Anchor Loads

[philocat]

I mentioned nylon rode previous post. I could not find any nylon type in Wests 2009 catalogue. Do you guys use nylon in the States?

Although nylon is a good structural choice for efficient anchoring system with high elasticity it does sink. So to avoid bottom chaffe perhaps a polyethelene 'silver' floating one - which will get cut up by propeller instead!

Or the ultimate?: nylon rode on a spring loaded reel to eliminate the loose scope if the wind dies with a small float at the chain/rope join to keep the rope off bottom.

[MichaelC]

We do have nylon line here. Even if West carried it, it would probably be of poor quality. We here in the states are afflicted with all sorts of 'box' stores which are putting the quality places out of business. West is one of those 'box' stores. Can't get quality gear there, can't get quality wood from Blow's or Home Creepo. But those are all the stores that are for many communities here. You have to seek out commercial gear stores now to get quality line and bolts, etc. Sad.

[klem]

Yes, West carries nylon line by New England Ropes which is very highly regarded by many people. If you search their website, it is on there. When I worked commercially, we used this line and felt that it was very good(we got it direct though). Another brand that is common in the US is Samson.

[Ocean Girl]

Fantastic replies, thanks so much for taking my question seriously.
1/4 G4 WLL is 2600
1/4 G7 WLL is 3150

MichealC, I love the technique of fitting an attachment point down there, but my breast plate is designed for loads in the direction of the bobstay (upwards say 30 deg). I have thought about fabricating a new one with a separate attachment point for the snubber, I want it designed so that if it fails it will not also endanger my rig. Problem is, if it is higher than the bobstay it will rub the bobstay, if it is lower than the bobstay it will more than likely be under water and hard to inspect for corrosion...this sound like another thread and another project, I will tackle it when I design my snubber, but thanks for the suggestion! I do know one thing, I want at least on attachment point at the bow that is so strong it could pick the whole boat up.

Nautical62, I think the load figures are in relation to the anchor giving way, as in dragging. I have been unable to find any report of an anchor breaking upon load test except for a bent fluke. But the reports talk about giving way, I read this as the sea bed giving way, that is what started leading me towards a bigger anchor than I previously considered.

If I am reading the ABYS table right my extreme loads (storm anchor) will be around 1400. The Global analysis link will take me a bit to go through but thanks for the link. And the windlass sizing is just what I was looking for also.

Also thanks for all the other links and advice. I will cuddle up in bed and enjoy the new batch of information. I am quite amazed the level of knowledge on this forum, and how helpful everyone is. I love it that I can talk with people who are just as interested in this stuff as I, my friends at work just give me a blank star if I try to engage them in any of my projects. One day when I am anchored in a south pacific cove, I will raise a toast to you all.
Cheers,
Erika


PS
I realize that none of this is gospel, just collating data as they say.

[GordMay]

Originally Posted by otya

... A little history: Van Hoon Dorn in his 1974 book Oceanography and seamanship was the first I know to advocate this nylon combination approach and he backed it up with many tables and graphs...

“Oceanography and Seamanship” was written by William G. Van Dorn (Illustrations by Richard Van Dorn), and was updated reissued in 1993 (2ND Ed).
Excellent text!

[lancelot9898]

Originally Posted by Ocean Girl

MichealC, I love the technique of fitting an attachment point down there, but my breast plate is designed for loads in the direction of the bobstay (upwards say 30 deg).

That's exactly the reason why I did not ever rig the snubber to that bobstay fitting on my Tayana 37 plus the fact that I could never locate the backing plate to that fitting. For a number of years I used just a 35 lb CQR on a combination of 5/8 inch nylon 3 stand and 3/8 inch BBB chain. That combination worked in a Cat 1 hurricane which I never want to be aboard again. The main problem that I saw was possible chafe. Looking at the rode under load made me think that I could pluke it much like a banjo string. In the 90 knot gusts the line would stretch and then release much like a rubber band and we would be like sailing. Over the last couple of years, I've switch to a 45 lb manson but still use a combination of nylon 3 stand with the BBB. I found that the 3 strand just may have better chafe resistance than the other type of construction out there, but really no proof to base that on. The real concern is not the static loading, but the dynamic loading in the gusts and there the displacement of the boat has a bigger influence that the wind loading of the freeboard. Having a 25k pound plus boat moving a speed X and coming to a stop will put a some pretty horrific loading on the system. Dynamics was never my favorite subject in college and I've forgotten much so I'll leave that to others, although some simple physics calculations can give some sort of answer.

