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'1986 251 I/O conversion to twin O/B's

Instigator

Well-known member
Always wanted to do this and finally threw the switch.

A short bio for those that done know me:

I've owned two 24' Sonic twin O/B's. An '84 and a '85, both for 7 yrs each.
Ive owned little boats (<20') and big (>25'), slow and fast and those two Sonics were my favorite boats of all.

We raced anything/everything willing w/them, explored, traveled, cruised, camped etc.

We had the 2nd one while in Fla and I wrote and posted a story on OSO.com about a 5 day trip w/it in the Keys.
Thinking that was all big/expensive/rich stuff I figured the story would flop.
Called it "5 days and 4 night on a 24' cuddy in the Keys" and the story exploded.

That really changed my previous view of no one boating like this anymore.

So theres me and now back to the project.

I know they built twin O/B 25's (and larger) but they had splash wells which eliminated the sun lounge and the area underneath.
I added a lounge to our last Sonic and loved it.

So the plan was, find as clean of 251 I/O as I could, ideally w/a blown motor (making it affordable) and bonus points for an aluminum trailer to take it to salt water.

Just found/bought a '86 w/a stroker 454 w/a dropped valve, hooked to a Bravo drive.

I figure if all goes well, I will recoup 1/2 my initial investment by unloading all the car motor funk.

We just moved and I lost my shop so the boat is stuffed under a carport till spring while my new shop is built.

Plan is to fill all the holes in the transom left from the I/O stuff then screw on a integral platform/bracket for the twin O/B's.

This will give me a HUGE storage space under the lounge where the car moter used to be.
That will hold our two fold up bicycles,$40 Walmart inflatable dinghy, beach chairs, table, grill, etc, etc.

We do a lot of weekends on Lake Erie where we get on the boat Friday afternoon, head to the islands, anchor out (saving $1.75 per ft dockage), dinghy in, bon fire, dinner on the grill etc.
Then bikes to shore via dinghy to explore the islands (Keys).

An issue delaying this project has been fuel capacity. I sold Mates in '89/90 and remember that being an issue.
My Sonics both had 89 gl tanks and I ran them out of gas many times.
The new project has a 67 gl tank!

I called and talked to Kip and Dean at the factory (now 45 mins from me :thumb:) about the project.
Based on age of boat they were both scetchy on details.
Dean remembered that center floor panel over tank stopped at a bulkhead at forward edge of tank.
Mine goes all the way to cabin entry but was replaced by previous owner so doesnt tell me much.
He expected it to stop a couple feet short of cabin. Meaning, room for a larger tank.

Based on not wanting to affect balance, I will verify existing space to expand tank before doing anything else on that end.

I got a quote for a custom bracket from Armstrong in Fla and it was $5K!

Being the skin flint that I am, that means either A., I draw up prints for a fab shop to build me one or B., I build one myself out of fiberglass.
My second Sonic had a glass bracket.

I am also brainstorming on motors.
Unfortunately I don't have $50K for a new pair of 300's.

So they will be used.
I have established a $10K budget for ready to run units and they will be 2 strokes.

As in used/good condition, or rebuilt/newer motors.

Im an OMC guy but Ive looked at everything.
I'd really like to have a pair of the newer direct injected, way efficient motors but w/a $10K budget it will be a crap shoot at best.

I have a buddy that owns a pair of OMCs I had on my last Sonic for a while and will sell them back to me.
They are '1998 250 V-6 Ocean Pros. Same as their 225 HO's.
These in tact, are very, very rare.

They have under 250 hrs on them and are perfect.
If I go that direction, I will paint them silver to match the stripes on the boats and add graphics to them in either white or black.
Should look really slick.

Heres the pix's I have so far.

Hope you enjoy.
 

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moh pixs
 

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Two things hooked me on this boat.

The color scheme which Ive never seen before and the 2 yr old aluminum trailer.
 

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Great post. I like what you have planned, and where you're starting from.

I think the East coast twins owners owe you a visit one day for an'Up-Norf Bash!'. Where are you located?
Of course you are always welcome to visit our event - last weekend of June every year in Annapolis on the Chesapeake. We only have 5 twin o/b Convincors there for now - always room for another.

On your tank thoughts - you should definitely be able to get a new tank to hold at least 90gals between the cabin bulkhead and about 12-18 inches forward of the bilge. Worked for me!
The thing to be thinking about is where you want to fill it from.

When I replaced mine, I had to reuse the fill near the stern. Getting a new fill near the windshield was going to be too much hassle (legroom, fitting the pipe behind the dash among the cables and steering).
With the weight of 2x 250hp 3L Mercs on the back (no transom bracket, just 6" jackplates), the bow sits high, and filling the tank is very difficult without putting weight on the bow to prevent airlocks when moored at the fuel dock. I try to always fill it when on the trailer.

