[PUP] NOSE JOBS/Bulb bows/fuel use

[Peter Pisciotta]

> I would suggest looking very carefully at 
> other boats in the sub 60 foot 
> range before adding any bulbous bow 
> protuberances to a sub 60 foot boat.
> 
> That is about the lower range of usefulness.

I believe Nordhavn/PAE toyed with bulbous bows in the
early N46 models. While I hesitate to speak for their
conclusions, I assume they did not find the
efficiencies they had hoped for which is why the
appendage was abandoned in the N46's, and didn't
appear in the N47's, N43,s N40's, etc. I can tell you
from personal experience with N57's that the bow slap
that Scott mentions is extremely annoying when heading
to weather. My guess is that the water 'claps' when it
rejoins atop the bulb (or perhaps slaps the hull) and
makes a rather thunderous noise throughout the boat.
While there's no structural downside to it, it can be
really annoying after a few days. I personally
wouldn't have one on a boat, but its a personal thing.
I have never read anyting to suggest an efficiency
improvement of more than a couple percent, even in
large ships. For a large ship burning tens of
thousands of gallons of fuel a year, for 30 +/- years,
a 2% improvement adds up. For a recreational boat -
even heavily cruised, I doubt it makes financial
sense.

At the risk of getting beyond my technical tether in
boat design, I suspect a better place to look for
efficiencies is properly matching the hull form to the
desired speed/engine/displacement factors. I believe
the naval architects refer to one aspect of this as
Prismatic Coefficient ('PC' - there are probably other
parameters too). My guess is a properly designed hull
matched with optimized machinery operated within it's
design parameters will be the most efficient option in
the size range we are dicussing. 

Peter
W36 Sedan (no idea what my PC is)
San Francisco



=======================
Peter Pisciotta
415-902-8439