Anchor chain size advantages

[conachair]

Originally Posted by Herreshoff

but It's the weight of the chain trying to pull tight between the anchor and the bow that keeps the pressure off the anchor most of the time. In winds under 20knots you would put very little load on the anchor itself. The heavier the chain, the greater this effect is.
In my opinion at least.

Unfortunately any load damping from the chain disappears much quicker than you might think. Even with relatively small forces the chain will be off the seabed leaving nothing in reserve for the next big gust. When the weather pipes up well designed snubbers work much better in lowering the loads seen by the anchor than chain weight. Kellets do little to help either in more robust conditions. Physics don't lie

Rode - Static Behavior

[Stu Jackson]

Originally Posted by kmacdonald

Put the weight in the anchor. Use a little chain and mostly rode.

It may be appropriate to leaven this suggestion with what I can only assume is your experience with the smaller boat you are sailing.

As we've noted with your contributions on other threads and topics, it is important to qualify your recommendations based on use. IIRC, you once wrote that your small 22 foot boat has the same size anchor as I have on my 34 footer!

As noted on those other topics, most of the discussions here relate to much larger boats that are cruising.

For example:

You most likely are anchoring in shallower waters.

You most likely are using 1/4" chain.

You may not have a windlass. Properly sized windlasses for mid-30 foot boats usually have gypsies for 5/16" chain.

Cruising rode choices often requires all chain to avoid entangling a rope rode on underwater debris, rocks, coral, etc., while your cruising grounds may be all soft mud and no rocks down below.

Just some considerations for others reading this thread.

[thinwater]

Originally Posted by Herreshoff

I know what scope is. Thanks for that.

What I was getting at is that it isn't just the angle that is important. The right angle helps the anchor dig and stay holding but It's the weight of the chain trying to pull tight between the anchor and the bow that keeps the pressure off the anchor most of the time. In winds under 20knots you would put very little load on the anchor itself. The heavier the chain, the greater this effect is.
In my opinion at least.


Sent from my iPad using Cruisers Sailing Forum

In winds under 20 knots it doesn't matter. A rock on a bit of clothes line would hold (literally). What happens >40 knots is what matters.

[paulnolla]

I really like what Hereshoff said regarding chain size (Reply#11). That makes sooooo much sense. Thank you!

[UNCIVILIZED]

The only way to really start to be able to answer many of these questions is to do more real world studies & analysis of what happens to the part of chain rodes that are underwater, when heavier loads come on them. To include a good bit of quality video footage, & some engineers & statisticians going through the testing results.

Since at the moment most of the information on this is pretty limited. But I've seen a good number of reports from sailor/divers which said that while at times sections of chain rode at, or near the water's surface was made bar taught by weather conditions, the portions of the chain which were well submerged still had lots of catenary in them. Often enough this was in conditions where it previously was thought (& stated) that the entire rode would be drawn taught by local conditions.

So it seems like a lot of what's written about the performance of chain rodes in heavier conditions is relatively unknown. Which does make a fair bit of sense when you consider how difficult it could be to dive & stay close to anchor rodes in such conditions. Though ROV's would surely help with a lot of this anymore. So who wants to fund it?

[thinwater]

Originally Posted by paulnolla

I really like what Hereshoff said regarding chain size (Reply#11). That makes sooooo much sense. Thank you!

Unfortunately, the science and every anchor manufacturer has determined that is simple not the case. So while the thinking is inviting, like many of the things people want to "believe," the basis in fact is lacking. Up to 20-30 knots, yes, after that, the catenary is gone and it's mostly scope + anchor. The world isn't flat either, though it certainly does appear that way when viewed in ordinary circumstances.

[thinwater]

Originally Posted by UNCIVILIZED

The only way to really start to be able to answer many of these questions is to do more real world studies & analysis of what happens to the part of chain rodes that are underwater, when heavier loads come on them. To include a good bit of quality video footage, & some engineers & statisticians going through the testing results.

Since at the moment most of the information on this is pretty limited. But I've seen a good number of reports from sailor/divers which said that while at times sections of chain rode at, or near the water's surface was made bar taught by weather conditions, the portions of the chain which were well submerged still had lots of catenary in them. Often enough this was in conditions where it previously was thought (& stated) that the entire rode would be drawn taught by local conditions.

So it seems like a lot of what's written about the performance of chain rodes in heavier conditions is relatively unknown. Which does make a fair bit of sense when you consider how difficult it could be to dive & stay close to anchor rodes in such conditions. Though ROV's would surely help with a lot of this anymore. So who wants to fund it?

I fear that like proving the non-existence of God, if you succeeded, no one would believe you, because they don't want to. They would say "but you didn't test this." So what is the point? For those that want to listen there is lots of research out there and they have become convinced. Just warm up your Google ** and find it. The answers arn't simple because there are so many cases. There is truth in many points of view, so long as they are not held as absolutes.

[Steven UK]

"I fear that like proving the non-existence of God, if you succeeded, no one would believe you, because they don't want to."

there are a few billion 'god bothers' out there with almost as many Gods...!

i'm going to hide...

[kmacdonald]

Originally Posted by Stu Jackson

It may be appropriate to leaven this suggestion with what I can only assume is your experience with the smaller boat you are sailing.

