Got The Shaft

I mentioned in an earlier blog that Pachuca's propeller has way too much pitch ("bite") for the new engine.  The initial plan was for me to take the propeller to Port Townsend with me and have the pitch reduced, but then I floated the idea to Mark of me simply purchasing a new propeller.  He suggested a "feathering prop". This put me into a crash course of Propellers 101 and I soon learned the pros and cons of standard, folding, and feathering propellers.  The big attraction of a feathering propeller is that the reduced drag results in higher boat speeds.  Mark's customers report gains of 0.5 to 1.0 knots.  This would be a significant advantage on the long sail back to Australia.

Feathering props are not exactly given away and I became concerned about the fit of a new propeller on my existing shaft made to the same specifications as the original one built in Australia in 1983.  Although one of the members of the Palapa of Knowledge was emphatic that shafts were standard and fitting would not be an issue I wasn't so sure.   There are issues of taper, key width, etc.  One of the big issues that emerged was the length of the hub of the new propeller.  My current propeller has a hub only 83mm long and some of the new props have much longer hubs - the point being that if the hub is too long there won't be enough tapered shaft to accommodate the propeller. 

Mark suggested that I contact Fred Hutchison at PYI and he as turned out to be very responsive and helpful.   He made the important statement that PYI can fit their props to any shaft, as long as they know the specifications.  From the measurements of the existing propeller that I sent to Fred, he suspected that the shaft was made to SAE standard, because that is the one generally used in Australia.  But he needed to know if the thread on the shaft was coarse or fine.

In the meantime I explained propeller problem to Ib of Aeolus and he told me about his propeller size problems after repowering his boat with a 30 HP Yanmar in Mazatlan, mentioning that he had a spare feathering prop that was too big for his engine. A day or two later I asked him for the specifications and the fit seemed very promising: it was a Luke 1814R feathering prop for a 1.25" shaft and a 40 HP engine, and yes, he would like to sell it.  I visited the Luke web site and almost immediately spotted a likely problem: the hub was 120mm long vs my existing hub length of 83mm.

I then got the bright idea of contacting Ernesto, the man who had fabricated my  propeller shaft, to see if he still had the old one.  I telephoned him yesterday morning and yes, he had the old shaft and he would provide the measurements when he got back to his shop in 45 minutes.  I telephoned him at 11 AM and after a brief discussion offered to deliver the old shaft to me.  Less than 30 minutes later one of his men delivered the old shaft to my boat.  (Now that's what I call post sales service!) 

Mark soon suggested that I cut off the propeller end of the old shaft and take the stub with me to Port Townsend so that they could use it to train me on fitting the new propeller. That made sense to me.

I soon visited Ib with the shaft and he dug out his Luke feathering prop.  It is a beautiful piece of gear: solid, well made, and nearly new.  Unfortunately though not surprisingly we ran into the problem of the long hub.  The only solutions that we could see involved the removal of the new propeller shaft which was out of the question because I would have to either lift up the engine to draw out the shaft through the cabin, or risk bending the shaft by forcing it past the rudder. 

I took photographs of the propeller end of the old shaft along with some measurements which I will document here for the record:

Shaft Diameter: 32mm (1.25")
Shaft LOA: 1.61m (63.5")
Taper: 6.1mm over a length of 92mm
Keyway: 65mm long, 7.5mm wide

I passed this information to Fred who replied that it is consistent with SAE standard.