Mooring Question

[lmitchell]

There is a mooring at my club that is available for rent. My question ... is a 1/2 inch chain strong enough for an 18,000 lb boat. I'm being told, "no problem" but my instincts tell me that seems on the light side for a boat of that displacement.

Thanks,
Lawson

[sailingdog]

Lmitchell-

It really depends. If it is G70 or G40/43 chain, it probably is just fine for your boat. 1/2" chain is pretty massive.

I doubt that your windlass uses more than 3/8" chain.

BTW, 1/2" G43 High-test chain has a SWL of 9200 lbs. I seriously doubt that the mooring itself can handle that much strain, unless it is a large diameter square-shaft helix mooring. The mooring system is only as good as the weakest link, which would probably be your mooring pennant.

[LittleMissMagic]

If you can get your hands on a Mar/Apr issue of Good Old Boat there is a good article concerning moorings. If I remember correctly, there is a formula for figuring out what size chain, weight, etc. you need for your boats displacement.

[Missionary]

Has the chain been inspected by a diver. Chain wears it may have started at 1/2 but has worn to only 1/8 in one place and may break any time. Inspection will ease your mind.

[merttan]

There are some unknown factors if you want to share;
Mooring weight.
Mooring line lenght.
Your boats hull height from the waterline.
Type (grade) of chain.

Then I may be able to make a calculation for safety of the chain for known/perfect condition. The known/perfect condition is being that we assume you don't have a weak link such as a weak connection on mooring weight or line, and your cleats are permanent to the boat...

Your boat is moored by the weight of the mooring post, suction of the mud at the bottom,chain strength, and the angle of mooring line (That's why they recommend using a 7:1 ratio for over night anchorages)...

[deniseO30]

I had the guys put 20ft of 5/8" for bottom chain and I have 5/16 for my 11,000 lb oday 30. the river here has a tidal rush up to up to about 8 knots.
I would rather the mooring move then the chain break because it just resets not too far away. when the chain breaks... bye bye boatie!

[sailingdog]

Merttan-

Not all moorings are weight depended, and the mooring anchor's material makes a huge difference in its holding ability. A 500 lb. block of iron is going to be far better than 500 lbs. of concrete, since iron is far denser and has a much higher effective weight underwater. Many new moorings are helical screw, and basically limited by the type of bottom and what size screw they used. In some tests these helical mooring anchors rated well over 20,000 lbs of resistance before yielding.

[CapnHand]

Originally Posted by LittleMissMagic

If you can get your hands on a Mar/Apr issue of Good Old Boat there is a good article concerning moorings. If I remember correctly, there is a formula for figuring out what size chain, weight, etc. you need for your boats displacement.

It was graciously posted here by the good people at Good Old Boat: http://www.sailnet.com/forums/showthread.php?t=36497