converting I/O to Outboard

Due to an injury to my left hand I am having to transition to a small powerboat in the 24' to 26' range. I no longer have the grip strength to pull on the sheets and other lines on my Gulfstar 37.

I am not interested in going fast. Cruising at 6 to 7 knots with a top speed of 8 to 10 knots works for me. Seems like all of the boats I am considering have I/O's. This boat will live in saltwater. No way to get an I/O drive out of the water. So I will convert to an outboard.

One way to do the conversion is to attach a pod to the transom for the outboard to mount on. I don't really like that for a variety of reasons. So my other thought was to cut the transom so that the outboard mounts on the transom. I will be filling in the hole in the transom from the I/O drive no matter what mounting system I go with.

What problems will I have to consider in mounting an outboard on the transom?

 

At your target speed for cruising (6 knots) there should be no problem. However, 8 to 10 is right on the hump before planing and that uses a lot of power and fuel with little advantage. I/O live happily in salt water as long as the anodes are changed regularly. If the boat has one, my advice is to run it for as long as it runs. If it ain't broke, don't fix it.

 

Every time I surveyed a boat with a Mercruiser for a client who intended to moor it I told them it would break their heart, for the ones who went through with it anyway, that was often the case, whatever the series of MC.\

One main bellows pinhole in a Mercruiser can put your boat on the bottom, and there are numerous points that fail regularly and allow water ingress.

Volvos handle mooring much better, but both need storing with the sterndrive down to allow the bellows to relax. I guess it becomes "which option is the lesser evil?"

Good luck whatever you chose to do.

 

There are so many threads about that process on the forum that's there's already a wealth of information.

But what kind of powerboat? What hull form? The power demand for low speed is so moderate that you're looking at a small outboard.

 

I have read lots of threads about the conversion from I/O to outboard. They all involve attaching a pod/bracket/ whatever to the transom and attaching the outboard to that. I am asking about cutting a hole in the transom and mounting the outboard to that. The old catalina 27's with outboards had the outboard mounted on a cutout in the transom. I am asking about doing the same thing on an old I/O power cruiser.



Bayliner made some semi-displacement boats for example that have been converted to outboards mounted on a bracket attached to the transom. 2670 and 2270 models for example. And I like the styling of some of the older boats.

 

I can't see any good reason why it won't work Chuck. You might need to adjust or add weight for trim.

 

Have you thought about electric propulsion.
Last summer I saw a sailboat with a wake behind it like a speed boat, it was a MacGregor 26x with a 50 or 60 hp. I have though about slalom skiing and sailing at the same time in the past but never thought is possible till now.

 

Cold day in hell that I will ever go to electrical power for a variety of reasons. If you want to discuss electrical power please do it in a different thread.

I have thought about the MacGregor 26's. A good friend of mine had two of them. It would work for me. They are starting to drop in price.

 

You'd need to reinforce the transom appropriately, but that's just carpentry. Build a splashwell, same comment. There are boats that come in an OB version and an I/O version. Absolutely reasonable, I think, but cut down to a proper cut out and splashwell.

 

Most production boats 24-26’ long are made with a one piece cap. That presents a problem removing a chunk because the strength is derived in part by the top going from port to starboard.

This means the transom itself is probably not strong enough when you cut off the cap. And then, lotsa work to fix the cutdown and add splashwell.

Of course, this is conjecture because we have no knowledge about specifics of the boat.

If you are talking all general terms; you would want to install an outboard on the existing transom on a bracket. This way there are a couple of big gains. The transom height is maintained and no splashwell required. The existing transom would be strong enough for a small outboard in most cases if integrity of the hull is not lost. The engine sounds are muffled better and the full height transom is safer in broaching seas (may not matter, sound does).

The costs are way less as well. The time and money to modify the hull in the fashion proposed is many weeks or months depending on builder skills, and the costs would be about a grand for plywood or coosa and epoxy and supplies. The cost for a jackplate or bracket for OB is less than $300 for a small ob.

Your idea is not without merit, but cutting the transom is not ideal.

 

You only need a pod for a large outboard. You can use a simple jackplate for a smaller ob. You don’t see this method because all the conversions are done for 250hp ob.

Vance JPL4500 6'' Setback Adjustable Outboard Boat Jack Plate https://www.vancemfg.com/vance-jpl4500-6-setback-adjustable-outboard-boat-jack-plate/

 

@fallguy at the speed he is aiming for the transom should require minimal reinforcement due to a relatively small outboard, and absence of the shock loading which occurs in high speed boats offshore.

If it has had a sterndrive the transom will be heavily built. I would add a couple of knees attached to the transom and engine beds/stringers; and the loss of deck molding at the stern could be compensated for by using suitable framing for the motor well.

It will cause loss of deck space at the stern, but will be kinder to the outboard, and I feel that aspect is significant.

 

Also the jack plate looks like it will impede tilting and steering on a full height transom, but I have never used one so am unsure if that is correct.

 

This is what I did for my sailboat to trawler conversion. It's a San Juan 23 ft.

 

A fair point. Without specifics, things are hard to pin. The full height transom might allow one of the longer legs, but a splashwell is probably going to be needed to tilt out..