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

Instigator

Well-known member
Tank is done and on its way and I’m almost ready for it.

Glassed in the knees, tank sub floor, bilge pump mount and plugged all the holes in the transom including the trim tabs which I’m not sure I’ll re-use.
 

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Instigator

Well-known member
And it fits!

Yay.

My motor deal fell through though.
After months of waiting.
Argh!

Anyone know the heaviest O/Bs put on a 25?
Pixs?

I’m coming up with alternative motors but don’t like the weight.
The 3.0 liter loopers I’m trying to find/stay with are only 455.
Everything else is 500+, x 2.
 

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Instigator

Well-known member
That's a real bummer on the motors man! Hopefully you'll find something as good as or better.

Yep.

I’m oh and three on motors at this point.
My bargain basement budget don’t help.

At this point I’ll continue looking for similar.
They’re what I know, have tons of parts and knowledge for.

Shot happens.
 

Instigator

Well-known member
Excellent.
Thx Knarloid.

I will have approx 20” more setback but shouldn’t change at rest, attitude much.

Thx too to whoever sent me their fuel tank prints. Can’t find the orig message.
Basically identical other than adding length for more capacity.
 

knarloid

Well-known member
Excellent.
Thx Knarloid.

I will have approx 20” more setback but shouldn’t change at rest, attitude much.

Thx too to whoever sent me their fuel tank prints. Can’t find the orig message.
Basically identical other than adding length for more capacity.

Do you really think adding 20" more of setback won't affect it at rest?
You should probably know that I had to add 5 bags of sand into the nose (behind the mirror and v berth) to help with the porpoising I had been experiencing previously.

I think I sent you my tank prints earlier in the year. Glad they were of benefit.

Looking forward to seeing it all come together into 2019!
 

Instigator

Well-known member
Basing most of it on my experience w/both my twin O/B 24' Sonics.

Boat #1, twin 250 Johnrudes at 450 lbs per, 20" setback, zero hop.
Added 6" jack plates (now 26" setback) and got zero hop.

Boat #2, identical to above, w/24" setback.
Started w/Mercs identical to yours. Zero hop.

Repowered w/twin JohnRude 250's, w/zero hop.
Weird thing was, it was 10 mphs slower than #1.
I tried EVERYTHING to find it but never did.

I built and tried a pair of Lightning gear cases that are semi crescent leading edge (bad for heavy vee bottoms) and picked up 2 mph but now took full up trim to fly the boat.

Also tried a pair of 26" Bravo Ones and it they made it hop! I cut the lips off the back of the hubs and cured 90% of it but not all.
Took full up trim to fly it and I wont put up w/that.
If the motors arent vertical at speed somethings wrong.

Those boats were 1' shorter but 6" narrower and not sure on weight but Id guess close.

So to answer your question, I dont know.
But one of my faults is, Im willing to bet heavy and be wrong.
Wouldnt be the first time but I will be shocked if it doesnt work.

First experiment will take place as soon as I build/install the bracket.
Ill screw on motors, fill the new tank w/water and head to the ramp for a test float.
Ill start w/batteries out of the boat then see where they need to be.

Remember too, that its more than adding their weight to the bow (wherever) Im also removing their weight from the stern so its a double whammy.
Can also add a ballast tank to the bow if needed.

Im fairly confident I can get it to fly at speed but low/mid range we'll see but trim tabs can handle that.

As you probably know, propellers have a huge influence on curing/creating hop as do their running depth.
Ive had a lot of fast vee's that I ran the motors deeper than most in order to get bite for the props to be able to carry the bow.

We shall see ;)





Do you really think adding 20" more of setback won't affect it at rest?
You should probably know that I had to add 5 bags of sand into the nose (behind the mirror and v berth) to help with the porpoising I had been experiencing previously.

I think I sent you my tank prints earlier in the year. Glad they were of benefit.

Looking forward to seeing it all come together into 2019!
 

Instigator

Well-known member
Headway on the bracket.

Basically laid up the platform portion and motor board the rest is just forms for the glass.

Built the platform upside down in the mold and had nightmares about the angle for the transom being bass ackwards.
 

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Instigator

Well-known member
Just had a client being in a ‘92 for a quote for a floor and we were comparing his to mine and I learned something.
His is gutted too so easy to compare cabins.

His vee berth looked wider than mine and setees appeared longer.
So after 5 mins w/a tape measure I discovered:


His vee berth is 3” taller than mine which it wider.
His cabin bulkheads are placed flush w/the bottom/aft edge of deck making his seats 6” longer than mine.
Another 6” there, is huge!

I’m going to raise my vee berth, maybe even higher and delete the anchor locker, which both will yield a larger vee berth.

