Lakesailor wrote:
Just wondered what type of rode would handle this force? On your site, you
recommend the 10Kg anchor for cruising boats up to about 30'. What would
teh corresponding chain/rode dimensions be to match teh anchor strength?

Up to 33', at light displacement. Our sizing is conservative; in practice,
even a boat of that size will need up around 70 knots of wind to generate
something like a tonne of force. Wave action etc adds to the equation but if
you restrict the model to considering only wind, you can see how we are
talking about "extremes"; most boats, especially of that size, are not set up
to handle those conditions. Accordingly you can't really expect the rode to
be strong enough - and what about whatever the rode's attached to?

Anyway, you would normally use 6mm chain with a Rocna 10, 8mm if you wanted.

G40:
6mm - SWL: 350Kg, break 1000Kg
8mm - SWL: 800Kg, break 3200Kg

so you would use the 8mm, or a high tensile grade of the 6mm, if you needed
the strength. Rope matched to chain is usually stronger, so that's not an
issue.

2. The web site does not give the size of the attachment slot for the
shackle. Can you fit a shackle that will take a 1 tonne working load through
the slot?

Shackles: use the largest size the pin of which will fit through the last
link of chain. So the chain dictates the size used, and the slot on the
Rocna's shank is ample. A quality tested 8mm shackle for 6mm chain or 9/10mm
for 8mm should not introduce a weak-point.

The Rocna anchor looks quite interesting and seems to be a good idea, at
least for some anchoring conditions.

For all anchoring conditions, that's the point

1. Testing by pulling with a truck with little or no scope angle does not
really prove anything ( but is easier to film!)

It levels the playing field as I said above. The guy going on about shanks
etc and scope affecting setting behavior is wrong and also missing the point.

If you set your anchor using the relatively weak power of a sailboat's engine
and prop, if you're using decent rode then the actual angle of pull you're
placing on the anchor during setting is not the same as the scope; i.e. if
you have out 5:1, the angle is not dictated by that trigonometry, but rather
the catenary of the chain, which will make the pull surprisingly flat - it
may even be horizontal, with part of the chain remaining on the bottom.

Does not apply to powerboats with 1,000 HP using two meters of chain and a
bit of string.

- Would it not be better to do a comparison of the anchors with a larger
scope angle and typical rode/chain combinations. This may take a lot of
testing using a boat, a diver, undewater cameras etc, but as you said "Get
to the bottom of the theory, do your own research, get some experience, and
make your own decisions". Seems to me that pulling an anchor along a beach
with a truck is not the best way to make a scientific conclusion.

Yes, it would be better, but our video is supposed to be a simple
demonstration of why the traditional plows and claws are bad, and simply why
we've bothered coming up with the Rocna.

A "proper" video would be an hour long and would still be hurt by the fact
that we are not independent, so the validity of such a production would
always be vunerable. So, we're not really the people to do it - although I
would like to at least re-do our existing one at some point, to address some
of its problems.

- What happens if the bottom is soft mud or weed as we often see in the
Great Lakes - Will the roll bar still work, or will it just sink in and not
roll? I would like to have seen some comparisons of anchors setting in less
ideal conditions.

No it works fine, the roll-bar's radius is quite large for exactly that
reason.

Weed and grass are difficult for any anchor. It's also pointless testing or
doing demonstrations, because every patch of weed is different to the next.
The cynical viewer could claim we just did the test over and over again
before it happened to work.

The important factors are a certain amount of tip-weight, a low profile fluke
with sharp edges, and dynamics that encourage force from the rode's pull to
be transfered to the anchor's tip, so it cuts in. So the Rocna meets this
requirement, and is a further improvement on the WASI or German Buegel, which
is very popular now in the Mediterranean (weed city).

- The part showing the difficulty of getting the anchor unstuck is not too
encouraging for those of us with bad backs

Well that was after over a tonne of force was applied to it - most of the
time you'll never get it that stuck, and if you do, you probably won't mind a
bad back as payment

Although, it's not really a problem. Reduce the scope to 1:1 and leave it for
a few mins, and wave action will work it out. Or if you're in a hurry power
it out backward.


In our area, most boats seem to have a Bruce or knockoff - But, more
recently we see Delta or knockoffs. Nothing really works well in weed and
soft mud but weight helps. The knockoff Bruces are a cheap way of getting
weight, so I suspect that might be the driving force. In fact, I have just
added a 15Kg Bruce type because my 10Kg Delta just does not work that well
(10M, 5T cruising sail).

GBM

Deltas are generally good, except in soft mud. They simply don't have the
fluke area. Peter used to have a 40Kg Delta on his boat, and incidents in
soft stuff were one of the main reasons for designing the Rocna - and he had
already eliminated other types over the course of his lifetime, selecting the
Delta as the then best option.

I am sure that a 15Kg Delta would have offered a similar if not better
upgrade in your case. Understand your point about cheap weight, but you get
what you pay for.

But the simple solution is try a newer type - you don't have to put up with
those problems any more. Bulwagga, WASI, Rocna.

--
Craig Smith
Rocna Anchors
www.rocna.com

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