N08 56.231
W079 33.480
Balboa, Panama
Yesterday we gave Swan Song our best stability test to date. We've done the
series of CG tests in the past for our own satisfaction and for the
parameters to design ART.
As you know we have a water tank on top of our pilothouse which works as our
roll stabilizer, ART. It contains 1500 lbs of water and at a near zero roll
rate, aka a minute or so, acts like any free surface tank. This means at a
constant heel the water stacks at the lower end. Without any dynamic force
of wave action it will just sit there. However it's very seldom that a body
of water is truly static. At least not the waters we have ever sailed in!
So we can badly trim Swan Song and have 1500 lbs sitting on the outboard
edge of the pilothouse about 13' above the water line. This will result in
3-5 degrees of heel depending on the fuel/water in our tanks.
In Colon Panama, I finally managed to get our Marquipt crane installed,
functioning and able to lift our tender. The crane and chocks have added
about 400 lbs to the boat deck which is 10' above the waterline. The tender
weighs in at 1350 so we are close to 1800 lbs of additional weight.
Yesterday was fuel day. Our 500 gal ea side tanks were empty and I
intentional emptied our 400 gal water tanks so we were as light as possible,
about 10,000 lbs under our full capacity.
We then picked the tender up off the deck and swung out off the port side
and let it hang. This moved about 1500lbs of crane and tender 11' off the
centerline or 4' beyond the beam 10' above the waterline. In addition the
1500 lbs of water in ART also was stacked in the tank end 13' above the
waterline.
The result of all this was that Swan Song heeled just under 10 degree static
and the rolls of the wakes would add another 10 degrees max to the heel as
we rolled without ART benefits. It works only with less than 5 degrees of
static heel.
These weights and lever arms are way more than we would expect in anything
less than a full storm where we might have tons of green water aboard
briefly. So avoiding hurricanes is still a good idea ;-) Having had the
hurricane experience once I know that it calls all bets and usually wins
especially with small boats like Swan Song.
Anyhow, that's the unscientific result of our tests with empty tanks. This
has raised my confidence in the stability of Swan Song and its ability to
shake off a green water dynamic load, a side wave impact, wind load or a
combination there of. Having this confidence gained thru actual tests sits
much better with me than some specifications of an NA based on his design
goals. Lay a boat over, walk around on/in it and see how it reacts is my
kind of specification ;-) If the stuff stays in the cabinets, the engine on
its beds and all the air intakes well above the low side waterline then we
have the workings of a sea boat.
After fueling with 1100 gals (~8000 lbs & $2.02/g) and 400 gals H2O (2,400
lbs) we are sitting much lower in the water. Darn I need to raise the
waterline again!
Next fuel stop will be Mazatlan or La Paz, about 2500 k/m up the road, in
3-4 months.
As always YMMV.....
Dave & Nancy
Swan Song
Roughwater 58
Hawaii Passage '08/09