Short Wave Sportfishing wrote in message
...

The Contender is a little different. I go get bow lift, but I
actively trim the engines on take off which reduces bow lift and when
I do it right (and I'm pretty good at it now), the boat just kind of
zooms up and we're off to the Race.

Get it - off to the Race?

Never mind.

I get the Point.

Eisboch

On Mon, 22 Nov 2004 08:29:29 -0500, Harry Krause
wrote:

When, exactly, is a boat on plane and how can you tell, precisely, when
this happens?

==================================

Good question. We all know it when we see it, but the formal
definition is tougher.

I think it relates to how much of the hull is riding above the water
as opposed to plowing through it. That implies that planing could be
defined as a percentage of hull lift versus displacement, for example
50% or more of the hull normally below the water, rises above water
level when "on plane". This jibes reasonably well with the popular
phrase "out of the hole", meaning "on plane".

Another definition might involve flow separation at the transom. Most
times a boat "on plane" will have little or no transom surface
directly touching the water even though the bottom of the transom is
still below the water line.

It is also tempting to define planing as a ratio of actual speed to so
called "hull speed" but there are plenty of heavy displacement boats
that exceed theoretical hull speed by wide margins without actually
giving the appearance of being on plane. Motor yachts and fishing
trawlers come readily to mind as examples. They do it through sheer
power, pushing aside a lot of water as opposed to actually rising
above it. By the time a boat is going over two or three times its
theoretical hull speed however, it usually gives the appearance of
being on plane regardless of weight.

There might be another mathematical approach worth considering. As a
boat begins to exceed theoretical hull speed it takes huge increases
in power to increase speed by relatively small percentages. Typically
power required varies as the cube of speed. As a boat begins to plane
however, the power required still increases exponentially with speed,
but at a slower rate, more like the square of speed opposed to the
cube. Using that approach, planing would be defined as the
mathematical inflection point where the speed/power exponent begins to
decrease.

Comments?

Wayne.B wrote in message
...
On Mon, 22 Nov 2004 08:29:29 -0500, Harry Krause
wrote:

When, exactly, is a boat on plane and how can you tell, precisely, when
this happens?

==================================

Good question. We all know it when we see it, but the formal
definition is tougher.

I think it relates to how much of the hull is riding above the water
as opposed to plowing through it. That implies that planing could be
defined as a percentage of hull lift versus displacement, for example
50% or more of the hull normally below the water, rises above water
level when "on plane". This jibes reasonably well with the popular
phrase "out of the hole", meaning "on plane".

Another definition might involve flow separation at the transom. Most
times a boat "on plane" will have little or no transom surface
directly touching the water even though the bottom of the transom is
still below the water line.

It is also tempting to define planing as a ratio of actual speed to so
called "hull speed" but there are plenty of heavy displacement boats
that exceed theoretical hull speed by wide margins without actually
giving the appearance of being on plane. Motor yachts and fishing
trawlers come readily to mind as examples. They do it through sheer
power, pushing aside a lot of water as opposed to actually rising
above it. By the time a boat is going over two or three times its
theoretical hull speed however, it usually gives the appearance of
being on plane regardless of weight.

There might be another mathematical approach worth considering. As a
boat begins to exceed theoretical hull speed it takes huge increases
in power to increase speed by relatively small percentages. Typically
power required varies as the cube of speed. As a boat begins to plane
however, the power required still increases exponentially with speed,
but at a slower rate, more like the square of speed opposed to the
cube. Using that approach, planing would be defined as the
mathematical inflection point where the speed/power exponent begins to
decrease.

Comments?


I am not sure I'd buy paragraph #2 which relates to flow separation at the
transom.
Certainly true of a speedy, planning hull, it is also true of some of the
boats you described in paragraph #3. I've seen and been on large, heavy,
but highly powered boats that certainly are not planning, yet are going fast
enough to have none of the transom in the water, other than at the water
line. In fact, if powerful enough, they will create a "roostertail", but
still be plowing through the water.

I like your first explanation. Your math approach is probably correct, but I
get a headache doing it in my head.

Eisboch

Around 11/22/2004 8:07 PM, Eisboch wrote:

Wayne.B wrote in message
...

On Mon, 22 Nov 2004 08:29:29 -0500, Harry Krause
wrote:

When, exactly, is a boat on plane and how can you tell, precisely, when
this happens?

==================================

Another definition might involve flow separation at the transom. Most
times a boat "on plane" will have little or no transom surface
directly touching the water even though the bottom of the transom is
still below the water line.


