I've got a 17.5' alum deep-V fishing boat with a 60hp tiller steer Merc.  Occasionally, it will begin to porpoise if there's a lot of wave action.  It came with a hydrofoil to get it on plane faster, but I was wondering if anyone has opinions on trim tabs, which were suggested by some boaters I know.  If I trim down the engine, it will go away, but I lose about 3-4 mph (not a critical issue).  I would think this probably affects fuel efficiency, though.

If you don't mind drilling holes in your transom, you can try trim tabs, but trim tabs and hydrofoils are just bandaids. The other potential solution to cure this condition is to move your motor down a hole or two and if that doesn't work, try a different prop - no additional holes that may leak. Has your boat always done this? What is the max hp of your boat? If you are underpowered this problem may never go away.

" If I trim down the engine, it will go away" but I lose about 3-4 mph (not a critical issue).

You answered your own question.

Moving some of the weight in the boat forward if possible might help.