anchor sizes?

[rtbates]

Originally Posted by bene505

Is this the best method of anchoring? I usually lower chain and let the windlass take the strain. Now you have me thinking that I'd be better off putting the load on a cleat, using a bridle.

Is is really bad practice to leave the strain on the windlass?

everything I've read says, yes, it is bad practice.

[bene505]

That makes sense. Consider it done.

How long a bridle is needed to absorb the load? Is 20 feet (nylon) enough?

[s/v Jedi]

Originally Posted by bene505

Is this the best method of anchoring? I usually lower chain and let the windlass take the strain. Now you have me thinking that I'd be better off putting the load on a cleat, using a bridle.

Is is really bad practice to leave the strain on the windlass?

Yes it is. The windlass is not designed to be the strong point. Check out it's manual, it should explain how to use it. Also think about a chain stopper, it saved our boat once already.

I'm so glad this thread is here because I can now tell you about our 99% rule. It goes like this: In 99% of all cases, you use one anchor. This includes all conditions except severe storm or worse. If your primary anchor doesn't hold you, you need to upgrade it to a better design or more weight, instead of deploying a 2nd anchor. You also want it to hold in squalls with 50-55 knot gusts. So what's the 1%? Anchoring in tidal water that turns the boat with the tide like rivers etc. (use Bahamian mooring technique) or severe storms.

We have tested different techniques for anchoring and consistently found that lowering by letting go the clutch on the windlass is the best way. The anchor gets down on the seabed the quickest so you get it where you want it; when the anchor reaches the seabed, it punches a crater which helps digging in, your chain runs out as fast as the boat moves backward so you don't drag it at this phase. Once we are at 3:1 scope, we tighten the clutch a little so that the chain still runs out but we take up slack, at 5:1 we increase clutch so that anchor starts digging in but some chain still runs out and at 6:1 we bring the clutch slowly to full on. This should give a hard pull after which the boat moves forward again. Next is the chain-stopper and engine in reverse-pulling a bit with foot on the chain to feel what's happening down there and looking at other boats and the shore to see is we're holding. After that, we take chain in to bring the scope to what we want and set the snubber like Dave writes.

For your boat I would sell both Danforths and buy a 40-60 pound primary that is designed to turn in the seabed when the wind changes direction (original Bruce if you can find one, Delta, Rocna, Spade or similar designs. For a Bruce I would keep that 60 pound in mind and more modern designs that 40 pound range. Do be too obsessed about weight of the anchor because the chain weighs much more. For a cat I like the designs where the anchor-roller is behind the trampoline, which brings it all more to the center of the boat and the bridle can be left on.
For second anchor (if two anchors is all you want) I would choose an aluminium Fortress (no rust, light, only used in 1% of anchorages/situations).

cheers,
Nick.

[Ancora Latina]

Originally Posted by bene505

Is it really bad practice to leave the strain on the windlass?

Yes absolutely... no doubt about that!

The strain load MUST be put on a cleat, a Samson Post... using a bridle. It will be far better for the windlass and the bridle will procure the necessary elasticity to your all chain rode...

João

[maxingout]

Originally Posted by bene505

Is this the best method of anchoring? I usually lower chain and let the windlass take the strain. Now you have me thinking that I'd be better off putting the load on a cleat, using a bridle.

Is is really bad practice to leave the strain on the windlass?

My windlass is alive and well after 14 years. If I had left a load on the windlass when anchored, it would have died years ago. I don't even back down on the anchor while the chain is putting a load on the gypsy. The bridle and cleats take all the strain.

