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Old 25-03-2013, 09:21   #16
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Re: Setting the anchor

Not sure how much pull, but you are in the ballpark. At 1500 rpm the chain should be pretty bar tight and be entering the water way ahead of the boat. That sounds like about 25 knots to me. Increase rpm gradually to 1500. The anchor will continue to dig in over time and the slow process is better than trying to jerk it in IMHO.
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Old 25-03-2013, 10:35   #17
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Re: Setting the anchor

Quote:
Originally Posted by estarzinger View Post
^^

Nice, thanks.

But regarding Bollard Pull, if you go look at the cell in the spreadsheet that does the bollard calculation you will see it in fact uses exactly the formula that I posted above.
When I put in the data in the I get 757 lb with the forward gear ratio and 711 lb with the reverse.
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Old 25-03-2013, 10:53   #18
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Re: Setting the anchor

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Originally Posted by cwyckham View Post
Shouldn't the chain be slack when you're bouncing up on that wave? You're right that that's the dangerous part, so that's why the snubber should be taking the load.
You are right. Most of our anchoring is in less than 15ft of water. We back down on the anchor with just the chain, and I stand on the chain while my wife backs down. When we get that done, the snubber goes on (if we are not into the 250ft of nylon that comes after the 100' of chain). I should have done a better job with my phrasing. I should have said anchor rode and anchor rode/snubber.

Anyway, I suspect (without numerical data, only by standing on the anchor rode or snubber) that the load we see at anchor with the wind up is greater than the propeller's reverse thrust. I also am fairly sure that the biggest load comes when the boat swings out to one side flying like a kite in the wind. The bouncing of the waves adds to it. Thus, I don't see reversing as 'pooof testing', I see it as giving the anchor an initial set.
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Old 25-03-2013, 11:10   #19
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Re: Setting the anchor

Simple.

Put a load cell on your rode when you power in reverse and measure.

Then measure again for each wind load.

Then compare.

I do not think there is much power in reverse, not as much as forward. Props are optimised forward (except for the ones that shift the blades accordingly).

b.
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Old 25-03-2013, 11:30   #20
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Re: Setting the anchor

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Originally Posted by wsmurdoch View Post
When I put in the data in the I get 757 lb with the forward gear ratio and 711 lb with the reverse.
That's because the spreadsheet calculates that you have (should have) a different diameter prop when you put in the different (reverse) gear ratio.
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Old 25-03-2013, 13:43   #21
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Re: Setting the anchor

I don't think backing down is "over thinking". I normally set mine with a low rpm but once set I normally go a lot more tham 1500 rpms (by sound as my tach lost the war 2 years ago).

I don't know if this helps anything, but I figure it doesn't hurt so see no reason to not do it.
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Old 25-03-2013, 15:38   #22
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Re: Setting the anchor

G'Day all,

Our practice is to deploy between 2 and 3:1 scope, set with the engine, using enough rpm to get a healthy but unmeasured pull. We continue this for around a full minute, watching transits. Usually the transits show no movement after the catenary is minimized. Once we are happy with things we veer enough chain to meet the scope requirements for the situation.

My feeling is that besides starting the digging in process, this method identifies those rare occasions where we have managed to drop the anchor on some manner of fouling material. Over the years this has included patches of eel grass, many plastic bags, a pair of board shorts, a plastic bottle, a discarded tire, bits of rope and so on. I can't but wonder how the folks who don't back down at all have managed to avoid these situations, for we have found that when thus fouled, the anchor will hold to some degree but then break loose at higher rpms and then NOT reset.

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Old 25-03-2013, 17:16   #23
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Re: Setting the anchor

Quote:
Originally Posted by barnakiel View Post
Simple. Put a load cell on your rode when you power in reverse and measure. Then measure again for each wind load. Then compare. b.
+1.

Thankfully an owner of a boat like mine went to all that trouble and established motor pulling capability and anchor loads. Damned decent of him really.
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Old 25-03-2013, 17:30   #24
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Re: Setting the anchor

Be aware that if you sit there grinding away in reverse in shallow muddy harbors your engine will be sucking up all sorts of crap, despite any normal strainer on there, and you will eventually pay for it in clogged cooling passages.
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Old 25-03-2013, 17:31   #25
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Re: Setting the anchor

I've written this before... but I will repeat.

I use all chain with a 40' 1" nylon snubber with a rubber mooring compensator w/ 3 turns.

Once the proper scope has been run out... I hook on the snubber and run out more chain so I can see the snubber. When the wind pushes back on the boat the catenary lifts and the snubber twists will begin to unlay... a clear sign that the rode is under sufficient load and the anchor has dug in.

