[hpv-boats] re Flex Shaft

[Rick Willoughby]

Mark
While you are testing in the workshop can you measure the torsional  
stiffness.  If you just give me the degrees it flexes with a certain  
load at a known radius I can calculate the torsional stiffness.

 From this value I can work out the apparent loss in the drive  
train.  If this is similar to the CF shaft I have I will be  
interested in testing one.

My CF shaft is 3.1m long but it only needs to curve over 1.2m of its  
length.  It would be easy to make a rigid extension from your shaft  
to get the required length for an aft mounted prop.  The one-off CF  
shaft cost me AUD300 but the cost would reduce for higher quantity.

I am now mounting the prop behind the hull so it can easily flex  
upward if it hits something solid.  I used a 10mm X 3mm tension strut  
on V15 that can slide upward.

A friend, building a pedal boat here, copied one of my fixed bladed  
props and has moulded aluminium and bronze blades from the resulting  
pattern.  He is also working on a lighter nylon/glass version.  He  
only has a couple at this stage and he gave me one with aluminium  
blades for testing.  It suits a ratio around 1:4 or a bit lower if  
the hull moves easily.  The linked image gives an idea of what the  
bronze one looks like:
http://www.rickwill.bigpondhosting.com/Bronze_Folding_Prop.png
He has talked about selling them if there is enough interest.

Rick


I now have delivery of the flexible cable shafts I ordered. They are 2
meters long, have a 7.94 wound core, and are made of 316 stainless
steel. The female couplers on each end accept 12 mm  shafts and have
an offset 6.35 mm hole drilled for a cotter pin to hold the shaft with
a corresponding half cut (per Rick's suggestion). The cable is covered
with a .5" o.d. nylon tube so that the cable can be clamped at various
points.

These shafts can flex around objects and can even bend to 90 degrees
with enough curve radius. Possible advantages include using the prop
for steering and easy prop raising for shallow water.

I am just now setting one up in my workshop, along with an MPB
MitrpakDrive and our PlanetDrive to see how well they work together.
All our water is frozen here, so I cannot test outside.

Rick, if you are interested, I will send you one for free given all
the help you have provided. The shafts can be purchased for US $225,
US shipping included.

Email me if you are interested and I will send photos.

Thank  you,

Mark A. Vermilion