[Ocean Girl]

Originally Posted by lancelot9898

The real concern is not the static loading, but the dynamic loading in the gusts and there the displacement of the boat has a bigger influence that the wind loading of the freeboard. Having a 25k pound plus boat moving a speed X and coming to a stop will put a some pretty horrific loading on the system. Dynamics was never my favorite subject in college and I've forgotten much so I'll leave that to others, although some simple physics calculations can give some sort of answer.

I am assuming the ABYS and other sources of load statistics includes this in account? Isn't the high end of these loads the extreme loads? Should I factor in more load? I do want a tackle that can handle a Cat 1 at the least. The combination rodes make the best sense to me BUT while in the Pacific I need an all chain due to the coral heads, I have heard too many stories of chafe on coral heads with nylon rode (scared me straight!!).

I am thinking 200 ft of chain min. then the rest 200+ nylon. The sizes are yet to be determined. My snubbers will also be carefully thought out to take the strain off my hardware, so in essence I will always have a combination rode.

I attempted to decipher the Global analysis link but it seems a bit over my head, (I can't even get it downloaded ). SO if anyone has deciphered the info, can you give me an idea of what you found? Are the loads seen in those figures around the same as the extreme loads figures found elsewhere? And the "it's the end of the world" extreme loads I have bookmarked in my head is 5000lb. Does that sound like a good number? I thought of just simply using the weight of the vessel as the bookmark but I have yet to see any information or data that would support this.

I would like a tackle that can handle the big loads, I then work toward reducing the opportunity of these loads (snubbers/nylon rodes).

Cheers,
Erika

[klem]

The rode that you propose seems like it is the best to meet your needs although it will add significant weight to the bow but that is a compromise that you will have to make. In a really heavy blow, I would certainly prefer to have an all chain rode with a very good snubber than a mixed rode. The reason is that chain does better in a chafe situation so you get your shock absorption from the properly sized snubber but if it every chafes through, you are still attached to your anchor. There are many reports of people in hurricanes loosing their snubber from chafe and the boat being saved by the chain being made fast.

On my own boat, I have a mixed rode because of weight concerns (and I don't have a windlass) but on the boats that I have worked aboard, we have always had all chain.

One technique that the fisherman on the schooners used to use when anchored on the banks in a blow (they anchored on hawser there due to depth) was to ease the hawser a few feet every hour in a really bad storm. The idea was to keep any one area from chafing through while the rest of the line was relatively chafe free.

[thinwater]

Originally Posted by Ocean Girl

I am assuming the ABYS and other sources of load statistics includes this in account? Isn't the high end of these loads the extreme loads? Should I factor in more load? I do want a tackle that can handle a Cat 1 at the least. The combination rodes make the best sense to me BUT while in the Pacific I need an all chain due to the coral heads, I have heard too many stories of chafe on coral heads with nylon rode (scared me straight!!).

I am thinking 200 ft of chain min. then the rest 200+ nylon. The sizes are yet to be determined. My snubbers will also be carefully thought out to take the strain off my hardware, so in essence I will always have a combination rode.

I attempted to decipher the Global analysis link but it seems a bit over my head, (I can't even get it downloaded ). SO if anyone has deciphered the info, can you give me an idea of what you found? Are the loads seen in those figures around the same as the extreme loads figures found elsewhere? And the "it's the end of the world" extreme loads I have bookmarked in my head is 5000lb. Does that sound like a good number? I thought of just simply using the weight of the vessel as the bookmark but I have yet to see any information or data that would support this.

I would like a tackle that can handle the big loads, I then work toward reducing the opportunity of these loads (snubbers/nylon rodes).

Cheers,
Erika

Please look a the "tuning anchor rode" link I listed above. He takes all of the tings you mentioned into account, and then merges them into a worksheet at the end that you can just drop your numbers into. Try it.

