Overpowering an 11'4" Boston Whaler

[Sonie]

I have a 1974 Boston Whaler- 11'4" LOA, 5' Beam, weighing 250 pounds.
My understanding is that the max. HP is 20 for this boat. I have found a 35hp, 1984, 2-stroke Merc that I want to use.

Is this safe? Anyone have any reccommends?

Thanks, Andre.

[Corpus Skipper]

The max HP is there for a reason. Some folks ignore it and get away with it, but i'd be really careful. If you go with this set-up, first check the boat for level floatation. I don't believe there's that much weight difference between 20 and 35 HP, but check how the boat floats with the new engine. Run the boat slowly at first to check the handling, and increase speed in small increments while turning the boat side to side, as if running a slalom course. If she starts to slide out on you, the motor's too much.

Originally Posted by Corpus Skipper

The max HP is there for a reason. Some folks ignore it and get away with it, but i'd be really careful. If you go with this set-up, first check the boat for level floatation. I don't believe there's that much weight difference between 20 and 35 HP, but check how the boat floats with the new engine. Run the boat slowly at first to check the handling, and increase speed in small increments while turning the boat side to side, as if running a slalom course. If she starts to slide out on you, the motor's too much.

Thanks for the advise... I have gone with a 25hp merc... Problem is it is a longshaft, and is in the water half a foot or so too deep. I am thinking of using an aluminium plate to mount the motor higher and therefore have less of the lower unit in the water. I havn't tested the boat out yet and wonder if I will even need to raise the engine. What kind of performance drawbacks would come from using a longshaft on a short transom?

Also... I am hooking up controls to the 25 merc(late 80's). Problem is when I throttle up, the cable "pulls" When it should "push" the throttle on the engine. The control box is from an older merc o/b.
It never ends....

Thanks, Andre,.

Regards, Andre

[SailDesign]

You may want to check with whoever insures the boat, too. If the motor is above "max power", then you may no longer be insured...

Steve "the practical one"

[dereksireci]

I was agreeing with you folks until I saw the alternative. I'd much rather have 10hp too much than a shaft that is too long. Granted, per ABYC H-26 the max power for this vessel is 25hp. However, I had a friend who tried to do the aluminum transom modification you describe on his skiff. At one point he took a wake and the motor dislodged and flew right into the boat. He and his wife were finally able to pitch the screaming motor into the drink.

Get yourself a copy of ABYC H-26 and follow the instructions for determining maneuvering speed with the 35hp engine of the correct shaft length. This is what Corpus Skipper is describing. When operating the boat, stay below the safe speed.

Anybody who disagrees with this, just take a look at the huge powerplants installed on the transoms of some bass boats. You'll notice that they post a warning at the helm about safe speed.

djs

[pungolee]

Dont put that longshaft motor on there.Serious.You try to rig up that mess and The Whaler will still float but they may not find you for days.A fifteen will push you just fine,a four stroke fifteen would be even better.