Anchor Chain Length Versus Weight

[Kettlewell]

"Ultimate holding" is a situation rarely encountered and for that situation you want a long length of stretchy nylon in addition to whatever chain you have down there. I have been in situations where long lengths of chain became bar taught and when that happens tremendous snatch loads will be put on your boat and on the anchor. The nylon can absorb that whether in the form of a long snubber or a length of the anchor rode. You need both chain and nylon for ultimate holding in most conditions, but there are some places where the chain will resist burying in the bottom, therefore not allowing the anchor to bury sufficiently. There is very gelatinous mud in parts of the Carolinas that will float your anchor and chain. Several experience boaters and one marina I know of put short lengths of cable between the anchor and a long nylon rode in order to allow the anchors to bury sufficiently for hurricane conditions.

[Ziggy]

Originally Posted by Dockhead

Bay of Saint Malo -- highest tides in the world except in one spot in Newfoundland.

It is pretty wild sailing there. 10 knots currents in some places.

Actually, Bay of Fundy tides are supposedly higher. See here: http://co-ops.nos.noaa.gov/faq2.html#26

[Kettlewell]

Anchoring in the Bay of Fundy can be strange as you have to tend your anchor line throughout the day in order not to swing out of the deep enough water to anchor in, because at high tide you might need 300 feet of rode out while at low tide you might want or need only 50.

[klem]

Given that you are going to are going to the Caribbean, I would want the ability to put out 5:1 scope with no nylon on the bottom in 40' of water meaning that you need 4*40'=160' of chain minimum which is basically what everyone is suggesting. Having something like 150' of 5/8" nylon after that would let you anchor basically anywhere you wanted to.

5/16 G40 should be plenty strong since it has a WLL of about 3900lbs which represents pretty extreme conditions with your boat. Don't worry, your ultimate holding power will not change significantly, we have already debated that one plenty in other threads.

So basically, I agree with everything that has already been said.

[Expeditious]

Thanks for all the insight, we newbies need that. To answer a few questions raised, the boat is just under 37 feet LOA, draws only 4 feet and weighs a mere 12,500 lbs dry. I expect to be anchoring pretty shallow given the option. Light as she is, the ground tackle weight makes a discernible difference so I would rather not add another 85 pounds in the bow to get to 150' of chain, going with 5/16' should get me 150' with very little added weight.

I also have a horizontal manual windlass at present which works just fine but I may well opt for an electric before doing any extended cruising. Any opinions on vertical versus horizontal, powered versus gravity down and any other things I don't even know to ask?

[Kettlewell]

Make sure whatever you do you match your chain to your windlass gypsy or they won't work together. It is a very good idea to send a sample of your chain to your windlass supplier or to try it out yourself to make sure the fit is perfect. For example, there is 5/16" proof coil and 5/16" Grade 40 (which some call Hi Test). The majority of windlasses these days will take the 5/16" Grade 40 well, but still worth checking with the manufacturer.

[boatman61]

Originally Posted by SailFastTri

What you wrote has nothing to do with boat length.

Ok... let me try and simplify for you.....
I like to anchor normally with 3.5 times my boat length + drop to bottom....
When it blows I like to be able to put out at least another coupla boat lengths of chain... despite the catenary crap... its how I've anchored for 40plus years and I aint changing for something where folks watch me go past backwards rather than my current practice... watching them go backwards...
Also its nice to be able to drop in 15m occassionaly if needed.....
Hence on my 21ft I carry 170ft of chain..
so... so's you understand...
me 21foot...
depth 30foot
Chain out = 30ft(depth) + 75foot(3.5xboat length) = total 105foot...
If thats to complicated let me know...

[Dockhead]

Originally Posted by Ziggy

Actually, Bay of Fundy tides are supposedly higher. See here: Frequently Asked Questions - Tide Predictions and Data

Yes, that's exactly the place I was thinking of. If that's not in Newfoundland then my bad on Canadian geography.

