omc i/o to ob

[sprdty]

hey
i have currently rescued a 1969 20ft thunderbird arapaho that came with a omc i/o.

my goal is to fill in both holes in order to use a armstrong style bracket.

ive heard & read all the stories, but the boat is so cool looking i dont mind spending the time or funds to do this project.

i need advice on where to start & what materials to use to complete this task,

i understand that a support system from the stringers to transom has to be frabricated to assist in weight support.

any & all suggestions will be greatly appreciated.
thanx

 

[tashasdaddy]

Re: omc i/o to ob

99% chance you are going to have to remove the upper cap of the hull to totally reconstruct the transom, from the inside, to handle the weight of the bracket and the 225 you are thinking about putting on it.

 

[sprdty]

Re: omc i/o to ob

wow,, 2 posts 2 kills. im 0 for 2.
let me re-phrase the question.

i have a 1969 boat that has had its I/O completely removed, leaving one large hole & one small hole.
i wish to fill these in, so i need some suggestions on what to use & how to do it.
i have never used fiberglass & wood like this before, therefore i need any & all help i can get to do this project.

after looking at skanybeasts transformatiom, i believe any thing is possible, to me that boat came out great.

thanx
-

 

[Mark42]

Re: omc i/o to ob

I prefer an outboard to inboard power. So while looking for project boats, I was open to the idea of modifying an i/o to outboard. I did a lot of research on the net, and it is not uncommon for people to convert i/o to outboard. Basically, you need to fill the hole(s) and glass them over. I saw two basic methods:

1) cut plywood to fit in the holes, and then reinforce with a large piece of ply from the inside.

2) remove the entire transom plywood and install new plywood.

Both of these methods end up adding two large "knee" braces that are basically a triangle brace that ties the transom to the stringers. Because the stringers are easilly accessable once the motor and i/o are removed, it is rather easy to add this needed support. Also, a splashwell needs to be added.

Remember that with an outboard the transom takes the entire force of the motor pushing the boat. An I/O setup passes the stress (mostly) directly to the motor/stringers. So the "converted" transom needs to pass the stress on to the stringers via knee braces. Also, it is not a bad idea to add a large "fillet" along the perimeter of the transom to help tie the transom plywood to the hull sides.

To me, it seems to be not much more work than a regular transom replacement. Othes will disagree....

Mark

 

[recess]

Re: omc i/o to ob

I am in the final stages of my conversion from I/O to outboard. I took a 1976 Grady White Gulfstream (walkaround). Fortunately my transom was solid as the day it was made, and also close to 3 inches thick. I was able to cut 3 pieces of 3/4 ply and epoxy and screw to another 3/4 piece that filled in from the inside as much of the transom as I could get to fit in. Do not use pressure treated; too wet. Once this was epoxied and screwed (stainless), I then glassed over the entire inside using resin, not expoxy, and gel coated it. The outside required a few layers of glass to build up to the thickness I needed, then applied multiple layers of gel coat. Read up in these forums on how to seal the gel coat to get it to cure properly. Make sure it is flat for the bracket or you will put unnecessary stress on small parts of your transom. It is a time consuming process, but well worth it IF....... your transom is good and solid, and you have the ability to reinforce it as stated earlier in the replies. A knee brace or possibly some angle aluminum or SS bolted to the transom from top to bottom in 2 places, then attach the brace from the stringer to the angle would give you some nice stiffness needed to support the outboard.
Is there any reason you are going all the way up to a 225hp outboard?
My Grady weighs in at about 3200 lbs and a 150 to 175 will be plenty. Dont forget that I/o motors rate their hp at the crankshaft, not the prop like the outboards. My original I/o was a 4 cylinder 140 hp, which means at the prop I was lucky to get 120hp. It moved it at about 28mph. The 175 should push me around at about 40 mph. Again, my best advice is to read, read, read these forums. I read everything I could find on the conversions for over a year. You will get some responses saying dont waste the time and money, others will encourage you to try. But please, learn how to do fiberglass work properly. Its not hard, just very very time consuming.
Good luck.

