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Malibusteve

optimum cruising speed

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Malibusteve

Boat tests show this all the time, but is there a way to calculate this without a gauge? I have a VTX with the LCR 320 and am interested in knowing the most fuel efficient optimum cruising speed for my boat. I think its based on RPM and other factors. Anyone know?

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footnlongline
Boat tests show this all the time, but is there a way to calculate this without a gauge? I have a VTX with the LCR 320 and am interested in knowing the most fuel efficient optimum cruising speed for my boat. I think its based on RPM and other factors. Anyone know?

I like 3500 rpms but I found that off uses less fuel.

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WAKE-RIDER-01
Boat tests show this all the time, but is there a way to calculate this without a gauge? I have a VTX with the LCR 320 and am interested in knowing the most fuel efficient optimum cruising speed for my boat. I think its based on RPM and other factors. Anyone know?

I like 3500 rpms but I found that off uses less fuel.

True, but off=no fun

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BlastRlxi

Boating magazines all use fuel flow measuring equipment to find optimum cruising speed. I would agree that most boats hit the most efficient cruising speed about 3000 - 3500 rpm.

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VinRLX
Boating magazines all use fuel flow measuring equipment to find optimum cruising speed. I would agree that most boats hit the most efficient cruising speed about 3000 - 3500 rpm.

Ditto.

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electricjohn

Here are some numbers from a boat test conducted by Trailer boats magazine.

1000 rpm....6.9mph...1.5gph...4.6mpg...170 mile range...75db...1*run angle

1500 rpm....9.2mph...2.8gph...3.3mpg...121 mile range...94db...4*run angle

2000rpm...17.1mph...4.2gph...4.1mpg...150 mile range...92db...5*run angle

2500rpm...24.6mph...6.2gph...4.0mpg...146 mile range...83db...3*run angle

3000rpm...30.2mph...8.1gph...3.7mpg...138 mile range...88db...2*run angle

3500rpm...35.4mph..10.8gph...3.3mpg...121 mile range...82db..2*run angle

4000rpm...39.2mph..14.2gph...2.8mpg...102 mile range...88db...2*run angle

4500rpm...43.0mph..18.7gph...2.3mpg....85 mile range...86db...2*run angle

4900rpm...45.5mph..23.9gph...1.9mpg...70 mile range...91db....2* run angle

This was for a 2004 Rlxi with the Monsoon With a 13x12 prop. Hope this answers your question, but different hulls displace and plane differently.

Edited by electricjohn

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UWSkier

Wow. So in other words, stay off the loud handle if you're out for a cruise!

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VinRLX
Here are some numbers from a boat test conducted by Trailer boats magazine.

1000 rpm....6.9mph...1.5gph...4.6mpg...170 mile range...75db

1500 rpm....9.2mph...2.8gph...3.3mpg...121 mile range...94db

2000rpm...17.1mph...4.2gph...4.1mpg...150 mile range...92db

2500rpm...24.6mph...6.2gph...4.0mpg...146 mile range...83db

3000rpm...30.2mph...8.1gph...3.7mpg...138 mile range...88db

3500rpm...35.4mph..10.8gph...3.3mpg...121 mile range...82db

4000rpm...39.2mph..14.2gph...2.8mpg...102 mile range...88db

4500rpm...43.0mph..18.7gph...2.3mpg....85 mile range...86db

4900rpm...45.5mph..23.9gph...1.9mpg...70 mile range...91db

This was for a 2004 Rlxi with the Monsoon. Hope this answers your question, but different hulls displace and plane differently.

John, do you have the magazine or link to online review? Most performance numbers I have seen show a drop off in MPG from 1500-2500 RPM, IIRC.

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skicrave

Seems like the lowest engine speed that will plane the hull would be the most efficient. That's when the drag is the least compared to fuel economy.

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99response

I like the change from 4500 RPM to 4900 RPM, alot more noise, alot more gas, and 2.5 MPH to show for it....

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electricjohn
Here are some numbers from a boat test conducted by Trailer boats magazine.

1000 rpm....6.9mph...1.5gph...4.6mpg...170 mile range...75db

1500 rpm....9.2mph...2.8gph...3.3mpg...121 mile range...94db

2000rpm...17.1mph...4.2gph...4.1mpg...150 mile range...92db

2500rpm...24.6mph...6.2gph...4.0mpg...146 mile range...83db

3000rpm...30.2mph...8.1gph...3.7mpg...138 mile range...88db

3500rpm...35.4mph..10.8gph...3.3mpg...121 mile range...82db

4000rpm...39.2mph..14.2gph...2.8mpg...102 mile range...88db

4500rpm...43.0mph..18.7gph...2.3mpg....85 mile range...86db

4900rpm...45.5mph..23.9gph...1.9mpg...70 mile range...91db

This was for a 2004 Rlxi with the Monsoon. Hope this answers your question, but different hulls displace and plane differently.

