Reply
 
Thread Tools Search this Thread
 
Old 25 December 2013, 16:29   #21
Member
 
Country: UK - England
Town: London
Boat name: Jeepster
Make: Marina 16 GT
Length: 5m +
Engine: Outboard, Petrol, 30
Join Date: Sep 2012
Posts: 52
Quote:
Originally Posted by bartiny View Post
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.
__________________

__________________
jeepster is offline   Reply With Quote
Old 25 December 2013, 16:58   #22
RIBnet admin team
 
Nos4r2's Avatar
 
Country: UK - England
Town: The wilds of Wiltshire
Boat name: WhiteNoise/Dominator
Make: Ballistic 7.8/SR5.4
Length: 7m +
Engine: Opti 225/Yam 85
MMSI: 235090687/235055163
Join Date: Jul 2005
Posts: 12,645
RIBase
Quote:
Originally Posted by jeepster View Post
1lbs thrust = about 1.5-2 hp
__________________
Need spares,consoles,consumables,hire,training or even a new boat?

Please click HERE and HERE and support our Trade Members.

Join up as a Trade member or Supporter HERE
Nos4r2 is offline   Reply With Quote
Old 25 December 2013, 17:32   #23
RIBnet supporter
 
Pikey Dave's Avatar
 
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 7,579
RIBase
Quote:
Originally Posted by Nos4r2 View Post
Gets comfy & pours a large one
__________________
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5
Pikey Dave is online now   Reply With Quote
Old 25 December 2013, 18:03   #24
Member
 
Country: UK - England
Town: Margate / Ramsgate
Boat name: Ballistic
Make: Ballistic
Length: 7m +
Engine: Yam HPDI 250
Join Date: Feb 2002
Posts: 2,835
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 :-(
__________________
Daniel is offline   Reply With Quote
Old 25 December 2013, 19:44   #25
RIBnet supporter
 
bartiny's Avatar
 
Country: UK - England
Town: Accrington
Length: no boat
Join Date: Oct 2012
Posts: 451
Quote:
Originally Posted by jeepster View Post
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??
__________________
bartiny is offline   Reply With Quote
Old 25 December 2013, 19:52   #26
RIBnet admin team
 
Nos4r2's Avatar
 
Country: UK - England
Town: The wilds of Wiltshire
Boat name: WhiteNoise/Dominator
Make: Ballistic 7.8/SR5.4
Length: 7m +
Engine: Opti 225/Yam 85
MMSI: 235090687/235055163
Join Date: Jul 2005
Posts: 12,645
RIBase
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.
__________________
Need spares,consoles,consumables,hire,training or even a new boat?

Please click HERE and HERE and support our Trade Members.

Join up as a Trade member or Supporter HERE
Nos4r2 is offline   Reply With Quote
Old 26 December 2013, 03:22   #27
Member
 
Country: UK - England
Town: Alton
Boat name: Douggie
Length: 4m +
Engine: 40 mariner
Join Date: Jun 2009
Posts: 112
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!
__________________
Bieny is offline   Reply With Quote
Old 26 December 2013, 04:09   #28
Member
 
Country: UK - England
Length: 3m +
Join Date: Sep 2008
Posts: 2,250
Quote:
Originally Posted by bartiny View Post
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...
__________________
ShinyShoe is offline   Reply With Quote
Old 26 December 2013, 05:00   #29
Member
 
Country: UK - England
Town: Alton
Boat name: Douggie
Length: 4m +
Engine: 40 mariner
Join Date: Jun 2009
Posts: 112
Quote:
Originally Posted by ShinyShoe View Post
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!
__________________
Bieny is offline   Reply With Quote
Old 26 December 2013, 05:19   #30
Member
 
A1an's Avatar
 
Country: UK - Scotland
Town: Fort William
Make: Humber Destroyer
Length: 5m +
Engine: Yamaha F80
Join Date: Mar 2012
Posts: 2,239
RIBase
Quote:
Originally Posted by ShinyShoe View Post

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?
__________________

__________________
There is a place on this planet for all of Gods creatures.........right next to my tatties and gravy.
A1an is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 03:12.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.