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Old 03-04-2008, 14:34   #31
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I don't see that the chain on a vertical windlass can mess up the windlass, but it's not a good idea to let the windlass carry the load of the anchor. For all chain use a mooring / anchor snubber which attaches to the chain and is led to a deck cleat. I've see bridle type snubbers tied of to 2 cleats. You need them to absorb the shock loading and some stretch which chain ain't gonna do, as it relies on catanary for shock absorption.
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Old 03-04-2008, 18:32   #32
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what are people do for all chain?
We have a stainless steel bollard with a cross bar in it forward of the windlass. Chain comes back from bow roller on starboard side of bollard - first I belay the chain with a short rope strop which is permanently fixed to the toerail (we have a very strong punched toerail) which is also the safety strop belaying the anchor when sailing. This strop is on the toerail so I can keep it clear of the chain when not being used (don't ask why I have found that to be a good idea, but is related to the fact that the rope and the chain don't fit down the chain pipe very well together and is even harder to get out again after it happens ). I relieve some chain from the locker to give some slack and take the chain around the back of the bollard then up from underneath and over the cross bar on the port side then back to the gypsy on the windlass. I then let go the rope strop and pull the chain between the bollard and the windlass so it is just on tight with the windlass. This has always been sufficient to keep all the load on the bollard and not the windlass - mainly because the cross bar on the bollard is sized small enough so that when the chain is passed around it, it "latches" the links.

Have never ever felt the need for a snubber and so have never used one - I guess it gets down to the boat and its systems as to whether needed or not. We have sat on the above with single anchor in low hurricane force conditions (Force 12), 12 ton boat shaking and rattling but no problem.

An easier alternative is to use a GOOD quality chain stopper such as the ones Maxwell make ( Winch Accessories , scroll to bottom of the page), NOT one of the el cheapo ones folded up out of sheet stainless steel), but must have sufficient reinforcing under/in the deck. The only reason I have not used one of those is that I am a little uneasy about the localised load they place on a chain link, but I suspect my uneasyness is not warranted - I would be interested in GMac's view on that .
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Old 03-04-2008, 22:48   #33
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An easier alternative is to use a GOOD quality chain stopper such as the ones Maxwell make ( Winch Accessories , scroll to bottom of the page), NOT one of the el cheapo ones folded up out of sheet stainless steel), but must have sufficient reinforcing under/in the deck. The only reason I have not used one of those is that I am a little uneasy about the localised load they place on a chain link, but I suspect my uneasyness is not warranted - I would be interested in GMac's view on that .
I've no worries with a good stopper like the Maxwells (fitted to extra meat as you mention) and agree with you view of the cheap folded ones. I've seen a couple collapse under big load. I think you're doing good ML1.

Interesting your comment about not Snubbering up as such. Some smart good looking bloke once said anchoring systems are very much a 'Horses for Courses' sort of thing and every boat and user is different. Whom was that?? Oh yea, Me

You're another example of one not following the standard route and yet not having issues. See there is many ways to get to the same place.

What sized rope strop have you ML1?
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Old 04-04-2008, 02:13   #34
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What sized rope strop have you ML1?
Exactly, I don't recall but is sized to easily pass through 10mm chain links so must be 10mm dia (pretty sure it's not 12mm) - is polyester braid.

So, normally pass the free end through a link of the chain and then rolling hitch back on itself. When I have got the loose chain around the bollard I flip off the rolling hitch, the chain weight transfers to the bollard and I pull the end of the rope strop out of the chain link.

To some it might sound like a bit of a rigormarole but we typically anchor in water around 15-25m deep and those lengths of 10mm chain are awfully heavy to hold the weight of by hand.
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Old 04-04-2008, 02:26   #35
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Just goes to show how little anchors have to hold a lot of the time doesn't it. I'm guessing a 12mm is about as big as you'll get through.
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Old 04-04-2008, 02:44   #36
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Yes, takes a fair old blow to just straighten our chain out on the bottom. I suspect the forces from wind load are often greatly over estimated. Some examples -

We are 40 foot and highish freeboard - a grown strong man standing on the dock with nothing to brace himself against can just hold the boat when beam on to the wind in around 15 knots, so the wind load is small.

With a line off the bow and a line off the stern with 2 men on each line 4 of us standing on the dock could only just hold a 43 foot yacht beam on to the wind in 25-30 knots (the physics of that works out with the above example in that wind load varies with the square of the wind speed so 30 knots is 2x 15 knots so load is 4x at 30 knots, so 4 men instead of 1 - clever eh! ). Ended up a bit of a panic as the boat just about beat us and got loose but even so the loads are very small compared to the working loads of normal anchoring system's capability.

