Choice of Material for Snubbers

[s/v Jedi]

Hmm, I'm starting to think that the way this works in reality is not fully grasped yet

When the weather gets really bad and the chain has come bar tight, you don't need a snubber anymore. I'm serious. All that matters at that point is the holding of the anchor and the strength of the chain. Snubbers are done stretching and chains are done straightening at that point. This leaves surging action from swell on top of a high static load from the wind. Because the shock loading from that swell is on top of the high static load, it is out of the working range for snubbers to absorb it. That is when they break. Now is the time you need that chain stopper and be happy that water is softer than steel and allows the bow to split the wave which all works as yet another way to absorb shocks. I guess we have all been slapped on the beam by a wave now and then which shows the potential force of the wave; the swell passing by at anchor is only a fraction of that energy as the rest is diverted around the boat.

[CAELESTIS]

I would like to see a photo of the combination snubber Evans uses. How are these various lines attached? Spliced? How long should a snubber be to perform as intended?

My current snubber is a bridle style with 2- 5/8 3-strand lines of about 25 ft in length secured to deck cleats.

[Strygaldwir]

I am not certain that the principle concern is breaking the tackle. I'd think your concern is unsetting your anchor. I believe it best to keep your anchor set and not worry about whether it is going to reset or not.

Having said that, I believe the idea of cantenary and by extension, stretch is the distribution of force over time. Something that stretches is going to be able to handle the load over the period of time associated with the stretch.

The best annology is driving a car into a wall with no elasticity at 60 miles an hour. 60 to 0 in 0 seconds. The force apply over the time duration is going to make for one broke car/wall/occupants. Now go from 60 to 0 it 20 seconds. Everyone will be much happier, care/wall/occupants. Same with anchoring. Instant jerk, things break or come lose. Slow pull, release, and spring back, heat get's absorbed, every thing stays good.

[Cotemar]

Originally Posted by CAELESTIS

I would like to see a photo of the combination snubber Evans uses. How are these various lines attached? Spliced? How long should a snubber be to perform as intended?

My current snubber is a bridle style with 2- 5/8 3-strand lines of about 25 ft in length secured to deck cleats.

Your snubber is good just the way it is.
If your having trouble keeping your bridal to chain hook on then you may want tot try a Soft Shackle.

[DumnMad]

Originally Posted by s/v Jedi

Hmm, I'm starting to think that the way this works in reality is not fully grasped yet

When the weather gets really bad and the chain has come bar tight, you don't need a snubber anymore. I'm serious. All that matters at that point is the holding of the anchor and the strength of the chain. Snubbers are done stretching and chains are done straightening at that point. This leaves surging action from swell on top of a high static load from the wind. Because the shock loading from that swell is on top of the high static load, it is out of the working range for snubbers to absorb it. That is when they break. Now is the time you need that chain stopper and be happy that water is softer than steel and allows the bow to split the wave which all works as yet another way to absorb shocks. I guess we have all been slapped on the beam by a wave now and then which shows the potential force of the wave; the swell passing by at anchor is only a fraction of that energy as the rest is diverted around the boat.

I would still like DennisG to give us the catenary figures for 75ft, 150ft and 300ft of chain rode.
I reckon 300ft or longer of chain with no snubber but good catenary effects might be best strategy for high winds and big seas.

[hpeer]

Originally Posted by estarzinger

This is my last thought for now on this topic, until I have more direct experience with and have fined tuned my 'new solution' . . . .

(1) Clearly an all nylon snubber works and is a perfectly adequate solution. It's the traditional and well proven solution. I don't think anyone will say that all nylon is 'unreasonable'.

(2) I personally think that if you want to move from 'adequate' to 'best' than some sort of hybrid will be the solution. I have some significant engineering support in that thinking from both MIT and New England Ropes. As mentioned in some posts above the difference between 'adequate' and 'best' will probably only matter in significantly severe conditions, OR when you are thinking about perhaps leaving your boat on anchor alone/unattended for a length of time.

This thread (and the other one) mostly talks about dyneema and Dacron and nylon very generally, but each of those comes in a number of very different constructions, which have very significant differences between them. So, the question of which line construction is 'best' is almost as interesting/important/difficult as the fibers.

(3) In all this, I think the 'soft shackle' is the most useful/practical development . . . . more so than the rode discussion. Both the rolling hitch and chain hook obviously generally work, but IMHO the soft shackle is just simply day to day "easier and better" than both with zero downside.

