What size snubbers (compensators)?

XDC

XDC

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Our boat weighs around 6 tons (factory figure) and 16mm shore lines have proved more than adequate in the 10 years we have owned her.

There have been a few storms along the way plus the joy of the FastCat arrival in Guernsey :) but I have never feared for their suitability.

However we have recently moved to a marina that around HW suffers from awful swell.

Just about every boat has snubbers and or spring chains but I can’t see any pattern much in the way that people rarely tie up the same.

My cleats/fairleads are large enough for 20mm permanent docklines, one rope, one cleat, but I’m wondering would 18-20mm snubbers on 16mm rope work?

My (possibly confused) thought is that if I overdo the snubber size it is doing “all” the work and could actually fail early whereas the load would be shared better by perhaps a 16mm line and 14-16mm snubber working together.

My other confusion is that looking at pre-spliced dockline on my 3 major chandlery sites they all seem to max out at 16mm .

Force 4 show 18mm in the description box but not in the purchase option.

https://www.force4.co.uk/force-4-shock-absorbing-mooring-lines-m.html

So, 20mm line and snubbers? Really expensive compared to:

16mm line, 18-20mm snubbers. Snubbers stressing?

16mm line, 16mm snubbers. Strong enough for conditions not experienced long term over the past 10 years??

Cost is a consideration but so is comfort/ safety.
 
XDC said:
https://www.force4.co.uk/force-4-mooring-compensator-for-18-20mm-rope.html?sqr=Compensaors &

One aft line, two springs, two bow lines. Finger pontoon.

The side.
Click to expand...

Floating dock with fenders?

In my experience, bigger and more fenders and eliminating slack works best when stuck against a bulkhead. Allowing motion just adds chafe and gives the fenders more opportunity to shift out of place.

And I may misunderstand the situation. My surest suggestion is that you stay at the dock during a nice strong storm and play with it for as long as it takes. Repeat as needed. This is the best way to understand the situation. I never seem to get it just right the first time, since every boat and situation is different. It is about reducing bouncing to the extent possible.
 
For a 6 ton boat, the 16mm snubbers should be absolutely fine. We're over 10 and had 16mm and they still lasted quite a while before the ends tore out. I then drilled through them and fitted some Dyneema loops, which after another years and a bouncy night at a poorly sheltered town quay tore out too. Now they're on their third life, with a rolling hitch around the knobby end. Will probably get the next bigger size when that breaks off too.

If you oversize them, they'll be too rigid for your boat and not absorb much. Ours did very well, stopping the lines yanking on the cleats and absorbing the noise and sudden movements that wake you up in the night.
 
Do they all need snubbers/
I ask because one difficult week in Ostend I hung my anchor off the bow line at the mid point ( secured with a light line) & whilst it went up & down a lot it did not come to any harm & took a lot of the "snag" out of the line
Certain types of line have more inbuilt stretch in them which also helps.
 
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I think that upping the diameter of your lines is unnecessary. My boat weights more like 15 tonnes and I actually reduced the lines to 14 mm 3-strand polyester from the 20 mm stuff she had. The initial motive was to allow smaller or weaker crew to handle the lines comfortably, but that was 12 years ago now and I've never gone back! In that time we've been in some really quite rough places (I mean by virtue of tidal range, or swell, or industrial harbours or rock walls etc, not the people), from Svalbard to Brazil and the bits in between, and never had a line part.

It should be realised that breaking strain is remarkably high with modern ropes: 14mm polyester for instance has a breaking strain of 3.6 tonnes. Ok, it's reduced in knots and at cleats, but it's still going to be well over 1.5 tonnes which is plenty for tying up. Windage on a 42 foot boat will be about that in a F11, and one uses more than one line under these circumstances. The reason for over-sized ropes is thus not for strength, but chafe resistance. I'd recommend not using braided ropes for warps as it's near impossible to judge whether they're still ok when the outer sheath is slightly chafed whereas 3-strand is obvious: what proportion of the strands have worn through? 20% -> 20% strength reduction whereas 20% of a braid-on-braid sheath gone could mean anywhere from 10% to 90% strength reduction - you just can't tell. It's also easy to re-splice 3-strand to cut out a damaged bit.

For snubbers, we have definitely needed them in some places, and have gone for the rubber types where one feeds the rope through so if the rubber parts the rope is still intact. I have bought the size which I can just pass my 14mm ropes through each end with 3 to 5 turns around the rubber middle. This arrangement gives the non-linear stress-strain curve one desires. But equally important is to tie up so that there is minimal snatching. This means long lines - which in the CI you'd need anyway due to the big tides there. Thus, if alongside:
- Springs from the quarters not from a mid-ships cleat, and to somewhere well beyond the end of the boat, maybe 1/2 a boat length beyond, and longer if possible. These can be reasonably tight at LW. They should not need snubbers.
- Breast ropes not to cleats opposite but to cleats at least 1/2 a boat length behind or in front. Put in snubbers and/or weights and have them quite loose lest you get hung on them as the tide falls.

If stern-to, with a buoy or anchor at the bows - which is very popular abroad:
- cross the stern lines if at all possible so they run behind the transom, and separate them quite well if poss. One's aiming for each line to be at least 1/2 a boat length long. If to a floating pontoon or in a tideless area (it will be, or this is a crazy way to tie up) make them quite tight but with snubbers.
- long but slightly lazy lines from mid-ships cleats to the shore to stop surging back and forth.
- make the transom as far from the quay as your boarding plank allows (2m is reasonable).

You probably know all this anyway, so apologies for rambling on...
 
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I saw no rambling just lots of useful advice based on experience for which I’m grateful.

I’m going to go for 16mm 3-strand all round and 5 snubbers.

A kind of compromise of the suggestions.

Many thanks.
 
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