Anchor chain, 8mm or 10mm?
Tony of Judicious
presently 8mm The question is: a 60m length of 8mm or a shorter (45-50m)
of 10mm. 60m of 10mm chain will not fit into the chain locker.
10mm is about 50% heavier per m than 8mm.
About once a year, in extremis, I have had all the 60m out. Usually anchor
in <10m, so depth is not the issue.
My gut feeling is that the shorter length of heavier chain would be
adequate, but I start to get a headache where hyperbolic functions get
involved.
(BTW, if Craig, of Rocna, is lurking out there, be sure to comment.)
Richard
The nylon will be forming the near vertical part of the catenary anyway
It has the benefit of :-
1. a quieter night
2. a softer "ride"
3. Less weight to pull up
4. Less weight on the boat
5. Most importantly - Nylon won't scuff up your hull as you rub against it.
So, for up to a 5 tonne boat I'd go for 8mm then nylon
for over that weight I'd use 10mm then nylon.
This all assumes your windlass is happy with winching nylon.
If anchoring every night for an extended period then maybe all chain and a
nylon snubber.
Richard
"Tony of Judicious" <to...@deletethis.thoward.me.uk> wrote in message
news:h3k6h7$9ns$1...@news.albasani.net...
Ronald Raygun
> As I'm fitting an electric windlass to J this winter I will need new
> chiain, presently 8mm
Is there a particular reason why the existing chain is unsuitable?
Is it too worn, and has it therefore drifted out of calibration, or
has it always been uncalibrated?
If you're getting rid of it anyway, then I would not replace it
with new 8mm but go for 10mm instead, because I think that's the
more appropriate grade for your size of boat.
But if your old chain is basically OK and its calibration is
compatible with the windlass 8mm gipsy, I'd keep it. Then, at a
future date, when replacing the chain I'd move to 10mm, and it
should be possible to change to a 10mm gipsy without having to
replace the whole windlass.
> The question is: a 60m length of 8mm or a shorter (45-50m)
> of 10mm. 60m of 10mm chain will not fit into the chain locker.
I don't know what your locker arrangement is, i.e. whether at
present you have a big open locker and you just bung the chain
into it by hand as you raise the anchor, or whether it's already
fed in through a small pipe. The thing to watch out for is that
once you start feeding the chain down a pipe at a steady rate from
your electric winch, it might tend to heap up in the locker and
block the pipe. This problem will tend to become more severe the
fuller the locker gets.
> 10mm is about 50% heavier per m than 8mm.
>
> About once a year, in extremis, I have had all the 60m out. Usually
> anchor in <10m, so depth is not the issue.
>
> My gut feeling is that the shorter length of heavier chain would be
> adequate, but I start to get a headache where hyperbolic functions get
> involved.
Your gut feeling is right.
My calculation indicates that you can match the performance of 60m of
8mm chain with 50m of 10mm chain, but 45m won't be enough.
Details of calculation available on request. :-)
There is a caveat, though. This performance matching applies only up
to the point where the chain still meets the anchor horizontally. If
you increase the horizontal pull further, so that the anchor angle
goes positive, the 50m of 10mm will make a bigger angle than the 60m
of 8mm. But you'd expect that anyway, because as the chain gets more
and more straight, the catenary will approach a straight line, and so
being shorter it has to make a bigger angle.
You can compensate for this by making it longer, but if you really need
more than 50m, you might as well start adding nylon instead of more chain.
Keith
<to...@deletethis.thoward.me.uk> writes
An interesting question, Tony.
Based on your premise that 10mm is 50% heavier than 8mm I'd go for the
10mm if you can get more than 40m in your locker.
And the idea of adding 10m of nylon warp is no bad thing, even if the
electric winch won't handle it. You can always haul it up the old way,
then engage. In a serious blow that extra 10m is not something you want
to be worried about...
You'll be needing some Ankatags.... :)
--
Keith replace nospam with ilf0rd
Mark
I just did a quick web search and found this:
http://www.ankatags.co.uk
Has anybody tried these? Are they any better than putting cable ties/
paint/wool at intervals?
