according to your last paragraph, such
a ruling might eliminate a whole class of boats. Small class racers like
the Mumm 30 come to mind.


Heck, the Mumm 30 would be real easy to put positive
flotation in. Not much of a premium on cabin space, anyway.

The bottom line is that positive flotation is *definitely*
possible... as I said, all you need is to fill the boat with
foam up to the static waterline, and put your cabin floor
over that. Or apply that same volume of foam to a carefully
distributed set of unused voids & crannies.

Is it desirable? Depends. If I were going to do a lot of
ocean crossing, making passages along rough & rocky coasts,
etc etc, I would want it. There are tremendous advantages in
a boat that just plain will not ever sink. It's possible
that I would make it a high enough priority to put in
myself. Do I expect anybody else to? Not really, especially
the people who rave about the advantages of Wal-Mart type boats.

DSK