Anchoring systems

[dLj]

As I'm in the midst of rebuilding my entire anchoring system, I went to the ABYC Standard H40 "Anchoring, Mooring, and Strong Points".
For my boat, I need to be using design loads of 4800 pounds. Nothing about this boat seemed to demand anything "unusual". But when I read the standard and realized the implications of rode sizing and component sizing throughout the system, I realized that virtually everyone I know is likely running undersized anchor components. So I throw this out there as food for thought.

Design loads according to that standard use a safety factor of 8 for rope rode. Translating this, 4800 pounds X 8 = 38400 pounds. So this 38400 pounds should be the minimum breaking strength of rope rode. For 3 strand nylon, I'll need 1 1/2" diameter line!

How many here are using rope rode that meet the design requirements for your boat size?

I've certainly never been thinking in those sizes. Anyway, just thought I'd put this out there as I was flabbergasted at the sizing requirements this standard requires for rope rode.

Factor of safety for strong points is twice the design load strength. I'm attaching two images from the standard - I'm pretty sure this is OK by copyright as it's my understanding that excerpts from a standard may be put out there, just not the whole standard. I'd recommend buying this standard (or just become a member of ABYC) if you are looking to get more details...

dj

 

[dlochner]

Under what conditions would your anchor be under a 4800 lb load?

 

[dLj]

Under what conditions would your anchor be under a 4800 lb load?

Read note 2 in the first table.

dj

 

[shemandr]

1 1/2" is massive. The corresponding chain would be 1/2" or maybe 9/16"? That would be replacing the windless as many can handle those sizes and most mortals aren't going to lift up chain that heavy. And you may have to replace or upgrade backing plates for the cleats. By those standards I would venture to say that almost all of us have undersized rides!
The only times I've dragged was when the anchor pulled out from the bottom. I would venture to say that few of us have had a rode part. I would say that the safety factor of 8 * is arbitrary and impractical.
The last time I got into the weeds about this I found that it was the shackle pin that was the limiting factor. If the pin is large enough, it won't go through the chain link.

 

[Davidasailor26]

Those loads do seem pretty crazy. By the table you could argue I should design for a load of 6000 lbs. (37’ LOA, 12.8’ beam, canvas dodger and Bimini). Even not counting the canvas and going purely by LOA I’d be at 3600 lbs.

I don’t remember my rode size exactly but looking at my windlass specs I’m pretty sure what I carry has a working load limit of about a quarter of what the table says.

 

[dLj]

1 1/2" is massive. The corresponding chain would be 1/2" or maybe 9/16"? That would be replacing the windless as many can handle those sizes and most mortals aren't going to lift up chain that heavy. And you may have to replace or upgrade backing plates for the cleats. By those standards I would venture to say that almost all of us have undersized rides!
The only times I've dragged was when the anchor pulled out from the bottom. I would venture to say that few of us have had a rode part. I would say that the safety factor of 8 * is arbitrary and impractical.
The last time I got into the weeds about this I found that it was the shackle pin that was the limiting factor. If the pin is large enough, it won't go through the chain link.

Or you can go with grade 40 chain.

My experience with rope rode does tell me that is not really oversized. If you are anchored or moored and the stink really comes up, I think those sizes are about right.

dj

 

[dLj]

Those loads do seem pretty crazy. By the table you could argue I should design for a load of 6000 lbs. (37’ LOA, 12.8’ beam, canvas dodger and Bimini). Even not counting the canvas and going purely by LOA I’d be at 3600 lbs.

I don’t remember my rode size exactly but looking at my windlass specs I’m pretty sure what I carry has a working load limit of about a quarter of what the table says.

37 LOA with 12.8 beam puts you at 4800 working load.

What I'm seeing really is that the rope rode we are all using is undersized pretty much across the board. If you are running grade 40 chain, you are likely good there.

The next area I'll bet folk need to look at are their shackles... But rope - I bet pretty much all of us are undersized....

dj

 

[jon hansen]

your not a 50' boat, first of all. ....... so let's keep it real.

 

[jon hansen]

your not picking up your boat with a single line of rope. if you try something that poorly conceived you will prolly rip your windlass right off the deck of your vessel.

just keeping it real

 

[jon hansen]

my mooring pendant is 11/4". aeolus came with a spare 75lbs danforth and 250' feet of 1" rode. it has been stored in the basement of my house for 48 years. looks nice in the corner. i have used 200' of 5/8" with my 35 lbs danforth, that also came with the boat, for 47 seasons, never has it failed me. chain is never used up on the lakes by me. zero need

 

[thinwater]

The 8:1 safety factor for nylon rope is common and well founded in experience. That is not a mistake.

