Installing new depth/speed transducers

[Dave]

Hello all,I have a 1988 Hunter 28.5 with what I believe is the original depth sounder. It was made by Signet Marine. The plastic face of the unit is warped and cracked from sun and rain and allowed water into the unit which caused it to fail. I have a replacement Raytheon Raydata depth/speed sensor.I would like pull the boat out of the water and install the new transducers.Unfortunately the new ones are a different size than the old ones. The original hole sizes are 1-7/8" and 1-5/8" while the new transducers each requre a 2" hole. I would like to enlarge the original holes rather than drilling new ones, to minimize the total number of holes in the hull.It would be relatively easy to buy a 2" hole saw a drill new holes, but I can't figure out how to widen these original holes, because hole saws require material in the middle to guide the bit. To make it more difficult, I want to do the work while the boat is hanging in the hoist, so I don't really have time to temporarily fill the holes with epoxy and come back and drill them out later.Any ideas out there?Thanks, Dave

 

[Stevec]

I did the same thing earlier this year......

on my 37. Original STOWE instruments crapped out and I replaced them with Rayethon ST60's which required larger holes. On the bottom exterior of the hull I traced the outline of a 2" hole over the smaller existing holes. Bought a few 'rasp' bits for my electric drill and ground the excess material away until I reached the outline of the 2" hole. Then used 60 grit to finish off. You don't have to have 'machined' holes for the project. The key is to use enough sealant so that it squishes out all around when the housing is installed. Incidently, the ST60's self sealing thruhull for the knotmeter is great. When you remove the paddle for cleaning, you don't get that flooding stream I was used to.. Use a sealant that is designed for 'below the water' but NOT the 5200 that will never come off..

 

[Allan Hadad]

Two ways to drill the larger holes

The two ways I have used to enlarge a hole:1.) Use the 2" hole saw to drill out a piece of plywood. Use that as your template. Have someone hold it over where you want to drill. It will guide the hole saw enough to get it started in the hull where it will continue without the center bit.2.) Put a board on the inside of the hull and have somebody stand on it (No, not directly where the hole saw will come through). The center drill will be guided by that board until you cut through the hull.Allan

 

[Justin - O'day Owner's Web]

reconsider the 5200...

I replaced my through hull ducers this winter and I used 3M 5200 as the bedding compound. 5200 is simply not impossible to remove, and I feel that the added security of bedding with it outweighs the diffifculty in trying to get it undone. For those of you struggling to get a 5200'd item off your boat: go to your favorite large chain discount store and buy a package of guitar strings. Take one of the heavy ones, the ones with the copper winding around the core, and wrap each end around a broken pencil. Then use the guitar string as a garrotte to cut the object free from your deck. A razor blade will get rid of the residue.Justin - O'day Owner's Web

 

[Thorp Thomas]

I do it the quick and dirty way

When time hang time is clicking away I put on a heavy glove and steady the hole saw over the existing hole and slowly start it. Once it’s started I speed up and cut right through it. It works for me....

 

[ES]

Bang in a wood plug

Bang in a tapered wood plug with a pilot hole in the middle, drill it with a hole saw. Or plug the hole with fast setting epoxy putty (hardens in about 5 minutes) then drill it with a hole saw.