Propeller gap

[Maudesmaster]

On fitting Propeller to through shaft there is a gap between front of prop tapered face and aft face of through tube to stern gland of about 1 1/2” 

This is mid engined so shaft from Gear box to through shaft is bespoke and cannot be altered I can recut key way in shaft and chop off end 

So how much gab would be about correct between shaft and through tube 

Also would a flexible coupling be advisable between shafts 

thank you in advance 

Richard 

[RLWP]

The gap sounds right, don't shorten it

[Tony Brooks]

It seems that typically the maximum advised "gap" prop overhang is about11 x shaft diameter or a little more so you are OK - as Richard says. Personally for canal work where it is always possible for something to stop the prop dead I would like mine to be smaller providing it still gave clearance when any rubber engine mounts deflected under drive, but that is personal, not the often quoted view.

[Boater Sam]

I'm thinking you meant one and a half times diameter Tony?

[RLWP]

12 minutes ago, Tony Brooks said:

It seems that typically the maximum advised "gap" prop overhang is about11 x shaft diameter or a little more so you are OK - as Richard says. Personally for canal work where it is always possible for something to stop the prop dead I would like mine to be smaller providing it still gave clearance when any rubber engine mounts deflected under drive, but that is personal, not the often quoted view.

 

I'd go for about 1 x shaft diameter as I think that looks neater. A personal thing again

 

What you don't want is it tight against the stern tube, otherwise one day you'll be scratching your head trying to work out how to get that rope/wire/plastic sack/carpet out of the gap

 

Richard

[MtB]

1 hour ago, Boater Sam said:

I'm thinking you meant one and a half times diameter Tony?

 

 

I've always thought between 1 and 1.5 times shaft diameter 'looks' about right. Too little gap and stuff gets wedged in there, too much and the shaft is at risk of bending with a serious prop foul by say a nice hard lump of oak. 

[Boater Sam]

Mmmm, with an inch and a half diameter shaft, I would settle on one diameter as well. There is also the gap to the rudder forward face to consider.

Tony?

[BEngo]

27 minutes ago, Mike the Boilerman said:

 

 

I've always thought between 1 and 1.5 times shaft diameter 'looks' about right. Too little gap and stuff gets wedged in there, too much and the shaft is at risk of bending with a serious prop foul by say a nice hard lump of oak. 

But Don'T forget to allow space for the shaft movement if you have a Gardner cone or Kelvin box. A reverse bladeful is a real bugger if the shaft won't go forward because the cr@p is stopping it coming out of gear.

N

 

 

 

 

 

[Tony Brooks]

2 hours ago, Boater Sam said:

Mmmm, with an inch and a half diameter shaft, I would settle on one diameter as well. There is also the gap to the rudder forward face to consider.

Tony?

And the distance from the stern post if the boat has one for optimum prop efficiency. I agree about the gap between prop and rudder, especially if the rudder has very larger balance. Messing with that can create handling problems and excess tiller vibration. I suspect its all a great big compromise for most canal boats.

 

Yes - I did manage to put an extra 1 in my last post. 1 x shaft diameter.

[Maudesmaster]

Great thank you guys the shaft is 1 5/8” so about right then 

with everything else was a bit of a shock when fitting prop 

plenty of room behind prop for folding chairs etc 

Richard 

[X Alan W]

6 hours ago, RLWP said:

The gap sounds right, don't shorten it

As Richard says usual Gap quoted is 1to11/2 times dia of tail shaft

[Guest]

A small diversion....

The gap between my prop and the back of the boat is currently about 25 metres!

It dropped off when slowing down to moor in Brum after a particularly foul trip up the 21. ?

All attempts to recover have failed.

[bizzard]

[WotEver]

43 minutes ago, Floating Male said:

A small diversion....

The gap between my prop and the back of the boat is currently about 25 metres!

It dropped off when slowing down to moor in Brum after a particularly foul trip up the 21. ?

All attempts to recover have failed.

Gone paddling?

[Guest]

It was about 4 feet deep at bank, so decided against paddling. (I can't swim!)

 

Was hoping when bizzard posted he had invented a brass magnet. Life is full of disappointments.

[MtB]

1 hour ago, bizzard said:

 

Gosh your canal down there in Bishops Stortford looks PHANTASTIC bizz....

[WotEver]

2 hours ago, Floating Male said:

Was hoping when bizzard posted he had invented a brass magnet. Life is full of disappointments.

It’s very simple; all you need is some anti-brass. Once you’ve obtained some drop Bizzard a PM and he’ll send you the instructions.