T-Pain Is On A Boat: Re: [Electric Boats] RE: 5KW or 10 KW

Saturday, March 22, 2014

Re: [Electric Boats] RE: 5KW or 10 KW

Eric,

Thanks. I wasn't sure if we were talking long tons, normal tons, or what the coast guard documented my boat as being, which makes no sense whatsoever. So, back to the 1KW/ton rule of thumb. It appears this is based on the drive manufacturer's nameplate which none of us seem to be able to reach, at least for very long, and one guy's 10KW system could vary from another's. Example, I have 2X10KW systems and 13.5 ton displacement. This would give me 1.48 KW per ton. Since I know I'll never get 20KW from my system, except for maybe when docking, the 1.48 number really isn't correct. Also, for the KW number are we talking strictly about DC volts X DC amps into the controller, KW into the motor or power at the propellor. It seems our rule of thumb has no rules.

Chris

Sent from myPhone

On Mar 22, 2014, at 18:30, <ewdysar@yahoo.com> wrote:

Hi Chris,

Short answer. One ton is 2000 pounds, just like they teach in elementary school. When we refer to 1kW per ton, we are referring to the boat's design displacement. As an example, my 10,200 pound 30' ketch is 5.1 tons.

For more fun facts about "tons", from Wikipedia:
The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of mass, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.
It is derived from the tun, the term applied to a barrel of the largest size. This could contain a volume between 210 and 256 gallons (800 to 1000 L), which could weigh around 2,000 pounds (900 kg) and occupy some 60 cubic feet (1.7 m³) of space.^[1]
In the United Kingdom the ton is defined as 2,240 pounds (1,016 kg) (avoirdupois pounds).^[2] From 1965 the UK embarked upon a programme of metrication and gradually introduced metric units, including the tonne (metric ton), a non-SI metric unit defined as 1000 kg. The UK Weights and Measures Act 1985 explicitly excluded from use for trade many units and terms, including the ton and the term "metric ton" for "tonne".^[3]
In the United States and formerly Canada^[4] a ton is defined to be 2,000 pounds (907 kg).
Where confusion is possible, the 2240 lb ton is called "long ton" and the 2000 lb ton "short ton"; the tonne is distinguished by its spelling, but usually pronounced the same as ton, hence the US term "metric ton". In the UK the final "e" of "tonne" can also be pronounced (/ˈtʌnɪ/),^[5] or "metric ton" when it is necessary to make the distinction.
Where accuracy is required the correct term must be used, but for many purposes this is not necessary: the metric and long tons differ by only 1.6%, and the short ton is within 11% of both. The ton is the heaviest unit of weight referred to in colloquial speech.
The term "ton" is also used to refer to a number of units of volume, ranging from 35 to 100 cubic feet (0.99 to 2.83 m³) in capacity.
It can also be used as a unit of energy, expressed as an equivalent of coal burnt or TNT detonated.
In refrigeration, a ton is a unit of power. It is the power required to melt or freeze one short ton of ice per day. The refrigeration ton·hour is a unit of energy, the energy required to melt or freeze ¹⁄₂₄ short ton of ice.

Fair winds,
Eric
Marina de Rey, CA