[PUP] FW: Swan Song in Venezuela

[Carl H. Martin]

Very interesting post.  I've never heard of the stability tank.  How would I 
get ahold of the software to design one or have one designed for me?  Also, 
this would be an interesting post on the T&T website.

Carl Martin
Scout 30
Hudson Beach, FL
----- Original Message ----- 
From: "Dave Cooper" <swansong@gmn-usa.com>
To: "'Passagemaking Under Power List'" 
<passagemaking-under-power@lists.samurai.com>
Sent: Tuesday, August 29, 2006 9:13 PM
Subject: [PUP] FW: Swan Song in Venezuela


> Greetings all, just a quick note to let you know we arrived safely in PLC,
> Venezuela on Thursday AM logging 616.5 nm which included about 30 during 
> our
> sea trials. We made one stop in St Martin for supplies.
>
> Fuel used was 433 gals and the genset was running 90% of the time (200 
> hrs)
> for our air conditioning. Also the main engine alternator was not hooked 
> up
> yet so the genset was our sole source of AC and DC.
>
> We had two issues on the trip:
> 1. Lost the dinghy when the tow line parted. Found it and replaced the tow
> line with a new one and had no further problems in the 600 miles.
> 2. A fitting on the steering ram bypass valve failed and dumped all the
> hydraulic fluid. A bit tricky putting in a hose to bypass the bypass and
> then filling and bleeding the system while beam-to in 8-10' seas but 
> doable
> thanks to the roll tank which stabilizes Swan Song.
>
> I guess we can take the cover off the top of our pilothouse now and let
> everyone see why Swan Song doesn't roll.
> We have a tank engineered with baffles that keep 200 gals of water 180
> degrees out of sync with the roll period of the boat. The net result is 
> that
> Swan Song doesn't roll enough to notice whether moving, at the dock or at
> anchor. When other boats a rolling and bobbing about she just sits there.
> Amazing!
> It does nothing for pitch so we still go up and down but very, very little
> roll.
> The tank is 12 ft long, 4' wide and 16" high and is firmly attached to the
> boat. Roughly 1500 lbs of water sloshing back and forth out of sync with 
> the
> boat.
>
> We have a solid state gyro with a DAC which feeds our laptop. Prior to
> filling the tank you could get Swan Song rolling at the dock 10-15 degrees
> by synchronously stepping on the side. You can do this with most boats. 
> Some
> will roll more some will roll less but all will roll..even a catamaran.
> After filling the tank you can't even get the rolling to start!
>
> Timing 10 of these rolls will give you the roll period of you boat. In 
> Swan
> Song's case it was 4.1 seconds per roll. This goes into the formula that
> helps define the tank.
>
> The second item is the stiffness of the vessel. For this you need to do an
> inclination test. Putting weights on one side then the other and 
> accurately
> measuring the heel angle in calm water. In Swan Song's case we got 500 lbs
> per degree to about 5 degrees and then it goes to 600 lb/degree and is 
> 1000
> lb/degree at 10 degrees static heel.
>
> So 1500 lbs of water on the top of the pilothouse stacked at one end 
> (which
> is impossible as the tank is only 16" high) would result in a worst case
> added heel angle of 3 degree. The conclusion is that the boat has plenty 
> of
> reserve stability for the roll tank.
>
> The last part of the input is the hull lines. In our case there were none 
> so
> we measured the hull at 15 stations in one foot depth increments. From 
> this
> a wire frame computer model was generated and input into the software.
>
> The output is a set of parameters that allow one to design a tank with 
> fixed
> baffles that will delay the free surface effect of the water such that it
> becomes an advantage to you vs. a detriment. No power, no pumps, no 
> valves,
> no maintenance, no drag, no deployment/retrieval effort, no nothing. It 
> just
> sits up there and works 100% of the time.
>
> We expect over time that we will find that adjusting the amount of water 
> in
> the tank in various wave heights will improve it even more. The trip down
> was 350 miles of beam sea ranging from 5 to 12' and except for the
> occasional "drop thru a wave" we were very comfortable. With an eye height
> of 12' in our seat looking out the Port side window and up at the wave 
> tops
> on occasion did get that knee jerk reaction but it never was required.
>
> Our new Fly By Wire system performed flawlessly. We have zero mechanical
> controls...no steering nor engine controls. Interesting it was the 
> steering
> ram bypass valve that failed. If we' had a conventional system and lost 
> all
> the hydraulic fluid I doubt we could have repaired it at sea in 2 hours if
> at all.
>
> A great trip down, the Marina folks are great and the officials are very
> polite. There is a very visible show of various law enforcement people. 
> Sort
> of like the local police, the state police, the harbor patrol, the coast
> guard and the Navy all keeping an eye on a parade in Boston Harbor.
>
> Is there crime here? Is there crime in New York? You better believe it. 
> Same
> thing.
>
> More reports, etc. as we get settled in. My work list is ten pages long 
> and
> the "honey do" list is even longer. Sure hope the hurricane season ends
> quickly so I can get out of the marina ;-)
>
> Dave & Nancy
> Swan Song
> 1974 Roughwater 58
> Caribbean Tour 2006
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