[hpv-boats] Murray Marathon

[Rick Willoughby]

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