Fill hole with what?
 

We just had to drill a 1 inch hole on the transon on my sons polar for his new fish finder and I'm not sure what to use to fill it We don't want to buy a can of insulation for just a very small hole What else can we use Thanks

above or below water line?

Whats in the hole? What is the space to be filled?

Is it the cable above water line? Fill it with 5200 or 4200 or silicone and put one of those stainless cable feed covers on to make it pretty.

Above the water line, it to get the transducer cable thru

Do like Skunk said.
Get a clam shell cover large enough to cover the hole after filling it with 5200, 4200 or a premium grade silicone.
You may need to replace the cable later in time.

1" is a big hole for a cable. I'm guessing you had to get the plug through. Was it wood or composite cored? I'd coat the inside of the hole with epoxy before putting in a filler. Might even be able to get a transom drain tube to fit

Definitely do what's stated here (coat raw core material with epoxy or a reduced resin) then fill with 5200 and clam shell over hole.

For large holes you can also make 5200 go further and fill easier by mixing in some sawdust. (The coarser the better) Squeeze 5200 into a mixing cup, add no more than 1/3 by volume sawdust. Mix thoroughly so all sawdust is coated with the 5200. Trowel into the hole after coating the inside of the hole with epoxy. Hold in place with plastic wrap and scotch tape until the filler has set up so it doesn't run out. Remove the plastic wrap, cover with the clamshell and you're good to go. :beer:

Epoxy the inside of the hole and put a single hole laboratory stopper under the clam shell. Secure enough yet easy to remove.

https://www.medical-and-lab-supplies...ole-qty-1.html

great idea, jv. don't tell it's going on a boat, it'll be $10.76

I like the idea but 5200 is impossible to remove some time in the future wouldn't 4200 be better?