STRONG ENOUGH? NOT REALLY THE ISSUE WITH MOORING LINES SINCE 10MM IS LIKELY TO HOLD A 10 TONNER IN MOST SITUATIONS. INSTEAD, YOU NEED TO THINK OF WHAT IS BIG ENOUGH TO HANDLE COMFORTABLY (YOU TRY PUTTING A HEAVY LOAD THROUGH A HAND HELD THIN HIGH STRENGTH ROPE) AND WHAT WILL WEAR WELL IN TERMS OF COPING WITH SOME FRAYING AND STILL BEING OK. ON A 4 TONNE BOAT, I USE 14MM NYLON MULTIPLAIT WHICH IS AMPLY STRONG, WILL WITHSTAND SOME FRAYING, IS PLEASANT TO HANDLE, AND DOESNT SQUEAK LIKE SOME BRAIDED ROPES DO WHEN THE BOAT MOVES.
APOLOGIES FOR THE CAPS. DIDNT REALISE CAP LOCK WAS ON
Nylon is good because it is very elastic. In fact the multi-plait stuff is woven to enhance this quality. It will put much less strain on your deck fittings (and the pontoon cleats) when the boat is bouncing around or "surging" than (say) a polyester line or something that used to be a halyard.
3 lines at 150% boat length
3 lines at 60% boat length
These lines can be 10mm no problem.... and I advise 'coarse multi-plait' or 3 strand ..... more hard wearing than the fine surface multi-plaits you see on a lot of boats.
Plus if you can get it ....... 30mtrs of 6mm as a throwing / safety line......... with a small sandbag or similar to give the throwing weight.
For my marina berth .... I have standing lines ..... The springs stay on the dock set at the lengths necessary to hold the boat correctly and also when berthing I pick up the aft spring, put the eye over the mid cleat and the boat doesn't 'over-run' into the dock .... I can then leave the engine ticking over, go forward slip on the forward spring eye and then sort the head and stern lines from my locker stock !
Finally see if you can fit a reasonable mooring cleat each side amidships ........ believe me - a godsend !!
Good luck
Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !
For length 2 X 200% LOA and 2 X 150% LOA should suffice in most situations.
N.B. If you raft up or tie to tidal docks you will need longer - long lines to allow for how far out you are rafted (though many wouldn't object to a 6m not running shorelines if they are big enough).