 

[sprdty]

Re: omc i/o to ob

thanx mark42 & recess for the reassurance.

to answer the ?? as why i chose a 235 hp (not a 225 as listed above)
i got 2 complete 1985 235's with 25in shafts for a really good deal including controls & props (1stainless, 1 alum).

i was looking for a 150 or 175 when i came across the 235's.
after looking at the NADA site & comparing weights the 150 is 385lbs,
175 is 398lbs & the 235 is 400lbs.
so im still in the same weight range. i then did a search on this site for the 235 and found a post that Dhadley responded to, saying the 235 was actually rated 175 hp at the prop by omc in 1985.

the boat a 1969 20ft thunderbird made by formula boat co. just looks cool to me.
the hull, deck & transom are solid, but the boat had been repainted at one time - so it will have to be redone.
i also like the cathederal hull design for stability.
i wanted a Splendor boat (catameran) but the price was to high.
they build their boats as inboards and if you want an outboard they just dont cut out the transom & install a platform bracket.

the transom on the t-bird is almost 3in thick and there is alot off room to work where the motor was. the stringers in that area are also solid.
it has 2 side saddle 18 gal fuel tanks midship and if i put the 2 batteries in the cabin - i figure that will help with the aft weight of motor & bracket

do you have any pix of your project?
i like the idea of the alum support, as i plan to use a platform bracket.

thanx

 

[recess]

Re: omc i/o to ob

Sounds like the boat is solid and should accept the platform bracket well. Do you have any idea of which bracket you will use? They are not cheap, but this is an area you can't afford to skimp on.
Don't relocate the batteries too far from the motors. Even though you may think you want to re-distribute the weight, the voltage loss on the battery cables will adversely affect your starting once you spin that 235 too many times. The boat is going to squat in the aft end due to the weight of the motor on the transom, but once you run it up to speed it will actually lift the boat so the squat will be nill.
Not sure how to post pics. If I can figure it out, I can put up some of my Grady shots to show how it would look. I'm hoping to splash mine this July. The only thing left now is to have a Yamaha mech link and sync the motor that I picked up. Some of the things you have to think about with the engine swap that initially I didn't, and ended up costing some bucks, was things like guages, shifter, and steering. I watched ebay and picked up all the yamaha guages I needed. No big deal with yours, but..... the steering from the old OMC was integrated into the I/O design so a whole new steering system needs to be installed. I went with hydraulic which ended up costing some, even buying on ebay and rebuilding the cylinders. It wasn't hard, but easily chewed up close to $400.

 

[sprdty]

Re: omc i/o to ob

thanx,
i had the chance to get a 92 21ft sunbird cuddy on a trailer for $100 - which had an omc 4.3. cobra type drive.
the boat was pretty stripped out but it still had the steering. a side control (missing the handle) with cables & all the gauges with complete wiring harness.

so i have all that, plus the inside hull part with the power steering ram & outer transom piece. these i plan on selling or giving away.

the transom bracket platform is around $2000 and i think it includes a place for a kicker.

the tbird has a offshore toilet so that will probably be removed.

i got the boat hull for $200 & the trailer that came with the sunbird for a $100.
i just really like the hull design and like to tinker with things, so i figure this will keep me occupied for a long while.
thanx

 

[TD_Maker]

Re: omc i/o to ob

Sprdty,
I converted an old Thunderbird OMC I/O to an outboard several years ago. This was B4 the Outboard brackets were available. I rebuilt the entire transome to accept an outboard motor, and built a new splashwell as well. Like many people have said, the glassing is not hard. Just take your time and be creative, and you will be surprised at what can be done.

Let me know if you need some advice. You will have fun doing this project.

