All depends. A 3 blade prop will almost always be faster at top end than a
4 blade prop due to the decrease in blade surface. However, a 4 blade prop
will almost always plane faster and give better acceleration (assuming we
are talking about similar props in terms of design and similar pitch).
Having said that, in theory they will both be about the same economy wise at
say 3000 rpms since they are both the same pitch and about the same
efficiency wise in the mid rpm area.
Each person has to decide if they want better low end or better top end.
There is no perfect combination. Even the shift props will be less
efficient on top end than a regular prop of the same pitch. Again, you
compromise absolute top speed for acceleration. Just like gearing in a car.

Now for trim tabs. Great for slow planing but will kill fuel economy doing
so. They create a lot of drag to force the bow down at slower speeds. Of
course you can raise them and get the efficiency back. Dolfins work the
same way by forcing the bow down (not as much as a trim tab but it does
help). You just have to trim the motor out to stop the bow push. Of course
you always get some push since it is in the water unless you have the engine
raised to the point that it is out of the water at higher speeds.

--
Tony
My boats and autos - http://t.thomas.home.mchsi.com



"F330 GT" wrote in message
...
Hey Barry

I am basically am looking to be able to plain at a slower speed than I am
currently achieving. My boat doesnt like to hold a plain at under 25mph,
and
when it gets rough, I'd like to go slower than bouncing from one wave to
another. And yes I am also looking to maximize my range.

Thank you all, I appreciate your inputs...

Rick








Rick,

Sounds like trim tabs would do more for you than changing props. Their is
probably no better way to achieve slower planing speed than good trim
tabs. Of
course, that certainly won't be the most economical speed. Most new
outboards
are most economical in the 3500 to 4000 rpm range.

At certain rpm ranges, I imagine a 4 blade could be more economical than a
3
blade but I'd still be real surprised if you took an outboard motor on a
typical v-hull boat and tried just to maximize the most mileage per gallon
possible that could be gotten out of that engine, a 3 blade prop would be
the
winner.

What do you think, Tony?

Barry

writes
Rick,

Sounds like trim tabs would do more for you than changing props. Their is
probably no better way to achieve slower planing speed than good trim tabs.
Of
course, that certainly won't be the most economical speed. Most new
outboards
are most economical in the 3500 to 4000 rpm range.

Surely you mean most efficient, not most economical. There is no way an
outboard running at 3500rpm gets less gph than one running at 1000rpm.
Equally, there is no way it gets better mpg than one running at 1000rpm.
Only, m/g/h would it be more economical. I can run all day on a river at
1000rpm (6mph) and only use half a tank. Run on a lake at 25-30mph and
3500rpm and I get through a whole tank in a few hours!
--
Nick



I mean the highest miles per gallon. I'd consider that the most efficient and
most economical if I'm trying to to get from point a to point b.

The most economical from your perspective would be to leave it in the garage on
a trailer.

Barry

Now for trim tabs. Great for slow planing but will kill fuel economy
doing
so. They create a lot of drag to force the bow down at slower speeds. Of
course you can raise them and get the efficiency back.

I've found the opposite to be true.

"Joe" wrote in message ...
Now for trim tabs. Great for slow planing but will kill fuel economy
doing
so. They create a lot of drag to force the bow down at slower speeds. Of
course you can raise them and get the efficiency back.

I've found the opposite to be true.

Really, JoeTechnician? Please do tell how you think that trim tabs
don't create drag when they are deployed? And, if they are creating
drag, unfortunately, they are also hurting fuel economy.

"basskisser" wrote in message
om...
"Joe" wrote in message
...
Now for trim tabs. Great for slow planing but will kill fuel economy
doing
so. They create a lot of drag to force the bow down at slower speeds.
Of
course you can raise them and get the efficiency back.

I've found the opposite to be true.

Really, JoeTechnician? Please do tell how you think that trim tabs
don't create drag when they are deployed?
and in And, if they are creating drag, unfortunately, they are also hurting
fuel economy.

Who said they didn't create drag?

But, if the drag they do create is less than the drag they reduce (stern
dive, pushing a wall of water against the bottom of the hull), and
inefficient prop angle (wasted energy pushing the bow up instead of the boat
forward) then the overall decrease in drag will result in increased fuel
efficiency.

In article , F330 GT
writes
writes
Rick,

Sounds like trim tabs would do more for you than changing props. Their is
probably no better way to achieve slower planing speed than good trim tabs.
Of
course, that certainly won't be the most economical speed. Most new
outboards
are most economical in the 3500 to 4000 rpm range.

Surely you mean most efficient, not most economical. There is no way an
outboard running at 3500rpm gets less gph than one running at 1000rpm.
Equally, there is no way it gets better mpg than one running at 1000rpm.
Only, m/g/h would it be more economical. I can run all day on a river at
1000rpm (6mph) and only use half a tank. Run on a lake at 25-30mph and
3500rpm and I get through a whole tank in a few hours!
--
Nick



I mean the highest miles per gallon. I'd consider that the most efficient and
most economical if I'm trying to to get from point a to point b.

The most economical from your perspective would be to leave it in the garage on
a trailer.

