420/44 DB Owners Club

sea salt said:
Don't you have smartcraft and instaneous GPH guage with those 480CEs?
Click to expand...

As you can see from my sig. my boat has 450Cs, which are mechanical engines and they don't come with SC gauges. So, I have to manually calculate the numbers.
 
Alex - just looking at the data you posted, I would think that you should run at around 2250-2300 at the cost of 2 NM per tank vs. 2100 rpms. Remember the numbers posted are probably the best case scenario. Since weather conditions and boat conditions (growth, prop pitch, etc) can vary greatly from boat to boat, I believe you will notice an improvement if you run at a greater rpm. The only thing that throws me for a loop is your calculated .55 mpg. Are you sure this is correct? Can you still reach rated rpms/speed? If not, maybe you have some growth you need to have cleaned from your bottom.

Doug
 
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Doug,

At this point that's my plan to run faster and cut down the engine hours to get from point A to point B. Even though using 2000-2150RPMs gets me great GPH rate the speed=time spent getting from point A to point B is just too long and throws the MPG numbers way off. We just came back from a long trip and my AVG burn rate turned out to be .56MPG with AVG 20GPH.

I totally understand that boattest numbers are taken in ideal seas conditions with 1/2 fuel, 3/4 water, no gear, no lift with donghy and 3 people on board. Most likelly they also have the bridge enclosure off to minimize wind resistance. I understand and expect to have slightly lower numbers since I ran in rougher waters in the ocean and LI Sound. But, at the time when I did the 110NM run the conditions were fine. So, just b/c I had fully loaded boat I think that drop from boattest .75-.76 down to .56MPG is too big of a drop. I never had such difference in my 320DA, which was always loaded. My AVG (.81MPG) was pretty much matching to boattest numbers while running in similar conditions I just ran my 420DB.

I don't want to compare apples to oranges here (320DA vs. 420DB), but at this time I see no reason at all to have such big difference with boattest numbers. My engines and running gear are tuned to the specs, the bottom is as clean as it can be. I guess it's just one of those things where due to the lack of SC I have to manually figure out the best crusing sweet spot for her.
 
Alex, I find it useful to use the Cummins engine baseline data to inform the kinds of issues you're trying to solve. Here are the Cummins numbers for your engine:

[FONT=Arial,Bold][FONT=Arial,Bold]FUEL CONSUMPTION - PROP CURVE[/FONT][/FONT]

[FONT=Arial,Bold][FONT=Arial,Bold]rpm l/hr gal/hr[/FONT][/FONT]
[FONT=Arial,Bold]

[/FONT]
[FONT=Arial,Bold][/FONT]
[FONT=Arial,Bold]
[/FONT]
2600 90.7 24.0

2400 65.9 17.4

2200 50.8 13.4

2000 39.5 10.4

1800 30.2 8.0

1600 22.7 6.0

1400 15.8 4.2

1200 10.9 2.9

1000 7.2 1.9

800 4.3 1.1

600 0.0 0.0
The complete data sheet is at http://www.cmdmarine.com/Products/Recreational Inboard/6C/fr90215.pdf .

The difference between what you experienced at 2000 RPM and the Cummins data is striking and I think bears further investigation. I believe it's true that, at a given RPM, the fuel consumption should be pretty close to the rated numbers, and your consumption looks like it's approaching twice rated. The speed you achieve from that RPM would vary based on lots of boat-specific factors like hull fouling and weight but I think consumption should be roughly the same. I backed into 34 gals/hr using the numbers you provided (200gals)/(110NM/19KTS) and Cummins' number is 20.8/hr at 2000 RPM.
 
Alex

While a bit different boat, we have the same wet surface. Something seems off a bit. I run at 2150-2200 typically, my speed will be 22.5-24 knots depending on conditions. At 2000 rpm's, I will be at 20-21 knots. Your boat should be a bit faster. I have run others with the 480ce's (they have all had smartcraft). Their speeds were a bit more but the fuel burn was very close to mine. My boat has always been within 3-5% of the cummins data published for my engines. You should be able to add smartcraft very easily, as the CE's already have the proper ECM to output the data.
 
Here are the numbers I measured on my boat back in January. Calm day in still water. Full fuel, full water, 5 adults aboard. RPM's and GPH (total) are per SmartCraft. Speed is per SeaRay Navigator GPS. Trim is indication of where tabs are - I trimmed for best speed at each RPM measurement. NVH = Noise/Vibration/Harshness. My props have since been reworked and balanced and some of the vibration is now less.

