I/O to OB Conversion

[IwanaBrich]

I own an old Grady (1979) 21' with an old tired OMC Stringer I/O. The rest of the boat looks great, hull and floor are solid. I'm considering converting to OB using a OB bracket along with some stringer and transom reinforcements. I can do all the work myself, so labor is free and my buddy has a nice 175HP he'll let go cheap. I spoke to Grady who says it can be done, but offered no advice. I also spoke to the bracket manufacture, who claims that it works great, but I wouldn't expect them to say otherwise. Has any one done this? How did it turn out? How did the boat handle afterword? If so, can you post some pics?

Thanks!

 

[seasick]

I own an old Grady (1979) 21' with an old tired OMC Stringer I/O. The rest of the boat looks great, hull and floor are solid. I'm considering converting to OB using a OB bracket along with some stringer and transom reinforcements. I can do all the work myself, so labor is free and my buddy has a nice 175HP he'll let go cheap. I spoke to Grady who says it can be done, but offered no advice. I also spoke to the bracket manufacture, who claims that it works great, but I wouldn't expect them to say otherwise. Has any one done this? How did it turn out? How did the boat handle afterword? If so, can you post some pics?

Thanks!

My concern would be trim. You would be removing a lot of weight from the aft middle and hanging it off of the aft.

 

[IwanaBrich]

That is one of my concerns. I figure the I/O weighs about 800 lbs and the OB with bracket weighs about 600, but it sticks out 30". If you calculate the bending moment about the center of the boat they are about the same. The I/O is 8000ft-lbs (10'x800=8000) and the OB would be 7800ft-lbs (13'x600lbs=7800)...so it seems like a wash.

There is however 7800 ft-lbs of torque on the transom that wasn't there before, so I'm sure it needs beefing up.

Another issue to deal with is how the I/O transfers power to the boat. I'm told the Stringer I/O transfers power right to the stingers where the engine mounts.

 

[enfish]

I own an old Grady (1979) 21' with an old tired OMC Stringer I/O. The rest of the boat looks great, hull and floor are solid. I'm considering converting to OB using a OB bracket along with some stringer and transom reinforcements. I can do all the work myself, so labor is free and my buddy has a nice 175HP he'll let go cheap. I spoke to Grady who says it can be done, but offered no advice. I also spoke to the bracket manufacture, who claims that it works great, but I wouldn't expect them to say otherwise. Has any one done this? How did it turn out? How did the boat handle afterword? If so, can you post some pics?

Thanks!

I've not seen anyone do a Grady, but have seen old Wellcrafts and Skipjacks converted. The handling does change and you may have to add some more weight to the bow, but it can be successfully done. Here's a link that might be useful showing a Wellcraft conversion from an OMC I/O.

http://www.bloodydecks.com/forums/check-out-my-boat/111785-pimp-my-wellcraft.html

I know I've seen other posts about i/o to outboard conversions. I just can't find them...

Good luck!

 

[NOTHING ELSE MATTERS]

You should pay a visit also at this place
http://forums.bateau2.com/
a lot of boat builders here ready to help you.

 

[gerrys]

I did it on an old 22' Invader cuddy. Pulled the Chevy 350 and added a Yammi 225 (I believe - it was a long time ago). At any rate, the stringer broke about 1/2 half way up the boat due to the cantilevered load.

The lesson to be learned is that additional reinforcement is needed well forward of the transom as a flexing load will be added all the way through mid-ship.

I have to say the boat ran like a scalded dog until we almost sank. The good part of the story was that I bought a new boat from the dealer that sold me the motor and he applied full credit toward the new boat.

 

[IwanaBrich]

That was also one of my fears! You convinced me.......time to look for another boat!

What boat did you end up with?

Thanks

 

[gerrys]

I got a Parker 2510, great boat! Then I got a Marlin 300, great boat! and a 17' Key Largo for river fishing, great boat! Then I got a Ranger 2400 Bay, great boat!
I guess I never met a boat that I didn't like. :lol:

 

[jtsailjt]

That was also one of my fears! You convinced me.......time to look for another boat!

What boat did you end up with?

Thanks

If you like your boat, but are worried about structural issues with an OB, why not just put in a new (to you) IO? A new one might be more pricey than you'd prefer, but you see lots of not terribly old bayliners and such around for sale cheap that you could transplant an alpha drive and 350 V8 from.

 

[IwanaBrich]

Repairing the IO was my original thought, but the outdrive is shot. I'm told that OMC Stinger outdrives are hard to find parts for and are very expensive to fix. I was told the outdrive should be replaced with another make and I'd have to do a lot of transom work to make it fit. It just wasn't worth the work, its too old.

 

[JeffN]

Repairing the IO was my original thought, but the outdrive is shot. I'm told that OMC Stinger outdrives are hard to find parts for and are very expensive to fix. I was told the outdrive should be replaced with another make and I'd have to do a lot of transom work to make it fit. It just wasn't worth the work, its too old.

You were going to put a bracket on it but putting in a new or newer I/O is too much work? If the transom is fine fill the old hole and cut a new one. Yes get rid of the old OMC (all of it - motor, drive, the works) by all means.

 

[Amigo]

I did a conversion on an 18 ft. aluminum boat 8 years ago. Very happy with the results. She gets a lot of hours on Lake Michigan and in northern Ontario.

I removed a 4 cylinder Mercruiser and installed a bracket (50#) and a 115 HP Johnson 2 cycle (350#) It sits very well in the water and is a great fishing machine.

I added plywood in the transom for a total of 2-1/4" thichness. I also had two knee braces made out of stainless.. The braces are through bolted to the transom and lag screwed to the stringers.

 

[IwanaBrich]

JeffN....I agree I could replace the IO and do the transom work, but I couldn't get past the fact that the boat is over 31 years old. I considered the OB bracket idea for 2 reasons, first I could always take the OB engine off and put it on another boat if I choose to. You can't easily move an IO to another boat. Second, I would have gained a whole a lot of space in the boat. If the boat was 10 years newer, I would have done something.

So I'm now looking for a 1985 or newer 228 Seafarer or an Offshore (24'). I really like the 23' Gulfstream, but I'm told its a tad too wide to trailer in NY.