"Maxprop" wrote in message ink.net...
|
| "DSK" wrote in message
| . ..
| No reason why other boats couldn't have positive flotation.
|
|
| JimC wrote:
| Actually, there is. 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****.
|
| How much volume does the boat have immersed (ie below the waterline)? The
| is the exact amount, no more. "Heavy weighted keel" or any other sort.
|
| 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.* 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. 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. So I'm not quite sure Jim is wrong. Can you
| provide some documentation to the contrary, beyond just your opinion?
|
| Now, if you're talking about a flush-deck boat with 2' of freeboard, then
| maybe there wouldn't be much cabin room to spare... there wouldn't be much
| in the first place.
|
| Positive flotation probably wouldn't be offered by manufacturers
| voluntarily. 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. 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.


Have you ever heard of ETAP? Their boats have positive flotation. They have a nice 28-footer just
out that's so fine. It's not hard to put positive flotation in sailing yachts. You loose some interior volume,
of course, but much of the space used is not much good for anything else, anyway.

http://www.etapyachting.com/index.cfm?Part=Yachts

When you do the math, you don't need as much flotation as you would expect. To figure it you must come
up with specific gravities of the various boat components. Fiberglass, for example is lighter under water
than above water. All the wood in boats is positive flotation already. Things like lead or iron ballast have
to be compensated for pound for pound but most of the other things boats are built out of you can weigh
them in the air and cut the weight in half for the pounds of flotation you must add to compensate for them.

Paladin
(Have Blue Water Positive Flotation Yacht - Will Travel)



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