Your Marine Performance Parts Specialists Offer You the Best Suggestions On Rode Strengthening
Stainless Marine your marine performance partsÂ professionals would like to share with you these topics we thought would be of interest to you this month regarding how to strengthen your rode.
In the March 2016 article âChanging views on chain hooks,â we pointed out that the major manufacturers of marine anchor chains caution that some chain hooks can weaken chains under extreme loads. Your marine performance parts analysts know that these chain hooks are often used to attach an anchor snubber to the anchor chain.Â
I would like to respond to the article in the March 2016 issue of Practical Sailor, ‘Changing views on chain hooks,’ which challenges a commonly accepted practice of using chain hooks to attach snubbers to the chain.
âThe article claims that the Mantus chain hook reduced the breaking strength of the chain by 40 percent. The article suggests that any device promoted to attach a snubber to an anchor chain should not detract from the strength of the chain.Â
As the April 2016 article pointed out, there exist cradling hooks designed for shortening chain that will not weaken chain. However, most stainless-steel hooks on the marine market are of a different design, which do impart some point loading. Made of stainless-steel and designed specifically for marine use, the Mantus hook is no different in that regard. However, the assertion that Mantus hook exacerbates the point loading was derived using an undersized Â¼-inch hook with larger 5/16-chain.
I am concerned that some sailors may interpret your report to mean that chain hooks are potentially not safe to use for attaching a snubber line to chain.Â
The American Boat and Yacht Council publishes standards used by manufacturers as guide to help design marine hardware.
The very reason to use a chain hook is to connect a snubber to the chain and dissipate these loads. This is quite different from using a chain hook for attaching two stretches of chains together or for shortening the chain as is done in the lifting industry.Â
Shock loads are usually assumed to be three times the static loads. A recent article on snubbers published in the March 2016 issue of Practical Sailor explores this topic.Â
Go to http://www.stainlessmarine.com/product-category/diesel-exhaust-risers-elbows/ and see how you can always find more information as well as get assistance on marine performance parts and on how to strengthen your rodes at Stainless Marine.
âThe March 2016 issue, which focused on snubber loads, tabulated the loads for a 40-foot monohull boat in 60-knots with the following scenarios:
â¢ Chain with no snubber (not elastic system, shock loads present) â 4,140 pounds
â¢ ABYC worst case (assuming not elastic system, shock loads present) â 4,898 pounds
â¢ Chain with a 30 foot Â½ inch three strand nylon bridle (shock loads mitigated) -1,574 pounds (62 percent reduction in peak loads or about 1/3 of the ABYC worst case)
â¢ 5/16 Grade 30 chain breaking strength â 7,600 pounds
âFor reference, the Mantus hook designed for 5/16 chain has the working load limit of 1,877 and an ultimate breaking strength of 7,511 pounds.
To summarize these loads on the rode for a 40-foot boat in sustained 60 knots of wind:
â¢ Maximum load predicted on the chain with a 30-foot bridle: 1,574 pounds
â¢ Bridle working load limit (30-feet Â½-inch three-strand nylon bridle): 1,874 pounds (overestimate, see above. Also assuming brand new line)
â¢ Working load limit for a 5/16 Mantus chain hook: 1,877 pounds (ultimate breaking strength 7,511 pounds)
â¢ Working load limit for 5/16 Grade 30 chain: 1,900 pounds (ultimate breaking strength 7,600 pounds)
âRopes, however, can indeed fail due to age related ultra-violet degradation and chafe, and if the snubber fails loads on anchor chain may actually get to the ABYC predicted 4,898 pounds and certainly chain, the anchor, swivel and the deck hardware should be adequately sized to handle these loads.â
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