Evans.....before you run I'd like to ask your opinion on a few points.

We just replace our sprit with a new one and I made some modifications to the anchoring scheme.

A..I moved the rollers out near the tip of the sprit because they fouled the bob stay making anchoring a PITA.
B.. I welded the old forstay tang, with two 3/4" holes on to and below the bob stay attachment. The weldment will actually reinforce the stay attachment. So, I now have a tang with three holes at the waterline.

My "plan" is to attach my snubber to the tang at the waterline, below the bob stay, with a 5/8" shackle, and leave it there permanently. I'll have to fish it up when retrieving the anchor. The snubber will be a little too short to foul the prop if I dropped the end. Having the attachment point low should make the effective length better than attaching to a cleat and provide a straight pull. Also I don't really want to have the stress way out on the tip of the boom.

1... Does this sound reasonable, are there fatal flaws?
2... Why not apply TWO snubbers in bad conditions, one a little longer than the other? If the short one snaps the long one will then take the load.

If this doesn't work I could run the snubber down through the old anchor aperture and things would be similar to the way they were, but the snubber would again foul on the bob stay.

[Kettlewell]

My "plan" is to attach my snubber to the tang at the waterline, below the bob stay, with a 5/8" shackle, and leave it there permanently. I'll have to fish it up when retrieving the anchor. The snubber will be a little too short to foul the prop if I dropped the end. Having the attachment point low should make the effective length better than attaching to a cleat and provide a straight pull. Also I don't really want to have the stress way out on the tip of the boom.

1... Does this sound reasonable, are there fatal flaws?
2... Why not apply TWO snubbers in bad conditions, one a little longer than the other? If the short one snaps the long one will then take the load.

I don't have a bowsprit, but I installed a bow eye down low, just above the waterline, and I keep a 3/8" nylon snubber permanently attached to it, but no shackle, just cow hitched on to keep it silent. There is nothing to chafe on, the line provides a lower angle of pull, and it stays mostly in the water so it is water cooled. I also have a deck-level snubber rigged up with a chain hook which I use too. The lower snubber is great in heavy weather, and keeps things quieter too.

I have used two snubbers in heavy weather, though the first one has never let go.

[Kettlewell]

Found this article by Yale on arborist ropes, which bears on what we have been discussing here. Basically, you need a rope that absorbs energy for a snubber. Here's an excerpt.

One of the most misunderstood aspects of rope selection is the disconnect between breaking strength and a ropes ability to absorb dynamic loads. Many people wrongly assume that the stronger a rope’s rating the harder it is to break. That is not the case as a rope can be parted if called upon to carry a load greater than its breaking strength or, if asked to absorb a dynamic load greater than its energy absorption capability.

Everyone is used to talking about a rope’s breaking strength but almost no one describes a rope’s energy absorption capability. This is obtained by studying a stress strain curve of load vs. elongation. The area described under the stress strain curve pertains to force acting through distance (or the work required to break it).

On the previous page you will find the bar graphs of our ropes’ dynamic characterists. The first shows each types’ working energy absorption which describes how much energy each will absorb before reaching its working load, which in the case of rigging ropes is 1/5 or 20% of its breaking strength. The more work the rope can do getting to 20% of breaking strength the longer it will last. A very stiff rope, with little or no elongation, gets to its working load without doing much work and quickly becomes loaded beyond its safe working load, regardless of how strong it is. These ropes are poor choices for rigging with the single exception where stretch cannot be tolerated, such as working with a zip line over a roof with limited clearances.

[estarzinger]

Originally Posted by hpeer

My "plan" is to attach my snubber to the tang at the waterline, below the bob stay, with a 5/8" shackle, and leave it there permanently.
1... Does this sound reasonable, are there fatal flaws?
2... Why not apply TWO snubbers in bad conditions, one a little longer than the other? If the short one snaps the long one will then take the load.

Attaching snubbers to bow eyes near the waterline used to be more common and works well - zero chafe, with better angle on the anchor. The only disadvantage I have seen is that you don't inspect the bow attached end of the snubber as closely/often and it can get damaged and you don't notice it. I did not do it on Hawk because I was concerned that ice would cut/damage the snubber.

Two snubbers in difficult conditions is also typically a good idea. I do it, but only relatively infrequently for forecast 'storm force'. The only downside I have seen is that if you want to adjust or let out more scope/chain, its a little more work and a little slower.

