How big is too big?

[Stumble]

Originally Posted by a64pilot

Chain weight is irrelevant once the wind begins to howl, chain is straight and tight. A kellet may accomplish more than chain weight?
WLL is a concern though, which now has me thinking I ought to go to grade 70 chain, up from my current 40.
Good source of grade 70 galvanized chain?

Adding weight to the anchor chain adds roughly 1lb of holding power per pound of weight added. It's actually a little less, but idealized it works out to about 1:1. Weight in the anchor (really a shortcut for the physical size of the anchor) adds holding power at a ratio of about 75:1 - 100:1 depending on the design, with modern SHHP anchors closing in on 200:1.

So it isn't that bigger chain doesn't help, it does, it just doesn't help much.

So on your boat let's assume that you can dedicate a maximum of 500lbs to the anchor system, and want 300' of chain. And let's assume the anchor design adds 150lbs of holding for each pound of weight.

3/8 G43 galvanized chain weights in at 1.5lbs/ft and has a MWL of 5400lbs. So for 300' of chain you have 450lbs in the chain and can carry a maximum of a 50lb anchor.

450*1+50*150=7,950lbs of holding power.

Switch to G70 chain...

5/16 G70 weighs in at 1lb/ft and has a MWL of 4,700lbs. For the same 300' of chain you have 300lbs of chan and can swing a 200lbs anchor.

300*1+200*150=30,300lbs of holding power.

In either case you have exactly the same weight on the boat, the same max load on the windlass, but the holding power on one is four times higher than the other. The G70 chain set up has almost four times the holding power of the G43 chain.

Now do you need a 200lb anchor? Good god no, even I am not that crazy. But say a 100lbs anchor would give you roughly 15,000lbs of holding power, and max out the MBL of the chain anyway, so bigger doesn't help here. And you get to shave 100lbs of weight off the bow. Which isn't a bad result either.

So as long as you are price insensitive, smaller higher strength chain with a bigger anchor is absolutely the way to go.

[charliehows]

i got some attitude from a guy i was anchored next to a couple of years ago - he wanted me to move so he could pull his anchor - i refused because there was plenty of room as far as i could see. It ensued that in order to lift the oversized anchored he needed to haul the windlass til it ran out of power and then run his boat in circles til the anchor broke free. In general it is a good idea to match the anchor size to the boat. My 38' uses a proportionate CQR and has never dragged on me so far.

[barnakiel]

Except that one thing that our number crunching posters oddly disregard: the energy required to drag the chain ACROSS the bottom and water.

Chain is not just about SWL and pounds added to the holding power. It is also about what your boat will do in squally conditions - and most boats will start to sail.

Now it does matter if the chain is long or short and it does matter if it is heavier or lighter. In other words, one may become hesitant to 'sacrifice' the weight in the chain (in order to) add weight to the anchor.

And so some of our 'is heavy chain pure nonsense' rant is, as the French put it, "my arse". Because we may have less weight in the bow now but we may be sailing at anchor more and so we might want MORE HOLDING power again. Pretty contradictory, isn't it. Or skip the extra weight in the anchor put the extra weight in your chain ... ;-)

Yep. I know. Life sucks.

PS I can tell you what we did about the above in our own boat. While holding the weight the same (this was our constant - no winch and so I am limited by how much I can handle), we got smaller gauge and longer piece of it. I believe the boat sails less now. I am not sure, just a judgement from this cockpit here.

I am not sure what others found: given constant weight, should one use a shorter heavier (per ft) chain or rather a longer and lighter (per ft) chain? Or is this all the same?

Assuming the anchor is already "big enough".

Cheers,
b.

[Snowpetrel]

With too big an anchor you will struggle to properly set the thing. This will likely leave part of the fluke sticking up that can be caught by chain and possibly pull out the anchor. With a poor set in a windshift you are more likely to rip it out. Raising the monster anchor in some bottom types might result in dangerous snatch loadings. I would go the 33. Still oversize but not stupidly. In fact if you are getting a new anchor id look at the spade, excel or mantus due to the more reliable resetting.

Simple rule of thumb (boat length×boat length in ft)/weight of anchor in lbs should be somewhere between 20 to 30. The dashews 83 footer has a 240lb anchor for a relatively poor ratio of 28.7. I have always sat around 25. Beth and Evans had about 20 with a Bruce anchor. A rocna 40 would give you about 16.4, far to low.

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[sailorboy1]

In the end - get the biggest anchor that makes YOU comfortable and don't worry about what other boaters think about it, especially internet boaters!

