JBUB, hydrofoils will definitely work on your seaswirl. I've used them on boats form 17-23 and have good results. Will reduce your time to plane and keep the bow from rising. Only drawback is your top end may suffer a couple of knots.
I have a friend that has one on his 17Grady and I had them on my twin engine 25Grady.. they work.I could even level my 25 Grady my just raising or lowering one.It also had trim tabs but the tails didn't seem to slow it dow like tabs.(Tabs are known as flaps on Aircraft wings to slow down like breaks for landing)
FNG You posted 9.9/15hp I was once on a Canadian Fishing Trip with a few friends.I brought my 15hp.They had rented 9.9s.We both ran wide open back to camp 9miles.same boat,same wt.2 people,14ft.alum.boats.I was maybe a mile ahead of him at the end of the trip.So I'd say the difference was 1mph.