R.W. Behan wrote:
I'm not terribly impressed with Hurth transmissions. I had a 100 mated to a
35hp Perkins in my Westsail 32 that failed after only a couple of hundred
hours. I had it rebuilt, and then it failed again. Thinking the
transmission was simply too lightweight to shove the Westie around, I
replaced it with a 150, a much huskier transmission. (None of these
shenanigans were covered by Hurth, btw.) That seemed to do the trick, and
two subsequent owners of the boat, as far as I know, have not had any
further problems.

We now have a Victory Tug with a 150 hp. Cummins and a Borg Warner Velvet
Drive transmission: a truly honkin' gearbox.

This gearbox is now the ZF 10 M

The HBW 100's torque rating is pretty low. For a 2.045 ratio, the
maximum HP / RPM is 38 HP @ 3000 RPM. So while a 35 HP / 3000 Perkins
may just be under the maximum rating, if you miss the footnote you
might be in trouble, depending on the number of cylinders.

Note: For all "M" (Mechanical) transmissions reduce power capacity by
the following shock factors: 1 cylinder engine ÷ 1.25, 2 cylinder
engine ÷ 1.20, 3 cylinder engine ÷ 1.15"

The "Pleasure" rating isn't very high either:

"Highly intermittent operation with very large variations in engine
speed and power
Average engine operating
hours limit: 500 hours/year
300 hours/year for mechanical gearboxes"

Translation - don't expect too much at this rating. Don't run it all
day at full power.

Here's the ratings page:
http://zf-marine.com/ZFR/Transmissio...ngs&GN=ZF_10_M

We had one on a 23 HP, 3000 RPM Isuzu. Put 1800 hours on it over 4
years. Never hiccuped. I suspect that the box is just undersized for
that size engine

Evan Gatehouse