Mooring ropes - breaking strain

[MogM]

Hello all

I am new to boating and would appreciate some advice.

How does one calculate the breaking strain strength required for mooring ropes ?

Is there a formula for working it out ? Say for a vessel of 25 foot weighing 3500Kgs I am making the presumption that a SWL would be 2-3 times that of the actual calculated breaking strain.

Also, (and this is really going to show my ignorance) why is rope still used when there are such things as chains, steel wires, ratchet straps and possibly other things too all available ?

Thanks

Mog

 

[whisper]

Can't help with the techie bits of your question.
But as to why rope is still used , it's because it has a number of advantages over the other things you mention.
These are - as a first try :-
Lightness - you don't want to carry heavy chain/cable about on the boat or handle it to make connections/disconnections.
Softness to handle - usually don't need gloves.
Elasticity - has give/stretch - which can be a great bonus especially in extreme tidal conditions. Protects the deck fittings and fenders from shock loads.

Welcome to the Forum.

 

[sarabande]

don't bother working out what you need; it's all been done before, with masses of empirical feedback.

try Jimmy Green's site for the size you need.
http://www.jimmygreen.co.uk/technical/mooring_alongside_warp_size_guide

 

[Bandit]

See english braids site:

http://www.englishbraids.com/Yacht-Anchoring-Mooring/yam-3-strand-polyester-standard.html