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Old 23-08-2011, 01:55   #16
Marine Service Provider

Join Date: Oct 2005
Posts: 1,659
Re: Mooring Buoy Holding-Block Weight ?

Bigger the better. 2 tonnes isn't large in either size or weight.

Concrete is fine as long as you spud the air out of it. As mentioned above if you just pour it into a mold it'll retain a lot of air so lose that and it goes from OK to damn good.

A 'spud' is like a vibrator, yes probably the vibrator you are thinking of, a ladies personal friend one might say. The concrete ones buzz away as you pour the concrete and it makes the air rise and come out. You can usually rent one for a couple of hours quite cheaply. I doubt diving into the girlfriends drawer when she isn't looking would have the power for concrete. Did I say that all nicely enough?

Steel is also good especially in deeper waters or when there is a soft bottom. That will often sink into the mud and increase the holding hugely. Rust shouldn't be an issue as you want a stinking solid lump of something. Train wheels are very good but you'll probably need a few of them. Some old huge flywheeel is a goodie as is a forklift counterweight. If you go with a counterweight make sure there is enough water over it at low tide, you'd look pretty stupid running aground on your own weight.

If going concrete and making your own, which is easy to do, try to make it flat or do-nut shaped and with a concaved bottom if you are on a soft bottom as that will create a vacuum and increase the holding. Use some reinforcing stell in it and into that tie a coule of the biggest sized mooring lugs you can, 2" is good. Use big as they last longer and put in more than one so when one wears out, assuming it does, the block is reuseable and not becoming seabed clutter.

Also don't muck around with bottom chains less then 1", get some old ships studlink and use that. It'll last so much longer and I've seen bottom chains last over 20 years comfortably. Less than 1" and you'll probably have to replace it a lot more often.

From the bottom chain (length being the same as water depth at high tide long) chuck in a length (again water depth long) of 5/8" or 3/4", if you have a bigger boat, of a good open link chain and then to a good sized headrope, nothing less than 3/4", with chafe protection on it. Rope to be another water depth length plus waterline to your bollard. Small rope off that to a pick-up buoy. All done, clean simple and very very effective. Adjust lengths to suit water (mostly waves) conditions i.e. if it often ugly go long, if flat water and only wind you can shorten a bit.

Put a good swivel at the top of the chains between them and the rope, that will eliminate any twisting issues. Use a big swivel, anything under 1" is probably a little small.

And use black or sometimes called 'self-colour' chains, not galvanised. They last longer.

The idea of using a the staged chains is to soften the boats ride in crap weather. If it's set up right the studlink on the bottom will only come into play in nasty weather and the block will have no load on them except in horrendous extreme weather. As the weather gets worse the boat leans back on the mooring so it has to lift an increasing amount of weight so staging the chains allows it do to this without suddenly going fro some load to a huge load, hence the softer and safer ride for the boat.

The idea behind the lengths is you effectively end up with a 3:1 scope, again a softer ride for the boat and better holding.

That does exclude local regulations and swing room constraints if any apply. Check those out 1st, there maybe (usually is) some silly rules somewhere to trap the unwary.

I was a mooring contractor looking after 6000 odd moorings and the above is common as muck here. They last 3 years easily and next to none ever wonder off, those that do usually do so as the owner didn't check his head rope now and again i.e chafe. Many of those moorings are just off the beach and beyond them the only wave break is Chile, 6000 naughtycal miles away. I now supply the mooring dudes, which isn't as much fun but a lot drier and warmer in winter
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Old 23-08-2011, 03:40   #17
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Re: Mooring Buoy Holding-Block Weight ?

What you need, and how much of it, depends on the bottom. We have sand/mud around here and three train wheels sink deep and hold virtually anything. And that's with fore'n'aft moorings, not swing.

Re the chain, that's getting expensive and, anyway, is always more expensive than rod; thus we use rod. We take eight foot lengths of 19mm mild steel rods and bend in connecting loops at each end. The only wear happens where these loops meet. Thus it's easy to judge the extent of wear when pulled, and easy to fix those wear problems when necessary by welding in another arc of rod.

Sure beats checking and re-welding every link in a chain - and much cheaper.
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