Anchor questions...

ferryden · 07 August 2011, 11:09

More noob questions I'm afraid (but want to do things right)..

I've bought a 6kg anchor, with 6m of chain and plenty of rope and am planning ahead for when I'm out in Mallorca next week. Mainly anchoring in 15ft of sand in sheltered bays. But many such sites are likely to have plenty of other craft around.

Firstly, can I get away with a warp of say 3:1 in such benign conditions for an hour or two?

Secondly, how much space around me do I need to be consider allowing myself, given hardly any tide (mainly wind/wave factor)? Assuming I anchor from the wind side in 15ft of water?

Or maybe Im worrying too much (I've seen others over there just dropping their anchor right beside one another...)

And LASTLY, where do you all store your anchor onboard in order to: protect the tubes, keep tidy, keep secure (I keep thinking if the sib did flip at some point, the anchor would cause real hassle..)

Sorry for all but I had to get these questions off my chest!

:-)
Ferryden

Poly · 07 August 2011, 11:24

6kg for 3.4m SIB sounds massive to me. What design of anchor?

longjohn · 07 August 2011, 11:26

a 6Kg anchor and that amount of chain is well over the top for the conditions you are describing - it would hold a boat 2-3 times the size. I anchor my 4.7m rib with a 2kg Bruce type anchor and 3-4 metres of chain - always holds well.
Just remember that all the boats will move in the same direction - but you should be at least the length of your rope and chain from other boats. -- But all depends for how long and wether you are leaving the boat attended or not.
Stowed anchor needs to be in a tied down bag at least assuming you have no lockers. When I had a sib used to keep it amid ships in the under seat storage bag.
John

willk · 07 August 2011, 13:35

You're a bit overspecced in the ground gear department (I used to use something like yours for my 6.5m twin engined RIB). For what you describe, a 2.5kg Bruce, 4-5m of LIGHT chain and a long FINE rope would be more than OK. You don't have a huge amount of space on that boat and keeping the weight down is quite important. 25m of fairly fine rope will coil very small and still be strong enough to suspend your SIB from, never mind hold it at anchor.

I keep my ground gear in a cordura sports bag (closed) and clipped to the safety line in the bow. In a capsize it would hang down and possibly slow the boat's drift somewhat.

Fenlander · 07 August 2011, 22:55

Just how thin do you guys go on the anchor rope for a SIB? My current setup is from my previous GRP boat where space was greater, the rope isn't that thick but it's cheap stiff stuff and takes up a huge amount of room in a SIB.

willk · 07 August 2011, 23:24

My 75m warp is 6mm nylon braid, it's very compact, and I figure the bridle D-rings will fail before it does.

I carry about 20m of 8mm braid too, it's easier to haul for general anchoring purposes.

Chain is 6 milly x 4m

I often keep a 10m hank of 14mm "nylon twisted" secured on the airdeck, for tying off to things and looking purposeful, a tricky job in an airbed

ferryden · 07 August 2011, 23:44

It's a Bruce anchor... ach well, sounds like I got worried by some prior threads saying always go on the safe side when choosing warp n anchor...

OK Willk, I'll now get a 2kg lump, 3.5m of light chain and 25m of 6mm rope ...thanks also for the storage tips...

Assuming I switch to this kit, what sort of scope for lunch/snorkle stop?..would 3:1 work?

(Even if she's a bit slooow, I'm determined to have some fun Willk!)

Thanks very much all!
x
Ferryden

Doug Stormforce · 08 August 2011, 01:23

Quote:

Originally Posted by ferryden

It's a Bruce anchor... ach well, sounds like I got worried by some prior threads saying always go on the safe side when choosing warp n anchor...

OK Willk, I'll now get a 2kg lump, 3.5m of light chain and 25m of 6mm rope ...thanks also for the storage tips...

Assuming I switch to this kit, what sort of scope for lunch/snorkle stop?..would 3:1 work?

(Even if she's a bit slooow, I'm determined to have some fun Willk!)

