Does anyone have a calculation you use to figure out the length of bridle for the chain while anchoring.
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All you do is,
make sure the chain is slack at the windlass. Then the bridal takes the load. No formula for that.
make sure the chain is slack at the windlass. Then the bridal takes the load. No formula for that.
Bridle Length
Bridles and Snubbers should be between 20% to 40% longer than the chain they displace. The main purpose of a rope bridle on a chain anchor rode is to provide shock absorption, through stretch (elastic elongation). As rope stretches, it absorbs energy (strain energy), and it’s safe working load (strength) decreases. So we have a trade-off: More stretch (longer bridle) = More Shock Absorption = Lower Working Load. A ½" Nylon Rope can stretch between just under 20 to over 40% of it’s length at failure (about 6,000 Lbs). At 75% Loading (about 4,000 Lbs), the Elastic Elongation figures are reduced: (Double-Braid 18% - 14%, Three-Strand 30% - 22%, Brait +40% - 25%). I prefer to increase shock absorption, accepting a reduction in working strength. If a bridle “breaks” under load, it will provide a good alarm that my ground tackle assembly is approaching it’s upper limits. Hence: I would use a bridle that is about 6- ½ Feet to 7 Feet Long (3-Strand or Brait), attached to the chain rode at about 5 Feet down from the bow. ie: 3-Strand = 5' x 1.3 = 6.5' long Bridle Brait = 5' x 1.4 = 7.0' Double-Braid = 5' x 1.18 = 5.9' For “Snubbers”, which are generally longer, you would increase the rope length accordingly. Assuming a 20' Snubber length: ie: 3-Strand = 20' x 1.3 = 26.0' long Snubber Brait = 20' x 1.4 = 28.0' Double-Braid = 20' x 1.18 = 23.6'
Bridles and Snubbers should be between 20% to 40% longer than the chain they displace. The main purpose of a rope bridle on a chain anchor rode is to provide shock absorption, through stretch (elastic elongation). As rope stretches, it absorbs energy (strain energy), and it’s safe working load (strength) decreases. So we have a trade-off: More stretch (longer bridle) = More Shock Absorption = Lower Working Load. A ½" Nylon Rope can stretch between just under 20 to over 40% of it’s length at failure (about 6,000 Lbs). At 75% Loading (about 4,000 Lbs), the Elastic Elongation figures are reduced: (Double-Braid 18% - 14%, Three-Strand 30% - 22%, Brait +40% - 25%). I prefer to increase shock absorption, accepting a reduction in working strength. If a bridle “breaks” under load, it will provide a good alarm that my ground tackle assembly is approaching it’s upper limits. Hence: I would use a bridle that is about 6- ½ Feet to 7 Feet Long (3-Strand or Brait), attached to the chain rode at about 5 Feet down from the bow. ie: 3-Strand = 5' x 1.3 = 6.5' long Bridle Brait = 5' x 1.4 = 7.0' Double-Braid = 5' x 1.18 = 5.9' For “Snubbers”, which are generally longer, you would increase the rope length accordingly. Assuming a 20' Snubber length: ie: 3-Strand = 20' x 1.3 = 26.0' long Snubber Brait = 20' x 1.4 = 28.0' Double-Braid = 20' x 1.18 = 23.6'
Pretty fancy Gord,
A couple of things come up with your latest dissertation. You say "The main purpose of a rope bridle on a chain anchor rode is to provide shock absorption, through stretch (elastic elongation). As rope stretches, it absorbs energy (strain energy), and it’s safe working load (strength) decreases." I always thought it was to take the load of the chain off the windlass. That component is not designed to hold even the 'working load' of anchor chain. And then you prefer to "I prefer to increase shock absorption, accepting a reduction in working strength. If a bridle “breaks” under load, it will provide a good alarm that my ground tackle assembly is approaching it’s upper limits." My Gawd Gord, were giving advise to a newbie here. You're talking as if your chain can break as a matter of everyday use! I submit that it would not break in SURVIVAL conditions if properly maintained. The anchor would have long before, dragged. But, as they 'say', anything can be expressed with numbers.