The M-GPH, M-MPH and M-MPG columns are for marginal - meaning the difference from the previous reading. M-MPG is a simple division of M-MPH/M-GPH which means for every extra GOH, how many more MPH do you get? This shows where your efficient speed gains come at the lowest extra fuel consumption. For example, going from 2100 to 2200 adds only 2.3 GPH to the burn but delivers 2.3 additional MPH. This is much better than going from 1200 to 1300 where an extra 1.6 GPH only nets .4 additional MPH.

It is also interesting to note that MPG doesn't change significantly from 2000 - 2300 RPM. I tend to cruise at 2200 as it is 400 below rated power and I like that margin for not overworking the engines for long runs. I also spend a lot of time at 1100 RPM as it gets me 2 MPG and we are not usually in a hurry to get anywhere anyway...

RPM GPH MPH MPG *M-GPH M-MPH M-MPG Trim NVH
600 1.3 6.8 5.23 Full Up Smooth
700 1.5 7.6 5.07 0.2 0.8 4.00 Full Up Smooth
800 2.2 8.4 3.82 0.7 0.8 1.14 Full Up Smooth
900 2.9 9.1 3.14 0.7 0.7 1.00 Full Up Vibration
1000 3.9 9.8 2.51 1.0 0.7 0.70 Full Up Smooth
1100 5.2 10.4 2.00 1.3 0.6 0.46 Full Up Smooth
1200 6.3 10.9 1.73 1.1 0.5 0.45 Full Up Smooth
1300 7.9 11.3 1.43 1.6 0.4 0.25 Full Up Smooth
1400 9.2 12.0 1.30 1.3 0.7 0.54 Full Up Smooth
1500 10.8 12.7 1.18 1.6 0.7 0.44 Full Down Smooth
1600 12.9 13.7 1.06 2.1 1.0 0.48 Full Down Slight Vib
1700 14.5 15.5 1.07 1.6 1.8 1.13 Full Down Slight Vib
1800 17.9 16.7 0.93 3.4 1.2 0.35 Full Down Slight Vib
1900 21.1 18.4 0.87 3.2 1.7 0.53 Full Down Less Vib
2000 24.3 20.5 0.84 3.2 2.1 0.66 Full Down Smooth
2100 27.2 22.3 0.82 2.9 1.8 0.62 Anywhere Smooth
2200 29.5 24.6 0.83 2.3 2.3 1.00 Middle Smooth
2300 32.2 26.7 0.83 2.7 2.1 0.78 Middle Smooth
2400 35.5 28.5 0.80 3.3 1.8 0.55 Full Up Smooth
2500 39.6 30.2 0.76 4.1 1.7 0.41 Full Up Smooth
2600 43.8 31.6 0.72 4.2 1.4 0.33 Full Up Smooth
2680 47.0 32.6 0.69 3.2 1.0 0.31 Full Up Smooth
* "M-" = Marginal or change from previous measurement

I have now edited this post about five times trying to get the chart spaced out so it is more readable. Even tried exporting from Excel as HTML. So far nothing works. Anyone have a suggestion?
 
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alnav said:
Alex, I find it useful to use the Cummins engine baseline data to inform the kinds of issues you're trying to solve. .......

............The difference between what you experienced at 2000 RPM and the Cummins data is striking and I think bears further investigation. I believe it's true that, at a given RPM, the fuel consumption should be pretty close to the rated numbers, and your consumption looks like it's approaching twice rated. The speed you achieve from that RPM would vary based on lots of boat-specific factors like hull fouling and weight but I think consumption should be roughly the same. I backed into 34 gals/hr using the numbers you provided (200gals)/(110NM/19KTS) and Cummins' number is 20.8/hr at 2000 RPM.
Click to expand...

Al,

I was using the same matrix you posted as my guide. I find that my issue is not GPH. On my trip I calculated AVG total 20GPH, which I thought was pretty good. My problem is the speed that translates in to the MPG. This kind of reminds me operating my 320DA, where anytime the RPMs drop below the sweet spot of 3700-3800 it looses the efficiency of MPG and SC shows a drop from .8 to .6. I think that my 420 has the same running attitude. From what I've noticed in my last test, is that I need just a little more RPMs to gain a lot more speed.

I'm not really following you calculations here:

alnav said:
I backed into 34 gals/hr using the numbers you provided (200gals)/(110NM/19KTS) and Cummins' number is 20.8/hr at 2000 RPM.
Click to expand...

