What size of cleat to hold a 40 tonne boat?

[Jamesuk]

Worried about the loads on the cleats the other day I started to think what cleats should a yacht have on the dock. We have 4 bolts running through a 316 Stainless Steel cleat. The cleats on the dock only have 2 bolts and appear to be Galvinised (Walcom cleats) Got me thinking: are they strong enough because in Palma and Plymouth where we are moored on occasions we have much larger "bollards" to tie up to which usually are bigger than the cleats on board the boat.

Any thoughts, Rules etc to go by?

Cheers

 

[jonjo]

I think cleats need to be sized inversely to the competence of the boat owner who abuses them and not to displacement.

During the whole winter at my last marina I saw a mid displacement Moody (say 6 tons) putting horrible loads on the pontoon cleats. The mooring lines were large diameter braided sheets, the vertical gradient to the bow fairlead was about 45 degrees and to make sure there the bow was held rigidly in 3D space another taught line held the other side of the bow with an opposing force. The boat could not move 3 inches without snatching.

 

[Neil_Y]

It's not the size of the cleat it's the size/thickness of the backing plate that counts. I've seen a cleat ripped through the deck of an Ovni, when a big swell came into a marine in Madiera. My 40' Bav cleats at the same time showed no sign of moving, although I was worried, you could hardly walk along the pontoons.
Using rope with a good bit of elastic stretch helps as there is less shock loading, I think this was why the Ovni's failed and in rough weather keep your lines as long as possible.

 

[Yngmar]

The pontoon cleats are bolted through the planks onto large galvanised steel bearers. In case of the main pontoons, the bearers are bolted into the concrete floats and in case of finger pontoons (due to the large leverage) into the galvanised steel beams forming the backbone of the finger pontoon.

The planks eventually rot and soften and then the bolts can have some wiggle room, causing the cleats to move slightly under load. I've observed this last autumn, told the marine office and they sent around someone to tighten the bolts.

The thing I have seen break is one of the four large bolts where the finger pontoon frame bolts onto the main pontoon. This was on a (typically) undersized finger pontoon with two 40 footers after a gale. You can inspect these yourself by looking down the gap between finger and main pontoons - one bearer was clearly missing a bolt, but the other three still held it all together.

When the pontoons are being replanked, you can see their guts. This is a Walcon main pontoon, without the steel beams you find in fingers, but you can see the cleat bearers:

 

[Lucky Duck]

When I was last in Brighton headed down channel one of the pontoon cleats was held in place using a ratchet strap, I decided it might be best to take a second line to a different cleat :ambivalence:

 

[Yngmar]

When I was last in Brighton headed down channel one of the pontoon cleats was held in place using a ratchet strap, I decided it might be best to take a second line to a different cleat :ambivalence:

That wasn't holding the cleat in place, it was using the cleat to hold the pontoons together. When the above described bolts attaching them to each other fail, the maintenance crew puts the strap on until they can get the bolts repaired.