1976-1983 JOHNSON SEAHORSE 90 HP MOTOR.

I SPUN THE ORIGINAL PROP AND HAVE SEVERAL OLDER SPARES.

I HAVE LOST SPEED AND CAN NOT PLANE ANYMORE.

WHAT SIZE PROP SHOULD I USE.

I USED TO DO 22MPH AT 4K RPM.

NOW I CAN ONLY DO 15MPH AND AT 3K AND THE BOAT WILL NOT PLANE.

MY THREE SPARE PROPS ARE ALL SMALLER THAN THE STOCK PROP.

IT WOULD BE GREAT TO DO MORE THAN 22MPH................

"sonofadocker" wrote in message
oups.com...
1976-1983 JOHNSON SEAHORSE 90 HP MOTOR.

I SPUN THE ORIGINAL PROP AND HAVE SEVERAL OLDER SPARES.

I HAVE LOST SPEED AND CAN NOT PLANE ANYMORE.

WHAT SIZE PROP SHOULD I USE.

I USED TO DO 22MPH AT 4K RPM.

NOW I CAN ONLY DO 15MPH AND AT 3K AND THE BOAT WILL NOT PLANE.

MY THREE SPARE PROPS ARE ALL SMALLER THAN THE STOCK PROP.

IT WOULD BE GREAT TO DO MORE THAN 22MPH................




Try em all.

On Aug 9, 11:48 pm, sonofadocker wrote:
1976-1983 JOHNSON SEAHORSE 90 HP MOTOR.

I SPUN THE ORIGINAL PROP AND HAVE SEVERAL OLDER SPARES.

I HAVE LOST SPEED AND CAN NOT PLANE ANYMORE.

WHAT SIZE PROP SHOULD I USE.

I USED TO DO 22MPH AT 4K RPM.

NOW I CAN ONLY DO 15MPH AND AT 3K AND THE BOAT WILL NOT PLANE.

MY THREE SPARE PROPS ARE ALL SMALLER THAN THE STOCK PROP.

IT WOULD BE GREAT TO DO MORE THAN 22MPH................



That is a tough question to answer without knowing some important
information about your boat. This information is the same no matter
what size your motor is or how long your boat is. So, what do you need
to know?
First, you need to know. What is the maximum recommend RPMs for your
motor? You can find this out my looking at the manual for you motor.
If it is not there, look on the web or call the manufacture. The key
to getting your boat to perform is getting the motor in that range a
full throttle.
The second thing you need to know is what RPMs your motor is turning
at full throttle. For that you need a tachometer. If your boat does
not have one, I recommend one of these www.tinytach.com or www.sendec.com
these are inductive tachometers that measure RPMs by counting when the
spark plug fires. Please make sure you order the correct one for your
motor. Both manufactures offer two and four cycle models. They also
offer a model that can be used on both.
The third item you need to know is, the current pitch of the prop you
have now. This info is the most important. With out it you will not
know what size to get when you buy your next prop. It should be
stamped somewhere on the prop. If not there may be a part number you
can lookup. If either of that info is not there a prop shop may be
able to tell you.
An optional piece of equipment you might like is a GPS. This will tell
you how fast you are going. The speedometers that use a water pick up
are not accurate. The paddle wheel types are much more accurate. With
GPS receivers available for under $100.00 you can also use it to save
your favorite fishing holes.
You have gathered all the equipment from above. You are now wondering
how do I make my boat go faster or improve my hole shot. Here you go.
Load your boat to the normal load you carry when you go fishing 90% of
the time. Start your motor and head out at full throttle. Once your
boat reaches its top speed for a minute look at you tachometer. Is it
within the max RPM range from the data you gathered from above? If it
is, that is all the faster your boat will go. If it is higher that the
maximum RPM you should be able to get more speed by buying a larger
pitch prop. You should do this anyway because you risk the chance of
damaging your motor. If the RPM is below the max RPM rating you can
lower the pitch of your prop. This should allow for a better hole shot
and increase boat speed by getting the motor into the RPM range where
it makes the most horse power.
If you remember from above I said load your to what you would use it
at 90% of the time. What about the other 10%? Those other times are
when you bring or leave that extra person. One 175lb person and his
fishing equipment with change how your boat performs. If you have
great performance with just your self and a buddy with a prop with a
pitch of "Y" you may find you add another person and their equipment
you can not get on plane and you notice your motor RPMs is below the
max RPS allowed. This is where you need to have an extra prop with a
pitch of "X". The lower pitch will allow the motor RPMs to reach up to
where the motor makes the most HP allowing your boat to plane better.
Now the opposite is true. If you go out in your boat by yourself you
find out your boat get up on plane at break neck speeds, the RPMs are
way high and top speed is low. This is when you need a prop of pitch
"Z" with the lighter load you can get way with a higher pitch prop
increasing top end speed.
After experimenting you will know what prop to put on before you leave
your house. If I am going by myself I'll put on my 13" pitch prop. If
the wife or a friend come along I put on the 11" pitch prop. With the
right prop on before I leave, I always have the best performance.
On last thought to help you. Think of the pitch of a prop like a gear
in a car. The lower the pitch the lower the gear. The lower the gear
the more power but less speed. Since boats do not have multi-gear
transmissions like a car we need to change gears by changing the pitch
of the prop.
Hope this helps.

On Aug 10, 10:36 am, Paul wrote:
On Aug 9, 11:48 pm, sonofadocker wrote:





1976-1983 JOHNSON SEAHORSE 90 HP MOTOR.

ISPUNTHE ORIGINALPROPAND HAVE SEVERAL OLDER SPARES.

I HAVE LOST SPEED AND CAN NOT PLANE ANYMORE.

