[hpv-boats] Rigid Shaft

[v garza]

Why a dead spot with the flex and not the rigid is what I am wondering? If 
it because of the torsional difference, then a stiffer flex shaft (CF) like 
Rick is using might be a consideration. Or perhaps a thicker but longer 
steel shaft with some flex might be a consideration, if it can bring the 
prop closer to the horizontal. Flywheels either with a heavy prop or crank 
or eliptical? sprockets might be a consideration to take up a dead spot but 
seem like a lot of trouble and introduce other issues.  A 4 blade may give 
you more flywheel effect but also not be as efficient under HP due to 
increased water friction on the blade surface, from what I have gathered. 
The 4 blade alone will not change the angle and you will still have the 
other side of even more blades not aligned to the horizontal at any one 
time,  it would seem to me.

Hope there's some ideas you can use in there, but again you may have 
considered and rejected due to cost or negative trade offs in your design.

Vic
----- Original Message ----- 
From: "Ian Cassell" <iancassell at optusnet.com.au>
To: "Human Powered Vehicles --Boats" <hpv-boats at bikelist.org>
Sent: Wednesday, January 19, 2011 6:01 AM
Subject: [hpv-boats] Rigid Shaft


> Vic
>      I have previously been using a flex shaft but I could
> never do a flat out sprint because of the shaft going
> through the dead spot. The rigid shaft allows me to
> go as hard as I can but the prop is not at the vertical.
> I use an involute gearbox connected directly to the
> shaft, this makes things simple to build and setup.
> I could improve the angle but would get 11 deg max.
> and involve a bit of work on the boat.
>       My prop blade starts at 20 deg off the horizontal
> next to the hub and gradually increases to 55 deg at
> the tip. The prop is 400mm dia, with the prop angled
> at 16 deg off the vertical the angle of the blades to
> the water increases. If I make a prop with the blades
> at 36 deg next to the hub and increase to 71 deg at
> the tip the blade should be at the same angle as a
> vertical prop. However on the other side of the prop
> the angles will be way out and may cause drag on
> the prop. A four blade prop might be better in this
> regard as there would be more prop blades closer
> to the optimum.
>        I don't have any data worked out as prop design
> is a bit over my head, I use java prop for sizing.
>
> Ian
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