"Hull speed" is voodoo science
 

Is it your position that drag on the hull does not increase with
speed?

the induced drag on a hull goes up at the cube of speed and has nothing to do
with "climbing the bow wave". A cubic function is mathematically well behaved,
meaning nothing untoward happens anywhere on the curve.

"Hull speed" is voodoo science
 

comments interspersed.

Is it your position that drag on the hull does not increase with
speed?

the induced drag on a hull goes up at the cube of speed and has nothing to
do
with "climbing the bow wave". A cubic function is mathematically well
behaved,
meaning nothing untoward happens anywhere on the curve.

Then it follows from observation of this well behaved curve that,
given sufficient horsepower, a displacement hull is not limited in
speed.

this is true, though a cube function explodes in magnitude. But it does so in
a mathematically well-behaved way.


Or perhaps, to put it another way, the wave system created by the hull
passing through the water is not limited in speed, either.

specious arguement unrelated to the discussion.


Thus, given the mathematical example, both the hull and the associated
wave system could travel at, say, 45 MPH for a 25 foot boat ....
assuming adequate available horsepower.

see above


--



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"Hull speed" is voodoo science
 

could travel at, say, 45 MPH for a 25 foot boat ....
assuming adequate available horsepower.

**assuming** the 25 foot boat takes 1 hp to go 1 mph, then it would take 4 hp
to go 2 mph: 16 hp to go 4 mph; 64 hp to go 8 mph; 256 hp to go 16 mph; 1024 hp
to 32 mph; ~2000 hp to 45 mph.

note, this is the hp needed to overcome induced drag at greater speeds. note
also that there is no break point anywhere on the hp vs speed curve due to
"climbing the bow wave"

note-2, **if** a boat were REQUIRED "to climb the bow wave" rather than slice
through wave, the extra hp needed is only about 40% more at 2x hull speed than
is needed just to overcome induced drag. Even at 4x hull speed, the increase
due to the alleged requirement "to climb the bow wave" not huge compared the hp
needed to overcome induced drag.

In fact, **if** the boat were REQUIRED "to climb the bow wave" (it is not
required) the extra hp needed only starts to become truly substantial only when
boat speed starts to get VERY high, i.e. two or three or four orders of
magnitude (that's 100x, 1000x 10,000x) greater than hull speed.

it ain't "climbing the bow wave" that limits the speed of a boat.

"Hull speed" is voodoo science
 

Is it your position that drag on the hull does not increase with
speed?


JAXAshby wrote:
the induced drag on a hull

A hull doesn't usually have "induced drag." That is a term specific to
the behavior of foils.

... goes up at the cube of speed

wrong

... and has nothing to do
with "climbing the bow wave".

wrong again, at least in practical terms.

Wow, a hull speed discussion with Jax and I almost missed it!




... A cubic function is mathematically well behaved,
meaning nothing untoward happens anywhere on the curve.

Can I quote you on that?



Gene Kearns wrote:
Then it follows from observation of this well behaved curve that,
given sufficient horsepower, a displacement hull is not limited in
speed.

If other factors are not considered, true. But what hull can withstand
the force generated by the nearly infinite horsepower that is required
for marginal increase in speed? Is the hull's reserve bouyancy
sufficient to keep it above the water level of it's own exaggerated wave
train at higher speeds?


Or perhaps, to put it another way, the wave system created by the hull
passing through the water is not limited in speed, either.

Actually, it is. Waves can only travel so fast... this is a physical
property of the fluid that forms the wave.


Thus, given the mathematical example, both the hull and the associated
wave system could travel at, say, 45 MPH for a 25 foot boat ....
assuming adequate available horsepower.

Probably yes.

The difference between "planing" and "displacement" is one of the most
misunderstood things about boats. But very few people can be as
consistently wrong, or as funny, as Jax. He was gifted even as a child.

DSK

"Hull speed" is voodoo science
 

a.) bull****
b.) bull****
c.) bull****
d.) you miss most things in life.

Is it your position that drag on the hull does not increase with
speed?


JAXAshby wrote:
the induced drag on a hull

A hull doesn't usually have "induced drag." That is a term specific to
the behavior of foils.

... goes up at the cube of speed

wrong

... and has nothing to do
with "climbing the bow wave".

wrong again, at least in practical terms.

Wow, a hull speed discussion with Jax and I almost missed it!




... A cubic function is mathematically well behaved,
meaning nothing untoward happens anywhere on the curve.

Can I quote you on that?



Gene Kearns wrote:
Then it follows from observation of this well behaved curve that,
given sufficient horsepower, a displacement hull is not limited in
speed.

If other factors are not considered, true. But what hull can withstand
the force generated by the nearly infinite horsepower that is required
for marginal increase in speed? Is the hull's reserve bouyancy
sufficient to keep it above the water level of it's own exaggerated wave
train at higher speeds?


Or perhaps, to put it another way, the wave system created by the hull
passing through the water is not limited in speed, either.

Actually, it is. Waves can only travel so fast... this is a physical
property of the fluid that forms the wave.


Thus, given the mathematical example, both the hull and the associated
wave system could travel at, say, 45 MPH for a 25 foot boat ....
assuming adequate available horsepower.

Probably yes.

The difference between "planing" and "displacement" is one of the most
misunderstood things about boats. But very few people can be as
consistently wrong, or as funny, as Jax. He was gifted even as a child.

DSK

"Hull speed" is voodoo science
 

Although you are a block head, you are not as well behaved a cube function.

JAXAshby wrote:
a.) bull****
b.) bull****
c.) bull****
d.) you miss most things in life.

"Hull speed" is voodoo science
 

I'd be very interested in hearing your explaination of how "induced drag"
occurs when moving a hull through water at or below hull speed.(or air for
that matter). I have a pretty good understanding of induced drag when moving
keels and rudders...hulls OTOH, I don't know about. Also, every formula that
I've looked at for calculating the induced drag coefficient is a square
function, not cube. But I'm always willing to learn when presented with a
valid argument based on facts.

"JAXAshby" wrote in message
...

the induced drag on a hull goes up at the cube of speed and has nothing to
do
with "climbing the bow wave". A cubic function is mathematically well
behaved,
meaning nothing untoward happens anywhere on the curve.

"Hull speed" is voodoo science
 

qweaver, listen up. "induced" drag does indeed go up by the square of the
speed. *however* the ***horse power*** required goes up at the sum of the
induced drag plus the additional hp needed for increased speed. in other words,
hp needed goes up at the cube of speed.

of course, *you* are not required to believe anything you don't understand, or
don't wish to "when presented with a valid arguement based on facts".