 

[recess]

Re: omc i/o to ob

Sprdty, you have invigorated me tonite. I couldn't figure out how to post pics on here, so I went to the www.shareaproject.com site and set up a project page. Go to the site as listed, in the center of the page click on "boating". Then once that page loads up, go over to the "search" on the left. Type in "1976". You will get a few hits on this. Mine is the Grady White I/O that I put together tonite. Let me know if I can be of any assistance.
Your steering and throttle for the OMC gear will not work for the outboards. There is plenty of info on these forums to search from. It's a great way to learn about your boat and what is out there.
Looking forward to hearing from you.

 

[tashasdaddy]

Re: omc i/o to ob

recess nice job. Sprdty, you got good advice, and a cool boat to work on. i remember them well. get plenty of ventilation into the cabin, as the get hotter than Heck.

 

[sprdty]

Re: omc i/o to ob

thats what is kool about the boat, the front port holes have a slide that spins around to open up the top half so air can circulate.

i also like the front windshield by the way it folds forward so that when you are sitting you can get a good airflow.

i have thought about putting back the OMC V6 stringer system, but i would need a donor boat with all the parts & then there is the repair / parts prices.

but if a donor boat happens by before i start on transom i mite consider it.

i think when its done it will get alot of looks because they are not seen that often if any.

there is a guy up the street that has a 25ft older chapperal that he had repainted with auwl grip (spelling is wrong) that came out great.

recess thanx for the pix,

TD-Maker do you have any pix of before & after?

it has also crossed my mind to cover the complete transom with aluminum after the holes are fixed or atleast a 1/4 sheet of marine ply for added support.

library here i come!

 

[sprdty]

Re: omc i/o to ob

double post

 

[recess]

Re: omc i/o to ob

Dont even think about keeping the old OMC system. Its hard enough to find parts, even harder to find someone to work on them. I tried to keep mine up for the first 2 years then decided to bite the bullet and go with the conversion.
The piece of plywood you are talking about is what I put inside the transom as a back-up plate. The small pieces you cut and fill in the old hole is really just to keep water from coming in. There really is no structual integrity to the hole filler. But, the backing plate locks the hole-fillers to the backing plate, which is then screwed in place. Once you add the bracket, you now have 1/2" SS bolts coming through locking it all together. If you look at my pics you can see the large bolts/nuts and the 1/4" aluminum plates that tie 2 bolts together. When I bolted mine through the transom, only 1 bolt went through a portion of the new filler plate. All the others went directly into the original transom. As it turned out, my OMC sterndrive was off center by about 1 inch. This is why I decided to add the 3/4" ply to the inside.
If you go with a platform type bracket, you will really add some strength to the transom. having the bracket extend all the way across will add rigidity and strengthen the transom. There will be less weight and torque per bolt that way and the entire load will be distributed evenly across, rather than right in the center like mine.

 

[sprdty]

Re: omc i/o to ob

thanx-

it was kinda of a thought, i have seen many omc i/o's converted to mercruiser.

i have been to all the high to low dollar boat dealers/shows (about 8yrs of looking) and i am amazed at how much money they want for a boat with very poor construction.

i encourage everyone to look hard into every openning you can & you will be amazed at how shotty the workmanship is.

in my opinion you are better off getting an old boat and spending the money to bring it back.
but yet if you are in a hurry you get what you paid or signed up to pay for.

no offense intended !!

 

[sprdty]

Re: omc i/o to ob

Here is semi-good question, could a fiberglass truck bed cover be cut up and used to fill in void left over from out drive?

or is it to strong and will not bond properly for the strength needed?

or is plywood the best route?
thanx

 

[sprdty]

Re: omc i/o to ob

okay if the top isnt capable to cut up and use , how about using it as a hardtop for the boat after a custom bult frame is done to support it?

thanx just trying to think of things to use it for - if it doesnt sell on ebay.

 

[TD_Maker]

Re: omc i/o to ob

A single sheet of aluminum to cover the transom will work well for you. Here is a little hint. Go and visit your local county's road and bridge department. many time, they will have old street or highway signs laying around which are no longer used. Sometimes, they can be "obtained" for a song (or fishing trip)