1990 Sea Nymph SunCruiser 24' - max engine size?

[bolt0017]

Newb here -

This boat is in very good shape and is not costing me a dime. I have more smiles per dollar spent on this boat than any other on the St. Croix River.

That said, I want to upgrade the motor from the 70HP Evinrude on it now. The manual says the max size motor for this boat is 115 hp, but I'm sure that's referring to two-strokes from the day which are typically a lot lighter. I would like to go to a 115 hp four stroke but they are in the 500 lb range. My motor is about 260 lb. What are the guidelines for motor size and weight for an older boat like this? BTW - the PO had oversize tubes put on it after the originals were damaged.

Ron B.

 

[ahicks]

I updated a 99 24' Sea Nymph to a 90 hp Honda (about 400 lbs) that turned out pretty well. I was doing a total redeck at the time, so it was down to the frame anyway. I installed 2 extra cross members to handle the extra weight (matched the size of the original c channel rails) and laminated up a new ply transom. Engine pod bolted to ALL cross members it crosses (original only had 4 bolts total). Then I moved the entire cage forward about 24" to help counterbalance the extra weight of the 4 stroke. Permanent folding swim ladder installed at the rear of the RH tube is pretty popular. Have had it like this for 4-5 years now, and it's worked out really well. Lightly loaded, speed is about 26mph at 5500rpm. Plenty of power for pulling the grand kids tubing for sure. No regrets....

I think you'll find that the Merc, and Yammi 75, 90 and 115 are about the same as my Honda - something pretty close to 400.

 

[Scott Danforth]

There are two ratings.

Horsepower and weight

The horsepower rating is how much power before the force from the prop tears the transom off

There is total weight rating, as how much total weight of motor, people and gear you can load in the boat

Do not exceed the horsepower rating

As you add motor weight, you need to deduct people and gear weight

 

[jlh3rd]

the weight of my 2021 Merc 115 hp, CT is 363lbs......
My pontoon is an '06, 24' , twin tube, 25" diameter tubes....the pontoon came with an '05 merc. 60 hp, 4 stroke......so I used 4 stroke weight in the max rating...
Max rating is 115hp.....
the motor also costs $11,000+.....

 

[legalfee]

I just repowered my 1995 Sylvan 24' from 90HP Force 2 stroke at 300 lbs to a 2023 Suzuki 115 at 400lbs. The boat is rated for a 150 and the 115 runs perfectly so far. The stern sits about the same in the water. I'm still breaking it in and haven't been above 3000 RPM though.