I am not sure I'd buy paragraph #2 which relates to flow separation at the
transom.
Certainly true of a speedy, planning hull, it is also true of some of the
boats you described in paragraph #3. I've seen and been on large, heavy,
but highly powered boats that certainly are not planning, yet are going fast
enough to have none of the transom in the water, other than at the water
line.

Yeah, my dad's Chris does that, even though we don't usually take her
above 8 or 9 knots, and she's definitely not on a plane then.


Aside: I can remember when we were breaking in the new Crusader about 12
years ago and we were supposed to run it up to full throttle for a
while. Commando was, if not fully up, darn near up on a plane and making
well over 15 knots, almost keeping up with the Mukilteo-Clinton ferry.

It wasn't a pretty sight since she was really unstable and tended to
wallow from side to side; my dad said it was like watching a little old
lady hitch up her skirts and try to run. :)

--
~/Garth - 1966 Glastron V-142 Skiflite: "Blue-Boat"
"There is nothing - absolutely nothing - half so much worth doing
as simply messing about in boats."
-Kenneth Grahame, The Wind in the Willows

Harry Krause wrote:
Eisboch wrote:

Short Wave Sportfishing wrote in message
. ..

On 21 Nov 2004 17:35:54 -0800, (Big Daddy) wrote:


Hello. I have a 29' Chaparral (great boat) with twin v-6's and Volvo
duoprops. It comes on plane extremely fast if I work the trim tabs
full and use the outdrive tilt. You almost don't even know the bow is
raising!

My question is...in lieu of the damn gas prices, I'm wondering if I
could get better mileage if I added larger trim tabs so that the boat
would plane at a slower speed. Right now, I have to get it to 3,000
rpm's to bring it down on plane.

Any thoughts?

Based on my experience, I've never used trim tabs to bring a boat on
or off plane. On my Contender, it's more a question of lateral
balance in unfavorable sea conditions and for keeping proper bow entry
in seas. Then again, I have outboards, so the conditions may be
different.

I don't think larger trim tabs are going to help much because of drag
issues. I'm not all that familiar with I/Os, but with outboards,
plane is more a function of proper engine trim and throttle setting.
On my Ranger, a 20 footer which doesn't have trim tabs, it's all
about engine angle and throttle setting. On the Contender, I hardly
twitch the tabs unless I absolutely have to.

I would think that larger trim tabs would create more drag, thus less
performance, thus more gas used.

Later,

Tom

IMO and personal experience, the results of using trim tabs and probably
their optimum size varies from boat to boat, so there is no generic answer.
Like Tom pointed out, trim tabs are primarily for lateral positioning due to
heeling into the wind or unbalanced lateral loads. Many boats that are
under or marginally powered benefit from lowering the tabs to help get on
plane, but it is a balance of lifting the stern and generating more drag.

If the OP's boat is underpowered, my guess would be that larger tabs might
help lift the stern to get on plane which will the significantly reduce
overall hull drag. Once on plane, he should slowly raise the tabs back up,
while watching his tach until he finds the "sweet spot" of max RPM for a
fixed throttle setting.

Somewhere I think I remember reading that tabs should have an inch of width
for every foot of boat length.

Just my opinion.

Eisboch





When, exactly, is a boat on plane and how can you tell, precisely, when
this happens?

It certainly is easy enough to tell in small boat, but it's not always
so easy to tell on a larger one. My Parker, for example, breaks onto
plane at around 17-19 mph, but seems to remain on plane down to about 13
mph...in that the bow is still raised a bit, the wake still is fairly
flat, and if there is any chop, the spray is tossed off in the usual
manner. But that exact moment of being on or off plane seems difficult
to determine...


Crumbs this lying idiot doesn't even have the brains to properly
understand the magazine test he tried to steal this from, as self
serving evidence he owns a boat:-) Too too sad:-)

K

On Mon, 22 Nov 2004 22:38:45 -0500, Wayne.B
wrote:

On Mon, 22 Nov 2004 08:29:29 -0500, Harry Krause
wrote:

When, exactly, is a boat on plane and how can you tell, precisely, when
this happens?

==================================

Good question. We all know it when we see it, but the formal
definition is tougher.

I think it relates to how much of the hull is riding above the water
as opposed to plowing through it. That implies that planing could be
defined as a percentage of hull lift versus displacement, for example
50% or more of the hull normally below the water, rises above water
level when "on plane". This jibes reasonably well with the popular
phrase "out of the hole", meaning "on plane".

That makes sense, but I'm more inclined to describe "plane" as the
least amount of hull in the water at cruise. I'm also not sure you
can apply the word to boats like yours and Mr/Mrs E's as they are not
true planing hulls.

