Propeller nut set sizes

[Dazzler44]

Hi, I recently bought a Colvic Watson 23.5 which didn’t have a prop as it fell off for the previous owner. It’s a 1.5 diesel BMC with a 1” shaft in right hand drive. I managed to find a propeller that (I hope) fits, but I’m really struggling with what size but set to buy and from where.
The prop is for a 25mm shaft that tapers to 22mm. The nut end obviously starts at 22mm tapering to 20mm at the tip.
could someone please advise me what size but set is needed.

many Thanks in advance.

 

[colhel]

M22x2.5 (standard course pitch) kinda tallies with your measurements.
Measuring pitch is tricky without the right tools. What you can do though which might confirm the above is to measure the amount of threads over a given length, ie. over 25mm if 2.5 pitch you'll count 10 thread peaks.
Mind you it could be an imperial thread as your shaft is 1". So 7/8" (22.2 mm). If you can get hold of a vernier and measure the thread diameter, if it's 22.1(ish) mm it'll be 7/8". If it's 21.8 ish to 21.9 is, it'll be metric m22.

 

[penfold]

You will need to measure the outer diameter of the thread and the pitch of the thread(or more likely the number of threads per inch for this given the vessel, but there are no certainties); a vernier caliper will allow you to do this with sufficient precision.

 

[ChromeDome]

Prop pitch and dia might be guess-work

 

[scottie]

there are many propeller calculators on lines or ask a propeller supplier to suggest size for you
you will require engine details plus reverse gear reduction ratio plus boat detail
there are two different tapers that are normally used ie 1 in 12 for imperial or inch and 1 in 10 for metric
BMC 1500 could likely use imperial and it would be appropriate to measure in inches
you need to sort this out first or you are talking apples and oranges
once you have sorted that out then start on prop nut sizes
i may be missunderstanding your post of course and you already sortEd this out

 

[Tranona]

Imperial shafts are usually 1:12 taper and nuts are usually either BSF or Whitworth. There is also a keyway which you need to measure. A 25mm prop is no good - it has to be exactly 1" (25.4mm) of the correct taper and keyway. The size of the prop (diameter and pitch) is determined by the type of boat (length beam and displacement) HP of engine and reduction ratio of the gearbox.

To buy the correct prop and nut suggest you contact here lakesterngear.co.uk/catalogue.pdf with all the information. They are a major supplier, but of course there are others such as T Norris in London, Castle Marine in N Wales, Hamble Propellers, Clements to name a few. Lake have made a number of shafts and propellers for me over the years.

 

[bristoljim]

, I recently bought a Colvic Watson 23.5 which didn’t have a prop as it fell off for the previous owner. It’s a 1.5 diesel BMC with a 1” shaft in right hand drive. I managed to find a propeller that (I hope) fits, but I’m really struggling with what size but set to buy and from where.
The prop is for a 25mm shaft that tapers to 22mm. The nut end obviously starts at 22mm tapering to 20mm at the tip.
could someone please advise me what size but set is needed.

many Thanks in advance.ew prop

You need to start with establishing the ratio & make of the gearbox.Are you out of the water ?. What size is the "new" prop ?
Jim

 

[colhel]

M22x2.5 (standard course pitch) kinda tallies with your measurements.
Measuring pitch is tricky without the right tools. What you can do though which might confirm the above is to measure the amount of threads over a given length, ie. over 25mm if 2.5 pitch you'll count 10 thread peaks.
Mind you it could be an imperial thread as your shaft is 1". So 7/8" (22.2 mm). If you can get hold of a vernier and measure the thread diameter, if it's 22.1(ish) mm it'll be 7/8". If it's 21.8 ish to 21.9 is, it'll be metric m22.

For some reason I thought you were after a prop nut. How did I mis-read that?

 

[penfold]

For some reason I thought you were after a prop nut. How did I mis-read that?

You didn't, that's what the OP is about.

 

[Tranona]

You didn't, that's what the OP is about.

But he says the prop he has found is metric for a 25mm so won't fit his 1" imperial shaft - wrong bore and taper.

So 2 issues first find correct size prop and determine the actual thread size on the shaft.

Hence the advice to talk to a specialist

 

[penfold]

Mission creep; you've answered a question the OP didn't ask. I agree the prop may well be an ornament, but we do not know and nor does the OP and they will still need a nut at the end of it.

 

[Tranona]

Mission creep; you've answered a question the OP didn't ask. I agree the prop may well be an ornament, but we do not know and nor does the OP and they will still need a nut at the end of it.

If the OP is correct and the prop is for a 25mm shaft and he has a 1" then it will definitely not fit - no ifs and buts - independent of its diameter and pitch. If he has an imperial shaft it will probably have an imperial thread, but there are 2 or 3 different possibilities. It could also be a metric thread although this is unlikely.

 

[ChromeDome]

This thread is adding value by iteration

 

[Dazzler44]

Ok so after some time and being finally lifted the measurements for prop shaft are 25mm with a 1:10 taper. The keyway is 6mm. And I’ve got a 14”x13” prop to fit but I seem to get confused with the locking nut size. Can anyone help now I’ve provided more info please. Many thanks.

 

[Dazzler44]

Ok so after some time and being finally lifted the measurements for prop shaft are 25mm with a 1:10 taper. The keyway is 6mm.

 

[scottie]

I think that you will find that you have already been advised to measure the thread on the shaft
Be aware that there are coarse and fine metric thread
Using the relevant table of sizes will reduce the choice but remember thar nothing is written in stone when dealing with older boats not even concrete ones

 

[Tranona]

Ok so after some time and being finally lifted the measurements for prop shaft are 25mm with a 1:10 taper. The keyway is 6mm. And I’ve got a 14”x13” prop to fit but I seem to get confused with the locking nut size. Can anyone help now I’ve provided more info please. Many thanks.

A 14*13 propeller sounds small diameter for the boat/engine. How did you arrive at that size?

The normal nut for a 25mm shaft is an M16*1.5 castellated with a split pin to lock