Picked up a new HB unit today because the side imaging unit i ordered with my boat was mistakenly replaced with a regular 2D sonar unit.  I need to run the cable for the new transducer.  This screw in the pic that holds the cable....should I just squirt some silicone in that hole before re-tightening when I run the new cable?  Or is there something else I should use?  Thanks!

Silicone would probably work fine for that small of a screw but I like 3m 5200 "for all your thru-hull applications" 

 

Wheres that screw in relation to the water line ?

5 minutes ago, TnRiver46 said:

I like 3m 5200 "for all your thru-hull applications"

Only if you are 5200% sure it never needs to come out.  

It sits a bit above the usual waterline, but I’ve no doubt it gets plenty wet. 
 

 

Silicone would be ok. Just use a decent one.  I’d personally use the 3m 4200. The 5200 will definitely do the job but is considered permanent (as in not able to be removed).  Whether that’s actually true I can’t say as I’ve never had to  take something apart where 5200 was used. 

Just now, BassWhole! said:

Only if you are 5200% sure it never needs to come out.  

Well crap, I’ve only had the boat a couple months and I’m already pulling it out.  Probably a little less than 5200% chance I’ll need to do that again...

1 minute ago, Cyclones said:

Well crap, I’ve only had the boat a couple months and I’m already pulling it out.  Probably a little less than 5200% chance I’ll need to do that again...

LOL. We had to drill a 4" hole in the bottom of the 26' Center Console we fished out of when it was brand new to fit the thru hull transducer. Felt a little nauseous, measured 20 times, still have the "hockey puck" that came out somewhere. I think we used 4200 if I remember correctly. 

Loctite makes a very good silicon that can be submerged.  I used to for aquariums. 

 ANYTIME, you make a hole in your hull, put silicon in it, before the screw and again on top of the screw.  

as a civil engineer we squirt Sikaflex into some of our structural members to try to keep rust at bay.  that stuff last forever, and stay pliable.  it is really good stuff.  

 

I do what @Way2slow does.  but honestly I bet that hole would be fine dry.

On 5/7/2021 at 4:42 PM, BassWhole! said:

Only if you are 5200% sure it never needs to come out.  

I use 5200 all the time it’s a adhesive sealant not permanent as people claim. My motor has been remounted several times over the years with JP changes and removal, with no issues. 3M makes an adhesive removal solvent also. 
 

I do recommend 3M4200 for most sealing applications but 5200 is definitely more reliable under the water line.

 

*********************************************
To answer the OP’s question for small screws like that; 

remove the screw

put a light coating of sealant on the threads 

screw it back into the hole 

The turning on the screw seals the screw head with sealant. Allow at least 48 hours to dry, but 7 days is better.

 

Thru bolts require much more sealant. Put sealant on what your are bolting to transom, under the washer, under the bolt head. Wipe off excess. Let dry for 7 days.

Years ago I used 5200 to seal the bolts on a jack plate.  About a  year later I removed that jack plate to install a different one.  In doing so, I also removed several large chunks of fiberglass from the transom.  The other jack plate covered them, but I still didn't like the idea of it ripping off the fiberglass.  

5 hours ago, Way2slow said:

Years ago I used 5200 to seal the bolts on a jack plate.  About a  year later I removed that jack plate to install a different one.  In doing so, I also removed several large chunks of fiberglass from the transom.  The other jack plate covered them, but I still didn't like the idea of it ripping off the fiberglass.  

I’ve only had aluminum boats. That may be the difference. They had to initially remount the motor 3 times on my Triton. The only sealant that worked was 5200