Well fuel is so expensive here in the UK that your suggestion is about
the best way to save money...
--
Nick

I know my boat gets on plain using them if I don't use them and have allot
of people onboard I never get on plain and it would be very inefficient to
keep trying I would think, but then again I don't have a flow scan and a gps
so I can't tell u for sure, but I know if I'm not on plain I'm not going
anywhere fast. Just sitting back relaxing, taking a cruise. Happy boating

"Joe" wrote in message
...

"basskisser" wrote in message
om...
"Joe" wrote in message
...
Now for trim tabs. Great for slow planing but will kill fuel
economy
doing
so. They create a lot of drag to force the bow down at slower
speeds.
Of
course you can raise them and get the efficiency back.

I've found the opposite to be true.

Really, JoeTechnician? Please do tell how you think that trim tabs
don't create drag when they are deployed?
and in And, if they are creating drag, unfortunately, they are also
hurting
fuel economy.

Who said they didn't create drag?

But, if the drag they do create is less than the drag they reduce (stern
dive, pushing a wall of water against the bottom of the hull), and
inefficient prop angle (wasted energy pushing the bow up instead of the
boat
forward) then the overall decrease in drag will result in increased fuel
efficiency.

"Wildest Dream" wrote in message

I know my boat gets on plain using them if I don't use them and have allot
of people onboard I never get on plain and it would be very inefficient to
keep trying I would think, but then again I don't have a flow scan and a
gps
so I can't tell u for sure, but I know if I'm not on plain I'm not going
anywhere fast. Just sitting back relaxing, taking a cruise. Happy boating


If you can't plane at full throttle without tabs, but can plane with them,
there is no doubt that using the tabs on your boat is improving your fuel
consumption.

"Joe" wrote in message ...
"basskisser" wrote in message
om...
"Joe" wrote in message
...
Now for trim tabs. Great for slow planing but will kill fuel economy
doing
so. They create a lot of drag to force the bow down at slower speeds.
Of
course you can raise them and get the efficiency back.

I've found the opposite to be true.

Really, JoeTechnician? Please do tell how you think that trim tabs
don't create drag when they are deployed?
and in And, if they are creating drag, unfortunately, they are also hurting
fuel economy.

Who said they didn't create drag?

But, if the drag they do create is less than the drag they reduce (stern
dive, pushing a wall of water against the bottom of the hull), and
inefficient prop angle (wasted energy pushing the bow up instead of the boat
forward) then the overall decrease in drag will result in increased fuel
efficiency.

****, here we go again, JoeTechnician, I even have to explain what to
hell YOU responded to. Read the second sentence of the original post:
They create a lot of drag to force the bow down at slower speeds.
Of course you can raise them and get the efficiency back.

At slower speeds, they definately DO create more drag. AT SLOWER
SPEEDS, get it? You are plunging a planar piece of material, at an
angle, into the water. Do you think that is creating drag, yes or no
please. Now, that in turn, pushes the bow down, again, we are AT
SLOWER SPEEDS. So, you are essentially putting more of the hull in
contact with the water. Do you not think this, AT SLOWER SPEEDS,
creates drag? Yes or no, please.

****, here we go again, JoeTechnician, I even have to explain what to
hell YOU responded to. Read the second sentence of the original post:
They create a lot of drag to force the bow down at slower speeds.
Of course you can raise them and get the efficiency back.

I know exactly what I responded to and stand by my statement.

At slower speeds, they definately DO create more drag. AT SLOWER
SPEEDS, get it? You are plunging a planar piece of material, at an
angle, into the water. Do you think that is creating drag, yes or no
please.

If not correctly adjusted they might (extended too far).
Here's a shocker for you, they usually work better at slower speeds and
rougher seas than they do at higher speeds and calmer seas.
I'm not talking about idle speeds when I say "slower speeds" but they will
begin to be efficient approximately at the point that you can plane with the
tabs adjusted down.

Here's real world scenario for you- On my boat (21.5' CC 200hp), at 3000rpm
the boat will ride with a bow high attitude with stern dive. As I actuate
the trim tabs the stern rises, the bow lowers and the boat planes. Once
planed the rpm's will immediately climb (without touching the throttle) and
my speed increases. I then can reduce throttle back to 3000rpm and continue
along on a plane.

Now, tell me, do you think my boat is more, or less efficient at 3000rpm's
with my tabs down or tabs up?

Now, that in turn, pushes the bow down, again, we are AT
SLOWER SPEEDS. So, you are essentially putting more of the hull in
contact with the water. Do you not think this, AT SLOWER SPEEDS,
creates drag? Yes or no, please.

Trim tabs, when activated, will *always* add some drag, and as I said-

"But, if the drag they do create is less than the drag they reduce (stern
dive, pushing a wall of water against the bottom of the hull), and
inefficient prop angle (wasted energy pushing the bow up instead of the boat
forward) then the overall decrease in drag will result in increased fuel
efficiency."


Here's some reading for you.

http://www.bennetttrimtabs.com/whatdo.htm
http://www.trimmaster.net/id114.htm
http://www.boatus.com/boattech/trimtabs.htm
http://www.powerandmotoryacht.com/fe...abs/index.html
http://www.h-ri.com/Product/Duraplane/Duraplane_01.html