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  1. #51
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    Aug 2013
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    Default Re: Deliberately starting an anchor thread.

    Quote Originally Posted by Zing View Post
    I’m oversized too. It’s a total no-brainer.
    I wonder if the anchor companies have realised this and reduced their recommended sizes?
    "Seamen are always wanting to do things the proper way; and I like to do them my way."

  2. #52
    Join Date
    Jul 2008
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    East coast UK. Mostly. Sometimes the Philippines
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    Default Re: Deliberately starting an anchor thread.

    I thought it would be interesting to post Claud Worth’s recommendations - we may usefully keep in mind that these are for anchors used by sailing cruising yachts which either had no engine or which had a very small engine and seldom used it. Basically everyone anchored under sail and got their anchor under sail. Worth goes on to say that some people have hydraulic (reliable) and electric ( less so!) windlasses but that these are not necessary or helpful in a boat of less than sixty tons!

    Hiscock says that a CQR may be half the weight of a fisherman type so long as it’s at least 30 lbs.

  3. #53
    Join Date
    Nov 2007
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    Boat Orwell - Me Norwich
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    7,894

    Default Re: Deliberately starting an anchor thread.

    Quote Originally Posted by Neeves View Post
    Bizarre!

    Claud suggests a 45lb, for a 7t vessel
    Note that's 7 tons Thames Measurement, not displacement.

  4. #54
    Join Date
    Nov 2011
    Location
    Sydney, Australia.
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    5,277

    Default Re: Deliberately starting an anchor thread.

    Quote Originally Posted by GHA View Post
    I've a 20Kg rocna which was near flawless for years though now a size up 25kg spade as well. Both just work. Other than a few quid no downside to having a bit bigger as one of the options.
    Dear Sir,

    The perfect opportunity for you.

    Your 20kg Rocna was 'near flawless' (and to me anchors work or they drag (with nothing in between) - so why was your 20kg anchor, flawed, slightly or largely - what prompted you to 'up-size' (to a 25kg Spade- as you would not detect the difference in hold (unless you use a load cell every time(like the Knox Anchorwatch) with a 5kg difference in anchor weight. It would be useful to know yacht characteristics and the conditions under which it was not flawless.

    The information may well support your contention that a marginal increase in weight is beneficial - without some background - we are left to guess. It would also be useful if you define why - if the 20kg Rocna was almost flawless why you then chose (a more expensive, per kg, Spade) instead of a 25kg Rocna. It seem odd to reject a 'almost flawless' design, because it was, apparently too small - and then buy a totally different design.

    One is left with the nagging suspicion you are not quite comparing apples with apples and if this is your basis for suggesting 'bigger is better' - it is valuable we have a better understanding of your decision process.

    My understanding is you carry both anchors? and presumably use the 25kg Spade as your bower? with the almost flawless model, 20kg Rocna, kept as a spare (or to anchor in a 'V'?)

    Jonathan
    Last edited by Neeves; 08-08-19 at 02:49.

  5. #55
    Join Date
    Jul 2008
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    East coast UK. Mostly. Sometimes the Philippines
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    9,393

    Default Re: Deliberately starting an anchor thread.

    Quote Originally Posted by LittleSister View Post
    Note that's 7 tons Thames Measurement, not displacement.
    Elsewhere in the chapter, he writes that Thames measurement, rather than displacement, is the best measure to use in determining the size of ground tackle, because a heavy displacement boat with short ends will lie quiet whilst a light displacement boat with long ends will sheer about.

  6. #56
    Join Date
    Feb 2014
    Location
    The Northern Powerhouse
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    2,739

    Default Re: Deliberately starting an anchor thread.

    Quote Originally Posted by JumbleDuck View Post
    I wonder if the anchor companies have realised this and reduced their recommended sizes?
    Recommended size is not a mathematical, incontrovertibly precise calculation. Safety factors and assumptions are a part of it and I choose bigger safety factors and more conservative assumptions. Don’t worry though. I won’t say you were complacent when I pull you off the reef when you drag.
    Last edited by Zing; 08-08-19 at 08:31.

  7. #57
    Join Date
    Jul 2005
    Posts
    3,287

    Default Re: Deliberately starting an anchor thread.

    I think the best advice for a cruising boat is to fit the largest anchor the boat and crew can comfortably manage. There are exceptions where this rule does not work, but it is at least a great starting point.

    Anchor tables are worth consulting, but there are lots of anomalies. If you follow these, unfortunately you would select in most cases a much smaller Delta or Kobra anchor than when using the manufacturers’ tables for much higher performing anchors, which is obviously wrong.

    If you can comfortably manage a larger anchor you will not have “wasted” your money, rather you will have an anchor that will have a higher maximum holding ability, greater security in substrates with lower holding, and greater security if forced to use a shorter scope than would be desirable for the circumstances. These are all valuable properties.

