Mac wrote:
On Thu, 27 Oct 2005 16:22:26 -0700, Robert or Karen Swarts wrote:


Let us suppose the mast is 4" in diameter and 25 ft long, stepped 4 ft above
waterline. The weight of water it displaces is 138 lb. Let us suppose half
if that is the weight of the mast. That leaves 69 lb positive buoyancy. The
center of buoyancy of the mast is about 16 ft above waterline. That will
create a righting moment of about 1100 ft lb when the boat is flat on the
water. That is not inconsequential, and could be a large help in preventing
a total capsize.

BS


[snip]

This all seems very doubtful. I am not sure if you understand how dynamic
the sea-state is in conditions likely to cause a knockdown in the first
place.

Maybe you should ask a real naval architect (marine engineer) about
this. I think it is a very bad idea which you will regret if you do it,
but I am not an expert.

--Mac


It seems, if you are worried, that if the mast is reasonably tight,
it would not flood immediately after being whipped into the water.
It's speed of descent would provide a great deal of drag through
water to decellerate the rolling momentum, and would provide some
righting bouyancy until it filled.

Sealing a mast may be impossible, but slowing its flooding, possibly
with external halyards and a wad of foam or some pop bottles and
even pumping it once horizontal with a small hose to the mast head,
might be a better plan, strange as it sounds.

Once on it's side, a keel boat will want to right itself, until it
fills with water. Keep the properly designed companionway bottom
board in place. On a trampoline / catamaran, you will want righting
accessories like possibly a self inflating "Mae West" at the
masthead. 200 lbs bouyancy might to, and that is about 1.5 cubic
feet of balloon, 10 pounds of tennis balls?

Many catamarans have servicable rope loops rigged, to enable
overboard capsized crew to pull the boat upright once it has landed
on it's side. They take a moment or three to turtle after resting on
their sides, with the mast flooding and because of their geometry,
wanting to continue rolling inverted. The floating mast is their
only hope, however faint.

The dynamics of weather tending to capsize the boat will be greatly
diminished, once you come to a stop and the sails are horizontal on
the water. The sail itself would prevent rapid sinking of the mast,
if it did not simply tear, sheeted in. The mast may well break open.

Dare I suggest floating line shrouds as an adjunct, or even a
floating, sealed at the ends hollow wooden mast?

Once turtled, a long enough halyard or spare detached from the sail
head and "lowered" from it's submerged cleat now only a foot or so
submerged, brought to the surface athwartships, can haul the boat
back upright, if enough bouyancy and counterweight can be found
amongst swimming crew with lifejackets, coolers, floating cushions,
gas tanks, rescue assist vessels, and whatever.

Flooding one completely upside down cat hull to make it sink so the
boat is suspended by one floating hull also helps. Once it is a
little more downwind than the floating hull, raising it is easier,
since all you need do is counterbalance the submerged, reduced
weight and especially, the mast, once horizontal at the waters
surface, and which, we hope, is still trying to float, at least a
little. Pumping the submerged hull will right the boat. Crossed hull
pumping lines and a pump tied on to avoid it's loss, able to inflate
the hull with air or extract water complete the scheme. Such serious
righting arrangements are able and can be seen on serious cats if
you ask their skippers.

Flooding the hull may seem difficult, but an "air syphon" hose will
do it easily and dependably, if a hatch can be opened aside from
this air vent / pumping hose.

One would hope the design permits a loaded cruising cat to still
float, even with one hull full of water, purposely flooded. Small
cats are a natural, larger ones will want bouyancy compartments
sufficient to minimally float the boat even when capsized and
flooding if the companionway hatches are not watertight. Just one
more reason to keep those through hulls closed, eh?

Terry K