Propeller shaft

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CJ1

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Hi I’d like to instal a propeller shaft anode, but I can’t figure out with confidence what the diameter of the shaft is. I know it’s either 1 inch or 25mm, but deciding which it is with a ruler and my less-than-perfect vision is impossible. The engine is a 2008 Yanmar 3YM20, and all other specifications are metric, so I’m assuming it is 25mm. Does anyone with a similar engine know what it is ?
Thanks in advance.
 
The UK started going metric in 1965.

Is your engine the original to the boat in 2008? Which engine is fitted will not indicate a shaft size.

Where was the boat made? If made in the EU in 2008, then will definitely be metric.

My 1980 Fulmar has a metric shaft.

Perhaps you should provide more information about what the boat is rather than the engine.
 
Thank you all for your replies. It’s a 1985 Moody 27. Sounds like it’s a good bet that it’s 25mm.
I didn’t realise vernier gauges were so cheap- I’ll get one of those to be sure a useful addition to my tool kit anyway.
 
I have found both 25mm and 1" on boats of that era and I suspect it depended on cost and availability of material to the manufacturer at the time.
Definitely measure using a vernier or equivalent. Also useful to determine if your rigging is 1/4" or 6mm etc
Or buy both sizes of anode and take back the one you don't use?
 
Got to measure. You can never be sure. If you measured TG you would find the shaft is an inch and a quarter. If you looked at the half coupling you find it is 25mm. I was never going to waste a decent shaft and stern gear for the sake of a new engine! An engineering shop turned the end down...Best to measure or RR's last sentence..
 
Definitely measure it. My Sigma was built in 1986 in the same yard that Moody boats were made (Marine Projects). It has a Volvo-Penta engine (all metric) and a 1 inch prop shaft.
 
CJ1 said:
Thank you all for your replies. It’s a 1985 Moody 27. Sounds like it’s a good bet that it’s 25mm.
I didn’t realise vernier gauges were so cheap- I’ll get one of those to be sure a useful addition to my tool kit anyway.
Click to expand...
Moodys were produced with 1" prop shafts. Even though you have a new engine doesn't mean that the prop shaft was changed because the cutlass bearing in the P-bracket would also be affected. Measuring is all.
 
My '87 Sadler had a 1" shaft and I think there was one occasion when I couldn't get hold of a 1" anode, so reamed out a bit of a metric one. The boat survived in spite of my bodging habits.
 
My moody is 1979 and the shaft is 1" diameter. Renewed when I re-engined also with 1". Get a cheap vernier gauge or borrow one. My mate fitted a 25mm anode to a 1" shaft last year - it took a lot of hammering to get it to fit! Or as mentioned get one of each and see which fits and return the other.
 
Thanks everyone for your replies.
My digital vernier gauge has just arrived. Sod’s law the result will be 25.2mm, as the manual says the gauge is accurate to within .2mm.
 
When I was at such school, the conversion from inches to cms was not an exact figure. Some years later I was having an argument with my late sailing friend, also John, about this, since he insisted the relationship was 2.54:1 exactly. Unfortunately, I had been otherwise distracted when the masters of the universe decreed this change and so lost my argument, something I hate doing.
 
Hi,

A 1985 Moody 27 was definitely built by Marine Projects with a 1" shaft. That doesn't mean things haven't changed in the ensuing 35 years if, for instance, a previous owner had to replace the shaft while cruising in Europe where 1" stainless bar is like hens' teeth.. Presumably something like that happened to Concerto because Westerly were definitely fitting imperial shafts in 1980 (1" in a Fulmar).

The UK may have adopted a policy to metricate in 1965, but little happened outside government owned institutions until it became mandatory in a few sectors in 1978 before everting to voluntary in 1980 with the metrication board being wound up, so the whole thing stalled about half done. That accounts for the mess we find ourselves in with measurement in the UK. Boatbuilders, being traditional folk, never did anything voluntarily, so metrication had little effect on them and they soldiered on with feet and inches until the end of the 20th century

Of course, Jeanneaus, Beneteaus and Dufours all come from the home of the metric system and were built with metric shafts from the day those companies were founded.

Pretty sloppy vernier - a decent one will do +/- 0.1mm. You could try calibrating it by measuring something known to be 1" or borrow a micrometer.

Peter.
 
CJ1 said:
Thanks everyone for your replies.
My digital vernier gauge has just arrived. Sod’s law the result will be 25.2mm, as the manual says the gauge is accurate to within .2mm.
Click to expand...
No problem.
A fool-proof confidence test is to try it on a set of feeler gauges and record the deviation. You'll then know with considerable accuracy what errors there might be and thus compensate for them.
 
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