Propeller Speed

[Arnot]

As part of the process of restoring Orianne, along with the infamous Ruston 3VRO, I am trying to design/develop the hydraulic drive system. The rated power output of this engine is stated as 33hp at 1000rpm but I can't seem to find any torque curves for it and suspect that the peak torque will be at considerably lower than the rated speed.

 

The reason for using hydraulic drive is partially to allow constantly variable drive to better match the engine speed to the cruising speed and partially to allow a low roofed back cabin enough headroom to be usable (i.e. no prop shaft)

 

At the moment I have got hold of an Eaton 72400 hydraulic pump with a 40cc per stroke delivery. This has come from a friends boat and should do the job, it’s not perfect but pretty close and it did come well within budget!

 

I am thinking of using an SAI GM05 radial piston hydraulic motor with a displacement of either 40 or 60 cc per stroke. I like the idea of the very short length and the ability to deliver high torque and good control at low speed. It also seems to have the appropriate speed range for propeller drive.

 

At the moment the propeller is a 22 x 16 three blade and although this may well be OK I suspect that I may migrate to a 22 x 22 three blade to keep the propeller speed down a bit. At the moment there is a bit of tendency to create a cappuccino effect in the wake.

 

My thoughts are that I should be aiming for a 10mph theoretical top speed to allow for river and tidal eventualities.

 

My question is, how do I find out what sensible speed range can be used with either of these propellers and how much torque are they likely to absorb under a variety of conditions. Obviously I would find this information useful in specifying the hydraulic components, can any one help or point me in the right direction?

 

Regards

 

Arnot

[ditchcrawler]

As part of the process of restoring Orianne, along with the infamous Ruston 3VRO, I am trying to design/develop the hydraulic drive system. The rated power output of this engine is stated as 33hp at 1000rpm but I can't seem to find any torque curves for it and suspect that the peak torque will be at considerably lower than the rated speed.

 

The reason for using hydraulic drive is partially to allow constantly variable drive to better match the engine speed to the cruising speed and partially to allow a low roofed back cabin enough headroom to be usable (i.e. no prop shaft)

 

At the moment I have got hold of an Eaton 72400 hydraulic pump with a 40cc per stroke delivery. This has come from a friends boat and should do the job, it’s not perfect but pretty close and it did come well within budget!

 

I am thinking of using an SAI GM05 radial piston hydraulic motor with a displacement of either 40 or 60 cc per stroke. I like the idea of the very short length and the ability to deliver high torque and good control at low speed. It also seems to have the appropriate speed range for propeller drive.

 

At the moment the propeller is a 22 x 16 three blade and although this may well be OK I suspect that I may migrate to a 22 x 22 three blade to keep the propeller speed down a bit. At the moment there is a bit of tendency to create a cappuccino effect in the wake.

 

My thoughts are that I should be aiming for a 10mph theoretical top speed to allow for river and tidal eventualities.

 

My question is, how do I find out what sensible speed range can be used with either of these propellers and how much torque are they likely to absorb under a variety of conditions. Obviously I would find this information useful in specifying the hydraulic components, can any one help or point me in the right direction?

 

Regards

 

Arnot

I have a hydraulic drive, details at http://www.harnser.info/html/building_harnser.html If you want any other info please email me

[Yoda]

I think that the 33 hp at 1000 rpm is the maximum continuous rating of the engine but as you do not want a direct drive, that is not what you want to use.

 

The engine could be run at its most efficient speed (sfc) ie where the power output and fuel consumption are best and the stroke of the hydraulic pump chosen from that. So say the best speed was 750 rpm and the pump produces 40cc/rev, the motor stroke could be 40 for 1:1, 60 for 1:0.75 and 80 for 1:0.5 ie half prop rpm. This would reduce your fuel consumption considerably and still allow max rpm. It just means that you are using your engine better.

 

Therefore you will be able to use a range of props that suit your cruise speed.

[billh]

I think that the 33 hp at 1000 rpm is the maximum continuous rating of the engine but as you do not want a direct drive, that is not what you want to use.

 

The engine could be run at its most efficient speed (sfc) ie where the power output and fuel consumption are best and the stroke of the hydraulic pump chosen from that. So say the best speed was 750 rpm and the pump produces 40cc/rev, the motor stroke could be 40 for 1:1, 60 for 1:0.75 and 80 for 1:0.5 ie half prop rpm. This would reduce your fuel consumption considerably and still allow max rpm. It just means that you are using your engine better.

 

Therefore you will be able to use a range of props that suit your cruise speed.

 

Hi,

33hp at 1000 is exactly the same as a Kelvin J3, these run with about a 22 inch prop with direct drive, ie prop runs at engine speed, so I would think you should be looking at 1:1 for the hydraulic drive. I have first hand experience of hydraulic drive on a dredger- the engine is Lister HR2 , 29.5 HP at 2200 rpm, the 20 inch prop turns much slower than the engine and progress is best described as " slow". Personally, I would avoid a hydraulic system if at all possible, the best efficiency comes from a direct drive from a relatively slow revving engine(like your Ruston). The power losses in the hydraulic system can be quite high and there can be problems with oil leaks from pipe joints working loose with vibration, note that the system could be running at around 2500 psi . Hydraulics are brilliant for powering excavators etc, I remain less than impressed for propulsion purposes. No doubt someone will be along soon to tell you they have hydraulic transmission in their boat and it's 99% efficient and goes like a rocket.

