Anchor problems while diving...

captnjack · 10 January 2008, 00:01

I have a boat, a 15.5ft RIB actually. This is my 2nd "dive boat", the first being a much smaller soft bottom 12.5 sport boat inflatable.

I have upsized my anchor from my previous version but it still ain't cutting it. I have dragged the 15lb Navy anchor several times, mostly on gravel bottoms. Even with oodles (7 or 8 to 1) scope. So I'm looking for a replacement. I have 6ft of lightweight chain attached to 8ft of super heavy 3/8" chain. The pull on the anchor tends to be horizontal and its still dragging. Last weekend I had to manually set it in a tire. The Navy is fine for sand and mud but drags on gravel for some reason. The flukes aren't pointy enough to dig between the rocks I guess. The grapel style (tried it) drags too.

I have used Danforths in the past. They don't seem to work good on dive boats cause they require lots of scope to set. Even though I have 365ft of rode aboard in 100+ft of water at a dive site its not enough.

As far as I can tell this leaves:
Claw, aka Bruce and other copies. 11lb is about what I can manage by hand. Not too pricey which is good. Supposedly good on short scope.

A 15lb CQR. Probably the highest quality but pretty expensive ($300)

A 14lb Delta. Has not gotten very good reviews lately. Hard to tell if it sets well on short dive site scopes. Slightly smaller than the Claw designs which is good for stowing.

What are other folks using when anchoring on (dive) sites where the scopes we're "supposed" to use are physically impossible?

Thanks
Richard

BassBoy · 10 January 2008, 10:07

Google 'ROCNA'. They look great.

Jono · 10 January 2008, 10:32

First pair of divers down set the anchor properly and ensure the trip is not tangled Etc....

jwalker · 10 January 2008, 11:14

Quote:

Originally Posted by captnjack

.. I have dragged the 15lb Navy anchor several times, mostly on gravel bottoms. Even with oodles (7 or 8 to 1) scope.

Richard, I think you may be struggling to get an anchor to hold well on gravel. There's nothing stable to get a hold of, kinda like a big bag of marbles, and they're lighter under water too. If you could bury something deep you may have half a chance. Err, a diver and a shovel?

codprawn · 10 January 2008, 11:19

Hard to guess what you mean by "navy anchor" is it a fishermans traditional design or a Hall's stockless? Either way they usually need to be huge to work properly.

The Delta is a great all rounder. It is basically a CQR with a welded shank to make it easier to set - it usually performs better not worse than the CQR.

With most anchors surface area is what counts not weight - that's why a fishermans style is poor because you only have one thin fluke in the ground. The time a fishermans excels is when you have to cut through something like kelp or when you are amongs rocks and it can hook onto something.

Grapnels I have found to be a total waste of time unless you are in rocky areas. I could pull a 15lb grapnel through sand with 1 hand.

There are plenty of fancy expensive anchors out there but most of them seem to be copies of the Delta/CQR so the gains they claim will be quite small.

To sum up I reckon the Delta would be as good as anything else in your area.

codprawn · 10 January 2008, 11:19

Quote:

Originally Posted by jwalker

Richard, I think you may be struggling to get an anchor to hold well on gravel. There's nothing stable to get a hold of, kinda like a big bag of marbles, and they're lighter under water too. If you could bury something deep you may have half a chance. Err, a diver and a shovel?

I agree - get a builders 1 ton sand bag and bury it!!!

mark-f · 10 January 2008, 11:45

I would second what Jono says, the only difference we sometimes do is for the first pair down to tie the anchor into the wreck if possible, then the last pair back untie it and make sure its not going to snag before asending, if the dive site does not allow for a long line then you can even send up the anchor on a lift bag and assend the line whilst drifting, for this approach you just need a heavy weight at the bottom rather than an anchor.

regards

mark

codprawn · 10 January 2008, 11:49

Looking at your comments again you only have a scope of about 3:1 which isn't very good in marginal conditions. you probably need 5:1 or more which in your depth of water means a lot of rope.

Maybe you should try an angel or buddy on the line - a heavy lead weight.

Paulmac · 10 January 2008, 15:27

Hi,
We don't dive as deep as you Captnjack and we don't have the tidal races in NSW that you Brits do but we do anchor in some tricky, deep fishing spots.
To help set the anchors, we always use two when diving in close, we made up small concrete blocks with an eye bolt through the centre and clip them to the chains, or using thick rubber 'o' rings, slide them down the anchor rope when necessary.
Paul

jyasaki · 10 January 2008, 16:27

Jack; there's 2 things that you need to have for a solid anchorage: something for the anchor to hold onto, and enough scope for the given configuration such that the direction of pull is maintained in a direction the hooked up anchor can handle.

I find that a Danforth works quite well in soft bottoms, as it buries itself pretty easily (not so well in grass, but then again, neither does anything else. I don't anchor in grass much.) It does take up some room on-deck or in a box, but that's better, IMO, than coming up to find no boat. Oh, one other thing: get a quality, original Danforth (or one of the more expensive copies); the cheap stamped and welded steel knockoffs suck. A couple of friends of mine have cut off part of the side rods to make storage easier. Doesn't seem to affect too much. Tha Danforth style (not that others don't) tend to bury themselves deeper as they get pulled on, so unless you're in something like gravel over bedrock, you should hook up eventually (one of the spots I dive is a thin layer of sand over shale; a challenge to set the hook to say the least.)

