Stresses on Mooring Lines

Stemar

Stemar

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The question of stress on anchor rode has been done to death, but has any research been done on the forces on mooring lines?

The lines that came with Jazzcat (8m Catalac, weighing in at around 6 tonnes are a little tired, so I want to replace them. Obviously they need to be strong enough, but I don't want to oversize them, as I'm a firm believer in elasticity to reduce shock loads. Then there's the question of cost. After all I've put into her over the winter, I'm feeling seriously impoverished; another reason for not going supersize!

She's pretty much rectangular, and my usual way of mooring is to have springs the length of the boat, plus bow and stern lines from the outboard cleats to the pontoon . I've seen too much vicious snatching to use the nearside cleats, resulting in lines barely a couple of feet long!

Thoughts, suggestions, recommendations?
 
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Whenever I visit a marina I use climbing rope that has been retired. Nice and elastic and easy to handle. If it comes on to blow a bit strong I double up.
If I kept my boat in a marina I would use 3-strand nylon with chafe protection.
 
I have never seen a boat break its mooring lines unless they were abraded. The usual damage in extreme situations seems to be to the boat, such as a torn-out cleat rather than a broken line. I favour lines that are comfortable to handle, which for my 5-ton boat is 14-16mm, which leaves plenty in reserve for normal wear and tear. Perhaps there is a place for yacht cleats that are sprung or with shock-absorbers. I can't be bothered to patent the idea, so you can have it for free.
 
Stemar said:
The question of stress on anchor rode has been done to death, but has any research been done on the forces on mooring lines?

The lines that came with Jazzcat (8m Catalac, weighing in at around 6 tonnes are a little tired, so I want to replace them. Obviously they need to be strong enough, but I don't want to oversize them, as I'm a firm believer in elasticity to reduce shock loads. Then there's the question of cost. After all I've put into her over the winter, I'm feeling seriously impoverished; another reason for not going supersize!

She's pretty much rectangular, and my usual way of mooring is to have springs the length of the boat, plus bow and stern lines from the outboard cleats to the pontoon . I've seen too much vicious snatching to use the nearside cleats, resulting in lines barely a couple of feet long!

Thoughts, suggestions, recommendations?
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Roughly what I do with my 9m on my mooring and when visiting other marinas.
The lines on my mooring are I believe 22mm nylon but then she does stay there regardless of the weather. Elsewhere I use about 14mm nylon or polyester rope and I have watched that stretch in a blow.
Jimmy Green have 14mm 3 strand poly, 100m for £56 plus delivery. Not a lot of money compared with what you have possibly spent this winter.
 
Many years ago, when yachts were generally smaller than today, it used to be said that a yacht's mooring line should be capable of holding half the gross weight of the yacht. 6 ton yacht = 3+ ton working load ropes. I'm a bit hazy on working load calculations, but think this would correspond to about a minimum 10mm or 12mm diameter three-strand nylon. Working load strength is generally rather lower than the rope's measured tensile strength.

I think the logic was, back in the days before marinas, if a yacht was moored to a harbour wall and had misjudged the fall of tide, the ropes would hold it dangling! Mind you, these days the cleats on an AWB would probably pop out before the mooring lines snapped.
 
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I use LIROS 16mm Octoplait Polyester on my 10 metre 5 tonne Gib'Sea. Over specified, as they do a 14mm, but in a storm 18 months ago a lot of mooring 'string' that some owners in the marina thought they could get away with had snapped.
 
I stayed on board in the marina during one gale last year and was surprised by the steep chop raised in an enclosed marina. Heavier boats weren't too affected but smaller and lighter ones fairly leapt about. The problem was chafe not strength (although thicker means more wear before parting). I think that wave action and swell surge could create substantial shock loads.

Agree that octoplait is a good rope to use but I confess to using old halyards for some of my lines. I am slowly replacing them but they are good for rough and dirty use. I always make sure there are two springs each way (eg pontoon mid to bow plus pontoon end to midships cleat). And then I can double them if the forecast is bad. Important to balance the tension so that its spread across different ropes, not all on one. I carry plenty of heavy octoplait and other lines but don't feel them necessary in a well sheltered berth.

My anchor V bridle is 18mm octoplait with chafe protectors and is under far more load than the mooring lines ever are.
 
Sandy said:
I use LIROS 16mm Octoplait Polyester on my 10 metre 5 tonne Gib'Sea. Over specified, as they do a 14mm, but in a storm 18 months ago a lot of mooring 'string' that some owners in the marina thought they could get away with had snapped.
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I also like a heavier rope to chuck ashore when docking single handed. Particularly hammerhead and linear type mooring pontoons.
 
Sorry but no - I have not measured tensions on mooring lines - primarily because we use a swing mooring and for the tensions to be useful I'd need to be able to moor in a marina in strong wind - when marinas tend to fill up with people looking for shelter :(



Porthandbuoy said:
Whenever I visit a marina I use climbing rope that has been retired. Nice and elastic and easy to handle. If it comes on to blow a bit strong I double up.
If I kept my boat in a marina I would use 3-strand nylon with chafe protection.
Click to expand...

