Hi, Tim,
I agree on there being a shear pin. Another good system is a couple of
discs with holes around them, like, say, clock faces with holes where
the numerals are, and steel balls between the discs, and one disc
static, the other sprung towards the fixed disc. One is driven, the
other a driver.
With properly adjusted tension, there should be no constant slippage of
a vee belt????, although maybe there is, as a natural way the belt
'rolls' into and out of pulley contact.
I am a fan of toothed belts too, we think alike. But, I think it would
be impractical to not have a tensioner, as it would entail having the
pulleys spaced very accurately. It would also not allow for any initial
stretching during the first few hours of service, and would be open to
failure if belt manufacturing tolerances are too wide. And you are
right, they do look cool.
I know that this is probably off topic for the group, but I am actually
currently looking into, and starting discussing off-group with another
group member, an idea of a propeller that is inverted, that is, the
blades are inside a tube, and the whole tube rotates. It would look like
the static blades of a jet engine, that stop the gases rotating with the
regular blades. My thinking is that the pressure developed immediately
behind the blades could then not 'spray out' from the sides of the
prop., but would be forced to release pressure at the rear
Also, the vacant middle would take in water as the boat moved, which
might, and I haven't figured this out yet, but might, further feed the
pressure area at the rear of the prop.
The snags are difficulty in setting up bearings, and also the
requirement that the shaft would have to be horizontal, not angled.
Another snag might be that it just will not work for some reason that I
have not yet arrived at.
John
2a. Re: Outboard conversion
Posted by: "Tim"
haywardt@gmail.com haywardt
Date: Wed Feb 8, 2012 8:15 am ((PST))
I think the slippage issue is better handled by a shear pin or a clutch,
as you don't pay such a high cost in reduced efficiency due to constant
slippage.
Toothed belt drives don't require or benefit from dynamic tensioning,
they are far more efficient, impart less side load, cleaner, quieter,
last longer and are way sexier.
For shallow drive and in weeds I know of a patent on a small jet drive
that was made for foldboats and canoes that worked like the Dyson
blade-less fan. It was highly efficient and worked very well in shallow
water and weeds. It might be worth resurrection.
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