How to replace the shaft while in the water…without sinking! Part 1
So, it’s the end of July and the diver who cleans my hull monthly mentions that the prop is loose. Turns out, the threaded area has been eaten away by electrolysis after being submerged for 50 years…go figure. So, we pull pull the shaft (it took 45 minutes!) and discover that the 3/4″ bronze shaft has been eaten away too much to be re-machined.
What to do?
Well, I ordered a new Aqualoy 22 stainless steel shaft from Deep Blue Yacht Supply (http://www.deepblueyachtsupply.com) along with an aggressive 10×12 Michigan MP3 prop to compliment the electric drive’s high torque curve. It should be here by the end of August, so I will let you know how it works out!
As of October 28, 2013, the prop project is complete! And to top everything off we only let in about a cup of water to boot!
|Aqualoy Stainless Propeller Shaft A_22 – 29″ x 3/4″ – Single Taper – –|
Here is a photo of the new Aqualoy stainless propeller shaft from Deep Blue Yacht Supply (http://www.deepblueyachtsupply.com/prop-shafts) lined up with the original bronze shaft. I have no idea what the original shaft’s composition was, if it was bronze or silicon bronze or melted down pennies with a little tin added. All i know about it is what you can deduce from the photos: It was old, severely eaten away through electrolysis, but not from wear.
I also replaced the original 10×8 prop (ten inches in diameter with an eight inch pitch) with a 10×12 over pitched prop to take advantage of the electric drives massive torque at low RPMs (you don’t have to rev the engine up to someplace like 900-1,100 RPMs to keep it from stalling). As of this writing I have not tested its theoretical performance so I don’t have any real world numbers, yet…
Here is a side by side comparison of the old 10×8 and the new 10×12 prop and you can clearly see the change in pitch. The new prop is a custom made MP3 Michigan Prop in bronze (http://www.deepblueyachtsupply.com/propellers/mp3-propeller). Along with the prop they also sent a machinist’s report. I am not versed in what everything means, but I can deduce that it is in balance.
Oaky, so now it’s time to also replace the stuffing box! I have to admit, this is what caused me the most sleeplessness with nightmare scenario dreams of water gushing into the boat and me being the little Dutch boy with his finger in the dike.
Michael Gunning said:
Make sure Scott knows what you are doing with the prop. There are guys out there who are over propping their boats. Scott normally engineers the motor to drive a prop about 80% the diameter. If you over prop the boat, the motor likely will need to be re-engineered/pullies.
Sailing Sine Metu said:
When we originally setup the system, it was designed around a 10×12 prop, but I acquiesced to staying with the original 10×8 prop. That said, I’ve finally transitioned back to the idea of having an over-pitched, 10×12 pitch prop fabricated — and it should be ready mid October . I will invite you down to witness and document the performance of over-pitching a prop by 20% for the electric drive system.