The only toy that gets better as it gets less efficient...

[tdc_worm]

So we need someone to conduct an experiment.

run 60 mins at 4000rpms 5k ballast.

run 60 mins 4000RPMs no ballast.

Case of beer says they suck the same amount of fuel.

We all run this experiment every time we tow our boats to the ramp. My Tundra gets about 13 mpgs at 60mph/1800ish RPMs without boat in tow. With boat in tow, 60MPH/1800ish rpms, I get about 9.8 mpgs.

I will take a mix of craft IPAs. Thanks.

[nyryan2001]

Tdc- we are talking boats in the water with prop slip, not trucks on pavement.

apples and oranges. Thanks.

[SkiTower]

The only toy that gets better as it gets less efficient...

Tdc- we are talking boats in the water with prop slip, not trucks on pavement.

apples and oranges. Thanks.

not quite apples and oranges, it's a motor under load vs not under load. But to your point, I don't buy that TDC runs at the same RPM with and without boat. Mine goes from 1800 to 2400ish. And it's the starting and stopping that kills me, not so much the cruising load.

And I also think the original argument is engine wear, not so much efficiency.

[beach]

not quite apples and oranges, it's a motor under load vs not under load. But to your point, I don't buy that TDC runs at the same RPM with and without boat. Mine goes from 1800 to 2400ish. And it's the starting and stopping that kills me, not so much the cruising load.

And I also think the original argument is engine wear, not so much efficiency.

Your torque converter is slipping under load or you're running at a lower gear when you're towing. TDCs tow vehicle is doing neither. That's why you see a increase in RPM and he doesn't.

I can tow in overdrive if it isn't too hilly. My mpg drops from 22mpg to ~12 mpg. Same rpm.

[tdc_worm]

Tdc- we are talking boats in the water with prop slip, not trucks on pavement.

apples and oranges. Thanks.

You may want to contact Correct Craft and inform them that their boats are not operating correctly. I ran the RPM test that you suggested today, albeit at 2600 rpms instead of 4000 rpms. I ran the test with the Perfect Pass set on RPM control. I made one run completely unloaded, then another run with the stock ballast plus full plus the 750s that are piggy backed in the rear lockers about 50% full. that should have allowed for about 1600lbs of extra weight over empty. The tank was completely full. hydrogate was in the rear position.

The HrL function returned completely different results between then two tests. For those that don't know (page 4-29 of the 2007 manual) "Hours Remaining: The time remaining display shows the approximate number of hours the boat can operate based on the fuel remaining in the tank and the current fuel useage rate. The display will show XXXX.XHrL."

http://www.planetnautique.com/Correc...2007vdrive.pdf

The results:
Unloaded, 2600 RPM, 7.3HrL, 16.7mph

Loaded, 2600 RPM, 6.4HrL, 10.1mph.


The unloaded boat is estimated to run nearly a full hour longer given the fixed RPM, indicating that fuel useage us variable and is dependant on load in addition to rpm. Of course, I wasted my time humoring you by running the test as Newton's 3 Laws of motion already told us that your physics don't apply to the real world. But hey, I was out and I am often wrong so it was kind of fun. For your review:

http://csep10.phys.utk.edu/astr161/l...wton3laws.html

Finally, in mechanics where there is 1:1 transmission, slip is essential to reduce driveline shock. every car has slip. when you let the clutch out on your car, you are slipping the transmission. the torque converter in your automatic slips for the same reason. without slip they all would stall without more fuel which would allow them to spin their tires (another example of slip). in your boat, the water is your clutch.

I did say IPAs, didnt I?

[nyryan2001]

TDC- that is not the experiment I described, but thanks. Your ECM has analgorithm>>to ESTIMATE fuel usage, and then spit out and estimated run dry time based on what fuel is left in your tank. Its based on Speed, and RPMs, where an uloaded boat MPG/GPH curves meet somewhere at 22-26mph. it doesnt measure actual GPHs unless you were to have installed a fuel flow meter. I stand by my position-- your actual, not estimated GPHs in this scenario at 2600rpms... whether at 10 or 16mph will be so close its silly.

So, getting back to my original point of your orginal post..... explain to us again how 11mph 3000-3300rpm wakesurfing is harder on the engine than ballasted 4000rpm 23mph wake or 5000rpm+ barefooting?

[tdc_worm]

TDC- that is not the experiment I described, but thanks. Your ECM has analgorithm>to ESTIMATE fuel usage, and then spit out and estimated run dry time based on what fuel is left in your tank. Its based on Speed, and RPMs, where an uloaded boat MPG/GPH curves meet somewhere at 22-26mph. it doesnt measure actual GPHs unless you were to have installed a fuel flow meter. I stand by my position-- your actual, not estimated GPHs in this scenario at 2600rpms... whether at 10 or 16mph will be so close its silly.

