Hi THarris and all,
In the following, I will assume that all have read the article and I do not need to repeat the over-all thesis.
Tharris, thanks for your comments
You are correct, of course, That there will always be catenary: even nylon or wire cannot be pulled straight no matter how much load is used. There will always be some “droop” and gravity will always be unable to be ignored.
And I also agree that scope is a remedy for many anchoring challenges: when there is room.
I do not have my paper in front of me, so I do not know how clear I was in that discussion, but what I hoped to convey, but perhaps I should have gotten across more successfully, that the effective result in gale conditions (certainly 40kn and above) was not that catenary actually disappears (as it never actually does), but that your chain rode reaches a point where the catenary/droop is effectively bar tight.
Bar tight means that shock loads will be transferred pretty much unmitigated from bow to anchor. There just is not enough catenary to absorb and average out the shock loads (shock loads come from primarily 3 sources: surging, fore and aft movement which allows the boat to gather speed; yawing, which allows wind and wave to strike to side of the boat and exert far greater pressure; and waves/swell, which causes the bow the rear up and pull hard on the rode. The greatest danger is when two, or worst case all three, of these shock loads occur simultaneously.
When the statistically likely event of these shock loads coincide, without effective shock averaging in your ground tackle, the danger is that forces will just snatch the anchor out of the bottom. Shock load averaging can certainly be accomplished by catenary in higher winds, but often at scope lengths that unreasonable or are hard to come by. Weight can also contribute, but the weight that would be necessary to keep catenary effectively in the picture at say 5 or 7-1 scope is more than most of us are willing to carry.
In high wind conditions, one’s snubber is the most effective shock load averaging element of one’s ground tackle: catenary plays a part in the lulls, but effectively disappears in the predictable high load moments. The snubber, in addition to averaging loads in all wind conditions, and thereby making for a more comfortable boat all around, is attached to the rode in order to stretch and absorb the shock loads and therefore averages out the forces over a longer period, protecting the anchor from being snatched out of the bed.
My goals in this writing were two-fold; to challenge the catenary myth when anchored heavy winds (when you want catenary the most), and to suggest, when buying chain, to buy with strength being the more important criteria rather than weight. If you have weight “to spare”, I suggest that ground tackle effectiveness will be best served by putting weight in the anchor, a new generation anchor, rather than in the chain. Once chain strength is established, put the weight the next size anchor (or even a 2-size jump) in a new generation bower. Weight in the anchor pays far greater dividends than weight in the chain in ground tackle effectiveness.
I think it is an excellent suggestion for getting chain out of the bow by routing excess down to the bilge near the mast step. I keep 150 of my 280 feet in my bilge amidships, ready to run out easily in the few occasions a season where more than the 130 feet in the bow is necessary. Not all boats can accomplish this, but if you can, it makes a big difference in trim. (see Alchemy’s method of accomplishing this elsewhere in the Forum)
I do disagree about simulating Merchant Marine ground tackle practices on an average cruising sailboat. Some practices do not scale. In essence, in casual observation, I see that they substitute weight for design. Their anchors are primitive, and they make up for that by veering lots of their very heavy chain attached to their very heavy, but inefficient, anchor when in their off-shore anchorages where there is a lot of room for great scope. They are able to handle long lengths of heavy chain and a big anchor with massive windlasses and a skilled crew and are 24/7 “manned”: someone awake on watch. Moreover, their vessels appear “better behaved” at anchor in a blow than our far lighter vessels which “dance” around a good deal.
Finally, you say: “boats must have a snubber or a proper full load rated chain stopper”. I would suggest that vessels are wise to have both*: the chain stopper will protect the windlass if things go pear shaped but will do nothing to average out loads: that is a snubber’s job and, in moderate winds, catenary will accomplish averaging also. The danger of no snubber is that shock loads can get transferred directly to the chain stopper and/or the windlass. If they survive, it should be noted that chain has great strength, but that shock loading forces can and does break chain. Consider the not-unheard-of event of having your chain wrap around a coral head or a boulder, thereby becoming short-scoped. And then some larger swells come through and the bow is thrown up. In this event, a snubber might survive, but there has to be: in the chain, chain stopper or windlass, the likelihood of damage.
My best, Dick Stevenson, s/v Alchemy
• Those vessels without a chain stopper are wise to leave their windlass set to run free (or with just a bit of friction) to save the windlass from damage if the snubber breaks as Neil just reported his did once upon a time. Ensure the bitter end is adequately secured.