Re: [AtkinBoats] Did Atkin mean BHP or SHP?
- The ratings of older engines were a bit conservative, more like
"contiuous" or maybe "medium duty" for the "high speed" engines, rather
than the "peak" horsepower most modern engines are advertised at. An old
engine rated at 2000 rpm is designed to run at 2000 rpm all the time. So
my guess is that the ratings are BHP, but conservative. Most of the Atkin
designs don't use a power robbing reduction gear either, though you'll
usually need to use one with modern engines in the same designs.
But. I've run across a curious thing in the listings of marine engines in
old Rudder magazines I've been looking at, some manufacturers give the
rpm. of their engines at the output shaft if there's a reduction gear.
Thus an engine that is rated at 2000 rpm with a straight through reverse
gear is rated at 1000 rpm. if it has a 2:1 reduction gear! That points to
the possibility that hp. is rated at the output shaft too, except that the
hp. figures are the same for the same model engine whether it ahs a
reduction gear or not... <shrug>
On Thu, 19 Jul 2007 18:42:27 -0700, adharvey2 wrote:
> I'm wondering if when Wm. Atkin wrote about those older small gas
> inboard engines like the Grays, Scripps, Universals, etc., should the
> HP ratings he quotes be thought of as BHP or SHP? I'm thinking that
> since they were marketed as marine engines, often with gear included,
> that maybe the HP figures were meant to be taken as SHP, but I"m just
People say that life is the thing, but I prefer reading. <Logan
- Gears are very efficient. According to Mark's Handbook, the efficiency
of single reduction spur gears is 93-96%. Since most marine gearboxes
are single-reduction, this means that SHP is almost identical to BHP.
If you think anything on a boat is designed to better than 7% accuracy,
- That is welcome news. I read in some remote corner of the Glen-L
website that to get SHP from BHP multiply by 87%. That is quite a loss.
--- In AtkinBoats@yahoogroups.com, "alankornhauser" <alkorn@...> wrote:
> Gears are very efficient. According to Mark's Handbook, the efficiency
> of single reduction spur gears is 93-96%. Since most marine gearboxes
> are single-reduction, this means that SHP is almost identical to BHP.
> If you think anything on a boat is designed to better than 7% accuracy,
> think again!