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Thread: Chum

  1. #61
    Join Date
    Oct 2004
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    I know how fast I'm going, but not where I am
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    Default Re: Chum

    Quote Originally Posted by lw395 View Post
    There is drag and there is inertia.

    It takes more force to start moving a paddle through the water than to keep it moving at a steady speed.
    That extra force is due to the inertia of the water.
    Once the paddle is moving so is the water to some extent so the relative velocity between the water & the paddle is reduced, the u squared term in the drag equation decreases & hence the force decreases.

    I still suggest that the hydrodynamic drag of a chum is trivial with my (admittedly simple) analysis & you have not countered it with anything convincing other than dubious use of the term inertia.

  2. #62
    Join Date
    May 2007
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    38,210

    Default Re: Chum

    Bumblebees can't fly because simple models say so.

    I'm starting from the point of having observed an effect and looking for the best explanation.
    You're starting from a point of wanting to rubbish simple explanations that go some way to explaining what is observed, without doing any observations of your own, or offering better explanations.
    I'm only bothering with the discussion because I'm open to better explanations.

    I'm quite happy with the observed effect.
    The observed fact, from my point of view is that 10kg of lead 10m down the rode alters the behaviour of a boat at anchor in several circumstances, often in a way that I judge to be beneficial.
    There is no point denying the observation just because neither of us can analyse it adequately.

  3. #63
    Join Date
    Dec 2013
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    Deale, MD, USA
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    1,789

    Default Re: Chum

    Quote Originally Posted by lw395 View Post
    Can you show me the maths of my boat yawing at anchor in Whitsand bay?
    I don't have the maths of the problem, let alone the solution.

    I do have a lead brick that helps.
    I have done a good number of yawing tests. If the yawing rate excedes 1.5 knots, something is VERY wrong that a chum will not solve (several minutes for a swing). So starting with 2 feet per second, the viscous drag of a chum through water is a fraction of an ounce.

    D = (1/2)(C)(ρ)(v2)(A).

    I have also experimented with much larger objects (drogues and weighted fenders) and found that unless the boat is dancing in a ridiculous manner, they do very, very little. There are other solutions that work.

    That said, I do find a kellet useful with rope rode in light winds, to make my boat swing like boats on chain. This is because the kellet is dragging on the bottom, like chain. In my case the kellet is a loop of chain (I like that I can just recover it over the roller), so it drags a great deal like chain.

    I find that calculation and observation generally match very, very well. When they don't that means the calculation has missed a factor and the model must be refined. No magic. But some times it is easier to just measure the thing and report the findings, which I have also done. In this case, observation shows that a kellet helps on rope, until the wind is strong enough to consistently lift it off the bottom, after which it does much less, something equivalent to 10-30 feet of chain as catenary. This is because the calculations changes at that point. If the kellet is still on the bottom, that means it is either very, very heavy and/or the wind is not really blowing yet.

    To really reduce yawing requires changing the aerodynamic balance of the boat.

    (Note the boat in my avitar uses all chain. I have another, lighter boat that uses rope.)
    Last edited by thinwater; 07-06-19 at 12:43.

  4. #64
    Join Date
    Nov 2011
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    Sydney, Australia.
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    Default Re: Chum

    I note that some use chums/angels or kellets to advantage, or say they find them useful - call it advantageous.

    I wonder what prompted the use, in the first place - what manifestation demanded a solution. They are an extra bit of kit, they can be a bit fiddly to deploy - so what makes them worth the effort

    Did the anchor drag? is the yacht simply more stable, how is the device used (suspended or on the bottom). How has the success of the chum been defined etc.

    I'm not doubting the effectiveness claimed - just looking for education.

    Jonathan

  5. #65
    Join Date
    Sep 2010
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    West Sussex / Hants
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    28,771

    Default Re: Chum

    Neeves,

    in my case I've not had the anchor drag, I use the angel as prevention rather than cure...

    As I mentioned earlier, rather than carry a lump weight around I have a 7kg folding grapnel kedge - which might be handy in an emergency on weed covered rocks where one wouldn't normally choose to anchor.

    In normal ' Angel ' use it makes a smooth shape when folded, I tie it with a short sail tie - say 12" doubled - in a loop around the main bower warp attached to a long berthing line, lowered to about halfway down the main bower warp.

    This gives a lot lower, more benefial angle of pull on the anchor, Ive been in gales and seen the benefit of this.

