Anchor Sizing . . . Newbie Grateful for Help !

[ti325v]

Hello all....
Looking for more great advice from you guys who know a heck of alot more then I do.
I am looking for recommendations for both ideal and practical suggestions for my anchor size and type requirements.
I have access to Danforth type anchors here in the middle of no where in Vietnam, also the possibility of shipping on in from overseas at considerable expense and massive headache with customs.
Ideally a danforth type, but if there is a better option that is really superior I will import it.
I have a 15 x 4 meter wooden hulled dive boat. pictures found here..
Scuba, vietnam, Con Dao, Snorkeling
By necessity we have to anchor it on short scope as we are often pushed away from the reefs we dive as a result of winds or current. It is not ideal to lay out lots and lots of scope.
We are always on clean sand bottom, 100% of the time.
The boat when on this anchor will always be manned by a dedicated captian and two support crew.
We have on hand a big back up anchor.
We rarely anchor in heavy current or strong winds as these conditions keep us on the moorings.
I have a 2000 watt horizontal windlass.
I really need advice as to proper anchor sizing, I have been reading all over the place and just getting confused as heck !
Ideally the anchor goes on a roller on the bow. Will a Danforth work on a roller ?
Is Danforth ideal for short scope, sand bottom in mild conditions ?
How much scope and size of chain ?
What is a realistic weight for the anchor, I would like to keep it much lighter then the current 70 pounds we have.
What diameter for the nylon anchor line ?
Any other suggestions, ideas, thoughts are most welcome.
Thanks in advance !

[TassieBloke]

Oh boy, here we go

[cat man do]

anchor sizing chart - Google Search

and images

http://www.google.com.au/search?q=an...IuuViQfjgaGCDg

[Bash]

Originally Posted by ti325v

Is Danforth ideal for short scope, sand bottom in mild conditions ?

You are on the right track. Danforth has great holding power in sand. In your particular usage, you don't have to worry about it resetting after a change of currents or tides, and since the anchor will always be tended you can get away with shorter scope.

Using such an anchor in a commercial application, you may find that you break/bend/wear out anchors much more quickly than most cruisers. A dive boat may end up anchoring several times a day, seven days a week. So one consideration will be how much lifespan a given anchor can anticipate in your usage. The good thing about the Danforth is that it gives a lot of holding power for the money.

[ti325v]

Originally Posted by TassieBloke

Oh boy, here we go

I know I was opening a can of worms ! But the answer escapes me !
I think with the absolute predictability of conditions, bottom type, no storms, short scope, and ease of purchasing all addressed....I doubt I could possibly eliminate more variables. Though this would make it easier.... Really looking forward to advice.
Thanks !

[ti325v]

Originally Posted by Bash

You are on the right track. Danforth has great holding power in sand. In your particular usage, you don't have to worry about it resetting after a change of currents or tides, and since the anchor will always be tended you can get away with shorter scope.

Using such an anchor in a commercial application, you may find that you break/bend/wear out anchors much more quickly than most cruisers. A dive boat may end up anchoring several times a day, seven days a week. So one consideration will be how much lifespan a given anchor can anticipate in your usage. The good thing about the Danforth is that it gives a lot of holding power for the money.

Hi Bash.. Thanks for your input !
A couple of questions please, good point about durability...
We tie up to established moorings about half the time the boat is out....
We might possibly anchor it 2 times a day 180 days of the year.
But that number would certainly be high.
Now the biggie...how heavy would you go ? Diameter of line ? Chain ??????
Oh I forgot to mention, maximum depth of anchorage 60 feet.
Thanks
Larry

[Bash]

One thing to remember here is that the anchor line on a dive boat is also a tool for controlling ascents and descents of the divers. For this reason, it's probably best not to go too oversize. You want something that still fits the hand. A lot of dive boats use 1" line, but 3/4' might be worth considering.

Match the chain to the nylon.

[GordMay]

The “Danforth” fluke-style anchor performs quite well in sand, and stows easily on most bow rollers.
A 25 to 36 pound Danforth “Deepset” (or a 21 to 32 Lb “Fortress”) should suffice for attended day stops on your 15m/49Ft dive boat.
I’d use a short (6'?) Length of ±7/16 - 1/2" chain with a 3/4 - 1" rope rode.
Initially set the anchor with longer scope, only then shorten up as required.

[ti325v]

Okay, now these are the kinds of answers and thoughtful discussion I was hoping for....
Thanks GordMay.
Any thoughts about the durability of the danforth in these conditions ? as mentioned by Bash. Replacements are not easy to come by on this island, I have to go up to Saigon to get it. If indeed I can find it ! I have only rumors.
We actually drop a dedicated descent line from the back of the boat and rarely if ever use the anchor line for ascents/descents.

[Jimbo485]

You want generalisations or a specific answer? In your situation, I would do the following:

Imported Fortress FX-37 with the lifetime guarantee.
5 metres of G30 chain, 16 mm diam, 45 mm pitch, followed by 100 metres of 20 mm, 3-strand nylon rope. (Shorter scope means heavier chain near the anchor. Weight saving on the fortress anchor is used on the short length of chain.)

