Comments about Fuel usage

Haven't y'all (yankee trying to talk southern) taken a gander at the boattest.com efficiency charts? When they test a boat, they show a curve of MPG vs RPM. It always shows maximum efficiency at idle, rapidly falling off until you hit transition and then increasing to a sweet spot and then falling off again. I find it interesting to see which boats have a wide sweet spot and others with a few bumps in the curve as engine efficiency moves the curve about.

My boat was tested with 22" pitch props, I have 20". For the test, Sea Ray loaded the engine up to get a high max speed. I thought about repropping and talked the "oracles" at my dealer... their concern was over a little 5L working that hard might be detrimental to the longevity of the engine... at least I never have trouble getting on plane and my max RPM's still sit where they're supposed to. So I had to generate my own curves and for the most part, the shape, sweet spot, aren't too different... but your milage may vary.

Now anyone want to debate efficieny with a hydrofoil?!
 
Four Suns said:
How can something be above the surface of the Sun but yet be less than 7% of the radius of it? Is this a trick question?
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Let me simplify this for you. “47,000 kilometers is less than 7% of the radius of the Sun.” It is merely a statement that 47,000 kilometers above the surface is fairly insignificant when compared to the entire radius. I said nothing about the center of mass being 47,000 kilometers from the center of the Sun.
 
BTW, if getting there is half the fun... the maximum value would occur below the sweet spot (running the engine less than maximum efficiency). If you're more interested in getting to where you're going, your time has value and running the boat a bit faster than the maximum fuel efficiency point is where you would want to be... if sea conditions allow that is...
 
Jim240 said:
Haven't y'all (yankee trying to talk southern) taken a gander at the boattest.com efficiency charts? When they test a boat, they show a curve of MPG vs RPM. It always shows maximum efficiency at idle, rapidly falling off until you hit transition and then increasing to a sweet spot and then falling off again. I find it interesting to see which boats have a wide sweet spot and others with a few bumps in the curve as engine efficiency moves the curve about.

My boat was tested with 22" pitch props, I have 20". For the test, Sea Ray loaded the engine up to get a high max speed. I thought about repropping and talked the "oracles" at my dealer... their concern was over a little 5L working that hard might be detrimental to the longevity of the engine... at least I never have trouble getting on plane and my max RPM's still sit where they're supposed to. So I had to generate my own curves and for the most part, the shape, sweet spot, aren't too different... but your milage may vary.
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Your anecdotal and real-world results are far less impressive than the theoretical trash spewing from my keyboard... even though the results are the same.
 
Aarrhh & Aarrhh said:
Let me simplify this for you. “47,000 kilometers is less than 7% of the radius of the Sun.” It is merely a statement that 47,000 kilometers above the surface is fairly insignificant when compared to the entire radius. I said nothing about the center of mass being 47,000 kilometers from the center of the Sun.
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OK... I got it. But the world is still flat.
 
Jim240 said:
Haven't y'all (yankee trying to talk southern) taken a gander at the boattest.com efficiency charts? When they test a boat, they show a curve of MPG vs RPM. It always shows maximum efficiency at idle, rapidly falling off until you hit transition and then increasing to a sweet spot and then falling off again. I find it interesting to see which boats have a wide sweet spot and others with a few bumps in the curve as engine efficiency moves the curve about.

My boat was tested with 22" pitch props, I have 20". For the test, Sea Ray loaded the engine up to get a high max speed. I thought about repropping and talked the "oracles" at my dealer... their concern was over a little 5L working that hard might be detrimental to the longevity of the engine... at least I never have trouble getting on plane and my max RPM's still sit where they're supposed to. So I had to generate my own curves and for the most part, the shape, sweet spot, aren't too different... but your milage may vary.

Now anyone want to debate efficieny with a hydrofoil?!
Click to expand...

In contrast, the MPG vs RPM curve on a displacement hull is roughly a smooth curve from 1 knot to the hull's maximum. As a result, reducing the speed of any displacement hull at any speed will always result in better fuel efficiency.
 
Jim240 said:
Haven't y'all (yankee trying to talk southern) taken a gander at the boattest.com efficiency charts? When they test a boat, they show a curve of MPG vs RPM. It always shows maximum efficiency at idle, rapidly falling off until you hit transition and then increasing to a sweet spot and then falling off again. I find it interesting to see which boats have a wide sweet spot and others with a few bumps in the curve as engine efficiency moves the curve about.