WHAT SIZEPROPSHOULD I USE.

I USED TO DO 22MPH AT 4K RPM.

NOW I CAN ONLY DO 15MPH AND AT 3K AND THE BOAT WILL NOT PLANE.

MY THREE SPARE PROPS ARE ALL SMALLER THAN THE STOCKPROP.

IT WOULD BE GREAT TO DO MORE THAN 22MPH................



That is a tough question to answer without knowing some important
information about your boat. This information is the same no matter
what size your motor is or how long your boat is. So, what do you need
to know?
First, you need to know. What is the maximum recommend RPMs for your
motor? You can find this out my looking at the manual for you motor.
If it is not there, look on the web or call the manufacture. The key
to getting your boat to perform is getting the motor in that range a
full throttle.
The second thing you need to know is what RPMs your motor is turning
at full throttle. For that you need a tachometer. If your boat does
not have one, I recommend one of thesewww.tinytach.comorwww.sendec.com
these are inductive tachometers that measure RPMs by counting when the
spark plug fires. Please make sure you order the correct one for your
motor. Both manufactures offer two and four cycle models. They also
offer a model that can be used on both.
The third item you need to know is, the current pitch of thepropyou
have now. This info is the most important. With out it you will not
know what size to get when you buy your nextprop. It should be
stamped somewhere on theprop. If not there may be a part number you
can lookup. If either of that info is not there apropshop may be
able to tell you.
An optional piece of equipment you might like is a GPS. This will tell
you how fast you are going. The speedometers that use a water pick up
are not accurate. The paddle wheel types are much more accurate. With
GPS receivers available for under $100.00 you can also use it to save
your favorite fishing holes.
You have gathered all the equipment from above. You are now wondering
how do I make my boat go faster or improve my hole shot. Here you go.
Load your boat to the normal load you carry when you go fishing 90% of
the time. Start your motor and head out at full throttle. Once your
boat reaches its top speed for a minute look at you tachometer. Is it
within the max RPM range from the data you gathered from above? If it
is, that is all the faster your boat will go. If it is higher that the
maximum RPM you should be able to get more speed by buying a larger
pitchprop. You should do this anyway because you risk the chance of
damaging your motor. If the RPM is below the max RPM rating you can
lower the pitch of yourprop. This should allow for a better hole shot
and increase boat speed by getting the motor into the RPM range where
it makes the most horse power.
If you remember from above I said load your to what you would use it
at 90% of the time. What about the other 10%? Those other times are
when you bring or leave that extra person. One 175lb person and his
fishing equipment with change how your boat performs. If you have
great performance with just your self and a buddy with apropwith a
pitch of "Y" you may find you add another person and their equipment
you can not get on plane and you notice your motor RPMs is below the
max RPS allowed. This is where you need to have an extrapropwith a
pitch of "X". The lower pitch will allow the motor RPMs to reach up to
where the motor makes the most HP allowing your boat to plane better.
Now the opposite is true. If you go out in your boat by yourself you
find out your boat get up on plane at break neck speeds, the RPMs are
way high and top speed is low. This is when you need apropof pitch
"Z" with the lighter load you can get way with a higher pitchprop
increasing top end speed.
After experimenting you will know whatpropto put on before you leave
your house. If I am going by myself I'll put on my 13" pitchprop. If
the wife or a friend come along I put on the 11" pitchprop. With the
rightpropon before I leave, I always have the best performance.
On last thought to help you. Think of the pitch of aproplike a gear
in a car. The lower the pitch the lower the gear. The lower the gear
the more power but less speed. Since boats do not have multi-gear
transmissions like a car we need to change gears by changing the pitch
of theprop.
Hope this helps.- Hide quoted text -

- Show quoted text -

This is the most information I have ever recieved. 90% percent of the
rec boat users are
wasting time with political novels and racial rantings.....
I will look for a X prop the same size as the original.
the boat did 22mph at 4200-4400 rpm
Now it will do 17mph at 3000 rpm and will not plane.
That was using an old prop that was under the bow for years.

On Thu, 09 Aug 2007 20:48:16 -0700, sonofadocker
wrote:

1976-1983 JOHNSON SEAHORSE 90 HP MOTOR.

I SPUN THE ORIGINAL PROP AND HAVE SEVERAL OLDER SPARES.

I HAVE LOST SPEED AND CAN NOT PLANE ANYMORE.

WHAT SIZE PROP SHOULD I USE.

The original prop for that engine was 14"X13p.

That's the original recommendation.

That doesn't mean that's what you had based on what you stated.

In theory, at 5K , which is in the middle of the operating range for
WOT, with the original prop, you should be doing something nearer to
40 mph.

If you have the prop you spun, look in the exhaust side and the size
and pitch will be stamped on the hub. That will tell you what you
had. (Sometimes, the size and pitch will be stamped on the prop itself
- you might have to look around for it). Then you can compare the
prop you had to what was spec'd for it originally.

It would help to know the size and type of boat.

On Aug 9, 11:48 pm, sonofadocker wrote:
1976-1983 JOHNSON SEAHORSE 90 HP MOTOR.

I SPUN THE ORIGINAL PROP AND HAVE SEVERAL OLDER SPARES.

I HAVE LOST SPEED AND CAN NOT PLANE ANYMORE.

WHAT SIZE PROP SHOULD I USE.

I USED TO DO 22MPH AT 4K RPM.

NOW I CAN ONLY DO 15MPH AND AT 3K AND THE BOAT WILL NOT PLANE.

MY THREE SPARE PROPS ARE ALL SMALLER THAN THE STOCK PROP.

IT WOULD BE GREAT TO DO MORE THAN 22MPH................





Are you sure your boat has not gotten heaver?