<Brian wrote: But in a sea condition although the drag is there and it's taking fuel to power them keeping a boat trimmed helps a lot to keep it on course which saves fuel. So I would think if there is a fuel cost it's probably not much lots of variables to.> There are two direct "costs" with operating active fins. One is the drag that they add to the boat both when locked and operating. Less of course when locked and more when operating and more even when they are operating full on. Two is the cost of the fuel to operate the pump that is driving them. Little when they are locked but quite a few HP when the pump is working full on in a bad seaway. Trying to quantify the drag is quite difficult without tank tests. I am not aware of published results for any in various sea states/speeds. Barring this we can only try to guesstimate what it might be for various sea states and speed. As you are probably aware sailboat racers will go to extremes to fair their hulls to reduce drag. Adding two fins on either side in the water flow must create a relatively large amount of drag. Turning them from side to side to create lift increases that drag exponentially. A boat that is instrumented with accurate speed & fuel burn equipment should be able to see what the total effect of active fins "costs" in the way of fuel burn and/or speed for any given sea state. These would be interesting numbers to have if anyone has made such a table. Other wise we are all stuck with "1/2 to 1 kt" or "maybe 1 GPH" or some other non definitive number. I personally think the cost in fuel burn/speed penalty is a lot more than the "estimates" we see from the manufactures when you really need them in a contrary sea state. The systems that were spec'd for Swan Song all had hydraulic pumps in the 15 to 20 HP range with double belts. The manufactures were skeptical, as I have stated before, of the usefulness of these systems at 4-5 kts in rough seas unless the fins were very big. As you know we didn't opt for active fins. This much HP requires ~1 GPH and maybe more to deliver it by the time all the losses are figured in. On a long cruise this 24 GPD adds up if you are looking for range. OTH, for a coastal cruiser this usually isn't an issue. But on an ocean voyage it certainly would be as it affects range and the duration of your passage. Given a choice I'll take air conditioning and our no drag, no power stabilization tank vs. active fins and being hot and sweaty with no AC :-) YMMV Dave & Nancy Swan Song

On 10/11/06 8:26 AM, "Dave Cooper" <swansong@gmn-usa.com> wrote: > There are two direct "costs" with operating active fins. > One is the drag that they add to the boat both when locked and operating. > Less of course when locked and more when operating and more even when they > are operating full on. > Two is the cost of the fuel to operate the pump that is driving them. Little > when they are locked but quite a few HP when the pump is working full on in > a bad seaway. FWIW, in my experience with a 30 YO Naiad system, the pump is either on or off. It does not seem to work harder if operating the fins or holding them centered. But pressuring the system puts quite a drag on the engine, so I never operate them unless I need them, leaving them to flop back and forth in place. I am told that this could wear the shaft seals prematurely vs leaving the fins centered. I could manually center them by inserting the pin provided at the hull, but that is a pain. In 2700 hrs I have seen no leaking or any operational problems...except adjusting for the chatter which develops from time to time. Regarding the drag from the fins themselves 24/7, I am blissfully unaware of this cost...and I want to keep it that way! Bob ________________ Robert Calhoun Smith Jr M/V MARY KATHRYN Hatteras 58 LRC South River Annapolis, MD