I should be able to find some pictures to send you of mine apart (tank set in, etc). PM me an email address or cell number.
 
Good stuff knarloid.

Good point on aft filling tank. Mine is same.
I always fill it on trailer but when low would fill at dock.

Droptop told me about your Chesapeake get together and Id love to!

A northern/Lake Erie get together would be a hoot too. Ive boated up there all my life and know the western end (where the islands are) very well.

If I buy two running motors, I hope to have it wet this summer.
Two project motors would probably be Spring '19.

Im dying to get it in the shop and stripped to see what I have/bought.

Previous owner redid all the cockpit upholstery then let is set outside w/a leaking cover so all wood is wet and/or rotten.

Cabin is circa '1986 :bigthumb:

Im actually looking forward to gutting/redesigning it.

Also way up on the list is re-configuring dash to allow a hatch to aid cabin entry, another dig on the Convincor and positive to the 24' Sonic for a weekend boat.

Convincor is way better design and build quality though.
 
:drool: Is the colors, in the original gel or is it a repaint??? Looks great, just a little odd?? Good luck.

Deck is gel, sides of hull at run rail is paint.
And I agree. Very unique but one of the things that attracted me to it.


Should have the new shop done by spring. 1/2 hr north of Cols.

Stop in anytime in area.
 
Just read your 5 days, 4 nites in the Keys thread, you have been talking about this boat since 2012. Back in the 80's, in Trailer Boats mag, there was a guy and his wife doing a western river loop in a 17/18 foot Glastron with 115 Merc, he poked a hole in the bottom and had to use his coleman stove to get it warm enough for the glass to set. Anyway, first trip on our Bayliner this summer, the war department said it was for sale, made it about 3 miles upriver, she said how nice it was and when we docked her, the decision was she would retire in June and we would boat from Aurora, Ind, to Pittsburg in July!!!:banana:
 
Just read your 5 days, 4 nites in the Keys thread, you have been talking about this boat since 2012. Back in the 80's, in Trailer Boats mag, there was a guy and his wife doing a western river loop in a 17/18 foot Glastron with 115 Merc, he poked a hole in the bottom and had to use his coleman stove to get it warm enough for the glass to set. Anyway, first trip on our Bayliner this summer, the war department said it was for sale, made it about 3 miles upriver, she said how nice it was and when we docked her, the decision was she would retire in June and we would boat from Aurora, Ind, to Pittsburg in July!!!:banana:

Way cool Mark!

My plan/scheme is to get my wife back into this style boating and sell the cruiser.

But once I let her on a boat where she could plug in a curling iron and blow dryer...., I'm good but maybe not that good &#55357;&#56846;
 
Just curious where you dock at Lake Erie, good chance you blow right up 13 past my joint on the way there. I’m by Greenwich and head down 71 a few times a month heading to Cumberland. Small world!
 
Gary,
This is a 72 gallon tank:
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If you fill the casket area, you can squeeze in 90 gallons. You may be able to push the tank back into the bilge area a little bit. I like the idea of lowering the floor going into the stabbin cabin so I don't hit my head each time I go in and out. I'm not too quick and I keep forgetting how low the opening is.
 
The E-tecs in Fla were stored outside, improperly, exhaust up and open, and filled the cylinders w/rain water.
Cost me $200 to save $13k.

Sucks cuz it was a smokin deal.

Mark, I don't function w/o coffee.
Did I tell u the stories of my attempts of coffee on a boat w/no shore power?
Spent a ton trying D.C. and propane before giving up and buying an inverter and a $15 Walmart coffee pot 😎

EK, boat is at Gem Beach in West Harbor. 20 mls west of 13.
We just moved to just north of I-71 and Rt 61.

We'd pass your place when going to Huron, which we do.

Droptop, great pixs. Thx.
Knarloid sent some pixs and specs of his 90 gl tank which my current plan.
Based on his and your pixs, should be perfect.

Especially if I Stick w/the E-etc plan which at this point looks good.
A buddy rebuilds th for a living and is doing a good job of convincing me to buy a pair of donors and rebuild them.

We're going to Fla end of the month and I may tow the utility trailer down just in case.
 
Snow thawed enough to crawl in boat w/flashlight and tape measure and think I learned something.
The O/B Convincors fuel tanks are 2' longer (20+ additional gls) than the I/O tanks.

Mine is only 60" long and that is full length from step to cabin to bulkhead just forward of motor.

So once the I/O is out, I'll demo that bulkead, move it back 2' and have a new 8'/90 gl tank built.

Or add a 2nd tank where the motor was.

Never even considered that the OB boats had longer/larger tanks since you have no sun lounge/motor.

Interesting.
 
:drool: Whatcha going to do about the transom, I see a lot of talk about gas tanks, but not so much about the transom structure, what are your thoughts, bunch of knees or extra aluminum tubing from the transom to the (sh-t, forgot what they're called) 2x8's????
 
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