Another one of these threads.
There are so many misconceptions floating around about fins, foils, or whatever you want to call them that I don't know how a newbie could make a good decision about one.
First off, is what they are designed to do, the real purpose is to stop the prop from sucking air from the surface during hard acceleration, that's it, other uses are sort off label, just like how many medications are used, they may work for other things in some way, but it may not be the best way to get the job done. People always say if they were of any value outboards would come stock with them, well, they do, The AV plate is designed to do the exact same thing, you are just making it bigger by using a fin. It's no different than extending the hull with trimm tabs.
They can work well if needed on an outboard because by using a fin (I don't like the name "foil" because that part of the shape has little to do with how it works, it's really just marketing) you may be able to raise the motor higher and not have it ventilate. The benefits of this are reduced drag from the lower unit which may improve top speed and MPG. It can also reduce bow rise because when the motor is mounted higher it has less leverage on the transom.
These are only possible benefits, they only come into play if the boat and motor combination needs this type of help, on some boats they are of no value.
At no time did I say the benefit comes from having the fin drag in the water at speed, it should be totally out of the water when on plane, having it dragging in the water at speed is where all the negative comments come from. A person typically just bolts one on and heads to the water thinking every problem he ever had will be solved, only to find that it handles poorly and top speed has been reduced. This person has now decided that this tool is useless, and beyond that possibly a safety hazard.
There is work involved in finding out if a fin will help at all on any boat, you will need to raise and lower the motor, plus possibly change props to get the best possible results, and even then it may not help, it's only a possibility that it may.
This testing can easily be done with an OB, but with an IO there are no adjustments that can be made, so what happens when you bolt it on is what you get, it will most likely be dragging in the water at speed and possibly create all kinds of issues. Some may find that the negatives aren't that bad, or not that noticeable, and that the benefits are good enough that they really like it, the next guy may use his boat differently and hate it though.
Another thing to look at is how many different shapes and designs are available, one may work great, but another design may be terrible, and this will depend on the exact boat, motor, prop, plus how the owner uses the boat.
So it comes down to whether the boat owner finds the fin to be of any value in how he plans to use the boat, not whether someone that doesn't understand the tool deciding that they are evil and should never be used in any circumstance.
I almost forgot to say that for the problems most boat owners want to solve trim tabs are more likely to be the right tool, plus there is almost no down side to tabs.
opcorn:
