<[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > All I can remember from school about Horsepower was that one was equal to > 550 somethings-or-other per hour (but then a 40 year gap may have confused > my > recollections). On the other hand my dad says horsepower has no absolute > relation to engine power it is an arbitrary taxation calculation which was > based > on either engine cylinder bore or stroke, but illogically not both.
You're both right. They may (or may not) have been the same originally, in the early 20th century, but soon became completely different as engines became more efficient. In effect you can think of them as two different things (an engine power output, and an arbitrary tax calculation) that happen to be called by the same name. One horsepower is actually about 750 watts (0.75 kilowatts). Note also that a horse can produce considerably more than one horsepower for a short time - IIRC about 8 hp for a while - as the original unit related to the average power a horse could produce over a whole day (including time off for rests, mealbreaks, etc). > Clearly my 25 HP (or is it BHP?) is very different from the 20 ish HP from > an SR or JP2 or whatever. No it's exactly the same. The difference is that the old engine produced it at lower engine revs than your modern engine does. The modern engine is usually geared down so that the prop shaft revolves slowly; if it was geared down to the same speed as the old engine, then it could swing the same big prop if there was room to fit it under the boat, but more commonly on a modern boat you use a smaller prop and don't gear the engine down quite so much. -- Allan Jones - N/B 'Keeping Up' http://www.keeping-up.co.uk ------------------------ Yahoo! Groups Sponsor --------------------~--> See what's inside the new Yahoo! Groups email. http://us.click.yahoo.com/2pRQfA/bOaOAA/yQLSAA/ygtolB/TM --------------------------------------------------------------------~-> Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/canals-list/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
