420 Sundancer Gas Best Cruise

[copb8tx]

I've looked everywhere I know to look to find boat test numbers on an 03-05 420 DA, or 06-09 44 DA with GAS 8.1s 370hp engines. Nada.

I've found tons of diesel tests and one 380DA test but I'd really like to know what best cruise is on my boat. The 380DA tested weighed 4000lbs less than the 420 does. If I were to guess from what I've read so far best cruise would be around 3500rpms. But that's just a guess.

Does anyone have test numbers on these specific boats?

BTW, here's the 380 numbers I found:

RPM MPH Knots GPH MPG NMPG Range NM dBa
700 3.5 3.0 2.5 1.38 1.20 311 270 67
1000 5.8 5.0 4.2 1.39 1.20 312 271 66
1500 8.1 7.0 6.2 1.31 1.14 295 256 71
2000 9.6 8.3 9.9 0.97 0.84 218 190 74
2500 11.4 9.9 17.4 0.66 0.57 147 128 77
3000 17.6 15.3 28.6 0.62 0.54 138 120 79
3500 24.3 21.1 34.4 0.71 0.62 159 138 83
4000 29.3 25.4 44.0 0.66 0.58 150 130 86
4500 33.1 28.7 57.0 0.58 0.50 131 114 87
4750 34.7 30.2 61.8 0.56 0.49 126 110 87

Thanks!

 

[370Dancer]

what is your barely on plane RPM and speed?
How about halfway from there to full throttle?
How about idle?

Gas in a 42 is a rare puppy for sure. I think you'll have to make your own curve.
1 GPH for every 10hp at top RPM x 2 engines = 74 GPH at full throttle. Probably around 6 GPH at idle.

My happy spot for an under 10 mile trip is 1000 RPM. If I really have to go somewhere, it's about 3200 RPM and I'm getting a net .75 MPG in nice water.

 

[fc3]

Generally it's the slowest speed that planes the boat to an efficient angle. That would be a slight bow-up attitude on a Sundancer.

 

[copb8tx]

Thanks guys. I guess with some time on the boat and using the Smartcraft I'll create my own fuel flow map.

I wish I could get instant MPG or KPG readings instead of GPH readings on the Smartcraft.

 

[trit21]

MPH/GPH= MPG....simple math will give you your answer. I would think if you have smartcraft that there is a screen that shows this info but when I had my 320, it was incorrect. No matter where I was running, plane, idle, etc. it always read .7 and I got better than that.

 

[copb8tx]

Oh, I understand how to calculate MPG I just wanted a dynamic number on the screen where I can adjust the throttles and instantly see the results. GPH without the distance component only tells one side of a story.

Hmmm, I thought I really looked carefully at all the screens on the SC but never found anything except GPH. I'll look again. Thanks.

 

[copb8tx]

I see in the manual that MPG is available in a couple of places such as the Vessel Data screen but I 'thought' I went through all the screens very thoroughly and didn't see this data even though from the manual it looks pretty obvious.

Do you think that there are different versions or that my boat may not a required sensor?

 

[trit21]

There is a way to turn certain screens off if you don't want to use them, so maybe the previous owner turned that off. Not sure if you can turn that one off or not but maybe?

 

[AAK]

I've got a 39' Sundancer with gas 8.1L 370HP engines and the boat seems to cruise best around 20.1 MPH from a GPS reading. The RPMs are about 3,480 to 3,500 RPMs and the Smartcraft is showing 31.1GPH. I would think your boat would burn a little more with the added weight and be in the mid 30s for GPH. I was surprised with the performance of these gas engines with the weight of the boat. I really don't put alot of hours on each season to justify the cost to jump up to diesels.

 

[RollerCoastr]

AAK, when you say surprised, do you mean pleasantly surprised? I wouldn't be happy with those numbers. By my calcs, you cruise 6 mph's slower than I do, at the same RPM, while getting less economy.

I wonder if you're under-propped...?

 

[copb8tx]

There is a way to turn certain screens off if you don't want to use them, so maybe the previous owner turned that off. Not sure if you can turn that one off or not but maybe?

Excellent point! I'll look for that.

 

[AAK]

Roller Coastr,
I was pleasantly surprised on the fuel consumption on the 39’ Sea Ray based on my long ownership experience with a 1991 35’ Sea Ray Sundancer (7.4L gas carb motors, 13,800 pounds dry weight, v-drives). I cruised this boat for eight seasons and spent a lot of time accurately monitoring its fuel consumption. The first thing I did was to add a Flow Scan fuel monitor for each engine to obtain accurate GPH readings at different cruise speeds and RPMs. On a cruise I would usually run at about 20 MPH on a GPS and see approximately 29.5 GPH. If I remember correct it was running around 3,350RPMs at this speed. I know the speed and GPHs were correct.

With the 2004 39’ Sea Ray Sundancer (8.1L gas 370 HP, 19,300 pounds dry weight) I cruise at about 3,400 RPMs and get 20.1 MPH on the GPS and show 31.2 GPH on the SMARTCRAFT. These readings were made after the boat was at this cruise speed for quite awhile. The RPMs might be a little off because I was concentrating on the 20.1 MPH and 31.2 GPH readings while adjusting the trim tabs and slightly moving the throttles around. The props were pulled this spring, computer scanned, and were to specifications. The bottom was lightly sanded and painted. Engines got new plugs, all new gas filters, and oil changes. The boat has no known performance issues that would be out of the ordinary. The reason I’m happy with this performance is I’m sure the performance figures were right on for the 35’ Sea Ray and this boat weights another 5,500 pounds. I’m cruising at about the same speed and using just slightly more fuel. I don’t think the SMARCRAFT is off the mark since I had a 32’ Sea Ray with SMARTCRAFT and found the GPH readings from this system to be accurate. I’ve also talked to some other people with SMARTCRAFT and they haven’t experienced any problems with the GPH feature on their boats.

On your 1997 40’ Sea Ray what is the dry weight (around 22,000 pounds ?), the gas engines are EFI, what GPH are you burning at 20 MPH, and most importantly how are you calculating the GPH? Do you have Flow Scans, another fuel monitoring system like the Lowrance Fuel Monitors, or are you calculating the gallons used at fill ups?

This is not meant to be confrontational or the start of a GPH war. I’m just trying to understand how you are getting this performance from your boat and what you have done to it. It really sounds like you have found the sweet spot when cruising.
Thanks,
Al

 

[Surprise390]

AAK-

I'm getting the same fuel economy as your boat. I seriously thought that my boat used more gas than similar 390s for some reason.

Beats the fuel economy I got in my old '95 370 with 454 carbed gas hogs.

 

[AAK]

Surprise390,

I really think my GPH numbers are correct for this boat considering the weight and speed. Of course the load, current, and sea conditions can change alot. I tend to also be running with full fuel since I dock in an area that charges about 50 cents a gallon more than anyplace else. We all fill up in the other areas to avoid the rip off in our area and tend to carry more fuel than normal.

I really like the way this boat handles the rough weather as opposed to the old 35' Sea Ray. It's a much smoother ride, that's the thing I noticed the most in getting this boat.