Ronald Raygun
> I prefer shorter chain spliced to nylon
Ah, but the question is how much shorter.
> The nylon will be forming the near vertical part of the catenary anyway
True, but in a hefty blow it won't be near vertical, it'll simply take
the same slope as the steepest part of the catenary, which in extreme
conditions won't be particularly steep.
> It has the benefit of :-
> 1. a quieter night
Yes, but that is a mixed blessing. When the anchor drags, you won't
hear it.
> 2. a softer "ride"
True, and by thus minimising shock loads it can contribute towards
making it less likely to break the anchor out, causing it to drag.
But the cushioning effect of stretchy nylon won't help much unless
you deploy a fair amount of it. I'd prefer not to put out more rope
than there is depth unless it's likely it will always be under enough
tension for none of it to touch bottom, if there is jagged stuff
down there which could wear the rope.
> 3. Less weight to pull up
Not really. OK, in a flat calm it's less work because while you're
lifting rope, the weight is virtually zero, but once you have all
the rope aboard, you're still lifting the same weight of chain, you're
merely pulling up less of it.
But if you're lifting the anchor against wind or current, single
handedly with no crew to assist you in balancing the engine against
it, the weight becomes less significant as you're working against
something more than just the weight.
> 4. Less weight on the boat
We're talking about maybe 100kg of chain. That's hardly going to
make an awfully significant difference to a 5t boat. Or are you a
racing man?
> 5. Most importantly - Nylon won't scuff up your hull as you rub against
> it.
Not a big problem I would think, unless you have one of those vertical
bows.
> So, for up to a 5 tonne boat I'd go for 8mm then nylon
> for over that weight I'd use 10mm then nylon.
Fair enough, but how much chain would you go for? I'd recommend
20m as an absolute minimum, and would feel happier with 40 or 50.
> This all assumes your windlass is happy with winching nylon.
Most decent windlasses do have a rope gipsy as well, and it should
be OK even though I guess it will probably need to be tailed by
hand, the electrics just supplying any oomph which might be needed.
There again, unless fighting a wind or tide, one could probably
wheech up all the rope by hand without overexerting oneself, and
then plonk the first bit of chain onto the chain gipsy.
> If anchoring every night for an extended period then maybe all chain and a
> nylon snubber.
Quite. I think you'll find that the cruising area Tony frequents is
such that one does have to anchor nearly every night, moorings being
few and far between, and pontoons even more so.
Ronald Raygun
They *are* cable ties.
Keith
<3735384b-4f54-4ff8...@o7g2000yqb.googlegroups.com>, Mark
<MarkH...@gmail.com> writes
Err... no.
Craig Smith
anchor performance when selecting chain, when it really has nothing to
do with it.
You should select the size of the chain based primarily on strength
requirements. If 8mm G40 doesn't meet the standard, then consider
either G70 8mm (preferably) or the 10mm G40.
Thereafter, the required length again has more to do with practical
elements such as the cruising environment (typical depths and
proclivity of rock/reef/coral) and your preferences with regard to
deck handling (chain/rope transitions on the windlass etc).
These two factors are unrelated and it is not a case of "short and
heavy" vs "long and light".
An aside: extra weight is always undesirable, and if you are prepared
to carry it in the first place it would provide much more benefit in
the form of a larger anchor. Chain weight should always be minimized
subject to the above requirements.
The above comments are brief summaries of an in-depth topic. More at
these articles:
http://www.rocna.com/kb/Rode_optimizations
http://www.rocna.com/kb/Chain
http://www.petersmith.net.nz/boat-anchors/catenary.php
- Craig
On Jul 15, 9:12 pm, Tony of Judicious <t...@deletethis.thoward.me.uk>
wrote:
Tony of Judicious
Thanks Craig, on balance, it looks as if I would be best with the longer
length. I am unhappy at using warp on the main anchor.
BTW, I find with my brakin g out my15Kg Rocna, even with the chain vertical,
it is very difficult to break out from 'good' mud. More often than not it
needs a bit of winching up.