Sizing mooring lines correctly?

[Travelling Westerly]

Im looking to replace all of my mooring lines and wondered about the recommend sizings as quoted by sites like Jimmy Greens etc.

Boat is 12m approx 12t, currently have braided pre made 18mm lines.

JG's website quites the lines should be 16mm (going for Liros Handy Elastic) which has a breaking strength of 6000kg! It costs £8.10 per meter which when considering the lengths required gets quite costly.

If I went for the same line but in 12mm, it costs £4.90 per meter, a considerable saving overall.

12mm version has a breaking strength of 3900kg which to me seems more than enough to cope with most weather conditions experienced in a sheltered marina (understand thats the failure strength but doubt a 50kt wind would exert more than half that pull strength and the load is shared by 4 lines overall) .

Other consideration would be my deck hardware, would my cleats sustain a 6000kg pull?

So why the need for 16mm? I part tested my theory 2 nights ago when I used a single 12mm length of Liros Handy Elastic as a stern brest line. A storm blew through the marina side on to the boat directly and the wind peaked at 54kts. The line coped well, stretched during peak loading and did not over stretch so still retains its shock absorbing quality.

Have I missed something here? Seems 16mm is an overkill?

 

[dunedin]

For our home / winter berth we use three strand mooring ropes like these LIROS 18mm 3 Strand Polyester Mooring Warps
Slightly cheaper than your option, and much easier to splice loops.

We have different sizes of ropes in different places, depending on expected loads. The SW corner has a very thick rope (20mm) plus a rubber snubber attached to it. There is also a secondary rope of only 14mm, with loops in both ends and normally slightly slack. There in case rope or cleat breaks (also on differnt cleat on boat), and as light rope to cast off last when depart.
Other ropes sized various diameters in between, with snubber also on stern rope as very short distance so rope elasticity limited benefit.
12m boat, lighter than yours but wintered afloat through severe storms

 

[Rappey]

Add rubber snubbers to the lines and they take even less stress.

 

[Tranona]

I use this marinescene.co.uk/en/category/category-rope-3-strand-white-polyester sometimes manage to get end of reel offcuts at 10-15% less of lengths are suitable.

 

[Sandy]

I use Jimmy Green's recommendations.

Having seen the carnage in a marina after a storm, where owners prefer to use wet string to save a few beer tokens, I wonder why people don't follow the guidance.

Is there any qudos having your boat holed, spending a few months being repaired and the resulting increase in insurance costs for us all?

 

[geem]

Mooring snubbers from rubber or stainless springs on the lines that get snatched reduces load. We would double the lines over winter or if bad weather was expected. Large diameter lines allow for some chafe before they fail.

 

[Travelling Westerly]

I use Jimmy Green's recommendations.

Having seen the carnage in a marina after a storm, where owners prefer to use wet string to save a few beer tokens, I wonder why people don't follow the guidance.

Is there any qudos having your boat holed, spending a few months being repaired and the resulting increase in insurance costs for us all?

Thats really the question was it not? Other than carnage and wet string is there anything more scientific about why quality Liros 12mm at 3900kg break load wont securely hold my boat other than Jimmy Greens say so?

Not a dig but more of can you offer more than carnage and wet string given we are not talking wet string and 12mm Liros line already stood well against 54kt winds....

 

[IanCC]

Im looking to replace all of my mooring lines and wondered about the recommend sizings as quoted by sites like Jimmy Greens etc.

Boat is 12m approx 12t, currently have braided pre made 18mm lines.

JG's website quites the lines should be 16mm (going for Liros Handy Elastic) which has a breaking strength of 6000kg! It costs £8.10 per meter which when considering the lengths required gets quite costly.

If I went for the same line but in 12mm, it costs £4.90 per meter, a considerable saving overall.

12mm version has a breaking strength of 3900kg which to me seems more than enough to cope with most weather conditions experienced in a sheltered marina (understand thats the failure strength but doubt a 50kt wind would exert more than half that pull strength and the load is shared by 4 lines overall) .

Other consideration would be my deck hardware, would my cleats sustain a 6000kg pull?

So why the need for 16mm? I part tested my theory 2 nights ago when I used a single 12mm length of Liros Handy Elastic as a stern brest line. A storm blew through the marina side on to the boat directly and the wind peaked at 54kts. The line coped well, stretched during peak loading and did not over stretch so still retains its shock absorbing quality.

Have I missed something here? Seems 16mm is an overkill?

Also remember a line doubled back to boat has double the strength less the cutting effect of the turn around the cleat.

 

[AndrewB]

Mooring lines tend to fray, specially in bad weather. Regardless of break load, 16mm gives a margin of safety over 12mm if you are leaving the boat for any length of time.

 

[Jacana139]

I have a set of 12mm lines which I use during the season which are easy to handle.
I replace with 16mm if staying afloat during the winter. Between November and March I would only visit the boat once or twice and like a margin of wear incase of chafe.
I think it is too much to ask the harbour masters staff to be monitoring chafe and I view it that if I chose to take the risk, I am also risking cosmetic damage to my neighbour which doesn’t sit well with me.
Jacana is 6 tons.

 

[ylop]

Thats really the question was it not? Other than carnage and wet string is there anything more scientific about why quality Liros 12mm at 3900kg break load wont securely hold my boat other than Jimmy Greens say so?

Not a dig but more of can you offer more than carnage and wet string given we are not talking wet string and 12mm Liros line already stood well against 54kt winds....

