Sealing Transom-Mount Transducer Holes

D

dread

New member
My transom mounted Raymarine transducer and bracket had to be removed to properly attach the transducer to the bracket. When the yard reattached the bracket to the transom, they did not put new sealant in two old screw holes. I assumed that was because the old sealant was doing the job. They had to drill or enlarge a third hole (not sure why the old third hole wasn't big enough), and they didn't put sealant in that hole either. Their response was " It is a tight screw very short and does not penetrate the hull."
That response was after the boat was back in the water and I am concerned that they didn't want to haul it out again. Should I lose sleep over this?
 
dread":61j6bf6j said:
Their response was " It is a tight screw very short and does not penetrate the hull."
Click to expand...

Well maybe not to the inside of the boat, but it very well may be long enough to penetrate into the transom core.

dread":61j6bf6j said:
That response was after the boat was back in the water and I am concerned that they didn't want to haul it out again. Should I lose sleep over this?
Click to expand...

Their response wouldn't ease my worries, personally, without removing the fastener and getting a look for myself. The way I look at it, if there is transom damage it will be some time from now, and I doubt they would be covering the repair. Granted, I'm on the "I like to know it's right so I can relax" end of the spectrum, and it's not like your boat is going to melt instantly as-is.

But what I would do? First, I wouldn't bother going back to the same place. I know others might (and not saying my way is the right/best way), but I would figure that they've already shown me they're not terribly concerned, and I would trust myself to care more about the future of the boat and to do a better job.

I would haul the boat as soon as reasonably possible, and check it out for myself. I would remove the screws and see just what was there. If for some reason the transom is solid glass there (or the glass outer skin is thick enough), and so the screw only goes into glass, well then it could be replaced with just some sealant. However my guess is that it goes into core (mine did).

For sealing core below the waterline at the bottom of the transom, I would probably use one of a few approaches.

1) Overdrill/fill/re-mount
Overdrill the holes (make them larger), ream out even a bit more core (i.e. undercut the holes), coat inside of hole with neat epoxy, then fill with thickened epoxy. Chisel off excess while it's in the green stage. Then re-drill correct size hole and bed screw with sealant.

2) Mount block (starboard, fiberglass, other) and then screw transducers to block. (The block gives you a surface to mount any future/different transducers to.)
2a) Mount block similar to #1, then screw transducers to it.
2b) (This is what I'm doing now) Mount block with Weld-Mount fasteners (no holes into boat this way) and then screw transducers to block.

3) If going with #2, you'd want to take care of the current holes first (since they will be disused). You could use the "overdrill/fill" from #1, or, if you are really paranoid (I am :wink:) you might also patch (cover) them with fiberglass cloth/epoxy after filling them. Note that only the most paranoid do this last step, and that simply properly doing the overdrill/fill routine is going to be really, really good.

I'm mid-process doing this on my boat (removing and reinstalling transducers put on by original owner/shop). Luckily, the boat was always stored on a lift in a building, so even though the screws were just screwed into the core with a "bedding" of silicone caulk (! :amgry), there was no wet core. I'm going back with method 2b after filling/glassing the original holes (since the mounting block will cover them, I will do a tidy job with new gelcoat, but it won't have to be Sistine Chapel quality, aesthetically. If your boat is bottom painted, then gelcoat really isn't necessary (paint will shield epoxy from UV).

Sunbeam :hot
 
There's something called a Stern Saver (http://www.sternsaver.com) that which is basically a Starboard block with some cavities on one side. You mix some included epoxy, overfill the cavities, then slap the thing on the transom. The cavities are undercut such that when the epoxy hardens, it is solidly attached to the transom, but has a mechanical connection with the block due to the shape of the cavity.

I considered doing this on my boat, but instead I undercut and filled the old holes then put on my own shaped Starboard block with 5200 and screws into the epoxy plugs:

transducer_block_install_3.jpg
 
Thank you sir...I would second the suggestion to go to my comprehensive (added to be Ferret and several others) about the proper way to put a transducer onto the stern of a boat. Using the Starboard block you can adjust the tranducer to the exact position and angle. My transducer holds the bottom at 25 knots (top effective speed) down to at least 600 feet. You probably will not need that depth, but it is nice to know that you have that capability.
 
I see the term "undercut" being used. Overdrill I get. Can't visualize "undercut". Maybe undercut and overdrill are synonymous? Could somebody explain?
 
As it turns out, I did some drawings when I was trying to figure this out. To undercut, you use a dremel bit that looks like a router bit where the blade is wider than the bit shaft. It lets you make a cylinder shaped void below the hole, between the fiberglass layers that you can later fill with thickened epoxy to make a plug.

transducer_block.jpg
transducer_block2.jpg

This site goes into the process in great detail:

http://www.pbase.com/mainecruising/sealing_the_deck
105506491.RdyX2719.jpg
 
I've also used an old dental pick to undercut - sometimes I can't easily fit a Dremel tool in place, don't have corded power handy, don't want the noise or dust, etc. Balsa picks out pretty easily. Just another alternative to reach the same goal.
 
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