How long should an anchor snubber be?

[ReMetau]

Dockhead,

I don't understand your point in carry various sizes of snubber line based on conditions. If you are using a shorter, lighter snubber for light air, what is the point of it? With the size of your chain, you won't ever have the catenary go out of the chain in the light airs.
Why not just use the heavier snubber line all the time? If you are in light winds, then the snubber doesn't do much, but who cares? If the winds pickup, then you already have a snubber on to handle it.

[Alan Mighty]

Based on his extensive scientific research on anchors and anchoring, Professor John H. Knox, reckoned that snubber should be nylon (and he preferred nylon multiplait) and be:

* about as long as boat; and

* diameter of snubber line, in millimetres, should be about 1.5 times length of boat measured in metres.

JHK recommended making snubber to a stern cleat, so it could be attached to rode not too far forward of bow. Led Myne's deck and coachroof do not lend themselves to that arrangement, so snubber is made to Samson posts and runs way forward on the rode.

Al

[The Way]

Originally Posted by Horror Hotel

Mines 60' But I put out 15' normally. If some weather comes through and I need to let out more chain I don't have to adjust the hook (Mantus). I never anchor with less than 5:1 with 3/8" chain.

I use a 40-45' dockline as a snubber. I thought about using a longer one, as HH says, but I may want to veer 50-100' of chain, that's a long snubber. So if I want to let out more chain, I'd just untie the first snubber from the cleat, let it run out with the chain, and use a second snubber.

I use a rolling hitch, not a hook, so any dockline will work. I guess I might lose the first snubber in the scenario described, but that's less likely than if using a hook.

Jack

[MarkJ]

I have a nylon twist snubbber (actually two).
I never let the rope touch the water as I dont want barnicals growing inside the rope

[Dockhead]

Originally Posted by ReMetau

Dockhead,

I don't understand your point in carry various sizes of snubber line based on conditions. If you are using a shorter, lighter snubber for light air, what is the point of it? With the size of your chain, you won't ever have the catenary go out of the chain in the light airs.
Why not just use the heavier snubber line all the time? If you are in light winds, then the snubber doesn't do much, but who cares? If the winds pickup, then you already have a snubber on to handle it.

A fair question -- and you could use the heavier snubber all the time!

However, the lighter snubber is much easier to handle, and is less likely to touch the bottom in shallower anchorages. Also, my own light snubber is tuned to be a little stretchier than the heavy one.

I use my light one about 75% of the time.

Although I sail in a place where rougher conditions are more common, I naturally avoid anchoring in them when I can, like everybody.

[No Ice]

JHK recommended making snubber to a stern cleat, so it could be attached to rode not too far forward of bow. Led Myne's deck and coachroof do not lend themselves to that arrangement, so snubber is made to Samson posts and runs way forward on the rode.

Alan Mighty

Sorry to be a bit slow but i dont understand the above, Please explain in simple terms.

Brian

No Ice

[noelex 77]

I am still searching for the ideal snubber.

I went through a period of breaking a lot of snubbers, which seems to have been solved by getting quality name brand nylon from the UK.

I usually like to anchor with thought that the conditions might be worse than forecast. This means I sleep soundly.

Therefore I usually have a moderately long, but thick (sized for strong wind) snubber even in benign conditions. If conditions do worsen to the "oh my god" stage it is much easier to let out more chain and lengthen the snubber by attaching additional nylon.This gives more elasticity and more scope in one go. It is helpful if you can do this without pulling up chain as this is hard/impossible on the windlass without starting the motor, and who wants to start the motor at 3am. More nylon means you lengthen the snubber and just have to let the windlass clutch go.

I think it is possible to end up with too much elasticity producing a slingshot effect, but this is very hard to achieve with suitably sized nylon snubber.

One final danger of a snubber that has not been mentioned is the risk of getting it around the prop. Keep this in mind.

[Dockhead]

Originally Posted by noelex 77

I am still searching for the ideal snubber.