BTW - it is questionable that an anchor WAY oversize really sets and holds any better that the proper size since it probably wouldn't dig in far enough to make full use of its' large size

[Paul L]

I know you didn't buy your IP for its pointing ability or to make 200 mile days, but I assume that you do enjoy sailing it. Weight on bow does matter - it is way out on the pointy end, even more than the chain. While you can argue that 20 lbs here or there makes no difference, but it truly adds up. I see no reason on your boat with what I understand are your plans to go above the 33. This is one size larger than the Rocna spec and should do you fine. I have the Spade equivalent of the 40 on my boat that is fair bit larger than yours.

[HBWT]

I can comment that our ridiculous sized anchor sets no problem when backing down. I have dove on our anchor in multiple questionable holding grounds and has never let me down. We would not leave home without our Spade. We also have the A120 still oversized for our boat and spade does not recommend using a aluminum anchor as your primary unless you are a race oriented boat light displacement boat that is concerned with weight and NOT cruising. We use the A120 for a lunch hook or if we are in a protected anchoring ground and use the S200 for everything else.

[a64pilot]

It will set, I believe. I can drag my 25 in sand, but an Autoprop is as efficient in reverse as it is in forward as the blades spin around and the leading edge is still the leading edge, so I have way more pull than normal.
I can break it out I'm sure, without spinning circles. It is only about 33% more weight and surface area, not three times as much. The 25 holds well, you can feel it dip the bow when prying it out, but the 40 will break out, just maybe have to wait a little longer.

Weight is I believe not such a good way to size anchors, is it weight or surface area that gives an anchor its hold? I believe surface area mostly or else how do alloy anchors work? Weight I believe may help in setting, but maybe not so much in holding. But we buy anchors by the pound don't we and compare them by the pound etc.
On a normal day chain weight I'm sure will help with sailing, but my concern is with very high winds, winds that I'm sure would straighten any reasonable chain, but since weight is an issue, I'd rather have lightweight chain and carry the extra weight in an anchor.
Yes weight matters, I have loaded my boat down so much that it's sailing performance has suffered, my new headsails with the Genoa increasing in size from 110% to 130% has only returned the boat speed to what it was before I added all the weight and windage, but I want a dinghy in Davits and Solar panels, Radar and a barbecue grill and a full Bimini etc.

For all normal anchoring it seemed the 25 was fine, but I want a Storm anchor, and in all honesty I have never heard anyone worry they had too much anchor in stormy conditions ?


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[Tayana42]

a64, did you consider a large Mantus like Noelex and his Mermaid use? I'm not sure but it appears to have more surface area for the weight than Rocna. I've never used one. I'm happy with my Rocna.


S/V B'Shert

[Stumble]

A64,

Other than the Fortress which is aluminium anchors are all pretty much built out of steel. So weight is a pretty good corrilary for size, or at least volume. And it is far, far easier to measure weight than it is fluke area.

The only other anchor I know of is a titanium anchor that was built as a demonstration piece. It is far lighter than a steel anchor the same size, but I think the retail on it was about $40,000 for a 25kg equivilant. So I don't see it entering production.

[barnakiel]

Originally Posted by Snowpetrel

(...)

Simple rule of thumb (boat length×boat length in ft)/weight of anchor in lbs should be somewhere between 20 to 30. The dashews 83 footer has a 240lb anchor for a relatively poor ratio of 28.7. I have always sat around 25. Beth and Evans had about 20 with a Bruce anchor. A rocna 40 would give you about 16.4, far to low.

Petrel,

Is this not the case where lower is better?

Just asking. For look at this:

boat 38 ft x 38 ft = 1444

anchor 40 (88lbs) , ratio = 16.4
anchor 80 (175lbs), ratio = 8.25.

So the bigger anchor returns the lower ratio (?). Unless it is my brain fart as it is very late here. If so, PLS just disregard my query.

Regards,
b.

[Snowpetrel]

^^ quite right B, the lower the better. Good for comparing like for like anchors on differnt sized boats.

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[Panope]

Concerning retrieval break-out force of larger anchors......During my extensive testing of 16 different anchors, I found that break-out force had much more to do with setting force and very little to do with anchor design or size.

Steve

[Snowpetrel]

http://www.setsail.com/anchoring-system-logic-2/

Note the sundeer 64 (jedi's boat I think it was) sat out a very bad cyclone on a 176lb Bruce. This gives a number of (64x64)/176= 23.3 .A low number, but also a low holding anchor type, and a lower windage boat for its length.


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[Panope]

Snow, does your formula work for ever larger boats and ships?

Steve