Anchor Rope Size Rules?

accentphoto

Petty Officer 2nd Class
Joined
May 4, 2011
Messages
128
Just out of curiosity, are there any charts about what strength of rope is needed for an anchor for various size boats? Mine is a 17' Grumman 5.0 that weighs in with the motor, boat hull and accessories at around 1200 lbs. The anchor is probably around 12 lbs with about three feet of chain on it. Maybe the question is silly but in my area the river can get might strong (Cape Fear River in NC) and I had a motor go out before on me and when I dropped anchor I thought the items in the water were moving fast (crab pot markers) only to find out it was me and the dragging anchor. What a nightmare. So I don't want a rope that is too big and I don't want one that is too small ... and just like the baby bear, I want it just right.
 

soggy_feet

Senior Chief Petty Officer
Joined
Oct 10, 2009
Messages
713
Re: Anchor Rope Size Rules?

I have a 15,000lb boat, and I have maybe a 5/8" line (maybe a little bigger, came with the boat and i've never put much thought into it) on what I'm guessing is a 16lb dansforth.

The line is easier to figure out, they all have a working load thats easy to look up, but its amazing how much a little piece of line is able to handle.

The anchor, the reason you were dragging, is another story. Anchor style and size depends on what you're trying to grip into. Some anchors work better with some bottom materials, others better with other materials. You'll have to make the call on that yourself.
I like the dansforth, but it fouls easily on a weedy bottom, which usually isn't a problem for me, as Im usually anchored in 30-50ft of water, but occasionally, depending on where I am, it might take me a few tries to get it to grab.
 

Fireman431

Rear Admiral
Joined
Sep 17, 2007
Messages
4,292
Re: Anchor Rope Size Rules?

With your boat, a 1/2", 3 strand twisted anchor line is more than enough. Go with the twisted because it has the stretch that the braided line doesn't have. I would also suggest another 7 or so feet of chain on your rode. 3' really isn't sufficient. The more chain you have lying on the bottom, the better holding power the anchor has. With 3', the movement of the boat can easily lift up that short chain and that's what pulls the anchor loose.
 

Beefer

Lieutenant Commander
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Aug 4, 2008
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1,737
Re: Anchor Rope Size Rules?

Like fireman said, 1/2" is plenty for your boat. Realistically, you could get away with 3/8" or even 1/4" :eek:; 1200lbs is a light boat. My beast is 4800lbs dry and empty, and I use 1/2". You won't want to use the 3/8" though, it's tough on your hands. 1/2" is much easier to work with.
 

Beefer

Lieutenant Commander
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Aug 4, 2008
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1,737
Re: Anchor Rope Size Rules?

Here, a quick Google search came up with this from the BoatUS website:

Rope
You can attach the boat to the anchor with rope, chain, or a combination of the two. Rope is the overwhelming favorite, usually with a length of chain at the anchor end. Use nylon rope only. Nylon rope is strong, light, easy to handle, and elastic, the latter a most desirable characteristic in an anchor rode. Three-strand offers the dual advantages of greater elasticity and lower cost, but where the anchor line will be fed through a deck pipe for stowage, the added flexibility of braided nylon can make it a better choice.

Determining how long your anchor rode should be is as simple as multiplying the deepest water you expect to anchor in by 8. As for rope size, the rule of thumb is 1/8" of rope diameter for every 9' of boat length. So if you expect to anchor your 26' boat in 30' of water, you need 240' of 3/8" nylon rope. Unlike oversizing the anchor, oversizing the line is not recommended because that reduces its beneficial elasticity. As a practical matter, however, rope with a diameter smaller than 3/8" is difficult to grip.

In an emergency the line can be tied to the chain or the anchor using an anchor bend, but for regular use give the end of the line an eye splice around a thimble, and shackle the line to the chain.
 

smokeonthewater

Fleet Admiral
Joined
Dec 3, 2009
Messages
9,838
Re: Anchor Rope Size Rules?

also, most people don't put out nearly enough rope.... strong current + 30' deep = at least 150' of rope
 

Beefer

Lieutenant Commander
Joined
Aug 4, 2008
Messages
1,737
Re: Anchor Rope Size Rules?

also, most people don't put out nearly enough rope.... strong current + 30' deep = 150' of rope

With a strong current, I'd go to as much as 7x, or 210' of rode. My rule of thumb is; calm - 3-5x; strong current or wind - 5-7x; strong current and wind 7 - 10x. Wave height will also play into this as well.
 

accentphoto

Petty Officer 2nd Class
Joined
May 4, 2011
Messages
128
Re: Anchor Rope Size Rules?

Wow ... I feel better educated and yet a little lacking in the rope length. And I thought 75-100' was enough. So do you use guys use a complete line only on these 150' + runs or do you keep anchor line of different lengths that can attach to each other if need be?
 

Fireman431

Rear Admiral
Joined
Sep 17, 2007
Messages
4,292
Re: Anchor Rope Size Rules?

Any point of attachment is a weak point. You can buy a 300' spool of 1/2" rope, complete with a stainless steel thimble, for around $60. Add 10' of SS or galvanized chain (and your anchor) and you're set. Only play out what you need depending on conditions. If you find you need more, it's easiest to just uncleat it and send more overboard.

When your pulling all that line up, bumping the boat in to gear a little at a time so that the boat is slightly moving foreward makes it easy to drag in the rode. Even better if you have help.
 

Home Cookin'

Fleet Admiral
Joined
May 26, 2009
Messages
9,715
Re: Anchor Rope Size Rules?

two things about the "rules":

I like to have a line that is thicker than necessary b/c it is easier on my hands. The compromise is extra weight and space.

The 7:1 ratio is for overnight anchoring a big boat in windy conditions; you seldom if ever need that for casual use. And the more chain, the less rope you need.
 

accentphoto

Petty Officer 2nd Class
Joined
May 4, 2011
Messages
128
Re: Anchor Rope Size Rules?

Fireman431, its been so long since I had a boat in the water I almost forgot about running up to the anchor a little to help save the old arm muscles. Thanks for the 7:1 ratio Home Cookin'
 

sw33ttooth

Chief Petty Officer
Joined
Apr 24, 2011
Messages
498
Re: Anchor Rope Size Rules?

also, most people don't put out nearly enough rope.... strong current + 30' deep = at least 150' of rope

if i anchor out on lake michigan i will use about 50-60 foot of rope in 10 foot of water if i am anchoring for fireworks in a calm lake i will add maybe 2-3 extra feet with anchor straight down.
i also use 1/2 inch line for both my regular anchors on a 23 foot boat, my spare has 5/8 inch rope. the 5/8 is nicer but storing it takes up a lot of room since its bigger line
 
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