I/O (Sterndrive) Conversion to Outboards

[tpenfield]

Guess I'll have to take you word for it. Being 2X the force than I don't see how the Crap --- arrel stays together going from a SSX 30 to a 280 OSX. I have no stringer extra anything inside the boat. Sure my 280 only has a 25.5 ft hull

Than we can compare the Formula 310 sterndrive or OB, the interior hull is the same less the holes going to OB

Here is the difference in those 2 boats (Formula 310 I/O vs OB)

The outboard version has the hull extended at the full height of the transom and distributes the load to the outer areas of the hull. (actually a clever design)
.

.
.

.
The I/O version does not have the hull extended and is transferring the forces more directly to the stringers. So, if you took the I/O version and converted it to OB's you would have to/want to add the support braces, as is the case with most conversions.

 

[Scott Danforth]

Ted, since you ran these past the naval architect, I would say, keep with the current plan.

 

[tpenfield]

Transom support structure is roughed out.
.

.
Now onto the final grinding . . . Oh joy . . .
.

.
My cordless angle grinder is being put to the test.

 

[Pmt133]

Love cordless tools. Had to go to air for mine as I kept burning them out. Obviously you have a wee bit less grinding to do than I did though.

 

[Scott Danforth]

I have a 35 year old "Craftsman Pro" angle grinder which is a DeWalt with a black housing and Craftsman labels. its corded, and has gone thru 3 sets of brushes, a cord, and countless spindle nuts and backing pads to date. it has rebuilt 4 boats, and about a dozen hotrods over the years.

the cordless ones I used have all come and gone, however that old craftsman is a workhorse.

 

[Pmt133]

That's like the black and decker rotary buffer I have... thing is like 50 years old. Buffed every boat dad owned and I pulled the brushes out of it last year thinking they may be due and slapped them right back in because they weren't even half worn. Probably out last any replacements I got too.

Gives you a hell of a workout using it though.

 

[tpenfield]

Ted, since you ran these past the naval architect, I would say, keep with the current plan.

I'll probably run my changes by the N.A. to see if there are any concerns. He was pretty good with the design and safety factors that I had applied.

 

[tpenfield]

I have both a cordless and corded angle grinders. Running 40 grit flap disks.
.
Progress so far . . .
.

.
I've been using the cordless, since the corded goes too fast. I was getting a lot of static electricity as I was grinding, which I was not too keen about. I kept a mist spray bottle handy and that has helped.

Not sure if other folks have experienced static when grinding and have any tricks/tips to share.

 

[Pmt133]

My transom was so water logged it didn't matter. I've heard of using static guard or water mist though.

 

[tpenfield]

Interior grinding is done. I still have the grinding outside the transom to do . . .

 

[Pmt133]

36 grit belt on a belt sander worked well on flat surfaces FYI. May make short work of the outside.

 

[tpenfield]

I made the mistake of touching an area of the fiberglass that had been ground . . . ouch . . . microscopic fibers in my finger

I used the Hull & Deck putty to set these pieces of the transom support structure in place.
.

.
OMG !!! . . . It's warm enough outside to have the resin cure on its own!

 

[Scott Danforth]

Ted, you still have grinding to do. you are not completely thru the gel yet

 

[tpenfield]

Ted, you still have grinding to do. you are not completely thru the gel yet

I am finding the surfaces are quite un-even, and the top surface of the transom and stringers is 1808 fiberglass, which has the texture like those corduroy pants from 50 years ago. The gel goes down into the crevasses

So I was concerned about grinding some areas too much, as there was only 0.14" of fiberglass thickness on the inside. I may do a wee bit more grinding before glassing, but it is kind of a judgement call.

The outside areas are thicker and smoother, so I'll be able to grind into clean glass.

 

[tpenfield]

I got my bolts, so the fastener portion of my installation is ready.

I have been planning the adhesive aspect, being the hull & deck putty. I consulted with our good friend (Jody) on the compatibility of VE resin and polyester resin. He stated that they are 100% compatible. So, my plan is to wet the transom and extension bracket mating surfaces with VE resin and then apply the polyester putty in between.

I ran a test piece of that combination, and it came out OK.
.

.

 

[alldodge]

I am finding the surfaces are quite un-even, and the top surface of the transom and stringers is 1808 fiberglass, which has the texture like those corduroy pants from 50 years ago. The gel goes down into the crevasses

So I was concerned about grinding some areas too much, as there was only 0.14" of fiberglass thickness on the inside. I may do a wee bit more grinding before glassing, but it is kind of a judgement call.

The outside areas are thicker and smoother, so I'll be able to grind into clean glass.

Would epoxy resin create a better hold?

 

[redneck joe]

I'd gring a wee bit more, up to a smidge....

 

[Scott Danforth]

like those corduroy pants from 50 years ago. The gel goes down into the crevasses

Maybe use a wire cup brush in the angle grinder to get in the crevices

 

[tphoyt]

That a good plan Scott. I did that once in hopes that it would at least provide a wee bit of tooth. As far as the poly and epoxy being compatible there was once a time when they were not. I’m not up to speed on what’s out there these days.

 

[Pmt133]

Epoxy over poly is fine. Poly and vinyl shouldn't go over epoxy. Gel can't go over epoxy either. There are bond coats that you can allegedly use on epoxy to put gel over it but I've never tried.

Due to the nature of the chemistry of epoxy, the other resins will not form much more than a light mechanical bond. Epoxy and it's chemistry will still form a really good mechanical bond over prepped poly/vinyl.

Without going too far into the rabbit hole of the chemistry.... poly and vinyl work really well in a chemical bond but don't form the best mechanical bonds. Epoxy forms a fantastic chemical bond and coincidentally also works really well in mechanical bonds. If you take a peak at the chemical work ups of each reaction, it makes more sense but only if you get chemistry... that's when you also learn that vinylester is like a hybrid of sorts of both poly and epoxy and is why it is popular in place of one or the other.