[MHml] Friction in lines and blocks

[Dave Howorth]

On Tue, 2007-12-04 at 09:41 +1100, Paul Nudd wrote:
> > From: martin.schoon at gmail.com Hello all, some time ago I started to
> > wonder how much friction there may actually be in a main sheet say.

Very interesting, Martin!

> The problem I have with the system is not so much 'getting it on' but rather
>  'letting it out'.

I'd agree. I noticed that Martin washed his lines and oiled his blocks
before doing the experiment. I wasn't so wise in my first season with a
Dart 18 and kept capsizing. I was amazed by the difference once I
learned that washing the mainsheet was a good thing to do!

>  Sailing in about 8 knots of wind, we round the
>  windward mark and release the traveller and the mainsheet. Then we
>  have to pull the traveller down to leeward and then we have to pull
>  the mainsheet through the blocks to get the boom out, it wont run out
>  without help in 8 knots. What's the problem?

Was the ratchet off? :)

> What Martin does not discuss is the friction comparison between plain
>  and ball bearing sheaves on 'run out' and verry low load, practically
>  negligible. This  is where I perceive an advantage in using the ball
>  bearing blocks.

Agreed. A similar situation arises in trimming spinnakers in light
airs. 

Martin didn't test roller-bearing blocks. I'd guess they are
intermediate between plain and ball-bearing but it would be interesting
to know.

Cheers, Dave

PS Martin - you say you couldn't measure the speed of the line. If the
line was marked somehow, is it possible to measure speed with a video
camera?