A couple of things come up with your latest dissertation. You say "The main purpose of a rope bridle on a chain anchor rode is to provide shock absorption, through stretch (elastic elongation). As rope stretches, it absorbs energy (strain energy), and it’s safe working load (strength) decreases." I always thought it was to take the load of the chain off the windlass. That component is not designed to hold even the 'working load' of anchor chain. And then you prefer to "I prefer to increase shock absorption, accepting a reduction in working strength. If a bridle “breaks” under load, it will provide a good alarm that my ground tackle assembly is approaching it’s upper limits." My Gawd Gord, were giving advise to a newbie here. You're talking as if your chain can break as a matter of everyday use! I submit that it would not break in SURVIVAL conditions if properly maintained. The anchor would have long before, dragged. But, as they 'say', anything can be expressed with numbers.
My apologies and A Clarification
Of course, Fred is “right” (in the “practical” sense) - but Denise asked for a “formulae”. Obviously, I was ambiguous in my explanation. Sorry. 1. Not all boats have a windlass - even those with all-chain anchor rodes. 2. When a windlass is installed, the gypsy is NEVER used to secure the chain (carry the anchor load). Chain anchor rodes should be secured to a “chain stopper”. (Ie: http://www.sailnet.com/store/item.cfm?pid=14183 ) Thus, the anchor load should never be on the windlass gypsy (bridle or not) !!! 3. The purpose of an anchor “bridle” is to absorb the shock that occurs when an inelastic chain anchor rode is lifted taut under high loading. This shock would be transmitted to both the boat (deck hardware) and to the anchor (perhaps, pulling it loose). 4. A more elastic (stretchier) bridle, of smaller diameter & strength, will offer greater protection from these shock loads than will a larger diameter & stronger bridle. 5. Under ultimate conditions, this stretchier (but weaker) bridle could break. The bridle has much less breaking-strength than the properly sized chain. If the bridle should break (long before the chain is overloaded), it will provide an obvious and dramatic “alarm” that things are getting out of hand. In this extreme case, the chain is not likely to break (as Fred points out) - but something might let go - the anchor, the deck hardware, etc. To rephrase Fred’s good advice: Make certain the chain is NOT secured (belayed) to the windlass, but to a purpose-made deck fitting, such as a “Chain Ctopper”. Attach a “Bridle” so that there is “some” slack in the chain (between the stopper and the chain claw). I recommend that “some” slack be quantified at between 20% & 40% depending upon the composition of the bridle rope) of the slacked chain. By formulae: Bridle (or Snubber) Rope Length = distance from chain stopper to bridle attachment @ chain x 1.2 (to 1.4)
Of course, Fred is “right” (in the “practical” sense) - but Denise asked for a “formulae”. Obviously, I was ambiguous in my explanation. Sorry. 1. Not all boats have a windlass - even those with all-chain anchor rodes. 2. When a windlass is installed, the gypsy is NEVER used to secure the chain (carry the anchor load). Chain anchor rodes should be secured to a “chain stopper”. (Ie: http://www.sailnet.com/store/item.cfm?pid=14183 ) Thus, the anchor load should never be on the windlass gypsy (bridle or not) !!! 3. The purpose of an anchor “bridle” is to absorb the shock that occurs when an inelastic chain anchor rode is lifted taut under high loading. This shock would be transmitted to both the boat (deck hardware) and to the anchor (perhaps, pulling it loose). 4. A more elastic (stretchier) bridle, of smaller diameter & strength, will offer greater protection from these shock loads than will a larger diameter & stronger bridle. 5. Under ultimate conditions, this stretchier (but weaker) bridle could break. The bridle has much less breaking-strength than the properly sized chain. If the bridle should break (long before the chain is overloaded), it will provide an obvious and dramatic “alarm” that things are getting out of hand. In this extreme case, the chain is not likely to break (as Fred points out) - but something might let go - the anchor, the deck hardware, etc. To rephrase Fred’s good advice: Make certain the chain is NOT secured (belayed) to the windlass, but to a purpose-made deck fitting, such as a “Chain Ctopper”. Attach a “Bridle” so that there is “some” slack in the chain (between the stopper and the chain claw). I recommend that “some” slack be quantified at between 20% & 40% depending upon the composition of the bridle rope) of the slacked chain. By formulae: Bridle (or Snubber) Rope Length = distance from chain stopper to bridle attachment @ chain x 1.2 (to 1.4)
Stu's Back
Well, it's obvious that Stu - the politician, board spell checker and board monitor for "stupid questions or comments" is back. Good to see you Stu. Glad you're here to show us your intelligence. Geez.
Well, it's obvious that Stu - the politician, board spell checker and board monitor for "stupid questions or comments" is back. Good to see you Stu. Glad you're here to show us your intelligence. Geez.
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