Backing pads size

[oldbilbo]

I'm looking to fit 'rather substantial' backing pads under the foredeck below the new mooring cleats I'm fitting, which will be used with paired boat ropes on a fore-and-aft mooring.... and I'm musing over how large to make 'em.

There are 45mm x 300mm x 125mm ply pads above the deck/below the cleats, which bring the cleat-base to the height of the toe-rail, and a 3mm s/s plate for chain and warp to run over, protecting the teak of the toe-rail. Six 8mm s/s bolts....

I'll be using solid 12mm GRP sheet below the foredeck, which I just happen to have lying around ( ! ), and I could make the under-deck pads the same size as those above. Or I could make 'em somewhat larger.....

If so, how much larger....?

What does the team think?

 

[sarabande]

I suspect OB is thinking of possible towing situations as well as mooring.

If there's any risk of torsion (perhaps bcs of the height of the cleat above deck level- 45mm plus height of cleat) then I'd extend the GRP sheet to as near the hull-deck join as possible so that any large stresses are transmitted to a very very tough piece of moulding. Not that the C27 deck is very flexible, anyway...

 

[johnphilip]

Is the foredeck solid or sandwich?

 

[Ardenfour]

i wouldn;t make them the same size - any flexing of the deck would create a 'hinge' effect at the edges of the pads which could lead to stress cracks. Bottom one larger

 

[Blueboatman]

I would make a card template and shape ONE triangle of GRP , if you can get it in there past any bulkheads...(?). This way, everything gets tied together by the thru bolts. Might as well bed it on epoxy paste too, pulled up nice n tight with some over length bolts...
( By the way, over length bolts. Extra penny washers and nuts are brilliant for attaching bungee or netting.. I keep a storm jib and spare chimney up there in otherwise wasted space agin the deck head )

You are dead right about the towing btw.. The forces can be significantly huge and yaw too .

Why fret, build it TonkaToy Tuff eh? Jobs a good 'un

 

[oldbilbo]

Thanks, guys. This is the general arrangement....

The deck is solid layup. It is a minimum of 10mm thick and, as shown, in places twice that. The expression 'clyde-built' comes to mind.

I take Ardenfour's 'hinge-effect' point fully on board.... and all of Blueboatman's - except I cannot quite visualise what is meant by 'ONE triangle'. P'rhaps he'd kindly expand?


In an afloat mooring situation, the boat ropes will pass through the cleats a la 'closed fairleads' and on back to a hefty foredeck post. In wilder situations such as being towed, this will be backed-up further aft. Thoroughly. Same thing with anchoring, using a nylon 'snubber' or two, with loads spread aft.

Alongside a pontoon now and then, the cleats will serve as simple cleats, and I reckon loads in such situations - even surge loads, when stretchy springs and snubbers would be used - should be well within the load-capacity of the above arrangements.

 

[Blueboatman]

Sorry, poorly described. What I am suggesting is instead of cutting two oblong backing pads, why not one continuous one that spans the whole under deck area? Thus strength for each cleat is 'borrowed' from the other as well. You would need to key it all up a bit and apply useful amounts of epoxy paste to mayonnaise consistency ..blurry strong tho

My last boat I fitted oversize aluminium cleats from a wrecked marina! And a stout oak Samson post

My boat previous to that, a wee Corribee, ( with custom 6mm stainless stemhead arrangment) a friend towed half way down the Portugese coast once, behind a large Rassy with plenty of horsepower , at nigh on Corribee hull speed. She towed heavy but well!
Make em as strong as you can , is my experience..usi g every trick and opportunity to reinforce and spread the loads into the whole bow section.

 

[oldbilbo]

why not one continuous one that spans the whole under deck area?

Good idea. PM sent.