What Anchor Line Would You Get?

[Dennis.G]

My boat is 48' ketch, fairly low windage, and 23 tons. I currently have 300' of 3/8" BBB chain with 65# CQR and a Muir 1000W windlass.

I recently wanted to anchor in an area with 105' depth. I think I would have held OK in the current conditions with 300', but I was not comfortable getting off of the boat with that short of scope, so moved on elsewhere.

I want to keep an extra length of anchor line to shackle on to the end of the chain should this situation come up again (plan to revist the area soon). Also want line long enough so it count serve as a back-up anchor rode by its self. Trying to decide between:

1. 250' of 5/8" 3-strand nylon
2. 250' of 3/4" 3-strand nylon
3. 250' of 5/8" mega plait nylon
4. 250' of 3/4" mega plait nylon

The 3/4" size seems an overkill and would add significant bulk, but maybe I should use anyway?

What do you use, and recommend for use based on my boat?

Thanks for your input

[colemj]

Definitely the multi-plait - it will store in a fraction of the space of 3-strand. As for size, look at a recommendation table. 5/8" is probably stronger than the chain you have.

Mark

[micah719]

Wet nylon under cyclic loading isn't quite so strong anymore. 3/4 rather than 5/8, but it's your pocket.

[Mardav]

3 would be my choice

[Dennis.G]

Originally Posted by colemj

Definitely the multi-plait - it will store in a fraction of the space of 3-strand. As for size, look at a recommendation table. 5/8" is probably stronger than the chain you have.

Mark

Well, almost exact match:
3/8" BBB 11000 lbs breaking strength
5/8" multi plait 10400 lbs breaking strength where 5/8" 3-strand about 11000 lbs.

Storage space is important. Will likely store in a bag in a locker, but able to keep ready on deck.

[zeehag]

for your 48 ft boat i would buy all chain---3/8 inch all chain rode.

[Dennis.G]

Originally Posted by zeehag

for your 48 ft boat i would buy all chain---3/8 inch all chain rode.

Well, already got 300' of chain. Not very often I use all of that. But sometimes would like more length, so shackling on a nylon line in that case just seems to make sense in those occasions.

[colemj]

Originally Posted by Dennis.G

Well, almost exact match:
3/8" BBB 11000 lbs breaking strength
5/8" multi plait 10400 lbs breaking strength where 5/8" 3-strand about 11000 lbs.

In that case, I would go with 3/4".

Mark

[donradcliffe]

You really want the 3/4" rode--quoted breaking strength is for the rope under ideal conditions, and does not take into account knots, splices, or chafe. BTW, let the chain out first, and don't add more nylon than the water depth if you are in an area of coral and/or rocks.

[Dennis.G]

Originally Posted by donradcliffe

You really want the 3/4" rode--quoted breaking strength is for the rope under ideal conditions, and does not take into account knots, splices, or chafe. BTW, let the chain out first, and don't add more nylon than the water depth if you are in an area of coral and/or rocks.

I guess in the best case I would have at least an eye splice on the end of the line. How much does that reduce strength of line?

Agree with your point. If in 100' of water would not see letting out more that 100' of the nylon line in most cases (in addition to the 300' of chain). If really deep, and really blowing, and coral - well might be beyond comfort level at that point.

[Caribsailors]

I'm not as big...but I have 150' of 5/16 G-4 and 200' of 3/4 3 strand anchor spliced on the end. Bite of 3 strand ready for another anchor.
Have 2 spare danforths so ya never know.

Cheers

[Jim Cate]

G'Day Dennis,

Hmm, lots of differing advice above... how unusual in an anchoring thread!!

So, here's my addition:

When anchoring really deep (ie your 105 foot neighborhood), I have found that the scope requirements seem to be less stringent, and 3:1 isn't so scary as it would be in 10 feet. But having some additional line available isn't a bad idea per se.

Because it would be seldom used, I think a smaller "safety factor" would be feasible, since wear and tear, sun damage etc would be minimal. Thus the 5/8 inch size would likely be ok. Further, if nasty conditions are f/c, one would likely try to find a shallower spot to anchor in.

Because of the storage factor (as others have mentioned) the plaited line will be better for you than 3-strand. An eye splice with thimble and a good shackle is the best means of connecting the two rodes (don't forget to mouse the shackle pin!)

Don Radcliffe's advice about not letting the nylon lie on the bottom is well said. If there are coral bommies sticking up from the seabed anywhere nearby, even more care is required to avoid the nylon coming in contact with the coral if you should swing a bit.

A further option would be to use dacron rather than nylon. I know that it has less stretch, but when coupled with 300 feet of heavy chain this becomes less of an issue, especially if you have close to 100 feet of the line to act as a shock absorber. The dacron will have better wet chafe resistance, a bit more strength, and possibly a better price... maybe!

FWIW, we cruised for 17 years and 86000 miles in our previous boat. We had 275 feet of chain and a very long bit of 3-strand 5/8" on the end of it. In all those years and miles we used the nylon ONCE. On our current boat we just have the (approximate) same length of chain and no nylon... no worries yet after a mere 42000 miles and 9 years!

Good luck with the decision!

Jim

[Ziggy]

Originally Posted by Dennis.G

Well, almost exact match:
3/8" BBB 11000 lbs breaking strength
5/8" multi plait 10400 lbs breaking strength where 5/8" 3-strand about 11000 lbs.

You should go by the working load limit (WLL), not breaking strength. The WLL for 3/8" Acco BBB chain is 2650 lbs.

WLL is usually not specified for rope. New England Ropes has this advice:

Working Loads:
No blanket safe working load (SWL) recommendations can be made for any line because SWL's must be calculated based on application, conditions of use, and potential danger to personnel among other considerations. It is recommended that the end user establish working loads and safety factors based on best practices established by the end user's industry; by professional judgment and personal experience; and after thorough assessment of all risks. The SWL is a guideline for the use of a rope in good condition for non-critical applications and should be reduced where life, limb, or valuable property is involved, or in cases of exceptional service such as shock loading, sustained loading, severe vibration, etc. The Cordage Institute specifies that the SWL of a rope shall be determined by dividing the Minimum Tensile Strength of the rope by a safety factor. The safety factor ranges from 5 to 12 for non-critical uses and is typically set at 15 for life lines.

You can decide whether the anchor rode is "non-critical use" or a "lifeline".

[Dennis.G]

Thanks Ziggy

If use a safety factor of 12:
5/8" mega plait nylon: 10,400# BS / 12 = 866# SWL
3/4" mega plait nylon: 15,000# BS / 12 = 1250# SWL
Both of which are significantly less than the chain's 2650# WLL.

Looking at it another way, if assuming the desired line SWL is 2650# (the WLL of the chain), the safety factors would be:
5/8" mega plait nylon: 10400 / 2650 = 3.9
3/4" mega plait nylon: 15000 / 2650 = 5.7

Of course this assumes that the definition of SWL for line and WLL for chain are somewhat the same (which may not be the case, for if using the same approach, the 3/8" chain safety factor would only be 11000/2650 = 4.2). Also assumes that maximum tensile strength and breaking strength mean the same thing (which I think is correct).

Anyway, this discussion is pushing me towards the 3/4" size line as a choice.

[Ziggy]

The safety factors are different for different products and applications. I think they may be higher for rope than for chain because of potential effects of dirt, UV, etc. FIW, for my anchor rode I use 5/16" G4 chain with 5/8 plait nylon rope for a 32' boat, ~10,000 lbs displacement.