Short Wave Sportfishing wrote:
This morning, while burning some old gas in the Ranger.....
2.5K - the shape of the wake is fully formed, but we're not quite
there yet.

http://www.home.earthlink.net/~tomf1...tfivestern.JPG

Actually, at this point, you're planing. The crest of the boat's stern
wave is noticably past the transom, and therefor by definition you're
exceeding hull speed... therefor planing. Of course, it's not an
either/or thing in the real world. The boat's weight is still largely
supported by displacement rather than dynamic lift, hence the hole in
the water which the wake is closing up.


3K - this is the transitional stage where the boat comes fully up on
the planing surface. It doesn't happen in short bursts on this boat -
it literally goes from 3K to 4K all at once and your on plane. The
planing wake shape is now fully formed.

http://www.home.earthlink.net/~tomf123/threeKstern.JPG

Notice the lack of bow wave.

http://www.home.earthlink.net/~tomf123/threekbowave.JPG

The bow wave is there, it's just behind you

I commend you for taking the time & effort to put some observation on
the wake. Far too many people pretend it's not there.

Somewhere floating around I have some pictures taken astern from the
Johnson 18 when it's planing, when close-hauled and under spinnaker.
When "fully planing" there's no wave train at all, just a flat swath of
white water. Of course the hull shape is much more efficient....

Fair Skies
Doug King

On Tue, 23 Nov 2004 21:46:53 -0500, DSK wrote:

Short Wave Sportfishing wrote:
This morning, while burning some old gas in the Ranger.....
2.5K - the shape of the wake is fully formed, but we're not quite
there yet.

http://www.home.earthlink.net/~tomf1...tfivestern.JPG

Actually, at this point, you're planing. The crest of the boat's stern
wave is noticably past the transom, and therefor by definition you're
exceeding hull speed... therefor planing. Of course, it's not an
either/or thing in the real world. The boat's weight is still largely
supported by displacement rather than dynamic lift, hence the hole in
the water which the wake is closing up.

Good point.

3K - this is the transitional stage where the boat comes fully up on
the planing surface. It doesn't happen in short bursts on this boat -
it literally goes from 3K to 4K all at once and your on plane. The
planing wake shape is now fully formed.

http://www.home.earthlink.net/~tomf123/threeKstern.JPG

Notice the lack of bow wave.

http://www.home.earthlink.net/~tomf123/threekbowave.JPG

The bow wave is there, it's just behind you

Yeah - I wondered how to phrase that. Thinking about it, I should
have said the bow wave moved aft.

I commend you for taking the time & effort to put some observation on
the wake. Far too many people pretend it's not there.

This boat has always interested me in that, as I've mentioned about a
zillion times, it has no bow lift and it's theoretical top speed is
about fifteen mph above what it actually gets (40 vs 55). It doesn't
act like it's supposed to. :)

Somewhere floating around I have some pictures taken astern from the
Johnson 18 when it's planing, when close-hauled and under spinnaker.
When "fully planing" there's no wave train at all, just a flat swath of
white water. Of course the hull shape is much more efficient....

I'd like to see those. I'm not sure I could agree about efficiency -
the Ranger hull is pretty efficient if only because of it's odd
performance.

TTFN,

Tom

"Bodies are for hookers and fat people."
Bender - "Futurama"

.... The boat's weight is still largely
supported by displacement rather than dynamic lift, hence the hole in
the water which the wake is closing up.

Short Wave Sportfishing wrote:
Good point.

I think most people overlook the real meaning of "planing" and prefer to
think of it as much faster than when it really begins to happen. But it
also effects steering, so it's important to know about.



I commend you for taking the time & effort to put some observation on
the wake. Far too many people pretend it's not there.


This boat has always interested me in that, as I've mentioned about a
zillion times, it has no bow lift and it's theoretical top speed is
about fifteen mph above what it actually gets (40 vs 55). It doesn't
act like it's supposed to. :)

No bow lift is nice, I bet the steering is well balanced through the
transition as well. Hull design has come a long way in the past 20
years, but then engineering costs money and most boat companies know
they can sell the same old same-old.

I'm curious about the top speed issue- have you gone into the prop
question? Is your motor getting up to rated RPM? Is the boat over weight?




Somewhere floating around I have some pictures taken astern from the
Johnson 18 when it's planing, when close-hauled and under spinnaker.
When "fully planing" there's no wave train at all, just a flat swath of
white water. Of course the hull shape is much more efficient....


I'd like to see those.

I'll hunt around for them. The shots were taken with a throwaway camera
and I never scanned them. The only reason I took them at all is that we
were in a race with the boats too spread out to be much excitement, and
I was concentrating on getting some shots of wife with the spinnaker.
The wake shots were kind of an afterthought

... I'm not sure I could agree about efficiency -
the Ranger hull is pretty efficient if only because of it's odd
performance.

heh heh look at the difference in horsepower. The Johnson 18 carries
about 600# total at 25 knots on about 10 or 12 horsepower. I'm sure your
boat is much heavier but if you wanted to plot both boats on a
power/speed/per pound graph, I'd bet a *lot* that the Johnson 18 is far
more efficient.

