WOT vs speed Sea Ray 280 Sundancer Also fuel level quesrion

The key to me would be to know that the boat performs within specs. If not, then something is wrong.....

Bennett
 
That's a good measure. I would be curious what the intended specs are. Seems as though there is consistent reports that the boat should top out in the mid to upper 40's.
 
Are you sure your GPS is set to MPH rather than Knots? 35Knots x 1.2=42MPH. Add trim and you could be at 45. I recently sold my boat. It didn't like much trim at cruise but at full throttle I could add a decent amount.
 
I'll check again, but I am pretty sure its mph. The gps and smartccraft match within a few mph's of each other. I wouldn't know how to change smartccraft from knots to mph.
 
Were you able to confirm the pitch or your props?

I recently bought a new to me 280 with the same set up as you. Mine is an 06 with 56hours on the motors, how many hours are on yours?

Mine came with 20P props. I swapped them with the new style 24P Bravo 3 props (4 blades front 3 rear). I've seen between 50 to 51MPH on GPS (using both Smartcraft enabled and iPhone app, both are almost identical at speed above 20MPH). Even with the new props, I can still hit the engine overspeed alarm with 6 adults on board.

Prior to changing the props, I was seeing RPM/MPH very close to what you are reporting
 
I thought 24 P but I'll have to check when I am hauled.
 
I can decrease fuel burn rate by 1.5 to 2 gph just by adjusting the drive trim. Since a decrease in consumption is caused by a drop in load, it would add a few mph to the top end. So drive trim may be a factor. Lately we have had some fairly wide tide swings creating some strong tide currents. That could account for 2-3 mph depending when and where you were going.

Henry


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Henry, do you calculate your fuel burn by MPG? I realize you are running a big block single but I was curious as to what you burn was on a per mile basis. I was running fuel use calculations and came up with 1.1-1.5 MPG. Basically divided miles traveled by gallons used. I am using fuel receipts to figure this not Smartcraft...although ongoing I plan to use both to see how accurate Smartcraft is.
 
I upgraded the dash to SmartCraft, including a SystemView display. There is a page in the SystemView that shows the current burn rate. I just adjust the drive trim to find the lowest burn number.

I'm not concerned with mpg numbers because there are too many variables that influence mpg.

Henry


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Last edited:
I upgraded the dash to SmartCraft, including a SystemView display. There is a page in the SystemView that shows the current burn rate. I just adjust the drive trim to find the lowest burn number.

I'm not concerned with mpg numbers because there are too many variables that influence mpg.

Henry


Sent from my iPad using Tapatalk HD

Same software as is in my SC5000 gauge cluster? In your opinion are the fuel readings accurate? I don't think my gauge has gph...I think its only mpg and range.
 
Yes, and no. Obviously, the SV displays much more than the speedo tach pair.

SC determines fuel burn rate by calculating based on rpm, injector bursts per time and probably other stuff. So short of installing flo-scan hardware it's as good as it is going to get. Obviously a new in spec engine will be right on the money, and an older worn engine's actual consumption might be greater than what was calculated.

In the past I found that my elapsed fuel consumption from previous fill up to be a few gallons greater than what SC has predicted. By a few I mean like 75 actual to the 70 predicted by SC. This season I have not reset the trip computer, and won't do so until I haul out with a final fill up. And since I've logged all of the fuel purchases I should be able to get a pretty good notion of the average consumption rate.

As an FYI the trip computer has us at 1.2 nmpg (X1.15 for mpg) for the season so far.

Henry


Sent from my iPad using Tapatalk HD
 
I upgraded the dash to SmartCraft, including a SystemView display. There is a page in the SystemView that shows the current burn rate. I just adjust the drive trim to find the lowest burn number.

I'm not concerned with mpg numbers because there are too many variables that influence mpg.

Henry


Sent from my iPad using Tapatalk HD
I'm going to make a trip from point A to point B, my twin 5.0's burn 20gph at cruise.....will I make it?
 
