Problems Sizing Ground Tackle for 50' , high windage cat

capta said:

I don't understand your reasoning here. Why would you think HT chain with WL of 6600lbs would be any better than bbb with a WL of 3700# when the boat weighs 25,000 pounds or more, especially considering the weight in the water is less per foot.

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Well, I was simply answering the OP's question.

He obviously feels chain with a WL of 5400 lb is inadequate. The 3/8 G30 BBB you are recomending usually has a listed WL of 2650 lbs

I don't know the vessel, but 3/8 G40 is on the low side for a "high windage 50 foot cat". G30 is worse. If we use the ABYC guidelines for a 50 foot monohull the WL load limit for G30 BBB is exceeded at just 38 knots. The ABYC formula perhaps overestimates the forces, but this is a high windage cat not a monohull.

The low displacement is a mitigating factor, but the OP announces that they anchor in tough conditions "I live at anchor through named storms".

Chain rarely breaks but if it does, without any drag from an anchor the boat moves very rapidly. Not nice.

I would rate the extra weight of G30 BBB (over G40 or G70) chain a drawback rather than a bonus especially on a light displacement cat with a manual windlass. Weight in the anchor is more efficient than weight in the rode. I would opt for the lightest weight rode that provided adequate strength, abrasion resistance etc.

I think it is up to the skipper to decide the safety factors he feels is appropriate but personally I would not be comfortable with your recommendation of 3/8 G30 chain on a 50 foot cat especially if there was a possibility of anchoring in a named storm.

Stu Jackson said:

An 88# new gen anchor is horribly mismatched with 3/8" chain.

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3/8 G7 is stronger than 1/2 G30 or BBB chain and a little weaker than 1/2 G40 HT chain. With G7 chain the normal procedure is for the chain maker to incorporate a larger link on each end. So appropriate strength shackles are not a problem. With G8 shackles you can just get away with a normal sized link in most cases, but it is not expensive to order the chain with the larger links added.

So generally you need not be concerned about a strength mismatch dropping down one chain size at the same time as going from G3 or even G4 chain to G7.

Steve Dashew was one of the pointers of the of the philosophy of adding weight to anchor and reducing the weight to the rode as avway to increase the performance of anchoring equipment and /or save weight.

He uses 3/8 G7 chain with a 240 lb (wow ) Rocna. So an 80lb Manson Supreme with 3/8 G7 is not extreme by any means.

You can read about his anchoring equipment here:

SetSail » Blog Archive » Anchoring System Logic

The Rocna website also suggests there is no mismatch. They actually list thinner 8mm (or 5/16) as the "appropriate" G70 chain to match with a 40kg (88lb) Rocna. The Rocna and Manson Supreme are very similar anchors.

http://kb.rocna.com/kb/Chain

G4 chain is easy and cheap to get. If you have an oversized electric windlass and a boat where the chain weight has little impact it is a good simple choice. If you want to improve your anchoring system without adding more weight. G7 chains are worth considering. The combination of heavier anchor with longer chain (so you can enjoy deeper anchorages and use a longer scope in bad weather) has got appeal.

My ultimate cruiser would incorporate a chain locker well back from the bow with a big anchor winch so lots of standard G4 chain could be carried, but sadly few boats are built this way.

I have some sympathy for those that want to keep things simple and reliable, but I agree that an electric (or hydraulic) anchor winch is almost essential, especially on a larger vessel. The rapid recovery of chain is an important safety feature and the fuss free nature of anchor handling encourages skippers to re-anchor if things are not right.