Actually excited to build my own cabin.
 

SCT

Well-known member
Gator, I’m guessing your client’s boat is a 251 GTX and your’s an original 251 Convincor?
 

Instigator

Well-known member
*UPDATE*

Bracket is coming together and waiting on me to sling some more glass at it.
I am happy w/how its coming together.

Motors are home from Fla and waiting on me.
Got lucky and scored matching '2000 200/225 OMC V-6 loopers.
From opposite sides of the state.

Hooked the trailer to my '97, 1/4 million mile GMC and headed south.
As soon as I pulled the truck out of my shop into the -11* temps, the windshield washer fluid froze!
The first two gas stops had frozen washer/buckets!
17 1/2 hrs later we (my bro and I) pulled into my friends house in Vero Beach.
The next day we strapped one motor in the bed of the truck and the second one on the utility trailer next to my new ('1985) Suzuki GS 700 es.

We took the next 3 days drinking/playing tourist before heading north.

At 14 hrs in, a 1/2 hr N of Atlanta, an idler pulley on the truck seized and sawed through the serpentine belt.
I discovered that after loosing power steering (alternator, water pump etc) in the middle of a steep/sharp down hill curve and nearly driving into the door of the truck in the next lane!

We got lucky and made it to the next exit w/a gas station to park/work.
I googled the nearest NAPA store, knowing most delivered, and whined enough to convince the manager to send me the parts!
Had us back on the road in 2 hrs.
Would have been 1 hr but missed the seized pulley and had to get a 2nd delivery.
Got back on the road and did 2 more hrs before bagging it for the night.
Awoke to everything being under a layer of snow.

The 200 becomes a 225 when I screw on a set of 225 carbs that are on my shelf.

They are also both RH which I will correct w/a LH gear case. Ill sell the extra RH and end up with $2/300 in the conversion.

The plan is to build a pair of 300ish HP drop on p.heads to be able to switch back and forth.

Also found a $500 Bomar bow hatch on e-bay for $50 to replace the damaged, orig.
Shopping for a smaller, second unit to install forward which is key for air flow on hot nights in the cabin.
 

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Instigator

Well-known member
Bracket progress.

I doubt the bike liked being towed backwards 1100 mls through melted snow/salt.

Cool little bike though.
Im a big fan of the classic muscle/sport bikes.
 

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knarloid

Well-known member
Do you have any pics of the old hatch you replaced with the Bomar?
Curious to see if I may be able to use parts of it for my one ('82 model).
 

Instigator

Well-known member
I’ll try to remember to get u some tomorrow.

It’s not square like most. Leading edge comes to a slight vee.
Locks w/two knobs that slide in forward track.

Hatch is like rest of boat.
Mostly there.
Previous owner painted it black so it allows zero light into cabin and one support is off/damaged.

Pay shipping and it’s yours if u can use it.

Do you have any pics of the old hatch you replaced with the Bomar?
Curious to see if I may be able to use parts of it for my one ('82 model).
 

knarloid

Well-known member
I’ll try to remember to get u some tomorrow.

It’s not square like most. Leading edge comes to a slight vee.
Locks w/two knobs that slide in forward track.

Hatch is like rest of boat.
Mostly there.
Previous owner painted it black so it allows zero light into cabin and one support is off/damaged.

Pay shipping and it’s yours if u can use it.

Sounds exactly like mine - except for the paint.
http://checkmate-boats.com/forums/showthread.php?t=31724

I will take it if you can send the pic so I am sure. Mine has a few parts missing and I would need to rebuild the frame around the glass, so I should be able to get a complete one together with parts from yours also.

PM me the price for shipping to 08807 when you get a chance! Can Venmo or Paypal. :cheers:
 

Instigator

Well-known member
Thats it.

Mine is intact other than one support is removed but I think salvageable.

On the paint, you could probably sand it off or heat/scrape and then polish the plastic back into shape if you wanted.

Dont know when Ill get to removing it but it now has your name on it and cool to see it going back into service.

Sounds exactly like mine - except for the paint.
http://checkmate-boats.com/forums/showthread.php?t=31724

I will take it if you can send the pic so I am sure. Mine has a few parts missing and I would need to rebuild the frame around the glass, so I should be able to get a complete one together with parts from yours also.

PM me the price for shipping to 08807 when you get a chance! Can Venmo or Paypal. :cheers:
 

Instigator

Well-known member
Knarloid, here yah go dude.

PM your address and I’ll get cost of shipping.

Other than painted window, it’s perfect w/exception of one missing bolt where upright pivot goes through hatch frame.
Easy fix.

You may owe me beers at next yrs rally when we come calling ��
 

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