As we've noted with your contributions on other threads and topics, it is important to qualify your recommendations based on use. IIRC, you once wrote that your small 22 foot boat has the same size anchor as I have on my 34 footer!

As noted on those other topics, most of the discussions here relate to much larger boats that are cruising.

For example:

You most likely are anchoring in shallower waters.

You most likely are using 1/4" chain.

You may not have a windlass. Properly sized windlasses for mid-30 foot boats usually have gypsies for 5/16" chain.

Cruising rode choices often requires all chain to avoid entangling a rope rode on underwater debris, rocks, coral, etc., while your cruising grounds may be all soft mud and no rocks down below.

Just some considerations for others reading this thread.

All true. I also like to keep the boat as light as possible. Even with the Rocna 10 (22 pounds) I still drag a little in the bays soft silt. When anchoring in sand it never drags no matter what the winds are.

[brianlara 3]

Originally Posted by thinwater

Unfortunately, the science and every anchor manufacturer has determined that is simple not the case. So while the thinking is inviting, like many of the things people want to "believe," the basis in fact is lacking. Up to 20-30 knots, yes, after that, the catenary is gone and it's mostly scope + anchor. The world isn't flat either, though it certainly does appear that way when viewed in ordinary circumstances.

TW, I read your posts always and you always demonstrate logic and so to argue with you is not my intention.
You say that "20-30 kts yes, above that no"
Well I have the tiniest boat on the hook 24/7 on CF. Very very small boat and I sleep with my head at the sharp end, just inches from the anchor bulkhead. And getting out of bed isnt an option because if I have to sleep with fear of dragging I might as well sit in the cockpit all night.
I often/regularly sleep in 50' of water and winds well over 40. And in open roadsteads!
If my chain straightened at all life would be murder.
My chain doesn't straighten because it's way too heavy (by usual parameters) and my pick ditto....for a boat this size.
In summary, if a chain is heavy enough relative to boat mass there will always be catenary.
It's what works on this little boat anyway.
Cheers.

[thinwater]

Originally Posted by brianlara 3

TW, I read your posts always and you always demonstrate logic and so to argue with you is not my intention.
You say that "20-30 kts yes, above that no"
Well I have the tiniest boat on the hook 24/7 on CF. Very very small boat and I sleep with my head at the sharp end, just inches from the anchor bulkhead. And getting out of bed isnt an option because if I have to sleep with fear of dragging I might as well sit in the cockpit all night.
I often/regularly sleep in 50' of water and winds well over 40. And in open roadsteads!
If my chain straightened at all life would be murder.
My chain doesn't straighten because it's way too heavy (by usual parameters) and my pick ditto....for a boat this size.
In summary, if a chain is heavy enough relative to boat mass there will always be catenary.
It's what works on this little boat anyway.
Cheers.

Agreed 100%. If you run the math on 50' of water with that boat that is exactly how it works, and that is why I have said there is truth in many points of view. For your situation it is a very good solution.

On the other hand, I mostly sail the Chesapeake Bay and US east coast. 95% of the time I anchor in 6-8 feet. In 30 years, I've never had to anchor in more than 15'. The water just does not run deep. If I anchor in 5' in an open roadstead (and I did just that for a bunch of worst-case testing for a magazine article), I only have ~ 60' of chain out, catenary is useless above ~ 12 knots, and by 20 knots it is a jackhammer without a long snubber. The reason I did the testing there was because it was a worst case, and because it confirmed the reality of the ABYC numbers; the impacts got huge with no snubber.

So both are true, as well as many hi bred positions. It's all in the math, which unfortunately, is complex.

[brianlara 3]

Im impressed and envious that you are a magazine contributor TW. Cheers.

[brianlara 3]

THAT was supposed to be a PM. duh.

[thinwater]

Originally Posted by brianlara 3

TW, I read your posts always and you always demonstrate logic and so to argue with you is not my intention.
You say that "20-30 kts yes, above that no"
Well I have the tiniest boat on the hook 24/7 on CF. Very very small boat and I sleep with my head at the sharp end, just inches from the anchor bulkhead. And getting out of bed isnt an option because if I have to sleep with fear of dragging I might as well sit in the cockpit all night.
I often/regularly sleep in 50' of water and winds well over 40. And in open roadsteads!
If my chain straightened at all life would be murder.
My chain doesn't straighten because it's way too heavy (by usual parameters) and my pick ditto....for a boat this size.
In summary, if a chain is heavy enough relative to boat mass there will always be catenary.
It's what works on this little boat anyway.
Cheers.

How much scope do you generally use in 40' to get a reasonable ride (the chain does not seem to come tight suddenly)? I'm figuring about 6:1 would keep the chain on the bottom an 40 knots sustained, depending on the chain. Given that there will be waves, I'm not sure I would reduce that. But I'm interested in your experience.

[brianlara 3]

TW, in 40' either on the coast or in more sheltered waters, I use the lot. I.E. 250'.
Because I rarely look for particularly sheltered anchorages I'm usually the only boat for a mole ot two and sometime many more than that. And so even in the absence of wind or tide I'm in nobadys way.
Reason I anchor a bit distant is that I detest the noise of bow thrusters, noisy parties and in addition people who are incompetent anchorers can't drift down on me when it pipes up.