Floating rope size?

[Networks]

What size / strength floating rope would I need for stern too mooring of a 38ft 7ton yacht?
I have considered flat tape but the noise would drive me crazy overnight, although I am told rats can't walk them!
Any other recommendations appreciated.

 

[sarabande]

If you insist on floating...



Liros 8mm 3-strand White Polypropylene with BS 1040kg

Endless River 12mm yellow/red 12mm braid with core, BS 1770kg

Marlow 3str polypropylene 12mm BS 2387kg





Polyprop is uncomfortable to handle IMHO.



Ah...easier on the hands:-

Marlow 8plait Marstron 10mm BS 1310kg

 

[VicS]

What size / strength floating rope would I need for stern too mooring of a 38ft 7ton yacht?
I have considered flat tape but the noise would drive me crazy overnight, although I am told rats can't walk them!
Any other recommendations appreciated.

Based on the sizes suggested by Jimmy Green for polyester and Nylon you'd be looking for rope with a breaking strain in the region of 45 to 50kN or even a little more .

That would appear to require 22 or 24mm in polypropylene.

Considerably more than Sarabande is suggesting

 

[estarzinger]

mmmm . . . . there are fundamentally three different types of "floating rope":

Polypropylene - this is the cheapest, weakest and most sunlight UV vulnerable. There are many grades of polypropylene available and the stuff offered to the recreational market is mostly pretty nasty. If you are going to get this I suggest going to a commercial fishing chandlery. They carry some pretty nice polypropoline and you will get a decent price.

bi-polymer olefin - This is the least well known of the three - samson ultra blue is an example - it is 35% stronger than polypro and twice the chafe resistance, but of course also a bit more expensive. It would be my choice for a stern line.

Dyneema/spectra - This is the most expensive and the strongest and most chafe resistant (by far on all three). Its beautiful stuff but few people want to pay the price to use it as shore lines.

As to the desired strength - the loads are actually not huge and this is mostly about how much extra reserve strength do you want to be able to deal with chafe and wear. My recommendation is to get the same strength as your anchor rode - I would have said for your boat - expect at max load of 1000kg, have a 5:1 safety/wear factor or 5000kg breaking strength, which would be 14 or 16mm samson ultra blue.

 

[RupertW]

We are quite happy with 12mm nasty polypropolene for a 42ft boat. At £35 for 200m of it we find it works a treat and as we are not yet liveaboards it's in the sun for a lot less than 5 weeks a year. Regarding breaking strain we tend to use two lines and will get a huge amount of shock absorbency from the 40 or 50m of anchor chain. When it is fully stretched the lines are a bit slack, and when the lines are taut they share the load.

 

[Tranona]

14 or 16mm polyester 3 strand is fine. Can't see any advantage in floating lines in this application. Loads are not a big issue in normal day to day use as usually the lines are doubled. More important is easy handling and coiling. If you are worried about lines getting round the prop or rudder then you can always do what big ships do and have a light messenger line to use when arriving or leaving.

 

[Hadenough]

Regarding breaking strain we tend to use two lines and will get a huge amount of shock absorbency from the 40 or 50m of anchor chain. When it is fully stretched the lines are a bit slack, and when the lines are taut they share the load.

Do not understand this can you elucidate please.

 

[sarabande]

sorry VicS, I assumed that a prudent yachtsperson puts out a line from each quarter. That doubles, well very very almost, the strength of the retaining system.


Here , for interest, is a table, much simplified, of wind forces on various boats at a couple of angles (well, 6 to be accurate ). From ABYC, figures in daN, to convert to lbs, multiply by 2.2.

View attachment 44713

There is some comment that the actual force will be less than the calculated data in the table, because of the wind gradient (i.e. wind speed is slower near the surface than at the standard height of 30ft.

I imagine that surge loads from wave action or passing Greek ferries will need to be taken into the prudent skipper's decision on what size line to employ. My original comment was a gentle challenge to the OP's need for floating line in preference to the stronger 'normal' lines of the same diameters.

 

[lenten]

i don t know what modern polyprop is like now but when i had a new coil----i would attach one end to a tree and and the other to a spinner tied to the car and stretch it-----this made it lose its memory and it was kinder to use-----regards lenten

 

[estarzinger]

sorry VicS, I assumed that a prudent yachtsperson puts out a line from each quarter. That doubles, well very very almost, the strength of the retaining system.


Here , for interest, is a table, much simplified, of wind forces on various boats at a couple of angles (well, 6 to be accurate ). From ABYC, figures in daN, to convert to lbs, multiply by 2.2.

View attachment 44713

There is some comment that the actual force will be less than the calculated data in the table, because of the wind gradient (i.e. wind speed is slower near the surface than at the standard height of 30ft.

I imagine that surge loads from wave action or passing Greek ferries will need to be taken into the prudent skipper's decision on what size line to employ. My original comment was a gentle challenge to the OP's need for floating line in preference to the stronger 'normal' lines of the same diameters.

For what it is worth . . . . the max loading will be at a wind angle of 90 degrees, not the 30 degrees shown in that table - the 90 degree loads will be (very approximately) double those shown in that table. And NO, lines from each quarter do NOT double the strength when the wind is on the beam - in that case only the windward quarter line (and the anchor rode) will be taking load (assuming the quarter lines are out at an angle rather than straight back, and an angle is prefered for a couple reasons).

 

[RupertW]

Do not understand this can you elucidate please.

We use the floating line when moored stern to shore, dropping anchor a long way off then ending up perhaps 30-40 metres away from the shore. We drop anchor and motor backwards towards the shore, letting out maybe 40m of chain, then take a floating line to the shore, tie on, and take the end back to the boat, giving us two lines to a fixed point on the shore. Then tension up the anchor chain enough to hold us in position but usually with a fair curve to the chain, and the floating lines with enough slack to touch the water (although there's still a fair bit of tension).

So if the wind gets up from the bows and the anchor chain is taut, the floating lines will be slacker. If the wind gets up from the shore then the anchor chain will slacken and the floating lines will share the load. Either way there is anything from 5-10m slack in the whole system for the boat to range backwards and forwards to absorb any shock loads.

 

[pipemma]

Bumping this slightly elderly thread with the same question:

37-foot, 7.5-tonne yacht, looking to buy yellow floating lines for long-lining in Greece.

Does 16mm sound about right?

TIA