The way I know it, to get GPH you take Hours engine used / Gal used. In my case this adds up to 20, which is kind of in line with cummins data. This is an indication that my engines burn what they should and something else has to change.

SR400DB said:
Alex

While a bit different boat, we have the same wet surface. Something seems off a bit. I run at 2150-2200 typically, my speed will be 22.5-24 knots depending on conditions. At 2000 rpm's, I will be at 20-21 knots. Your boat should be a bit faster. I have run others with the 480ce's (they have all had smartcraft). Their speeds were a bit more but the fuel burn was very close to mine. My boat has always been within 3-5% of the cummins data published for my engines. You should be able to add smartcraft very easily, as the CE's already have the proper ECM to output the data.
Click to expand...


I'd say the biggest difference is the weight. 400 dry is 22,000lbs while 420 is 28,000lbs. We have the same engines 6CTAs 450Cs (mine is not 480CE), so I cannot add SC gauges. My boat turns 2680RPMs running at 28kts at WOT, which is within the specs for both RPMs and the speed.
 
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Sorry, didn't notice the engine model. The 400 dry weight is with gassers. My boat weighs right at 33500 #'s with 3/4 fuel and full water and all my crap. My boat has always weighed over 30000 #'s btw.

Your numbers should be much better. I have made numerous runs over 100 nm and have never used more than 140 gallons (with the genny running as well). I generally will budget for 120 gallons for a 100 mile run. Hopefully others will chime in with some ideas.

Sent from my DROID PRO using Tapatalk
 
First_Mate said:
Here are the numbers I measured on my boat back in January. Calm day in still water. Full fuel, full water, 5 adults aboard. RPM's and GPH (total) are per SmartCraft. Speed is per SeaRay Navigator GPS. Trim is indication of where tabs are - I trimmed for best speed at each RPM measurement. NVH = Noise/Vibration/Harshness. My props have since been reworked and balanced and some of the vibration is now less.

The M-GPH, M-MPH and M-MPG columns are for marginal - meaning the difference from the previous reading. M-MPG is a simple division of M-MPH/M-GPH which means for every extra GOH, how many more MPH do you get? This shows where your efficient speed gains come at the lowest extra fuel consumption. For example, going from 2100 to 2200 adds only 2.3 GPH to the burn but delivers 2.3 additional MPH. This is much better than going from 1200 to 1300 where an extra 1.6 GPH only nets .4 additional MPH.

It is also interesting to note that MPG doesn't change significantly from 2000 - 2300 RPM. I tend to cruise at 2200 as it is 400 below rated power and I like that margin for not overworking the engines for long runs. I also spend a lot of time at 1100 RPM as it gets me 2 MPG and we are not usually in a hurry to get anywhere anyway...

RPM GPH MPH MPG *M-GPH M-MPH M-MPG Trim NVH
600 1.3 6.8 5.23 Full Up Smooth
700 1.5 7.6 5.07 0.2 0.8 4.00 Full Up Smooth
800 2.2 8.4 3.82 0.7 0.8 1.14 Full Up Smooth
900 2.9 9.1 3.14 0.7 0.7 1.00 Full Up Vibration
1000 3.9 9.8 2.51 1.0 0.7 0.70 Full Up Smooth
1100 5.2 10.4 2.00 1.3 0.6 0.46 Full Up Smooth
1200 6.3 10.9 1.73 1.1 0.5 0.45 Full Up Smooth
1300 7.9 11.3 1.43 1.6 0.4 0.25 Full Up Smooth
1400 9.2 12.0 1.30 1.3 0.7 0.54 Full Up Smooth
1500 10.8 12.7 1.18 1.6 0.7 0.44 Full Down Smooth
1600 12.9 13.7 1.06 2.1 1.0 0.48 Full Down Slight Vib
1700 14.5 15.5 1.07 1.6 1.8 1.13 Full Down Slight Vib
1800 17.9 16.7 0.93 3.4 1.2 0.35 Full Down Slight Vib
1900 21.1 18.4 0.87 3.2 1.7 0.53 Full Down Less Vib
2000 24.3 20.5 0.84 3.2 2.1 0.66 Full Down Smooth
2100 27.2 22.3 0.82 2.9 1.8 0.62 Anywhere Smooth
2200 29.5 24.6 0.83 2.3 2.3 1.00 Middle Smooth
2300 32.2 26.7 0.83 2.7 2.1 0.78 Middle Smooth
2400 35.5 28.5 0.80 3.3 1.8 0.55 Full Up Smooth
2500 39.6 30.2 0.76 4.1 1.7 0.41 Full Up Smooth
2600 43.8 31.6 0.72 4.2 1.4 0.33 Full Up Smooth
2680 47.0 32.6 0.69 3.2 1.0 0.31 Full Up Smooth
* "M-" = Marginal or change from previous measurement
Click to expand...


