Winch Backing Plates

[MJH]

Last year I replaced my two primary jib winches and had a difficult time aligning the backing plate holes with the winch holes despite the backing plate holes being drilled using the new winches as templates and slightly larger.

The backing plates are original, free moving, a substantial stainless steel thickness, and difficult drilling even with cobalt drills. I also used a 90 degree square to drill the vertical holes through the fiberglass coaming after the old holes were filled with epoxy.

This year I plan on replacing the next pair of cockpit winches. I am open to any ideas on how to make this next replacement easier and it all depends on drilling the winch-backing plate holes perfectly aligned through the fiberglass. I should add that I have limited working room as the winch teak mounting pads are recessed down inside the cockpit coaming and access to the backing plates is limited as well.

Lastly, I want to use the original backing plates and not fender washers.

[Cheechako]

-The backing plate holes can be a bit larger than the bolt holes. I would say 10-15% larger in diameter is not an issue . You use a big flat washer anyway right? I would say for 3/8" bolt maybe a 7/16" hole.
-Aluminum is fine for backing plates, much easier drilling. Almost 2/3 lighter than SS. So in theory, if you are using 1/8" SS you could use 3/8" ALuminum to no deficit.
-Nylok nuts are a PITA, especially working in tight places. Use conventional nuts and lockwashers.

[stormalong]

Make a drilling template from thick paper. Put it against the winch and lightly tap with a ball peen hammer. That should cut through the paper, or at least mark it clearly.

Some winches do not have equally spaced holes. They have to work around the mechanism. Be sure to use the correct side of the template for drilling.

[Greatest Lakes]

Winches have an expected load position, where they designed the load to pull from. Holes should be a little oversize, it allows sealant room to keep things separated and seal best. Most cabin tops have fiberglass that isn't quite smooth underneath. If you have a solid backing plate, you can have uneven load placed on the glass. Using fender washers on each bolt rather than a large plate is generally easier to install, and reduces these uneven loads on the glass. I also use nylock nuts as they can't back off from vibration. Pretty unlikely anything will fall off anyhow due to the sealant even if you don't though. If you feel you have to use the original backing plates, your best bet is very sharp drill bits. Fastenall sells high quality bits individually if you know the size you will need. Ordinarily, you would want to lubricate and cool the cut with some kind of oil as well, but you don't want that to soak into anything.