I need more speed

[threadrep1]

I have a 115 hp Yamaha 4 stroke on a 18' flat bottom sholewater. I am wanting more top end speed. I have a 13" 17 pitch stainless prop.my top speed is 35 on the GPS at WOT at 6000 RPMS. Is there a way to get the boat to go faster than what it's going right now. The take off is very good will throw a person out of the boat if not paying attention lol.

 

[paddlers]

If you want top speed you lose the hole shot ( acceleration) , it's all about compromise !! What's your priority ?

 

[Scott Danforth]

going up to a 19p will give you more top speed, however you will sacrifice a bit of the hole shot.

 

[steelespike]

Based on the numbered you gave us your slip is really high at 22% normal is usually the low double digits.
Your tach may be off high I think you should verify the tach before we go any farther.What is the weight as tested?
You could try lowering the motor one hole.Does the boat respond to up trim?Any ventilation issues?

 

[Lager]

Steel spike might be onto something here? Flat bottom boats running at that speed will force a lot of air into the water that your prop is running in. So, instead of your prop running in clean water, its an aerated mix causing a lack of traction . This account for your lack of top speed but good accel from a stop as you mentioned. Dropping your motor will reduce your skinny water capability tho.

 

[jestor68]

Are we talking about a "Shoalwater" boat; made in Texas or what?

If that's the case, a 4 blade(at least) prop is required.

The Solas HR Titan 4 (17 pitch) might be a good place to start looking. Yamaha also makes a "Performance series" 4 blade(minimum of 18 pitch).

 

[Sea Rider]

If 6 K is the max wot rpm factory stated for that engine you're spot on with that current prop, speed and performance. Don't pass that limit by whichever prop pitch you choose to increase speed with, no good for engine...

Happy Boating