For one thing, the hull of a saliboat is shaped for much less drag than
a planing motorboat... it has to be, sailboats spend too much of their
time not planing and with too little horsepower available, so to shape a
sailboat for planing only cripples it. To get it to plane at all
requires more lift from the little power available... actually there are
exceptions to this, such as the unlimited skiffs. Secondly, things like
spray strakes add drag (they also stiffen the hull) and cost a lot,
efficiency-wise. It's like the difference between a jet & a glider. The
glider is more efficient, but then the jet doesn't need to be
efficient... but it does have other critical performance parameters.

Fair Skies
Doug King

On Wed, 24 Nov 2004 07:33:09 -0500, DSK wrote:

.... The boat's weight is still largely
supported by displacement rather than dynamic lift, hence the hole in
the water which the wake is closing up.

Short Wave Sportfishing wrote:
Good point.

I think most people overlook the real meaning of "planing" and prefer to
think of it as much faster than when it really begins to happen. But it
also effects steering, so it's important to know about.

Also a good point.

I commend you for taking the time & effort to put some observation on
the wake. Far too many people pretend it's not there.

This boat has always interested me in that, as I've mentioned about a
zillion times, it has no bow lift and it's theoretical top speed is
about fifteen mph above what it actually gets (40 vs 55). It doesn't
act like it's supposed to. :)

No bow lift is nice, I bet the steering is well balanced through the
transition as well. Hull design has come a long way in the past 20
years, but then engineering costs money and most boat companies know
they can sell the same old same-old.

It's odd that you should mention that - the steering is almost exactly
neutral at all speeds. I can turn against the engine torque as well
as I can turn with the engine torque - it's pretty much effortless.
The engine does have hydraulic steering, but I would expect some
feedback turning against the torque. I could be wrong.

I'm curious about the top speed issue- have you gone into the prop
question? Is your motor getting up to rated RPM? Is the boat over weight?

It something that has puzzled me since the git go (the boat is a 2000
and I bought it left over in 2001). I've gone up/down in location,
up/down in size and pitch, I put a test prop on it and ran it - it is
producing 200 hp where it's supposed to - the boat is heavy, but
normally, I'm the only one who uses it, so weight isn't really a
factor. Compared to the fellow over in RI who has the identical boat
except that he has a 200 Yamaha HPDI, it is short of top end by 15 mph
- on a GPS - his boat will do 57 Mph compared to 40/43 for mine at
WOT. He has a couple hundred more RPM than I do, but I don't think
that's significant.

To give you an example, I'm running a 14 1/4 x 23 SS now and have gone
up as high as a 14 1/2 x 23 and have changed every pitch from 17 to 23
- no change in speed. No joke - no change in speed. Change in RPM,
no change in speed.

It's going to drive me nuts eventually. :)

~~ snippage ~~

I'll hunt around for them. The shots were taken with a throwaway camera
and I never scanned them. The only reason I took them at all is that we
were in a race with the boats too spread out to be much excitement, and
I was concentrating on getting some shots of wife with the spinnaker.
The wake shots were kind of an afterthought

... I'm not sure I could agree about efficiency -
the Ranger hull is pretty efficient if only because of it's odd
performance.

heh heh look at the difference in horsepower. The Johnson 18 carries
about 600# total at 25 knots on about 10 or 12 horsepower. I'm sure your
boat is much heavier but if you wanted to plot both boats on a
power/speed/per pound graph, I'd bet a *lot* that the Johnson 18 is far
more efficient.

Good point.

For one thing, the hull of a saliboat is shaped for much less drag than
a planing motorboat... it has to be, sailboats spend too much of their
time not planing and with too little horsepower available, so to shape a
sailboat for planing only cripples it. To get it to plane at all
requires more lift from the little power available... actually there are
exceptions to this, such as the unlimited skiffs. Secondly, things like
spray strakes add drag (they also stiffen the hull) and cost a lot,
efficiency-wise. It's like the difference between a jet & a glider. The
glider is more efficient, but then the jet doesn't need to be
efficient... but it does have other critical performance parameters.

I'll admit, I don't know a whole bunch about hull design because I've
never had to get into it. I'm not much of a sailor either, so I can
see where it would be of interest to guys with sticks in the middle of
their boats compared to us brute hp types. :)

Need to do some reading over the holidays. :)

Later,

Tom

On Wed, 24 Nov 2004 11:52:02 GMT, Short Wave Sportfishing
wrote:
This boat has always interested me in that, as I've mentioned about a
zillion times, it has no bow lift and it's theoretical top speed is
about fifteen mph above what it actually gets (40 vs 55). It doesn't
act like it's supposed to. :)

Have you tried a high rake prop? That should increase your bow lift.
Also a setback engine bracket can also increase bow lift.

Dave