Twin I/O to Twin Outboard Conversion Project

Fair . . .

I'm planning on doing more fairing once I have the extension bracket mounted, bolted and scarfed.

 

Test fitting . . .

I moved the extension bracket out to the boat to test the fit and the installation process, that I will hopefully be doing soon.


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It is a tight fit . . . too tight. I had figured this might happen, so I'll be trying a few spacers in the morning to see what works best. Ideally it could use 5/8" (15-16mm) of spacer on the transom.

 

Ideally?

Ideally, there would be no need for a spacer.

Why would you want a 5/8" spacer?

Why didn't you build to a clearance fit?
With your micrometer!

 

I’m with Tom on this one and not comprehending a 5/8” spacer.

All I can think of is pinpoint or pressure point where a 5/8” spacer as a washer has a small bearing surface, but like I said, probably not understanding.

 

A substantial way along with it.

 

Then there was the magnificent OMC Seadrive which didn't need the additional buoyancy of a transom bracket, just a bilge pump under the engine lid.

 

Such a short-lived product though...I've only seen a few back in the day and never had experience with a vessel so equipped.

Not all transom bracket designs provide additional buoyancy at rest or very low speed...some are open frame. Most provide no buoyant (or dynamic) lift while the vessel is on plane.
In some cases it is helpful that the "buoyancy box" associated with a particular bracket design provides roughly the same lift force as the motor weight...especially when considering a conversion from inboard or I/O.

 

I understand

 

Ted,
Ignoring my questions won't make them go away.
Don't shoot the messenger.
Perhaps it's time to grind down to a clearance fit.
Thoughts?

 

I thought they were rhetorical questions, not looking for an answer

After a couple of days figuring out what the issue(s) are . . .

The port side is out about 1/8" on its bevel piece. Probably happened during the framing
The 'wing' area of the top plate on the starboard side tilts 'up' about 1/8"

The top part of the transom mating plate was fine (1/2" to spare) the bottom part of the mating plate was too wide, mostly on the port side as mentioned. Up/down dimension is fine (3/16" to spare).

Essentially the fit was too tight on the bottom . . . (note to self . . . allow more clearance ) However, knowing the geometry of the transom, I always knew that I could add a spacer at the transom mating to give more clearance

I did some grinding and now the fit is better.

Port side:

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Starboard side . . .

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The grinding has improved the fit. So, a 1/2" spacer/shim will be more than adequate. My nautical engineer buddy suggested that I use hull & deck putty rather than adhesive to secure the extension bracket (along with the bolts and scarf joints). Probably a good idea.

I need to make sure everything is aligned to the center line of the hull. Got to find my laser straight edge. Then I can add shims accordingly to make it all straight.

 

Why would you not fair it all to fit closer? For that matter, a good one hour epoxy/cab mix and v groove it 3/8” and press it together?

Of course plastic on preferred non bond side. Then sand it a bit and fill the grooves.

still not understanding the 1/2”

 

Here is a series of diagrams (with some exaggeration) that I can best explain it . . .

Essentially the extension bracket 'as built' is acting like an interference fit (which I had thought could happen) . . . So the transom mating face of the extension bracket does not come in contact with the boat's transom (First image). With some grinding of the beveled areas, the fit has been improved, but still not 100%. . I don't want to grind too much so as to weaken those areas

When installing the E-B with an interference fit, it can/will go off center, since the contact areas are the beveled sides (not the transom). (2nd & 3rd image)

The solution is to provide spacers to give the E-B a hard stopping point that is in alignment and use a gap-filling solution (Hull & Deck Putty) (4th image)



The spacer approach not only addresses the 'fit' problem, but also allows for any adjustment of the alignment of the E-B to the boat's (hull) centerline.

That's all I got . . .

 

I got my laser line thingy today, so I tried mounting the E-B with 1/2" spacers. It fits a lot better, no interference on the beveled sides.
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Here is the laser line . . . Looks pretty good.
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I did not realize that the 5" keel pad went so far forward.

 

I'm working on the transom modification structure. A few more pieces to go, then on to glassing it all in. IIRC, my laminate schedule for the supports is 3-4 layers of 1708/1808.
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All those who hate grinding fiberglass raise your hand . . .
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More to go . . . hope to get done today.