Bill

[colin stone]

Max prop tip speed should be less than 30mtr/sec to minimize cavitation - which on a 22 inch prop is 1025 rpm.

[blackrose]

Max prop tip speed should be less than 30mtr/sec to minimize cavitation - which on a 22 inch prop is 1025 rpm.

 

What is the figure for a 19" prop? (x 13" pitch)

 

My Isuzu 55 engine is supposed to rev up to 3000 rpm and I have a PRM150 gearbox - does anyone know how fast the prop actually revs?

[Arnot]

Max prop tip speed should be less than 30mtr/sec to minimize cavitation - which on a 22 inch prop is 1025 rpm.

Magic, just what I was after!

 

Could you point me in the direction of any sites that explain this?

 

Regards

 

Arnot

[Albion]

Blackrose asked:

What is the figure for a 19" prop? (x 13" pitch)

 

My Isuzu 55 engine is supposed to rev up to 3000 rpm and I have a PRM150 gearbox - does anyone know how fast the prop actually revs?

 

 

The PRM 150 box is offered with a choice of three reduction ratios (1.5, 2.0 ad 2.8 to 1) so unless you can confirm what ratio your box is, it is impossible to say. It is more likely to be the 1.5 or 2.0 option but that still leaves the calculation rather open. IIRC the ratio is probably stamped on the gearbox serial number plate.

Roger

[ChrisPy]

What is the figure for a 19" prop? (x 13" pitch)

1025 x 22/19 = 1186rpm

[blueprince]

inane reply, you may wish to stop reading,

 

A maximum speed for prop rotation would be "c" or light speed, ignoring the fact that the prop and boat would disintegrate, this gives an approximate forward speed of 733 miles per second.

 

While you would be speeding, it would be very hard to complain to you.

[Yoda]

inane reply, you may wish to stop reading,

 

A maximum speed for prop rotation would be "c" or light speed, ignoring the fact that the prop and boat would disintegrate, this gives an approximate forward speed of 733 miles per second.

 

While you would be speeding, it would be very hard to complain to you.

 

This is OK (I won't correct this) such to say that the acceleration will cause severe headaches to the constructors.

[colin stone]

Magic, just what I was after!

 

Could you point me in the direction of any sites that explain this?

 

Regards

 

Arnot

 

30/(Prop diameter inch x 22/7 x 25.4/1000) x 60

 

30/(Prop diameter mm x 22/7 / 1000) x 60

[blackrose]

Blackrose asked:

What is the figure for a 19" prop? (x 13" pitch)

 

My Isuzu 55 engine is supposed to rev up to 3000 rpm and I have a PRM150 gearbox - does anyone know how fast the prop actually revs?

 

 

The PRM 150 box is offered with a choice of three reduction ratios (1.5, 2.0 ad 2.8 to 1) so unless you can confirm what ratio your box is, it is impossible to say. It is more likely to be the 1.5 or 2.0 option but that still leaves the calculation rather open. IIRC the ratio is probably stamped on the gearbox serial number plate.

Roger

 

Thanks I'll have a look this evening.

 

Mike

[blackrose]

The PRM 150 box is offered with a choice of three reduction ratios (1.5, 2.0 ad 2.8 to 1) so unless you can confirm what ratio your box is, it is impossible to say. It is more likely to be the 1.5 or 2.0 option but that still leaves the calculation rather open. IIRC the ratio is probably stamped on the gearbox serial number plate.

Roger

 

Well if the reduction ratio is stamped on my gearbox it's certainly not very obvious. The serial number plate has the serial number and also PRM150 2D if that means anything to anyone?

[Albion]

Blackrose said:

Well if the reduction ratio is stamped on my gearbox it's certainly not very obvious. The serial number plate has the serial number and also PRM150 2D if that means anything to anyone?

 

 

PRM state in their handbook that:

The top line on the plate is the serial number and the lower line is the spec of the box (model number, ratio etc). So it would seem likely that your box is a 2:1 ratio. If that is correct (and it seems likely as PRM have stated it) then your prop speed will be 1500 rpm for an engine speed of 3000 rpm.

Failing that, then ring PRM direct on 024 7661 7141 or e-mail mail@newage-prm.co.uk

Edited April 7, 2009 by Albion

[Arnot]

Well if the reduction ratio is stamped on my gearbox it's certainly not very obvious. The serial number plate has the serial number and also PRM150 2D if that means anything to anyone?

The 2D at the end of the part number indicates a 2:1 speed reduction. Unusually PRM make it that simple....

 

Regards

 

Arnot

[blackrose]

Thanks.

 

So according to Colin's figures my 19" prop should be spinning an no more than about 1187 rpm to minimise cavitation, which means my engine rpm should not go higher than about 2370 rpm.

 

I think I've only ever taken it above 2500rpm once when entering Limehouse lock from the Thames.

Edited April 8, 2009 by blackrose