John, do you have the magazine or link to online review? Most performance numbers I have seen show a drop off in MPG from 1500-2500 RPM, IIRC.

Jack, I just cut the chart out of the magazine about a year or two ago and tossed the rest of it, It was (I'm guessing) from the spring of 04. They compared 4 boats. IIRC there was also a Moomba, Tige', and either a SN or MC. They liked the Moomba best, but mainly because of price.

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99response
John, do you have the magazine or link to online review? Most performance numbers I have seen show a drop off in MPG from 1500-2500 RPM, IIRC.

yeah *IF* you recall correctly, which seems to be getting harder and harder...

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UWSkier
Seems like the lowest engine speed that will plane the hull would be the most efficient. That's when the drag is the least compared to fuel economy.

I'd submit that's when drag is the least period with static hulled ski boats.

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skicrave

Good clarification. My intent was to paint the picture that because it's a static hull, drag stays virtually the same regardless of how much faster than planing speed you're going, which just uses more fuel.

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UWSkier
Good clarification. My intent was to paint the picture that because it's a static hull, drag stays virtually the same regardless of how much faster than planing speed you're going, which just uses more fuel.

I think due to the negative attitude of the propshaft, drag actually increases as speed increases and the nose is forced downward. That's why there are such diminishing returns by modifying the engines and props on these boats to try to get more speed. If you could somehow trim the propshaft to be parallel to the direction of travel and let the hull lifting strakes do their job, you'd probably have a more linear speed vs drag relationship. That and with 340+ HP, you could really get these boats moving. Thumbup.gif

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MalibuTime
Here are some numbers from a boat test conducted by Trailer boats magazine.

1000 rpm....6.9mph...1.5gph...4.6mpg...170 mile range...75db

1500 rpm....9.2mph...2.8gph...3.3mpg...121 mile range...94db

2000rpm...17.1mph...4.2gph...4.1mpg...150 mile range...92db

2500rpm...24.6mph...6.2gph...4.0mpg...146 mile range...83db

3000rpm...30.2mph...8.1gph...3.7mpg...138 mile range...88db

3500rpm...35.4mph..10.8gph...3.3mpg...121 mile range...82db

4000rpm...39.2mph..14.2gph...2.8mpg...102 mile range...88db

4500rpm...43.0mph..18.7gph...2.3mpg....85 mile range...86db

4900rpm...45.5mph..23.9gph...1.9mpg...70 mile range...91db

This was for a 2004 Rlxi with the Monsoon. Hope this answers your question, but different hulls displace and plane differently.

John, do you have the magazine or link to online review? Most performance numbers I have seen show a drop off in MPG from 1500-2500 RPM, IIRC.

Jack, I just cut the chart out of the magazine about a year or two ago and tossed the rest of it, It was (I'm guessing) from the spring of 04. They compared 4 boats. IIRC there was also a Moomba, Tige', and either a SN or MC. They liked the Moomba best, but mainly because of price.

We were out in our neighbors Grady White w/ twin 250 Yamaha's and I recall seeing the fuel flow at .8 or something like that. Might have been up to 1.5 as we sped up. BTW, that is gallons/mile.

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VinRLX
John, do you have the magazine or link to online review? Most performance numbers I have seen show a drop off in MPG from 1500-2500 RPM, IIRC.

yeah *IF* you recall correctly, which seems to be getting harder and harder...

Watch it, punk. ;)

John, I remember that article--might even have it around somewhere. And yes, their criteria was an all-around family boat. Though the Malibu didn't win, they kept comparing to it.

Jason and Matt, after looking back through some tests at boattest, I believe you have a point. It looks as though a DD ski boat is most efficient between 2500-3000, which is different than the figures I have seen on most boats. VDs look to fall into the 3000-3500 category. This is based on limited review materials available.

However, as I mentioned before, there is a drop in MPG between 1500-2500. This drop is not demonstrated on the figures John posted and seems to be atypical. The numbers may in fact be accurate, but it wouldn't be the first time I've seen a misprint.

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skicrave

It would make sense that MPG would go down from above idle to just below planing speed. The engine is working harder and harder, with not much return.

I wonder how Tige compares in fuel consumption. Like Matt said, prop shaft angle is a big part of the equation, but the other component is the amount of hook at the transom of the boat. That's what really pushes the bow down as the speed goes up. Tiges don't have that hook so that the TAPS plate can provide maximum effectiveness.

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thethrillofspeed

I was just having a discussion with some of my friends why I didn't want to leave the glass in the coves to go back to the marina, so I looked up this article to see how much gas my boat burns.

http://www.boattest.com/oem/general-info.a...=295#TestResult

I don't think you see as much of a difference on an inboard because they don't plane like an I/O. My old I/O would get a lot more boat out of the water when it was on plane.

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electricjohn

The chart I posted in post #6 did also take into account "run angle". I will add it to the chart.

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