Thanks Rick - good info. The only thing it doesn't take into account is chafe,
and that nylon can be as much as 20% weaker if wet. I'd want a pretty big
margin for that.
I am considering the Yale Maxi-Moor pendants, good elongation, good protection
against chafe etc, but they seem to recommend pretty big lines.
From: rickbr...@earthlink.net
To: pjbake...@hotmail.com; cnc-list@cnc-list.com
Subject: RE: Stus-List Deck hardware for mooring
Date: Sat, 14 Mar 2015 21:59:02 -0400
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 stormBoat size25’ 490lb 980lb
1440lb30’ 700lb
1400lb 2800lb35’ 900lb
1800lb 3600lbThese 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”=3195At 8:1
540 710 900
1115 1600 For boats anchoring in 30 knots of wind,
Mantus and others recommend:20-30’ & 11000pounds 9/1630-35’ & 15000
½35-40’ & 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, they’re 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 don’t 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 BrassImzadi C&C 38 mk 2la
Belle Aurore C&C 25 mk1Washington, 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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