200' of 5/16" chain: How much space?

[coreywoodworking]

Not a quite a thread, but I need some guidance and havent found any charts that show chain volume.

I'm redesigning and substantially deepening my anchor locker and dividing it fore-aft in three compartments. Port side 250' of 5/8" nylon rode, center section a narrow but almost to the waterline compartment for 200' of 5/16" chain, and starboard another 250' of 5/8" nylon. It'll have drains port and starboard. SN'ers have suggested that an enclosed anchor locker, that doesn't drain into the bilge, is best. I don't have much of a bilge, just a keel sump, so I second that view.

Can any of you experienced sailors give me an idea of what volume to provide for the chain? It's 190 lbs. of chain. I'm told that a narrow high compartment is better for chain so that it falls/pays out more smoothly, but not so high that it raises the CG.

I have a 28' sloop, 7200 lb. displacement.

[bljones]

I have to ask- why do you want that much chain rode? It will affect trim, it's not cheap, and unless you are consistently anchoring in deep water, it's just a lot of undesirable ballast, IMO.

[coreywoodworking]

My plan is to sail south next summer, for a year or three of scuba and snorkeling, in and around the Caribbean. SN'ers advised an all-chain rode as nylon gets chewed up on the coral and volcanic rock. 200' of chain gets me 7:1 scope in 30' of water. But I'm totally open to suggestions.

Oh, also the boat isn't insured and I want to sleep well.

[jrd22]

200' only allows for anchoring in 20' of water at 10:1 scope if you only use the chain. Not an unusual situation.

I found this at Wooden Boat Forum, don't know if it's accurate.
I would call a chain supplier and see if they can tell you, I'm sure it's a common question.


Skene's Elements of Yacht Design offers the following formula for calculating the volume of a chain locker:

Volume in Cubic Feet = (1.7 * Fathoms of chain * (Chain Size in Inches)^2)/2

So, if you have 40 fathoms of 7/16" chain you would need:

(1.7 * 40 * (7/16)^2)/2 = 6.5 cubic feet

n.b. ^2 means squared -- so you are squaring the chain size

Full disclosure: I have never used this equation so I cannot vouch for its accuracy.

[donradclife]

The formula seems a bit high--200 lbs of chain, steel weighs over 600 lbs/ft3, means less than 1/3 of a ft3 of solid metal, and my eyeball says less than 2 ft3.

[tommays]

Galvanized Proof Coil Chain

Size
Pounds Wt. per Foot in Pounds
3/16" 0.33*
1/4"* 0.63
5/16" 0.93*
3/8" 1.41

[GaryHLucas]

Stop in Home Depot and see how big the buckets of chain are! Bring your ruler.

Gary H. Lucas

[jrd22]

Using that formula I get 2.76 cu. ft. Since I've never been known as a math wizz don't go to the bank on that. I think that sounds somewhere in the ballpark though based on my 300' of 3/8" BBB which makes a pile about 1'+ high and almost 3' in diameter in the back of my car and the formula says it should be just shy of 6 cu. ft.

[coreywoodworking]

Thanks for your help on this. If I allow 3 CF plus add another 1 CF to assure proper chain fall, that would fit nicely. I am concerned though about the comment that I should allow 10:1 scope. In what situation? Does chain require greater scope than nylon or am I just accustomed to coastal non-storm anchoring.

BTW, JRD, thanks for your time and your Brewer is gorgeous. Isn't he talented? When I was still a wannabee, I drooled over his book on yacht design. It's still one of my favorites.

My latest thread: Finding half models of 420s to use for our high school sailing team. Any ideas where I'd find them?

[sailingdog]

I wouldn't recommend going with all chain as that adds a lot of weight to the bow of your boat.

BTW, the chain is generally never going to stow as compactly as you'd like... unless the locker is really properly designed to allow that to happen.

When I re-designed the anchor locker on my boat, I sloped the bottom of the locker so that the rode slides aft and down, allowing the boat to balance better. I lined the locker with UHMWPE to protect the fiberglass from abrasion and help the rode self-stow.

Bene505—

Just curious, what kind of chain is it?