Chain Size and Type

My boat displaces about 100,000 pounds and carries a 110 pound bruce with 440 feet of 5/16" HT chain. I made that selection when the boat was commissioned, 6 years ago. I remember concluding that, at the swl of the chain, the catenary effect with a 4 to 1 scope would keep the pull sufficiently horizontal that additional chain strength was not needed. My theory was that greater force would pull the anchor before the chain would fail. At the time, I had found and used a catenary calculator and other tools to conclude that additional chain strength (and weight) was not useful. Now, however, in looking at some on-line guides, I am thinking that I should have gone with at least 3/8" HT. That said, I have survived 40-knot winds without breaking the chain (or pulling/dragging the anchor). So, maybe I should focus on worrying about other things that could go wrong.

I'm using 5/16 on a 65000# boat at full load. I have not had any issues, but have felt that 3/8 would be more appropriate. I think the PO (who specced the chain and windlass) went for the minimum as he did not plan on anchoring much. But to upgrade I would need a more powerful windlass, not just a different wildcat for it. So unless I start to find it inadequate it is well down the 'to do' list. I am curious as to what the experts will have to say on this topic.

I'm no expert but experts sized our chain for us and for our 30,000 pound boat they recommended 5/16" chain.

For a twice-as-heavy boat with more windage it might be prudent to go to a larger chain size than 5/16" but I'd want to consult someone who knows more about the subject than I do.

We have 3/8's G43 on our 90,000LB + boat.

Upgraded to 10 mm G30, 350 feet, not high test, boat weighed 36k last time in slings. Anchor 65#. Working load of chain just under 3000#. I think the high-test is slightly over 5000. So far, so good. Entertaining the thought of the new Rocna, Vulcan.

Our Grand Banks had 3/8" chain and was a little under 60,000 lbs. Our Nordy has 1/2" chain for a 130,000 displacement.

I'm thinking 3/8" would be more appropriate for your boat, or perhaps even 7/16" if there is such a thing.

I think your 5/16" chain is strong enough for three times the load you have already put it through. And by the looks of your vessel I'd say it's better to save the weight. There's no doubt that going to 3/8" chain will improve your comfort and safety at anchor but at what cost with regards to the boat's ride. Both Dashew and Fexus designs seem to favor light ends so if it ain't broke don't fix it.


Via iPhone.

1st Chain Supply has a nice website with tables showing data for chain sizes and types. Check the columns for breaking strength as well as WLL, it may give some comfort to us light chain users.

On most boats except an FPB, the winch, cleats or other vessel tie points will rip out well before the chain breaks. The FPBs will hang from a crane by their anchor rode tie point if one were to do that test.

The weak link would seem to be swivels and shackles breaking before the chain. This is why I abandoned my expensive swivel that bent one stormy night.

Thanks for the advice, everyone. Seems like I am undersized, and the irony is that 3/8" wouldn't cost or weigh much more. What was I thinking?

First, I do not think the weight of the boat has as much to do with the forces applied to the chain as we might think.

We are not holding up the boat with the chain. We are merely holding the boats position, countering the effect of wind and current.

The only time I believe boat weight comes into play is if the boat is moving and suddenly reaches the end of the rode length. Then a heavier boat would take more force to stop its momentum.

Wind force seems to me to be proportional to the area above the waterline and its shape.

Current force seems to me to be proportional to the area below the waterline and its shape.

So...

My boat is what I would call a mid profile pilothouse cruiser 47' hull length 44' water line length. Beam is 15'. I call it mid profile because sitting next to say a Hatteras 48 LRC or a Defever, or a Sea Ranger 48' pilothouse my boat is a little shorter than these. Just looking at my boat in comparison to these boats my boat has some amount less mass above the waterline, meaning to me less wind area. How much I do not know, but somewhat less. (which actually makes me happy because it means that my Bayliner is probably not top heavy when compared to these great designs. Probably also why my boat performs unexpectedly well in rough seas.)

Below the waterline I have a SD hull form, which means that my boat will exert somewhat more force against an anchor rode in a current. How much, i do not know, but in my opinion more.

We have been using 100' 3/8" BBB chain and 5/8" 8 plait rode for several years tied to a 66 LB bruce clone anchor. This has been a successful system except it is a PITA to haul the line in using the capstan.

We have just switched to 5/16" HT all chain rode, 550' and a 80 lb SARCA EXCEL anchor. The chain was chosen because 3/8" bbb works and 5/16" HT has a higher working load than the 3/8" bbb. This gave us an about 1/2 lb per foot weight savings.