The problem is that the details of the testing basis for H40 has been lost to the sands of time when the developers passed. The understanding is that a series of experiments were conducted, anchoring boats in exposed and somewhat shallow waters using all-chain rode. Not the impact zone, but a survivable worst case senario. I have repeated these experiments (34-foot cat and 36-foot mono), and those test values were in line with those in H40. The loads in Table 1 are not crazy and can be reached in bad anchoring situations (think open roadstead).

However, when anchoring with rope rode, the loads are reliably 3-5 times lower, due to reduction in impact forces. In fact, the H40 loads can only be reached in horrible conditions where the chain is snatching tight. The load will normally be 2-3 times lower. Applying this lower force on rope rode, the diameters fall back in line with traditional recomendations. In fact, the safety factor is generally quite large, far more than 8:1, but this is good, because of chafe.

Conventional rope sizing rules are correct and are confirmed by long experience. H40 simply does not explain that it is based on all-chain rode. They want the boat to be built for whatever rode the user may install. Makes sense.

 

[dLj]

your not a 50' boat, first of all. ....... so let's keep it real.

Reread the table - I'm a 41 foot LOA with 13 feet beam. Puts me squarely in the 50 foot LOA line.

And you have no idea how real I'm being!

dj

 

[thinwater]

The only failures of rope rode I am aware of (please post examples!) were either chafe (bottom or roller area), or because less than 15 feet of rope were deployed (the balance was chain) in an open roadstead situation and the rope was forced to endure chain-like impacts without enough length to reduce the force. NEVER deploy less than 25 feet of rope; either all chain, or enough rope so that it can absorb the energy.

 

[dlochner]

Read note 2 in the first table.

dj

Yes, but the note fails to qualify the force of those factors. Are you preparing for typical loads? Or extreme loads like remaining anchored in a hurricane?

 

[BigEasy]

That table is totally unrealistic. For my 35 ft boat, I should use a 1" rhode! I am presently using 3/8" chain and 5/8" 3 strand nylon: my windlass gypsy is sized for those components. I am quite confident and comfortable with this combination. I would refer to a specific anchor manufacturer's recommendations for anchor size, chain, & rhode sizes that corresponds to your boat size & weight.

 

[Stu Jackson]

i found these tables from Calder's Cruisers Handbook. You could compare them with yours.

Anchor System Sizing Tables (Reply #6) & Swivels Ground Tackle & Anchor System Sizing TABLES & Swivels

 

[dLj]

Yes, but the note fails to qualify the force of those factors. Are you preparing for typical loads? Or extreme loads like remaining anchored in a hurricane?

I'm only relaying the information found on the standard. I don't know anything more than you. I imagine those are for worst case loading, but @thinwater appears to know more about the history etc. surrounding how those numbers were generated. Looking at the implications of those tables I figured I'd post here as I don't see that the rope rode requirements are being observed in the general boating community. I simply thought folks should be aware.

Concensus standards such as this one provide a lot of good information. I would not be one to simply discredit it because I felt it was overly conservative.

I put this out there as an insurance company might be looking at this standard against a claim that may be presented to them and deny coverage based on improper design.

I think knowledge is power and I'm just transferring knowledge.

dj

 

[jon hansen]

all the above is correct. ultimate possible usage vrs. a given sailor's needs do vary quite a bit. chaffing is the big concern. or rusting. and proper weight loading on a vessel. deep below the water line? certainly not above the water line. lots to consider.

 

[Jollyroger]

I’ve done enough anchoring in adverse conditions to know that these figures, like a lot of ABYC standards, are theoretical, and I think these particular rode figures are extreme. Being a brigantine schooner my boat has more than the normal windage and I have anchored using all my 250 feet of chain and 100 feet of 1” line, but I can’t remember thinking it might not be strong enough. Under those load conditions, I believe the anchor(s) would be the first to let go.
Anyway, who would anchor with rode alone in conditions which might impose these extreme loads, indeed, who would anchor at all, but run for the nearest marina or very large tree…

 

[thinwater]

ABYC H-40 table one is based on testing, not theory. I've had long conversations with committee members. Yes, the figures are extreme. They are the WORST case scenario, as they should be. Yes, your anchor will drag first. Obviously. That's better than pulling the cleats out.

The worst case happens when you anchor in an open roadstead and the winds rotate to on-shore with the passage of a strong front. Yes, you should have moved to deeper water or found shelter, but somehow it did not happen. Yes, this happens.
Cabo San Lucas, 1982 is a well known case. I have also seen this in local waters, with boats anchored in the open on a nice day, and then a thunderstorm hooks around the wrong way and blasts them (the gust front does not ALWAYS come from the west--it is radial).