[Cheechako]

I have tried double systems, sometimes in preparation for a blow, sometimes after it's coming up by rowing out the second anchor etc. Virtually every time I have felt afterward that it put me more at risk than had I just had the "big one " down to start with. Wind shifts occur when the fronts move through. With two anchors you often end up with a tangle rendering the only option being to let one go hoping to retrieve it later. The other problem is that you often end up with one rode under the boat raising the possibility of prop entanglement, this will definitely remove further options to save your boat. I have actually had to drop the rode before and have tangled the rode in the prop also. (fortunately I realized it just when it got picked up, went to neutral and reversed the prop and got it out) Many people just hang on one large anchor and if necessary run the engine to reduce load in the worst of it. Everyone has to deal how they are comfortable I guess. If leaving the boat in a pending hurricane I would definitely put two out. A real situtaion in FL in 1999: at day break a micro cell came through the anchorage pegging the anemometer at 70. The single anchor came out almost immediately due to the near 180 degree windshift. If I had a second anchor out at the correct angle for the new wind shift, the original rode would have been under my boat disallowing me to run the engine, avoid other boats and get things straightened out. Also, I would not have had another anchor "at the ready" (do we all have 3 available and ready to use in 30 seconds in unpredicted events?)

[bene505]

Sorry all, the winter has gotten to me a bit I guess.

I DO use the bridle. I've been using it from inboard of the anchor roller to one of the cleats at the bow. That means only 2 feet of bridle. And I release the tension on the windlass too. I haven't been putting the strain on the windlass.

The diagram above had a much longer brindle that looks much better for absorbing shock loads. I'd probably have to set it up with 2 bridles, on to each cleat (starboard and port).

My real question is how much bridle is enough? 15 or 20 feet good enough? (And probably should not use just 2 feet, right?)

[svskyus]

Bene505, are you talking about a snubber or a bridle? Cats use bridles, which are lines from each bow meeting the rode at the V. each bridle are is typically about the length of the beam of the cat. Monohulls more typically use snubbers, a single line from a cleat to the chain rode that whose purpose is to lessen shock loads transmitted from the rigid chain to the cleat. 2' would do little. A snubber should be somewhat elastic, not some hi tech no stretch nylon line.

Back to earlier comments about anchor size for cats, it was mentioned that because cats have more windage, they need bigger anchors. I don't believe that this is a valid reason for requiring a larger anchor. Using a bridal, a cat will sit calmly at anchor, and not sail at anchor. I have seen 100's of monohulls violently sailing at their anchor, putting huge loads at different angles on their anchors. A heavy monohull sailing at anchor thus would require a much heavier anchor to an equal length but lighter cat sitting calmly to its bridal.

[bene505]

Good point svskyus, I should have said snubber.

[thinwater]

A sailor did an excellent job of computer modeling rode reactions to wind; I wish I could find it. While computer models have MANY limitations, this one clearly pointed out one thing; when an abrupt gust hits a boat on an elastic rode, the boat moves backwards and then the rode has to resist both the wind and the energy of stopping the boat. The resulting force is nearly independent on the length of the rope; the longer the rope, the faster the boat moves, but the more rope there is to stop it. The conclusion: an elastic rope doesn't soften the blow. With either chain or rope the answer is the same; the gear will feel about 2x the peak wind force. Odd but sensible. The one condition of the model is that the wind is still blowing when the boat comes up tight, which sees reasonable. A chain rode, with the catenary, reacts differently, but I suspect his model may over state the surges, since in reality we know there is enough damping that the boat does not bounce in the manner his models suggest.

Waves are a different matter because the time period is short; the boat won't begin to move backwards signifigantly before the wave is past. A long elastic rode or a very long chain will damp them almost completely; some effect from the friction of the line through the water. However, if the boat is in relatively shallow water, there is big chop, and the scope is short, a boat on chain can hammer against the chop with no damping. The answer is a snubber long enough for the waves only. This will vary with the setting, but might be as much as 60 feet (4 foot waves) or as little as 15 feet (1 foot waves). Since the chain catenary will do something, perhaps 60% ofthis figure is a minimum chain snubber length. As stated, this is most important where the chop is material.

Not my theories, but the logic is sound and seems to reflect experience, at least in aproximation. It also explains why several schools can all think that they are right... because under specific circumstances, they are.

Comments?

[thinwater]

Rode - Dynamic Behavior

Rode - Static Behavior

http://alain.fraysse.free.fr/sail/rode/dynam/dynam.htm
This last one has a lot of details in the photos I could find fault with. I'm sure you will spot them.

But all criticisms aside, lets respect the work it took to put the links together and post it. It is thought provoking.

I hope you like math!