Scope, All Chain Rode and Breaking Strength

[Mara Mae]

Originally Posted by Manateeman

To what structure are you going to attach a 9,000 pound load. At one point chain becomes a solid link between your boat and anchor.
I would spend more time thinking about snubber calculations, chafe and a waterline attachment point.
All the elements are important not just the chain.
It’s difficult to recommend anything without knowing what’s in the rest of your anchoring system.
Happy trails to you.
The manatee crew.

I believe that a rode safe working load must be based on complete snubber failure

[tenchiki]

Another issue is the shackle to attach the chain to the anchor. The smallest Crosby alloy (HT) shackle is for 5/16" HT or G70 chain. I have yet to find a suitable galvanized shackle for 1/4" HT much less G70 chain. What do people use?

[Adelie]

I took a drift to the the end link in the chain. Tap it in a little. Pull it out. See if the shackle pin fits. Repeat until it fits.

[Breaking Waves]

Originally Posted by Adelie

I took a drift to the the end link in the chain.

yup that works . . . might locally damage the galvanizing and need to be recoated.

You can also get bigger end links welded in.

On breaking strengths, in the 'real world' chain breaking is an astonishing small failure rate - almost never even in severe storms - virtually always the failure point is somewhere else than the chain. This is consistent with Thinwater's comments about the loads vs chain strengths.

On length - 100m or 300' is the standard world-cruiser 'all chain' rode length - only very very rarely would more be needed (which usually has to do with med-mooring or shore tieing distance miscalculations rater than great depth), across a truly wide range of real-world anchorages. And generally, you can do with rather less - how much less would depend on your boat design, intended cruising depths, and comfort level with sneaking into shallow water). It does not make much sense to carry chain length you essentially never put out - that is just dead weight in a bad place on the boat. In any case it just makes sense to have some extra length of rope attached to the end of the chain.

As to chain 'quality' - personally, I think the G4 variant hits a sweet spot, for strength vs cost vs weight. Despite the various theoretical debates, there are some real-world benefits to weight in the chain. There is an optimum point.

[thinwater]

Originally Posted by Mara Mae

A table that does list ABYC working load is on the Mantus website.
https://www.mantusmarine.com/mantus-...e/rode-sizing/

No, this is not the current ABYC table 1. The wind speeds are NOT a part of the ABYC statement and they do NOT represent the load on the rode.


Mantus has been clever in redrafting the ABYC table 1 to scare people. Actual loads at those wind speeds are 3-5 times lower, depending on the scope and rode. MANY testers have confirmed this. The ABYC figures include a fat safety margin.


Read ABYC H-40. Otherwise, you are taking this out of context. The table does NOT represent actual loads. It also does NOT give credit for a shock absorbing snubber (assumes all chain). That said, the gear should be sized to this table, because snubbers can and do fail. That way, you are still safe.

[cr180]

Originally Posted by thinwater

No, this is not the current ABYC table 1. The wind speeds are NOT a part of the ABYC statement and they do NOT represent the load on the rode.


Mantus has been clever in redrafting the ABYC table 1 to scare people. Actual loads at those wind speeds are 3-5 times lower, depending on the scope and rode. MANY testers have confirmed this. The ABYC figures include a fat safety margin.


Read ABYC H-40. Otherwise, you are taking this out of context. The table does NOT represent actual loads. It also does NOT give credit for a shock absorbing snubber (assumes all chain). That said, the gear should be sized to this table, because snubbers can and do fail. That way, you are still safe.

Is ABYC H-40 available on line without buying standard from ABYC?

[cr180]

To put some context to the ABYC values. I’m an old Bruce Van Sant disciple. In his book “Passages South”, he lists wind drag loads at anchor at 80 Kts wind strength. For a 30’ sloop wind on bow force is 1310, ketch rigged wind on bow 1830, trawler wind on bow 1812. These numbers are close to the ABYC storm anchor value. For what it’s worth.

[noelex 77]

Breaking strength is not really the issue. The change in breaking strength when moving from standard size G30 or G40 chain to one size thinner G70 is generally so slight it has no practical impact.

