Re: 96 merc 75 3cyl two stroke
I'm not a huge fan of foils - have tried them out on my own motors (mostly so I could speak from experience).
I kinda see them as "the poor man's trim tab", but there definately is a couple applications where I think they are of benefit.
A hydrofoil (fin, whatever you want to call it) does help the bow down quickly once forward motion starts. It will help the average boat get on plane a little faster and keep it there at a lower speed.
That can be a benefit if you do alot of running in "no wake zones" or restricted speed limit canals. Keeping the bow down at slow speeds definately improves your forward visibility.
They definately make the boat track in a straight line but the flip side of that is, it makes the motor alot harder to turn. So depending on your set-up, if you already have to reef on the wheel in a turn the effort required will almost triple.
Contrary to the claims of more speed and fuel economy, while not scientific by any means, my gps and floscan gauge have never supported that - I saw no noticable difference between running with or without a fin.
The fin does put severe stress on the cavitation plate of the outboard (which is where it's mounted). While Merc's official position is they neither support the use nor specifically advise against it, I'm of the opinion that if increasing the total area of the cav plate was a great idea, they would have already incorporated it into their design.
A few years back there was a number of Suzuki models that ended up with cracked gearcases because they couldn't handle the stress the fin placed on them. So even if you don't end up with a problem it is still probably affecting the integrity of the metal.
In your case it would be a lower cost alternative than trim tabs (which come in all kinds of configurations with the low end/least technical "smart tabs" selling in the 100-150 dollar range).
Again, personally, I would spend the extra bucks for trim tabs, and smart tabs (or similar) are more than adequate. In addition to keeping the nose down, they will also stablize side-to-side since each works independantly.
But, a fin would be better than nothing in your particular situation..
