On Fri, 4 Jul 2008 15:19:27 -0700, "Calif Bill"
wrote:


"Richard Casady" wrote in message
.. .
On Fri, 4 Jul 2008 08:15:19 -0400, "Floyd"
wrote:

I've read that the jet boat's impeller system is about 30% less efficient
than a similarly powered outboard. Does that mean that a jet boat will
get
beat by an outboard, or just use more gas?

The jet will have a lower top speed. It will burn more fuel at any and
all lower speeds.

Casady

It will burn more fuel. May or may not be faster. There are different type
pumps. There are axial flow, low pressure pumps that are slower speed, but
handle white water better at reloading up after losing intake water, and
there are the high pressure pumps that are faster. Kodiak and Hamilton are
examples of the first, Berkeley and American Turbine are examples of the
second. Jet ski pumps are probably the most inefficient of all the pump
designs. Small engine and high RPM's trying to move lots of water through a
small impeller pump. The newer Hamilton 212's etc are about 95% efficiency
of props.

Our Turbocraft is axial flow, and in fifty years has never sucked air
into the intake. Weeds once. Once the ski tow rope. Had to turn the
engine and pump backwards, with a pipe wrench on the driveshaft, to
get it out. The pump is a licenced copy of a [New Zealand] Hamilton.

Casady

"Richard Casady" wrote in message
...
On Fri, 4 Jul 2008 15:19:27 -0700, "Calif Bill"
wrote:


"Richard Casady" wrote in message
. ..
On Fri, 4 Jul 2008 08:15:19 -0400, "Floyd"
wrote:

I've read that the jet boat's impeller system is about 30% less
efficient
than a similarly powered outboard. Does that mean that a jet boat will
get
beat by an outboard, or just use more gas?

The jet will have a lower top speed. It will burn more fuel at any and
all lower speeds.

Casady

It will burn more fuel. May or may not be faster. There are different
type
pumps. There are axial flow, low pressure pumps that are slower speed,
but
handle white water better at reloading up after losing intake water, and
there are the high pressure pumps that are faster. Kodiak and Hamilton
are
examples of the first, Berkeley and American Turbine are examples of the
second. Jet ski pumps are probably the most inefficient of all the pump
designs. Small engine and high RPM's trying to move lots of water through
a
small impeller pump. The newer Hamilton 212's etc are about 95%
efficiency
of props.

Our Turbocraft is axial flow, and in fifty years has never sucked air
into the intake. Weeds once. Once the ski tow rope. Had to turn the
engine and pump backwards, with a pipe wrench on the driveshaft, to
get it out. The pump is a licenced copy of a [New Zealand] Hamilton.

Casady

Mine is a Kodiak 3 stage that is a licensed copy of an older hamilton. I
have sucked weeds several times and sticks a couple times. Does not take
much of a stick stuck in the impeller to cause cavitation. Makes me think
a lot of prop boats with small dings in the prop are effecting performance
huge amounts.

"Calif Bill" wrote in
m:

Mine is a Kodiak 3 stage that is a licensed copy of an older hamilton.
I have sucked weeds several times and sticks a couple times. Does
not take much of a stick stuck in the impeller to cause cavitation.
Makes me think a lot of prop boats with small dings in the prop are
effecting performance huge amounts.




Jetboat Economy.....ha ha ha....you guys are too funny!

Isn't that an oxymoron??

"Larry" wrote in message
...
"Calif Bill" wrote in
m:

Mine is a Kodiak 3 stage that is a licensed copy of an older hamilton.
I have sucked weeds several times and sticks a couple times. Does
not take much of a stick stuck in the impeller to cause cavitation.
Makes me think a lot of prop boats with small dings in the prop are
effecting performance huge amounts.




Jetboat Economy.....ha ha ha....you guys are too funny!

Isn't that an oxymoron??


I did not buy an aluminum jetboat for the economy. I bought it to run
shallow and tree filled rivers. Better economy than a jetski. My 351W
engine got me about 2 mpg, 3400# 21' boat. The newer 5.7L mpi gets better,
but have not really checked on the mpg yet.

"Calif Bill" wrote in
m:

I did not buy an aluminum jetboat for the economy. I bought it to run
shallow and tree filled rivers. Better economy than a jetski. My
351W engine got me about 2 mpg, 3400# 21' boat. The newer 5.7L mpi
gets better, but have not really checked on the mpg yet.



What's really unfortunate is the unscrupulous American dealers for the
Mercury Sport Jet-powered boats and PWC dealers who purposely DON'T tell
new owners their jets will be destroyed if they suck up a rock the diameter
of a quarter and get it wedge between the whirling impeller and the stator
1/8" behind it in the flow. Many PWC and jetboats are destroyed here
because owners don't know the difference between Australian-style flats
boats powered by filtered jets with no stator and what's being sold as
jetboats in the USA....never made to handle a rock.

"Larry" wrote in message
...
"Calif Bill" wrote in
m:

I did not buy an aluminum jetboat for the economy. I bought it to run
shallow and tree filled rivers. Better economy than a jetski. My
351W engine got me about 2 mpg, 3400# 21' boat. The newer 5.7L mpi
gets better, but have not really checked on the mpg yet.



What's really unfortunate is the unscrupulous American dealers for the
Mercury Sport Jet-powered boats and PWC dealers who purposely DON'T tell
new owners their jets will be destroyed if they suck up a rock the
diameter
of a quarter and get it wedge between the whirling impeller and the stator
1/8" behind it in the flow. Many PWC and jetboats are destroyed here
because owners don't know the difference between Australian-style flats
boats powered by filtered jets with no stator and what's being sold as
jetboats in the USA....never made to handle a rock.


You need to look at the Hamilton and Kodiak pumps online. They have
stators. Most have stainless impellers and aluminum stators. And the grate
only filters to about 1/2". The clearance is close enough that the rock
does not lodge between the impeller and the stator, but will ding both.

I just outfitted my Yamaha with a Garmin 545s, and on the next fill-up, I'll
report what my MPG is with the twin MR-1s. I don't expect anything
outstanding, but I thinl it will be better than expected.

--Mike

"Calif Bill" wrote in message
m...

"Larry" wrote in message
...
"Calif Bill" wrote in
m:

Mine is a Kodiak 3 stage that is a licensed copy of an older hamilton.
I have sucked weeds several times and sticks a couple times. Does
not take much of a stick stuck in the impeller to cause cavitation.
Makes me think a lot of prop boats with small dings in the prop are
effecting performance huge amounts.




Jetboat Economy.....ha ha ha....you guys are too funny!

Isn't that an oxymoron??


I did not buy an aluminum jetboat for the economy. I bought it to run
shallow and tree filled rivers. Better economy than a jetski. My 351W
engine got me about 2 mpg, 3400# 21' boat. The newer 5.7L mpi gets
better, but have not really checked on the mpg yet.