I went through a period of breaking a lot of snubbers, which seems to have been solved by getting quality name brand nylon from the UK.

I usually like to anchor with thought that the conditions might be worse than forecast. This means I sleep soundly.

Therefore I usually have a moderately long, but thick (sized for strong wind) snubber even in benign conditions. If conditions do worsen to the "oh my god" stage it is much easier to let out more chain and lengthen the snubber by attaching additional nylon.This gives more elasticity and more scope in one go. It is helpful if you can do this without pulling up chain as this is hard/impossible on the windlass without starting the motor, and who wants to start the motor at 3am. More nylon means you lengthen the snubber and just have to let the windlass clutch go.

I think it is possible to end up with too much elasticity producing a slingshot effect, but this is very hard to achieve with suitably sized nylon snubber.

You have to tune the snubber to get the right amount of elasticity for conditions. I find that there are unpleasant resonance points which you need to get around by pulling in or letting out some of the snubber. That's another reason why it's good to have a variety of them on board.

I'm surprised you've broken many snubbers -- was that chafe? Or overload? I've only broken one in my entire life.

Estarzinger's supersnubber would be the ultimate anti-chafe solution, if you need that.

Otherwise, I find decent nylon octoplait to be really robust. It doesn't hockle like three-strand, and is more pleasant to handle. It has more elasticity for a given amount of strength, too.

I lead mine over the second bow roller and fix it to my innerforestay chainplate, so it is almost free of chafe, unless the bows blow off or oscillate and the snubber touches the cheeks of the stem fitting. But in those conditions, I find that fixing a second snubber and leading it to a cleat on one side, and adjusting the relative lengths of the two snubbers, can allow you to find a stable position. Yet another reason to keep multiple snubbers on board.

[noelex 77]

Originally Posted by No Ice

Sorry to be a bit slow but i dont understand the above, Please explain in simple terms.

Brian

No Ice

Nylons stretch is determined partially by its length. Longer means more stretch which is what you want.
Attaching the snubber on the stern cleats means you can have a whole boat length with only a few feet hanging off the bow reducing the problem of marine growth on the snubber and chafe on the sea-bottom, but you can end up with a lot of chafe from the deck and it is not practicable in many boats.

[noelex 77]

Originally Posted by Dockhead

You have to tune the snubber to get the right amount of elasticity for conditions.

Yes and no . I am not woried about introducing elasticity in mild/moderate conditions. Chain catanery does work in mild conditions and and anchor holding is not a concern until the wind becomes strong.
So my snubber is set, and sized, on the assumption that the winds may be strong even when only light winds are forcast.

Originally Posted by Dockhead

I'm surprised you've broken many snubbers

Me too . My current theory is that it is the lousy rope that sold in the local chandleries (mainly to fishermen). I kept going up in size which dramatically reduces the stretch.
Some new good quality octoplat seems to be holding up well, but it's not been in winds over 40knots yet

[El Pinguino]

I don't do 'rough' but I have done a bit of 'windy'..... in the pic ( Sparrow Cove F.I.)it is moderate windy but even with windy windy I simply use about 2 metres of (18mm approx ) nylon.

Chafe has been negligible... previous snubber was replaced at 10 years cos it was looking daggy... nada mas.

Even when the catenary has gone walkabout ( I normally drop out 60 metres of chain regardless of depth ) it works ok but we aren't talking about 'snatch' loading, typically just a fairly constant load... 40 gusting 60 sort of stuff with no appreciable sea.

[Pelagic]

Assuming a boat has enough sea room, I have never understood the mindset of being conservative with scope.

I lay it all out, stretching towards the closest danger regardless of anticipated wind direction and mark 2 radar range rings which denote:
1 Anticipated max stretch
2 Definitely dragging.

Never understood the
Philosophy of putting out more chain once you discover you are dragging.

Is it because your anchor windless is too slow or the chain wash too weak that you keep the chain onboard at night?

