Backing pads

[zoidberg]

I've removed a pair of 'OK' foredeck cleats - close to toerails about 3 m. from bow - and will mount a pair of 'much heftier' 300mm replacements onto teak pads on deck, using 4 x 10mm s/s bolts. These to take anchoring/mooring snubbing loads imparted by a ~3-ton boat kept on a trot mooring.

I'll mount substantial backing pads under the 12mm grp deck, and I have the choice of 48mm teak, 2" oak or 2 x 25mm epoxy-coated ply.

What does the team think is optimum - and why?

 

[thinwater]

I'd go with 10-12 mm structural fiberglass plate is all that is required. If I really wanted it strong, I would mount the plates with thicken epoxy. Then the plate becomes a part of the hull and can share the sheer load. Assuming the hull is solid glass, they shroud extend about 1.5 inches outside the bolt area.

The bolts will break before this gives. I know because I have done the testing. Wood, on the other hand, has a tendency to compress and the bolts loosen. Also, if the backing plates are in an anchor locker or open to the bilge, they will get wet or feel humidity.

 

[B27]

Raising the cleats on teak pads means the bolts are no longer in shear, there is a more significant turning moment trying to distort the deck.

 

[doug748]

Personally I prefer stainless plates, they are probably overkill on a low cleat and fine for something raised from the deck.
I think there is a point were the deck would give well before the cleat; fibreglass has a finite strength and you risk putting in a lot of bulk to no great effect.

 

[PCUK]

I would use 10mm epoxy coated steel.

 

[Neeves]

I would use 10mm epoxy coated steel.

I think you mean, and I under stand you to mean, stainless steel as per Post 4

and I agree with both of you.

I'd actually add a sheet of heavy duty fibre glass cloth, with the stainless plate embedded in the thickened cloth and good overlap - as per thin water.

We did exactly this for the pad eyes for our prodder bob stays. Our pad eyes were on a flat hull section - much more difficult for a horn cleat which will inevitably be at the deck/hull interface. I might suggest instead of a 'simple' plate - use a piece of cloth covering the interface and a 'L' section plate (if that makes sense) embedded in both hull and deck.

Jonathan

 

[boomerangben]

It all depends on the over all geometry of the cleat, height above deck etc. for perspective, using the weakest A2/A4 grade steel for your M10 bolts, 2 will support the entire displacement of your boat (just). A piece of your deck (assuming it’s solid and not balsa/foam cored) 4” wide will also support your entire boat. In theory, penny washers would be sufficient under the aft end of the cleat for it to be strong enough to hang you boat from it. They would need to be well bedded onto the underside of the deck. So from a strength point of view, you could pretty much use anything that gives more area than a penny washer. I don’t think I would brave enough with just penny washers but any of the suggestions above would be more than strong enough.

 

[srm]

I used to use alloy bar, around 30mm x 3mm (or whatever the local engineers have in stock) as easy to cut/drill and would not compress or deteriorate. This was always bedded in car body filler paste and bolts tightened before it set to give complete contact with the hull or deck area.

 

[thinwater]

I should have questioned "why the pads?" As B27 points out, they actually weaken the bolts. The only reasons are:

• Alignment with something. Not likely.
• Looks. Not a reason.
• Leaks. Will probably make it worse unless the pads are GRP bonded to the deck.
• To spread the load on a cored deck. I think this is solid.

So I think lose the pads.

A lot of this depends on geometry. In fact, one option that is often overlooked is skipping the backing plate, laying up a lot of glass on the inside, and using double thick fender washers. This can be the smart way if space is tight and the surface is curved (not flat) on the inside. But it is tricky in tight spaces. If you think about it, the backing plate on most keel bolts is just a big washer. It's the heavy glass that does the work.

 

[PCUK]

I think you mean, and I under stand you to mean, stainless steel as per Post 4

and I agree with both of you.

I'd actually add a sheet of heavy duty fibre glass cloth, with the stainless plate embedded in the thickened cloth and good overlap - as per thin water.

We did exactly this for the pad eyes for our prodder bob stays. Our pad eyes were on a flat hull section - much more difficult for a horn cleat which will inevitably be at the deck/hull interface. I might suggest instead of a 'simple' plate - use a piece of cloth covering the interface and a 'L' section plate (if that makes sense) embedded in both hull and deck.

