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Anchor size

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cclark
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USA
104 Posts

Initially Posted - 06/23/2004 : 03:00:48

Okay, I can't seem to find any information regarding this in the archives;
What size/type anchor should I use for my primary anchor.
I know, it depends. Here are the specifics that I think are important:
'83 SKTR
Puget Sound cruiser (relatively protected)
Usually anchoring in 60-90 feet of water

The reason this comes up, is that this evening I tried to anchor Downtown Seattle and listen to a Concert on the pier. Between the wake from the Ferries, and the little chop from the wind, we kept dragging the little folding anchor (sorry, don't know the name) I currently have.
Thanks for any help from some of you more experienced anchorers.
Chris

Yam Ka '83 SK/TR #3749

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 06/23/2004 : 07:09:59

I use a Danforth 920 and find that it works well. A CQR deepset 14 lb would be good if you fit a bow roller to hold it. It will not fit into the well. You need to have almost 200 feet of line out to anchor in 60 feet of water. Thats a lot for most of us. I also have come to like having about one boat lenght of chain between the rode and the anchor. I use 30 ft. of 1/4 chain on our boat. Dave

Edited by - on

cvwall
1st Mate

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USA
56 Posts

Response Posted - 06/23/2004 : 08:38:51

I use a 13# Danforth with 12' of 3/8" chain on 200' of 1'2" nylon for a primary anchor and a 16.5# Bruce on 30' of chain and 200' of 1/2" nylon as a backup. The Danforth with plenty (7:1)of scope holds well in most conditions, and the Bruce is used when you don't have the room for the greater scope (the Bruce is OK at 4:1 except in heavy air). Pick the area you intend to anchor in carefully, the kind of bottom makes all the difference. The Danforth-type have difficulty in areas with lots of weeds or shell. For peace of mind, I usually set both anchors at about 30 degrees apart in an open anchorage. With this setup I've experienced no problems after a night with winds in the 25-35 kt range, other than trying to break them free after they dug in really deep.

Edited by - on

Bill Holcomb
Admiral

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USA
769 Posts

Response Posted - 06/23/2004 : 09:17:44

Hi Chris,

~12 or 13 lb Danforth or 16 lb Bruce or Claw are minimum for our boats. In heavy swell or strong current areas (Puget Sound certainly qualifies) the next size up may be warrented. Always use at least the same length of chain as length of boat (25 feet minimum). And, you must have adequate scope to keep the rode more horizontal. 4 or 5 to one is pretty much a minimum. So, if you are anchoring in 90 feet of water, the minimum amount of rode let out must be 360 feet. In strong current or heavy swell you probably should let out 6 or 7 to one. That's up to 630 feet of rode. Check out books like the Annapolis Book of Seamanship or Chapman's Piloting....or the West Marine Catalog to get some more specific ideas.

If you put out 150 feet of rode for a 90 foot depth of water you'll drag.

Bill Holcomb - C25 Snickerdoodle #4839

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 06/23/2004 : 09:57:36

It sounds like he should raft up to a big boy for the next concert.

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 06/23/2004 : 10:20:49

IMHO follows:

As a safety item, you should have at least two decent anchors and rodes rigged in a "ready to go" state. Imagine a dead engine, no wind, a stiff current with a nasty rocky shore to leeward. Things can happen in a real hurry and it's critical to be able to stop the boat when you need to.

Note that different anchor designs work better depending on what kind of bottom you are over.. so I recommend carrying types... that fit the prevaling bottom conditions in your cruising grounds.

Personally, I carry a 14 lb Danforth style as my 'regular' anchor and a 22 lb claw as my 'I really want to stay put and I mean right now' anchor.

Edited by - on

sdaly66
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USA
143 Posts

Response Posted - 06/23/2004 : 11:15:19

My primary anchor is a Danforth 14 on my 250. I found that the rail bracket from WestMarine keeps it nicely on the bow and out of the way of the headsail (I do use a bungee to make sure it doesn't "jump" out in heavy weather. I stow the chain and rode in the ancjor locker on top of my backup anchor (a smaller Danforth). The Danforth works well for the goo at the bottom of Chesapeake, but I can't speak to its merit in other surfaces.

