Aluminium winch backing plates, how big, how thick ?

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Boo2

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Hi,

There's not much depth between the cabin roof and headlinings on my boat so rather than use ply I want to use alloy plates as winch backing pads for a pair of 30 size Lewmar winches.

What was fitted before was a pair of flat strips of 6mm ply with penny washers but I want to do better than that. So, q.a.t. : Aluminium winch backing plates, how big, how thick ? And while you're here, which alloy ? And if the answer to that is anything other than 6082, where from ?

Thanks,

Boo2
 
Boo2 said:
Hi,

There's not much depth between the cabin roof and headlinings on my boat so rather than use ply I want to use alloy plates as winch backing pads for a pair of 30 size Lewmar winches.

What was fitted before was a pair of flat strips of 6mm ply with penny washers but I want to do better than that. So, q.a.t. : Aluminium winch backing plates, how big, how thick ? And while you're here, which alloy ? And if the answer to that is anything other than 6082, where from ?

Thanks,

Boo2
Click to expand...

same as dia of winch & any grade 1/8" thick will do the job
 
Anything between 4-5mm (don't think you can get alloy in imperial thicknesses).

Don't forget to round the corners, if square. I'd double the area of the winch-base, but it's very dependent in layup, composition and thickness of the substrate.

Most good layups have integral ply within the thickness of the winch-base mounting, in which case penny washers do the job OK.
 
Aluminium and salt water don't go well together. You'll need some special metals primer and a good quality paint. I use Hammerite smooth, but rumour has it it's nothing special these days so I guess any enamel/good quality gloss would do.

The steel bolts and ally pad will have a "dissimilar metals/electrolyitic corrosion" potential which is why the OEM fit was ply/penny washers.

If you used 4mm SS you could tap threads into the back pad and use locknuts on the exposed threads after you bolt the winches down. 2mm SS pads, slightly over the winch base diameter with clearance holes drilled would work as a "super" penny washer. Smear winch base with silicon sealant. Bolt down with nylocks. Simples!
 
I much prefer stainless steel backing plate, 6 mm is easy to find and don't forget to include a bedding compound to ensure the load is spread over the entire plate without point loading.

Good luck.
 
You're not installing them underwater but inside the cabintop. If you seal the underside of the winch properly with butyl or Sika Flex they will never get wet.
Aluminum is fine, any alloy will work but the 6000 series you mentioned is a marine alloy. I would coat the threads with TefGel to allow easy removal in the future.

If the cabintop is cored best to overdrill and epoxy fill to keep the core dry and rot free if there is ever a leak.
 
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