Boring a prop.

[pandos]

I have a folding prop from my previous boat. The size and rotation are correct for my current boat but the shaft size is smaller.

Question. Can I get the prop bored out to a larger size?. It's a 30mm shaft rather than a 25mm.

It's an old Radice two blade folding prop. My boat is difficult to reverse at the moment, would it be utterly impossible or just a little worse with a folding prop?.

 

[Praxinoscope]

Try contacting Carwyn Williams at Castle Marine in Caernarfon have always found them very helpful and haveextensive prop experience.
castlemarine@gmail.com

 

[jamie N]

Alternatively, you might consider machining the shaft?

 

[pandos]

Alternatively, you might consider machining the shaft?

That would let me with a fixed prop which would not fit. I'd rather stick to having the fixed one in reserve in case the folder made things too difficult.

 

[fisherman]

C&O engineering?

 

[Amlov]

C&O engineering?

Sadly no longer in business

 

[pandos]

I should clarify.

I will have no trouble finding a local engineering shop to do the work. My query is about whether it is ok to have it done.

I was thinking there may be some issue with balance or some other unknown consideration.

 

[fisherman]

Sadly no longer in business

That IS sad

 

[DownWest]

You are talking 5mm difference, one would expect the prop to take it. Maybe look closely (with your machinist) at it to see if there is enough meat to allow the increase.

Worth talking to Radice?

 

[Daydream believer]

Depends on how much meat there is on the boss of the prop. 2.5mm is not a lot to remove If the boss has sufficient material, then no problem. A properly machined job should maintain balance if set up correctly.Will the material removed interfere with the gearing for the fold mechanism? Just measure it & then decide.
If there is an issue with taking something off the shaft it may be possible to bush the fixed prop. Ask the machine shop first.

 

[pandos]

.....
If there is an issue with taking something off the shaft it may be possible to bush the fixed prop. Ask the machine shop first.

That's a nice piece of lateral thinking...

I'll have a good look when I get the shaft out...(changing it anyway)

thanks

 

[penfold]

A bush would be perforated by the keyway and a special deep key would be needed, a tricky operation to get right compared to boring out the prop hub.

 

[Daydream believer]

A bush would be perforated by the keyway and a special deep key would be needed, a tricky operation to get right compared to boring out the prop hub.

It is not a difficult job. I could do it in my shop with a bit of thought.

 

[vyv_cox]

Try contacting Carwyn Williams at Castle Marine in Caernarfon have always found them very helpful and haveextensive prop experience.
castlemarine@gmail.com

I have used Castle Marine. Top quality outfit. They provided the prop that I had copper plated. Copper plating a propeller

 

[pandos]

They provided the prop that I had copper plated. Copper plating a propeller

Have been looking at that process....might be a way to go.

 

[Tranona]

I should clarify.

I will have no trouble finding a local engineering shop to do the work. My query is about whether it is ok to have it done.

I was thinking there may be some issue with balance or some other unknown consideration.

Yes. Props are often supplied pilot bored and bored to size so a prop specialist like Castle Marine would be able to do it. Just make sure you measure the taper and keyway accurately or take the shaft to the machinist. Metric shafts are usually 10:1 but not always. For example Volvo supplied Westerly with metric shafts but imperial taper (12:1). Slight aside, I have a 30mm shaft but a 25mm prop because the Featherstream hub that we wanted to use (to get the largest blade area) will only take up to 25mm. However it is a one way street and doubt you could sleeve a 30mm down to 25mm.

Personally I would not waste money on a prop of that type. I think you will be disappointed. I am assuming it is for your HR. It is not the best folder for performance and worse in reverse. You say the size and rotation is right - have you done the sums? as a 2 blade folder will be a very different size from a 3 blade fixed. The only way you can improve performance in reverse just through changing props is to bite the bullet and fit a feathering 3 blade like the Featherstream or a Maxprop where you can set the reverse pitch different from forwards. For example mine has 10" pitch in forward and 8" in reverse. This makes reverse more progressive and reduces prop walk on a heavy long keel boat. you have to be careful choosing the pitch because it depends on the reverse ratio in the box - mine is 2.5:1 both ways but some boxes have different forward and reverse ratios.