I am a masochist that I keep playing this game...I guess I just like to make sure we are all getting smarter. you seem to be the only one that argues against physics, and I still prefer IPAs but mix in some craft lagers if its not too much trouble, its hot here in TX:

http://cdn.jotun.com/images/fixed-rp...cm29-10263.pdf

So, getting back to my original point of your orginal post..... explain to us again how 11mph 3000-3300rpm wakesurfing is harder on the engine than ballasted 4000rpm 23mph wake or 5000rpm+ barefooting?

now we are back on topic...and this whole exercise may help us attempt to address some of those questions. if there is any truth to the paper above that "power demand increases secondary to hull friction and attack angle of the prop at a fixed RPM" then we can hypothesise that increases in vessel mass are going to increase hull friction due to increased wetted surface and water displacement and a nonoptimized prop attack angle. to answer the surfing vs boarding vs barefooting question, I don't think we can do that without fixing all the other variables (same hull, same ballast, same prop, same wind drag, etc). which brings us back to my original questions:

"will the higher operating RPMs of these less hydrodynamically efficient boats (i.e higher load) have a negative impact on engine service life?"
"if so will it be significant or negligible?"

Just using F=MA (Newton's second law), the force needed to accelerate a greater mass (without outside variables) HAS to increase with greater mass. That force will increase the power demand of the engine:

Power=Work/Time
Work=Force*Displacement
Work=Mass*Acceleration*Displacement
Power=(Mass*Acceleration*Displacement)/Time
therefore as mass increases, power has to increase if everything else remains fixed.

Off course this is all classroom physics and discounts other known variables. In theory, it would seem to have a negative impact on the engine...but maybe only time will tell...

[aZ`]

The only toy that gets better as it gets less efficient...

Ryan, are you sure that's the way the ecu works out time 'til empty and/or GPH? It seems like an over complicated method when you could simply use injector average duty cycle/time. But injector cycle is directly related to load*rpm and would discredit your theory. The ecu has all of the information it needs to work out fuel usage without a fuel flow meter. MAP sensor can tell it the desired fuel pressure and inj duty cycle completes the equation. There is no need for fuel flow sensors. Just like in cars, fuel flow sensors haven't been used since we ditched the carburetor in the 80's.

[Ryan1776]

TDC- You get your IPAs yet??

[4th ski-doo]

Most heavy big lake or ocean cruisers spend their entire lives in the "surf" range. Low rpm plowing under plane.

Wear and tear? Sure, use good oil

High rpm's better? No, every engine formula of life vs rpm. Closer to red line shorter the life. The 200 is designed to suck into the water for tracking not skim the top and 36mph slalom every morning is high rpm. Footing around a big lake every morning is big rpm's and as damaging.

Change your oil at the right times, use good oil, take care of your boat and it will last.

Marine loads are way different than road loads and hardly comparable, they just don't line up.

[tdc_worm]

TDC- You get your IPAs yet??

Oh, I did get some IPAs, but had to spring for them myself as I didn't have time to wait on Ryan. Desperate times call for desperate measures, haha.

[CincinnatiCC]

Seems like it doesn't much matter. If the approximate conversion is 100 hours equals 10-15 thousand miles on a car engine, you've got a lot of hours to put on to get these to the point where they need to be rebuilt. And for me, the more hours, the better!

[Rbt]

Tdc- you are killing me.

the exact same forces are put on the engine and drive train at 4000 Rpm whether at 11mph, 23mph or 37mph. There is no thing such as an easy 4000rpms. Next thing you'll say is 4000rpms at 23mph with 3k ballast uses less gas than 4000rpms at 12 with 5k ballast?

Yes at 11mph it's mainly hull friction, at 35mph it becomes wind drag . Thrust will be the same at a given rpm, then the variables are weight, prop slip and prop shaft angle.

Gph's are solely a function of RPMs. Load on the engine is defined by RPMs. When the "load" gets heavy, you induce prop slip.




Now, as to your question on the 550s and their OEM 15x14 props? They are not ideal because the 17x17s are too big.... And 16x15ish to 17x15ish are not yet available by Acme or Oj.

The exact same forces are not placed on an engine at equal rpm. Do you think it takes the same throttle position and fuel requirements to run the engine in neutral at 4000 rpm as it does when full of ballast going 23mph?

[greggmck]

The exact same forces are not placed on an engine at equal rpm. Do you think it takes the same throttle position and fuel requirements to run the engine in neutral at 4000 rpm as it does when full of ballast going 23mph?

That's correct. The ECU will increase fuel flow to hold rpm under load. In neutral, fuel flow will be much lower than at full ballast for the same rpm. If we are looking for a proxy of load on the engine fuel flow will be pretty close. Fuel flow while surfing is about 6.5 to 7 GPH in my H6Di. At wakeboard speeds it is closer to 15+ GPH.

Sent from my SM-G965U using Tapatalk

[nyryan2001]

The exact same forces are not placed on an engine at equal rpm. Do you think it takes the same throttle position and fuel requirements to run the engine in neutral at 4000 rpm as it does when full of ballast going 23mph?

That’s not what I said, scroll back up and read.

the forces per a given rpm are the 99.9% same whether at 11.5 mph or at 23mph.

no one is talking reving the engine in neutral.