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Old 12-10-2012, 06:49 PM   #21
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another alternative on the Portsmouth
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Old 12-10-2012, 06:56 PM   #22
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Adjacent to the above wikipedia photo, it says:

Mushroom anchor

The mushroom anchor is suitable where the seabed is composed of silt or fine sand. It was invented by Robert Stevenson, for use by an 82-ton converted fishing boat, Pharos, which was used as a lightvessel between 1807 and 1810 near to Bell Rock whilst the lighthouse was being constructed. It was equipped with a 1.5-ton example.
It is shaped like an inverted mushroom, the head becoming buried in the silt. A counterweight is often provided at the other end of the shank to lay it down before it becomes buried.
A mushroom anchor will normally sink in the silt to the point where it has displaced its own weight in bottom material, thus greatly increasing its holding power. These anchors are only suitable for a silt or mud bottom, since they rely upon suction and cohesion of the bottom material, which rocky or coarse sand bottoms lack. The holding power of this anchor is at best about twice its weight until it becomes buried, when it can be as much as ten times its weight. They are available in sizes from about 10 lb up to several tons.

Deadweight anchor

This is an anchor which relies solely on being a heavy weight. It is usually just a large block of concrete or stone at the end of the chain. Its holding power is defined by its weight underwater (i.e. taking its buoyancy into account) regardless of the type of seabed, although suction can increase this if it becomes buried. Consequently deadweight anchors are used where mushroom anchors are unsuitable, for example in rock, gravel or coarse sand. An advantage of a deadweight anchor over a mushroom is that if it does become dragged, then it continues to provide its original holding force. The disadvantage of using deadweight anchors in conditions where a mushroom anchor could be used is that it needs to be around ten times the weight of the equivalent mushroom anchor.
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Old 12-10-2012, 07:44 PM   #23
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The mushroom anchor works by weight. It sinks into the bottom and is hard to "suck" out. It wouldn't work on rocks.

As far as the cinderblocks acting as a mushroom anchor, it's possible that they might, but since this guy used only rope, not chain, the cinderblocks will chafe the rope and it will break.

So far, there have been no storms or strong winds, just the normal tidal currents. I just hope that when it breaks free, the tide is going out and the current will be away from my marina.
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Old 12-10-2012, 08:27 PM   #24
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Thanks Mark and Ron for the explanations of how and why a mushroom anchor works.
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Old 12-11-2012, 10:03 AM   #25
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Marin's pictures of the Columbia remind me to highly recommend the Columbia River Maritime Museum in Astoria, OR, where that boat is moored and those pictures taken. A destination that should be on any all-things-maritime lover's bucket list. A scenic and an easy day trip by car from Portland if you have limited time. Better yet, visit by boat!

Columbia River Maritime Museum, Astoria, Oregon | Maritime History of the Columbia River
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Old 12-11-2012, 12:00 PM   #26
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Thanks Mark and Ron for the explanations of how and why a mushroom anchor works.
You're welcome.

I've seen mushroom type anchors marketed to those who fish from small boats (jon boats, mainly). I suspect they don't work well at all because they only weigh ten pounds or so and won't likely be in place long enough to become really effective.

The advantage (if there is one) is that they have no sharp edges to mar the boat. Another advantage is, they can be thrown much farther than a traditional anchor.
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Old 12-12-2012, 08:19 AM   #27
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I came across this today, anyone any idea what type of anchor it is supposed to be? Click image for larger version

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Old 12-12-2012, 10:13 AM   #28
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Andy that's a take off on the very good Northill. Fishermen like the Northill so much in CB Canada they make their own or have them made in a welding/fab shop.
This imitation looks nice and seems to be SS but it looks a bit flimsy. It's pieces look more like Danforth pieces. And of course this type gets both flukes involved only in very oosy mud so the effective fluke area is small. On a real Northill the stock (or cross piece) is a small channel and when it engages the bottom the holding power probably does go up.

Yes. OFB has a Northill and in his waters it's not an unusual anchor. Here is a home made Northill I saw in Shawl Bay in the Broughton's last summer.
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Old 12-12-2012, 12:38 PM   #29
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Here's a shot of the folding Northill anchor that was used on a lot of flying boats including the Boeing 314 Clipper.
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Old 12-12-2012, 11:54 PM   #30
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Yes that appears to be an excellent design Marin.

I was told the Northill was designed specifically for flying boats. Do you think or know that that's true?
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Old 12-13-2012, 12:40 AM   #31
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Quote:
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Yes that appears to be an excellent design Marin.

I was told the Northill was designed specifically for flying boats. Do you think or know that that's true?
Northill

Neat site.
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Old 12-13-2012, 12:53 AM   #32
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Yes that appears to be an excellent design Marin.

I was told the Northill was designed specifically for flying boats. Do you think or know that that's true?
You were told correctly. The website Spy put in the previous post is the one where I learned awhile back what I know about the Northill. Check it out.
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Old 12-13-2012, 06:15 AM   #33
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I believe the SS was also chosen to affect a compass the least.

The Navy flying boat P5M guys were probably the worlds best at time/distance/fuel /howgoes it.

Seems when a squadron would deploy 6 aircraft would go to a base that frequently would only have 3 or 4 hauling cradles.

First in time , first in line. So as flying boats , not amphibians , a few would have to be manned wet 24/7 .

The Pilot who got his boat hauled was LOVED by his crew! NO anchor watch!!

The Skipper and XO would leave 15 or 30 min ahead of the group. RHIP

The fun game was to make up that 1/2 hour with out running out of fuel due to the higher power setting.

Amazing performance on lumbering tubs can be had by the motivated!
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Old 12-13-2012, 06:00 PM   #34
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I came across this today, anyone any idea what type of anchor it is supposed to be? Attachment 14695

Attachment 14696
This is an almost identical design that is used on virtually every shrimp boat in the Gulf of Mexico. These boats anchor in relatively shallow water (20 to 30') to relatively deep water (60 to 100') and hold without dragging in winds well in excess of 50 MPH. They travel along the coast from Florida to South Texas and the Mexican Border. Coastal being up to around 60 miles or more from land. Most are made by a local welding shop - nothing fancy or high tech.
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Old 12-14-2012, 06:58 AM   #35
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"Most are made by a local welding shop - nothing fancy or high tech."

What works works,,,,perfect for the commercial fish guys.

The big nonsense claims come from the new guy on the block that wants to get more per pound for his latest creation than GE gets for an aircraft engine.
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