On Fri, 02 Nov 2007 12:37:20 +0700, Bruce in Bangkok
wrote:

Something I have always wondered about is that everyone talks about
anchors but nobody seems to talk about the anchor rode.


Because the answers with rode questions are relatively clear cut, but
not so with anchors because there are many more options and many more
variables.

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.


Breaking strength is not always the issue, rather it is Safe Working
Load, abrasion resistance and shock absorption. Kevlar has low
stretch, poor abrasion resistance, and is also averse to splicing and
tight radius turns. Poor choice in my opinion.

Chain has poor (no) stretch but good abrasion resistance.

Nylon has good shock absorption and good strength but poor abrasion
resistance.

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.

And that is correct. Catenary virtually disappears after the chain
load exceeds 1,000 to 2,000 pounds. That is about the force that we
generate when backing down with both engines at idle speed to verify
that the anchor is set (one advantage of a power boat with big props).

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?

I don't think it gets ignored, it's just that the choices are limited
and more clear cut. My personal choice is 3/8ths HT chain (G40) which
has a safe working load (SWL) of about 5,500 lbs and a breaking
strength over 20,000 lbs. I combine that with a 7/8ths nylon snubber
which has about the same SWL and breaking strength. The nylon gives
shock absorption and can be chafe protected at the hawse pipe. It
also takes the strain off of the bow pulpit and lowers the angle of
pull. In a serious storm I rig a second nylon snubber line for
backup. Most of the serious cruisers that we see are using something
similar.