Backing plate?

[Norman_E]

I have just bought a Spinlock XTS/2 clutch to add to my boat and allow reefing lines to be brought back to the cockpit. It bolts on with four 8mm bolts. I could just use washers and nyloc nuts underneath the deck, but it occurs to me that a backing plate made of 1.6mm or 2mm stainless steel might be called for to spread the load. I can make one. The question is, should I? What have others done?

 

[thomashoebus]

Washers will do the trick since the load on the line isn't direct anymore and in line with the the deck.

 

[DanTribe]

If it is a foam or balsa sandwich deck you should really remove the infill to ensure a solid fixing or the fill will be crushed and allow water to seep in. If that is done, penny washers will do the trick.

 

[snowleopard]

Fore heavily-loaded items I get a strip of aluminium, say 25mm x 4mm and drill it to match. This sort of strip can be bought in any big DIY store.

 

[gardenshed]

Nice big backing plate (extending fore and aft of the clutch) and penny washers to spread the load to the backing plate, all made from the same material (stainless) would be my recommendation. Even although the pull is along the deck, there will be a twisting moment (pulling up the rear, pushing down the front) and the backing plate will spread this load far better than washers. Don't over tighten the nuts and crush the deck laminate.

 

[Skyva_2]

1) You could ask Spinlock, though their website says consult your boatyard!

2) These are shear loads which penny washers don't handle that much better than small washers; they are better under tension. If it is really highly stressed, like a sheave or winch, I would consider a 1/4 " teak plate glued to the inner deck, with a SS plate in addition. In any case I would glue the plate in place. Belt and braces, but why not, you would then be confident in the fitting.

In practice I would guess reefing lines have less tension than most controls because of the friction in the system, but I am happy to be corrected on this.

All the cautions on foam or balsa cores are very relevant.

 

[Norman_E]

Thanks to all who replied. On balance I think I will put in a backing plate. At least it cannot do any harm. The deck is balsa sandwich, but the location for the new pair of clutches is between two other sets, and I think the area has already been reinforced. I will find out when I drill the holes.

 

[charles_reed]

Better

to use marine ply or aluminium, always making sure the corners are rounded.

Ply is better because it deforms under load, whereas SS or aluminium have hard edges which cause delamination of the GRP.

 

[Blueboatman]

Re: Better

So bed the ally or s/steel plate in a (very) thin layer of sikaflex or better is 2 part polyester car filler putty,same with stantion backing plates etc

 

[charles_reed]

Ouch

Most boats have the balsa sandwich replaced by marine ply in high stress areas, such as winches and clutches.

If not you need to insert a hard plastic sleeve from above to take the compressive load. I always bond in the spacer with epoxy (even though it doesn't bond to plastic it waterproofs) the superior alternative is to use Sikaflex.

Don't use SS on a sandwich, the rectification can be expensive.