Originally Posted by Adelie

If you change yo 1/4” you would need a new gypsy for windlass.
After the galvanizing starts to wear away, because of its larger diameter the HT can afford to loose more section area to corrosion before the chain needs to be condemned.
If you can regalvanize the chain the HT should lose no strength, the higher strength is due to alloying. G70 is heat treated so regalvanizing will affect strength.

The above is a good summary of the more important issues (although the loss of strength when re-galvanising is only slight). The other things to consider is that the life of galvanising and therefore the life of the chain seems considerably less. This probably relates to the lighter chain rolling around on the seabed more and therefore producing more abrasion.

However, arguably the most important factor is the impact on the anchor's holding ability. The decrease in holding ability seen when using lighter chain is not enormous, but the decrease in holding ability is seen more in poor substrates where the ultimate holding ability is particularly critical.

The big advantage is the reduction in weight, and as most of the weight of the ground tackle for a cruising boat is the chain, the advantage is very substantial. The calculations are easy to do. This reduction in weight allows for more weight to be added to the anchor and for chain length to be increased. Even with these steps the overall weight can be reduced.

Originally Posted by Mara Mae

Thank you. Based on this feedback I am going to investigate 350' of 1/4" G70 galv. all chain rode on a Mantus M1 or M2 45 lb anchor.

The size of your boat is not clear, but most cruising boats when reducing the size of their chain increase the size of their anchor and occasionly increase the length of their chain. These steps are to make sure there is no reduction in holding ability. Despite these measures, the overall weight can be still be reduced.

350' of chain is great to have, but make sure this is not at the "expense" of a decent sized anchor. Anchor design and size is the most import element in ensuring adequate holding ability, so don't skip on these factors.

[Breaking Waves]

Originally Posted by noelex 77

350' of chain is great to have, but make sure this is not at the "expense" of a decent sized anchor.

Yea, I for sure would prefer to have 300' of chain with a heavier anchor than 350' of chain and a lighter anchor.

[Cheechako]

Generally the higher the heat treatment, the more corrosion prone the steel is. I think G40 is a good compromise. Of course in a perfect world the steel will always be covered with galvanising, but I dont think it's a perfect world.

[Clivevon]

"But you won't often anchor in over 15 feet"

Depends where you sail. The tidal range in parts of the English Channel is commonly 4 metres & can be over 6 metres at times. 6 metres = say 20 feet. With 6 foot draft & wanting a minimum of say 3 to 4 foot under the keel at low tide in average conditions, then say 5 foot from the water to the bow roller, you have 15 foot before you add in say that much again for tidal range & you are up to 30 foot minimum.

[BillKny]

Originally Posted by Adelie

I took a drift to the the end link in the chain. Tap it in a little. Pull it out. See if the shackle pin fits. Repeat until it fits.

This seems like an incredibly bad idea. No, it IS an incredibly bad idea, and just plain dangerous advice to give. You have NO IDEA how much you have weakened the chain doing this, and neither does anybody else!

Stretching the link like this would immediately condemn the chain in any industrial application.

If you are really going to use 1/4" heat treated chain, do it right and get a proper larger link welded onto the end. Of course, you still have to wonder... how strong is that shop made link?

[Adelie]

Originally Posted by Clivevon

"But you won't often anchor in over 15 feet"

Depends where you sail. The tidal range in parts of the English Channel is commonly 4 metres & can be over 6 metres at times. 6 metres = say 20 feet. With 6 foot draft & wanting a minimum of say 3 to 4 foot under the keel at low tide in average conditions, then say 5 foot from the water to the bow roller, you have 15 foot before you add in say that much again for tidal range & you are up to 30 foot minimum.

And there are a significant number of Pacific anchorages that are 50’ or deeper.

[Breaking Waves]

Originally Posted by Adelie

And there are a significant number of Pacific anchorages that are 50’ or deeper.

mmmm . . . we have been across the pacific a couple of times, both ways, and you can almost always find a nice shallower place to anchor. I can only remember twice we have been in over 40'. Ofc you can choose to anchor in deeper spots, but if you don't want to there are typically options.

[CarlF]

Chain length is really based on where you cruise. In the Pacific, UK, and Med you want 300'. On the East Coast US, Bahamas, and Caribbean you'll be fine with 150' chain and 150' rope. Cruising these waters with 150' of chain, I only see rope come out of the locker about twice a year. On most sailboats you'll feel a positive difference under sail with less weight in the bow.