Advice need on proper chain for a mooring.

S

sillawydna

New member
Hey everyone, hope you summer is going well. I’m looking for a little advice on chain for a mooring.

I have a 300 lb anchor I’ll be dropping to secure a mooring buoy in about 35’ of water in a protected cove south of Bellingham. All my research says to go with 1 ½ times the depth of the water with heavy chain that lays on the bottom, attached to a lighter length of chain that’s goes up to the buoy. I haven’t been able to pin down what exactly what is meant by light and heavy chain.

I’m thinking 3/8” for the heavy chain, and 5/16” for light chain. All chain is galvanized 30 proof coil. Does that sound about right?

Boat is a 22’ Cruiser.

Thanks for input!
Andy
 
Is this a 300 lb mushroom? The 22 would call for a 200 lb mushroom--but nothing wrong with going up in size. For the 300 lb mushroom the heavy chain would be 5/8 "and light mooring chain would be 5/16. For a 200 lb mushroom, the heavy chain would be 1/2" and the light chain would be 1/4. (The heavy chain is twice the size of the light chain). You will be OK using PC or BBB chain). The wind load on a C Dory22 at 64 knots is going to be somewhere just a little under 2000 lbs. To be safe if you want a block of concrete--it should be 4000 lbs!
I moved a 40,000 lb stern mooring with my large cruising sail boat which displaced about 70,000 lbs.

The length of the heavy chain is 1.5x the maximum depth. The light chain is the same as the maximum depth, and the rope pennant should be 2.5x the maximum depth. The buoy should support 2x the weight of the light (or riding) chain.

If the anchor is other than a mushroom, then some of the factors may change.

These figures are from "The complete book of Anchoring and Mooring" by Earl Hinz. I knew Earl and we corresponded extensively on his last edition of the book. He is conservative in his numbers.
 
If a cast iron pyramid, the same numbers would hold. If concrete--the holding power will be less and I would go to 500 lbs, and the heavier chain, with more scope--2:1 on the heavy chain.

The pennant should be doubled the second one about a foot longer than the primary as a "safety". The length of the pennant is often cited as 4x the depth--in sheltered harbors you may get a way with less.--Also a lot depends on bottom conditions. Where there is silt or mud, and the anchor can work its way down, is better than sand--and the worse is rock or gravel bottom.
 
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