    The above is sometimes disputed, but is really just common sense. A larger anchor has higher maximium holding ability than a smaller anchor (assuming the same design and material). Poorer substrates will produce a lower maximum holding ability, as will reducing the scope (an anchor’s maximium holding ability is not reached until a scope of 10:1 or higher). Thus a larger anchor may have the same maximum holding ability in a poorer substrate or at shorter scope, as a smaller anchor.

    If you go significantly smaller than these recommended sizes, you will have to accept some compromises. Some of these are reguarly mentioned such as needing to deploy two anchors to increase the available holding in winds above 30 knots, or never anchoring overnight at less than 5:1. If I was using an aluminium Spade A80 (this anchor is recommended for a multihull less than 25 feet and less than 2 tons displacement) on a 38 foot catamaran with a 7 ton displacement, I would take the same type of precautions (in fact I would even be a little more conservative).

    The approach of using very small anchors is not always a cheaper option. You will need to carry multiple anchors for different substrates, and if regularly deploying two anchors, more spare anchors will be needed to provide a back up.
    I am not even sure there is an overall weight saving carrying two small anchors (plus spares) to substitute one larger anchor (plus spare), especially when the extra rodes are considered. The weight of two smaller anchors can be distributed better, but many boats only have practical storage for a second anchor in outside lockers that are near the ends of the boat so the differences are not great.

    I would not suggest people follow my example either. My 68 kg anchor would not fit the definition of “comfortable to manage” on most 50 foot boats. I have been fortunate to be able to equip this boat with a large anchor winch and sturdy bow roller assembly. Storing the chain significantly back from the bow means that a very large anchor can be carried with less overall bow weight than would typical for a yacht this size.

    However, many cruisers select an anchor that is slightly oversized to provide the benefits I have suggested in the third paragraph. Providing this fits within the definition of “comfortably manageable” I think this entirely sensible.

    The benefits of even a small increase, for example from 20 to 25 kg, has been dismissed as negligible, but studies have shown (Professor Knox’s for example) that this change equates to a 25% increase in the anchor’s maximum holding ability (assuming the same design and material). Even the pessimistic data would suggest a around a 20% increase in the anchor’s maximum holding ability. In my view, this is a very worthwhile gain for only an extra 5 kg, but this is a decision that every boat owner must make for themselves.

    Anyway just my view. I think it is important to offer a counterpoint to the frequent posts suggesting small anchors have no drawbacks or even by some magical properties provide better holding than larger models.

  8. #58
    Join Date
    Nov 2011
    Location
    Sydney, Australia.
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    5,277

    Default Re: Deliberately starting an anchor thread.

    [QUOTE=noelex;6868535]

    The benefits of even a small increase, for example from 20 to 25 kg, has been dismissed as negligible, but studies have shown (Professor Knox’s for example) that this change equates to a 25% increase in the anchor’s maximum holding ability (assuming the same design and material). Even the pessimistic data would suggest a around a 20% increase in the anchor’s maximum holding ability. In my view, this is a very worthwhile gain for only an extra 5 kg, but this is a decision that every boat owner must make for themselves.


    /QUOTE]

    You do like to ignore what has been said. You also love to repeat your mantra with not an iota of substantiation - excluding your common sense.

    John Knox used different rodes when he conducted some of his tests that formed the basis of the information you quote, from memory, wire, polyester and nylon. You cannot compare hold using different rodes.

    John defined each rode in each of his experiments - you have the links - read the article carefully - as has been mentioned to you a number of times. Nothing gets more correct by constant repetition

    But if you have any evidence for your comments, other than common sense, many of us, including GHA who likes a technical basis, would welcome the certainty.

    Until then its all just fluff - constantly repeated based only on that common sense.

    Jonathan
    Last edited by Neeves; 08-08-19 at 09:51.

  9. #59
    Join Date
    Aug 2013
    Location
    SW Scotland
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    19,408

    Default Re: Deliberately starting an anchor thread.

    Quote Originally Posted by Zing View Post
    Recommended size is not a mathematical, incontrovertibly precise calculation. Safety factors and assumptions are a part of it and I choose bigger safety factors and more conservative assumptions. Don’t worry though. I won’t say you were complacent when I pull you off the reef when you drag.
    How many sizes above recommended did you go? Why not more?
    "Seamen are always wanting to do things the proper way; and I like to do them my way."

  10. #60
    Join Date
    Feb 2014
    Location
    The Northern Powerhouse
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    2,739

    Default Re: Deliberately starting an anchor thread.

    Quote Originally Posted by JumbleDuck View Post
    How many sizes above recommended did you go? Why not more?
    1 size. It nearly doubled my safety factor. Two sizes wound nearly quadruple it. More would be better, but I have I feel enough and the next size is too heavy.

    As to recommenced sizing, I do not believe the Lewmar CQR sizing is correct or comparable to others. And you are wrong to think it can be relied on in my view. There is no standard or openness in respect of how calculation are done. The sizing by Rocna and others has a greater safety factor built in already as evidenced by their greater performance on a like for like recommended size.

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