I/O Conversion

[sogood]

Just a (mostly) hypothetical question, but if someone was considering an inboard to outboard conversion, what's the differences, advantages/disadvantages to installing a pod or extension, as opposed to hanging an outboard off the transom.
This is assuming that the transom has already been newly rebuilt, so there wouldn't be any concerns or issues in that regard. I assume cutting the transom down somewhat to create a well would be a given.
Just for clarity, if, such a conversion was to take place it would be on a 1990 Wellcraft 250 Sportsman. I've seen many of this particular model online running on outboards, but they all seem to have pods fitted.
Thanks in advance.

 

[Offshore57]

Couple of reasonable size outboards on a gill bracket would work....inboard space can be used for fuel tank or extra storage.....balance fore and aft is the thing to get right....

 

[sogood]

Thanks for the response. Is a gill bracket a type of pod and if so, back to my original question. What's the benefit of using one, apart maybe from less work to do in altering the transom. If I did do such a conversion I'd continue to use the existing 75 gallon fuel tank. Lots of extra space once the engine comes out.

 

[Bajansailor]

For reference here is a 250 Sportsman for sale with a single I/O engine.
https://www.yachtworld.com/boats/1987/wellcraft-sportsman-250-3532834/

I think that one advantage of using a pod is that the engine can be raised slightly higher compared to if it was mounted on the transom directly.
If it is mounted on the transom the anti-cavitation plate has to be level with the bottom of the keel.
And on a boat with a fair amount of deadrise that can mean that the engine has to be immersed deeper than is desirable if it is not a long (or extra long) shaft.
It is easier with twin O/B engines - they can be mounted higher, as the keel is higher where they are because of the deadrise.
And one can generally say that the higher the outboard engine(s) is / are out of the water, the better.

 

[QBhoy]

Other than in the type of boat you happen to mention, I think they look pretty odd. But some like the boat you said take it in their stride.
The trim of the boat would be really changed dramatically, especially with modern 4 strokes.
There is no doubt you’d gain some space, but the cautious bit in me might think the boat and it’s ability might be seriously compromised if it wasn’t done right.
I’d also maybe think that with the cost of doing it and adding a couple of big twin modern 4 strokes at about 15-30k EACH !...I’d maybe much rather Replace the current inboard with a superb modern MPi engine. Serious power, keeps the boat as it was designed and so good on fuel. Also half the price perhaps.
All depends on what you’re after and what you have now.
Just my rambling thoughts. Would love to hear what you decide and follow the progress either way !

 

[sogood]

Thanks for the input. I imagined that to get an outboard at the preferred height, the top of the transom would have to be cut down to suit. Then there's the cost issue as it would need quite a big hp engine to come near the power of the current 5.7 Mercruiser. I'm just finishing off my transom, stringers and engine mounts replacement and got to thinking. It's not on my immediate "to do" list, but I was mostly wondering about the pod versus no pod approach. Thanks again.

 

[QBhoy]

Thanks for the input. I imagined that to get an outboard at the preferred height, the top of the transom would have to be cut down to suit. Then there's the cost issue as it would need quite a big hp engine to come near the power of the current 5.7 Mercruiser. I'm just finishing off my transom, stringers and engine mounts replacement and got to thinking. It's not on my immediate "to do" list, but I was mostly wondering about the pod versus no pod approach. Thanks again.

Would you not be tempted to drop a 350 mpi into her. Would drop straight in...big power increase over the old 5.7 carb. Amazing fuel efficiency too. Or even a 5.0 mpi would do. Same power as any 5.7 carb or more...and ridiculous fuel economy Would be much cheaper than converting and buying outboards that are capable of producing equal performance to what you have now.
A 5.0 mpi would be about 11k or so in a crate. Fitted with a new alpha one would be about 15k. Similar for 350 mpi (5.7). 260hp and 300hp respectively. No way you’d get 300hp outboard for less than about 20/25k. Then you need to spend to adapt the hull to suit.

 

[sogood]

Thanks for the information but there's no way I'd spend 15k on a 1990 boat, even if I have practically rebuilt it. The next time I spend money on a boat it will be for the purchase of my next one.

 

[QBhoy]

Thanks for the input. I imagined that to get an outboard at the preferred height, the top of the transom would have to be cut down to suit. Then there's the cost issue as it would need quite a big hp engine to come near the power of the current 5.7 Mercruiser. I'm just finishing off my transom, stringers and engine mounts replacement and got to thinking. It's not on my immediate "to do" list, but I was mostly wondering about the pod versus no pod approach. Thanks again.

Thanks for the information but there's no way I'd spend 15k on a 1990 boat, even if I have practically rebuilt it. The next time I spend money on a boat it will be for the purchase of my next one.

Totally agree. Think you’ve now answered your own hypothetical question. The outboard idea would be even more expensive and an unknown in terms of how it would end up.

 

[Assassin]

It comes down to several basic issues:

What size and weight of outboard are you looking at fitting.

How would any pod mount to the transom.

How would this connect to the structural stringers of the boat.

If the transom is bearing the full thrust it will flex and crack any GRP work unless it is of sufficient strength to counter the motor thrust, and be capable of transfering that load throuhout the rest of the hull so simply strengthening the transom is not enough, therefore you have to connect it to the longitudal stringers in such a way that the transom load is distributed throughout the hull to spread the load, and this brings the next issue, are the existing stringers strong enough to take the load? Put to big an outboard on and you will have to do a lot of work to get this correct and this could eat into the freed up space you are hoping to achieve, put too small an outboard on and as previously stated, you could get the deadrise totaly incorrect and submarine by virtue of it being to light.

Without wishing to be offensive, seeing others do things doesn't make it correct and the internet is littered with fanciful ideas and huge numbers of incorrectly engineered products modified by the uninitiated and this can cause huge future problems and possibly put you and others in peril.