Fuel Burn on 04/05 390 Sundancer with 8.1s

I was telling a friend the other day I was installing FloScan ... He looked at me and said why?... I can tell from here your burning diesel.. He said when you get low on fuel just put some more in.
 
Did he change your mind?
No... I was just saying there are always two points of view. Some people don't care about burn and cost and some do... it doesn't make either one right.
I am in the process of converting my analog to Digital and FloScan was just a nice to have while I was at it.
 
To me it's not about cost of fuel. It's about a boat that runs at it's potential vs. one with problems, and then those problems being accepted as normal.
 
To me it's not about cost of fuel. It's about a boat that runs at it's potential vs. one with problems, and then those problems being accepted as normal.

Now that I agree with! For me knowing my live burn rate is knowing if my boat is performing well. If below a threshold I set for my boat then I have a problem to solve immediately. The other is when I refill, I know exactly what each tank will take before I get a blowback from the fill!!! If the grenny had ran prior to filling up, say 10 hours then I add 10 gallons more fuel in Starboard side count. Works everytime.

Bottom line once in awhile open the throttles up to full RPM to ensure your boat reaches its manufacturer RPM range. Not over and not under. If it's in range then you are generally in great shape!

Mark
 
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Yes, the 390 Sundancer gas range and 0.55 MPG are not good. The Cruisers 48 Cantius and 54 Cantius get about 1 MPG and 0.7 MPG. However, these are diesel engines with IPS drives which increases fuel efficiency. Looking forward to my next boat.

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I'm including this handy info - 390 Sundancer and 40 Sundancer - Hidden Locations:

Fuel sender access
• Port sender is under cockpit icemaker/frig; Stb is in aft birth cabinet with removable panel in the bottom.

Windshield Washer Solenoid
• Pull the cockpit refrigerator ... look forward and you'll see it mounted to the bulkhead.

Windlass Breaker
• Located on engine room bulkhead next to bilge MDP

Generator Sound Box
• Standard on Gas, Not enough room in bilge for Diesel sound box.

Switch for Hard Top Lights
• The switch is on the switch panel labeled "Overhead Lights" it is a three position switch, first position is OFF, second position should light up the aft two lights, and the third position should light up all four lights.

Flux Gate Compass
• Located in salon cabin center floor storage.

Air Horn Compressor
• Located in the starboard v-berth hanging locker, behind the TV.

Air Horn Module
• Located under dash to the left of the fuse block

Stereo Amplifier
• Both amps are located behind the backrest of the salon couch.

TV Splitter Location
• Located behind the MDP

AC Relay
• Located behind the MDP

Wiper Module
• Located under dash to the left of the fuse block

Galley Television
• Fold down television motor only is a Duff-Norton (800-477-5002)
TMD 02-1406-8 total weight on lift is not to exceed 30 lbs.

Spotlight control module Inside rope locker

Water Heater
• Aft Berth under aft seat cushion, next to water manifold

Galley/Head Blower Motor
• Accessed by removing the microwave

Sirius Sat Receiver
• Behind salon sofa backrest

Water Tank Sender Access
• In the aft stateroom pull out the seat as if to make it into a bed, behind the seat back you will see a storage area that holds the filler cushion. Remove the cushion inside this area and to the port side you will see a black access panel. Remove this panel to access the sender.
Part # 1744162 SENDING UNIT, WATER

Forward Head GFI
The forward head GFI is located in the upper medicine cabinet outboard

Galley GFI
The galley GFI is located in the upper aft center storage
Salon GFI
The Salon GFI is located forward in the center storage behind the salon seat back
Cockpit GFI
The Cockpit GFI is located port outboard of cabin entry door with a exterior outlet cover with doors
 
Marc, YOUR 390 is performing way below potential. I've run a 40DA carrying a 3-passenger SeaDoo on a hydraulic lift at a higher speed while burning less fuel.

My guess would be your boat is drastically under-propped, but bottom or mechanical issues could be at play too.
 
The 2005 39 Sundancer gas is a redesign from older years - not the same as your boat. The chart I posted was conservative too. I've since had a running gear overhaul. But cruising is still about 0.65 MPH at best. This is the way 2005-2006 era 390 / 40 sundancers perform with gas. C'est la vie. Looking forward to my next diesel boat with IPS or Zeus.
 
I'm intimately familiar with the 390/40DA. Correct, it's not the same as mine, which is a 400DA. The 400DA is larger, yet I can easily do better than .65 sMPG and much faster than 20 MPH at 3,500. I'm glad that you overhauled your running gear. I'm not convinced it's optimal though, and that would've been a good thing to mention when you posted those lousy performance figures!
 
