power is it enough?

[Graeme LinskeyParticipant @graemelinskey75588]

Hi there,

is 115 watts at the shaft unloaded enough to run a 1 metere boat its a small frigate class weighing around 6kgs

thanks

Graeme

[Graeme LinskeyParticipant @graemelinskey75588]

[shipwrightParticipant @shipwright]

Hello Graeme,

The short answer is yes – plenty of power. In fact I would say too much power. My destroyer has 2 shafts and each motor consumes about 14 watts. The real destroyer should be capable of 30 knots at full displacement – my model does about an estimated 18 knots flat out when translated to full sized ship (scale factor is 50 and speed scales as square root which is approximately 7 in this case – ie my model does 18/7 which equates to about 2.5 knots). I should add that my model is 24 kg displacement which is about 2 kg over full load displacement. The model is about 2 metres in length.

I didn't understand what you meant when you said that the motor consumes "115 watts at the shaft unloaded". If this means that the motor consumes 115 watts when the ship is out of the water then something is amiss. The no load power of a motor should be a few watts at most (unless the motor is a very high power brushless motor when the no load current can be quite significant).

Ian

[Graeme LinskeyParticipant @graemelinskey75588]

Ian,

Thats the power I was quoted its a steam turbine…..so how the figures equate to that I am unsure so how its measured I dont know this is the engine

http://www.ebay.com/itm/TS-532-Steam-Turbine-Engine-3-2-Blade-Wolfgang-Engineering-Live-/171483123287?pt=Model_RR_Trains&hash=item27ed30ce57

[Master ShipwrightParticipant @mastershipwright]

Hi Graeme,

Problem with this type of turbine is the very high rpm. You will need a reduction gearbox. They are not that efficient so you will need a large boiler to cope with the steam consumption. Not sure all this will fit into a 1 metre boat. There is a very interesting book 'Model Stem Turbines, How to Design and Build Them' by H. H. Harrison that provides all the background theory. It is available from Tee Publishing.

Martyn

[shipwrightParticipant @shipwright]

Graeme,

Thanks for supplying that information. I have had no experience of steam turbines. I concur with Martyn's comments. Warships such as frigates and destroyers have a large length to beam ratio (so that they can cut through the water at speed efficiently). One consequence is that they have relatively low displacement and there is not much space inside for boilers and pressurised butane gas bottle. It will be difficult to find a small gearbox that will give you the reduction ratio that you need and cope with the very high input rpm. For reference, I use DC brushed motors with a no load rpm of 1600 rpm at 12 volts that can drive the 70mm 3 bladed propellers at about 1200 rpm max (speed controllers are Mtroniks viper marine 10).

And for those interested in the turbines :

http://www.wolfgangengineering.com/turbines.php

Ian

[Malcolm FraryParticipant @malcolmfrary95515]

While it and its associated boiler and burner and fuel supply might fit inside a 6Kg frigate hull and not be too heavy, there might well be stability problems due to the components having to go where they need to go, rather than where they would suit you best. A 6Kg hull might well carry it all, but probably not a frigate shape. Perhaps, given that there is plenty of power there, a larger model, something that actually needs 1/6HP?

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