 

[pandos]

Yes. Props are often supplied pilot bored and bored to size so a prop specialist like Castle Marine would be able to do it. Just make sure you measure the taper and keyway accurately or take the shaft to the machinist. Metric shafts are usually 10:1 but not always. For example Volvo supplied Westerly with metric shafts but imperial taper (12:1). Slight aside, I have a 30mm shaft but a 25mm prop because the Featherstream hub that we wanted to use (to get the largest blade area) will only take up to 25mm. However it is a one way street and doubt you could sleeve a 30mm down to 25mm.

Personally I would not waste money on a prop of that type. I think you will be disappointed. I am assuming it is for your HR. It is not the best folder for performance and worse in reverse. You say the size and rotation is right - have you done the sums? as a 2 blade folder will be a very different size from a 3 blade fixed. The only way you can improve performance in reverse just through changing props is to bite the bullet and fit a feathering 3 blade like the Featherstream or a Maxprop where you can set the reverse pitch different from forwards. For example mine has 10" pitch in forward and 8" in reverse. This makes reverse more progressive and reduces prop walk on a heavy long keel boat. you have to be careful choosing the pitch because it depends on the reverse ratio in the box - mine is 2.5:1 both ways but some boxes have different forward and reverse ratios.

Changing to folding prop is driven by the urge to improve sailing speed rather than reversing, I have accepted that reversing is simply about me ensuring that I need to go where the boat wants to go, (like a telepathically controlled elephant).

Previous boat was similar size/displacement and engine so I expect performance will be adequate, at least for motoring when sailing will be the order of the day.

Prop numbers are 16 x 12 folding versus 15x13 fixed.
I won't be buying a new fancy pants prop.

No idea what the ratio in reverse is. I suspect it's the same as in forward. It's an interesting question. I'll have a look. Gearbox is on the saloon table awaiting rebuild needs input shaft seal so for a few more quid I'll change the remaining bearings and seals.

 

[B27]

I found that if you wait long enough, folding props turn up on ebay for varying sums of money, in varying states.
One possibility might be to find a prop with the correct taper for the shaft, and just use the hub, with your existing blades? I'd imagine the blades would interchange between similar props of the same brand, but you'd have to check that.

The problem with reversing with a folding prop is that until you have enough RPM for the centrifugal force of the blades to exceed the thrust, nothing much happens. It's like dropping the clutch in a car. I haven't looked at the rev counter while powering astern, I'd guess it all happens about 1200 or 1500rpm? So I use shorter bursts of louder noise, and try to err on the side of needing a touch of ahead rather than a touch of astern. I try to avoid situations where subtle reversing is required, but I'm still (re) learning.

 

[Tranona]

Changing to folding prop is driven by the urge to improve sailing speed rather than reversing, I have accepted that reversing is simply about me ensuring that I need to go where the boat wants to go, (like a telepathically controlled elephant).

Previous boat was similar size/displacement and engine so I expect performance will be adequate, at least for motoring when sailing will be the order of the day.

Prop numbers are 16 x 12 folding versus 15x13 fixed.
I won't be buying a new fancy pants prop.

No idea what the ratio in reverse is. I suspect it's the same as in forward. It's an interesting question. I'll have a look. Gearbox is on the saloon table awaiting rebuild needs input shaft seal so for a few more quid I'll change the remaining bearings and seals.

OK. The sizes are reasonably comparable although the 2 blade pitch maybe a bit low but should work OK. The gearbox ratios will be on a plate on the box, or you can look it up if you know the make/model of the box. You don't say what the engine is, but props of that size are usually on 30hp with 2:1 reduction.

Folding props are very variable in terms of reverse. I had a Flexofold 2 blade on 2 boats and reverse was instant, no real difference from the fixed 2 blade, but the Radice is not as sophisticated in terms of blade shape as newer designs. BTW I have checked and the hub used on the 16" will go out to 35mm so plenty of meat to bore it out. Lake Engineering are the agent in the UK and would be able to do it for you.

 

[pandos]

In both boats the engines were/are about 50hp.

Getting the parts to the UK and back for machining would be a pain due to the Bx thing, of which we dare not speak.

Local precision guy is very able.

Good to hear that there are no issues with boring to accommodate 30mm.

I used to race on a boat with an old style folding prop which had an underpowered engine...I still suffer PTSD from some of the near misses in the marina...I think this is the main reason the Radice sat on the shelf since 2004...

Time will tell...

Thanks all.