Check Regime When Anchoring In Storm?

[linnupesa]

Ozzie

Two tons breaking strain for the rope sounds pretty high and good. SOUNDS.

Do consider that you do not really ever want to get close to the BK strain loads. Again, any type of knot except for a splice will almost halve the BK strain figure... 30-45% reductions for the common types of bowline, fig 8 etc. and even a smooth splice reduces the BK-loads by about 20%.

It all adds up unfortunately. The biggie with chain is that jerking forces can triple the loading, so it's almost imperative to use a snubber. I agree with you knotting or securing the "chain-hasp" whatever, excellent precaution that. Better yet is the idea of the snubber integral with the rode... use chain against coral chafe and keeping the rode down along the ground but use rope for the rest. Also saves chain weight up front, where it hurts performance most.

Not my idea at all, but it was suggested by some anchoring blurb I read. They actually measured dynamic loads, which are way different from the static ones published by WasteMarine et al. Just a tiny little give in the rode is enough to prevent the catastrophic jerking loads. The tons of boat moving just a few inches..
mass times distance=ft-lbs or ft-tons. It's a real eye-opener.

Having the chain looped too loosely with a snubber in place is very dangerous. If the snubber parts or slips, the boat will accelerate off until the chain is tight as a bar. That is when those ft-lb can easily snap the weakest link or knot, or jerk out the set anchor. You do not want to find out the hard way, like that Hartley ferro ketch did. ( Mico, what was that post again: $200 to fix the bridge?? :-)

Ivo s/v Linnupesa

[mico]

We use both a snubber - much like Aussie has set up but also use an anchor buddy which has saved our bacon a number of times

Usually carried by powerboats in Oz, it's simply a big loop of reinforced hose with a chain through it from which is suspended about 25lb of lead. At the top of the loop is a swivel attached to 15m of spectra line.

We simply dig the anchor in, loop the anchor buddy over the anchor chain and lower it down until it's sitting about a metre off the bottom. It's then tied off on the sampson post and we then attach the snubber.

The lead acts as a shock absorber and ensures the anchor chain sits parallel with the bottom even in the strongest of blows.

Sure, it's an extra bit of kit you have to contend with if you have to up anchor in a hurry but we think it's well worth the effort.

When we sailed in company with 8 other yachts through the northern islands of Vanatua we anchored inside Ureparapra - an extinct volcano in about 30m of water just off the village and its reef. The entrance to the volcano was a narrow passage created when it blew some hundreds of years previously.

We had only just dug in when a massive storm front swept down the throat of the volcano and before we knew it, everyone started falling back onto the reef. For those that could, they raised their anchors and spent the next two hours motoring around in the small cauldron as it was impossible to get outside with the swell coming down the entrance. A couple of yachts had to be fended off the reef with some minor damage.

Unfortunately for us, the moment we went to up anchor the spindle snapped on our Lewmar winch and we had to simply hang on and pray that we held. To this day I'm convinced that extra weight of lead bobbing up and down on our chain kept us from going ashore.

Quick tip for raising 60m of chain with a busted winch : Put your snubber hook on the end of your spinnaker hoist, hook it to the anchor chain and winch it up in stages. It takes forever but keeps you from damaging your deck and your back!

Fair winds,


Mico

[linnupesa]

Great pics Mico! It sure looks like it's blowing.

A very good idea to use the halyard winch and a super suggestion for that dead-man variation to hold the rode down. At extreme loads you'll find that 25lb lifting right up but it still will provide some snubbing effect. Even a little goes a long way.

Your tale makes me wonder if the Lewmar SNAFU was caused by the conditions or was bound to happen anyway. It definitely gives pause for thought and those 'what if' scenarios.

Anyway, you Ozzalites sure are an inventive bunch... probably because of regularly being up the creek with short paddles... but lots of baling wire and can-do ideas.

Ivo s/v Linnupesa

[mico]

There was a really surprising and wonderful ending to the winch failure story which I think I may have covered a long while back but will quickly recall here.

When we got back to Santos we called Lewmar in Oz and got them to ship us out a new internal pin axle that ran through one of the cogs. This had snapped.

It cost us $15 and $35 shipping but we had it within a week and it was there waiting for us we we arrived further south in Port Villa. It only lasted two anchorings and snapped again. We called Lewmar back and asked them to send 3 new pins because I thought I had caused the damage when the chain built up in the anchor locker and jammed under the deck before I could disengage the switch.

The Lewmar rep asked me what model we had and we told him. It would have had to have been at least 7 years old and we had no paperwork for it so I figured if I had 2 spare pins we'd get back to Oz in safety.

He replied he'd send me a new one straight away but warned me that shipping would be very expensive. I replied - they're only 3 inches long and it only cost me $35 last time - how expensive can 3 pins be?

He then said 'No No No - we're not sending you a pin - we're sending you a brand new replacement winch!'

It turns out that our winch model was from an earlier production run and the spindles were later proved to be under spec. A week later we were bolting on a brand new shiny $2200 Lewmar Pro winch for the cost of shipping.

Now that's service for ya!

[capta]

Originally Posted by linnupesa

Capta and others

snubbers are a great tool but do need some arithmetic to get a good result.

As a rough rule, 3-strand nylon can elongate (stretch) up to 10-15% up to near 30% of it's rated breaking load. Of course, heavier ropes will stretch less and longer ropes will elongate a longer distance.

You first need to ask "how much load will the rode need to handle?" A static load will be much less than a sudden dynamic one, like when getting smacked by a breaking wave. Only with that info can you figure both the size and the length needed for the snubber.

A 1" 3-strand nylon rode has an over 22 000lb breaking rating. We'd hope your anchor isn't typically strained over more than 2000 lb, which is under 10% of that ropes rating. Also, 10% stretch on 30' is 3' and quite a lot. Perhaps a both smaller and shorter rope would suffice. The trick would be to get the chain almost bar tight under maximum dynamic load, with just a little safety margin added. Smaller and shorter rope might actually be better, lighter and cheaper. The heavy rope would be better utilized if incorporated into the rode itself, after a decent length of chain.

Just mho.

Ivo on Linnupesa

What reason would there be to go down in size on the snub line? It has functioned perfectly well for two years of almost daily anchoring in all conditions. Even if it is "overkill" size wise, it gives me some leeway should we get into a blow and the chafe gear fails. Also, our cleats are on the foredeck, not at the rail, so with the height of the bow out of the water and the length from chock to the cleat, the system is not 30' of line from boat to chain.
Not to be rude, but this is the first time I think I've heard anyone suggest going down in size and strength, where the safety of the vessel is concerned. And I do consider our snub line to be the most important part of our anchoring system's safety net. I have seen the 1" nylon stretched out to about 5/8", or so it seemed. If finances permit, I would love even heavier chain, but of course that requires a stronger windlass, which requires heavier wiring and breaker, a huge bite out of the kitty.
Do take note of the Spike Africa quote below.