Drilling holes for transom mtd transducer

[kaliona]

I have a fiberglass boat and am about to install a new transducer. I've read several threads on how one should drill and attach the transducer. One method, which seems to be the "correct" way, is to drill oversized holes, fill with epoxy, then drill pilots in the epoxy for the smaller transducer mounting screws, and finally install the screws with 3M 4200 or 5200 for a watertight seal.

My questions:
1. Is there a certain kind of epoxy I should use? I'm assuming I have to wait for the epoxy to cure, then drill the pilot holes.
2. Won't the epoxy crack when I finally drive in the mounting screws?
3. Are all epoxies the same? Or should I get a particular brand for this application.

I have a West Marine nearby so I'm hoping I can get everything I need there.

Thanks

 

[bitone40]

Re: Drilling holes for transom mtd transducer

Great questions , I was actually going to ask the same ones today to mount my raymarine transdu. I will follow this thread for the answer. my method was the same as you said but i after i drill the oversize hole i was going to run a course thread screw or bolt in there to make grooves in the wood and then force some 5200 or gorilla glue into the hole and let it dry.. and after that then drill a slightly smaller hole and then cover the whole mounting plate with 5200 and attach with the mounting screws .. running the course threaded screw or bolt will give a better grip to the 5200 or gorilla glue when forced into the oversize hole and will be harder for the "plug" to pull out . but i will follow for some more options ..

bd

 

[Chris1956]

Re: Drilling holes for transom mtd transducer

Normally you drill oversize and plug with epoxy, only if you have a cored hull. I would drill correct size pilot holes, dip the screws into standard epoxy or marine silicone caulk and install screws. Wait for caulk or epoxy to dry and away you go.

 

[kaliona]

Re: Drilling holes for transom mtd transducer

Can you explain what a cored hull is? I'm not sure if I have that - or not.

 

[Chris1956]

Re: Drilling holes for transom mtd transducer

A cored hull is a sandwich of a lightweight wood, like balsa, with fiberglass skin on both sides. Since balsa rots easily, you need to take special steps to protect it from any water intrusion.

A standard hull transom has a plywood or solid glass transom.

 

[Pez Vela]

Re: Drilling holes for transom mtd transducer

I believe that the "oversized holes" method to which you refer is an improvement, but I believe a better way is to avoid making any holes in the transom whatsoever. If a transom mount transducer is your only option, I would consider using an adhesive to mount a small thin plate (polypropylene?) into which you may drill and mount the transducer. I made the "screws directly into the transom" mistake 20+ years ago, and I regret it to this day. Perfectly sealed holes in the transom are hard to come by. I switched to a thru-hull 'ducer and have never looked back.

 

[Seaclutter]

Re: Drilling holes for transom mtd transducer

The epoxy plug is the best even if the transom is fiberglass and wood. Dipping the screws in silcon is good but over time they can let water get in and it will eventually soak into the inner wood of the transom. Any standard two part epoxy will work.

 

[Fl_Richard]

Re: Drilling holes for transom mtd transducer

I've always been told, drill hole, coat screw with 5200 and tighten to just under snug. Come back the next day and tighten fully.

So far no rot

 

[Triton II]

Re: Drilling holes for transom mtd transducer

I agree with Pez Vela, it would be preferable to mount a stand off onto the transom and mount the transducer onto that.