Max engine sizes

[rdevoy76]

Hey all,

I just finished restoring a 1996 Sylvan. My question is regarding max engine sizes. I understand that the transom has a lot to do with it but is it also the cross members, log size, etc? I'm asking because the original max size engine for my pontoon is a 115. I wanted to put a 150 on there. I replaced the old transom while adding a number of more cross members. What do you guys think?

Rob

[teecro]

Your the one that built it do you think it is built strong enough to handle a 150 motor?

We once had an old 16' tri-hull bow-rider that ran just fine with a 55 Evinrude triple.... When the triple went to see Jesus Daddy went and hung a brand new 140V4 Johnson on it... His comment was the 140 was no heavier than a 115 and he intended to buy a bigger boat soon... You could all but sink that boat and it would still plane any amount of weight you could put in the boat; we were building a camp back then so it hauled everything from refrigerators to tires...

Name plate data is just a suggestion and no one can stop you from hanging any size motor you see fit... Just use common sence....

[RcgTexas]

I'll only post this in case you don't know.

There is a point of less return for your money. If you aren't going to a tri hull with strakes you may not see any or much increase in speed from a 115 to a 150.
Extra cross members is a good thing. Especially for the length of the motor mount.

[BoatCop]

There's more involved than just motor pod, transom and cross members. Center of gravity, overall boat weight, stability, etc. all come into play.

Boat manufacturers test their boats (either physically or virtually, via computer programming) to determine their capacity vis a vis person numbers, overall weight capacity and max engine horsepower.

While the USCG only requires capacity information on, and safe loading requirements only apply to, mono-hull, outboard boats under 20' in length, most manufacturers test and rate their boats' capacity for liability reasons.

The only one that could give you the ramifications of putting on a larger HP engine, and if your modifications would support it, is a marine structural engineer.

I do know that if there's an accident involving your boat and someone is injured, your purposely exceeding the manufacturer's capacity and HP recommendation will be a major issue in a civil action, and also cause for your insurance to deny coverage.

This is an area that you must tread lightly and decide whether the result is worth the risk.

[bassn386]

What Alan said!

[HandymanHerb]

Yep when you get into court there is all kinds of regs they can use against you, As an electrician, I knew there was a requirement for torquing the screws on an outlet, they don't make the tool to do it, you can't buy one and I heard of it used in court cases and winning, during refresher training I took every few years