Brian,

I own a Nordhavn 50 which comes with the bulbous bow.  I had read a
lot about the advantages of a bulbous bow, many of them from PAE
publicity literature. At that time couldn't understand why anyone would
even have a boat without a bulbous bow. In fact, when PAE introduced
the Nordhavn 47, I asked Jim Leishman why they didn't put a bulbous bow
on the boat.  With 20/20 hindsight, I feel like his reply was a little
vague and evasive, "We don't feel that a bulbous bow is effective in a
boat under 50'."  Subsequent designs from PAE have either not included
the bulb at all or included it only as an option.  I personally feel
that the largest driving factor in PAE getting away from the bulbous
bow is bulb slap in heavy weather. All of the propaganda that I read
and heard about bulbous bows is true as far as it went.  The bulbous
bow did indeed allow the boat to go faster, sometimes even faster than
what the theoretical equations stipulate.  The Nordhavn 50, and mine
is a fine example, is one of the fastest boats PAE produces and they
can't exactly explain why.  The bulbous bow does indeed reduce the
pitching moment, although I'm not sure that it's the 20% reduction that
the tank tests showed.  Finding out about the bulb slap was somewhat of
a surprise to me although I remember reading something about it
earlier.  It is something that I can easily live with.  The weather
conditions have to be just right for it to occur.  We have been in some
pretty heavy stuff without a hint of bulb slap.

I don't know if experimenting with different shapes would help.    I'm
not sure it's cost effective.  I have a suspicion that bulbous bows
cost more than the advantages you get from them.  I also suspect that
they are a marketing tool to convince prospective buyers that a boat
must truly be a passagemaker because it has a bulbous bow.  I have
heard of a short lived experiment on a Nordhavn 62, which has a bulb.
They attached stabilizing fins, naiids I think, to either side of the
bulbous bow.  The fins were to work in the same direction at the same
time to reduce pitching motion of the boat.  I can imagine what a slap
they must have produced when seas got rough enough to pull the bow out
of the water.

The critical factor in  our family is the fact that my wife doesn't
like bulb slap much.    I love my Nordhavn 50, but I am trying to trade
up to a Nordhavn 55 with a fine entry bow.  It comes under the heading
of "If Momma ain't happy, ain't  nobody happy."    The extra room will
also be nice as my brother lives aboard full time.

An interesting side story.  Recently I was discussing bulb slap with a
friend of mine.  He told me "Oh yeah, I've been through that when I
was in the Navy."  I asked him about it.  It was when he was on the
USS Eisenhower and they were going from the Atlantic to the Pacific.
As they rounded Cape Horn (too big for the Panama Canal), they got into
sixty foot waves and were getting bulb slap big time.  That conjures
up quite an image for me:  a nuclear aircraft carrier well in excess of
1000' getting bulb slap!

Phil Eslinger

Well, if you like your boat, you could cut it off. Would a "V" bottomed bulb
lose its beneficial chacteristics?

On a 50 foot boat, I assume that your bow thruster is aft of the bulb. The
hull is likely to retain its mysterious performance advantages even with the
bulb lopped off - just not as much. Go ahead, experiment for us!

In 1969, Mr. Stephens of S&S told me that my Tartan 27 far outstripped
theoretical performance parameters because naval architecture was 90%
science and 10% art. Even with computers and tank tests, the art factor is
likely still there.
Ron Rogers