Snubber Diameter for Larger Sailboats

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We recently had a letter from Teun and Chantal Bos, who were trying to determine what diameter anchor snubber to use. Practical Sailor did extensive testing in this area, but unfortunately some of the formulas used to determine the right size snubber—strong and chafe resistant yet elastic enough to absorb shock loads —were lost in translation as we migrated to the new website.

As a result, the equation online yielded some clearly absurd results. In the case of the Bos’s, it recommended a 12-inch diameter snubber for their 49-foot Oyster pilothouse, Beryl, clearly out of wack with reality.

As a result, we reviewed and updated the equation and the table in our original report, “What is the Ideal Snubber Size”  The updated equation below should bring you within the ballpark for your boat.

Diameter (inches) = 0.00067 x (length overall in feet) x (loaded weight in pounds)^0.3

Keep in mind, this is a rough guide for estimating the length and diameter of a snubber based on projected loads. It applies exclusively to 3-strand premium nylon from a reputable ISO-certified  rope manufacturer (Yale, Samson, and New England Ropes, Novabraid, etc.). The ideal snubber dimension can vary greatly from boat to boat, and conditions. The aim is to have rope that offers plenty of stretch, and a breaking strength with an ample safety margin under projected maximum loads. When in doubt, round up to the next larger size that what the formula recommends. For moorings or use in consistently windy conditions, go up one size from the formula recommendation.

In general, the snubber will be one size smaller than the boat manufacturer’s recommended nylon anchor rode. For more on rode loads, see “Anchor Testing and Rode Loads,” and “The Load on Your Rode.”

You will need to make a judgment call regarding whether your boat is light, medium, or heavy, bearing in mind that a boat with high windage or that yaws excessively at anchor, will have higher rode tension. In which case, you might have to take other measures to reduce yaw.

In truth, there are a range of right answers. Stronger lines last longer but absorb less shock. Lighter lines will need to be retired sooner but will put less stress on the anchor and rode. As long as you stay in the range, you should be fine. The biggest error we see in snubbers are that they are too short, not protected against chafe, or equipped with poorly engineered snubber hooks.

To really get to the bottom of anchors, rode, snubbers, and the specialized gear and techniques for ensuring your boat stays put, our four-volume series on anchoring “Anchoring the Complete Series,” presents more than two decades of research.

SNUBBER SIZING EXAMPLES

BOAT MAKE & TYPE BOAT LENGTHDISPLACEMENT SINGLE SNUBBER DIAMETER (estimated 3-strand premium nylon)BRIDLE DIAMETER
(estimated 3-strand premium nylon)
SNUBBER LENGTH
(estimated 3-strand premium nylon)
Type
(actual rode in use)
LENGTH
(actual rode in use)
DIAMETER
(actual rode in use)
MONOHULLS
PACIFIC SEACRAFT 3434 Feet13,500 lbs. 3/8” /9mmnot applicable44 feet3-strand premium nylon45 feet1/2” / 13 mm
MORGAN 41.6 42 feet27,000 lbs. 1/2” / 13 mmnot applicable54 feetClimbing rope50 feet3/8” / 10 mm
CABO RICO 38 38 feet21,000 lbs.7/16”/ 11 mm3/8” / 10 mm49 feet3-strand bridle30 feet5/8” / 16 mm
VAN DE STADT 4747 feet30,000 lbs. 1/2” / 13 mmN/A61 feetClimbing rope20 feet7/16”/ 11 mm
CATAMARANS
LIGHTWAVE 38 38 feet12,000 lbs.9/16” / 14 mm3/8” / 10 mm49 feetClimbing rope bridle25 feet3/8” / 10 mm
PDQ 32 32 feet7,800 lbs. 1/2” / 13 mm3/8” / 10 mm 42 feetClimbing rope bridle35 feet5/16” / 8 mm
STILETTO 2727 feet1,700 lbs.1/4” / 6 mm1/4”/ 6 mm35 feetDouble braid15 feet5/16” / 8 mm
bridle
The above table illustrates how Frye’s formula for estimating the length and diameter of a 3-strand snubber can vary greatly from what is being used in practice by experienced cruisers.

 

Drew Frye is technical editor of Practical Sailor, he blogs at his website www.sailingdelmarva.com.

Drew Frye
Drew Frye, Practical Sailor’s technical editor, has used his background in chemistry and engineering to help guide Practical Sailor toward some of the most important topics covered during the past 10 years. His in-depth reporting on everything from anchors to safety tethers to fuel additives have netted multiple awards from Boating Writers International. With more than three decades of experience as a refinery engineer and a sailor, he has a knack for discovering money-saving “home-brew” products or “hacks” that make boating affordable for almost anyone. He has conducted dozens of tests for Practical Sailor and published over 200 articles on sailing equipment. His rigorous testing has prompted the improvement and introduction of several marine products that might not exist without his input. His book “Rigging Modern Anchors” has won wide praise for introducing the use of modern materials and novel techniques to solve an array of anchoring challenges.