How much rode rests on seabed?

[ArmySailor]

Trying to determine my specific needs of chain vs rope on primary anchor system.
Given my current / future cruising grounds (Maine <-> FL <-> Carib) and my ship (30 foot, 10k LB).

The goal is to balance weight on the bow vs chafe on the rope portion, especially during rough winds in an anchorage. I can watch for gradual chafe, but losing the rope suddenly in the middle of the night / storm due to an acute chafing event is something I want to avoid, obviously.

--

If I have 100ft of 1/4" G4 and 200 ft 1/2" double braid, how much of the rope will ever be on the seabed?

1) If I'm in a shallow anchorage in benign conditions - I probably wouldn't even deploy more than the 100ft chain. For example, 15 ft (water and freeboard) I could still have 6-1 scope with just the chain.

That's plenty to hold me.

2) If I'm in a deeper anchorage, in a blow, say 25 feet (water and freeboard) I could deploy my entire rode (100 chain , 200 rope) and I doubt that rope would ever be touching the ground. Thus, the chance of getting cut by some random rock or debris is greatly minimized.

I think.

What say the hive?

(Anchor is spade 33lb)

[rslifkin]

In calm conditions, most of the rode beyond the water depth may sit on the bottom. In strong winds, very little or none may be touching.

Personally, I'd assess what areas you want to cruise and what the bottoms are like. For areas with risk of bottom chafe, figure out the deepest water you're likely to anchor in. Take that depth plus freeboard, calculate for 5:1 scope (or another preferred scope) and use that to figure out how much chain you'd need to avoid chafe. Figure that in places with a risk of bottom chafe, you want no more than 1 water depth (not including freeboard) of rope out, that way you'll only end up with chain touching the bottom.

[thinwater]

Originally Posted by ArmySailor

Trying to determine my specific needs of chain vs rope on primary anchor system.
Given my current / future cruising grounds (Maine <-> FL <-> Carib) and my ship (30 foot, 10k LB).

The goal is to balance weight on the bow vs chafe on the rope portion, especially during rough winds in an anchorage. I can watch for gradual chafe, but losing the rope suddenly in the middle of the night / storm due to an acute chafing event is something I want to avoid, obviously.

--

If I have 100ft of 1/4" G4 and 200 ft 1/2" double braid, how much of the rope will ever be on the seabed?

1) If I'm in a shallow anchorage in benign conditions - I probably wouldn't even deploy more than the 100ft chain. For example, 15 ft (water and freeboard) I could still have 6-1 scope with just the chain.

That's plenty to hold me.

2) If I'm in a deeper anchorage, in a blow, say 25 feet (water and freeboard) I could deploy my entire rode (100 chain , 200 rope) and I doubt that rope would ever be touching the ground. Thus, the chance of getting cut by some random rock or debris is greatly minimized.

I think.

What say the hive?

(Anchor is spade 33lb)

Since nylon is virtually weightless in water, if the wind or tide is non-absolute zero the rope will not be on the seabed. In even the lightest zepher, a few links will lift. But the rope will be close to the bottom and can snag.


For this reason 100 feet of chain is a common compromise. In most conditions (98% of the time) only chain is deployed. In deep water and strong conditions some rope may be deployed, but it won't be near the bottom. I use 100 feet of chain with the balance rope. I don't use the rope even every year, since in the Chesapeake I can anchor for a lifetime in less than 10 feet of water.

[ArmySailor]

Originally Posted by thinwater

Since nylon is virtually weightless in water, if the wind or tide is non-absolute zero the rope will not be on the seabed. In even the lightest zepher, a few links will lift. But the rope will be close to the bottom and can snag.


For this reason 100 feet of chain is a common compromise. In most conditions (98% of the time) only chain is deployed. In deep water and strong conditions some rope may be deployed, but it won't be near the bottom. I use 100 feet of chain with the balance rope. I don't use the rope even every year, since in the Chesapeake I can anchor for a lifetime in less than 10 feet of water.

Thanks for the gut-check on this. You're confirming what I've experienced (a little bit) and read about (a lot). Appreciate the reply based on your experiences.

[sailcrazy]

FWIW, we've been cruising in the NE Caribb for the past 6 seasons...and it's not uncommon to have 125'-150' of chain out (our rode is all chain). There are several places with mooring balls-for a nightly fee-and there are lots of places where dropping the pick is what we do. We use a 3-strand nylon line, with a rubber stetchy on it, for a snubber. That line runs over an unused bow roller.....and it shows signs of chaff after maybe only a week(changing winds, swells, etc! We put a chaff-guard over it-and it shows chaff, too! The stretchiness of the nylon going over that roller (it rolls) causes the chaff. For me....I'd look really seriously at using an all-chain rode, or at least the first 150'-200' of your rode.