To my mind, which is a strange and curious place I'll admit, the act
of planing on water is similar to how an airplane works. You use a
lot of power to get the boat up on plane, but once there, you throttle
back to maintain speed and attitude. To do that on the water, more
hull has to be out than in. Yes/No?

Another definition might involve flow separation at the transom. Most
times a boat "on plane" will have little or no transom surface
directly touching the water even though the bottom of the transom is
still below the water line.

I can't get into this one as I've been on big sport fisher's that
clearly weren't planing, but plowing, although easily and without much
bow lift. When you apply a lot of power to a small area, you will get
voids and that is essentially what is happening in this circumstance.

It is also tempting to define planing as a ratio of actual speed to so
called "hull speed" but there are plenty of heavy displacement boats
that exceed theoretical hull speed by wide margins without actually
giving the appearance of being on plane. Motor yachts and fishing
trawlers come readily to mind as examples. They do it through sheer
power, pushing aside a lot of water as opposed to actually rising
above it. By the time a boat is going over two or three times its
theoretical hull speed however, it usually gives the appearance of
being on plane regardless of weight.

I need to give that one some thought. My initial reaction is that
power can't replace the concept of the least amount to do the most
work which would imply that brute power is not a factor in planing.

There might be another mathematical approach worth considering. As a
boat begins to exceed theoretical hull speed it takes huge increases
in power to increase speed by relatively small percentages. Typically
power required varies as the cube of speed. As a boat begins to plane
however, the power required still increases exponentially with speed,
but at a slower rate, more like the square of speed opposed to the
cube. Using that approach, planing would be defined as the
mathematical inflection point where the speed/power exponent begins to
decrease.

Comments?

Oh - I like it.

The problem is that you'd have to build a set of universal variables
to account for weight, length, beam, deadrise, lift strakes, power,
blade pitch or perhaps solve for the individual variables, then use
those as plug in's for an equation for different speeds and power
settings....

~~ mutter - naval architecture - grumble ~~

Later,

Tom

On Tue, 23 Nov 2004 04:07:40 GMT, "Eisboch"
wrote:


Wayne.B wrote in message
.. .
On Mon, 22 Nov 2004 08:29:29 -0500, Harry Krause
wrote:

When, exactly, is a boat on plane and how can you tell, precisely, when
this happens?

==================================

Good question. We all know it when we see it, but the formal
definition is tougher.

I think it relates to how much of the hull is riding above the water
as opposed to plowing through it. That implies that planing could be
defined as a percentage of hull lift versus displacement, for example
50% or more of the hull normally below the water, rises above water
level when "on plane". This jibes reasonably well with the popular
phrase "out of the hole", meaning "on plane".

Another definition might involve flow separation at the transom. Most
times a boat "on plane" will have little or no transom surface
directly touching the water even though the bottom of the transom is
still below the water line.

It is also tempting to define planing as a ratio of actual speed to so
called "hull speed" but there are plenty of heavy displacement boats
that exceed theoretical hull speed by wide margins without actually
giving the appearance of being on plane. Motor yachts and fishing
trawlers come readily to mind as examples. They do it through sheer
power, pushing aside a lot of water as opposed to actually rising
above it. By the time a boat is going over two or three times its
theoretical hull speed however, it usually gives the appearance of
being on plane regardless of weight.

There might be another mathematical approach worth considering. As a
boat begins to exceed theoretical hull speed it takes huge increases
in power to increase speed by relatively small percentages. Typically
power required varies as the cube of speed. As a boat begins to plane
however, the power required still increases exponentially with speed,
but at a slower rate, more like the square of speed opposed to the
cube. Using that approach, planing would be defined as the
mathematical inflection point where the speed/power exponent begins to
decrease.

Comments?


I am not sure I'd buy paragraph #2 which relates to flow separation at the
transom.
Certainly true of a speedy, planning hull, it is also true of some of the
boats you described in paragraph #3. I've seen and been on large, heavy,
but highly powered boats that certainly are not planning, yet are going fast
enough to have none of the transom in the water, other than at the water
line. In fact, if powerful enough, they will create a "roostertail", but
still be plowing through the water.

I like your first explanation. Your math approach is probably correct, but I
get a headache doing it in my head.

I've got the ultimate definition.

Planing - the act of making a lot of wood shavings out of a large
piece of wood.

Later,

Tom

"Beware the one legged man in a butt
kicking contest - he is there for a
reason."

Wun Hung Lo - date unknown

On Tue, 23 Nov 2004 07:51:27 -0500, Harry Krause
wrote:
With a 225 four stroke, my Parker with a half load of fuel, two guys
aboard, and some "stuff" will hit between 39 and 40 mph at WOT,
according to my GPS. And that number is what's on spreadsheet Parker
sent me a year or so ago.

