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transom patch, from omc to bravo

Old 02-26-2012, 04:40 PM
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Default transom patch, from omc to bravo

So heres the transom, it was an omc previoulsy on there and i plan on using a bravo xr and extension box. The transom is solid just the edges of the cut out are a little weathered. I am hearing different opinions for patching the hole. Whether making staggered cuts a foot from drive edges and filling it in, or cutting to making a whole transom "bracket". Should i make my bravo cutout before i install the wood. I plan on using 3/4" marine ply okume maybe and biaxial cloth in between and 1708 after. And how do I start the skin, first layer of csm for the transom exterior? I want to keep the integrity for the 502 going in and the pounding i will sometimes give it. Tried to do some research but not too much on this extent. Appreciate any input or links everyone can help out with.


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Old 02-26-2012, 05:25 PM
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OMC cobra? or OMC stringer? if you are talking the nearly 2 foot square hole for old OMC's, i would replace the transom. ALSO, they called them stringers for a reason. the only thing attached to the transom is the outside ring for the gasket-seal-bellows whatever it is called. so the transom may well have been built with a lot less strength as it wasn't really needed for the old drive. if it is OMC cobra, unbolt the gimbal housing and bolt the bravo gimbal to the transolm as-is. same hole. then list the Cobra stuff on ebay.
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Old 02-26-2012, 09:46 PM
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Not sure which OMC, bought hull without powerplant/drive. The dimensions of the cutout are 13 1/2" x 21". The transom was already reinforced once as the boat originally came with dual straight 6's until this prior set up. Like I said the transom is damn near rock hard and was all the inner glasswork and stringers look and feel just as solid. Ive seen conversion "boots" and but they don't look to reliable as they aren't in production anymore. This cuout looks to big for a bracket swap but then again im unsure of the bravo cutout dimensions and give up searching for them. If i did decide to replace the transom, do i replace both sheets of 3/4" entirely or can they be tied in? Im assuming entirely for structural reasons but still curious. Thanks

Last edited by dx787; 02-26-2012 at 09:49 PM.
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Old 02-27-2012, 09:39 AM
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I recently replaced a OMC stringer drive with a Volvo 290 in a 1970 Monza I'm restoring. The transom hole was only slightly out of shape for the new drive soooooo........
Just watch the movie, a picture says a thousand words and i don't like to type. lol

[YOUTUBE]http://www.youtube.com/watch?v=PGTRIJr72y8&list=UUgjMt8W_HOufy0AI1DgW3HA& index=2&feature=plcp[/YOUTUBE]
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Old 02-28-2012, 05:55 AM
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nice presentation screenname. (or are you f-ing?) yes, DX that is old big hole OMC. Cobra and Merc Alpha-Bravo have a keyhole 4 tp 7 inches wide that is about a foot high. distinctive shape. look at transom repair thread in budget boating section. that is size hole when finished. OK, what is this boat? make-model-year-condition ot the rest of boat? what do you consider it worth? or what do you hafta pay to get it? do you already have the 502-XR package? or is this what you are planning on buying? either way, it is pricey power for a nearly 30 year old boat. you can usually find a running driving boat with any given engine set-up for less than the price of that power bought seperately.

Last edited by dereknkathy; 02-28-2012 at 06:07 AM.
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Old 03-05-2012, 09:18 PM
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The boat is a 26 corsa. I picked it up for a little over a grand with trailer. Bare hull, have driver and passenger consoles and also windshield. I plan to do my own because im tired of driving around wasting my time and money for everyone else's beat money pits for $12k. I want a 502 minimum, bravo one will do, doesnt have to be xr. I live in ft lauderdale and have pretty good marine connections, just want to do all the work myslef (therapy ). I have quite a bit of experience, just not to this extent. Ive also had quite a few people recommend getting a custom plate made, still a little unsure. Im going to take pictures of the inside of the transom tomorrow morning. The stringers also run up the back side of the transom about two feet. The hull is straight as an arrow and transom is rock solid. Just mainly cosmetics but plan on painting anyways. But i want it done right so im in a pickle here. Thanks for the advice everyone.

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Old 03-05-2012, 09:54 PM
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A plate will cost you 800 at a minimum. Unless you know someone for that to.
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Old 03-05-2012, 10:01 PM
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f screenname, the boat came out awesome to say the least. It looks as if the sides were just filled in just a bit on the sides. Everyone says if i do the transom to do the whole thing.
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Old 03-06-2012, 02:15 PM
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Hey DX,
It's not as simple as it looks and if there is any other issues with the transom that I would say to do the whole thing. In my case the transom was solid and I was using a Volvo 290 to replace the OMC. The Volvo 290 is almost as big as the OMC's cut out. The real issue with my case was the fact that when they put the OMC in it must've been a Monday morning or Friday afternoon because it was an inch off-center. As you saw in the movie the Volvo only required a couple inches on each side to be filled so the seal would have something to sit on.
The Monza's and most transoms are made of 3 layers plywood so what I did is slot out the center piece of plywood about 8 inches back with a metal grinder. Then I cut a matching piece of plywood, covered everything with glass and mat and while still wet drove the new plywood into the slot. Let it set up and then did the same thing with the outer layer but only went back about 4 inches on that one. And again I did the same thing on inside. So the wood is basically like a piece of tongue and groove hardwood except for the tongue is about 8 inches long.
As you also saw in the movie, when we put the new 290 shield up to the transom very little of of the repair actually shows. And really it's only there for so the transom shield seal has something to set on. There isn't many many cases I would do this but for a OMC to Volvo 290 with a solid transom it was the simplest thing to do.

PS, if the OMC would have been centered in the boat only about an inch in the center area of the repair would have stayed after the cutout was done for the 290. A 290 would cover the whole OMC hole and (if I wasn't doing the whole boat) could have left the outside fiberglass alone.

Last edited by f_inscreenname; 03-06-2012 at 02:27 PM.
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Old 01-05-2015, 01:44 PM
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Hey f_inscreenname. I've got the same project on the go and can't find you vid on YouTube. I'd really appreciate to see how you've done this so I don't have to replace my perfectly good transom, which happens to have a large 'OMC' hole in it. I plan on Volvo drive so I'd really appreciate your advice. I see this is almost 3yrs down the line, how did it hold up for you?
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