Sizing Mooring Lines

[markpj23]

OK - basic question: How do I choose the right size mooring lines for my boat? Not storm lines, just the 'everyday' use lines.

How do I choose the right size / circumference line?
How long should each line be? (Bow, Stern, Spring).

Boat is an Endeavour 52, 35000lb displacement. Single midships cleat each side plus bow / stern cleats.

My inclination is a 1" double braid line, about 50ft long for each station.

[capt lar]

Most folks oversize docking lines, including me, but by the West Marine chart, the Diameter of a Docking line for a 52' boat would be 3/4" so 7/8" is heavy and 1"is huge. On length - bow and stern lines about 2/3 of boat length and spring line equal to boat length. These lines should be able to stretch to ease motion and reduce strain, so 3 strand is fine. Double braid is stronger (you can reduce size) but stretches less.
I prefer nylon double braid because it seems to wear better and handle more easily.

Larry

[GordMay]

Mark:
Are you asking about permanent submerged moorings, or dock lines?

[markpj23]

Sorry Gord - asking about dock lines.

[GordMay]

Mark:
I’d recommend (all minimum lengths & diameters):
(2) 35 Foot long Bow/stern Lines @ 5/8" diameter
(2) 45 Ft Bow/Stern Lines @ 3/4" dia
(2) 50 - 60 Ft Spring Lines @ 5/8" dia

Any well-equipped boat should have at least six (6) dock lines: two (2) bow lines, two (2) stern lines and two (2) spring lines. The dock lines should be at least 2/3 of the length of your boat and the spring lines should be at least the full length of your boat. Note, the position of cleats on your boat and dock may affect the length of the docklines. The size (diameter) of your line depends on the size and weight of your boat.
The following is an approximate guide.
Boats 20 to 30 feet = 1/2" diameter
Boats 30 to 40 feet = 5/8"
Boats 40 to 60 feet = 3/4"
Boats over 60 feet = 1"

Here's a chart with suggested line sizes by boat size, published by West Marine.
0-27' = 3/8" diameter
28-36' = 7/16"
37-45' = ½"
46-54' = 5/8"

If your boat is heavy (or has higher ‘windage’) for its length, consider going up one size in diameter.

Cleats should measure one inch in length (tip to tip) for each 1/16 inch of line diameter. So, if you want to use a 3/4 inch diameter line, your cleats should be at least 12 inches long.

[markpj23]

Exactly what I was looking for - many thanks!!

[markpj23]

Forgot to verify.... when sizing wire the measurement is the diameter; and when sizing line the measurement is the circumference. Is that correct?

Or is it all measured diameter? A 3/4" line circumference seems mighty small.. so I'm assuming diameter?

[GordMay]

Rope/Line, Wire, & Chain are all measured by Diameter.

[Joli]

We use Max Braid 3/4" but double the bow and stern lines. No problems, weight 65klbs, 61 foot, 93 foot airdraft.

1" is so damn big it is tough to get around the cleat.

B

[markpj23]

Diameter makes sense - except that the US Navy measures line by circumference. Standard 6" mooring lines are not 6" in diameter.

So my Navy training let me down

Thanks everyone! Now off to the chandlery...

[Lodesman]

Gord - if I remember correctly, line traditionally was measured in circumference, but with metrification it was switched to measure in mm diameter. Since there is a direct correlation between C and D, it's easy to convert - inches (circumference) multiplied by 8 equals millimetres (diameter). I don't know if that's the case with smaller commercial cordage, but in the Navy we still refer to our hawsers in inches and circumference.

Kevin

[GordMay]

Kevin & Mark:

I didn’t know that ”... in the Navy we still refer to our hawsers in inches and circumference ...”.
Thanks also for the excellent approximation:
Circumference in Inches x 8 = Diameter in mm

Converting a 3/4" diameter line to ‘x’ mm circumference
pi = C/dm, or d = C/pi, and Pi = 3.1416, and 1" = 25.4 mm
(3/4 x 25.5) / 3.1416 = 6.0638 (near enough to 0.75 x 8 = 6.0)

I thought that heavy towing & mooring lines were called hawsers, only in sizes over 1-1/2" diameter (ie: over 5" in circumference)

[Lodesman]

Gord - hawser is the navy term for towing and mooring lines, but they can be smaller ie. 3" on smaller vessels. Small boats use boat ropes - the navy doesn't make it easy...

Kevin

[markpj23]

Hate to drag this thread up again... but

Any concerns with how old a line is? By this I mean when buying in bulk from a supplier, need I be concerned about how long the line has been sitting on the shelf since date of manufacture? Assuming it was stored indoors, etc, does the age make a difference?

I'm looking at a bulk purchase of dbl-braid nylon, not poly. Then I get to practice splicing dbl braid - a first for me.

[BC Mike]

I have a length of 1/2 inch polyester that I got new in 1982. I have used it for many farming type chores since then. It is still strong and serviceable although dirty.
Michael