boat doesn't plane

[3/4time]

Just installed 2003 90hp Yamaha 4 stroke (replaced 1989 60hp Mercury) on 1990 24ft two log Landau.
Boat runs at 13 mph at 6000 rpm with water filling motor tub and water hitting floor of pontoon.
What do I need to do, add third log? replace motor tub as existing tub only goes to below of motor bracket?
No signs of water in logs,

[GregF]

There is something else wrong. A 90 should get you well over 20 (24-25?) and you should be up on the step at 3000 RPM, around 15-16 MPH

[Bryden24shp]

Whats it got on it for a prop?
BTW, Welcome to the forum! Lots of awesome folks here... We'll try to find an answer for ya!
Bryan

[Liquid Asset]

Yeah I would also like to know what prop you have. Your rpms don't sound too bad but the speed is way wrong imo. Is the motor breaking free to get to the 6,000 mark ? There is something wrong ,maybe a pic of how the motor is sitting on the boat would help. What type of load was on the boat when you were getting 13mph? Is the tach at the correct pulse seting? I know my 20' tri toon with a 50 ( 115 blew up) will get 17 mph at 5k with just me onboard.

[PlaynDoc]

What are you using as a speedometer? The built-in, or a GPS? Sometimes the built-ins are wrong...

[ROLAND]

There is something else wrong. A 90 should get you well over 20 (24-25?) and you should be up on the step at 3000 RPM, around 15-16 MPH

agreed... 'cause I've got a 75 on the back of my 20 foot boat and I'll run approx. 22-23 mph or so wide open...

[Bamby]

Boat runs at 13 mph at 6000 rpm with water filling motor tub and water hitting floor of pontoon.

Is it possible for you to post a photo of the back of your boat and the motor. I'm reaching here, but I'm "guessing" that the motor may be mounted way to low and thereby creating excessive turbulence and displacing water where it shouldn't be like you stated in the quote above. But please post a photo of your current setup it would be of enormous help for people here to evaluate the problem...

[slingshot]

I'd start at the prop. You should be swinging about a 14x13.

[spurhunter]

Prop is the first culprit, second may be the tilit. I have a 24 (formerly) 2-log and my Honda 4 stroke pused it at 23.5MPH, (gps) when i found the right prop. I also had issues getting the tach to properly read my motor

[STEVEBRENDA]

Water is splashing on the floor, or htting the floor?

[oldcoot]

Boat runs at 13 mph at 6000 rpm with water filling motor tub and water hitting floor of pontoon.

Is it possible for you to post a photo of the back of your boat and the motor. I'm reaching here, but I'm "guessing" that the motor may be mounted way to low and thereby creating excessive turbulence and displacing water where it shouldn't be like you stated in the quote above. But please post a photo of your current setup it would be of enormous help for people here to evaluate the problem...

I would agree...I was going to ask where the trim/motor bracket was mounted...my 90hp is getting 20-25mph with me and Jillie on it....

[3/4time]

my prop is a 14 x 11 and speed was from the dash (no gps)

[GregF]

Look under the boat and be sure the trailer is not still attached

Seriously are the toons clean? Do you have any idea how heavy the boat is? (lots of extra furniture hard top or something)
Something doesn't seem right.

[slingshot]

Ok, you're under proped. Move to a 14x13. I know you say you're hitting 6000 rpm now but you may also be into your rev limiter which won't let you rev more than 6000 rpm. Give that a try before anything else. Many stores will let you return an undamaged
Prop if it doesn't solve your problem.

[Ron Burgundy]

You might want to bring a GPS with you if possible. My boat is no speed demon but I know it's faster than the 4mph that my dash speedo says.

You can even bring a GPS unit from your car if you have one. It won't do any good for navigation, but the speed will be accurate.