[Bash]

Just keep in mind that it's possible to bend a Danforth. I used to work within the dive industry in Monterey, on the coast of California, and most of the smaller boats used Danforths. This was 20 years ago, so I don't know what boats are using now. It was quite easy to mangle an anchor if it got wedged in rock. The best answer is don't anchor near rock, and if you have any trouble retrieving an anchor, ever, send a diver down to free it rather than muscling it up on the windlass. Use moorings whenever you can, and try always to anchor in sand.

[Adelie]

Originally Posted by ti325v

I know I was opening a can of worms ! But the answer escapes me !
I think with the absolute predictability of conditions, bottom type, no storms, short scope, and ease of purchasing all addressed....I doubt I could possibly eliminate more variables. Though this would make it easier.... Really looking forward to advice.
Thanks !

Tassie was making an in-joke alluding to the fact that anchor thread on this forum tend to become .... heated for some and a source of entertainment/amusement for others. There was a thread last summer discussing such contentious (sp?) topics: http://www.cruisersforum.com/forums/...ses-64137.html.

Given that you have an unusual (for us) situation: always on sand, short scope, always someone on board, ... I actually think this thread might not blowup, unless someone takes it off the original question.

My initial response without knowing more it to suggest you get the biggest Fortress you could afford. If you could replace the wildcat on the windlass I would up the chain 1 or 2 sizes then go to a rode with nylon in it. I would also get an outboard with a cage around the prop or put a cage around the main prop. If you have to use the engine to relieve load on an anchor that is dragging, you don't want to blender any of the paying customers.

Why do you want to change the anchor setup? Do you regualarly drag? Have you been burning out the windlass? Do you want to go to shorter scope?

[ti325v]

Hi Adelie:
Thanks for your answer, I saw that post, looked at anchor sizing charts and had a spinning head ! ( Allow this much for storm condition, this much for muddy bottoms, this much for short rode..... (BTW no problems with the windlass, no dragging....problems with current rig outlined below.

I can see this is a topic of heated debate. Of course I know absolutely nothing on this subject, other then the fact that that my current anchor is made of rebar, welded mild steel plate, rusts like heck and looks butt ugly. It was made by the guy two doors up the street from me by hand for about $60. (I try to keep the boat as pretty as possible).

I saw much of the debate was concerned about storm conditions bottom composition and all the unknown factors. Which in my case are all clearly defined, 100% of the time. And we do have scuba divers on board all the time to deal with any fouls.

I tend to like things small and well designed, ( I understand that small is not a selling point in the anchor department) and I do absolutely love to use the latest and greatest technology from the west, defined as anything that was produced in the last 30 years and proven in the west. The environment I work in is simply make it cheaper, not better.
I have quite possibly the only boat in the entire country with bilge pump float switches, an on demand pressurized water system, those things are just not necessary, labor is cheap people here believe in "work harder, not smarter"... I had some left over bilge pump float switches, my captain was enthralled, and was actually thrilled when I gave him one of my spares.
The electric winch ? leaves people with their heads shaking and muttering about how that is not possible. I was told I had to use an old car rear end with differential and hydraulic pump and motor as a winch, as that is what they use to pull up nets. It certainly works, but has no place on my boat !
It is not an issue of show off, but an issue of how to work efficiently.

70 pounds of welded up mild steel that bends a bit then fractures,when possibly 30 pounds of good design and quality construction will do the job properly means a lot to me. ( My shop faces onto a port, and every day I see anchors being carried to the guy up the road to have more scraps welded onto them to repair them) I recover about 5 broken anchors a year in the mooring areas where the boats are sheltered. Big ones ! (25 meter boats, 250 pound anchors), with the 2 inch rebar shafts snapped clean.
This is the only technology they know.
I like good engineering and quality construction, I think the design of the current anchor is inefficient and not durable.
Also I want to keep the weight down, so I can reduce the chain size, and be sure all the rode fits on the winch.

In short I believe in the right tool for the job, and since my parameters are very clearly defined, I do not need an adjustable wrench with a cheater bar, but a fine quality six point socket. The nut is not rounded off and I know if it is SAE or Metric.

I have access to BIG spring scales, and could wait for a rough day and see how much this rig is actually subjected to.
As you see already I have two reasonable suggestions, with one major difference, rode thickness 12 mm or 20 mm rope...now I have not looked at the numbers but I would image a huge strength difference in strength.

Sorry to be so long winded, for you guys who know about this stuff I think the more details you have, the more easily you can put me onto the "best"answer.
Again thanks all for your input, differing viewpoints and other options are gratefully solicited !
I am under the impression the Danforth may not be ideal as far as durability is concerned, as well as ease of setting it, any thoughts out there ?
Thanks very much for everybody's time.
Larry

[Astrid]

I am under the impression the Danforth may not be ideal as far as durability is concerned, as well as ease of setting it, any thoughts out there ?

Not so sure about durability, as that is probably a matter of how an owner uses his Danforth as much as anything else, but for setting the Danforth is not too bad. It sets well in sand and silt, but less so in clay or rocky bottoms. The flukes have trouble penetrating weed or kelp covered bottoms, but then so do most other anchors apart from kedge type anchors.

[cat man do]

The guys in Vietnam
I seriously doubt he will be able to get or afford one of the brand name anchors into the country, especially as I believe they may attract a 100% luxury tax.
My guess it will be a large chunk of chinese iron China Boat Anchor, China Boat Anchor Manufacturers, China Boat Anchor Suppliers and Companies on Alibaba.com