I realize I sound crabby. Sorry about that, but can you see why? Look how soon after you posted figures that you now admit were due to mis-tuned running gear that someone posted an "Ah-ha! My neighbor's boat runs just like that so it must be fact and Rollercoastr is wrong!"

Ok, so that's not a real quote, but it IS how mis-information becomes dock legend.
 
I agree that you should do everything you can to keep your boat performing to spec.

But the reality is that they are indeed gas hogs. I have a twin engine Floscan to keep an eye on things but it is deceiving in the sense you see a point in time gph and not an average. I would say that most recreational boaters have some percentage of motoring off plane where the gph is a lot better. So, on average.....fuel burn is better than what they see on a Floscan at 3200-3500 rpm.

The difference between .5 and .65 represents less than one fillup to me a year. No sense in wasting money but I gave up a long time ago worrying about the amount of irreplaceable fossil fuel I was burning.:)

Of course I'm jealous of the diesel guys and their burn rates but it does come down to the type of boating you do and how many hours you use the boat.
 
I have a twin engine Floscan to keep an eye on things but it is deceiving in the sense you see a point in time gph and not an average. I would say that most recreational boaters have some percentage of motoring off plane where the gph is a lot better. So, on average.....fuel burn is better than what they see on a Floscan at 3200-3500 rpm.

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That's why I like my NMEA meters. The constant calculation of economy and range are right in my face. I don't have to "worry" about it - I just use it. (this is an old screen shot. My new system calculates to the hundredth, so none of this rounding-up stuff)

The difference between .5 and .65 represents less than one fillup to me a year.

Maybe so, but the difference between .5 and .65 is what, 20-something% !?! That's a LOT! Not to mention the very-real possibility of attaining higher, while going faster and further.
 
That is a cool display. If I had it to do over again.....that would definitely win.

If I take your gallons per hour and your speed I get .69 mpg which is great number for a 40' boat. In fact, it is the best number I have seen on a 400DA.

Why is your Starboard engine burning more gas?:)
 
The 2005 39 Sundancer gas is a redesign from older years - not the same as your boat. The chart I posted was conservative too. I've since had a running gear overhaul. But cruising is still about 0.65 MPH at best. This is the way 2005-2006 era 390 / 40 sundancers perform with gas. C'est la vie. Looking forward to my next diesel boat with IPS or Zeus.
I don’t know if this is true, but I have heard the plain v-drive system is better for long term maintenance costs. Yes, you might pay more for fuel, but lower maintenance and lower initial price make up for higher fuel costs? I am not sure it makes sense to purchase a large boat and then have to pull it out of the water every year to get an expensive maintenance done on the pod drives, by a special mechanic. Maybe this has improved, maybe if you live up north where you have to pull it out anyway? I have no first hand knowledge of this, just relaying what I have gleaned from other posts.
 
That is a cool display. If I had it to do over again.....that would definitely win.

If I take your gallons per hour and your speed I get .69 mpg which is great number for a 40' boat. In fact, it is the best number I have seen on a 400DA.

Why is your Starboard engine burning more gas?:)

The new display is even cooler. I don’t have a good screenshot though. I’ll take one this summer.

27.5 mph / 36.2 GPH is actually .75, so my MFD rounded-up. That was under ideal circumstances. Light on fuel, waste, water and passengers, clean bottom...

If I dig the tabs way down and throttle down to the high 2000’s, hitting .75 MPG is easy even when heavy.

Good catch on stbd’s burn. She suffered a mechanical issue many years ago that reduced compression in cyl 7. Runs great, as you can see, but a little more thirsty than her sister. The meters help me keep an eye on it.
 
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That's why I like my NMEA meters. The constant calculation of economy and range are right in my face. I don't have to "worry" about it - I just use it. (this is an old screen shot. My new system calculates to the hundredth, so none of this rounding-up stuff)



Maybe so, but the difference between .5 and .65 is what, 20-something% !?! That's a LOT! Not to mention the very-real possibility of attaining higher, while going faster and further.

what brand is that fuel setup ?was thinking about foxmarine setup for my twin 7.4 efi
 
The new display is even cooler. I don’t have a good screenshot though. I’ll take one this summer.

27.5 mph / 36.2 GPH is actually .75, so my MFD rounded-up. That was under ideal circumstances. Light on fuel, waste, water and passengers, clean bottom...

If I dig the tabs way down and throttle down to the high 2000’s, hitting .75 MPG is easy even when heavy.

Good catch on stbd’s burn. She suffered a mechanical issue many years ago that reduced compression in cyl 7. Runs great, as you can see, but a little more thirsty than her sister. The meters help me keep an eye on it.

Still washing that cyl.? Sorry, not trying to be a smart a$$, just trying to learn.

PS; love this thread, Your post in particular.
 

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