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Old 07-14-2015, 12:33 PM   #41
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So Scary, in Flyrights example we are up to 3000 lbs?
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Old 07-14-2015, 11:58 PM   #42
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That's got me wondering what size my chain is. I'll have to go check.

Richard
7/16" Grade 43 (G4). 350' - that's 700lb in weight (21,600lb breaking strength).

Thanks for making me check - now I know!

Richard
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Old 07-15-2015, 12:04 PM   #43
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What winch

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7/16" Grade 43 (G4). 350' - that's 700lb in weight (21,600lb breaking strength).

Thanks for making me check - now I know!

Richard
You may own the throne on chain. What kind of winch.
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Old 07-15-2015, 12:27 PM   #44
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You may own the throne on chain. What kind of winch.
It's an Ideal Windlass. Slow but effective. We won't say what kind of anchor is on the end of the chain...

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Old 07-15-2015, 01:42 PM   #45
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won't say what kind of anchor is on the end of the chain...



Richard

I already know.... The wrong one!
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Old 07-15-2015, 02:57 PM   #46
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Straightforward enough. Measure the tension with a custom tensiometer. I'm sure some engineering firm would be happy to do the study for a fee. Figure on the mid 6 figures.

Another option: contact one of the big oil companies. I'll bet they have already done fairly in depth studies on the forces of currents and waves on their moored structures.


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Old 07-15-2015, 05:36 PM   #47
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A chain rigged tight across 2 posts (anchors) with 1000lbs (boat) pulling from the center exerts 2000lbs pull on each post not 500lbs as most would assume.
Or 0 as the case may be, and usually is. Unless of course you are trying to pull the boat apart.
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Old 07-16-2015, 06:23 PM   #48
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I thought the attached drawing would clarify the anchoring across a current situation. It is impossible to keep the boat in line with the anchors since the rode tension would be infinite. The tension can only be determined when the angle is known.Click image for larger version

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Old 07-16-2015, 07:57 PM   #49
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Right on Paul.

Nail on the head.
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Old 07-16-2015, 08:29 PM   #50
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We have had to deal with this situation once a few years ago. This was a Labor Day raft of about 10 boats. The raft was set up by a fellow who is very experienced at doing this, and it was oriented to the prevailing wind. There were six anchors used: at angles off the bows and sterns of the boats next to the end boats and straight off the bow and stern of the center boat.

However, the wind shifted after the raft was set up until it was blowing relatively hard 90 degrees to the boats.

We were the upwind boat, so the "raft master" had us deploy our Fortress FX23 stern anchor 90 degrees off our starboard side from the midships cleat. The pressure on that anchor and rode was considerable but it kept the raft in place. Some of the load was picked up by the angled anchors off the boat inboard of us.

So no calculations or hard numbers, only the evidence that whatever the pressure is, it can be a lot. This was from wind, not current.
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Old 07-16-2015, 10:27 PM   #51
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Our Maritime Authority decreed fore and aft moorings, more boats in a given space = more mooring licensing fees, but there was an outcry, and some expert opposition based on the loadings imposed, it got dropped most places. I`ve seen it at Angel Isl in SF, can`t be much fun hooking up.
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Old 07-16-2015, 10:42 PM   #52
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Our Maritime Authority decreed fore and aft moorings, more boats in a given space = more mooring licensing fees, but there was an outcry, and some expert opposition based on the loadings imposed, it got dropped most places. I`ve seen it at Angel Isl in SF, can`t be much fun hooking up.
The fore-and-aft mooring in Ayala/Hospital Cove at Angel Island is designed so boats face incoming wakes (mostly from ferries) but cross-wise to the currents.


http://angelisland.org/visitor-infor...ating-camping/


Raises the difficulty in hooking up, but I've always had help from a fellow TFer in a dinghy. Note current pushing boat away from the photographer:

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