Scope, All Chain Rode and Breaking Strength

[cr180]

Originally Posted by Breaking Waves

My understanding of the abyc numbers is that this is one of the main reasons that they are 3x or 4x the actually typically measured loads - to more than adequately account for these sort of added stresses.

Thinwater can correct me here if i remember this incorrectly. EDIT: I see up thread he already mentioned the abyc 'fat safety margin' and I believe they at some point explicitly pointed to these sort of difficult to determine additional environmental conditions beyond wind as a major reason.

Fat margin of safety for WHAT wind speed? It matters. 10 knots of wind or 80 knots of wind?

[cr180]

So can’t access latest ABYC H-40 standard on line without paying ABYC $50. NOT. But have found earlier versions on line. My conclusion is that the standard’s purpose is to specify boat deck hardware, ie cleats. Am not at all convinced that the boating industry is supporting an ABYC that is over specifying hardware. Nor am I Convinced that we as cruisers should be using this standard for our ground tackle. Do not believe it has a bunch of margin of safety. As I pointed out in a previous post, storm anchor loads listed in the standard have zero margin of safety!

[Breaking Waves]

Originally Posted by cr180

So can’t access latest ABYC H-40


Thinwater posted an image of it upthread

Do not believe it has a bunch of margin of safety.

Hmmm . . you don't have the table, but you are sure it has no margin for safety?

Some of us have actually measured loads, and it is quite conservative (like a 3 to 5x factor conservative)

.......

[cr180]

Breaking Waves
Please refer to post #14, ABYC Table, that I referred to in my post #22 comparing alternate source data to the ABYC Storm value. It is the latest revision of the entire text of the H-40 standard that I have not reviewed, although have reviewed earlier revisions on line. My contention is that by not publishing wind speeds, how can safety factor be knowable? And as I pointed out, alternate source data correlates to the ABYC Storm value leading me to believe no safety factor.

I am in the process of researching more contemporary tests and will post links in the coming days. Preliminarily, what I am reading the inconsistency to be is that tests that you may be aware of likely are wind drag only and do not include impact or shock loads due to the boat veering back and forth in gusts which exposes the beam nor likely include wave action. Both are real world conditions that cruisers encounter. Furthermore, it appears scope and elasticity of the rode are large factors.

At the end of the day, may conclude the ABYC storm values are reasonable to size ground tackle by, but believe we are naive to think there is a large safety factor.

Lastly, you may not agree. That’s ok!

[sailcrazy]

Following. We use 300' of all chain rode, 10mm, with a 25kgm Rochna. In the Medd we often used 200'-250', but (so far) in the NE Caribb we seldom see anything over 150' out.

[Breaking Waves]

Originally Posted by cr180

I am in the process of researching more contemporary tests and will post links in the coming days.

well, good luck with your research.

You might want to start with what the ABYC technical managers ( Tom Hale and Philippe Ras) have actually said about their numbers (hint: that they assumed a “worst case” situation, including all chain with no-snubber, and sea state and surge, and include safety factor) . And you might want to learn what wind speed conditions they meant by 'storm' (hint it is rather lower number than 80kts). And finally, you might want to look up the various people who have actually made measurements like Robert Smith (who did testing with a 4mile fetch to windward so certainly had waves and veering) and our own thinwater here (Sail Delmarva: Actual Anchor Loads).

I would be somewhat surprised if you reached a different conclusion than those of the rest of us who have been involved in all this.

[cr180]

Originally Posted by Breaking Waves

well, good luck with your research.

You might want to start with what the ABYC technical managers ( Tom Hale and Philippe Ras) have actually said about their numbers (hint: that they assumed a “worst case” situation, including all chain with no-snubber, and sea state and surge, and include safety factor) . And you might want to learn what wind speed conditions they meant by 'storm' (hint it is rather lower number than 80kts). And finally, you might want to look up the various people who have actually made measurements like Robert Smith (who did testing with a 4mile fetch to windward so certainly had waves and veering) and our own thinwater here (Sail Delmarva: Actual Anchor Loads).
I would be somewhat surprised if you reached a different conclusion than those of the rest of us who have been involved in all this.

Thanks. Had already found Sail Delmarva’s blog entry you point me to. Plan to spend more time understanding findings. Would encourage others to take a look as well. Initial read is that loads similar to the ABYC data are actually measured when using all chain and a short snubber in shallow water. By the way, this is exactly what I and hundreds of other cruisers do in the Bahamas. The author goes on to say that can significantly reduce loads by simply moving to deeper water, at least 20’ deep. Rub is most anchorages in the Bahamas are less than 10’. He further advocates for a long snubber from about 35 to 50’ long to reduce loads (nobody I know uses a snubber longer than the depth of the water). Finally, he says that even in a 60 knot wind, would be protected by trees. Unfortunately, squalls come with wind direction changes that turn a lee shore anchorage into an open anchorage with breaking waves.

So in summary, the conditions that the author found to yield test data close to the actual ABYC numbers are the exact conditions we Bahamas cruisers endure.

So where is the safety factor? Am I missing something?

[cr180]

On closer inspection, Sail Delmarva’s 60 knot numbers with all chain & short snubber exceed the current ABCY storm anchor values by 50%. And 60 knots is not unreasonable. Several cruisers clocked 60 knots in a squall in White Sound, Green Turtle Cay in May, 2021. I actually clocked 49 knots sustained with higher gusts in Black Sound during the same event.

[Breaking Waves]

The author of that is here @thinwater - you should discuss it with him.

but do note he says in the comments " In real world practice, I have never observed values higher than 1/3 of ABYC table 1." I believe that indicates that the 2nd table you are looking is attempting to explain/quantify the gap between wind load and the theoretical abyc numbers - the bottom row is calculated not measured - the real-world measured numbers are always lower than this. . . but ask him directly, no point in speculating when he is right here. (he has written a book on all this - might be worth your buying and reading if you are really interested).

