Putting Granny's propeller on securely

Halfie wrote recently of his frustration when taking his his friend's boat Willow up the Thames to the IWA Festival.  He told of:

• How the boat's propeller fell off when in the Thames.
• How he had an engineer replace it while the boat was still afloat and moored up.
• How the replacement itself fell off within hours.
• How another replacement was fitted.
• How he recovered the first replacement prop from the river by swimming for it (complete with pictures - including an amusingly triumphal one, perfectly timed!).
• How the replacement was re-fitted with what (hopefully) seems like a greater degree of confidence.

I'm surprised you can replace a propeller while afloat, and do it with any degree of security.  Surely a dry dock or slipway is needed?

I remember the last time Granny's propeller was changed, five years ago.  Actually, the propeller itself is still the same, original one fitted when the boat was new, but what was replaced was the prop shaft and bearing. 

It was done on the slipway at Streethay, and I remember being so fascinated with the process that I photographed it carefully at the time.

Granny was already dry docked and being washed down in the first photo here, which shows the propeller before removal.  (The flowing water is just the dregs of the water draining from the weed hatch section moments after settling on the slipway. 

The first thing was to test the propeller shaft for wear - this was ten years after the boat first went in the water - and the shaft did indeed show clear signs of wear.  Here's the original, as it came out of the water:

To remove the propeller they just cut through the shaft with an angle grinder.  A Gordian-knot solution.

I suppose just cutting it off was the quick & simple way.  After all, if the shaft and bearing were worn they are going to be scrapped and replaced anyway.  Nevertheless, seeing the propeller drop off like that, it did feel like an amputation.

To mix the metaphor, they carried the prop off like a newborn baby to check it over - and to grind off all the tiny spikes and sharp edges created by striking various objects over the years.

They then checked the shaft for wear, confirming what they'd expected.  I suppose it was a bit too late to change their minds, but maybe it was to reassure me that the bill was  justified. 

The bearing was then changed and the new shaft inserted. (By this time, the hull had been blacked, including the little bit shown here:

The cobalt-blue irridescence of the steel looked amazing to me. 

The propellor was then put back on (seen here from above, looking down through the weed hatch):

The securing nut was screwed back on:

... And then put under severe torque to tighten it correctly.

A hole was drilled through the nut:

.... and the split pin inserted.

 

... and folded back to secure.

Now just let this sucker try falling off!

I'd be interested to see how NB Willow's propeller looks when in place - and out of the water.

Comments

[Andrew Denny]

Paul, 
If memory serves, it took about three minutes. Though it was 5 years ago and it's the only time I've seen it done, so forgive me if memory plays tricks. 

[Paul]

how long did it take them to drill through the nut and shaft? I have to do the same on my boat! Ta, Paul

[Maffi]

And what is the correct torque for a nut of this size?

[Andrew Denny]

Max
In fairness to my beloved Streethay Wharf, I recall they were only doing that because it was a little hard to screw it on by hand, and they hadn't quite got to the 'high-torque' stage. 

[Max sinclair]

All the Engineers watching this will be unhappy to see an adjustable spanner being used, risk of rounding nut edges.Ring spanner or fixed jaw more positive.

[Andrew Denny]

Halfie,

Duly corrected, sorry!

[Halfie]

An excellent photographic record of the whole operation, Andrew.

A couple of corrections on the bit where you refer to me: Willow isn't my boat but a friend's; and the replacement propeller is what I found with my feet and which was refitted - the boat is now on 'only' its second prop.