[MHml] Friction in lines and blocks

[Martin Schöön]

Some comments on my part:

Perceived performance is not the same as actual performance.
I also *feel* lines fly out easier through ball bearing blocks. I even
perceived the ball bearing blocks to perform better while doing
my experiments but the measured data consistently told me
another story. My science and engineering training force me
to accept what measured data tell me.

The friction in a decently sized line is about an order of magnitude
larger than the friction in the block bearing. I can not see how
this line friction dominance can go away in the running out
scenario or for much higher loads than the ones I have covered.
I would love to confirm this by experiments and I will conduct experiments
as soon as I have figured out how. You are free to do it without waiting for
me.

What could happen in a high load case is of course that one
type of bearing starts to misbehave or even break down.

A java-application would be even better than posting a spread
sheet on my web. But I would have to learn java before that happens.
(Might be fun)

Paul, my main traveler used to get stuck like that until I changed my
main sheet. I used to have an 8x tackle with the line's tails going
to each cockpit: cockpit -> traveler (8 times between boom and
traveler) -> cockpit. The first season we used ball bearing (steel
bearings) blocks by Easy (a Danish manufacturer that might have
gone belly up) and a very generous 12 mm line. The problem was
the sheave diameter: maybe 30-35 mm (I don't have any left so I
can't check). We had a lot of friction. We then purchased those
big, plain bearing OH blocks plus similar Ronstan blocks and the
main sheet and traveler control worked much, much better. This
version can be seen here: http://hem.bredband.net/b262106/saillinks.html
(All this I had forgotten but it surfaced late last night.)

My present system is much different and traveler and sheet now work
without any interference. http://hem.bredband.net/b262106/Boat/controls.html

This brings us to the winch vs tackle question. I do mention this on the
controls page of my web: My boat may be the most powerful boat for
which a pure tackle main sheet works. If you need a more powerful
main sheet you will find a winch + tackle sheet to be lighter than all
the blocks and line needed for a pure tackle design.

Given the new insight my report provides us with it may be that I
should really convert my main sheet to winch + tackle. I don't like
the idea of winches and handles and all that for single handed
sailing though. I would be forced to use both hands for sheeting in anything
but the lightest breeze. Today I use both hands when the wind is up
but it is a very quick maneuver.

The Lightspeed guys have published similar concerns as the
reason for going for an all tackle design. They ended up with too
much friction so they tried winches and didn't like them. Now they
are aiming for hydralics.

Disclaimer: I don't have all that much experience of winch + tackle
main sheets.

Using a video camera for measuring speed would work but I don't
have one. The way I set up my experiments resulted in a rather
short distance between the blocks so it would be a bit tricky to try
out different speed. The speed I used is not great but not too unlike
the line speed while trimming.

-- 
Martin Schöön              "Problems worthy of attack
                                         prove their worth by hitting back"
                                         Piet Hein