Backing Plate Size?

WhatTheFoley · #1 (**permalink**) 04-27-2009

Hello,

Made a weekend project out of servicing the spinnaker winches on my boat. When I bought the boat I noticed that there were no backing plates on these winches. I hadn’t done anything about it, mainly cause we haven’t had a chance to play with the spinnaker yet, and figured I’d add a backing plate when I took them off to service them.

The question I have is... what is the rule of thumb for backing plates? I've tried to research the topic, and haven’t found all that much out there (I didn’t have too much time to research so forgive me if I've missed some obvious resources).

The winches measure about 5.75" in diameter (Barient #18). I was thinking about a 6.25" piece of 3/16” or ¼” aluminum? Does this sound right? Would Stainless be better?

Thanks for your comments!

blt2ski · #2 (**permalink**) 04-27-2009

You are going to get two trains of thought here. While both agree backing plates are needed, how you get there is another!

All of my winches have BIG fender washers under them vs one big plate with smallish washers. The fender washers are to me what is really helping to hold the nuts from getting ripped thru the deck. This is not to say a big piece of metal or plywood would not help! BUT, you winches also are more of a linear pull vs an upward pull on a sheave/pulley of some sort, so IMHO, a backing plate is not needed as bad.

Of course, this is not saying a winch will not pull out or off of a boat.......

I like BIG washers along with backing plates, or big washers alone depending upon the item being secured.

marty

WhatTheFoley · #3 (**permalink**) 04-27-2009

Thanks for the reply!

I was going to put washers on no matter what. The reason I was leaning towards a plate instead of individual washers was that when I removed the winches the washers that came off were all bent and deformed. They were small washers so I'm sure using a bigger fender washer would have a better result, but it made me think that perhaps a plate might be better...

sailingdog · #4 (**permalink**) 04-27-2009

If you're going to go with a big backing plate, make sure that the plate is in full contact with the underside of the deck... If there are any gaps or space, you really need to fill it with thickened epoxy, so the strain is spread properly by the backing plate.

WhatTheFoley · #5 (**permalink**) 04-27-2009

Thanks for the heads up. I eyeballed it when I took them out, and it seems pretty flat. I'll definitely take a better look at it when I got to remount them.

Any thoughts on Stainless vs. Aluminum? I'm leaning towards Aluminum from a cost perspective (I'm really not racing so weight is not a big deal). If I go that way, what can I do to avoid dissimilar metal corrosion between the plate and the bolts/nuts/washers?

sailingdog · #6 (**permalink**) 04-27-2009

Aluminum is much easier to work with, and far less likely to cause hard edges along the fiberglass, which can cause fatigue and flexing... If you're worried about dissimilar metals reacting, use polyethylene washers cut from a plastic milk bottle to isolate the aluminum from the stainless steel and use lanocote or tefgel on the bolts to isolate them from the plate.

kaluvic · #7 (**permalink**) 04-27-2009

I made my backing plates the same dia as the base of the winches.
Then as Sailingdog says, I installed them in a solid bed of thickened resin, polyester with micro balloons, in my case.

Your bent washers may be an indication that they're not backed solidly.

WhatTheFoley · #8 (**permalink**) 04-27-2009

Sounds like Aluminum is a better way to go!

Thanks for the tip on the plastic washers. I've read a lot of your posts (saildog) about lanocote, so I figured that'd be the way to go with the bolts.

Does the size seem appropriate? If I go with 6.25" it leaves about a half inch worth of overhang from the bolt holes (IE from the middle of the bolt hole to the edge of the plate), is that enough bite?

WhatTheFoley · #9 (**permalink**) 04-27-2009

kaluvic: Sounds like I might be leaning towards the overkill side of things! Better safer then sorry I guess, good to know I can get away with a plate that is the same diameter as the winch...

kaluvic · #10 (**permalink**) 04-27-2009

You could probably get away with "rings" like giant washer with holes around it.
Some winches have the possibility of adding an electric motor to them, on mine this is done by inserting the motors drive into the center of the base.
Using a ring may enable this addition later with out changing the backing plate.