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rgleason · 23-02-2022, 18:25

Thinwater, I agree that the load on the anchor is less than 500 lbs at 40kn, but the Rope %WLL is over 20%, in fact it is closer to 36%

Please see this calculation:
http://www.svamanda.dk/anchor/advanc...b=11000&sb=0.5

Note the "Energy/J" section which is used to account for veering, wind gusts and waves which set the boat into motion. I have entered .5 for Boat speed and the displacement at 11,000 lbs. This adds 270 lbs horizontal force to the anchor.

Next note that the "Rope load / % WL" is then 36%.
This is above the 20% of WL needed to have the rope recover.
That is my point. We have decided that in 33 years with this boat we have only seen 35 kn max 2-3 times while anchored, where the old 1/2" 3-strand was stretched beyond 20% of WLL. Also weather (and wind) has definitely become more volatile.

Again I went back to Defender, and was allowed to switch remnants from the bin that were the same price, which was much appreciated. This time I found 9/16" x 180' which seems much better and just a little heavier than our current 3-strand.

The 8-strand 9/16" is Buccaneer Nylon Windlass Rope - Champion 8
with average tensile strength is 8500 lbs. Note that 1/2" is just 6400 lbs!
Additionally there is a significant loss of strength of 15% when nylon gets wet as I said earlier.

Since Thinwater says that a rope/chain splice is the same strength, perhaps I will just do that, and save the cost of the shackle and thimble ...and perhaps I should have purchased 30'x1/4" as I originally planned, and saved the 11-12 lbs.

I've never done a chain/rope splice but it does not look difficult.

rslifkin · 23-02-2022, 18:32

I think you're confusing working load vs breaking strength. Working load is 20 percent of breaking strength. For 5/8 rated at 11,000 lbs breaking strength that'll be 2200 lbs. You don't need to stay below 20 percent of working load. You need to stay below 20 percent of breaking strength so you stay within the working load limit. So operating at 40 percent of working load is just fine.

rgleason · 24-02-2022, 07:57

Ok, so using Buccaneer 9/16" nylon 8 plait at 8000lb average breaking strength.
8000 x .20 = 2000lbs. Working load.

So 40% of Working load is 800 lbs and you are advising that that load will allow the rope to recover 100%?
Perhaps I have misread the specs, which is very good.
Thanks.

rslifkin · 24-02-2022, 08:00

Quote:

Originally Posted by rgleason

Ok, so using Buccaneer 9/16" nylon 8 plait at 8000lb average breaking strength.
8000 x .20 = 2000lbs. Working load.

So 40% of Working load is 800 lbs and you are advising that that load will allow the rope to recover 100%?
Perhaps I have misread the specs, which is very good.
Thanks.

Yes, that's correct. You can use the full working load without damaging the rope (although it's good to leave some safety margin). The 20% limit is how you define what the working load is.

rgleason · 24-02-2022, 11:46

Thanks, after running some calcs, I find that between 30, 35 and 40 kn comparing 30' of 1/4" to 5/16" chain there is virtually no difference. At 30kn I find the 5/16" chain has 1 degree less anchor angle.

The effects of the added 12 lbs of 5/16" chain will be seen in anchoring "comfort" at less than 30kn, something I really dont think I need...also in sailing performance, weight in the ends.

rslifkin · 24-02-2022, 11:49

Quote:

Originally Posted by rgleason

Thanks, after running some calcs, I find that between 30, 35 and 40 kn comparing 30' of 1/4" to 5/16" chain there is virtually no difference. At 30kn I find the 5/16" chain has 1 degree less anchor angle.

The effects of the added 12 lbs of 5/16" chain will be seen in anchoring "comfort" at less than 30kn, something I really dont think I need...also in sailing performance, weight in the ends.

Agreed. The smaller chain is strong enough, so I'd either save the weight or use the weight to add extra length for more chafe resistance. Unless you've got tons of weight capacity to spare, I see no reason to use bigger chain than necessary.

mitiempo · 24-02-2022, 19:12

Quote:

Originally Posted by rgleason

Ok, so using Buccaneer 9/16" nylon 8 plait at 8000lb average breaking strength.
8000 x .20 = 2000lbs. Working load.

So 40% of Working load is 800 lbs and you are advising that that load will allow the rope to recover 100%?
Perhaps I have misread the specs, which is very good.
Thanks.

Actually 8000 x .20 = 1600 lbs

rgleason · 25-02-2022, 02:28

Correct. Thanks. Buccaneer 9/16 8 plait is actually 8500 break strength so wll is 1700 lbs.

The Bjarne has added Buccaneer lines to his calculator now.

Here is our boat at 40kn with our 5/8 chain and 9/16" rode. I guess I would have prefered to have 1/4" chain and put the 12lbs into a new anchor.

http://www.svamanda.dk/anchor/advanc...b=11000&sb=0.5

rgleason · 18-07-2022, 17:00

Mathias has updated his Anchor Chain Calculator on Google playstore to include rope length calculations as well as chain length calculations.

Highly Recommended. Use it offline for your anchorages. Thank you Mathias!

One way of using it is to set the length of the chain at a fixed distance (the length of chain used on a mixed chain/rope setup), then switch screens to the rope screen by hitting the second horizontal chain down on the right side. Then leave the length of rope empty and hit calculation. You will be given the amount of line needed for zero degrees of anchor angle.

rgleason · 07-09-2022, 15:15

Here is a very interesting Anchor Rode – Calculating Capacity from a blog Cruising Aboard Monk36 Trawler Sanctuary

rgleason · 15-11-2022, 13:22

We recently bought a new Rocna Vulcan 12 at a discount, which is 27 lbs and 5 lbs more than our 40 yr old 22 lb original Bruce. With the heavier 30' x 5/16" chain I think we'll have good anchoring results and I'll still be able to haul it up without too much effort. Its rated for a 33' boat 6 tons (12,000 lbs) within our boat's parameters.