Edited by - on

cclark
Navigator

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USA
104 Posts

Response Posted - 06/23/2004 : 16:51:19

Thanks for all your advice. I have figured out that I probably have a #13 Danforth with about 150 ft. of rope. I have a chain rode but I don't know how long it is. I will check it when I get to the boat next.
My lingering problem is the math involved in figuring the amount of line required.
Please correct my math;
If you have a 7:1 scope, your scope angle is approx. 8 degrees.
If the bow of the boat is about 4 ft off the water, this means you should have about 28 ft of rope between the bow and the water surface.
I have yet to see anyone with this much scope.
Even if you use the lower end of the spectrum, you should have 16-20 ft of scope before the water line.
Are we all (in the Puget Sound) not giving enough line to our anchorage, or am I missing something?

Edited by - cclark on 06/23/2004 17:00:23

cclark
Navigator

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USA
104 Posts

Response Posted - 06/23/2004 : 17:01:05

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by fhopper@mac.com
 It sounds like he should raft up to a big boy for the next concert.
<hr height="1" noshade id="quote"></blockquote id="quote">
At least at High Tide, I think you are probably right.

Edited by - on

RichardG
Admiral

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USA
990 Posts

Response Posted - 06/23/2004 : 18:40:35

<blockquote id="quote">quote:<hr height="1" noshade id="quote">If you have a 7:1 scope, your scope angle is approx. 8 degrees<hr height="1" noshade id="quote"></blockquote id="quote">

Chris:

I don't think you can use the angle of the rode to determine scope because trigonometry doesn't apply well here as the rode usually isn't straight, especially with a chain/rope rode. The key to scope is the ratio of length of rode to the depth of the water plus the height of the bow over the water's surface.

No matter what anchor you have, my motto is more chain is better (my bow anchor has about 55', stern has about 25'). However, more chain means more weight. Even a small bow roller helps greatly when retrieving the anchor because you don't have to lean over the pulpit while trying to pull it up; instead you can sit back on the deck with your feet planted firmly in the anchor locker while pulling back horizontally.

Another important point in anchoring is setting it properly. I've never seen anyone set their anchor too much...I've seen lot's of folks not set it enough.

Like many sailing skills, a good way to learn (before you get in a crowded anchorage situation or an emergency) is to practice anchoring in a safe place, away from others and in calm conditions. That way you will feel much more confident later.

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 06/23/2004 : 18:57:13

"If you have a 7:1 scope, your scope angle is approx. 8 degrees."

If you were putting enough tension on the rode to pull it tight as a fiddlestring... that's what you might see. At the opposite extreme, if there were no forces acting on the boat at all the rode will hang straight down.

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 06/23/2004 : 20:02:59

Actually the multihull guys did the calculations and I checked them last year. There is only a 2% diference between the holding power at 3 to 1 scope versus 4 to 1. From 4 to 1 to 5 there is only a 1/2% increase in holding power due to decreased angle. If you were in large or breaking waves there would be an increase in effective holding power due to more elastic shock absorbtion with more scope. We find that for normal anchoring 3 to 1 does well even in heavy weather. Those that use really long scope can really screw up a crowded anchorage too. Dave

Edited by - on

At Ease
Admiral

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672 Posts

Response Posted - 06/23/2004 : 20:04:52

The angle of the chain/rode is irrelevant. A scope if 7 to 1 means multiply the depth of the water plus the distance to the bow (where the anchor is tied), times seven. In other words, seven feet of rode for each one foot of depth (including height of bow above the water). For example, if you are in 10' of water, and the bow is 4' above the water line, times 7 = total scope (chain and rode) of 98'(10 + 4 X 7).