I have measured anchoring loads up to 35 knts with a load cell and always found significantly less than abyc (that included situations where we had more fetch than I would have preferred). Never did over 35kts but have used 10mm climbing line for snubber thru cat 1 hurricane (47' boat), and its cover chafed on fairlead but did not break - says something about the loads.

honestly, if you are anchoring with significant fetch, in 60kts, with essentially all chain in shallow water and no snubber elasticity . . . well yea . . . (Note: there are definitely practical ways to get more snubber length/elasticity, like running it back along the deck to a stern cleat. There are also practical ways to reduce yawing, which can reduce loads significantly. You should honestly attempt to practice some seamanship here.)

[Panope]

I'll toss in another data point.

-20kt Breeze.
-2.5 mile fetch.
-wave height 1' (occasional 2')
-15,000lb boat.
-3/8" all chain rode with NO snubber.
-4:1 scope (depth 20' + 4' bow roller, 100' rode)

Average load appeared to be about 175lbs.
Very brief peak loads (twice) = 300 lbs.

https://www.youtube.com/watch?v=yyelkzylBFg&t=83s

[sv_pelagia]

The "Pacific" is a pretty big place!

Here in the NE Pacific, British Columbia, one often anchors in 50+ feet (at high tide). Sometimes 70-80'.

[Breaking Waves]

Originally Posted by Panope

Average load appeared to be about 175lbs.
Very brief peak loads (twice) = 300 lbs.

[

yea, my load math says steady-state 174.5lbs bow load (143.6lbs anchor load) for you in that situation (with 15 joule wave energy - that's the complicated part of a long fetch calculation, have to make some assumptions about surface turbulence).

out of curiosity what caused the two peaks - yawing or gusts or waves?

[thinwater]

Originally Posted by cr180

... By the way, this is exactly what I and hundreds of other cruisers do in the Bahamas. The author goes on to say that can significantly reduce loads by simply moving to deeper water, at least 20’ deep. Rub is most anchorages in the Bahamas are less than 10’. He further advocates for a long snubber from about 35 to 50’ long to reduce loads (nobody I know uses a snubber longer than the depth of the water)....

The blog post you refer to is just that. A blog post, a 5-minute sound bite. I've written many articles and a book on the topic, so that was certainly the short version.

Well ... maybe you should not use a short snubber in shallow water. This is ... obvious. Maybe some of these locations are simply not safe harbors and can't be made so. Once upon a time I used a short snubber with all chain, and it only took one afternoon at 20 knots to make me splice up something more suitable for that evening.

In fact, I sail the Chesapeake Bay, most commonly anchor in 6-8 feet, and the regular bridle I use is generally greater than the water depth (18-foot legs). If you think about it, most catamaran bridles will reach the bottom when anchored shallow. It's not a big deal and it is what you must do if you want a bridle long enough to damp yawing. If I expect a bumpy ride I use a long bridle does not anchor to the bows, it anchors to either the stern cleats or midships cleats, giving me about 45 feet of snubber. The routing around the bow and chafe gear take some thought, but it's not hard.

No, there are not always trees. Yes, we get fierce thunderstorms here, as good as anywhere. Most of my testing was off beaches with on-shore winds and at least 5 miles of fetch. I tested wind-only loads behind a low breakwater, but all of the rode tension results were fully exposed to wind and long fetch waves, and were still many times less than ABYC H-40 Table 1. The ONLY way I could reach the ABYC values was:

• Shallow water (just short of breaking, often 5-7 feet).
• All chain, no snubber (I used a Dyneema bridle to mount the load cell).
• Long fetch (typically 8 miles).

In other words, worst case, an unseamanlike way to anchor, and a mistake. The boat will be snatching violently at the chain. It should be obvious that something is wrong, and not just the weather. Otherwise, the results were 2-5 times less.

But many of my readers are Chesapeake Bay area, and you can always find a sheltered spot. Fetch (waves) are often more important than waves, and anchoring with on shore winds in an exposed area will ALWAYS be a serious matter, something sailors try hard to avoid. Most anchoring tragedies result from those conditions.

The ABYC numbers have not changed for at least 40 years because they work. Chains don't break and equipment built to that standard holds up. Anchors dragging is not related. If you want to anchor in the "worst case" locations and use a short snubber, yes, you are in the market for larger gear.

[Panope]

Originally Posted by Breaking Waves

out of curiosity what caused the two peaks - yawing or gusts or waves?

Perhaps all three.

The peaks occurred at the point of maximum yaw.

The boat being more "broadside" to the wind/waves could have contributed to the peaks.

Also, arresting of the rotation (momentum) of the boat could have contributed to the peaks.

Note: The boat was not "sailing" back and forth. It was only "rotating" back and forth very slowly.

Steve

[Breaking Waves]

Originally Posted by sv_pelagia

Here in the NE Pacific, British Columbia, one often anchors in 50+ feet (at high tide). Sometimes 70-80'.

perhaps you do - we did not.

we spent a month gunkholing around Prince Rupert, then a month around queen charlotte, and then a year around Vancouver/Vancouver Island.

I can only remember once we anchored somewhat deep - in Princess Louisa, where we used a shore tie and then the public dock emptied and we move to it to make walks easier.

We never skipped anyplace we wanted to see because of depth. I will comment that we do by choice prefer to spend some time exploring really nice anchorages rather than quickly skipping between less good ones.

Perhaps you prefer not to sneak into little coves and not to shore tie. That's fine, all good, but it is a choice to anchor deep and one certainly does not need to 'often anchor in +50' there.

Lovely area, one of our favorites.