You could probably have used 8mm and it would have held the boat too (but been less pleasant to handle). Jimmy Green has no idea how sheltered or exposed your dock is, has no idea how long you will leave the boat for between checks, has no idea if you have quick/easy way to get more line if you do those checks and discover some chaff, etc. Mooring lines take a lot of abuse - sharp edges, salt drying out between the fibres, UV, stored damp etc. Margin for lifetime degradation is a good thing and *may* mean you save money in the long term.

 

[dunedin]

Thats really the question was it not? Other than carnage and wet string is there anything more scientific about why quality Liros 12mm at 3900kg break load wont securely hold my boat other than Jimmy Greens say so?

Not a dig but more of can you offer more than carnage and wet string given we are not talking wet string and 12mm Liros line already stood well against 54kt winds....

In 15+ years afloat through the winter and some very severe storms, the only rope issue we have had was one key rope (circa 12mm) being cut through entirely in a storm. Must have been some sharp part of the pontoon that we hadn’t noticed. Didn’t “break” in terms of breaking load, but broke the last bit after being cut through.
Rope was checked and fine a week before we found it snapped. Boat was fine, as lying to our secondary rope, which we have at each corner just in case.

 

[V1701]

On my 12 ton boat I've got 18mm octoplait doubled at stern with a snubber on one part & the other part more loose so the snubber can do it's thing, same at bow & single springs. But that's mainly because I live on board and it's so much better than all the snatching, creaking and groaning that others endure. I think in your case 16 would be preferable for reasons already stated but if you double up, put some hose over to protect the rope where necessary & keep a proper eye on it then I think good quality 12 would be alright...

 

[Sandy]

Thats really the question was it not? Other than carnage and wet string is there anything more scientific about why quality Liros 12mm at 3900kg break load wont securely hold my boat other than Jimmy Greens say so?

Not a dig but more of can you offer more than carnage and wet string given we are not talking wet string and 12mm Liros line already stood well against 54kt winds....

Well, Jimmy Green is a reputable 'worker of rope' and I have more faith in their supply chain that some company on the internet I don't know. Should the unmentionable happen at least you can, hand on heart, say that you followed the guidance of Jimmy Green in sizing your warps in your insurance claim. I find that insurance companies are not brilliant at engineering and follow other people's standards/recommendations.

I am lucky they are only a few miles away and I can pop over and chat with them, they are very nice people, select the string and if necessary get them to work in it while I pop down to The Dolphin for some fantastic crab sandwiches and a pot of tea.

 

[Bobc]

50ft 15t.

I use a mix of 14mm and 12mm.

I tend to use 14mm for the bow/stern (doubled back to the cleats), and 12mm for the springs (also doubled back).

Never had a problem with this.

We use 12mm for the springs, mainly as we lasso from the midship cleat and the wife finds 14mm rope a bit heavy for this.

Just remember that 2 x 12mm rope (doubled back) has the same cross-sectional area as one piece of 18mm rope.

The fittings will rip out before the rope breaks.

 

[Travelling Westerly]

Well, Jimmy Green is a reputable 'worker of rope' and I have more faith in their supply chain that some company on the internet I don't know. Should the unmentionable happen at least you can, hand on heart, say that you followed the guidance of Jimmy Green in sizing your warps in your insurance claim. I find that insurance companies are not brilliant at engineering and follow other people's standards/recommendations.

I am lucky they are only a few miles away and I can pop over and chat with them, they are very nice people, select the string and if necessary get them to work in it while I pop down to The Dolphin for some fantastic crab sandwiches and a pot of tea.

I use Jimmy Green as well for all my lines, anchoring, rigging needs etc and think they are a good company, that was never in doubt only their sizing recommendations on this occasion which I wished to question.

From all the other helpful replies it looks as if the only advantage to larger diameter line is the ability to chafe a little more and still be serviceable to a certain degree. I think some good chafe protection will help and as I live full time/cruising abroad I will spot any issues the day it happens.

Miss the the crab sarnies at the pub too

 

[andsarkit]

Any reasonably sized line will not break under tension but is very quickly destroyed by chafe. I have had 14mm octoplait lines in a smooth fairlead nearly worn through in a single gale (2.5T boat).
I got a roll of this for my back up line to the main chain on a swinging mooring. I also have it on my anchor snubber which is designed to stretch and move in the fairlead.
Hose

It is so cheap you can afford to replace it every year or when it gets dirty.

 

[Refueler]

My Mates B31 went walk about when his spring snubber decided enough was enough ....

Like me - he now no longer uses snubbers.

The trick is to use the lines better. Instead of single line at positions - I prefer two lines which can be of reduced diameter but total gives better solution. If one does part - at least other is there to hold.

I think many of us 'budget' conscious boaters often take replaced halyards and divide up into useful lines such as use for berth mooring lines. Even a couple of 10mm would be IMHO better than a single 16 .. 18mm line.
Easy to handle a single line coming in / departing ... once alongside - second line added as security.

My 4 ton boat sits on such lines .......

 

[dunedin]

50ft 15t.

I use a mix of 14mm and 12mm.

I tend to use 14mm for the bow/stern (doubled back to the cleats), and 12mm for the springs (also doubled back).

Never had a problem with this.

We use 12mm for the springs, mainly as we lasso from the midship cleat and the wife finds 14mm rope a bit heavy for this.

Just remember that 2 x 12mm rope (doubled back) has the same cross-sectional area as one piece of 18mm rope.

The fittings will rip out before the rope breaks.

Are these ropes for “day to day” mooring up, winter unattended afloat or both?

We use much lighter ropes when cruising in the summer compared to ropes permanently attached to the pontoon in winter

 

[Bobc]

Are these ropes for “day to day” mooring up, winter unattended afloat or both?

We use much lighter ropes when cruising in the summer compared to ropes permanently attached to the pontoon in winter

Was all year round when we were in the Hamble.