Fill 8mm bolt hole below waterline in 6mm aluminium

[s/v Jedi]

Originally Posted by coopec43

Yes Marelon is reinforced nylon

Marelon is an injection molding grade of glass reinforced nylon. Marelon is absolutely fine below the waterline.25 Feb 2018
Marelon Alternatives - Boating and Fishing Forum

Those bolts are plain nylon, not Marelon. What makes you doing these posts about nylon bolts, I don’t see what you are trying to achieve? Just to argue?

[NBs]

Get a piece of the same Al alloy rod and apply the head with a hammer, first protect the aluminium with a stainless e.g. plate. When the end is slightly spread cut the bar 10-15mm longer than the plate strength in the body and push the piece through and rivet both sides, again use stainless protection so the iron does not touch the Al. See instructions for riveting

[Dr.No]

Fuss, welding would be my only option, despite the significant inconvenience. This is coming from an aluminum boat owner/aluminum boatbuilder. Cheers!

[carstendenmark]

OP, do you have photos of the depth sounder you've removed, and the threads ?
And, what kind of bolts was installed ?

[SofaKingFishy]

Originally Posted by Fuss

I need to fill two 8mm bolt holes that supported the old depth transducer in the engine room. Must I weld or could I use something like JBWeld?

I would prefer to weld but somehow, I think that an easier solution should provide a long term seaworthy fix as well.

Has anyone any experience with this??

I work on boats and we do a lot of metal fab- I’m in Annapolis. You are nuts to repair with anything but welding. You have HOLES IN YOUR BOAT! I know you want to save $, but it’ll be worthless if it sinks.

[jalmberg]

Originally Posted by Dr.No

Fuss, welding would be my only option, despite the significant inconvenience. This is coming from an aluminum boat owner/aluminum boatbuilder. Cheers!

I have to heartily second this motion. I can't believe my eyes about the other recommendations. We are talking about below the waterline, right? Talk about asking for trouble...

Here's an idea: ask your insurance agent.

[Fuss]

[QUOTE=carstendenmark;3963516]OP, do you have photos of the depth sounder you've removed, and the threads ?
And, what kind of bolts was installed ?[/

nothing removed yet, there are 2x 8mm stainless bolts through the hull and into 10mm - 20mm tapered teak.
the teak is sealed to the bottom of the hull over the epoxy barrier coat using sika 292 as well as the stainless steel bolts.

now while this has been seaworthy for a very long time, i now want to replace with a dst810 that does not need to exactly mounted vertically.

i do not believe that my chosen method of sealing using alu bolts and JBWeld is less seaworthy.

[Fuss]

please let me know your revised thoughts now that i explained a little clearer….

[carstendenmark]

Just to be clear, OP.
Is there an 8mm thread through the 6mm alu hull, or was the two sounder bolts mounted with a locking nut on the inside of the hull, through an 8mm hole ?
I guess there are 3 holes, two bolt holes and 1 sounder hole.

Will you mount the new sounder in the same hole as the previous one ?

[Fuss]

Originally Posted by carstendenmark

Just to be clear, OP.
Is there an 8mm thread through the 6mm alu hull, or was the two sounder bolts mounted with a locking nut on the inside of the hull, through an 8mm hole ?
I guess there are 3 holes, two bolt holes and 1 sounder hole.

Will you mount the new sounder in the same hole as the previous one ?

No, 8mm bolt but no thread in the aluminium. Locking nut on the inside.
Yes a sounder hole as well… maybe a 50mm hole that will have the new sounder and through hull fittings.

[s/v Jedi]

To everyone calling it ridiculous to not weld this: these bolts have been there all the time and no boat was sunk. It used to be that every seacock was through bolted and I never heard of any leak other than those caused by rotting backing blocks.

[Flagfish]

Originally Posted by Fuss

Thanks for the replies so far, I don’t want to use stainless below the waterline especially with the dissimilar aluminium issue.
I know welding is best but I then would have to re-epoxy inside and also the hull outside.
Someone with an aluminium boat must have been faced with the same in the past.
I read that often 5200 is used to plug these small underwater bolt holes and lasting 10 years, but this is going a bit far for me. I would have thought that JBweld would be a seaworthy solution as the holes are so small.

I had similar and used a 1/4" thick aluminum plate, 5200 slathered heavy, stainless steel washers and bolts. Aluminum corrodes preferentially to stainless steel in a dissimilar metal situation, so the 1/4" aluminum gives more mass than will be needed.

[Icarus]

I would get it welded..simple
Or clean the holes and use an epoxy filler
Don't plug the holes with a stainless bolt, if u do use aluminum alloy bolts

[DShant]

Well you asked if anyone had experience with this and I am loath to post this as everyone is in a panic about these small screw holes but here goes. I had a similar situation in Honduras where I could not haul or otherwise do a permanent fix.

First of all if you have adequate pumps the screw hole is not going to sink your boat no matter what happens although I must say you get the willies watching water squirting in. But it is nothing for today's bilge pumps. And although they could probably handle that volume forever, you can put in some toothpicks or whatever is at hand to close the screw hole until you can fix it if whatever you do doesn't work.



In my case I had a diver go down and put in some epoxy underwater. I forget if it was JB Weld or not. The locals recommended it. I then sailed to Florida and for several reasons did not haul the boat for over a year. The epoxy performed just fine. Maybe I'm too old but in my younger days my wooden boats were always leaking. Stuffing boxes, between planks, decks you name it.


Don't get to sweaty about it, an epoxy fix will last just fine until you feel like doing something else. I do like Jedi's idea of an aluminum bolt and epoxy though. That sounds almost permanent.

[Fore and Aft]

I didn't want to say anything, but can everyone imagine instead of it being an aluminium hull it was fiberglass. What clown then would recommend just using two bolts to fill the holes? Get it welded, sure there's what a 100 ml of paint needed to prime the raw aluminium. But cheap fixes like this are major red flags to us surveyors. When I see repairs like that it I start to wonder what else has been compromised on the boat.
Cheers