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Old 10-01-2009, 12:02   #16
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Thanks for the show. I almost forgot about the genius intellect of Ma & Pa. Took me back to a simpler time of my life...
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Old 10-01-2009, 15:37   #17
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I have also heard that a Bruce will work on a rock bottom. I have not tried and probably never will.

What ever you use will be hard to retrieve.

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Old 13-01-2009, 00:40   #18
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The best rock anchor is a bog standard grapnel type. Cheap so if it doesn't come back no big loss.
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Old 13-01-2009, 03:33   #19
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If you know it's a rocky bottom, wouldn't you rig a tripping line before setting the anchor? I imagine it would make it a lot easier to retrieve the thing.

Not that I've ever had to deal with a rocky bottom. Sandy bottom, yes... usually from sitting on the beach...
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Old 13-01-2009, 03:41   #20
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Originally Posted by Pblais View Post
Not really. The mass always is the same so the force to move it is the same. F= mA (force = mass times acceleration). Buoyancy is not an issue here as rock is denser than water and has zero buoyancy. The density of water causes the rock to sink slower in water because it is a denser material than air. The fact that air and water are different does not change the rock. You can not lift anything under water that you could not lift on land unless it is unaided by buoyancy. What it's weight is means nothing. A submerged rock or anchor has no buoyancy what so ever. There is no other force pulling the rock to the surface to counteract gravity. It does not float on land for the same reason it does not float in water.

The concept of displacement is only the difference between the density of air and water. An object floats on water because it's net density is greater than air (or it would float above the water) and less than water (or it would sink to the lowest level). Gravity is the constant in all cases.

The problem is that weight is measured in pounds and force is measured in Dynes or Newtons in the English system. Since we are air breathing mammals that live on land, pounds will work for an English weight system that is too often used to speak about force. Weight has nothing at all to do with force. Anchors have everything to do with force.

An anchor holds by more than it's mass and those that don't usually prove to be the worst anchors. None of them float.
I have to agree with Gord on this one.
The resultant force downwards is the one that holds a rock in place. Take a moderate density rock of specific gravity of about 2.5 to 3 The bouyancy component reduces its resultant force downwards by between 30 and 40%. Include the loss of friction due to the lubrication of water, and there is significantly less holding than an equivalent rock on land. Some rocks have even lower density.
If the anchor is embedded in bedrock, then the limit is the strength of the tackle
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Old 13-01-2009, 05:00   #21
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would it be possible for the mods to stay on topic and not steer this conversation to show off their knowledge of physics?
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Old 13-01-2009, 14:14   #22
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I am not a mod, and I was replying to some erroneous material relevantto anchoring on a rocky bottom.
Personally I use a home made grapnel (Piece of waterpipe and two double over lengths of doubled over low tensile bar) with a retrieving line and a short length of chain. I am quite prepared to cut the line and abandon it if it gets stuck. I would never rely on it unless I had gone down to have a look at how it was lodged. It may be only held by a piece of weed, or a loose rock. If the rock is of low enough size and density, then it can let go if the conditions worsen.
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Old 03-02-2009, 23:06   #23
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Why Gamble?

If anchoring in a rocky area is a crap shoot, why do it? You've invested all this money in your boat, you value your life, and you want a good night's sleep. What is so great about this particular anchorage that you have to play the lottery to spend the night there? Coral heads are a similar situation. Apart from the damage to the natural area and the heads themselves and all the wonderful critters who depends on the coral, why not move to a different spot and find some sand or better yet, mud? Where to put down the hook is the most important decision a sailor makes in each anchorage. Rocks will catch and trap anchors, bend flukes and make a lot of noise if the wind comes up. Why do it?
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Old 04-02-2009, 04:38   #24
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LOL ... I wanna see the Ma and Pa Kettle one on anchoring!
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Old 04-02-2009, 07:58   #25
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hahahahahahaha got to love Ma and Pa..........
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Old 04-02-2009, 10:01   #26
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Lady- I don't know about Colorado but in the PNW and BC sometimes you can't find a nice muddy bottom to drop the hook in. The bottom drops so steeply from the beach in places that you drop the anchor 75' from shore in 80' (or a lot more) of water and reverse in and hope the anchor hooks on a rock or a ledge, and then you run a stern line to a tree to hold you there. Not the best but with narrow straits and no open water it's better than jogging back and forth all night in a howling wind. I use a Bruce anchor, has worked well in all situations (mud, rock, sand, etc).
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Old 04-02-2009, 12:02   #27
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I don't sail in Colorado, although there are a lot of sailors here. My point was that a lot hangs on that anchor. If you can avoid rocks you should. I was always a two anchor person and I always dove to check the anchor. That may not be an option in the NW either. Each situation presents unique challenges. The Drake passage with 70 mile an hour winds, deep water, tieing to rocks.etc., may not be something most sailors encounter either, but each situation requires creativity.
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Old 04-02-2009, 13:27   #28
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a Bruce type works good on rocky bottoms. With the Bruce use a very oversized anchor though for other uses.
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Old 04-02-2009, 13:42   #29
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Quote:
Originally Posted by Cheechako View Post
a Bruce type works good on rocky bottoms. With the Bruce use a very oversized anchor though for other uses.

Anchoring in a rocky area is « Russian roulette anchoring »...

On flat rocks, nothing will work
On Boulders, you may have the chance to wedge your anchor between two rocks, then the holding will be wonderful, but the problem will be to retrieve the anchor...

Anchoring in Rock has never been a reference for any anchor type...

But then you’re fully right, as the holding of the Bruce is very poor compared to any of the « new gen » anchors, the only possibility is to oversize it... but then you will have to deal with more weight located in the most wrong place.. Then the solution? buy a « new gen » anchor!..

Joćo
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Old 04-02-2009, 13:54   #30
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old car engines work great! They kind of press down the bow though.
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