IMHO you really need the weight of the boat AND the length to accurately size anchors and chain. I prefer the Rocna sizing guide as I find it more realistic.


Sizing Guide | Rocna Anchors // Rock Solid


This has you 1/2" chain (3 sizes up) of G40. If you're really concerned about weight look at G70 chain instead.


1/2" G4=2.54 lbs/ft (@ 440ft = 1,117.690lbs)
5/16" G4= 1.04Lbs /ft (@440ft = 457.6lbs)

Kevin, I believe you are much more correct than most.


Windage is about frontal area and not really proportional to length or weight.


Current is virtually not a factor at higher wind speeds...it is ore about stopping momentum cause by sailing at anchor, surging over waves and breaking waves....well.... I will say normal currents up to say 10 knots or so. For the most part the stronger the current the less likely you will sail at anchor in most boats.


The article about mooring from the stern by Jordan Drogue in another thread discusses boats that are stable or unstable at anchor and what forces that generate. The more stable a boat is at anchor...the less the forces usually exerted on the ground tackle.


The reason most large ships get away with smaller proportional anchors is because of a completely different philosophy of anchoring...read up on it if you have ever tried to use a comparison here...I think you will be surprised. A more accurate comparison might be of oil patch rigs and vessels anchored in the open sea and those requirements..but not just ships that anchor in port and stay that way through heavy weather because they don't experience the surge forces we do.

Where boat weight or displacement plays a roll is when the boat is at anchor in a windy, wave-filled anchorage. The boat will have removed some or most of the catenary from the chain and as it surges up and down it will subject all the components Sunchaser listed to an increased strain.

At the private island where we have property we used buoys owned by other island association members when we went down there. One in particular was always available. Supposedly it was dove on and checked every year, and we had no problems with it even on windy, wavy days.

A few years ago we were down there and friends with a 36' lobsterboat joined us and rafted to us. That afternoon the wind came up and closely spaced waves about 3' came marching across the fetch and into the bay. This was no big deal, we'd been on this buoy in worse. But now instead of 30,000 pounds of boat we had over 45,000 pounds of boat on the buoy.

Within an hour there was a loud bang and our raft was adrift. Our friends started their engine and powered us out of the shallow water we'd drifted into. Once clear we pulled the buoy up on deck to see what had happened. The chain that connected the buoy to the concrete block anchor was now about six feet long. It ended with an undamaged link so we could only assume the link attached to it had broken.

Which proved to be the case when the buoy's owner had a diver replace the chain.

The owner has a 25' fishing boat and the buoy chan was sized for it. So we were probably putting it to the test with our own boat on rough days as it was. When our friends added the weight of their boat it proved to be too much.

We still use the buoys today if conditions are forecast to be calm or minimal. But if there's a chance the wind's going to pick up we anchor. The anchoring is very good there, it's just less effort to use a buoy.

Kevin,
Your numbers are quite interesting to me as in a year or so I may increase my chain to possibly 100% so you and others w boats more than twice as heavy as ours using 5/16" get my attention. With you using 5/16" chain my using 1/4" HD chain should be plenty strong engugh for our little boat. I was thinking 1/4" would be too weak but it looks like that's not true at all.
This summer we will probably cruise w another Willard 30 that has a small typical winch, a Delta and 1/4" chain. I'll be observing how difficult or easy anchoring w a winch and chain is. As I get more familiar w chain and winches I may become more accepting of them.
Anyway thanks for the relevant numbers ect.

Our 90/90 is 33loa, 28lwl and under 20,000 overloaded for sea. 16251lbs light ship.

200 ft of 3/8 stored mid ships , under the mast for coral areas.

A few hundred pounds of insurance , ahould the bottom be sharp.

Marin said:

A few years ago we were down there and friends with a 36' lobsterboat joined us and rafted to us. That afternoon the wind came up and closely spaced waves about 3' came marching across the fetch and into the bay. This was no big deal, we'd been on this buoy in worse. But now instead of 30,000 pounds of boat we had over 45,000 pounds of boat on the buoy.

Within an hour there was a loud bang and our raft was adrift.

Click to expand...

Two 36 footers are like a 72'.



Via iPhone.

Pretty sure those charts are made up by an average frontal area of vessels....which are nothing more than wild a** guesses.

Certainly boat type factors in and could go either way with being additive... more or less windage.

A lobsterboat has considerably less windage than our boat. It was the combined weight surging up and down in the waves that broke the chain. I don't think the wind had anythng to do with it other than creating the waves themselves.

I think most issues with anchoring are water related rather than wind...just like water in a hurricane, storm surge and other, causes way more damage than just the wind.