Snubbers/Bridles
Why Use an Anchor Bridle/Snubber System?
- Bridle takes the strain of the chain rode, thus offloading the gypsy on the windlass and reduces the stress on the windlass deck joint.
- Allow the load to be taken by the cleats that are designed for high loads
- Reduces the wear on the boat, with all the load on the cleats via the bridle, there is no noise, no chain jerking and snagging on the foredeck.
- If the bridle is long enough/and or has enough stretch it can absorb the shock loads from waves and wind gusts
- With the long bridle the chain is lowered below the waterline and offers better effective scope and additional shock absorption
- It has been suggested by some that when using all chain rode the catenary effect from the sagging chain from its weight will provide sufficient shock absorption. While this might be true for large ships, on average size cruising vessel the catenary effect from the chain does not provide any significant shock absorption, one only has to look at the chain shape under water in a 25 knot breeze to see that the catenary effect is no longer a factor because the chain is oriented in a straight line.
So more simply said the bridle ensures that you anchor has the highest chance of staying put and your boat staying intact.
There are different ways of attaching the bridle to your chain:
Mantus Hook
We designed the Mantus Chain Hook, with these considerations:
- The hook needs to have no moving parts, thus can withstand harsh marine environment
- Is easy to use i.e can be quickly attached and/or removed, yet still be a reliable attachment and positively lock onto the chain without the fear of it falling off.
- Be as strong as all other parts that make up the bridle/snubber.
Mantus Bridle Line Sizing Recommendations:
The role of the bridle/snubber system is to be able to absorb the shock loads by stretching and yet be strong enough not to fail when exposed to these high loads conditions. Thus we make sizing recommendations keeping this in mind.
| Boat Size | 30 – 40 feet | 40 – 50 feet | 50 -70 feet |
|---|---|---|---|
| Line Diameter (inches) | 5/8 | 3/4 | 1 |
| Bridle Length feet | 25 | 30 | 34 |
Effort should be made to protect snubber/bridle line from chafe and inspect it for wear regularly.
Snubber should be properly sized and if done so can significantly decrease the loads on your rode.
For example:
So for a 40 foot boat in a 60 knot sustained wind storm, worst expected loads as predicted by ABYC would be 4800 lbs, most experts would agree that this is an inflated number that accounts for the dynamic loads that could be induced by waves and wind gust on top of the static wind loads and assumes the worst drag coefficients.
ABYC loads already account for the dynamic loads induced by the use of a non-elastic chain a condition mitigated with the use of a snubber.
A properly sized snubber can reduce these loads by 2/3. In our example from 4800 lbs to around 1600 lbs for a 40 foot boat in 60 knots.
Practical Sailor article on snubbers, by Drew Fry March 2016, studied this issue and tabulated the loads for a 40 foot monohull boat in 60 knots in the following scenarios:
- Chain no Snubber – 4,140 lbs (exceeds working load limmit for 5/16 Grade 30 chain)
- ABYC worst case – 4,898 lbs
- Chain with a 30 foot ½ inch three strand nylon bridle – 1,574 lbs (the only scenario where load on the chain is below working load limmit for 5/16 chain 1,900 lbs)
- Chain with a 6 foot 1/2 inch three strand nylon snubber – 3,249 lbs
- Working Load Limmit for 5/16 Grade 30 Chain 1900 lbs, Breaking Strength 7600 lbs.
-62% reduction in peak loads or about 1/3 of the ABYC worst case with the use if 30 foot bridle
-Only 22% reduction in peak loads with the use of the 6 foot snubber.
Thus the use of the a properly sized snubber can significantly reduce the loads on your anchor and you chain, by as much as 2/3 with a 30 foot bridle.
References:
NACM Welded Steel Chain Specifications
Sailnet & Cruisers Forum member input