prop for fletcher14" and yamaha40hp

[zanev]

Hi people and regards from EU! Here some data:
boat fletcher arrowflyte 14" dry weight 590lbs, outboard Yamaha 40hp enduro,2stroke,g.r.2:1,max rpm 4500-5500,weight 175lbs,propeller Yamaha 11,1/8 X 13

case 1: load on boat is 2 people+gear=800lbs
upstream to the river (stream of river 2-5mph)
wot 5500rpm,max speed 29mph
case 2: load 1 people+gear=400lbs
upstream to the river (stream of river 2-5mph)
wot 5900-6000rpm,max speed 32mph

I will bay a spare propeller for the second case,wich is most suitable: Yamaha 11X15 or 10,3/4X16 ?
Thanks!

 

[zanev]

Re: prop for fletcher14" and yamaha40hp

I meant to "buy" a second propeller. anti-ventilation plate is to the level of the bottom pad (V"-bottom boat with a flat surface at the very bottom called a "pad")

 

[steelespike]

Re: prop for fletcher14" and yamaha40hp

Is your speed by GPS and have you checked river flow with gps? A 15" pitch would knock about 300 to 400 off the rpm.
May slow your hole shot and may fade a little more when you add weight.But your light load might produce more speed.

 

[zanev]

Re: prop for fletcher14" and yamaha40hp

Yes,the speed of boat is checked with gps(i post gps reading). I also have a speedometer on the boat and thе difference between it and gps reading is speed of river flow, i think.Of course, speedometer readings are not accurate as those of the gps so i post 2-5mph for river flow. I drive my boat almost always alone, a slow start does not bother me. The idea is to not exceed the max 5500rpms and get a higher cruising speed. I always drive from point A to point B (about 30 miles) without stopping.

 

[steelespike]

Re: prop for fletcher14" and yamaha40hp

You could check river flow by drifting while checking the gps.
When you say cruising speed you mean speed at a reduced throttle?
You probably should change to a 15" pitch. The tricky thing is as you increase pitch you change the threottle setting for a given speed. Marine motors are working like they are going up up hill all the time when you increase pitch its kind of like shifting to a higher gear making the motor work even harder.I do think the 15 is ideal The motor can still rev freely yet you can likely increase your wot speed. Ideal cruising speed could be between just on plane and about 1000 rpm higher. You would probably need a flow meter to tell the difference between a good setup and a perfect setup.

 

[zanev]

Re: prop for fletcher14" and yamaha40hp

Тhis was very helpful,thanks! I check it when i was drifting and clonking for catfish and its average 3mph. No,I mean cruising speed at the same rpms that i drive usually (4000-4400) but at highest possible speed.I understand that the threottle + bigger pitch prop, will be more open and fuel consumption will increase. Now the threottle for 4000-4400 rpms and 13pitch prop is no more than 1/4 from wot(i have min fuel consumption for planing with this engine).I wonder if 2or even 3/4 of the thr. will be sufficient to deploy the motor to the same rpms with 16pitch prop..? I forgot to mention that the engine has a power trim and guess that would help me to go at planing with bigger pitch prop.In the other hand i fear that with 16pitch, the engine will not have reserve of power for summer storm and a strong headwind and waves,is it true that thought?

 

[steelespike]

Re: prop for fletcher14" and yamaha40hp

Approximately 200 rpm per inch of pitch change is the rule of thumb.
A 2" pitch change should net 300 to 400 rpm change. Your motor needs to be able to reach its rated rpm
or it will be lugging at any rpm. A 16 probably wouldn't be too bad for wot rpm but the motor may feel like it is going uphill in overdrive.
Its a difficult balance of throttle opening to speed. I can tell you that a 13" prop at 4000 guessing 18% slip would make about 20.2 mph, a 15" / 18% slip 23.3 and a 16, 24.8. Slip is likely to be a little higher but you get the idea. Does the speed make up for the throttle setting. You will likely need a flow meter to tell any fuel difference. 20.2 mph is about 1 1/2 hours to go 30 mi.
the 16" is about an hour and 15min. to go 30 miles.