What size engine to achieve 30-35 mph?

[rhino_160]

Hey all,
I have a 22' Manitou Oasis with a 2011 Suzuki 70 Fuel Injected. After playing with 3 props to achieve the best performance, the best i can get out of my toon is 20mph with 2 passengers a full tank of gas. I would like to trade/sell my outboard and replace it with something to get my MPH up to the 30-35 mph mark. What size outboard would i need to get there? A 115 or 150 perhaps? I want to be able to get across the lake when need be. Any suggestions or anyone with a 115 or 150 that can chime in? Thanks in advance.

 

[steelespike]

First of all pontoon speeds are a little unpredictable.Yours seems a little slow though in the bottom end of ballpark. I checked some performance reports about 2600 lbs A low of 21.7 to a high of 25 with a 70 hp. 22 footers 115 speeds a little under 30, 27 - 28.5 weights generally over 3000 lbs.A 20 footer @ 2500 lbs made 28.5.
150 a 22 footer 3300 lbs @ 40, 25 footer 39.7 @ 3700 lbs.
Your 70 uses about 7 gallons per hour @ wot, A 115 will use about 11.5 gph, a 150 about 15 gph.
Would be interesting to see your present prop size, wot gps speed and rpm.

 

[MH Hawker]

Some where around a 250 or a 300 HP

 

[craigmack]

Several questions first... 2 or 3 tubes? Do they have strakes? What is the max HP the boat is rated for? I max out between 35 and 37 depending on how many I have aboard but general cruise around at 20 (@ 3500). Something else to think about is the type of steering you have. It's recommended to use a hydraulic setup for 150 HP and above which would add to your total repower cost.

 

[Mi duckdown]

What is your pontoon rated For.

 

[Okieboatguy]

Also just another thought, Is the bottom of your deck skinned? That simple inexpensive fix can add a few MPH to your top end.

 

[1983 ercoa 21']

Yes okie brings up a very good point. The water will hit the cross members and slow you down a little or alot depending on how your boat sits in the water and the condition of the lake.

 

[WaterDR]

It won;t be worth it to power-up on your boat. You will need to sell ti and start over.

 

[1983 ercoa 21']

Question to water dr why do you say it would not be worth it to re power a toon or power up in this case? I have personally powered up my boat from a 25 hp to a 70 then a 115 and have a 150 that I'm putting on this winter and ever step has been well worth it

 

[Mi duckdown]

What max hp is the toon rated?

 

[rhino_160]

thank you all for the replies. i will try to answer most of the ?'s now. The pontoon is rated for a 115 HP, it has 2 toons underneath it. I do NOT have it skinned but Manitou did send me the stainless steel plates that attached to each of the cross members on the front side so there is little to no drag of the water. It's not one flat plate but angle plates on all the cross members (hard to explain without a picture). I have ran 3 different props, all 13". Those pitches are 11, 13, and 17. The results are as follows with GPS speed:
17 pitch was 20 mph with 2 people and 14 mph with 6 people turning 4400 RPM WOT (Motor is rated for optimum performance between 5000-6000 RPM)
11 pitch was 18 mph with 2 or 4 people turning 6000 RPM WOT
13 pitch was 19 mph with 2 or 4 people turning 5800 RPM WOT
Ultimately, I found that with the 13 pitch I was able to run a higher, constant top end regardless of the people aboard and when pulling a 1-person tube. When trying to tube with the 17 pitch, the speed would drop down to the 13 mph mark. The 13 pitch runs about 16 mph with a tuber and 4 adults aboard.
And, I already have a hydraulic steering setup on the boat. Hope I answered all questions in an effort to figure out a good starting point on an outboard. I am mainly curious where I will stand with a 115 HP with the correct prop??

 

[craigmack]

Legally you can't go above the boat's stated maximum HP so with a 115 HP you're looking at 27-30 MPH

 

[steelespike]

It appears the DF70A has a 2.59 gear ratio and usually calls for over 13" diameter.
According to the calculator your 13" pitch is running 31% slip.
I think a 4 blade 13" Solas at least 13 1/2 inches diameter should do better.
I wouldn't expect miracles but maybe 20 or 21.