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Old 08-04-2019, 09:53 AM   #1
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How to size anchor to windlass

My soon-to-be new-to-me Selene currently has a ground tackle set up consisting of a Muir Cheetah HR2500, an 80 pound Rocna, and 400 feet of chain.

I plan to swap out the Rocna for the largest size Mantus the windlass can handle. How do I calculate the maximum size anchor here? How do I calculate the load of my anchor/chain set-up? Do I calculate for all 400 feet in chain weight, or only the weight corresponding to the actual water depth at the greatest depth where I plan to drop the anchor, or something else?

(Assume no bow roller issues.)

Thanks.
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Old 08-04-2019, 09:57 AM   #2
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I would check the owners manual, which can be found online. Usually, the 2500 in the model number indicates the power of the windlass, in this case 2500 pounds, but I would check. I have a 105# Mantus on my boat and my windlass is only a 1500. Great choice of anchor, BTW.

Let us know what you decide.

Cheers, Bill
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Old 08-04-2019, 10:01 AM   #3
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Iím no expert, but I think Iíd want my windlass to be able to pick up the weight of my full chain and anchor, plus whatever nonsense it might be bringing up with it.
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Old 08-04-2019, 10:04 AM   #4
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I’m no expert, but I think I’d want my windlass to be able to pick up the weight of my full chain and anchor, plus whatever nonsense it might be bringing up with it.
Exactly! If somehow my anchor gets run out in 500 feet of water, it would be nice to be able to haul it back in. A nice rule of thumb might be the weight of the chain plus the weight of the anchor times 2.

What size chain are you using? 100 ft of 5/8” is 380 lbs, but 100 ft of 3/8” is only 144 lbs. 1/2” is 236 lbs per 100 ft.

I have a 121 lb anchor with 300 ft of 5/8” chain and my windlass is rated for 2500 lbs: 380x3 plus 121 equals 1270 lbs x 2 = 2540 lbs.
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Old 08-04-2019, 10:09 AM   #5
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The Muir 2500 has a maximum pull of 2,500 pounds and a working load of 624 pounds.

From what I gather a foot of 3/8 inch chain weighs about 1.4 pounds, meaning 400 feet weighs 560 pounds. The question is, how much of that chain weight shall I account for when I am calculating the maximum size anchor that my windlass will lift?

With a 105 pound anchor, should I be calculating for a working load of 665 pounds (560 in chain + 105 in anchor) or something else? Would that 105 pound anchor be too large for the windlass? Or is there only a potential problem if I am anchoring at a theoretical 400 foot depth (which won't happen)?

Yes on the Mantus. I was on a charter with a 65 pound Mantus for a month in Desolatuon Sound and had an EXCELLENT experience with it.

Thanks!
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Old 08-04-2019, 10:11 AM   #6
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Your windlass needs to be sized to lift your anchor chain, and anchor in whatever depth you might be anchoring in.

It also needs some extra margin to break out your anchor.

How large of a boat are you buying?

a 80 lb ROCNA anchor and 400’ of chain might be just fine.

My boat is 45,000 pounds, 47’ and I have a 80 lb SARCA excel, with 550’ of chain pulled by a Lofran Tigress windlass. This works just fine, and I have anchor’d in gale force winds before. I also anchor deep for fishing with limited scope and just last week pulled my anchor at well over 300’ water depth several times with no issues.

The ROCNA is no slouch of an anchor BTW.
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Old 08-04-2019, 10:17 AM   #7
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The boat displaces just about 60,000 pounds.

I subscribe to the nugget about the anchor being too small unless people are pointing and laughing.
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Old 08-04-2019, 10:43 AM   #8
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3/8 BBB chain is pretty puny for the anchor you are considering. Maybe a size down to about 90 lbs would be a better match. Have you anchored with your Rocna to assess if that size is acceptable?
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Old 08-04-2019, 11:06 AM   #9
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The boat displaces just about 60,000 pounds.

I subscribe to the nugget about the anchor being too small unless people are pointing and laughing.
OK, either way you size the windlass to the lifting load, plus a margin, not the total weight of chain onboard.

Agreed, nobody ever wished they had a smaller anchor.
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Old 08-04-2019, 11:19 AM   #10
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I'd contact Muir/IMTRA. What is the length of the boat? That counts in addition to displacement as a larger boat creates more windage. That Rocna could be plenty big (taking your mantra, which I adhere to as well) depending, and it's form factor is very similar to the Mantus. Personally I'd do some boating with the existing rig and then evaluate the need.
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Old 08-04-2019, 11:31 AM   #11
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Assuming it's the 40 KG / 88 lbs. Rochna, I would be interested in buying it.

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Old 08-04-2019, 01:27 PM   #12
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Iím no expert, but I think Iíd want my windlass to be able to pick up the weight of my full chain and anchor, plus whatever nonsense it might be bringing up with it.
Yes, because you might find yourself as I did, crossing the Gulf of Mexico, wondering why the boat was handling so bad, and discovering the entire chain and anchor had paid out and was swinging beneath the boat. (Thank God it happened in deep water).

It was pretty rough that night, and I really loved my windless that night as I watched as it just reeled all of the chain and anchor in at the push of a button .
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Old 08-04-2019, 01:58 PM   #13
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Simply adding the anchor weight and chain weight would leave no room for a foul bottom.

The boats movement would be used to break out the anchor , and the shape or weight of the vessel doesn't matter much as the windlass is only used to lift the anchor system.

