[hpv-boats] Murray Marathon

[Neal Smith]

Rick,
 
Can't you pedal backwards to rmove the weeds & leaves?
 
Neal

It is interesting with weed and even leaves on the prop.  They are guided down the shaft into the prop.  The shaft shields the strut.  So most weed wraps around the prop blades rather than just getting caught  on the strut.  If it did this it would be cut up by the prop but it just trails off the blades.  On the hot part of the day the trees shed leaves and these are driven to some points in the river by the wind such that they form a complete carpet. These are small leaves about 4" long and quite stiff because they are sun baked but I still manage to get a few caught on the blades.
 

--- On Fri, 1/16/09, Rick Willoughby <rickwill at bigpond.net.au> wrote:

From: Rick Willoughby <rickwill at bigpond.net.au>
Subject: Re: [hpv-boats] Murray Marathon
To: "HPV Boat" <hpv-boats at bikelist.org>
Date: Friday, January 16, 2009, 4:53 PM

Dennis
The spare prop - I did think about this.  I had a spare and shaft made up
complete with coupling for gearbox and flexible strut.  I carried it in the car
but of course I would still need to finish the day if I was going to use it.  I
carried a paddle on the boat as this covers all propulsion contingencies
including things like broken chain or gearbox failure.   By the way I never used
the paddle in the entire time.  I never carry on at the local lake.  The boat
operates in less than 6" of water so I can launch faster than most kayaks. 
Fitting my cycling shoes takes a bit of time because I wear socks to avoid
blisters.  (The paddlers have to wear gloves.  Some end up with sores on their
backside from sitting in water for long periods and resulting abrasion.)

Most boats carry a roll of duct tape to do quick hull repairs and I also carry
some basic tools such as keys to tighten the prop and multi-tool for anything
else.  Of course spares and tools add weight but my shaft and prop are lighter
than most paddles.

I have a few thousand kilometers on the gearbox I use most and It is usually
operated within its rating so is proving very reliable.  I should renew the
chain a bit before the race if I do it again.  So I am giving serious thought to
ditching the paddle and just carry a spare shaft and prop.  I am also thinking
about a more compliant prop, a smaller diameter prop and a stronger carbon fibre
prop.  The existing one is low temper 304 stainless steel so was not real
difficult to straighten.

The current 8mm shaft should give infinite fatigue life but I only had time to
get about 500km on the original shaft.  I fitted a new one before the race so I
had some confidence it would do the race.  However I would also carry a spare
shaft if I had a spare prop.  I was surprised I did not bend it when I bent the
blade.  8mm diameter is quite thin but being spring steel it has tremendous
toughness and high yield stress.

Folding prop- I have not really thought about the folding prop.  I am hopeful
of buying a benchtop lathe this year and a folding prop sounds like a good idea
for an early project.  It may actually shed weed very well if I just stop
spinning.  It will also coast better but still run in reverse.  These are real
advantages.  I am sure I can fabricate one that would not lose much performance.

It is interesting with weed and even leaves on the prop.  They are guided down
the shaft into the prop.  The shaft shields the strut.  So most weed wraps
around the prop blades rather than just getting caught  on the strut.  If it did
this it would be cut up by the prop but it just trails off the blades.  On the
hot part of the day the trees shed leaves and these are driven to some points in
the river by the wind such that they form a complete carpet. These are small
leaves about 4" long and quite stiff because they are sun baked but I still
manage to get a few caught on the blades.  The water is soil laden and murky so
you have to stop rotating and pull the prop up to see if it is fouled in any
way.  It would be great to just stop pedalling and have it shed weed without
much loss in speed.

If you look at my speed plots you will see regular speed dips to about 5kph.
Most of these are the times I inspect the prop. I usually combined it with
taking a sip of water and maybe having a snack.  Most kayakers use a drinking
tube but with my free hands I just use an ordinary drinking bottle.  I even have
the cycle style holder for the standard bottle.  I usually carried five of these
but always had at least one left.  It was relatively cool this year.

Rick Willoughby


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