Jonathan

No. Mild steel.

 

[rogerthebodger]

No. Mild steel.

I used mild steel backing pads on my old ferro boat painted with metal primer and are still rust free

 

[zoidberg]

Lots of good points above - which is what I'd hoped for.

Now, 'metal primer'. Interesting, as I have some left in two pots.

What happens to stainless steel if painted with primer.....?

 

[rogerthebodger]

What happens to stainless steel if painted with primer.....?

My simple answer is I don't know as I have never painted stainless steel as I oly use 316 even above the waterline.

I tend to polish the stainless steel as unpolished can tarnish.

Mild steel can also be galvanized and I have also acid washed galvanized mild steel and had it powdered coated black to give it a nicer looking finish

 

[Neeves]

I think I might argue with some of the recommendations.

The location is described as 12mm GRP. We don't know how old the yacht is, we don't know how well it was built and 12mm GRP, how much glass how much resin. We similarly don't know what the owner is going to use the cleats for (and whether the deck is actually strong enough). We can assume the deck is strong enough - but the fact the owner is asking the question and is intending to use substantial, 4 x 10mm bolts for each cleat, suggests he is looking for something fairly bullet proof - so maybe drogue in rather unpleasant conditions? I know the OP says for mooring - but what else might they be used for - that is outside plans?

If you follow Zoidberg's posts it is as if he is refitting (not sure that is the word) a smallish yacht for Round the World, or NW Passage, across the Arctic or a Round Antarctica record of some sort. He is not fitting out a project yacht for re-sale nor weekend sailing.

My answers are always belt a braces.

I have no problem with mild steel as its technical characteristics are not so different to 316. It just that if anything moves it will eventually corrode and I really don't know Zoidberg well enough and know nothing about his installation skills (and luck) (so belt and braces - if it is a critical application - pay the extra). If it might be a critical application forget the penny washers - go for a decent plate.

Jonathan (the pessimist - and one who used 6mm anchor chain on a 7t cat )

 

[zoidberg]

I'm tempted to mention 'the camel - a horse designed by a committee' but that would be unkind discourteous. I LIKE asking questions on here, for I frequently find slants and insights that are new to me. I'm not proud....

My refurb project doesn't have a Grand Plan in mind. However, the basic hull is robust/tough as old boots, and so the gear I'm fitting ought also IMHO to be robust. The original cleats are neat - two bolts each and no backing plate or even large repair washers - but suited to marina-finger pontoons and not bouncing all night in an exposed, gale-swept and unwise anchorage in the Isles of Scilly or being towed in from some where by a lifeboat with e.g. rudder failure or horizontal mast....

The original deck-mounted centreline samson post was OK, but the fastenings were suspect and it was in the way of the new inner forestay fitting.

My shiny new mooring cleats just WILL NOT FAIL.

I've also collected rather a lot of 'useful bits' over the years, and want to make use of some of them. I don't expect I'll do this 'refitting' job again.... so 'belt and braces' is appropriate.

Now, the fastenings on the quarters intended for attachment of the VERY robust Jordan Series Drogue.... they need to be 'bombproof'. And it is always possible I'd want to use them to tow someone else. I've taken deeply experienced pro advice from a structural engineer who's into modifying race boats, and that involves quite a number of layers of biaxial carbon cloth. Again, erring on the side of 'more than sufficient'.

And it keeps me off the streets.

post scriptum : I, too, have changed up to 6mm chain, which is proof-tested stronger than the weebly 10mm stuff that came with the boat..... which is half the weight and less than one-third the windage of Jonathan's block of flats.

 

[srm]

My refurb project doesn't have a Grand Plan in mind.

Oh dear, there was me thinking we might see you in Praia this summer with the Jester Challenge. Now where did I get that idea?

 

[Neeves]

I LIKE asking questions on here, for I frequently find slants and insights that are new to me. I'm not proud....

And it keeps me off the streets.

post scriptum : I, too, have changed up to 6mm chain, which is proof-tested stronger than the weebly 10mm stuff that came with the boat..... which is half the weight and less than one-third the windage of Jonathan's block of flats.

I'm with you -

and your chain is better than my chain, mine is only as good (actual strength) as the 8mm it replaced - I tested them both.

Jonathan