Can Chain Alone Anchor Your Boat???

[Maine Sail]

Hi All,

So over the years I have read many a diatribe by those professing that; "The anchor is not what holds the boat it is the chain and the anchor is not important." I personally find this type of information a little dangerous but like anything you can't always believe what you read on the net...

EDIT: Last week, on another forum, a poster said exactly this in a discussion around swivels:

For grins I once anchored for a week by just tossing out 150' of 1/2" chain in 20' of water - no anchor at all - I was painting it. Boat was 65' ketch that weighed 65,000 lbs. We didn't go anywhere and there were winds up to 15k in the bay. I did stay awake when the wind was blowing, got a little reading in. When I jumped into the water the next day, we'd only dragged about 70' of the chain across the bottom. Big pile was still sitting right were we'd dropped it.

I light of that I made a video that is rather long. It's about 10 minutes, because it is unedited. I wanted to leave no room for accusations of "tampering" by the "chain holds your boat, anchor not important" crowd.... Please fast forward through the longish parts like playing out the chain.

The results are fairly straight forward and just about what I had expected it to show, that chain, even lots of it, really adds little in the way of actually holding you in one place unless it is quite calm, and it may also hinder a proper set if you're not diligent in backing down on the hook..

For the experiment I used our 5/16" 185' long all chain rode. There was a total of 187' of rode for a bow chock to bottom depth of 24.5 feet, the extra two feet was the snubber between the load cell and the chain. This equates to about 7.6:1 scope. Most "all chain" users usually anchor with less than 5:1 and more often 4:1 or 3:1. This would mean less resistance to dragging. The average drag of approx 160' of 5/16" chain through a mud bottom was about 150 pounds. For context a 16" three bladed fixed prop at 4 knots is over 50 pounds of drag so 160' of chain dragging through a mud bottom is only 100 pounds more drag than a locked three bladed prop...

I did some math based on the posters statements also to make sure it was a fair comparison;

What he was basically saying is that 70' of 1/2" chain held a 65' and 65,000 pound vessel in winds up to 15 knots for a week with no mention of said chain wrapping around coral or a rock.

If the "pile" never moved, which would have been the remainder of the 150' minus 20' water depth, minus a bow height of 8' (extrapolated based on boat description), unless he used a snubber, but why would he with just chain, then one could surmise the pile could have been 52' of chain never even tugged on. 150'-70'=80' and then 80'-20'=60' and then 60'-8'=52'

This was the description of the vessel:

She is a 65' long ketch with a small mizzen (you'd think she was a Yawl if you didn't know where the rudder was). The main masthead is about 95' above the water, double spreader rig with jib and staysail on rollers (lots of windage there). Large cockpit hard dodger and roof (more windage). Centerboard design that has a 6' stub keel that houses the centerboard, a 6' deep skeg rudder. 18' of beam and weight of between 60,000 and 70,000 depending upon fuel and water loaded. Tankage is massive, fuel is 800 gallons and water is 1,200 gallons. They are set up to be used as liquid ballast and one never fills them all the way up.

Our 160' of 5/16" BBB, what was actually dragging on the bottom, weighs 192 pounds in total @ 1.2 pounds per foot (ACCO 5/16 BBB). If I take his post at face value, as written, 70' of 1/2" ACCO BBB chain weighs 189 pounds if that is what his chain actually was, if not, a few pounds +/- is possible.

The drag resistance with 70' of chain is clearly going to be less than our 160' because he was lacking 90' of friction resistance. His chain, if BBB type, would have also likely weighed a couple pounds less than our 160' (only counting the part actually sitting on the bottom) of 5/16".

To put it in perspective our 36 footer pulls at her mooring pendants with peaks of 220+ pounds in just 17-19 knots of wind in pretty flat water.

One thing that is a good take away is that if you use all chain you DO need to back down HARD on your anchor to get it set otherwise in calm conditions you may just be laying to the chain, and when the wind picks up, your anchor may just skate along the bottom until you're on the rocks.

As a point of reference our 44Hp diesel with three blade fixed prop can apply about 500-700 pounds of reverse thrust at 80% throttle. This is how we set our anchor at 80% to 100% reverse thrust. When you add the inertia of the boat moving backwards and the boat coming to a full stop when the anchor sets the snatching loads are well in excess of 1000 + pounds when we set the anchor. Using normal scopes for chain, the chain drag is about 9/10th, of what our power setting loads are.

I personally find it a tad difficult to believe that anyone anchored a 65' and 65,000 pound vessel for a week in winds up to 15 knots with only 150' of 1/2" chain in 20' of water and with winds to 15 knots...... . Remember our boat is only about 19-20k loaded, 36' and develops over 200 pounds of load on the rode in just 17-19 knots. This is a FAR cry from a 65' & 65,000 pound vessel that has considerably higher windage.

Approx 160' of chain dragging at 150 pounds +/-..

Our boat in 17-19 knots:

 

[wetass]

Great video, but couldn't help notice you got some acid on those shorts ;-)

While I didn't see any posts about someone claiming they could anchor without an anchor, I did see someone earlier this week claim that anchor size didn't matter, its mostly the chain - So its a fairly common argument I guess and you appear to have put it to bed. Thanks again.

