OJ 948 Prop test - 22 VLX/409 engine

[mrnate450r]

Ordered my 948 today. Hope to have a couple of weekends on it before we head to Table Rock in 3 weeks.

[Fman]

We ran the 948 at 2000' yesterday with 409 in 22 VLX, 5 passengers, boat heavy (food/water/gear).... here was my experience. For wakeboard with hard tanks, and wedge did great. For surfing with 800's in each locker, 650 lb bow bag, hard tanks full, wedge 2-3 clicks up max speed was about 10.8-11 mph. If I dropped wedge all the way down I could reach 11.2-4. With all ballast full (surfing config) I could not get the boat to plane out past 12 mph. On my next fill up I will be able to calculate fuel useage... I know my gauge was reading 0% when we came back to the Marina. So we definitely were chugging the fuel...

The 948 prop at 2000' with my engine is borderline not enough, the 945 would probably be a better setup for this altitude and weight we were running. Altitude is no joke, the boat just feels much different at 2000' from sea level.

[mrnate450r]

You've got me second guessing Fman!

[Fman]

What engine do you have? If you have a 450 I would bet it's going to be perfect. The 409 was at its limits with this prop.

[mrnate450r]

Yes I have the 450.

[Fman]

Are you at elevation or sea level?

[mrnate450r]

Roughly 1500' here in Kansas.

[Fman]

I think that prop will be a perfect match for you. Keep us posted...LOL, 1500' in Kansas? I always thought Kansas was flat land!!!

[mrnate450r]

Well, we are the state next to the Rockies! To be fair, I am at 1300' but one lake I go to farther west is closer 1600'. And, it is flat. A flat gradual slope to the Rockies.

[catalac]

We ran the 948 at 2000' yesterday with 409 in 22 VLX, 5 passengers, boat heavy (food/water/gear).... here was my experience. For wakeboard with hard tanks, and wedge did great. For surfing with 800's in each locker, 650 lb bow bag, hard tanks full, wedge 2-3 clicks up max speed was about 10.8-11 mph. If I dropped wedge all the way down I could reach 11.2-4. With all ballast full (surfing config) I could not get the boat to plane out past 12 mph. On my next fill up I will be able to calculate fuel useage... I know my gauge was reading 0% when we came back to the Marina. So we definitely were chugging the fuel...

The 948 prop at 2000' with my engine is borderline not enough, the 945 would probably be a better setup for this altitude and weight we were running. Altitude is no joke, the boat just feels much different at 2000' from sea level.

good info, glad I went 2315 on my 22vlx with a 350 then, I would never pull that 948 at 1500ft where I'm at.

[Fman]

So my next question. For the best fuel economy are you better to run a prop that will deliver for surfing with wot and lower rpms OR higher rpms (say 150 more) but you are not running wot when surfing. Cruising would be about the same, 150 more rpms at the same speed. Does one deliver better fuel economy than the other or is it a wash?

My gut says less throttle and higher rpms would be better for fuel economy, but I really have no idea.

[shawndoggy]

So my next question. For the best fuel economy are you better to run a prop that will deliver for surfing with wot and lower rpms OR higher rpms (say 150 more) but you are not running wot when surfing. Cruising would be about the same, 150 more rpms at the same speed. Does one deliver better fuel economy than the other or is it a wash?

My gut says less throttle and higher rpms would be better for fuel economy, but I really have no idea.

I think it's the opposite. More RPMs = more air pumping through engine = more fuel. I know it is that way in a car... like with a manual where you have to floor it in 6th to maintain speed up a hill that you could just have the throttle cracked in 4th (but higher RPMs), you will burn more gas in 4th than 6th.

But lugging engine can have other bad effects.

[Fman]

I also wonder if it's easier on the engine to not run WOT with higher rpms or run wot with lower rpms? It would be fun to do a test on the fuel consumption with these scenarios to see what the difference would be, significant or very little? I am pretty confident we sucked down over 40 gallons on monday, my tank is only 48. We even stopped for a lunch break and swim...I will get confirmation on my next fill up and I can see how much it takes to fill up, but we were at 0% on the fuel gauge. Having and few extra gallons for us would not be a bad thing at the end of the day, this is my reason to investigate the fuel consumption with different props. We are usually out late on the water, if we ever ran out of fuel we would be on our own and paddling back in. We rarely see anyone late in the evenings...

[nyryan2001]

I continue to contend that there is no such thing as "hard and easy" RPMs.

Higher RPMs= more fuel. Period.

I've had 4 different OJ props on my boat in 2 weeks for testing. Lower rpms = less fuel. 500rpms avg lower(in the 2500-3500range) = ~ 1.5-2gph savings avg. I do not think fuel GPH is linear... 3300-4k is a higher % proportionately than 2500-3k.

I have also learned that efficiency and performance for surfing and 23mph wake are not synonymous. Two entirely different activities, with ballasted weights that require different props to have A+ performance and low RPMs/low GPHs.

If you do more of one or the other, you should be geared(prop'd) for that and for the other activities you do. If you do both, split the difference.

[teamerickson]

I'm probably wrong but I thought RPMs and speed seemed correlated. I thought I had similar RPMs at a given speed regardless of ballast? If that's true then it should take more energy (gas) to move more weight if the RPMs are the same?

[Fman]

I'm on the fence, the 948 did pretty good overall at 2000', but surfing I was pegged at 11.0 mph and limited to amount of wedge we could use. I am confident the 2315 would give me more low end torque for surfing and wedge use but also bump me up approx 150 rpms. I don't think with the 2315 I would be at full tilt either on the throttle. We wakeboard 60%, and surf 40% on average. Some days are different than others... saving fuel ($) is great but for me it's more how much is left in the tank at the end of the day.

[mrnate450r]

I put my 948 on last night. We won't be out until this weekend. I will report how we do with the LS3.

[mrnate450r]

We didn't get a whole lot of time on the 948 today. The wind was blowing 20+, and we were all fighting for the same mediocre water by the dam. It definitely pulls harder out of the hole than my modified 12.5 pitch 1235. That confirms my suspicion of cavitation. I will have a whole week with it starting Friday. So far, I'm happy with it. But, we had a fairly light boat today too.