New Prop. Advice from the experienced?

[Spoiledrotten]

My boat is a few weeks old now. I've got 30 hours on it and want to purchase another prop for a main, and use the current 13.5"/15p for the spare. I'd like to go with a 4 blade prop. I currently get around 24 MPH at about 5200 RPM. I think I can do better than this but don't know which way to go with the new prop. The specs below show an RPM range of 5000 - 6000. At 5200, I think some power is being wasted.

 

What would you go with to get the max performance out of my F90?

 

My boat is the Bennington SLX20.

 



 

My motor specs. 

 

F90 Specifications

Engine Type In-Line Four Cylinder

Displacement 97 ci (1596 cc)

Bore x Stroke 79 x 81.4mm (3.11 x 3.20in)

Prop Shaft Horsepower 90hp @ 5500rpm

Compression Ratio 9.6:1

Fuel Induction EFI/SOHC/4 Valves Per Cylinder

Exhaust Through Propeller

Intake Single Throttle Valve

Ignition TCI Micro Computer

Spark Plug LFR5A-11-00-000

Alternator Output 25AMP

Starting System Electric w/PTT

Lubrication Wet Sump

Engine Oil Capacity 3.7L/3.5L w/without filter

Full Throttle RPM Range 5000 ~ 6000 rpm

Cooling Water/Thermostatic Control

Recommended Engine Oil Yamalube® 4M (See owner's manual)

Recommended Fuel Regular Unleaded (Minimum Pump Octane 87)

Recommended Fuel Filtration Yamaha Mini 10-Micron Fuel/Water Separating Filter (external)

Ethanol Blend Limit 10% Maximum

Gear Ratio (25:11) 2.27:1

Gear Shift F-N-R

Shaft Length L = 20" X = 25"

Degree of Tilt 70°

Degree of Trim -4° through +16°

C.A.R.B. Rating 3-Star

Dry Weight 25" shaft / 169 kg (372 lbs) ; 20" shaft / 166 kg (366 lbs)

Steering Angle (maximum) 35° from center, either direction

Warranty 3 Year Limited Pleasure Boat - 1 Year Limited Commercial

 

[Resqu2]

Gonna tag this as I'm curious as to what your told here, I run the same prop as you just on a 22' 115hp yamaha. I hit 6100 wot and the best I can do is 25-26 mph. Where I get lost at is I just picked up a Solas prop with the same specs as my original and it runs 5800 and 25-26 mph. Not even sure which one I should use? The one where it get 6100 rpm or the 5800rpm?

 

[Spoiledrotten]

I went out with just the wife and I and rechecked the speed. It still won't go over 5200 RPM, and I got 27 MPH out of it on smooth water, trimmed out. It did 25-26 MPH in choppy water. Still would like to get at least 5500 RPM to get the 90 hp like the spec states.

 

[CTays]

Below is a copy of post I made earlier. I forgot to mention that I am only running about 5000 rpm WOT. I was really suprised at the 115hp numbers above. It should be going faster unless it is a tritoon. I am doing very well with my setup and very happy with the performance. Please see the below for my prop experience. My numbers are based on the GPS from Navionics.


Repost:


My old boat was a 24' Aquapatio with small 19" toons and a 2013 70hp Yamaha. It would get about 16 MPH WOT with 4 adults on board. I would easily loose 50% pulling a tube. My new Bennington is a 22' SSLX with the 25" toons and a90hp Yamaha with a 15 pitch prop. I get 29 MPH with 2 people and about 26 MPH with 4. I have pulled the grandkids and friends on the tube (3 at a time = 1 @160 lbs and 2 @100 lbs) with 3 adults on board and get 22 MPH WOT. I tried several differnt props and got a little more speed with a 13 pitch but lost almost 50% speed pulling the tube. The 15 pitch was the all around best for cruising and pulling the tube with the least amount of speed loss. I would suggest trying a couple differnt pitches up and down to see what works best for you. My dealer worked with me when I bought the boat and let me try several differnt ones out before settling on the 15. I found that my boat did not match all the information I saw regarding speed and power with various pitches. In talking with others I realize that every boat seems a little differnt and trial and error is the best approach. I can tell you there is a big difference of the 90hp and the 70hp. I started to use my 70hp on the new boat but decided to get the new 90hp and I am very glad I made the choice. Good luck and happy boating

 

[Spoiledrotten]

Thanks CTays.

 

[Spoiledrotten]

Reporting back. I ordered a 4 blade - 13P prop to replace the 3 blade - 15P on my Yamaha F90. The boat shoots up to plain. I went from 5100 RPM WOT to 6100 RPM WOT. My speed is right there at the same 26 MPH. I talked to my dealer who told me that if I go to the SS prop, I would most likely want to stay with the 13P if I want to keep the RPM up. He said the SS prop would most likely bring my RPM down a couple of hundred since there's more cupping in the blades of a SS prop. That's all I have now, stay tuned for more after messages from our sponsors.

 

[kaydano]

Having both myself, my stainless (thanks Todd) is a LOT heavier than my aluminum prop. With a smaller motor that's a factor. Not only do you have to accelerate the weight forward, you also have to accelerate it rotationally. The extra weight counts 2x against you, and is magnified by the smaller motor. Food for thought.

 

[Bill N]

Having both myself, my stainless (thanks Todd) is a LOT heavier than my aluminum prop. With a smaller motor that's a factor. Not only do you have to accelerate the weight forward, you also have to accelerate it rotationally. The extra weight counts 2x against you, and is magnified by the smaller motor. Food for thought.

Excellent explanation.

 

[Spoiledrotten]

That is some good food for thought. Thanks for sharing! When I was in the local dealership today, I picked a SS prop up today and was very surprised at how heavy was actually was.

 

[Omike]

Resqu2, I have a 13.25 x 17 p aluminum prop on a 21 sox. I'm getting 34-36 mph with a 115. Your speed for not much bigger of a boat seems low to me.