My boat was tested with 22" pitch props, I have 20". For the test, Sea Ray loaded the engine up to get a high max speed. I thought about repropping and talked the "oracles" at my dealer... their concern was over a little 5L working that hard might be detrimental to the longevity of the engine... at least I never have trouble getting on plane and my max RPM's still sit where they're supposed to. So I had to generate my own curves and for the most part, the shape, sweet spot, aren't too different... but your milage may vary.

Now anyone want to debate efficieny with a hydrofoil?!
Click to expand...

Curves, surmves…. I’m burning the gas period.

When I am out with the boat I am not constantly thinking about some “sweet spot”. I told myself a long time ago, if I can’t afford the gas, then I can’t afford the boat.

Now granted I am now going to waste it if I can help it, but worrying about my speed for the sake of saving gas is not my concern out there. Weather and sea conditions dictate my speed. Actually I let her run a little bit last time out, I was truly impressed at just how fast this boat is.

Still the reading is interesting......and fun:thumbsup:
 
Funny! Then you'd rather overlay a bi-fluidic, transitory phasic, modified N-S FEM with turbulent correction and unsteady (time dependent) separation points. Oddly enough, I'm on the Cray right now... ;)
 
Jim240 said:
Funny! Then you'd rather overlay a bi-fluidic, transitory phasic, modified N-S FEM with turbulent correction and unsteady (time dependent) separation points. Oddly enough, I'm on the Cray right now... ;)
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Actually, I am waiting for my Flux Capacitor :thumbsup:
 
Actually.... His Navier Stokes program he is talking about probably does use some form of flux vector splitting....

You still use Crays? I took my son to the Air and Space museum and showed him the Cray YMP I used to work on... It's a bench now... literally.
 
Every is bored today I see, getting back to topic, The only time I do think about long runs is between available fuel stops. This was very helpful during my recent fishing trip some 65 miles off the coast of california. That equates to 35 miles west of Catalina island. This was first trip with fuel flow sensor and did help me to find my exact sweet spot and tell me when I needed to drop back down to no-wake speed. Before this, it was you own it, so quit thinking about the cost. I have developed my own fuel use chart based on full load and I added to the boattest figures. My sweet pspot rpm is slightly higher than boattest when fully loaded.:thumbsup:
 
Jim240 said:
...When they test a boat, they show a curve of MPG vs RPM. It always shows maximum efficiency at idle, rapidly falling off until you hit transition and then increasing to a sweet spot and then falling off again. I find it interesting to see which boats have a wide sweet spot and others with a few bumps in the curve as engine efficiency moves the curve about...
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I have been searching for one of these graphs. Anyone have any links to where I could obtain the 2002 Sea Ray Sundancer 380 MPG vs RPM curve jim240 is referring to above?

Thanks
 
Pseudomind said:
I have been searching for one of these graphs. Anyone have any links to where I could obtain the 2002 Sea Ray Sundancer 380 MPG vs RPM curve jim240 is referring to above?

Thanks
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I have the boattest results for the 380DA with 8.1s. It's saved as a word document. I don't know how to post a word doc here so PM me your email address and I'll send it to you.
 
Wow, what a thread! Almost got into Quantum physics or did we? I feel so useless and insignificant in the world. OK, I'll admit it, I'm just not smart..... I think my IQ is closer to Bubba's!
 
osd9 said:
I have the boattest results for the 380DA with 8.1s. It's saved as a word document. I don't know how to post a word doc here so PM me your email address and I'll send it to you.
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Sent a PM
 
Some of this sounds interesting and I'd like to participate but Stephen Hawking just called. Steve wants to bounce some new thoughts of me. I gotta go, I hope you'll all understand.
 
osd9 said:
I have the boattest results for the 380DA with 8.1s. It's saved as a word document. I don't know how to post a word doc here so PM me your email address and I'll send it to you.[/quote

Open the file click on edit and select all, then go to a post right click and select paste and it will post for you.:thumbsup:
Click to expand...
 
Woody said:
Some of this sounds interesting and I'd like to participate but Stephen Hawking just called. Steve wants to bounce some new thoughts of me. I gotta go, I hope you'll all understand.
Click to expand...

:smt043:lol::smt043

Have him explain a Quark and wormholes in laymans terms while your there!! :thumbsup:
 
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