I think you are on a good track with both thoughts.

Originally Posted by CAELESTIS

How are these various lines attached? Spliced? How long should a snubber be to perform as intended?.

I now have two 'new snubbers', in the 'primary one', the sections are now spliced, with the spliced loops cow hitched together. I believe that's generally recognized as the strongest and least chafe method and was specifically recommended in the MIT paper. I also have an 'experimental' snubber that is knotted, so that I can play around with adjusting the length and seeing what feels best. Specially the spectra piece has a spliced loop and the nylon piece is double sheet bended to that. Splices are theoretically much better, but I have used that double sheet bend in my old chain hook snubber for over a decade and it's never been a weak spot so practically speaking the sheet bend seems way good enough.

That brings us to your second question - best length - and I have to say I don't know. Right now my spliced one has the nylon section 15' long. So far I have liked the feel of that, but I can make excellent arguments that it should be up to 30' long (my experimental one is now 25' long). I don't really see any logical downside to the longer length and some theoretical upsides, but for some reason I cannot articulate I swing toward and prefer to use the shorter one. I have learned to listen to my subconscious when it speaks like this and usually eventually finds that it has a good historical reason for preferring something.

The spectra section obviously just needs to be long enough to get very well cleated (I am using a 'tug boat hitch' on the cleat) with some extra left over.

But there are obviously a lot of different opinions on all this, and I don't consider that I have any particular or special knowledge about snubbers.

[DumnMad]

Catenary calculator;
1/2" chain 2.4lb/ft, Working load limit = 4,500lb. Catenary calculator:

75ft length, 4,500lb load - 0.375ft sag. 3000lb - 0.56ft sag. 2240lb - 0.75ft sag.
150ft length, 4.500lb load - 1.50ft sag. 3000lb - 2.25ft sag. 2240lb - 3.02ft sag.
300ft length, 4,500lb load - 6.00ft sag. 3000lb - 9.10ft sag. 2240lb - 12.08ft sag.

If in storm conditions the vessel load on rode goes from 1 ton to 2 tons the 75ft rode straightens only 0.375ft whereas the 300ft rode straightens 6.08ft and still has plenty more to go. The dampening effect of the 300ft chain catenary straightening 16 times as far as 75ft chain must be invaluable.
Now I see why Estarzinger is more interested in snubber chafe than stretch when it comes to storms.
(If you had plenty of time a couple of car tyres chained midway along the rode would increase drag and dampening even more.)

[JonJo]

If you attach the snubber to the waterline, or near enough, the potential length of the snubber is then compromised in that if you anchor in 3m of water - either you have a snubber only 3m long or you have a snubber rubbing on the seabed. If the snubber is attached to an eye at the waterline its a fixed length you cannot alter or shorten it (should this be desirable for any reason), unless you run it through a turning block at the waterline and bring it back upto the deck.

A common solution to the bowsprit and the kicker wire (bob-stay?) running down to the waterline that cuts the snubber is (sadly for those that do not like them) the bridle (2 snubbers).

Evans - what do you consider are the downsides and upsides to snubber length?

Jonathan

[JonJo]

Originally Posted by DumnMad

Catenary calculator;
1/2" chain 2.4lb/ft, Working load limit = 4,500lb. Catenary calculator:

75ft length, 4,500lb load - 0.375ft sag. 3000lb - 0.56ft sag. 2240lb - 0.75ft sag.
150ft length, 4.500lb load - 1.50ft sag. 3000lb - 2.25ft sag. 2240lb - 3.02ft sag.
300ft length, 4,500lb load - 6.00ft sag. 3000lb - 9.10ft sag. 2240lb - 12.08ft sag.

If in storm conditions the vessel load on rode goes from 1 ton to 2 tons the 75ft rode straightens only 0.375ft whereas the 300ft rode straightens 6.08ft and still has plenty more to go. The dampening effect of the 300ft chain catenary straightening 16 times as far as 75ft chain must be invaluable.
Now I see why Estarzinger is more interested in snubber chafe than stretch when it comes to storms.
(If you had plenty of time a couple of car tyres chained midway along the rode would increase drag and dampening even more.)

DM,

Good stuff.

I do not want to seem too picky - considering the effort to which you have gone (and I was too lazy to do). The loads are impressively high - but there is still lots of 'room' for the catenary to work.

But how many people carry half inch chain? (and 100m of it). That's 750lb, or the weight of 4 healthy adults standing on my bow (all the time when I sail).