The hassle is the unknown goodies that can foul the anchor that must be lifted so the anchor can be cleared.

Having a bit of extra umph in the windlass can save the day , and some big bucks.

Plan B as always, is a trip line that might slip the anchor free.
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Old 08-04-2019, 03:16 PM   #14
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ksanders wrote;
“Agreed, nobody ever wished they had a smaller anchor.”

Unless you eliminate those that anchor by hand. They all would want a smaller (lighter) anchor. And everyone should “want” a smaller anchor as excessive weight is always undesirable or worse. Problem is we don’t know specifically how heavy a specific anchor should be or what the weather is going to be.

And out of that thinking comes “bigger is better”. But it’s only better if your anchor is too small and we’re right back to what anchor or how much chain. And that is too narrow a view as the above dosn’t even consider the biggest variable in anchoring .. the seafloor.

So one is left using various anchors in various high winds in various bottoms ect ect until one gets comfortable w a specific setup. And those of us that need to know usually go this route and succeed.

But that’s too much effort so most all just copy what the guy (that they respect) does. Very simple and no time wasted .... if the other guy knows what .....
But then the copiers usually choose products, methods and amounts that a very many use or/and do.

Most all of us copy in the beginning and continue copying as their mousetrap gets better. I started out copying w a 1/4” nylon line, no chain and a small Danforth. Boat was a 17’ light plywood OB cruiser. Use it now? I think not. But for my situation it was actually fairly good except I would need some chain.

Advice? Yup. Copy those that actually anchor in very similar conditions that you will be. In the same area, at the same depths ect ect. Then pay a great deal of attention to how it all works. And once you’ve anchored in 40+ knots successfully you’ll cross into a comfort zone feeling you must be doing something right.

But whether you figured it out all by yourself or copied the guy in the slip next to you you’ve done the right thing if you kept yourself and all on your boat safe. That’s the bottom line. Whatever works.

Lastly you don’t need the latest equipment for success ... but it usually works better. How much better is frequently a subject of anchoring threads. But they usually only test the newest anchors. But if you’re using older equipment you probably know how well your’s works.
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Old 08-04-2019, 03:24 PM   #15
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Quote:
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Simply adding the anchor weight and chain weight would leave no room for a foul bottom.

The boats movement would be used to break out the anchor , and the shape or weight of the vessel doesn't matter much as the windlass is only used to lift the anchor system.

The hassle is the unknown goodies that can foul the anchor that must be lifted so the anchor can be cleared.

Having a bit of extra umph in the windlass can save the day , and some big bucks.

Plan B as always, is a trip line that might slip the anchor free.


Thanks for all the responses. I would think - perhaps incorrectly - that the maximum pull amount of the windlass (instead of the working load) is the critical number to look at insofar as the anchor breaking power of the windlass and possible fouling are concerned. The maximum pull on the Muir HR2500 is about 400% of the working load.

I should have mentioned that the Mantus size charts indicates that the 85 pound is the right size for me. If my windlass would take it, I'd happily splurge on the 125 pound. I'm looking at the 105 pound, however, because of windlass concerns.

Thanks again.
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Old 08-04-2019, 11:40 PM   #16
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QUOTE: Most all of us copy in the beginning and continue copying as their mousetrap gets better.

I was very fortunate. My wife bought me a copy of "Complete Book of Anchoring and Mooring" by Earl Hinz for Christmas in the 80's, when we were starting to anchor out.

It turned me into an overnight expert!

Even though new anchors have been introduced since publication, the book is the definitive bible for anchoring.
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Old 08-05-2019, 01:33 AM   #17
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The Muir Cheetah 2500 is their biggest windlass and gets used on large Rivieras etc. I think it would cover most rodes on our kinds of boats. Now has a composite case which doesn`t corrode and bubble the paint. I`ve seen the smaller "Cougar" model on 40ft boats.
When the motor in our Cheetah died Muir stuck a 1200watt motor in it. Fried the ammeter in an instant, but pulls hard, and almost too fast.

Muir are based in Australia and are responsive to email inquiry.
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Old 08-05-2019, 05:13 AM   #18
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"I'd happily splurge on the 125 pound. I'm looking at the 105 pound, however, because of windlass concerns."

An additional concern is bringing it aboard.

With longer shanks a bigger anchor may be a PIA to get onboard,and secure.

Folks with a bow crane need to make sure a larger deck bed and lashing spot will work out.

The hawse hole carry should be examined to see weather bigger (always better) will fit with no modifications.
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Old 08-05-2019, 10:53 AM   #19
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Sizing Guide | Rocna Anchors // Rock Solid

Sizing is based on a combination of weight and size.

A 40 KG Rocna would cover a boat:
≤70,550 up to 52 feet
≤55,120 upto 59 ft

I would say a boat at 66K and ~55ft would fall into this size nicely. Also keeping in mind Rocna purposely oversizes their anchors and suggests you hold to their recommendations.

They recommend G40 7/16" (11mm) chain
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Old 08-05-2019, 11:35 AM   #20
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One responder suggested a call to Imtra/Muir. That seemed like a good idea. Just called this a.m. and the customer service was excellent.

Here is their advice. The maximum power for the Muir Cheetah is 2,500 pounds, and they recommend keeping the combined weight of anchor and chain/rode to <33% of maximum power or approx. 833 pounds.

Thanks.
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