One of the more common problems I see is not enough chain. Scope is good (more the better from a purely anchoring standpoint; makes a long swim to the dive site, though), but without something else to keep the pull horizontal, the anchor keeps getting dragged back up and out. A boat length of chain is about the minimum I'd recommend. Yes, it's heavy when it comes time to pull the hook, but you'll most likely be back on board rather than still in the water looking at the boat drift off.

For a boat the size of yours, you should only need about a 5 lb anchor; and about 15 to 20 feet of chain. For diving, I usually use a 2:1 to 3:1 scope, unless I'm deep enough that I do not have enough rode. In that case, I carefully place the anchor, and remain close enough to check on it frequently (needless to say, that doesn't happen too often...)

Navy anchors are pretty much worthless for recreational boaters, as they rely primarily on mass to secure themselves.

I carry a Bruce knockoff as a spare hook, but I find it hangs up in rocks a lot more than the Danforth. The solid design seems to work better on smooth hard bottoms. Tougher to recover, usually, as when it hooks up, there's nothing that moves, so it's harder to get an angle of pull to get it loose.

I agree with Cod's assessment of the grapnel (from experience) and the fisherman's anchor; and anecdotal evidence suggests he's right about the CQR/Delta (which, I believe also tend to be heavy for a given size boat, which is why I haven't used them.)

My $.02 (and based on my local experience, so YMMV depending on your local conditions);

jky

Pete7 · 10 January 2008, 16:39

We rarely anchor our dive rib but use a shot line instead, last pair of divers half fill the lifting bag attached to the weight so that when you start to pull up the shot it quickly fills and lifts.

For deep diving we use a breeze block attached to farmers bale twine rolled around a 25 litre drum which unwinds when you chuck it in.

Rib is kept moving patrolling the dive site.

Pete

captnjack · 10 January 2008, 17:05

I got what we call a Navy style over here cause with limited scope you do rely on mass and a friend's sportboat has had good success with his 15lb Navy. This is what they look like (attachment) to translate the English

I don't have access to the Rocna anchors here in the states. But basically I have no issues anchoring in sand or mud or rock (the anchor snags or digs in). But gravel is like marbles underneath and I just drag along even with 8 :1 (or more) scope (e.g. a shallow site).

Obviously I am rarely using what a yachty would even consider an anchorage. I mean its a divesite afterall, not a 30ft deep sandy bottomed embayment, lol.

Based on some local suggestions I'm going to try a Danforth style and see how it works. 8 or 9 lbs is fairly oversized for the boat but managable for my arms. The extra mass will help for deeper sites when suitable scope is impossible to pay out. I do have a sentinal I can use for these too.

I figure the points on the Danforth might be able to insert themselves in between the gravel/stones like the Navy has been unable to. I have the benefit of always being able to check and/or reset it if I don't like how its laying on the bottom or just marginally snagged at a rocky site.

Thanks

ps we do use a live boat with a vertical shot line for some sites. But I'd rather not arrange for a boat tender at a site where diving from an unattended boat is fine solely because I have a sucky anchor.

codprawn · 10 January 2008, 19:22

As I thought the navy anchor is a Hall's stockless or similar. The actual fluke area is still quite small - hence a Delta or Danforth will give better holding.

walruz · 10 January 2008, 19:57

I have always sworn by the CQR style anchour. I use a 15lb with 4m of chain and never have any problems.

Ian

codprawn · 10 January 2008, 20:04

The only drawback I have found with the CQR is the pivoting shank. It makes stowing harder and also makes it harder for the anchor to set - things designs like the Delta overcome.

captnjack · 10 January 2008, 23:40

Quote:

Originally Posted by codprawn

As I thought the navy anchor is a Hall's stockless or similar. The actual fluke area is still quite small - hence a Delta or Danforth will give better holding.

Yeah the lack of sharp points seems to allow the whole thing to "skate" along on top of gravel (in particular). Not so much a lack of fluke area, more the lack of bite through the surface gravel into something solid.

captnjack · 10 January 2008, 23:47

So 9lb or 14lb Delta??

codprawn · 11 January 2008, 03:01

Obviously the bigger the better!!! I have a 14lb one and it's great but our waters are ver shallow so nice long scope. Don't forget an angel on the line - it really helps a lot when your scope is limited.

keelhauled · 11 January 2008, 16:25

Pete 7

Surely you mean a cavity block. Breeze blocks float . Nearly!

captnjack · 11 January 2008, 16:32

Ahhh English...

I assume you all are refering to what we call a "sentinel". In the pic I stole its marketed as an "anchor buddy" These are extra weights either attached to an anchor rode somewhere down low or lowered on a ring down along the rode. Help keep the pull horizontal.

look like this...

In place of these I have the ~8ft of 3/8" chain. That stuff is heavy. Right now my ~15ft of chain is about 15lbs total weight, as much as any anchor I'm likely to buy.