Those are beam on, bow on to the wind the loads would have been much less. So even in 30 knots, which many would regard as reasonably heavy anchoring conditions, it would seem to me that the loads are very much lower than many make out (ignoring waves and boat riding back in gust type loads).
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Old 04-04-2008, 03:29   #37
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So even in 30 knots, which many would regard as reasonably heavy anchoring conditions, it would seem to me that the loads are very much lower than many make out (ignoring waves and boat riding back in gust type loads).
Any time I've anchored in 30 knots you were hard pressed to ignore the waves and gust loads. Pretty obvious I would say. No where near the same as standing at a dock. The bouncing of the boat does increase the load a lot. If you are using 10 mm chain that comes to almost 400 lbs at 160 ft of rode. As a wave would pitch the boat up just the load from accelerating the chain upward is going to make a very significant dynamic load. The boat displacement rises quite easily even with hundreds of pounds on the bow. The bounce of a 15 ton boat is not small.

Without ignoring these factors I would say the load is every bit as high as made out. An anchor holds pretty well with a static load just as hold a boat in the wind at the dock but the jerking motions of a dynamic load are what rips them out. Add a little bit of sailing on the hook and now the dynamic loads are a lot more.
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Old 04-04-2008, 03:40   #38
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Any time I've anchored in 30 knots you were hard pressed to ignore the waves and gust loads.
As I said, the examples ignored waves and gust loads.

But where I sail 30 knots in an anchorage is regarded as pretty common stuff so waves and gust loads in those conditions certainly are ignored here and not considered significant compared to what one may end up being exposed to in harsh conditions. I kid you not, as I am sure a couple of forumites who are familiar with the area could confirm .

So ones perspective probably depends on what one is used to.
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Old 05-04-2008, 18:16   #39
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We anchor in 30kts often, it's just what we do here and think nothing of it really.

Easter weekend we were anchored in 12-15 knots of onshore with a small ground swell coming in and a splash of small waves on top. Snorkling with D2 (daughter no. 2) we sussed our anchor 1st and it wasn't even trying to set. The chain was running off at 90 degrees. Checked again 3 hours later and the chain was now coming off at 60 degrees odd. The anchor didn't need to be there, we hung off the chain the entire time. I have 15mts of chain then rope and always park at 5:1.

I can hold my boat myself with the motor going full titty either forward or reverse.
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Old 05-04-2008, 20:19   #40
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It certainly takes quite strong wind to drag our chain out straight (and I mean strongish by our standards eg a longish 40+ knot gust in moderate nominal 20 knot type conditions has never been long enough, as far as I have observed).

I think forces from waves are less than many think also. I have tried to get some idea of the magnitude of those but is a complicated dynamic thing (haven't looked on his site for a long time but I recall Alain Fraysee said words to the effect it is all too hard and too many variables). The examples I tried working through used foredeck accelerations based on Marchaj's "Seaworthiness" which are for boats underway (so higher) and a pitching angle of 20 degrees which I would suspect means an untenable anchorage.

The force to accelerate the chain is not really significant - one has to remember it is accelerated most at the bow roller and not at all at the point it hits the sea bed and the acceration direction varies according to where one is on the cable. What impulse loads from waves on the boat are I have not looked at but as long as anchored bow to waves (which would, of course, be normal unless one has a stern anchor out which would not seem a sensible thing to do if the sea conditions were concerning) I suspect these are quite low.

There are actually some plus's in that if the bow pitches up 20 degrees AND no chain is lifted off the bottom then the catenary deepens so the forces in the chain from the catenary reduce - by over 12% if the water depth is 15m, cable length to point it hits the bottom is 50m and pitching 20 degrees. If chain is lifted from the bottom then the reduction is not so great dependant on how much is lifted, but if water depth is 15m, and all the pitching height is lifted from the sea bed with 20 degree pitching there is still a slight reduction in catenary forces.

In all that the lines of the boat make a big difference to the magnitude of the cable loads as do its longitudinal mass moment of inertia (in that it affects pitching angle), any tendency to resonant pitching and the boat's length.
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Old 05-04-2008, 20:50   #41
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I think forces from waves are less than many think also.
I'd agree. I was very surprised this week in 20-30 MPH (sorry for non-knot data) winds in Florida to still be able to pull up my 3/8" BBB chain with a 55lb Delta on the end BY HAND.

I also have a lot of windage (catamaran) and 12,000lbs of displacement.

Surprised the heck out of me!
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Old 06-04-2008, 07:59   #42
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Wind speed

I agree that most people over estimate wind speed. Using a hand held weather instrument to measure speed compared to subjective estimates shows that at 20 kts most folks guess 30 kts.

My boat is a bit different too, with no keel, prop or rudder and a 22" draft. It benefits greatly from a soft snubber and a drogue off the stern. I figure that this is a small tradeoff for a 30 kt cruise and plenty of time to setup the anchor.

Carl
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Old 06-04-2008, 08:07   #43
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Good book

By the way-
For a very good read check out The Complete Anchoring Handbook.
internationalmarine.com
Just came out and has full discussion of wind,wave and surging loads.
Including the formulas to calculate peak loads based on the speed of the boats movement and mass.

be safe

Carl
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Old 07-04-2008, 04:04   #44
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Old 22-02-2009, 16:56   #45
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GMac,

Where did you get those orange snubber rings? Google only shows some place in NZ.

Thanks,

John
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