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 06/23/2004 : 21:28:24

Actually, again, the angle is relavent cause when you really get a lot of strain of the anchor the rode does come pretty close to straight( there was a CQR ad years ago showing a 40 ft sailboat in breaking seas just off the beach and the chain rode appeared bar straight) The problem is that the angle does not go down much with reasonable increases in scope. I've also got a picture of a Coast Guard utility in big breaking waves with 1 inch chain stretched out so that it appeared straight too. 3 to 1 is 18 degrees 4 to 1 is 15 degrees and 5 to one is 11 degrees. Those sound like significant changes in angle but the relavent trig functions are hardly changing at all. Dave

Edited by - on

oldsalt
Admiral

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USA
578 Posts

Response Posted - 06/23/2004 : 22:49:42

I wonder if that's a function of the catanery which makes the rode appear to be more vertical between the bow and the surface than it really is between the boat and the anchor. I've seen tugs towing huge heavily loaded barges where the angle from the deck of the tow to the surface appears close to vertical but the actual angle of the remainder of the hundreds of foot long towing hawser was almost horizontal with a huge dip in it between the barge and the tug due to the catanery of the system. With the proper length of chain and rope rode, the forces on the anchor are far more horizontal than they appear at the surface.

Edited by - on

Gary B.
Admiral

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USA
969 Posts

Response Posted - 06/24/2004 : 15:46:05

I have had good success with a Danforth as my primary anchor, and it has never failed to hold in the mud bottom of the Columbia River, at anything over 3 or 4 to one. I have read that 7 to 1 is for STORM conditions, and I have rarely ever used that much scope.

However, in the San Juans, the Danforth is less than perfect due to a tendency to not like eel grass and or other bottoms that are not as forgiving as mud. I bought a Bruce knock off for use in cruising situations and find it holds VERY well in all the conditions I have faced. I like at least a boat length of chain. The Danforth STAYS on the boat (2 if not racing), but the Bruce comes out for the serious stuff.....

Gary B.
Vice Commodore
s/v Encore! #685 SK/SR

Edited by - Gary B. on 06/24/2004 15:47:16

Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 06/25/2004 : 08:25:20

I use a 14 lb Delta. With that said, I'm not sure if it would work for you as I think the anchor well is deeper on an 89.

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Raskal
Navigator

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USA
162 Posts

Response Posted - 06/25/2004 : 17:00:08

Once every 3 weeks somebody trots out this question of anchor/rode size and we all get on our soapboxes about our favorite combinations, but before I use up my turn to piss everyone else off let's look at what the manual does say (the 2 editions of the manual can be found on the home page under "brochures and manuals"):

first, the 1978 edition:

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Under normal weather conditions in a protected anchorage an anchor in the 9-13 pound range and of the "danforth type" may be used as a bow anchor in ordinary conditions. This anchor will only be effective with at least 12 feet of 1/4 inch or heavier gauge chain and at least 200 feet or more of 7/16" or heavier nylon line. An 8 pound stern anchor will require about 150 feet of scope and 10 feet of chain.

Under adverse weather conditions as much as a 20 pound bow anchor could prove necessary, and possibly a plough-type anchor might be required.

Inquire in your local area about anchoring procedures relative to the place you plan to visit. Get the opinion of several experienced people and always play it on the safe side in "making up" your anchor ahead of time for emergency use. Do not forget to wire all shackle pins so they cannot come loose underwater.

Remember: Lighter anchors are made more effective by increasing the scope, i.e. the ratio of length of line and chain to depth of water. A 7:1 ratio is recommended. This means using 7 feet of anchor line for each foot in depth of water. An anchor is a necessity aboard any boat, it is recommended you have a usable anchor aboard whenever you leave the dock.
<hr height="1" noshade id="quote"></blockquote id="quote">

This is a masterful little treatise that incorporates what is still considered the best current theory on all of these points.

The 1988 edition says pretty much the same thing but show some shift on the size issue:

<blockquote id="quote">quote:<hr height="1" noshade id="quote">
The anchor manufacturer suggests an anchor in the 13 to 16 pound range, to be used as a bow anchor in ordinary conditions. This anchor will only be effective with at least 6 feet of 1/4 inch gauge or heavier chain and at least 7/16 inch nylon line or heavier.
Under adverse weather conditions, as much as a 25 pound bow anchor could prove necessary and, possibly, a plough-type anchor might be required.<hr height="1" noshade id="quote"></blockquote id="quote">

My addition to all of this is that it makes no sense to be using a traditional steel Danforth anchor on a boat with no windlass when the super-light alloy Fortress and Guardian fluke anchors are available. Every foot of chain in the rode adds a pound to the weight of the rode, so you would have to be very strong and very confident to be hauling 20lb anchor plus 20lb+ rode when a Fortress FX-11 can shave about 12lbs off of that. They only set you back another $60 from a traditional steel fluke; it's really a no-brainer to make this choice.

