[hpv-boats] Folding Prop

[Rick Willoughby]

Hi Rick


Great prop.

I thought that you did not use a strut but let the shaft flex and  
find its
own position.

On the hinge pins are these riveted in or do you use a form of socket  
cap
screw.

Do you think the slots for the blade to fold  generate any drag.

Dennis A

Dennis
I have used props strutless but it is not practical for everyday  
use.  The prop hangs when the boat is carried.  The prop will  
sometimes hit the hull in a turn if there are waves.  The prop dives  
when you go in reverse.  I use a light tension strut that can be  
folded sideways to inspect the prop or to enable the boat to be set  
evenly on the beach.  Is costs about 2W.


I used a 6mm partially threaded bolt for the prop pivot.  The hole on  
one side of the blade is threaded and the other is a neat 6mm.  I  
bolted the blades firmly in place with bolt thread and head both  
exposed. I then cut these exposed bits and filed them flush with the  
curve of the hub.  It will not be easy to remove the blades.  I would  
need to mill or drill out the bolts first.

The slot behind the blades will offer no measurable drag.

I continue to be impressed with the prop.  I am still to get some  
calm weather for best comparison but comparing with data from the  
last couple years it seems my average speed is a little higher.   
There are three things that are contributing.  The boat is lighter  
and optmised for 11kph rather than 12kph so less wetted surface.  I  
do not need to stop forward progress to clean the prop of weed and am  
able to do this as soon as I suspect extra drag.  I am currently  
running a higher gear ratio, which improves biomechanical efficiency  
however is tough on the legs on windy days.  Not sure if I will stay  
with this ratio.

I did 25km on Saturday with wind to 50kph at an average of 9.0kph.  
The previous best in these heavy conditions over that distance was  
8.7kph.  I expect to get up to average of 10.5kph in calm weather.   
Time will tell.

The one weakness with the prop is reverse thrust.  I need to spin  
quite fast to go astern.  Quite different to a fixed bladed prop.

I noticed my previous link to the prop photo was missing a bit.  Here  
is the full link:
http://www.rickwill.bigpondhosting.com/folding_Prop.jpg

Rick Willoughby
rickwill at bigpond.net.au