Rob,
fact is comparing technology is tough. Many terms don't work the way expected because we understand them differently. HP came from a desire to compare how many horses were required to do the same work as the new implement. But in all fairness no farmer in his right mind would work his horse to death so the farmer didn't have figures he could work with in the real world.
Today we understand horse power to a level but little is said about torque to most. You must be hauling something to care. Things have been clouded to a level by the amount a builder has overpowered his boat. You might look at torque as a measure that defines a motors ability not to stall out. Also torque defines the ability of the machine to swing a prop with little slip. Slip can be defined as turning of the prop without as much work out, as the power applied to it. With an IC engine slip is very important to allow the machinery to bring a boat onto plane. With an electric drive slip is not as important when accomplishing this objective because full torque is available at all speeds. Gearing is required to increase torque in all cases, ICE, or electric. With electric gearing helps keep the power demand lower on the motor so it will not overheat. With ICE gearing is required to keep the motor from stalling (not enough low end torque).
I hope you can see where I am headed with this.
HP requires a time element to apply as time is part of the equation. Torque has no time element. Electric motors are better measured with torque, quite opposite with ICE. HP is however important! Not for getting movement no matter how violent. Rather for top end. But this too can be confusing. The HP of an electric motor is shaft HP. HP of ICE is before any required machinery is added. i.e. generators, cooling pumps, fans, or any hardware that is required to keep it running.
With this information we can see that electric motors are quite straight forward and honest. On the other hand ICE is deceptive about what it can put out. the design of an ICE can lead to better torque, or higher HP, depending on internal design, and thus can't be compared unless we understand and have this information from the manufacturer.
For the above reasons, It is hard to believe that comparison is an option unless quite specific about equipment being replaced with all information about drive train and boat.
A story.
I had a 14' dink. The boat was designed for 5hp max. One day I happened upon an 18hp outboard. For giggles I put that outboard on the dink and took it for a test drive. The boat still had a hard time getting on plane (low torque). When up on plane the boat would skip along on the outboards lower end and the boat would only skip on the water every once in a while. All this at less than 1/4 throttle after I got on plane. Moral? Don't overpower a boat! and, torque is king in the water, something not advertised to heavily in the ICE business.
Kevin Pemberton
On 05/22/2011 08:08 PM, Rob Johnson wrote:
Rob , I'm actually trying to find some data , to be able to compare cold hard facts.
Its proving very difficult to do !.
Regards Rob J.
-- AspireOne Netbook running Ubuntu 11.04 Safe, Secure, Easy to use, Free Open Source Linux OS. Leaving Virus worries to the Windows Users!
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