27 ft PONTOON PROP SELECTION help

[Pss3757]

Hello all, love the forum and the shared knowledge.

I just got a new triple tube pontoon boat and having problems getting the right prop. Dealer and suzuki says this motor runs better with the larger props on pontoons.

The boat:
27ft Avalon Pontoon, triple tube

The motor:
2015 Suzuki DF175 4 stroke
(designed operating rpm max of about 6100 rpm)

Boat and motor, dry weight is about 3500 lbs.

It came with a 3 SS blade, 16 x 20 prop....but WOT (all readings trimmed out, speeds on GPS) was 29mph @ 5000 RPM.

Swapped out for a 3 SS blade, 15-1/2 x 17 prop, and now i get 26mph @ 5000 RPM and WOT 34mph @ 6200 RPM.
(all above readings with about 1/2 tank fuel with med load of 3 persons)

Where should i go from here?? I am OK with the top speed, but would like to have a better, more economical cruise speed....something like 25 @ 4000 RPM or so.....

Any suggestions, here are my basic options...staying with Suzuki props. Dealer has been very friendly and will still let me try another prop.....no charge.

15-1/4 x 19
15 x 21
16 x 17
16 x 18-1/12

I am leaning toward the 16 x 17 but dealer thinks i will loose some WOT speed?

Thanks, any suggestions or thoughts are appreciated.

**Yes i have tried looking at some of the online prop calculator websites and either i'm not fully understanding or dont know how to compare my results***

 

[steelespike]

Your 175 will use about 18 gallons per hour at wot.Thats whether a runabout or a houseboat.
On a true planing hull the ideal cruising speed is from just on plane up to about 1000 more rpm.
I think your tri. requires a turn of speed to plane.
If you really want to fine tune your best cruising speed get yourself a flow meter. Some give a real time mpg calculation.
I'm Intrigued with the 16 X 18.5. If you lower pitch too much you lose some top end and very likely speed at various given rpm.
The 18.5 will probably knock off 200 or 300 rpm but may hold speed or tack on a little more.