Why exactly? On a smallish tin boat 12'-14' 15-40 HP range what are the benifit you see? I've never run one so I have no idea what to expect.
Well, first off, I’ve never seen any 14’ typical skiff w/ cross seats rated for anything > 35hp and usually 30hp on tiller motors.
It is primarily due to excessive bow RISE as one gets the boat up on plane, but it also completely eliminates any proposing at higher RPMs. They also add stability to the hull and in tight turns. Some tin hulls get ‘squirrely’ at WOT and a foil helps keep the boat level, trim and carving the water in turns.
I’ve seen bows rise soooooo high that you can’t even see where you’re going for a few seconds. It can be worse when running against the wind and can be a very dangerous situation. I just helped an older man on my river add a foil onto his 14’ Duranautic with 30hp tiller Johnson this past Summer and he could not be more pleased!
Adding a foil can help in many ways besides keeping the bow down. The boat gets on the plane faster and can stay on plane at a much slower speed, which can help in a chop or in heavier seas or waves.
My old 12’ tin with 10hp OB would not plane easily with 3 aboard, unless one went up to the bow, but the foil allows the hull to plane faster and stay on plane with the 2 seated in the middle seat. Not fast mind you, but at least were were planing (more efficient running attitude). The fin adds ‘stern lift’ which helps the trim.
Overall I find them to make running a small fast skiff a much safer and more enjoyable experience.