On the Yamaha "performance" site, the same boat with a 300 hp two stroke
DFI will hit 44.1 mph under similar load conditions...a 33% increase in
horsies only produces about 5 mph in top end. There are, however, more
worthwhile differences in the rpm/cruise speed curge.

================================================== ===========

OK, let's do the math. An increase from 225 to 300 hp is a ratio of
1.33 (300 / 225). Taking the square root of 1.33, we get 1.15, and
39 mph times 1.15 is 45 mph. That agrees fairly well with the notion
that speed increases in proportion to the SQRT of hp at planing
speeds.

Theoretical hull speed for a Parker 25 is about 6 mph which you could
probably achieve with a 15 hp outboard in calm conditions. To go from
6 mph to 12 mph, double the speed in non-planing conditions, takes a
lot more power, perhaps 8 times as much if power required is varying
at the cube root of speed. That would imply 120 hp which sounds about
right, perhaps half throttle on your 225.

At some speed between 12 mph and 20 mph, probably around 18 or 19,
the boat should begin planing and the power increase required for more
speed should drop back more towards the first set of numbers. That's
the basis for my conjecture that a mathematical definition might have
some merit. The problem of course is measuring the transition without
a whole boatload of instrumentation. :-)

For another data point, I have a 12 foot inflatable which will plane
off at 13 or 14 mph when lightly loaded, using about half throttle on
a 15 hp Merc.

Wow. Thanks for all the great comments. Let me clarify a few
things...
I don't even need to use the trim tabs to get on plane, even with full
tank and many people. I guess the duoprop twin outdrives do the
trick.
I will check into the flowmeters, but I think the reason I don't buy
them is that I'd like to get good at finding what you have all called
"the sweet spot" by watching the gps speed vs rpm while making
adjustments. All I can think of is all the gas I can buy for the 2 or
3 hundred dollars for flow meters for my twins! (I hope that isn't a
dumb answer).
What I really should have asked is; Would I get better fuel mileage
by running on plane at a slower speed with larger trim tabs versus
running at a faster minimum planing speed with the tabs I have now.
I think you have all answered my question. Leave it alone. The tabs
are Bennet and installed new on the boat. The boat runs great the way
it is. I really like the advice to watch rpm and speed while changing
things.

Thanks a lot.

Hey, one more quick one. Has anyone else noticed in some of the
magazine boat reviews where they show the rpm, boat angle, and mpg
that in some tests, the best mpg that they measure is when the boat
angle is at it's steepest, like 5 degrees? That seems odd to me.
That, I would think is the very worst angle for good gas mileage and
yet they show it as the best.

Thanks
Wayne

Short Wave Sportfishing wrote in message . ..
On 21 Nov 2004 17:35:54 -0800, (Big Daddy) wrote:

Hello. I have a 29' Chaparral (great boat) with twin v-6's and Volvo
duoprops. It comes on plane extremely fast if I work the trim tabs
full and use the outdrive tilt. You almost don't even know the bow is
raising!

My question is...in lieu of the damn gas prices, I'm wondering if I
could get better mileage if I added larger trim tabs so that the boat
would plane at a slower speed. Right now, I have to get it to 3,000
rpm's to bring it down on plane.

Any thoughts?

Based on my experience, I've never used trim tabs to bring a boat on
or off plane. On my Contender, it's more a question of lateral
balance in unfavorable sea conditions and for keeping proper bow entry
in seas. Then again, I have outboards, so the conditions may be
different.

I don't think larger trim tabs are going to help much because of drag
issues. I'm not all that familiar with I/Os, but with outboards,
plane is more a function of proper engine trim and throttle setting.
On my Ranger, a 20 footer which doesn't have trim tabs, it's all
about engine angle and throttle setting. On the Contender, I hardly
twitch the tabs unless I absolutely have to.

I would think that larger trim tabs would create more drag, thus less
performance, thus more gas used.

Later,

Tom

On Tue, 23 Nov 2004 10:24:06 -0500, Harry Krause
wrote:
With a smaller, open boat, you can see when you are on plane. On the
Parker, that's pretty much impossible, though there are certain "feels"
at various speeds.

================================================== ==

It's been my experience that the transition point gets much fuzzier as
boat weight and length increase. With something like a Hatteras 53
weighing 50,000 pounds or so, they never really look or feel like they
are on plane even when going 20 knots.

My Bertram 33 weighed about 23,000 pounds and was clearly on plane at
13 to 14 knots with a little help from the trim tabs. It really
didn't FEEL like it was on plane however until it got over 20 kts. At
that point the hull was well out of the water and it had the feel of
gliding over the water instead of plowing it aside.