 

[kloudie1]

The chain most certainly holds the boat..to the anchor that is. !!

 

[jfmid]

Fantastic video but I do have one question. Did your neighbors give you funny looks as you motored around backwards in that area????
I'm sure that someone is going to say that it would have worked better in sand and ask why didn't you test on various bottoms. I can almost hear it now.
"Mud is too slippery and reduces hold but when I drop just chain on sand I always stick."
No matter how much you try to show some people they just dont want to learn or improve.
I applaud your efforts and thank you for your dedication to making everyone who is interested safer and happier.

 

[Gary_H]

So you're saying that clothesline and a cinder block probably won't work.....

 

[jfmid]

so You're Saying That Clothesline And A Cinder Block Probably Won't Work.....

Roflmao

 

[Ross]

A farmer I know very well has a 20x20 foot chain harrow. It is a mat of chains with steel bowtiesevery third or forth link. He pulls this across corn stubble with a 55 horsepower farm tractor It would certainly be harder to pull than a single length of smooth chain.

 

[zeehag]

used to be a fella in sd would anchor his champion 24 ft sloop with a 5 gallon pail of water attached to a thin line. he invariably ended up on the golf course......he would also use large garbage baggies of water also tied to a clothes line...... other similar things... was fun to watch as long as he wasnt upwind from ye.....

 

[Bill Roosa]

Perhaps the chain snagged on some really well placed rocks. This is just another example of how our government is letting us down. We pay our taxes and they can't even give us rocks to anchor on!!!! ;-)

 

[Douglast]

used to be a fella in sd would anchor his champion 24 ft sloop with a 5 gallon pail of water attached to a thin line. he invariably ended up on the golf course......he would also use large garbage baggies of water also tied to a clothes line...... other similar things... was fun to watch as long as he wasnt upwind from ye.....

we used to do the same for the big motor in our power boats to slow the boat down for trolling if we didn;t have a trolling motor

 

[Deadhead]

Maybe Mr. 65k's chain snagged on the flukes of that anchor whose chain I snagged last month.

 

[thinwater]

Fantastic video but I do have one question. Did your neighbors give you funny looks as you motored around backwards in that area????

Nah. They know he drags all over the place, since he keeps all his anchors in his garage.

Good data, and about what I would have expected. Clearly, there is something missing from the tale. Perhaps the winds were over stated, prehaps the bottom was unique, prehaps the chain was snagged on something.

But the real point is that behavior at 15 knots means nothing at all, rather like be smug that a climbing rope holds body wieght without thinking about fall impacts. As soon as the wind comes up--50 knots is a reasonable thunderstorm--the dynamic load is going to reach 5,000 pounds and the chain isn't going to be on the ground...
http://alain.fraysse.free.fr/sail/rode/synthesis/synt.htm
... which goes right back to Mainsail's point about backing down.

 

[jibes138]

Perhaps the keel was stuck in the mud?

 

[dparilla]

I think the rumor comes from the old Navy axiom that says the same thing. This of course refers to massive anchors and chains. It gets misinterpreted many times, but in truth it is the catenary (droop) of the chain or rode that holds the boat by properly transferring all motion to the anchor in a linear direction. We also tend to pay out 5-8 chain to depth, typically 1 shot of chain (90 feet) for each 15 feet of depth. The anchor weighs 30 tons and the chain is 365 pounds per link. So 100 links would be another 3650 pounds which will put most of the chain on the bottom unless a really big blow, so in this case the weight of the chain does hold the ship in place, but it is the anchor that secures the chain.

 

[Ross]

I saw some chain on the bottom when I was in the Philippines. The links were about 18 inches long I guess and the wire was at least 4 inches in diameter. Forty or fifty feet of that shackled to my 3/8 inch chain would hold my boat in a blow.

At 365 pounds per link 100 links would be 36500 pounds.

 

[zeehag]

I saw some chain on the bottom when I was in the Philippines. The links were about 18 inches long I guess and the wire was at least 4 inches in diameter. Forty or fifty feet of that shackled to my 3/8 inch chain would hold my boat in a blow.

At 365 pounds per link 100 links would be 36500 pounds.

would make a great mooring anchor if stable.....

 

[Deadhead]

I know an old excavating contractor who needed to grade-off an extreme slope. He somehow obtained a long enough length of that heavy anchor chain to attach and run between two large bulldozers. The dozers drove across the top and bottom of the slope dragging the chain between them. He told me it worked like a champ.

 

[patrickfarley]

Sometimes I anchor with a 5 pound barbell. It is one of the barbells that is covered with the soft rubberized cover. It does not scratch the boat. It works great for anchoring my canoe.

I gave up an anchor once in Sarasota Bay. I was anchored on the artificial reef just north or the Ringling museum. There is a concrete post that marks the reef. I had been fishing for a few hours. A shark began swimming around the reef marker. It swam around the marker for hours. I even hit the shark with a bobber a couple of times and it would not leave. Not a big problem except my anchor was caught on something. Normally I would swim down and unhook the anchor but sharks scare me. I am sure the shark is gone by now and someone could retrieve the anchor and attach it to their chain....

 

[Anchor Down]

wetass posted: So its a fairly common argument I guess and you appear to have put it to bed. Thanks again.

I get it: "anchor" argument, put to bed. Good one.