You can also get the advantage of weight reduction with the aluminum version of the Spade ("plough-type") anchor, which for our size boat is 18lbs, but will set you back $475. If you're anchoring in conditions in the Pacific Northwest why not invest in the best ground tackle combination you can get for our boats--Fortress and Spade? And get all the advantages of weight reduction that come with them.

Rich Kokoska

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 06/25/2004 : 19:51:36

Ever try setting a lightweight Fortress in 4+ kts of current?
Hope you have better luck than I did.

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 06/25/2004 : 20:39:41

Most of us like anchors that sink, and stay sunk, aluminum is three times the density of water and steel is 9 times as dense as water. Aluminum requires twice (approximately ) the thickness to be as strong as steel. Those two factors make aluminum anchors better in theory than in practice. In fact CQR anchors(forged and cast steel) use lead (12 times denser than water) to add to their submerged weight. The problem has always been to get enough weight consentrated in one spot to reliably dig into the bottom. I've heard the sermon from any number of anchorers about Fortress etc. but my boat stays on steel. Dave

Edited by - on

Raskal
Navigator

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USA
162 Posts

Response Posted - 06/26/2004 : 09:34:07

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Aluminum requires twice (approximately ) the thickness to be as strong as steel<hr height="1" noshade id="quote"></blockquote id="quote">

Sorry Dave, you're simply wrong on this one. I'll let Fortress do the talking from their web site (http://www.fortressanchors.com/myths_and_facts.html):

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Many materials are now stronger than steel. For example, high-tensile aluminum-magnesium alloy is well suited for anchors and is, pound-for-pound, more than twice as strong as steel.
<hr height="1" noshade id="quote"></blockquote id="quote">

Weight is not the only factor in getting an anchor to set--after all, a Fortress can be the same weight as a Danforth but will be larger! Angle of pull, angle of flukes, sharpness of flukes, shape of flukes, weight of rode, etc., all come into play, which is why there are so many anchor types out there.

Everyone who's interested in the subject of anchors should familiarize themselves with the Practical Sailor anchor tests which have been published on the web at different places. (http://www.noteco.com/bulwagga/multimedia/practical_sail_pdf_Jan_01.pdf). The superlight Fortress and Spade anchors performed as well or better than other types, but always without the extra weight.

If anchoring in a strong current is the issue, then the problem may be choosing to use a fluke anchor rather than a plow anchor. It may be that any type of Danforth, light or heavy, will not be as good a choice as some type of plow with a dense head.

Now, shall we adjourn this eternal debate until next month when someone asks the question all over again?

Rich K.

Edited by - on

oldsalt
Admiral

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USA
578 Posts

Response Posted - 06/26/2004 : 14:18:27

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Dave Laux
 Most of us like anchors that sink, and stay sunk, aluminum is three times the density of water and steel is 9 times as dense as water. Aluminum requires twice (approximately ) the thickness to be as strong as steel. Those two factors make aluminum anchors better in theory than in practice. In fact CQR anchors(forged and cast steel) use lead (12 times denser than water) to add to their submerged weight. The problem has always been to get enough weight consentrated in one spot to reliably dig into the bottom. I've heard the sermon from any number of anchorers about Fortress etc. but my boat stays on steel. Dave
<hr height="1" noshade id="quote"></blockquote id="quote">

Dave we've been through this in the past time and time agian and I couldn't agree with you more. Aluminum Fortress anchors may do well under controlled test conditions, but setting them in a current and/or deep water is a real beast of a job since they like to sail through the water and skip merrily across the bottm under the kind of conditions when you really need your anchor most. In my opinion, one shouldn't confuse the advertised ultimate holding power of an anchor with its real world ability to find the bottom quickly and bury itself in, and that's where Fortresses fall short.

Not withstanding the information provided by Fortress on their website, my boat as well, is anchored on steel.

Edited by - oldsalt on 06/26/2004 14:25:32

Gary B.
Admiral

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USA
969 Posts

Response Posted - 06/26/2004 : 20:28:10

This thread is starting to sound nasty to me.

