Can my old boat handle the power

frog man 63

Aug 23, 2023
I have a 60 something Glassmaster boat and it has a Mercury thunderbolt 50 HP on it. I just bought a Mercury 85 HP from my nextdoor neighbor and everything matches I hope. So does anyone have any suggestions for me on anything that I may have missed. I am using the control box from the 85 HP motor also the steering cable is there anything I should know before I start I will appreciate all the advice thank you p.s yes I am still new at this


Petty Officer 2nd Class
Apr 7, 2008
The boat should have a capacity/rating plate on it, typically visible from the driver's seat. If that plate is missing you could be cited for not having it. It will tell you what the person/weight maximum is and maximum HP as well.


Jul 22, 2008
Being an older boat and fiberglass, the main skeleton of the boat was the transom and the stringers under the floor. Unless replaced within the recent past those are probably rotten and would not support the power of a bigger motor, and if really bad could compromise any motor. You really should check the condition of the structure inside the hull !! After 20 or so years a fiberglass boat needs a serious detailed structure inspection. Old glass boats rot from the very bottom upward, so you need to check near the bottom of the transom and under the floor. Wishing you the best, but dont want your well being sunk like a rock.


Supreme Mariner
Dec 20, 2005
Just a side note: On a rotted floor (deck), hull, I had a BIL set me up with a fishing guide on a trip to Florida where he lived. The boat was about 20' long, open skiff type hull, wood, flat bottom with a 90 Johnson. As we headed out to open water and waves started to occur, the bottom of the boat moved in and out with the waves and he never increased RPMs to get the boat on plane.....good thing. Guide was well up in years and the boat was probably too. The trip was uneventful thank goodness.