First_Mate,

Thanks for providing your numbers. Can you tell me what size props do you swing?

I just called my Cummins mechanic and he told me that most likelly my problem was exactly what I have concluded, which is running too slow for heavy baot like mine. He said that 450Cs have majic number of 2300RPMs, by some reason they love to run at that rate. According to my lates test this makes perfect sense since by advancing from 2000rpms to 2300rpms I gained 6KTS, which is 2kts per 100RPMs. He also pointed out is that if I have to use full tabs at 2000RPMs that means that she's not running at the proper angle and she needs more juice to level down so I can start bringing the tabs up for proper adjustments.
 
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Alex F said:
Al,

I was using the same matrix you posted as my guide. I find that my issue is not GPH. On my trip I calculated AVG total 20GPH, which I thought was pretty good. My problem is the speed that translates in to the MPG. This kind of reminds me operating my 320DA, where anytime the RPMs drop below the sweet spot of 3700-3800 it looses the efficiency of MPG and SC shows a drop from .8 to .6. I think that my 420 has the same running attitude. From what I've noticed in my last test, is that I need just a little more RPMs to gain a lot more speed.

I'm not really following you calculations here:



The way I know it, to get GPH you take Hours engine used / Gal used. In my case this adds up to 20, which is kind of in line with cummins data. This is an indication that my engines burn what they should and something else has to change.
Click to expand...

Alex, I was just using the numbers you put in the original post on this subject. If you went 110NM at 19 knots (your quoted speed at ~2100RPM), you should have taken 5.8 hours to do the trip. If you burned 200 gallons divided by 5.8, that would be a burn of 34.5 gallons per hour. I now assume you mixed up the speeds and completed the trip faster than my calculation, true?
 
alnav said:
Alex, I was just using the numbers you put in the original post on this subject. If you went 110NM at 19 knots (your quoted speed at ~2100RPM), you should have taken 5.8 hours to do the trip. If you burned 200 gallons divided by 5.8, that would be a burn of 34.5 gallons per hour. I now assume you mixed up the speeds and completed the trip faster than my calculation, true?
Click to expand...

Al,

Actually the true timing was about 7hrs instead of 5.8hrs. This makes it an AVG 28GPH total for this part of the trip. BTW, the reason it took this long was due to various running conditions and no wake zones. It's a bit hard to do precise calculation manually since there are so many variables. So, my numbers are not 100% accurate either. The main item that raised my concern after I completed the 110NM leg is that I had less than 1/2 fuel left, more like 1/3rd. With 350gal tank I was expecting a lot more fuel left in the tank. So, knowing that I have ways to go I filled it. When I saw that it took 200gal I was shocked and started thinking that something is not right and needs to be changed.
 
Andy,

I'm swinging 23 x 26 4 Blade Nibrals High Torque props that are Class 1 ISO 484-2 Standards.
 
Andy,

That's very interesting that you have 26x26 props. If your engines canswing those at 2680RPMS WOT that would mean that your boat can move faster since my props are 3" smaller and we have the same pitch. What's your WOT speed?
 
32.6 MPH which is 28.3 KTS. But that was with props that weren't totally straight. I will run it again this weekend to see the difference...
 
Alex

I know we have different engines, but otherwise very similar boats. The only significant difference I can think of besides the engines is your lift. I average anywhere between 0.6 - 0.7 mpg on any particular trip depending on fuel, water, waste and miscellaneous load as well as current and wind speed and direction. I find that running with my four strataglass cutouts open increase my speed as well as fuel efficiency more than almost anything else I change, with maybe the exception of those times I have full fuel taanks, full water and full provisions at the beginning of a long trip. Over each of the past three seasons, based on miles travelled per smartcraft and fuel burned (I start and end each season with full tanks so figuring fuel burned is pretty straightforward) I have averaged 0.67 mpg. A little lower than the Boattest numbers for my boat and engine, but it's been pretty consistent. I usually cruise at 2200-2250 rpms which gives me 24-26 mph. My WOT top speed is almost 36 mph with strataglass fully open and low fuel load, now water, waste, stores or miscellaneous junk on board. I swing 24x27 Nibral props that haven't been scanned or tuned in 3 seasons, though they will be if I keep this baot into next season. I wouldn't stress to much about it until you've got more trips under your belt.
 