[Cheechako]

Originally Posted by ArmySailor

Trying to determine my specific needs of chain vs rope on primary anchor system.
Given my current / future cruising grounds (Maine <-> FL <-> Carib) and my ship (30 foot, 10k LB).

The goal is to balance weight on the bow vs chafe on the rope portion, especially during rough winds in an anchorage. I can watch for gradual chafe, but losing the rope suddenly in the middle of the night / storm due to an acute chafing event is something I want to avoid, obviously.

--

If I have 100ft of 1/4" G4 and 200 ft 1/2" double braid, how much of the rope will ever be on the seabed?
NONE,
1) If I'm in a shallow anchorage in benign conditions - I probably wouldn't even deploy more than the 100ft chain. For example, 15 ft (water and freeboard) I could still have 6-1 scope with just the chain.
MOST OF THE CARIBE I WOULD PUT 5:1 OUT, OFTEN 75 FEET.
That's plenty to hold me.

2) If I'm in a deeper anchorage, in a blow, say 25 feet (water and freeboard) I could deploy my entire rode (100 chain , 200 rope) and I doubt that rope would ever be touching the ground. Thus, the chance of getting cut by some random rock or debris is greatly minimized.
I HAVE SNORKELED THE ANCHOR IN 20-35 KNOTS OF WIND AND THERE WAS STILL CATENARY IN THE CHAIN AND NO MORE THAT A FEW FEET OF CHAIN ON THE SAND at 25-35.
I think.

What say the hive?

(Anchor is spade 33lb)

Notes in bold...

[thinwater]

BTW, NEVER put out 2-20 feet of rope. It should either be all-chain with a >15-foot rope snubber, or >20 feet of rope. Deploying just a few feet of rope is asking to overload the rope, if the conditions get jerky. Rope needs length to absorb shock. A long chain can do it with catenary and has twice the working load limit (similar strength) as the rope attached to it.

[donradcliffe]

If you go with a rope/chain rode, there is a good probability of wrapping the rope around the back of your fin keel if you ever anchor where the wind can blow against the tide.

[ArmySailor]

Originally Posted by donradcliffe

If you go with a rope/chain rode, there is a good probability of wrapping the rope around the back of your fin keel if you ever anchor where the wind can blow against the tide.

No fin keel here. Modified full (front cutaway)

[ArmySailor]

Originally Posted by thinwater

BTW, NEVER put out 2-20 feet of rope. It should either be all-chain with a &gt;15-foot rope snubber, or &gt;20 feet of rope. Deploying just a few feet of rope is asking to overload the rope, if the conditions get jerky. Rope needs length to absorb shock. A long chain can do it with catenary and has twice the working load limit (similar strength) as the rope attached to it.

Ah yes. I have a snubber and 20 feet of 1/2 inch. I use a chain hook and piece of velcro to keep it from falling off slack.

But yeah. If it's all chain or less than 20ft rope, snubber if required. Some tiny gunkholes I've been in aren't worth the trouble.

[waterman46]

Originally Posted by thinwater

BTW, NEVER put out 2-20 feet of rope. It should either be all-chain with a >15-foot rope snubber, or >20 feet of rope. Deploying just a few feet of rope is asking to overload the rope, if the conditions get jerky. Rope needs length to absorb shock. A long chain can do it with catenary and has twice the working load limit (similar strength) as the rope attached to it.

Yep. If you want to put out a short amount of rope, attach a long snubber to the end of the chain and take the strain and chafe on that, while letting the rode go slack, with the rode acting only as a backup if the snubber fails. Snubber can easily be replaced if need be.

[rondelais]

I’ve thought about this a bit. Starting with some of Alan Fraser’s great analysis, I built my own mathmodel including wind resistance of my boat, expected yaw (based on experience) and came up with a set of curves that predict the minimum rode length required to keep the pull on the anchor at zero or at most 3 degrees as a function of wind velocity and water depth. What I came up with as a trade off between weight in the bow and rode length in any condition that I am likely to find is pretty much as you have - 100 feet chain plus 200 feet of nylon. We are in Maine, the bottoms are generally mud (avoid rock or kelp) and even if the nylon is on the bottom, the worst that happens is that you need to wash off the mud. Not a lot of threat from chafe. It’s usually pretty easy to find an anchorage where you never need to have any nylon out at all. Even in 20 feet of water at low tide (which is probably like 30 feet at high) I put out my 100 feet of chain, then put my snubber bridle on somewhere near the 100 foot mark, and then let out more until the snubber takes the load. At this point, I may be 20 feet into the nylon, but it will never reach the bottom. Sailing in Maine, it is almost always possible to find sheltered anchorages where wind over 10-20 kt is almost never experienced between April and October unless a hurricane comes up the coast, in which case it is well predicted and you can find a hurricane hole to hide in. There are just so many islands, coves and inlets that with a little warning you can be safe.