T&T: Active Fin Stabilizers

[Terrence Neill]

snip
>  < Does anyone have any before and after data on what speed and fuel
> consumption they got a given RPM prior to installing Active Fins VS  
> after
> installation what speed and fuel consumption they got at the same  
> RPM? There
> is a price to pay in economy as you are creating drag, >
> <For those slower trawler folks that have them........Are they still
> effective when you are only making 6 knots speed through the water?>

Not directly on topic, but related. We installed batwing stabilizers  
on Tamarack in '04. She's a 52 foot converted seiner with a true  
displacement hull form. Before installation she would roll on wet  
grass with a four second period.
The batwings are fixed roll stabilizing plates attached to the keel  
somewhat aft of midship...extending to within inches of the total  
width of the boat and comprising a total of some sixty (60) square  
feet of surface. I have forgotten the weight, but it is 5/8 steel plate.
The roll reduction underway is noticeable at idle (about 3-4 kts),  
increasing to approx 70 percent at cruise (8-9 kts). There is no  
effect when stopped.
The drag penalty seems to be directly related to speed (as expected)  
and reaches a maximum of somewhat more than 1/2 kt. The maximum speed  
obtainable at wot has been reduced to close to hull speed. I think  
that the drag at the higher speeds is somewhat counteracted by  
increased squatting, which on this boat with a long sloping counter  
increases the wetted length by several feet.
The increase in comfort from this (totally passive) system more than  
offsets the loss of speed.

An aside re: roll tanks - we considered them but gave up when we were  
unable to locate any statistical info on the boat...no lines or any  
of the stability data are known to exist, and producing them seemed  
to be just one obstacle too many. These kinds of data are essential  
to the design of effective roll tanks.

Terry
Tamarack