Permanent (Storm) Mooring Question

Flynny

Petty Officer 3rd Class
Joined
Jul 22, 2011
Messages
86
I'm looking for some advice on a storm mooring anchor for my recently acquired 2007 Baylier 285 Cierra.

I think we've decided on a granite block, rather than concrete, per the harbormaster's request. We also would like to use that rather than a dor-mor or screw anchor because this is only an emergency mooring that will hopefully be seldom-used.

The boat has a 7200 pound dry weight, and I imagine it will be around 8000 pounds with fuel, water, and gear. The storm mooring field for my yacht club is pretty much exposed. It is in Boston harbor at the opening of a river. So it's not "open water", but its certainly not protected, either.

Everything I've read suggests either a 3000 or 4000 pound granite block. What would you say?

I also plan on using the Cyclone Dyneema mooring pendant attached to a longer 3-strand nylon pendant. Any recommendations for line sizes?
 

shrew

Lieutenant
Joined
Dec 29, 2006
Messages
1,309
There is no stretch in Dyneema. That is going to transfer shock loads onto the cleats and (if installed) chocks). If a chock or cleat pulls then this can cause a cascading failure. The pennant will now be pulling on rail stanchions. These will fail. pennant is sawing across exposed screws, bolts, ripped fiberglass deck. This will eventually cause the pennant to part.

You are better with nylon pennants, which will stretch and absorb load gradually. It is better to double-up with 2 on each side. Make sure they are independently attached. I would consider making one set about 2-3 inches shorter than the other. This will begin to load the first set and allow some stretch, then when stretched far enough, the second set start taking tension and reducing the tension on the first set as it is distributed more evenly across all four.

1" line won't stretch enough for a boat that size and we're back to shock loading the hardware. 1/2" line will stretch better. 2 x 1/2" is still the equivalent of 1", and works more effectively as I've described above. If it is a true named storm, you will probable need to replace the pennants after the storm. Repeated loading and unloading stretches line until there is no stretch left. This is when it is time to replace.

The key during these storms, even on a mooring, is scope. I've seen storm surge rise so high, that the ratio of scope was so low that each swell would lift the boat and the mooring with it. You can watch boats slowly 'walk' backwards in a bad storm. I witnesses this with both Hurricane Irene and Hurricane Sandy in Long Island Sound. The storm mooring pennants should be very long. I would use as long as possible, before I starting getting into the boat behind me.
 
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Ned L

Commander
Joined
Sep 17, 2008
Messages
2,266
I can't improve on what Shrew wrote. Good advise.
 

Flynny

Petty Officer 3rd Class
Joined
Jul 22, 2011
Messages
86
Thank you for the advice, Shrew. I appreciate the insight on the nylon line size. I think I will probably go with two half inch lines, like you suggested. I'll make one a bit longer than the other.

As for the Cyclone penchants, the idea is that they're only for the last few feet of the penchant, because dyneema can withstand much more abrasion. See the attached picture.

So I'll go with two of those, one on each nylon pendant. The nylon stretches and absorbs the shock, and the dyneema ensures the lines don't abrade and fail (Like the lines on 5 other boats did at my yacht up last year...).

By the way, penchant or pendant?
 
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Ned L

Commander
Joined
Sep 17, 2008
Messages
2,266
It is "pendant". I would recommend real good chafing gear.
 
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