[Dockhead]

Originally Posted by Kettlewell

"Ultimate holding" is a situation rarely encountered and for that situation you want a long length of stretchy nylon in addition to whatever chain you have down there. I have been in situations where long lengths of chain became bar taught and when that happens tremendous snatch loads will be put on your boat and on the anchor. The nylon can absorb that whether in the form of a long snubber or a length of the anchor rode. You need both chain and nylon for ultimate holding in most conditions, but there are some places where the chain will resist burying in the bottom, therefore not allowing the anchor to bury sufficiently. There is very gelatinous mud in parts of the Carolinas that will float your anchor and chain. Several experience boaters and one marina I know of put short lengths of cable between the anchor and a long nylon rode in order to allow the anchors to bury sufficiently for hurricane conditions.

I have also been in situations where 330 feet of 1/2" chain was bar taught -- that's 800-odd pounds of chain -- scary. And that's why good practice is to use a proper snubber in all conditions. And a good snubber is not just two meters of thin nylon. I have two snubbers, one is six meters and 18mm, and the other is 10 meters and 22mm. I agree that your ground tackle is not complete without a snubber long and thick enough to be capable of handling those snatch loads.

Concerning floating chain -- that sounds weird but I have had some situationd where it seemed like just that was happening. My (former) 121 pound Rocna seemed to be floating on top of the mud. Doesn't make any sense -- surely the mud is less dense than steel -- but what you say describes the behavior exactly.

[cwyckham]

Originally Posted by boatman61

Ok... let me try and simplify for you.....
I like to anchor normally with 3.5 times my boat length + drop to bottom....
When it blows I like to be able to put out at least another coupla boat lengths of chain... despite the catenary crap... its how I've anchored for 40plus years and I aint changing for something where folks watch me go past backwards rather than my current practice... watching them go backwards...
Also its nice to be able to drop in 15m occassionaly if needed.....
Hence on my 21ft I carry 170ft of chain..
so... so's you understand...
me 21foot...
depth 30foot
Chain out = 30ft(depth) + 75foot(3.5xboat length) = total 105foot...
If thats to complicated let me know...

Not complicated, but not right either. The scope used should have nothing to do with boat length. Scope is all about the angle of pull at the anchor.

In 40' of water, you'll have 105' of chain out, or 2.5:1 and will drag in any kind of breeze. In 10' of water you'll have 85' or 8.5:1 and will hold in a hurricane, but will have so much swing room, you'll be in danger of hitting others in a crowded anchorage since they'll only have about 50' out.

[zeehag]

for a 35 ft boat, even a heavy one, 5/16 is good to 40 ft of boat length. i was advised i need 3/8, but i will continue with 5/16--i WANT 300 ft of it on my bow. i HAVE 194 ft total new. chain keeps the anchor in place when wind blows and a swell runs. works great.

[Lagoon4us]

I've always calculated depth + height of bow-roller to water times scope required for situation. e.g. 3 x d+h for safe stop staying on board and up to 7 x d+h for maximum hold. Works for me....Cheers

[sailorboy1]

it concerned about the weight of the chain verse the size, use the smaller chain and upgrade the the grade of the chain

everything is fixable with the proper application of boat bucks!

[Dockhead]

Originally Posted by Lagoon4us

I've always calculated depth + height of bow-roller to water times scope required for situation. e.g. 3 x d+h for safe stop staying on board and up to 7 x d+h for maximum hold. Works for me....Cheers

+1

[boatman61]

Originally Posted by cwyckham

Not complicated, but not right either. The scope used should have nothing to do with boat length. Scope is all about the angle of pull at the anchor.
where have I mentioned 'Scope'... or angle come to that....

In 40' of water, you'll have 105' of chain out, or 2.5:1 and will drag in any kind of breeze. In 10' of water you'll have 85' or 8.5:1 and will hold in a hurricane, but will have so much swing room, you'll be in danger of hitting others in a crowded anchorage since they'll only have about 50' out.

Sigh....
Funny... never swung into anyone yet... and rarely (except thick weed) dragged...
remember.... you guys also call a torch a flashlight... which I call an Aldis lamp...
and a spanner a wrench... which is someting that pulls my shoulder out...
You go your way and I'll stay on mine...
Save's buying a ROCNA to hold me...
PS; drop to water from roller is 3ft....ish