Which Outboard would equal OMC performance

[bill chisholm]

I have a 24' Tolley, 1980 Sportsfisher, Great Hull, with OMC Stringer, 350
4 barrel Rochester, and I am looking at a repower. I definitley going to keep this boat, I luv it and am willing to spend some money on it. I am on my 2nd 350 and have NEVER had much trouble with the outdrive. But I am going to put a swim platform and an outboard,

The question starts with the fact that I don't officially know the Horespower rating for my motor and outdrive combo but i do know the following. It runs at 28 mph at 3100RPM's with 100 gals of fuel onboard along with 2 fat people with big lunches. I very rarely run it past 3200 rpms and this motor has lasted for over 10 years with no problems.

What outboard would give me similar performance. I ocean fish a lot and don't need much more speed than 30 mph. Of course I don't want to spend more than I have to. There is a $5000 difference between 200hp and 250 hp.

Any thoughts, or better yet any real life, actual conversion stats would be great .

 

[RotaryRacer]

Re: Which Outboard would equal OMC performance

I won't be the guy who says it can't be done...however, going from an I/O to an outboard is a pretty significant change that may or may not work as you expect it to.

You will be changing the center of gravity of the boat pretty significantly. If you are using an Armstrong bracket with an integrated swim platform or similar, the motor is even further back.

I think you will need to learn more about the weight of the boat and powertrain before you can make a guess about the amount of power you will need for the performance you are looking for.

Now, that all being said changing from a OMC Stringer drive to an outboard is a big deal. The structure of the boat is currently not seeing much force on the transom currently. The way the stringer attaches to the boat and the way the prop thrust/force is driving the boat is completely different than what is needed for an outboard. There is a likelyhood that the transom/stringer arrangement of your hull will need to be significantly changed in order to support the loads an outboard on a bracket will generate.

 

[CaptainHook]

Re: Which Outboard would equal OMC performance

What makes you want to make such a drastic change? If anythingI would consider changing to a more modern sterndrive.

Probably cheaper and less work to be done to the transom.

 

[4JawChuck]

Re: Which Outboard would equal OMC performance

Cheaper to buy another boat.

 

[Dhadley]

Re: Which Outboard would equal OMC performance

A fairly common conversion. You'll obviously use an Armstrong, Gil or B Bracket type bracket. Maybe a Porta hydraulic. Also add knees to the transom / stringer for strength. No big deal. It will certainly help improve bow lift by moving the center of gravity.

Been done thousands of times. You like the boat, you'll gain interior space, lose weight (boat-wise) and most likely get better performance with more efficiency.

We'll assume your motor was a 280 but even if it was a 300 or 310 a modern 225 outboard will probably yield the same speed, maybe a tad more. A decent 250 outboard would probably surprise you.