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Author Topic:   Hydro-foil
polaris posted 06-16-2002 12:03 AM ET (US)   Profile for polaris   Send Email to polaris  
Any experience witht this product. It is similar in function to a Doel Fin or whale tail, but instead of bolting it through the cavitation plate, it has a bracket the slides on the plate. They are very specific to the type and size of engine.

Also, expensive $125 +

Any comments appreciated.

Tartansailor posted 06-16-2002 07:32 AM ET (US)     Profile for Tartansailor  Send Email to Tartansailor     
I have one on my 90 hp Yamaha, /Montauk
It effectively allows a slightly lower planeing speed, and definately dampens pitch and yaw in a chop.
jimh posted 06-16-2002 10:44 PM ET (US)     Profile for jimh  Send Email to jimh     
I would suggest this:

First, take the following measurements:

Boat Speed on DGPS or WAAS GPS -vs- Engine RPM
taking measurements in increments of 500 RPM

Take the measurements in calm water.
Take an average of measurements.
Tank measurements with the wind and against it.

If you can, measure fuel consumption using a Flow-Scan or similar fuel glow measurement device.

Bolt on the cavitation plate appendage.

Repeat all measurements, using exactly same conditions and boat weight and load.

Publish the results. I will be glad to help with that part.

Up to this point, we only have anecdotal citings of "improved" performance; nothing remotely scientific or containing any measured results. In addition, there are plenty of anecdotal reports of "tried one; no difference."

NoviceWhaler posted 06-17-2002 09:19 AM ET (US)     Profile for NoviceWhaler  Send Email to NoviceWhaler     
Regarding this item, does anybody have any experience with these long term? I have heard stories from people in my area that said that having one of these installed causes additional stress on the cavitation plate creating premature failure. One person claimed that his cavitation plate actually fractured off of the motor while running. Don't know if any of this is due to lack of maintenance and people are scapegoating the foil.

Please advise...


jimh posted 06-17-2002 10:02 AM ET (US)     Profile for jimh  Send Email to jimh     
Regarding the implied question "have heard stories from people in my area that said that having one of these installed causes additional stress on the cavitation plate":

I don't think you need a Nobel Laureate to figure this out. If you drill a hole in the cavitation plate you weaken it. If you attach something to the cavitation plate that is several inches long and then drag that through the water at high speed, you create forces which act on the cavitation plate.

As I mention above, inspite of a great deal of anectodal evidence ("rides better"), I have never seen one article published with any before and after performance data.

bsmotril posted 06-17-2002 03:49 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
I ran a "Stingray" fin on a Sea-Ray Laguna 21' centre console equipped with a 91' model Merc 175. I ran the boat that way for 8 years before replacing it with a Whaler Conquest. This is one of the one-piece fins that wraps around the front of the motor, with two mounting holes on each side of the exhast housing requred through the cavitation plate. I ran the boat in the Gulf of Mexico offshore through seas anywhere from 2-5'. My gaol was to obtain the slowest possible planing speed to keep the boat up on top, but not beat ourselves sensless. The fin made a tremendous difference in my case. Before the fin, any speed under 24mph and 3500 rpm would cause the boat to gradually slow down and come off of plane. Running through seas required constant throttle adjustment to hold the boat up on top of the water. After the fin, I could trim the motor in and maintain plane down to 18mph which made a big difference in the ride. I also did not have constantly adjust the throttle. The fin also eliminated tendency for the prop to suck air as it became overloaded while the boat was making the transition to up on plane, or coming down off of it. At cruise speed in smooth water, with the motor trimmed for highest speed (4000 rpms typically) the fin would be completely out of the water. I noticed no effect on top speed at all. The fin made the transition to plane a bit quicker, and almost totally eliminated bow rise. The boat would almost come up on plane level. This was on 22 degree vee hull with 2800 lbs dry weight. I was very happy with the fin, and had no problems with damage to the cavitation plate or motor.

Presently, my Whaler Conquest 23 has twins, and the added surface area of the two props (or maybe it's the superior hull design) have shown no tendency for bow climb, prop ventilation, or falling off plane. On the contrary, it will stay up on top all the way down to 2800 rpm. Ya gotta love those torquey optimax V-6s.

If I were going to install a fin again, I would do so with the following caveats:

Use a one piece design to minimize unequal stress on the cav plate

Use it on a light hull with a prop running near the surface at cruise

Use bedding compount on the screws to seal out corrosion.


bsmotril posted 06-17-2002 03:50 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Correction, the Stingray wraps around the BACK of the motor. It is likes a winged "U" with the open end facing forward.

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