Storm Damage & Mooring Lines

[svrevelations]

I thought my boat was securely moored with 10 mooring lines and each mooring line is about 30 mm (1.25 inch) in diameter. A recent storm in Grainger Bay, Cape Town, South Africa proved us wrong. A combination of strong wind, surge and the storm caused 8 mmoring lines to snap. Eventually the boat was only held in place by only 2 mooring lines. The result is substantial damage due to the transoms banging against the mooring the whole night until detected the following morning. The mooring lines are less than 3 months old and could surely not be that badly detiorated due to exposure, UV, salt, etc. This raises a number of questions;

1. What/which are the best mooring lines against breakage, salt, wear & tear?
2. What diameter mooring lines should be used (50' boat - 14 metric tons)?
3. How do you care for your mooring lines?
4. How often to do replace your mooring lines?

[Bloodhound]

Lines look, not like they frayed, but they snapped from sudden application of force. I have a 10 ton boat on which I use 5/8" braided mooring line (lower stretch than 3-strand), but each line wraps around a snubber to provide some elasticity so forces don't cause the lines to experience sudden force. I wonder if this would help in your case. Ten tons brought to a sudden stop can exert 20 tons on a mooring line, but I think the elastic snubber keeps stresses within reason.

[boatman61]

For storms never pull your lines tight... double up all lines with second lines slacker than the primary's...
If there's a swell there needs to be enough slack for the boat to ride...
I've often had folk tell me my lines are to slack... then theirs break and mine don't...
Go figure....

[daddle]

Wow. That's a reality check. Sorry for your loss. Look like it won't be too hard to fix though. Long lengths help too, because they stretch more. So make the springs tight and the shorter lines slacker.

Nylon is the best stuff for docklines.

[captain58sailin]

I echo boatman 61's advice, if possible, watch your surge and try to put enough slack in your lines to allow the up and down, and have your yaw stop just short of contact with the solid stuff. Each type of swell and each type of vessel has it's timing and if you can allow your vessel to move around some it should lessen the shock loading on your lines. It takes some time to learn what works for your vessel, but it is well worth it.

[Unicorn Dreams]

We use 3 strand nylon 5/8" for out dock limes. 50' boat should use that or 3/4" at least in my opinion.

Don't believe stretch to be a factor as dock lines are short so stretch would be minimal.

Strength over rules stretch at the dock...

[Pete7]

Double lines and rubber snubbers for us too. However, they may not be strong enough a boat that size. There are metal HD spring types which may be more suitable.

Pete

[Hud3]

My boat went through a hurricane at our dock. I had these mooring line snubbers on four primary mooring lines, then tripled the lines (looser) on the side facing the strongest winds, and doubled up on the other side. Sixteen lines in all, including springs. Plenty of chafe gear. She was bucking like a bronco, but made it through OK.

Epdm Mooring Snubbers 3/8" Black Rubber

.

[Vasco]

MooseMoney,

The black line that snapped, what was it made out of? It doesn't look like nylon.

[Mark Johnson]

I got my boat through a Cat 4 with storm surge of 13 - 15", by putting 21 lines on it. LOOSE... Some were of BIG stretchy 3 strand to absorb shock, and the 1.5' longer lines, as a final limit, were double braid polyester. Some lines popped, and some melted under "hose" chafe gear. (The textile kind is better about not causing this).

This was private dockage, (FIXED), and I was staying 300' away at the owners house, who had evacuated. Only by going out into the storm, (gusting to 150 MPH), and going down to adjust lines, was I able to save the boat. First it was up to my waste, then arm pits, then doing the side stroke. (At night of coarse)!

My pilings were WAY out from the boat, which made this much rise possible, along with adjustments, until I couldn't make any more. This is the most important. IF your outer pilings are 25 or 30' out from the boat, it allows for a LOT of rise in the water level. Of coarse this counts out most marinas. Otherwise, a REALLY good 3 anchor temporary mooring, (Fortress 55s), properly done, is your best bet. I set one up during this storm for a friend with a sistership, and it also made it. On our BAD side of the bayou, with over 100 boats, there was 95% loss, as the boats pulled the docks apart, or the improperly anchored ones drug!

For storms... GO EXCESS, and put your heart & soul into it! I know that in MY case, I was less likely to die in the storm, than in the effort to build another boat. As it turned out, I should've stayed on the boat. When the HOUSE was up to my armpits, I had to go out into it one last time, looking for higher ground! VERY sphinctorial indeed!

Mark

BTW... Neither the boats on jack stands in the boatyards, nor the fancy "downtown marinas" with floating concrete docks, made it. They floated up and over the tops of their 13' concrete pilings!