Reply
 
Thread Tools Search this Thread
 
Old 09 January 2008, 20:01   #1
Member
 
Country: USA
Town: Seattle
Boat name: Water Dog
Make: Polaris
Length: 4m +
Engine: Yamaha 60hp
Join Date: Apr 2007
Posts: 1,152
Anchor problems while diving...

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
__________________

__________________
captnjack is offline   Reply With Quote
Old 10 January 2008, 06:07   #2
Member
 
Country: UK - England
Town: cookoo land
Boat name: tba
Make: ribcraft 595
Length: under 3m
Engine: Suzi 140
Join Date: Sep 2007
Posts: 316
Google 'ROCNA'. They look great.
__________________

__________________
BassBoy is offline   Reply With Quote
Old 10 January 2008, 06:32   #3
Member
 
Country: UK - England
Town: Over here
Boat name: S.S. Nobstick
Make: Three Wise Monkeys
Length: 3m +
Engine: 44lbs of thrust....
Join Date: Nov 2003
Posts: 2,115
First pair of divers down set the anchor properly and ensure the trip is not tangled Etc....
__________________
Jono is offline   Reply With Quote
Old 10 January 2008, 07:14   #4
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
Quote:
Originally Posted by captnjack View Post
.. 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?
__________________
JW.
jwalker is offline   Reply With Quote
Old 10 January 2008, 07:19   #5
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
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 is offline   Reply With Quote
Old 10 January 2008, 07:19   #6
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
Quote:
Originally Posted by jwalker View Post
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!!!
__________________
codprawn is offline   Reply With Quote
Old 10 January 2008, 07:45   #7
Member
 
Country: UK - England
Town: knebworth
Boat name: phoenix
Make: xs
Length: 6m +
Engine: 115 opti
Join Date: Jun 2005
Posts: 193
Send a message via MSN to mark-f Send a message via Skype™ to mark-f
re anchoring dive RIB

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
__________________
mark-f is offline   Reply With Quote
Old 10 January 2008, 07:49   #8
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
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.
__________________
codprawn is offline   Reply With Quote
Old 10 January 2008, 11:27   #9
Member
 
Country: Australia
Town: Central Coast, NSW
Boat name: Grey Duck
Make: Avon- Sea Rider
Length: 4m +
Engine: Suzuki DT65
Join Date: Jan 2008
Posts: 15
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
__________________
Paulmac is offline   Reply With Quote
Old 10 January 2008, 12:27   #10
Member
 
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,653
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
__________________

__________________
jyasaki is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 22:38.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.