On Fri, 02 Nov 2007 11:11:59 -0500, Geoff Schultz
wrote:
Bruce in Bangkok wrote in
:
On Fri, 02 Nov 2007 05:50:42 -0500, Geoff Schultz
wrote:
Bruce in Bangkok wrote in
:
Something I have always wondered about is that everyone talks about
anchors but nobody seems to talk about the anchor rode.
For example, 3/8" Grade 30 BBB galvanized chain has a working
strength
of 2,650 Lbs., 25% of its breaking strength of 10,600 Lbs. 5/8th
inch
double braid nylon rope has a tensile strength of 15,000 Lbs. and if
we go to Kevlar core double braid we are talking 22,000 Lbs.
Yes, I know - catenary..... but Alain Hylas (Inventor of the 'Spade'
anchor) say the opposite. He says that once the wind gets 20 - 30
knots (a gale force wind) the chain becomes effectively a straight
line, in other words for all practical purposes the catenary is gone
(Note: you can never pull the chain completely straight) and wave
shock is transmitted directly to the anchor.
So why do nearly all cruising yachts use an all chain rode? And, why
does everyone talk about anchors but ignore the "thing" that
attaches
the anchor to the boat?
Bruce-in-Bangkok
There's an excelent article discussing catenary, scope and chain/rode
ratios at http://www.rocna.com/boat-anchors/catenary.php
-- Geoff
www.GeoffSchultz.org
Read it, about the same thing that Hylas says in excruciating detail.
I'm probably some what jaded with the discussion of anchors but the
N.Z. company sites seem, to me, to be advertizing written in the
format of a scientific test.
Bruce-in-Bangkok
Bruce,
I'd say that you are a bit jaded on this one. I went back and looked at
the article and only found a brief mention of Rocna's products where
they were quoted a holding force. The rest of the article has nothing
to do with Rocna and can be applied to any anchor. I personally like to
see that a company who produces anchors has a good understanding of the
physics.
-- Geoff
www.GeoffSchultz.org
I wasn't referring to a specific N.Z. site, but read several for the
Rocna, they have got one that is mainly stabbing the other company
that makes a similar anchor. They have references to anchoring "north
of the dock" and "south of the dock" hardly a scientific
specification.
I'd prefer to change the last sentence in your message to read, "I
personally like to see that a company who designed an anchors has a
good understanding of the physics." as not all anchors are
manufactured by people who design them.
Bruce-in-Bangkok
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