First boat looking for some speed

[flatheadsteve]

Okay, took it out today and with me and the wife about 400lbs total I got up to 19mph I definitely want more speed. 30 mph would be great I was reading that I maybe able to convert my 25hp johnson outboard to a 30 or 35hp motor anyone have any idea on that? Thanks for the help

Either the motor isn't running correct or it's not propped right. My alumacraft 1648 with 25 2 stroke would do 28mph loaded with fishing gear and 2 adults. 20hp tohatsu 4 stroke pushed the same boat/load 22mph before hitting rev limiter( wrong prop). Get a tach and find out what rpm your hitting

 

[Joshua Stansbury]

Either the motor isn't running correct or it's not propped right. My alumacraft 1648 with 25 2 stroke would do 28mph loaded with fishing gear and 2 adults. 20hp tohatsu 4 stroke pushed the same boat/load 22mph before hitting rev limiter( wrong prop). Get a tach and find out what rpm your hitting

I had the motor gone through when I first got the boat at a local marine shop where they replaced my prop because my other one was shot, but this is what they gave me.

 

[flatheadsteve]

I had the motor gone through when I first got the boat at a local marine shop where they replaced my prop because my other one was shot, but this is what they gave me. View attachment 116273

You need to put a tachometer on it and find out what it turns at wide open throttle it's the only way to know.

 

[airshot]

Need an RPM reading to know if the prop is correct and the motor is set up right. A pic from the rear showing motor on the transom at the cav plate. Trim or height adjustment might be needed.

 

[Joshua Stansbury]

You need to put a tachometer on it and find out what it turns at wide open throttle it's the only way to know.

Okay, do you have any recommendations on a tach? If not I can just Google it thanks for the help

 

[Joshua Stansbury]

Need an RPM reading to know if the prop is correct and the motor is set up right. A pic from the rear showing motor on the transom at the cav plate. Trim or height adjustment might be needed.

Okay, I'll get pictures tomorrow its dark right now, but I'm sure you know that. I tried to do the trim and height adjustment from what I read, but seeing how this is my first boat I probably didn't get it right.

 

[flatheadsteve]

Okay, do you have any recommendations on a tach? If not I can just Google it thanks for the help

Tiny-tach...about $25 on amazon

 

[airshot]

Okay, I'll get pictures tomorrow its dark right now, but I'm sure you know that. I tried to do the trim and height adjustment from what I read, but seeing how this is my first boat I probably didn't get it right.

We all can remember our first boat I am sure...

 

[Pappy]

There is quite a large thread on this subject in this forum you can find and peruse. Has all the information you may need.

 

[Pappy]

How are you measuring speed? Remove that propeller and see if there is a Dia/Pitch printed below the prop nut somewhere. Give that to us.
We NEED to cover basics before recommending changes. As has been suggested you will also need a tachometer if you are really serious about this.

 

[Joshua Stansbury]

How are you measuring speed? Remove that propeller and see if there is a Dia/Pitch printed below the prop nut somewhere. Give that to us.
We NEED to cover basics before recommending changes. As has been suggested you will also need a tachometer if you are really serious about this.

I'm using GPS, and when I run those numbers on the prop in the picture it comes back with
10.1" Diameter, 13" Pitch, 14-Tooth Spline
Rotation: Right Hand

 

[Joshua Stansbury]

Need an RPM reading to know if the prop is correct and the motor is set up right. A pic from the rear showing motor on the transom at the cav plate. Trim or height adjustment might be needed.

Here are the pictures

 

[moedelawn]

It's hard to tell in the pictures but it looks like the motor is in a tucked position and a bit low height wise. With the hydrofoil that will make the problem worse. When you are running is the foil out the water? You want to have the engine tilted at least level and only the bottom of the foil in the water. 13p is probably a bit too much but you have to set the engine correctly.
Run a straight edge under the boat to the plate above the prop.

 

[airshot]

Doesn't look bad from what I see, cav plate about level and parallel to the bottom of the hull as a starting point. Once you get your wot rpm, then some tweaking to trim angle and cav plate height to see if you can get more rpm at wot. Once you have found the max rpm your motor will turn, then look at prop pitch. Do you need more or less rpm to reach your max motor rpm recomendation. I run mine just above factory redline with one person on board. Then when I have two or three I get more getup and go. I do have ro watch my tach when running solo..

 

[Joshua Stansbury]

It's hard to tell in the pictures but it looks like the motor is in a tucked position and a bit low height wise. With the hydrofoil that will make the problem worse. When you are running is the foil out the water? You want to have the engine tilted at least level and only the bottom of the foil in the water. 13p is probably a bit too much but you have to set the engine correctly.
Run a straight edge under the boat to the plate above the prop.

Yes the foil is in the water when it's running properly about 6 inches down. Also do I run the straight edge on the very bottom of the hull or the bottom of the tunnel?

 

[Joshua Stansbury]

Doesn't look bad from what I see, cav plate about level and parallel to the bottom of the hull as a starting point. Once you get your wot rpm, then some tweaking to trim angle and cav plate height to see if you can get more rpm at wot. Once you have found the max rpm your motor will turn, then look at prop pitch. Do you need more or less rpm to reach your max motor rpm recomendation. I run mine just above factory redline with one person on board. Then when I have two or three I get more getup and go. I do have ro watch my tach when running solo..

How do I find the max factory redline the motor is a 1997 25hp johnson model J25EEUB? Also I don't have a tach yet but I ordered one today

 

[Pappy]

RPM range for that engine is 4500-5500

 

[moedelawn]

Yes the foil is in the water when it's running properly about 6 inches down. Also do I run the straight edge on the very bottom of the hull or the bottom of the tunnel?

The top of the tunnel. If the foil is 6 inches under the water then you will likely have to raise it that much if possible.

 

[Joshua Stansbury]

Okay, I got the tach installed and on the lake it was running between 4340-4360rpms

 

[FuzzyGrub]

Raise the motor so the cav plate is even with the top of the tunnel. It looks like you have a manual jack plate.

Then test it, again.