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Old 21 August 2019, 15:03   #1
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Rope and anchor for 6m rib

Hi there.

Can anyone advise on best choice for Anchor, chain and warp size, length etc for a 6m rib using for diving mainly in max 30 to 40 metres depth. I was thinking a Bruce Anchor for starters. Thanks.
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Old 22 August 2019, 01:26   #2
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Are you really going to be anchoring in 40m AND diving?
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Old 22 August 2019, 06:57   #3
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won't you be putting a shot line down and the boat maned ready to pick up divers if they drift off the dive site
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Old 22 August 2019, 07:28   #4
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Plus one on that Jeff. Anchoring in 40m might call for 160m of line, its a sh*t load to pull in and store!
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Old 22 August 2019, 09:51   #5
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Plus one on that Jeff. Anchoring in 40m might call for 160m of line, its a sh*t load to pull in and store!


Thatís where I was going with my query. SOP is; shot line, drop divers off & then stand off waiting for either SMBs or divers up the shot.
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Old 22 August 2019, 09:57   #6
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I've got about 6mtrs of 6mm chain and a 5Kg Bruce on about 40mtrs of 14mm wrap.

You can always go heavier and more chain but remember, you've got to haul it in by hand and that's about as much as I want to lift. You can't realistically deal with the 150 - 200 meters of rope you'd need to anchor in forty meters and you're going to want a vertical decent so as not to waste bottom time going down an anchor line.

I also carry a drogue in case I need something to "hold me to wind" beyond anchoring depth (never been out the bag).
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Old 22 August 2019, 11:59   #7
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I have dove numerous times over 120' (37m) off of my boat. And I have never had issues with using my 300' (90m) of anchor line. It has worked great in current and semi rough conditions. The only time I would not trust it is if the conditions (weather) were bad. But then, I would not be diving either. The general rule for anchor rope is letting out 3 times the depth. I have never found that to be necessary off of the smaller boats (25' or less), hard hull or RIB.

In your 6m RIB, 90 meters of anchor line is fine. What will be important is the anchor and using the right amount (length) of chain.

You can use galvanized chain or stainless steel. Galvanized is cheaper, Stainless steel is a lot more expensive. I would get a 3/8" size. The general rule is that your chain length should be half the size of your boat. So, as your boat is 20' (6m), you should get 10'. My boat is a Zodiac 550. I chose to go a little longer and used 10' instead of 9'. I would go 12' on yours. The purpose of the chain it to keep the anchor from pulling up and out of the sand.

When waves move your boat around on the surface, it pulls the rope, then the chain and finally the anchor. If the chain is too short, it will lift the anchor right out of the sand. By using a long piece of the right sized chain, the chain will not lift up all the way, and it will pull the anchor in a downward motion and, thereby securing it even further. This is how an anchor is designed to work. The chain it the key. The chain controls the effectiveness of the anchor.

There are only two anchors that would be good for your boat. The Bruce style anchor (also known as a claw anchor)is a great option, but its usually much more expensive, depending on whether you buy galvanized or SS. The cheaper alternative is also a great anchor and it works just as well. They are called the fluke style anchor (see picture). The weight of the anchor for your size boat should be 4-6 lbs for the Fluke style and 6-8 lbs for the Bruce or claw style. As far as the size of anchor rope, I would get 3/8".
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Old 22 August 2019, 12:43   #8
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The RYA's recommendation for anchoring is....

All chain...................4 X depth
Chain/rope combo......6 X depth

Sounds a bit OTT but a good starting point and common sense prevails.

If you're anchoring in 5 mtrs in a sheltered bay, staying with the boat then probably 1.5 > 2 X the depth will do. If it drags the anchor you have to put your cup down, start the engine, pull it back out and scope another couple of meters.

If you leave the boat with only twice the depth laid to have a dive in forty meters of open water, the consequences of it dragging while you're were down could be a lot more disappointing.

For weights....as recommended by "Bruce anchor"..

https://www.anchoring.com/pages/bruc...r-sizing-chart

14mm rope is probably more than what's required but it's better to handle.
and the chain doesn't need to be "calibrated" so that keeps the price down.
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Old 22 August 2019, 12:52   #9
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Quote:
Originally Posted by DiabloLoco View Post
I have dove numerous times over 120' (37m) off of my boat. And I have never had issues with using my 300' (90m) of anchor line. It has worked great in current and semi rough conditions.

Why do you anchor when diving, do you leave the boat un-attended ?
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Old 22 August 2019, 16:35   #10
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Quote:
Originally Posted by Last Tango View Post
The RYA's recommendation for anchoring is....

All chain...................4 X depth
Chain/rope combo......6 X depth

Sounds a bit OTT but a good starting point and common sense prevails.

If you're anchoring in 5 mtrs in a sheltered bay, staying with the boat then probably 1.5 > 2 X the depth will do. If it drags the anchor you have to put your cup down, start the engine, pull it back out and scope another couple of meters.

If you leave the boat with only twice the depth laid to have a dive in forty meters of open water, the consequences of it dragging while you're were down could be a lot more disappointing.

For weights....as recommended by "Bruce anchor"..

https://www.anchoring.com/pages/bruc...r-sizing-chart

14mm rope is probably more than what's required but it's better to handle.
and the chain doesn't need to be "calibrated" so that keeps the price down.
You can follow that rule if you want. The only way I would consider following that is if I had a windlass. I don't. So, pulling by hand is only option. Pulling 500' of rope is not going to happen. 35 years of boating and I have never had an issue using the method I use for dropping anchor rope.
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