[Alan Mighty]

Originally Posted by No Ice

JHK recommended making snubber to a stern cleat, so it could be attached to rode not too far forward of bow. Led Myne's deck and coachroof do not lend themselves to that arrangement, so snubber is made to Samson posts and runs way forward on the rode.

Alan Mighty

Sorry to be a bit slow but i dont understand the above, Please explain in simple terms.

Brian

No Ice

Idea of snubber is to absorb shocks. A snub is a jerk in anchor rode caused by wind gust or wave crest. A snubber originally was crew member who eased line to avoid such jerk.

Dry nylon cordage is springy, it stretches and absorbs snubs, dissipating energy of snub as heat. Degree of springiness relates to diameter of cordage: thin nylon cordage stretches (and rebounds like a spring) more than thick nylon cordage for a jerk of a particular size. Longer cordage means more spring. And longer nylon snubber means energy dissipation, converting mechanical jerk into heat, is spread over more nylon. So longer snubbers are less likely to melt.

Professor John H. Knox did the science and came up with simple guideline: snubber about as long (in metres) as LOA (in metres); diameter (in millimetres) about same number as number of LOA (in metres). So Prof Knox recommended that Led Myne (28 ft or 8.5 metres) should use a nylon multiplait snubber about 8.5 metres long and 8.5 millimetres diameter.

That's easy part.

Now hard part: Springiness of nylon is easily measured, when it's dry. If you soak nylon in water (rain, seawater, freshwater), the nylon elongates. And its ability to stretch rebound, i.e. its springiness, changes. Its ability to dissipate heat also changes (water is better at keeping nylon cooler than air is).

If a nylon snubber is wet, its springiness is not as good as when it is dry.

So Prof Knox reckoned smart thing is to make anchor snubber to a stern cleat, lead it forward over bow, and make it to anchor rode not too far forward of bow (and above water line).

That's not practice followed by most cruisers in anchorages Led Myne visits. Most cruisers make one end of their snubber to a cleat or strong point, such as bitts or Samson Post, at bow. And other end is attached to anchor rode 8 metres (to continue example of Led Myne) forward of bow.

That means much or most of snubber is below water surface. And is always wet.

Springiness of wet nylon is not same as springiness of dry nylon.

Other consideration is that snubber will carry the rode load. As I have pointed out in other thread (How best to set anchor), a 40 knot wind would load Led Myne's rode to 233 kg.force (about 514 pound.force). And snubber is going to be stretching and rebounding with every additional wave and gust cycle. It's not a lazy line. So it must be led fair. Any contact (with deck, deckhouse, coachroof, whatever) has to be smooth and not binding. Otherwise result is chafing (on snubber, on deck, on coachroof etc) and point load. And soon no snubber - it will part under tension, with violence.

So shape of deck and availability of a fair lead from a stern cleat is important consideration. Led Myne, just because of curvature of her deck, shape of boat, location of deckhouse etc, simply does not have fair lead from stern cleat to spare anchor roller. Perhaps your GB does?

Yet another consideration is safety. I would prefer not to be near a 8 mm nylon line carrying tension at 233 kg.f if it were to part.

So I compromise. (1) I try to keep as much of snubber as dry as possible. But much of it ends up in drink. (2) To compensate, I change snubber regularly - nylon work-hardens (loses some of its springiness with repeated load cycles) and dirt, salts and other chemicals migrate between fibres and into fibres (e.g. rust weakens nylon measurably, so rust stained nylon is not as strong as clean nylon). (3) I have a rubber dockline snubber block on snubber too.

Hope that helps

Al

[No Ice]

Thanks Guys for the answers which help a lot.

One question. If a snubber should be 1mm thick and 1M long in relation to the boats length how long and thick should it be if you use a bridle from the bow of the boat, do you half the thickness and length?

[lancelot9898]

In a perfect world each leg of the bridle would take of half the load that the rode sees, however if you watch the bow you'll see that the boat will "hunt" back and forth putting the entire load on one leg of the bridle and then the other. The bridle will reduce the hunting, but the sizing should still be based upon having just one leg at a time.