Great example! A reasonably fit person can produce around 100, maybe 150 watts, continuously. Even the very best athletes can only produce maybe 400 to 500 watts, and then only for relatively short periods of time.
As I, and others, have found, it takes very little power to keep a displacement hull moving in our canal system. The speed limit is 4 mph, there is no significant current and the canals are more often than not fairly well sheltered from high winds.
The secret lies in matching an electric drive system to the hull power requirements, and allowing for the significant excess power that is needed to stop and manoeuvre the boat. All that weight needs significant power to get moving, but very little power to keep it moving.
Narrowboats are pretty easily driven hulls, as they are pretty long and thin. They have a displacement hull speed that is much higher than the speed limit, meaning that virtually all the drag comes from wetted area. A simple calculation based on wetted are will give a pretty good approximation of power required for cruise, and the prop etc should be optimised for this condition. The motor needs to be capable of maybe five times the cruise power (or more) to give reasonable manoeuvre capability. It's very handy to have a good "emergency stop" capability on our canals!
--- In electricboats@yahoogroups.com, "Keith Russell" <mooncat_2005@...> wrote:
>
> It is true that a narrowboat needs little power to reach the 4mph
> speed limit. I once towed an eight-ton wooden boat, drawing 8",
> at a fast walking pace for 20 miles, no locks to negotiate. once
> you reach max speed, it needs very little to keep it moving.
>
> PS I wasn't built like a weightlifter, just an average teenager.
> --
> Keith Russell
> [1]mooncat_2005@...
>
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