18 foot tunnel and 25 suzuki

[keakar]

it should be ok but a little on the slow side, 18' is a lot of boat for a 25hp, they are better suited for 14-15ft boats.

my 15/48 was rated for 40hp so ....

I suspect that boat is rated for something like a 50hp at least so fully loaded it may have trouble planing but otherwise it should be ok provided you aren't in a hurry to get anywhere.

my guess is its going to top out at around 20mph or close to it so your expectations are about right.

maybe get it and sell the motor or see if you can buy it without the motor, sometimes selling just a motor isn't as easy as you might think so try and let the other guy worry about that.

see what the boat is rated for and put a 50hp at least on it, don't go over the rating or you might get ticketed by some diligent WLF agent but max out with the rating since most all boats are already under rated anyways.

one thing to note here is 25hp motors mount differently (2 bolt pattern in the center of the bracket) so you will need to patch or plug the holes from it and drill new ones for the bigger motor (4 bolt pattern near the corners of the bracket)

just my 2 cents