Horsepower = Thrust ??? - Page 2

jeepster · 25 December 2013, 21:29

Quote:

Originally Posted by bartiny

Probably a simple question but here goes

I am thinking about a electric outboard as a auxillery as my Mariner 4hp will not fit on the transom with the 25 hp (cannot get full lock) and it gets in the way carrying it in the sib.

So as the 4hp pushes the sib along very well I would like (I think) a simular powered electric motor so is there a formula to work out how many lbs of thrust I will need to equate to 4hp.

Also any positives or negatives for this approach?

Sorry just done a search looks like 17lbs = 1hp (uncle al) and judging by some of the comments it might not be such a good idea after all.

1hp= aproximately 746 Watts and Watts = Volts x Amps so if you know the current draw in Amps of your electric outboard and its Voltage you can easily work out its hp...Then you have to minus the losses due to propeller efficiency (the most efficient open prop is about 69% efficient. Using a Kort nozzle can add an extra 17% efficiency but most boaters don't use them. so assume 70% efficeincy to be is the best case senario) to get the actual final hp rating. 1lbs thrust = about 1.5-2 hp (there is no direct conversion but thats the factor generally recognised) so once you know how much final hp you have you can work out the approximate thrust in lbs. To work out the thrust in kg divide by 2.2.

Nos4r2 · 25 December 2013, 21:58

Quote:

Originally Posted by jeepster

1lbs thrust = about 1.5-2 hp

Pikey Dave · 25 December 2013, 22:32

Quote:

Originally Posted by Nos4r2

Gets comfy & pours a large one

Daniel · 25 December 2013, 23:03

My understanding of the kort nozzle concept is that it only improves efficiency at slow speeds and infact decreases efficiency at higher speeds. I think that's why they aren't found on fast leisure boats.

I'm not an expert on props or hydrodynamics but the concept of something for nothing always interests me... This isn't the case here :-(

bartiny · 26 December 2013, 00:44

Quote:

Originally Posted by jeepster

1hp= aproximately 746 Watts and Watts = Volts x Amps so if you know the current draw in Amps of your electric outboard and its Voltage you can easily work out its hp...Then you have to minus the losses due to propeller efficiency (the most efficient open prop is about 69% efficient. Using a Kort nozzle can add an extra 17% efficiency but most boaters don't use them. so assume 70% efficeincy to be is the best case senario) to get the actual final hp rating. 1lbs thrust = about 1.5-2 hp (there is no direct conversion but thats the factor generally recognised) so once you know how much final hp you have you can work out the approximate thrust in lbs. To work out the thrust in kg divide by 2.2.

How can 1lb of thrust = 1.5-2hp? if that is the case then a little 17lbs thrust electric motor is equal to app. 25>34hp?

Is this a case of "Bullshit baffles brains"?

As for the rest of the post??

Nos4r2 · 26 December 2013, 00:52

Take a read of his 'trailer build' thread bartiny. It might give you an insight. I take everything he says with several buckets of salt.

Bieny · 26 December 2013, 08:22

I sell Torqeedo outboards and have tried the whole range on a variety of boats in various conditions.
The Travel 1003 is the only model really suitable as an aux as it has an integrated battery, I use it regularly for trips in the harbour and I swap to it for fishing as the 2 stroke doesn't really like idling for long periods. However I would not want to be relying on it to get me back into the harbour against wind and/or tide, it has the power but not the battery life. It would be better than nothing though!

ShinyShoe · 26 December 2013, 09:09

Quote:

Originally Posted by bartiny

How can 1lb of thrust = 1.5-2hp? if that is the case then a little 17lbs thrust electric motor is equal to app. 25>34hp?

oooh... all excited coz the 1003 has a static thrust of 67lb so thats like MASSIVE power...

Would that be because thrust is effectively a measure of pressure rather than workdone but horse power is work done (i.e. pressure applied over a defined period of time)

Bieny's 1003 has a stated propulsion power of 480W which is 480Nm/s. 1HP = 550ft.Lb/s which seems to often be translated to about 750Nm/s. i.e. 1HP = 750W of OUTPUT power. By my calculations that makes it about 2/3rd HP.

Oh and based on Jeepster's principle he thinks the energy applied all comes out the engine and then 30% is lost by the prop. Well the 1003 consumes 1000W to give you 480W.

The 1003 has ~ 500Wh battery so in theory you could run the motor max out for 30mins. You'd muller the battery doing that though! So probably more like 20mins...

Bieny · 26 December 2013, 10:00

Quote:

Originally Posted by ShinyShoe

The 1003 has ~ 500Wh battery so in theory you could run the motor max out for 30mins. You'd muller the battery doing that though! So probably more like 20mins...

That's about spot on, flat out for about 26 mins. It's ok to run the battery to 0% - except once you've done that your buggered!

A1an · 26 December 2013, 10:19

Quote:

Originally Posted by ShinyShoe

oooh... all excited coz the 1003 has a static thrust of 67lb so thats like MASSIVE power...

Would that be because thrust is effectively a measure of pressure rather than workdone but horse power is work done (i.e. pressure applied over a defined period of time)

Bieny's 1003 has a stated propulsion power of 480W which is 480Nm/s. 1HP = 550ft.Lb/s which seems to often be translated to about 750Nm/s. i.e. 1HP = 750W of OUTPUT power. By my calculations that makes it about 2/3rd HP.

Oh and based on Jeepster's principle he thinks the energy applied all comes out the engine and then 30% is lost by the prop. Well the 1003 consumes 1000W to give you 480W.

The 1003 has ~ 500Wh battery so in theory you could run the motor max out for 30mins. You'd muller the battery doing that though! So probably more like 20mins...

You aren't related to Stephen Hawkins by any chance?

Nos4r2 · 26 December 2013, 11:59

Well, I'm convinced. I'm replacing the Opti with 6 of these:-

bartiny · 26 December 2013, 13:55

Quote:

Originally Posted by Nos4r2

Well, I'm convinced. I'm replacing the Opti with 6 of these:-

Carefull you might pull the transom off

See what you meant with the Trailer Thread Nos Jeeze!! I bet he is still looking for a Girlfriend

ShinyShoe · 26 December 2013, 15:00

He wont need to look for a grilfriend... he'll have made one that everyone said wouldn't be up to the job but he insisted he was doing it anyway...

...dya think he made a man doll?

Nos4r2 · 26 December 2013, 22:16

Quote:

Originally Posted by ShinyShoe

He wont need to look for a grilfriend... he'll have made one that everyone said wouldn't be up to the job but he insisted he was doing it anyway...

...dya think he made a man doll?

First sex doll launched into space reaches new heights, then blows over Nevada - YouTube