A practice I would thoroughly endorse.

Retired climbing rope goes to land fill.

Go visit you local rock climbing club - offer to recycle their old ropes, slab of beer. Its specifically designed to be elastic and its outer braided cover is designed to be as abrasion resistant as possible. It is difficult to knot - but not impossible.

As I retire my bridles (which came from retired ropes for rock climbing gyms) they become mooring lines. 12mm dynamic lead rope will be more than adequate for you.

There is some comment on our bridle in this article.

A Snubber & Hook for all Occasions - Practical Sailor

Jonathan
 
Stemar said:
The question of stress on anchor rode has been done to death, but has any research been done on the forces on mooring lines?

The lines that came with Jazzcat (8m Catalac, weighing in at around 6 tonnes are a little tired, so I want to replace them. Obviously they need to be strong enough, but I don't want to oversize them, as I'm a firm believer in elasticity to reduce shock loads. Then there's the question of cost. After all I've put into her over the winter, I'm feeling seriously impoverished; another reason for not going supersize!

She's pretty much rectangular, and my usual way of mooring is to have springs the length of the boat, plus bow and stern lines from the outboard cleats to the pontoon . I've seen too much vicious snatching to use the nearside cleats, resulting in lines barely a couple of feet long!

Thoughts, suggestions, recommendations?
Click to expand...

Yup, been done on a boat not to different from yours.
PS dock line tension report
 
Surprising how many use Nylon ropes here. It’s fine for anchor rode but UV will turn it to dust if used for permanent mooring lines.
depending on the marina I use either plain polyester 3 strand or 3 strand with rubber compensators. Prior to moving to Haslar I thought compensators unnecessary but some locations do call for them to stop snatching which at the very least is uncomfortable while aboard. I wouldn’t rely on elasticity of rope if there’s a chance of the boat moving much.
 
lustyd said:
Surprising how many use Nylon ropes here. It’s fine for anchor rode but UV will turn it to dust if used for permanent mooring lines.
depending on the marina I use either plain polyester 3 strand or 3 strand with rubber compensators. Prior to moving to Haslar I thought compensators unnecessary but some locations do call for them to stop snatching which at the very least is uncomfortable while aboard. I wouldn’t rely on elasticity of rope if there’s a chance of the boat moving much.
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I remember a chandlery that didn't sell 3 strand nylon rope unless to order. Like many, it's gone now.
 
lustyd said:
Surprising how many use Nylon ropes here. It’s fine for anchor rode but UV will turn it to dust if used for permanent mooring lines.
depending on the marina I use either plain polyester 3 strand or 3 strand with rubber compensators. Prior to moving to Haslar I thought compensators unnecessary but some locations do call for them to stop snatching which at the very least is uncomfortable while aboard. I wouldn’t rely on elasticity of rope if there’s a chance of the boat moving much.
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Never noticed mine falling to bits. I replaced them due to to age and that they had hardened to much or is the hardening what you mean 'going to dust'?
 
Thanks everyone. I'm really glad I don't have to wade through that British standard

I think I'm worrying too much about it all; the boat lives on a mooring with two 18mm pennants, each more than strong enough to pick her up. Mooring is usually only overnight, though the last time a really big storm cam through, I decided my 24' monohull was safer on the club pontoon than on the mooring, and there was no problem with doubled 10mm nylon lines, even though they were the best part of 10 years old.

I'll look into getting retired lines from a climbing wall - not many mountains around Southampton! If that doesn't work out, I'll get laid or octoplait 12 or 14mm nylon. In my experience, it goes hard long before it's significantly weakened, and the lines will only be coming out a few days a month, so UV exposure will be limited.
 
lustyd said:
Surprising how many use Nylon ropes here. It’s fine for anchor rode but UV will turn it to dust if used for permanent mooring lines.
Click to expand...

Yes, I thought that - I remember reading a comparison of synthetic ropes (I’ll see if I can find it and link to it), which said that polyester had higher uv resistance than nylon, but that didn’t matter for climbers as they didn’t leave their ropes out for days on end.

Edit: nope, can’t find it, and it seems polyester and nylon have similar uv resistance.
 
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I crawled along the club pontoon one very stormy day to try and re tie the many boats that had snapped mooring lines.
3 boats had those rubber snubbers in their lines and all 3 had no snapped lines. The other 7 boats with no snubbers all had snapped lines.
 
Rappey said:
I crawled along the club pontoon one very stormy day to try and re tie the many boats that had snapped mooring lines.
3 boats had those rubber snubbers in their lines and all 3 had no snapped lines. The other 7 boats with no snubbers all had snapped lines.
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Interesting. It is difficult to imagine how the boat and ropes get bashed around in a proper storm unless been there at such a time. As you note, unless had to crawl along a pontoon then not been proper storm (and indeed in the worst ones often the pontoons are closed off).
I certainly use doubled up ropes in winter, with rubber compensators on the main bow and stern rolee.
I did once find a 14 or 16mm spring worn through after a F10 - never did work out where it chafed on the pontoon but glad of the secondary rope.
Ultimately it is the pontoon cleats and the finger pontoon bolts that often feel like the weakest link
 
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