Thanks for the info, Brian. 0.6-0.7MPG is my expectation and I hope to get it by running her at 2250-2300rpms at 24kts/27mph. I was thinking about the front pannel, but looks like the PO didn't install the snaps as he didn't plan on having it open like he had the original strata pannels (the two snaps are the on the arch). Anyway, I was always taking my two side pannels off and it provided very easy storage and comfortable ventilation. So, I also don't plan on taking the front pannel off. We usually rolled only one (captain side) pannel on 320 when cruising long distance. I'm sure that admiral would ask to close the large front pannel on 420 as soon as all the wind would blast in to the bridge. So, I'll have to pay for the comfort with some lose of speed and mpg. I'm learning that my 420 has similar running attitude as my 320 (stern heavy). The lift sure adds to that. I'll be monitoring my future perfromance, including how much tabs I'll have to use at the faster speed. Changes are I'll have to come up with some sort of solution for weight distribution to better level the bow and use less tabs to minimize the drag.

I better make this work right before getting the "real" dinghy....LOL.
 
Alex,

My numbers are not as sweet as some of those posted. I think you may be running too fast, despite what the rep said. I tested mine last week with 5/8 fuel. I found that by increasing RPM from about 2100 to 2250, I sped up 4 mph and burned 4 more gph total - good deal. By speeding up another 150 rpm, I sped up 1 mph and added 4 gph - bad deal. I, too, use a lot of tabs. The numbers are from memory.

2250 is really my sweet spot, even though the tabs are most of the way down - I am carrying a light (10', 8hp) blow up dinghy with an inflatable bottom. I ran with a heavier dinghy a while back and maxed out at 2450 RPM instead of 2680, which I get with my dinghy - that was definitely too much dinghy.

I find that I get the same speed for any given rpm pretty much regardless of weight. When heavy, 2250 rpm burns about 2 - 4 gph more gas than when light, but I still get about 25 mph (a little less heavy, a little more light ( 24 - 26 mph)). I guess I am a bit faster light, but the fuel flow is more noticeable.
 
Hampton said:
Alex,

My numbers are not as sweet as some of those posted. I think you may be running too fast, despite what the rep said. I tested mine last week with 5/8 fuel. I found that by increasing RPM from about 2100 to 2250, I sped up 4 mph and burned 4 more gph total - good deal. By speeding up another 150 rpm, I sped up 1 mph and added 4 gph - bad deal. I, too, use a lot of tabs. The numbers are from memory.

2250 is really my sweet spot, even though the tabs are most of the way down - I am carrying a light (10', 8hp) blow up dinghy with an inflatable bottom. I ran with a heavier dinghy a while back and maxed out at 2450 RPM instead of 2680, which I get with my dinghy - that was definitely too much dinghy.

I find that I get the same speed for any given rpm pretty much regardless of weight. When heavy, 2250 rpm burns about 2 - 4 gph more gas than when light, but I still get about 25 mph (a little less heavy, a little more light ( 24 - 26 mph)). I guess I am a bit faster light, but the fuel flow is more noticeable.
Click to expand...

John,

IMO, the reason why you have to use a lot of tabs is b/c your stern is heavier than mine due to extended swim platform. We have the same lifts and the dinks might be in similar weight category (+/-), but that platform must add tons of weight to very stern heavy boat to begin with.

My latest test by running at 2300RPM doing 23-24kts gives me AVG .62MPG. I'll be testing more, but I feel big improvement by running her faster. As I mentioned earlier it's very noticable that she runs differently while sitting more above the water and I'm able to raise my tabs to about 30%-50%. When I was running at slower speed/rpm I had to keep the tabs all the way down.


Can you guys tell me at what setting do you keep your galley fridge?

If I recall correctly the dial goes from 0 to 5. I have to keep mine at 4.5, otherwise it doesn't cool as well. IMO, this a bit too pushy as all my previous fridges never had to cranked so much, more like ~75% of the dial. The first thing comes to mind is that the coil in the back of the fridge needs to be cleaned, but the only way to get to it is to pull out the unit. Is there a quick access that I'm not aware of? Any other suggestions would be greatly appreciated.
 
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If the coil and fan are clean, the refridgerant is not leaking, I believe your fridge setting is more about the temperature differential on the outside vs. inside of the fridge. With temperatures being in the high 90's to low 100's here in PA/NJ for the past week, it wouldn't surprise me if that has something to do with it.

Doug
 
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