Snubber sizing for All Chain Ground Tackle

[CaptainDana]

My boat is a 1986 Morgan OI41. Displacement is 23,500 lbs. Chain is 5/16 G4. I've done a bunch of research online and in books to figure out how best to construct an anchor snubber for this situation. The result is a 40-foot, 7/16", 3-strand nylon rope with an eye splice on one end and a 5/16" Grab Hook/shackle/thimble spliced onto the other. The method of deployment is to secure it to a waist cleat or stern cleat depending on conditions, run it forward, over the bow roller and secure it to the chain a few feet forward of the the bow roller.

I'm trying to trigger the armchair experts into telling me all the things that might be wrong with this because, there are probably some good ideas that I haven't considered. So, have at it.

Captain Dana USCG Master 100-tons Near Shore
S/V One Love

[Vasco]

Is 7/16 a bit light? Also line this small is difficult to handle. I use 5/8 on a 20,000 lb boat. Why a waist cleat or stern cleat? Are you not at the bow when anchoring or weighing anchor? It will be difficult to slack the chain and adjust the snubber if cleated so far aft.

[model 10]

We have an 18,000 lb boat and I have used a 3/8",1/2"and and 5/8" x 20' snubbers. Both the 3/8 and the 1/2" wore out too soon. The 5/8" jobs seem to hold up fine and have plenty of give.

[CaptainDana]

Great questions! As the forces on the boat push it back, catenary disappears and the snubber begins to stretch (hopefully without breaking) as it absorbs most (if not all) of the shock of the chain when (or just before) it becomes bar tight. 7/16 line is a compromise. Thirty feet of 7/16" line was chosen to provide up to 5% stretch distance (1-2 feet) without exceeding 20% of breaking strength. That's for an 11 ton boat with windage like mine in 15 knots of wind. To satisfy these conditions, a thirty-foot snubber is required and since I like for the grab hook to be visible above water, it has to be cleated 20' aft of the bow.

Make sense? Fatter line of a given length is stronger but stretches less (provides less shock absorption). Shorter line of a given strength can't stretch as far without breaking.

[Cheechako]

I'd like about 5/8 on that boat. It's amazing how much even that will stretch... too small and you'll start getting mini buckles in the rope when overstretched...

[Vasco]

Put a 3 ft. length of of good hose on the line before you splice it, you'll need it for chafe at the bow. That light nylon line chafes badly. I still have a problem with that line running aft along the deck.

[CaptainDana]

5/8" seems to be a size that people like for an 11-ton boat. One contributor liked 5/8" x 20' because a his thinner snubber (7/16" x 20') would wear out too quickly. What length does the forum like? Do most agree with the 5/8" x 20' suggested?

[Paul L]

I agree with the others who suggest 5/8th. The smaller line might be technically more correct for stretch but in practice I doubt it will last that long if you are fulltime anchoring. You also need a short snubbers that will get used in most situations.

[Cheechako]

20 feet isn't too bad. You will have probably 4 ft from cleat to roller. You want excess behind the cleat, even if that's only 4 ft you are already up to 8 ft. In the end I ended up liking 25 feet, makes me nervous without much line behind the cleat!
But another consideration is using a double snubber. Often this has pressure on just one of the two anyway. I like the double because I can cleat both sides of the boat and being Y shaped it clears a bobstay or anything like that.

[thinwater]

Originally Posted by CaptainDana

My boat is a 1986 Morgan OI41. Displacement is 23,500 lbs. Chain is 5/16 G4. I've done a bunch of research online and in books to figure out how best to construct an anchor snubber for this situation. The result is a 40-foot, 7/16", 3-strand nylon rope with an eye splice on one end and a 5/16" Grab Hook/shackle/thimble spliced onto the other. The method of deployment is to secure it to a waist cleat or stern cleat depending on conditions, run it forward, over the bow roller and secure it to the chain a few feet forward of the the bow roller.

I'm trying to trigger the armchair experts into telling me all the things that might be wrong with this because, there are probably some good ideas that I haven't considered. So, have at it.

Captain Dana USCG Master 100-tons Near Shore
S/V One Love

In fact a lot of testing, both practical cruiser experience and with load cells, has been done. There is a good bit in Practical Sailor and more in my book (see web site).

The reason for a long snubber, attached farther back is to take advantage of improved energy absorption while keeping the hook off the bottom. This is becoming modern practice.

7/16" is enough at that snubber length. A number of well-known and widely traveled sailors have been using climbing rope with that weight and length boat. Remember, however, that if 7/16" is used as a short (10-20') snubber it will NOT have enough length to absorbe energy and will fail. Remember also that the snubber is disposable and should be replaced every 100-150 nights, depending on the weather. A stiffer rope last longer, but places more force on the anchor. That is not opinion, that is documented fact.

Chafe at the bow can best be handled with either a turning block or by placing the snubber inside tubular webbing, where it will easily slide. Thinner snubbers are vulnerable to chafe and must be used intelligently. I used twin 3/8" snubbers on the cat in my avitar for many years with no wear at all. They were anchored to the mid-ships cleats for more stretch.

Search Practical Sailor and my blog.

[CaptainDana]

Good input. I did refer to the Practical Sailor work and other sources. What these contributors have added that I don't recall seeing in the literature was wear and service life. 150 nights is a great figure of merit for snubber life. I'd love to hear how long people think a snubber is supposed to last.

They don't take long to make and 35 feet of line isn't that expensive.

[Paul L]

Cruising fulltime we replace ours probably every year and half. I have broken one 12 strand plait 5/8 snubber.

[thinwater]

Originally Posted by CaptainDana

Good input. I did refer to the Practical Sailor work and other sources. What these contributors have added that I don't recall seeing in the literature was wear and service life. 150 nights is a great figure of merit for snubber life. I'd love to hear how long people think a snubber is supposed to last.

They don't take long to make and 35 feet of line isn't that expensive.

I might go longer than 35' I recall Starzinger was using more like 45-50 feet.


I suggested they would be replaced after 150 nights. I did not mean it would fail in that time.I like to replace stuff before it fails. But really, it comes down to the weather. It would last longer on the Chesapeake. The estimate was based on fatigue life and fairly breezy conditions.


And just think of how much wear and tear it takes off the chain and anchor.

[model 10]

Double snubbers are fun to set up just right. I found you can't use claw hooks on the inner snubber because they fall off.

[Delfin]

Originally Posted by CaptainDana

My boat is a 1986 Morgan OI41. Displacement is 23,500 lbs. Chain is 5/16 G4. I've done a bunch of research online and in books to figure out how best to construct an anchor snubber for this situation. The result is a 40-foot, 7/16", 3-strand nylon rope with an eye splice on one end and a 5/16" Grab Hook/shackle/thimble spliced onto the other. The method of deployment is to secure it to a waist cleat or stern cleat depending on conditions, run it forward, over the bow roller and secure it to the chain a few feet forward of the the bow roller.

I'm trying to trigger the armchair experts into telling me all the things that might be wrong with this because, there are probably some good ideas that I haven't considered. So, have at it.

Captain Dana USCG Master 100-tons Near Shore
S/V One Love

I've spent way too much time thinking about this, so keep that in mind....

I sized my snubber so that the breaking strength of the line would provide 20% stretch at a load that was just under the WLL of the chain. If I play out 30', then I lay 20% of that or 6' of chain after the snubber goes taut. That way, the loading is transferred to the chain at the extremes.

I would ditch the grab hook, since they are generally weaker than the line and go with a Dyneema soft shackle.

Where you secure the snubber is less important than having around 30' taking the load off the chain so you have at least six feet of shock absorber buffering loads.