It is best that a mooring be set up to give 3:1 to 5:1 of scope, just like an all chain anchor rode. Recommended practice is that the bottom ½ to 2/3 of the chain be heavier than the top section.
The mooring rules (Nayak Yacht Club?) recently posted in this discussion called for something like 30 feet of 5/8 chain topped by 20 feet of 3/8. I presumed that was for moorings in 10 to 15 feet of water. Trust me, youll get catenary if the mooring is set up right. When my 25 lived on a mooring in Delaware Bay, I had a 300 pound mushroom anchor, 40 feet of ½, and 20 feet of ¼ HT chain in about 15 feet of water with 3-4 feet of tide. During the course of the summer, the mushroom would work bury itself into the bottom, and it had a 5 foot shank on it. I helped a friend anchor his Benneteau 35 for Hurricane Isabelle, using a 66 lb. Bruce. We set it out about 4 days before the storm to let the anchor dig in. When we came back after the storm (the eye passed over us with about 60knots of wind) the boat had not moved. Used the windlass to raise the anchor, and the breaker tripped with the chain vertical and the bow going down. Tried raising the anchor by leading the trip line to a cockpit winch. Nothing. Finally ended up by cranking the windlass until the breaker tripped to pull the bow down on the chain. Went back to cockpit, had a beer, walked around a bit until the boats buoyancy lifted the anchor a foot or two. Repeat. Took over 4 hours to get that damn anchor to break free. We figured it was at least 10 feet into the mud. Thats one of the reasons that I have a 44 pound Bruce as the main anchor on my 38. Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Joe Della Barba via CnC-List Sent: Saturday, March 14, 2015 10:59 PM To: cnc-list@cnc-list.com Subject: Re: Stus-List Deck hardware for mooring I wouldnt be so sure about the catenary providing much shock absorption. In about 30 knots of wind my mooring chain is pretty much stretched out taught. I have 30 feet of chain in 12 feet of water. Speaking of stretch, in Hurricane Charlie we had 150 feet of ½ nylon in 10 feet of water. It was like being on a giant rubber band :) In the morning the anchor was dug in so deep we needed a CG patrol boat to help get it loose :( From the looks of the line the anchor was at least *6 feet* under! Joe Della Barba j...@dellabarba.com <mailto:j...@dellabarba.com> Coquina WWW.CRYC.ORG <http://WWW.CRYC.ORG> From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Rick Brass via CnC-List Sent: Saturday, March 14, 2015 9:59 PM To: 'Paul Baker'; cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> Subject: Re: Stus-List Deck hardware for mooring Like some of the others, I suspected your plan to use at least ¾ pendants to be overkill for a 27 foot boat. Someone else pointed out that you want some stretch to cushion the shock and ¾ line will have no stretch to speak of at the loads your boat will generate. But the desirability of stretch is more appropriate for an anchor rode and not a mooring pendant. At a mooring, the cushioning is a result of the extra chain and catenary between the mooring ball and anchor; your pendant would probably only have a few inches of stretch over its relatively short length. To see if ¾ line is really overkill, I spent a few minutes doing research on the Boat US site, Fortress and Mantus anchors sites, and a site having engineering standards for different types of rope. There is an ABYC table on the Boat/US site showing the following for the estimated load on an anchor and rode based on boat size and wind speed. The data is: Wind Speed 30kt 42kt 60kt Working storm violent storm Boat size 25 490lb 980lb 1440lb 30 700lb 1400lb 2800lb 35 900lb 1800lb 3600lb These numbers are pretty consistent with what I found on the sites for the anchor companies for anchor load numbers. The rope specs show the following for minimum break strength for medium lay 3-strand nylon: 7/16 ½ 9/16 5/8 ¾ 4320lb 5670lb 7200lb 8910lb 12780lb Recommendations vary on the working load to max break strength ratio. As low as 3:1, 4:1 seems common, but Mantus says 8:1. At 4:1 the working loads are: 7/16= 1080 ½=1420 9/16=1800 5/8=2230 ¾=3195 At 8:1 540 710 900 1115 1600 For boats anchoring in 30 knots of wind, Mantus and others recommend: 20-30 & 11000pounds 9/16 30-35 & 15000 ½ 35-40 & 20000 5/8 West marine suggests 1/8 of diameter for each 8 of length for heavy boats with high windage. So for a 32 boat that would be that would be ½ diameter. Add another 1/8 for storm conditions. Boat/US recommends the following in 30kts.: 25 boat=3/8, 30=7/16, 35=1/2. But, hey, theyre mostly talking to power boaters. On one of the sites there was a note that deck cleats are generally installed in such a way as to resist a minimum 3400 pound load. I dont know if that is some sort of standard or just an observation. You plan to run a single pendant, with a somewhat longer backup in case the first breaks. For a 30 boat, at 4:1 safety factor, at 42kt winds, it looks like you need ½ line. In a hurricane ¾. Or you could use the system I did when I was on a mooring and use two ½ diameter pendants of equal length. Smaller diameter would let you install a pair of chocks instead of heavy cleats with a high load. And you can use your existing deck cleat. The pendants would be less expensive and easier to handle when picking up the mooring. Two pendants would easily handle the loads from a severe storm. And the equal length pendants on either side of the bow would act, to a certain extent, like a bridle to reduce the extent the boat sails from side to side on the mooring. Good luck Rick Brass Imzadi C&C 38 mk 2 la Belle Aurore C&C 25 mk1 Washington, NC On 2015-03-13 9:28 PM, Paul Baker via CnC-List wrote: So, I am going to be moving my boat from a nice, safe and secluded slip, to a mooring buoy out in the harbour. Yes, the mooring is big enough, yes I will be using at least 2 unequal pendants of good quality (probably at least 3/4"), and yes I will be using chafe guard where appropriate. Assume also that any hardware would have backing plates as large as practically possible.
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