The majority of yachts sold, are sufficiently small to commonly use 10mm (or even 8mm) and there is a body of opinion (who think catenary overrated) suggesting use of G7 chain and going down a size. I wonder if rather than being 'elitist' and implying 13mm is the norm (or essential) - any chance you could produce the same data for smaller diam chain as this will produce a result, I suspect, suggesting catenary is of less value for smaller, or average sized, yachts?

Jonathan

[estarzinger]

Originally Posted by JonJo

Evans - what do you consider are the downsides and upsides to snubber length?

I don't have a well thought logical answer. Longer obviously offers greater energy absorption; shorter is more convenient, the old chain hook would fall off less with shorter (not relevant for the soft shackle solution) and I think shorter may causes less 'sailing around' (but don't have any data to support that).

Until last summer, Beth was always in charge of the snubber, and she seemed to put out just enough so that the chain hook was right at the water surface when the chain was stretched. Then we might let out some more if the wind was high. There was no particular analysis. That's just what our mentors did, so we did the same, and it seemed to work.

I just picked up snubber duty last summer, which is why you see me 'rethinking' it now. It's an extremely hard problem to tackle analytically, so I think empirically is the way to go, which is one reason I am interested in the mooring buoy experience, because that is the biggest base of empirical side by side experience with a very similar application.

The rule of thumb on mooring buoy pennant length (out past the bow roller) is 2.5 (or 3.5) x freeboard (or a bit more) . . . Hawk's freeboard at the bow is 5', so 2.5x would give me 12.5' (and 3.5x = 17.5'), which happens to be quite close to where I am with my current 15' (past the bow roller).

By the way, for those of you who still think all mooring pendants are nylon . . . here is a 'best practice document' recommending polyester, and another, and another and another and another . . . . there are also some that recommend nylon, but clearly polyester is in fact a common choice.

[JonJo]

Evans,

If I have this correct your have transferred from a nylon (climbing rope) snubber to a dacron snubber. Many, here, would have said that 11mm climbing rope was (far) too small for your yacht - and you seem to have scotched that comment (with your own experiences). Your current snubber is now a hybrid, with 12' of dacron. Its hybrid to overcome chafe, the length of the dyneema/spectra does not matter (in terms of the snubbing effect).The current snubber sits with the chain just above the water level when its extended, as did the previous nylon snubber.

My interpretation might be wrong but it seems you now have a shorter piece of dacron than you did nylon, because the nylon came up and through the bow roller to a strong point.

The nylon was both longer and thinner(?) than the dacron and had greater elasticity, a characteristic of the difference between nylon and dacron and as a result of a longer (thinner?) piece of nylon.

On the basis you have changed nothing else you ought, maybe, to be able to observe some difference between the impact of the stretch of the original climbing rope and the new (to you) dacron? Or if my interpretations are correct and you can find no difference then you have enough stretch - and maybe more elasticity is unnecessary?

Jonathan

[conachair]

Originally Posted by DumnMad

Catenary calculator;
1/2" chain 2.4lb/ft, Working load limit = 4,500lb. Catenary calculator:

75ft length, 4,500lb load - 0.375ft sag. 3000lb - 0.56ft sag. 2240lb - 0.75ft sag.
150ft length, 4.500lb load - 1.50ft sag. 3000lb - 2.25ft sag. 2240lb - 3.02ft sag.
300ft length, 4,500lb load - 6.00ft sag. 3000lb - 9.10ft sag. 2240lb - 12.08ft sag.

If in storm conditions the vessel load on rode goes from 1 ton to 2 tons the 75ft rode straightens only 0.375ft whereas the 300ft rode straightens 6.08ft and still has plenty more to go. The dampening effect of the 300ft chain catenary straightening 16 times as far as 75ft chain must be invaluable.
Now I see why Estarzinger is more interested in snubber chafe than stretch when it comes to storms.
(If you had plenty of time a couple of car tyres chained midway along the rode would increase drag and dampening even more.)

Though it goes to show how little give there is at those kind of forces there are a number of errors in there.. those figures look to be for horizontal attachment points in air, chain weights less in water and as the boat is higher than the anchor some of the force will vertical so the horizontal component will be less as well as the catenary behaving differently. Even so, the 300' chain will lengthen only 301.12709227 ft - 300.32033698 ft between 2400lb & 4500. Not much really.

The 6. 08' is how much sag there is in the middle.