    NB I have 3 metres of heavy 1/4" chain on the anchor to avoid chafe on shells, rocks etc then 30 metres of 14mm nylon warp but just set the recommended 6X maximum depth, with fishfinder alarms set to shallow - 6' in case of grounding, and deep say 40' in case of dragging the anchor depending on where.
    Anderson 22 Owners Association - For info please ask here or PM me.

  6. #66
    Join Date
    May 2007
    Posts
    38,210

    Default Re: Chum

    Quote Originally Posted by Neeves View Post
    I note that some use chums/angels or kellets to advantage, or say they find them useful - call it advantageous.

    I wonder what prompted the use, in the first place - what manifestation demanded a solution. They are an extra bit of kit, they can be a bit fiddly to deploy - so what makes them worth the effort

    Did the anchor drag? is the yacht simply more stable, how is the device used (suspended or on the bottom). How has the success of the chum been defined etc.

    I'm not doubting the effectiveness claimed - just looking for education.

    Jonathan
    In my case, I've owned a couple of boats with minimal chain. The first one had a lot of floating rope spiced to the anchor chain when I got it. So the first use of a weight was after a couple of fiascos involving rope around the keel.
    Later trying to share crowded anchorages where other boats seemed to have all chain.
    Since we have the handy weight, I've tried it a few times when the boat has been unsteady at anchor.
    Never owned a boat with a windlass, so chain is not my preference.

    I just tie the weight to the rode with some multiple rolling hitch effort.
    I don't like the tangle potential of additional lines.

  7. #67
    Join Date
    Nov 2016
    Posts
    2,620

    Default Re: Chum

    Quote Originally Posted by lw395 View Post
    .....trying to share crowded anchorages where other boats seemed to have all chain. I just tie the weight to the rode with some multiple rolling hitch effort. I don't like the tangle potential of additional lines.
    Some chain - some warp. That's my preference. And a length of line, a small snaplink and a buoyant fisherman's net float, for occasional use where snagging is a possibility.

    Then there's the warm-water trick of tying on some of those net floats along the rope rode, to lift it up above the sharp coral heads - but that's not a technique I'm likely to need any time soon!

  8. #68
    Join Date
    Nov 2011
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    Sydney, Australia.
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    5,487

    Default Re: Chum

    Seajet - I like your concept, caution rather than necessity. It is so much easier to be secure with a belt and braces technique than get up at 2am in the rain!

    I did make an angel from roofing lead. I simply melted it in a large rumbaba tin (blow torch and camping stove) leave to solidify. Make another and then fused the two halves together, flat to flat, more blow torch work. This gave a nice lead weight with a hole big enough to run chain through.

    However I found it too fiddly to use, need to thread onto the chain rode, lower with rope, ensure rope does not twist round rode - remember to lift before retrieval of rode.

    I found the angle worked best on the seabed and I then drilled holes in the lead, tapped the holes and fitted galvanised bolts into the holes (epoxy), so they extended about 50mm, it looked then like a hedgehog or large sea urchin. The bolts made its drag on the seabed more effective.

    It now sits forlorn in my workshop - I find deploying a second anchor more sensible (when we feel the need for extra caution). I don't like single use items, especially if they are heavy, and as we carry spare anchors - seems sensible (to me).

    We do carry a little grapnel - useful when you lose your rode!

    Floating lines are a real hazard. They either need decent floats (with lights) or be weighted. It can be polite to ask people already in a tight anchorage how much rode they have deployed - they then come close enough to talk to ... floating lines can be a hazard.

    Jonathan

  9. #69
    Join Date
    Sep 2001
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    Me - Zumerzet Boat - Wareham
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    12,284

    Default Re: Chum

    I have learned something from this thread, for my 15kg lead Chum to be more effective I need to add an umbrella to it
    I'm sure I will be corrected if wrong.
    Someone said why carry extra weight when you could use a spare anchor. My answer is that I might want to deploy that anchor, and as it will be on mainly rope rode, I will need to put the Chum on it.
    MontyMariner.co.uk
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  10. #70
    Join Date
    Nov 2011
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    Sydney, Australia.
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    Default Re: Chum

    Quote Originally Posted by LadyInBed View Post
    I have learned something from this thread, for my 15kg lead Chum to be more effective I need to add an umbrella to it
    I'm sure I will be corrected if wrong.
    Someone said why carry extra weight when you could use a spare anchor. My answer is that I might want to deploy that anchor, and as it will be on mainly rope rode, I will need to put the Chum on it.
    You cary only one spare anchor?

    Jonathan

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