[hpv-boats] Gearbox

[Rick Willoughby]

David
The box I have made could only be regarded as a prototype. I use  
standard size aluminium flat and round to make it.  It is held  
together with stainless bolts.  It took about 8 hours of effort to  
produce it.

A friend here is investigating having the casing cast.  This is some  
time off though as I am still playing around with other ideas for the  
gearing.

I have been working with Mitrpak but they can only make a 1:2 ratio  
at this stage.

I also have an Involute gearbox that has a 1:3.3 ratio.  George Tatum  
arranged for their manufacture in India.  I think George still has  
some and both Ian Cassell and I bought ours from India in the last  
few years.  These cost less than  the gears would cost to buy  
elsewhere.   Involute may be able to produce something in small  
quantity with 1:4 or higher ratio.

The Involute boxes weigh 3.8kg which is quite heavy but they are  
tremendously strong.  I expect the shafts would shear before the  
gears fail.  The gears I used are good for peak power somewhere over  
500W in normal boat application but a strong cyclist can exceed this  
quite easily.  I have been told sprint cyclist can shear standard  
shafts.

Rick

Hello Rick,

As always your writing is quite interesting.
As you know, I am working on a human power rotomolded kayak project  
with a rigid
shaft directly set on the gearbox.
As the propeller is located below, and protected by 2 keels, it is  
not possible
to set a big propeller, that’s why I tend to put a 1:4 box and an  
average size
prop (rather 340 mm in my case).
I currently build myself this box for the time being but it is  
difficult and
time consuming. That’s why I would be enthusiastic to be able to buy  
one.
Would you have some pictures of your 1:4 box and an idea of its  
selling price if
ever?

Many thanks, David,



Best regards,

David Adrian