What I find odd about these discussions on fins is that no matter what I put in print, people respond to things I didn't say, or list issues I already mentioned as if I didn't know about them. Most of the time I've already mentioned a very likely problem, yet people will respond saying something like "I put one on my 19' I/O and it did stage things, it slowed it down and the handling was scary". Then they go on about how there is no way one could work in any application and that the devil must have designed and marketed them. The person will then try to use this as proof to show me I'm totally wrong and that a fin can "never" work. This will be in a post immediately following one where I said the chances of it working on an I/O are slim, and that there could possibly be negative results.
The shape of most of them are like fishing lures, they are designed to catch boat owners, the performance aspect is secondary, but this doesn't mean that in some situations they work well. There are much smaller metal ones marketed to the high performance market, these are probably designed a little better than some of the huge bulky monsters on the market.
As for adjusting or tuning for best performance, they typically say nothing about it on the package, if they said you needed to start tinkering fewer people would buy them.
I/O,s are the least likely place they will work, and its because you can't do any adjusting, although in this application some people still find them acceptable, on certain hulls the owners feel the benefits outweigh the negatives. That's for them to decide.
Raising and lowering the motor to fine tune it after mounting the fin is very important, it's where you are going to find the improvements, if any are to be had. Not doing this can cheat the owner out of some (probably all) of the possible benefits of using one.
They may or may not help in any given application, there are just too many variables to say it will help before doing all the work. In the end it may be of no value at all, or hinder performance.
I say right up front that for what 99% of boat owners want fixed or improved about how their boat rides or planes can be solved far better with tabs, it's what tabs do, and they do it well. A fin may help to improve some aspects, but the chances of it helping without some negatives results is very likely unless the fine tuning is done, and still it may not help at all.
A foil is sort of a poor mans hydraulic Jack plate, the jack plate works by allowing you to have the prop deeper in the water at low speed so that it can get a good bite with no ventilation. When running at high speed the motor can be raised so there is less drag from the gearcase, resulting in a higher top speed and possibly other handling benefits. A fin "may" allow you to mount the motor higher to gain some speed and possible handling improvements and still let you accelerate hard without the prop ventilating. Or, it may not help at all, but you don't know without doing the work.
I have 8 or 9 boats, only one has a foil, and only because after a great deal of testing it was the only way to get it dialed in without a hydraulic Jack plate, and I wasn't going to spend that much on a boat I rarely use. I have tabs on another boat because that's the tool it needs for best performance, it's the boat I use the most.
opcorn:
