Concerned About Fuel Usage

[Rabbit]

It has been a while since we have had a boat, but we are looking to get another one. My wife and I really like the look of the 390 Motor Yacht, but I have read that it burns a lot of fuel. We would like to be comfortable, but don't really care about going fast. If I were to run at hull speed using the diesel engines, what type of gph/mpg would I be getting? Would I be causing problems with the engines to run them slower than they are really designed to be run? Most of the time there would be at least 3 of us staying on the boat for weekends/trips. I like having the 2 different sleeping areas and not having to convert a sleeping area every night. Thanks in addvance for your assistance.

 

[LG111]

First decide if you want older mechanical diesle engines or newer electronic. Ie 2006ish or newer Electronic. Electronic or digital like to run at 80-90% of full throttle. Mechanical can chug along all day at 8-12 knots. However, you still need to open them up every few hours to blow the carbon out. Most all diesle engines/boats 40ft to 55ft range at 8 to 12 mph will garner around 1.5 to 2.0 mpg. Planning hull diesels 18 to 25 mph garner between .50 to .65 mpg. Not to much else between those two ends.

Hope that helps ya,

 

[Rabbit]

First decide if you want older mechanical diesle engines or newer electronic. Ie 2006ish or newer Electronic. Electronic or digital like to run at 80-90% of full throttle. Mechanical can chug along all day at 8-12 knots. However, you still need to open them up every few hours to blow the carbon out. Most all diesle engines/boats 40ft to 55ft range at 8 to 12 mph will garner around 1.5 to 2.0 mpg. Planning hull diesels 18 to 25 mph garner between .50 to .65 mpg. Not to much else between those two ends.

Hope that helps ya,

That is interesting. It sounds like the older engines are the way to go, but I am sure that it can't be that easy. Is there a reason that I would want the electronic ones? The listing that I found was for a 2004 model, so it sounds like it might have the older engines. 2 mpg isn't to bad for a boat that big and comfortable!

 

[brewster16]

The newer common rail diesels burn cleaner and no diesel smoke ever

 

[Henry Boyd]

First decide if you want older mechanical diesle engines or newer electronic. Ie 2006ish or newer Electronic. Electronic or digital like to run at 80-90% of full throttle. Mechanical can chug along all day at 8-12 knots. However, you still need to open them up every few hours to blow the carbon out. Most all diesle engines/boats 40ft to 55ft range at 8 to 12 mph will garner around 1.5 to 2.0 mpg. Planning hull diesels 18 to 25 mph garner between .50 to .65 mpg. Not to much else between those two ends.

Hope that helps ya,

That’s not completely accurate. We have twin Volvo 6 liter turbocharged electronic controlled diesels. At 2800 rpm we burn just under 20 gph and can maintain 22 knots (abt 25 mph) yielding abt 1.3 mpg.

 

[alnav]

A 2004 390MY diesel would have the Cummins 480CE engine. Not sure about the fuel specs on this engine but it's probably roughly the same range LG111 described. These engines do have a history of some serious problems so if you pursue that listing I would recommend extreme diligence.
Some newer 390/40 MY's have the Cummins QSB 425 diesels. Mine will get around 3MPG at hull speed and from 1-.8 MPG on plane.

 

[mrsrobinson]

I cannot speak to diesel, however I recently had engine scans done on a gas boat I was looking to purchase. 80%+ of the hours were at below cruise RPMs. I was concerned, did some research, and the overwhelming response was "it's ok", "it must have been a booze cruise boat".

I think in general engines like to be run. Same applies for a car that is always used for city driving versus highway. I think you will be fine. Like another poster said just open them up from time to time to burn off carbon and make them happy

 

[Spark600]

I have QSB HO 6.7 And at 2700 RPM ( 27 MPH ) 30 GPH

 

[LG111]

That’s not completely accurate. We have twin Volvo 6 liter turbocharged electronic controlled diesels. At 2800 rpm we burn just under 20 gph and can maintain 22 knots (abt 25 mph) yielding abt 1.3 mpg.

Henry, you are missing very critical information when sharing, what size type boat are you running? Are those pods vs direct shaft? We have shared boat type and via the type the info is correct.

 

[Henry Boyd]

Henry, you are missing very critical information when sharing, what size type boat are you running? Are those pods vs direct shaft? We have shared boat type and via the type the info is correct.

My boat info is in the same place yours is. You made a categorical statement about planing hull electronic diesel powered boats that was significantly not correct.

 

[LG111]

Honestly, not challenging your data. Just can't see 1.3 mpg at that rpm and speed with a similar boat. Been boating my entire life and been around all types of boats and yachts and engine types. Still want to know your boat brand/style and underwater gear type. Always looking to learn something new. I can see pods at these numbers. Just struggle with direct drive achieving anything over 1mpg at 2800 and 25mph. Hence why I need more info to digest the data.
Rabbit mentioned most of his speed would be at slow cruising. Hence mechanical diesles especially cummins, do much better than electronic over long periods at low idle. But all need WOT at times to blow carbon is recommended.

 

[Woody]

 

[Henry Boyd]

Honestly, not challenging your data. Just can't see 1.3 mpg at that rpm and speed with a similar boat. Been boating my entire life and been around all types of boats and yachts and engine types. Still want to know your boat brand/style and underwater gear type. Always looking to learn something new. I can see pods at these numbers. Just struggle with direct drive achieving anything over 1mpg at 2800 and 25mph. Hence why I need more info to digest the data.
Rabbit mentioned most of his speed would be at slow cruising. Hence mechanical diesles especially cummins, do much better than electronic over long periods at low idle. But all need WOT at times to blow carbon is recommended.

The boat is a 2009 Sabre 38 Hardtop Express. The power package is a pair of Volvo D6- IPS450 (pods). I have data given to me by Sabre Yachts in the format of the Boattest reports that was generated in 2010 by Sabre. It confirmed the numbers I’ve generated from actual consumption. Most recently on a 29 nm trip from the boatyard where we winter store and our marina fuel consumption was 23 gallons. The bulk of the trip was on plane at our usual cruising 2800 rpm.

 

[LG111]

The boat is a 2009 Sabre 38 Hardtop Express. The power package is a pair of Volvo D6- IPS450 (pods). I have data given to me by Sabre Yachts in the format of the Boattest reports that was generated in 2010 by Sabre. It confirmed the numbers I’ve generated from actual consumption. Most recently on a 29 nm trip from the boatyard where we winter store and our marina fuel consumption was 23 gallons. The bulk of the trip was on plane at our usual cruising 2800 rpm.

Gotcha, Pods. As I guessed and thank you for confirming. The Sabre is a great looking boat! I had a 410 Dancer and loved it but it's nothing like my new to me 2007 440 sedan bridge performance at 12,000lbs more weight and with twin QSC 500's... awesome power package. Literally have to hold onto a rail when engaging forward gear... I'd like to note my earlier post was comparing direct vs direct. Most common package on the water.
Pod vs direct is more of apple and orange comparison via fuel consumption and maneuverability.
Cheers

 

[Blueone]

That is interesting. It sounds like the older engines are the way to go, but I am sure that it can't be that easy. Is there a reason that I would want the electronic ones? The listing that I found was for a 2004 model, so it sounds like it might have the older engines. 2 mpg isn't to bad for a boat that big and comfortable!

It’s that easy.... mechanicals are bullet proof.... all they want are good batteries and clean fuel.....mine have been trouble free for years now

 

[LG111]

So I see the curve lines on rpm and GPH. Those look accurate. However we are missing speed and size of boat too. Hard to determine MPG. However, those engines in a twin Application would double GPH. So we would be looking at around 40gph at a general speed of 23- 26mph depending on the hull and load. Hence approx .55 to .65 mpg. Not great but pretty standard for direct drives.

 

[ManteoMike]

See photo. This is from a 2005 390 Motor Yacht with twin Cummins 480CE engines. Both engines have newer heads. If you run engines at low RPM much of the time, then you should crank them up to 80% or 90% for 15 minutes or so every each day.

 

[hottoddie]

I am far more concerned about where the cost of fuel is headed than how much fuel my boat burns. This year fuel is 40% higher than a year ago. Remember when fuel was over $4?

 

[PlayDate]

I am far more concerned about where the cost of fuel is headed than how much fuel my boat burns. This year fuel is 40% higher than a year ago. Remember when fuel was over $4?

Unfortunately the morons and idiots pushing "Climate whatever" don't care about boaters. Fuel prices around the country are rising and I fully expect marine gas to be $4-5 next year. Historically the industry gets crushed when gas and diesel prices hit that level. Again.....the current political winds could care less and many eco terrorists would welcome if the entire industry disappeared "to save the planet from extinction".

To address the OP's concerns.......it comes back to calculating the acquisition and the operating costs of the boat correctly.

Scenario A

If your gas boat costs $100k to buy and you spend $3k per year on fuel and maintenance that gives you $8k per year operating cost on a 10 year life using a 50% end of life remaining value (not adding slip fees).

Scenario B

Lets say you find the perfect diesel boat and it is $150k to buy and fuel plus maintenance is $2,000 a year. That gives you $9,500 per year operating cost on a 10 year life using a 50% end of life remaining value (not adding slip fees).


While we can debate the numbers endlessly.....the best, simple equation is cash out of your pocket every year not mpg. So it comes down to the boating that you plan to do.

 

[Jaybeaux]

I am far more concerned about where the cost of fuel is headed than how much fuel my boat burns. This year fuel is 40% higher than a year ago. Remember when fuel was over $4?

Thanks Sleepy Joe!