Thanks very much all!
x
Ferryden

While the lighter ground tackle is a good idea 3:1 scope isn't, think more in terms of 5 or 6 to 1.

willk · 08 August 2011, 09:02

On a calm day with no tide and you there, 3:1 WILL work with the chain as you are very light and have almost no windage. However, you should be carrying MUCH more warp than required for mooring in the shallows, hence the 100m that I'm toting about. If you're leaving the boat unattended, then 5:1 is a sensible minimum.

m chappelow · 08 August 2011, 20:34

Another problem with using a short anchor line or scope is if there is any rise with the tide or even wash from a passing boat ,that will make the line even shorter pulling out the anchor or making it drag,
i have a minimum of 45 mtrs of 10mm braid line and 3 mtrs chain and anchor kept in a plastic box or you could fake it down into a bag or coil it on a reel .

ferryden · 08 August 2011, 21:19

Thanks guys..I'm taking it all in!...

But there's no way I'll get enough space to rotate round a 6:1 warp in many of the more popular coves...?

(non tidal, protected bay)

Doug Stormforce · 08 August 2011, 22:26

The 5:1 or 6:1 has nothing to do with rise of tide. I would encourage people to think in terms of 5 or 6 :1 times the maximum depth you expect to be anchored in allowing for any rise of tide.

As the OP says he has no rise of tide the it 5 or 6 : 1 the depth.

The reason for his amount of scope is that your anchor and chain work best with a horizontal pull across the sea bed. They are totally in effective if there is to much vertical pull. As already mentioned the wash of another boat can make this worse.

Peter_C · 10 August 2011, 18:23

Sibs are really light, but poor ocean conditions can lift half my 4m of chain off the bottom. I can't imagine having any less chain since my boat needs to be at the surface waiting for me where I left it when I return from scuba diving. My anchor is an 8lb (3.62kg) Hooker Danforth style anchor. I have 310ft (94 meters) of anchor rope.

To connect the anchor to the boat I built a bridle that goes from the two d-rings in the front into a loop that passes thru the bow eye. From there I tied a loop into the end. The reason for the loop in the end is that in case one of the d-ring breaks loose, the other will hopefully continue to hold. Thru the loop I pass a locking carabiner, and at the length I want I create an overhand loop in the anchor line, then toss the whole thing overboard. So far it has worked well.

My anchor and line are stored in a milk crate turned sideways in the bow, that is mounted to the front wooden deck (Aluminum rear decks) with eye bolts and held down with giant zipties. It just gets fed (Dropped) down into the milk crate, which is breathable, and so far has not tangled. I do tie the end off to the milk crate and figure if I ever flip the boat the anchor will hopefully self deploy but I doubt it, since the anchor ends slip tightly into the milk crate. Also with the anchor tucked into place it never flies out of place no matter how rough the water gets.

Scope: yeah I use some. It depends on how much wind chop there is, but rarely do I use more than 3:1 and sometimes less if the conditions are benign. I often anchor in 100ft of water and carrying 600ft of rope would be ridiculous. We dive in calmer conditions not hurricanes.

Poly · 10 August 2011, 19:58

Quote:

Originally Posted by Peter_C

... I do tie the end off to the milk crate and figure if I ever flip the boat the anchor will hopefully self deploy but I doubt it, since the anchor ends slip tightly into the milk crate...

I've always thought that was a bad idea, since a picture I saw in a book which showed a capsized dinghy being pulled under by a rising tide - but I suppose the force on the anchor would be huge to pull a SIB under...

Jorgos · 10 August 2011, 20:29

Quote:

Originally Posted by Doug Stormforce

While the lighter ground tackle is a good idea 3:1 scope isn't, think more in terms of 5 or 6 to 1.

A danford around 2,5 - 3 kilos , 10 meters of chain 4mm, and 25-30 mtrs of 6mm I think is ideal

Peter_C · 11 August 2011, 18:42

Quote:

Originally Posted by Polwart

I've always thought that was a bad idea, since a picture I saw in a book which showed a capsized dinghy being pulled under by a rising tide - but I suppose the force on the anchor would be huge to pull a SIB under...

Since we tend to operate fairly close to shore which is typically rocky cliffs with large waves crashing against them I would prefer to have my anchor hit the bottom and stop the boat from reaching shore. This would give me time to hopefully flip it back over. We also have slow tide changes that are not very large swings. Best thing to do is not to flip in the first place though.