If the rode lifts but the snubber does not untwist a bit, the there is likely not much load on the rode and the anchor might be dragging. A set anchor will show the snubber untwist when the ride is loaded... and it can only be loaded when it set in the bottom.

With no or light winds I have to back down to get the snubber to untwist.
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Old 25-03-2013, 17:36   #26
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Re: Setting the anchor

When the slack is out, increase rpm to about 1500 and hold it for 20 seconds
Let it slack, then back down on it again.
Let it slack, then back down on it again.

The real reason for doing this ritual 3 times is that your sailboat engine and propeller are not strong enough to do a good set on their own. You’re actually using the inertia of your boat weight going backwards to set the anchor, which is much more powerful than your engines in reverse.

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Old 25-03-2013, 17:40   #27
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Re: Setting the anchor

Wish I had a digital picture of the telephone cable we picked up - twice!!! Glad it wasn't a live electrical one.
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Old 25-03-2013, 17:42   #28
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Re: Setting the anchor

Quote:
Originally Posted by defjef View Post
I've written this before... but I will repeat.

I use all chain with a 40' 1" nylon snubber with a rubber mooring compensator w/ 3 turns.

Once the proper scope has been run out... I hook on the snubber and run out more chain so I can see the snubber. When the wind pushes back on the boat the catenary lifts and the snubber twists will begin to unlay... a clear sign that the rode is under sufficient load and the anchor has dug in.

If the rode lifts but the snubber does not untwist a bit, the there is likely not much load on the rode and the anchor might be dragging. A set anchor will show the snubber untwist when the ride is loaded... and it can only be loaded when it set in the bottom.

With no or light winds I have to back down to get the snubber to untwist.
I really like your method and description.

I just purchased a few of those Falcon Safety Mooring Line Snubber / Compensators

Falcon Safety Mooring Line Snubber / Compensator
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Old 25-03-2013, 18:15   #29
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Re: Setting the anchor

I helped a friend built a 40' yacht some years ago, and the day after launching we went in a harbour race for kicks. The race started in a brisk easterly (normal) but on the second lap it increased to a steady 50 knots. We were still doing OK but the boat we were gaining on lost their rig, and others started retiring, so we chickened out and went back to the marina (actually there's nothing worthy of the name in Lyttelton, but we went back there anyway)

It's rare for it to blow that hard from that particular direction, so we had to improvise to get into the upwind slip.

It was too dangerous, control-wise, to go in bow upwind (still blowing 45 knots in the lulls) so we had to run the Volvo (smallish but turbo) flat out, and go backwards upwind into the slot.

The prop was one of those Volvo saildrive three-bladed folders with sickle shaped blades, and it turned out to provide remarkable reverse thrust ....

I was relieved, because it had been my suggestion...

So, I infer that, on this particular boat, taking it to the black smoke limit in reverse when testing the anchor set would apply a steady load similar to at least 45 knots of wind, assuming that windloads are similar whether the wind is coming from ahead or from aft... (which I assume to be the case)
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Old 25-03-2013, 18:23   #30
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Re: Setting the anchor

I am a firm skeptic that predicted loads at anchor are anywhere near as high as we see in print, and one of my personal data points is that on my 38-foot motorsailor with a big Perkins 4.236 swinging a large (can't remember the size offhand) three-blade power prop I can just click it into gear, giving it no throttle above idle, which is only about 500 rpm, and she will slowly walk up to the anchor no matter what windspeed I have tried it in. I have found in higher blows that I really can't put it into gear to "ease the strain," which you occasionally read someone recommending. Even in a blow in the San Blas that was gusting 56 knots I just kept the engine going but in neutral, because she would start to go to windward if I put it in gear. I must admit that I don't think I have tried to go all the way up to the anchor much above 30 knots, but still, that indicates to me that there is less load than the tables would indicate. And, the load is highly variable. I was once next to a very traditional old-school boat--I think it was a Bill Tripp design with a nice low profile and beautiful overhangs, and that boat would not straighten out its chain no matter what it was blowing. I was sitting up on anchor watch through some pretty heavy squalls and thunderstorms and this guy was right next to me, and my anchor chain was bar taught in the gusts and his had a bend in it. That boat was just riding peacefully while the rest of us were trying to pull the anchors right out of the bottom. My point being that I'm not sure it is very clear cut how wind loads on an anchor can be simulated by engine power, though I am convinced it is important to give it some good tugs to make sure the anchor is well dug in.
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