Help me identify these Mystery Transom Bolts!

So my 23’ Formula, with twins had these bolts sticking out of the transom when I bought the boat.

The bolts on the port side of the drives were gone when I got the boat, having only the starboard bolts remaining. After a firm whack with a hammer the bolt near the port drive fell off, and the plastic cap over the starboard most bolt gave way also. These bolts are just simply thru bolted to the transom with no indication of their purpose at all.

The plastic cap was red, and looked to have a split in it, at the bottom, it looked like it was at one time secured onto the stud with a hose clamp.

Does anybody have any ideas what these bolts may have been used for, or why they were installed??

 

To me they look like archeological remnants of what once were fasteners with washers used as mounting points of a swimming or boarding platform. Something like this:

 

I hadn’t thought of that….

That’s a good idea, but I don’t think they were used for that.
There is not any evidence of anything having been mounted higher on the transom, and they had these strange plastic caps on them.

Here is another picture of them when I got the boat, before I started tearing it apart.
See the plastic cap??

 

Is there perhaps some evidence that they were holding something inside the boat? I can see a big protruding panel around stern-drive openings. The bolts might be mechanical connectors related to that panel. I'm guessing here, a closer inspection would be necessary. As about plastic caps, they might be there simply for mechanical and anti-corrosion protection of filleted parts. We have a nearby factory (just as an example) which produces only that - plastic caps for the mechanical protection of bolts and screws: http://www.bmp-tappi.it/ITA/catalogo.asp
Cheers!

 

I am not sure I quite understand “filleted parts”

Here is the inside. Just a bolt and a nylock nut.

I would like to think that they served a purpose, to drill 4 holes in the transom below the waterline for nothing??? It seams like a specialized bolt as well, with an interesting washer on the outside. I was thinking Pier Launch points, who knows….

 

That’s quite a lot of different caps....!!!! WOW!! Who knew this stuff existed. But no.. nothing like that. These were thick, almost 1.5" in diameter. With a wall thickness greater than 3/8", looked quite substantial.

 

Oooops sorry, it was an ugly and brutal translation of the italian "filetto". The right word is "threaded" part.

 

They do look like mechanical connectors for some panel or a transom reinforcement. But if you say it's none of the above then I call time-out...
In the meanwhile, we have lots of experienced repair-shop guys here - someone will drop by for sure.
Cheers!

 

I wonder it the stern drives were surface piercing, they would then have brace rods attached to the transom just about there.

 

Landlubber,
The drives are early “Type 1” Mercruser drives, and are definitely not surface piercing.
But thats a good idea too! Its the plastic caps that have me stumped, without them maybe it was a mounting point for something, but with the caps, i see no intended use.
The other strange thing is only the starbord side bolts were left, both the starboard bolts having been removed.

 

I wonder if they weren't mounting point for an optional swim platform that was never installed. The plastic caps my be to protect the threads and keep you from whacking various parts of your anatomy on them.

If they're not serving any visible purpose it's probably safe to fill them in.

 

Oh they are no threads on the portion outside the boat. The protruding portion is knurled, as to “hold” the plastic cap on.

For sure they are getting filled in. I was just curious as to what they were.
The boat has commercial California Fish & Game plates on it, and I hear it was used (briefly) as a commercial salmon rig. Maybe they have something to do with that??

They guys at the boat shop told me they have never seen anything like it, so I figured this place was a good place to try and figure it out.

Also, this boat is over 40 years old, if that gives any indication to how ancient these things may be.

 

maybe a first version of a Mercathode system?

 

This boat does have two Mercathode systems, but no wires connected to these bolts.

I think that may be the correct guess.... but i cant say for sure.

 

I\O's

they look like mounting brackets for the I\O's. they would have a bar running from one outboard to the other for steering purposes. I have twin F302's with OMC electric shifts. there are steering arms for both outdrives.