[Ocean Girl]

Yep Thinwater, already knew and read that site. I think it is a fantastic link and am thankful they took the time to dumb it down for the uh er mathematically challenged. In fact, it is what lead me down the road of rethinking the bigger is better theory. I still see no logical reason why 1/4 HT is better than say 3/8 proof coil or BBB except for an influence with catenary effect. I know logically 1/4 HT will work beautifully..but I also am coming to realize that I will probably get the darn 5/16 HT, my brain just can't seem to take my gut out of the equation. I have yet to hear of a cruising sailboat using 1/4 chain and singlehanding is scary enough. BTW-I could not and still cannot get the worksheet to work, for some reason it crashes my MSspreadsheet (computers seem to fall into mathematically challenged category).

So in light of my own incapability to reason with myself, I am thinking of ways to fit almost 200 lbs of chain in my nice fine bow. My instinct tells me she will only like about 150lbs of chain max, remember I will have a 25lb windlass, a 35lb anchor, and another 15lb of miscellaneous on top of my chain weight. I am pondering breaking up the rode into two piles (keeping it one continuous rode). What I mean by that is to put 75 feet in the deep part of the bilge and run a pvc pipe channel to the primary locker where the other 125 will live. On a regular basis I'd probably only use the 125 with another 30-50 ft of snubber. But on those occasions I use all the chain it would simply feed up through the pvc pipe. Retrieval will be another story but I bet I could figure something out. Haven't thought it through, just another idea rolling around in my head.

Thanks again for the help, you guys rock.
E


PS
as the great Spock once said-
Without facts, the decision cannot be made logically. You must rely on your human intuition.


Lord help me
　

[thinwater]

Originally Posted by Ocean Girl

Yep Thinwater, already knew and read that site. I think it is a fantastic link and am thankful they took the time to dumb it down for the uh er mathematically challenged. In fact, it is what lead me down the road of rethinking the bigger is better theory. I still see no logical reason why 1/4 HT is better than say 3/8 proof coil or BBB except for an influence with catenary effect. I know logically 1/4 HT will work beautifully..but I also am coming to realize that I will probably get the darn 5/16 HT, my brain just can't seem to take my gut out of the equation. I have yet to hear of a cruising sailboat using 1/4 chain and singlehanding is scary enough. BTW-I could not and still cannot get the worksheet to work, for some reason it crashes my MSspreadsheet (computers seem to fall into mathematically challenged category).

So in light of my own incapability to reason with myself, I am thinking of ways to fit almost 200 lbs of chain in my nice fine bow. My instinct tells me she will only like about 150lbs of chain max, remember I will have a 25lb windlass, a 35lb anchor, and another 15lb of miscellaneous on top of my chain weight. I am pondering breaking up the rode into two piles (keeping it one continuous rode). What I mean by that is to put 75 feet in the deep part of the bilge and run a pvc pipe channel to the primary locker where the other 125 will live. On a regular basis I'd probably only use the 125 with another 30-50 ft of snubber. But on those occasions I use all the chain it would simply feed up through the pvc pipe. Retrieval will be another story but I bet I could figure something out. Haven't thought it through, just another idea rolling around in my head.

Thanks again for the help, you guys rock.
E


PS
as the great Spock once said-
Without facts, the decision cannot be made logically. You must rely on your human intuition.


Lord help me
　

And we should use intuition when there are only unreliable facts. Storms are darn unreliable!

But, there is a counterpoint that took me a long time, as a rock climber, to get my arms around: a skinny little 10mm rope is safe enough to trust your life to and to take very long falls on. They simply never break unless cut by a rock. My understanding is that a UIAA approved rope has never failed, not over millions of falls and many thousands of very severe falls.

My thought is that for every story of nylon failing, a boat with all-chain dragged due to higher shock loads, but that possibility will always be overlooked, because it is hard to see. Chain "feels good" to the gut. Climbers use nylon rope because height tech lines don't stretch, and thus don't work. They do use high tech fibers for every other use, where stretch doesn't matter.

If you use snubbers to reduce impact, engineer the system. My nose tells me that snubbers fail because they are generally very poorly designed. I have moored cats using a briddle (like a snubber) for 20 years and never seen a spot of wear... but I am careful.