I think one needs to expect that some questions will come up often. In my experience, it's just a few of us (relatively) that keep these boats for a long time. Many C25s and 250s are kept for a few years and used as stepping stones as folks work up to the 30' +. As long as the turnover in owners is large, so will be the number of new members and owners, each asking questions and not realizing that most have been dealt with before.

I think referring to the "eternal debate once a month" comments serve mostly to make people feel stupid and afraid to ask another question for fear of a "gee, we've answered that before" type answer. If a guy can't be helpful, let the question be answered by those who are willing to be.

I don't know how many times people have asked about auxiliaries. I often chime in with my experience, realizing that many have seen it before, but the member asking the question doesn't know that. Referring to an older thread and providing the URL is often a good response.

But, hey, I don't know how I missed it, but I have seen relatively little on anchors on this forum in the last couple of years.......and I think it's a good question. Problem is....like outboards...too many good answers, each can be best depending upon conditions.....

Gary B.
Vice Commodore
s/v Encore! SK/SR #685

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 06/26/2004 : 20:38:23

Hi Mark, isn't it interesting that people who do not even understand what they are talking about will try to convince you that you are wrong. I mean I have been a Marine Engineer, Naval Architect, Boat Builder, Marine Surveyor, and general boat mess about person with about 50,000 sea miles behind me. Does this get any consideration? No, not much. Rich thinks that I, who have designed and built about 40 aluminum boats, have missed the point and do not understand how steel and aluminum compare. I don't disagree that aluminum can be stronger per lb than steel. I know it is. However its still twice as thick (approximately) and thick flukes do not penentrate the bottom as well as thin ones. This BTW is an advantage, say in hull plating, cause thicker sections are more ridgid than thin ones, but its a distinct disadvantage in anchor flukes. In any case the anchors I use, a 13 lb Danforth and a 14 lb Quickset CQR, do not strain my ability to pull them up. Even with 30 ft of 1/4 chain added on.
Right now, I mean yesterday, I finished rebuilding the structure of a pair of wooden spars that I engineered back in 1985 for an aluminum sailboat that I built. They are 55 feet long and about 9 inches in diameter at the partners. One of these will lay this 27,000 lb boat on its beam ends if caught in a squall in the Straits of Florida with no standing rigging whatever(BTDT).
I really do understand engineering highly loaded structures and I'm not guessing or referencing a manufacturers web site to make my point. I could even, easily, make you an anchor of GRP and foam that would be several times as strong as an aluminum or steel anchor of the same weight and would float. Wouldn't that reduce the strain of lifting the anchor?
Still on steel for anchors. Gold would be better, dense with good mechanical properties and corrosion resistance. But how would you feel if you lost one. Dave

Edited by - on

ronrryan
Admiral

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USA
561 Posts

Response Posted - 06/26/2004 : 20:55:38

I think the main issue with the specific situation you described is that the water is pretty deep for normal factors of scope, whether 5,6,7:1 or whatever. The bis issue with scope is to get the right angle of pull relative to the bottom and the shank angle of the anchor, and your situation would probably be helped by the use of a "kellet" or "rode rider" that would put weight partway down the anchor line and flatten the angle of pull. There are commercial models of these and you can also make your own by casting lead in a coffee can with a steel fitting in the lead can as it cures, or even by sliding a dinghy mushoom anchor down. I have known fellows who anchored in deep water to fish on the bottom, and sometimes they would use an anchor line to the anchor, then a piece of chain, then another anchor line to the boat. The chain in the middle changed the angle of strain down at the anchor. God bless, ron srsk Orion SW FL

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 06/26/2004 : 21:21:40

Another factor in deep water anchoring on the West Coast is that in general the bottom is slopeing. Thats because its deeper some where near. The direction that you are pulling on the anchor makes a big diference. I, unfortunately,(I would love to go there) have not spent any time on the West Coast but I understand that this is a big problem that is often solved by taking a line ashore. If the bottom is slopeing moderately (1 in 3 say), and you have an anchor out with normal scope, and the wind is off shore, you are not anchored at all. In the same situation if the wind is on shore you are anchored firmly. Dave

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