That's a good measure. I would be curious what the intended specs are. Seems as though there is consistent reports that the boat should top out in the mid to upper 40's.
From some 2005 SR literature I have for T5.0MPI, B3, 2.2 ratio, props 24P.....WOT45-49mph, WOT 5,000rpm.

I was going to try the new 4 x 3 props but didn't get to it. If Mortens results are typical it appears they work better than my 3 x 3.
 
I'm going to make a trip from point A to point B, my twin 5.0's burn 20gph at cruise.....will I make it?

Distance between A and B? Headwind? Tailwind? Cross current? Sea state? Fuel level?

Historical mpg is meaningless for navigation.

The only time mpg means anything is at the moment, and with the specific conditions when you are setting up the navigation for your course. You can be on plane burning 20 gph fighting a combination of headwind, current and waves with a SOG half of your normal cruise speed. In that case your mpg is also half of your normal cruise mpg. So in that case if you make fuel consumption assumptions based on historical numbers you will be wrong.

Henry


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Distance between A and B? Headwind? Tailwind? Cross current? Sea state? Fuel level?

Historical mpg is meaningless for navigation.

The only time mpg means anything is at the moment, and with the specific conditions when you are setting up the navigation for your course. You can be on plane burning 20 gph fighting a combination of headwind, current and waves with a SOG half of your normal cruise speed. In that case your mpg is also half of your normal cruise mpg. So in that case if you make fuel consumption assumptions based on historical numbers you will be wrong.

Henry


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Certainly all those things are factors, I agree and probably more so with gas power. To have an idea of your boats performance using any criteria is useful, including mpg. It's interesting that your first question was asking for distance between points.

If I eliminate some variables:huh:....my fuel tanks are 300gals, my boat burns 20gph at cruise and the seas are perfect, no wind, waves or currents....will I make it from point A to point B?
 
DTD divided by SOG equals time to destination. Time to destination times fuel burn equals fuel needed to reach destination (all things remaining the same). As long as fuel needed is less than fuel available you can get there.

BTW, the same screen that gives me burn rate also gives me the present range based
On current conditions.

So why use an average based on variables that may, or may not, exist for your present conditions when you can determine your fuel requirements based on real time calculations? Personally, I only get interested in fuel requirements for conditions where the possibility exists of running short. In those cases I want the best available data.

Henry

Sent from my iPad using Tapatalk HD
 
Y'all makin my head hurt.

I take my 240da to the Bahamas, it has 70 gallon fuel tank. Most times I burn about 40 gallons to get there. Sometimes when the weather is bad I have burned 68 gallons to get there. If I did all thoes calculations you guys are doing, I'd never be comfortable enough to go. But in 20 years of going, I've never run out of gas! Yet!!!! My cousin, well, he did......so we towed him the rest of the way. Haha
 
Just wanted to update. Took the boat out today. Perfect day...little wind and seas were like glass. Had my wife, my dog and my tender on the back and 3/4 tank of fuel and full water tank. Pushed the throttle wide open. Once on plane I started to trim up. Could instantly see a difference in speed. Trimmed enough to see 42 mph and RPms at around 5000. I think with a lighter load and little more trim I could see mid 40's...maybe more.

quesrion about ventilation- how do I know if I have trimmed enough or too much? Does trim come into play at any speed or only at top speed. I have never really used the trim...only the tabs. But if I am understanding how trim works I should be able to trim at my cruising speed and decrease rpm this increasing efficiency? Am I right on that?
 
Two things can tell you if you've trimmed up as high as you should go. One would be if the prop starts to ventilate - you'll know this if the RPM's jump up fast, whether it's by looking at the RPM gauge or simply by listening to the engine. The other way that you know you've reached the limit of the usable trim for the given conditions is if your speed no longer increases yet the RPM's continue to rise (uniformly, not rapidly like it would with ventilation). Through all of this, try to avoid going over your MAX RPM - although a tad bit for a quick burst won't harm anything.
 
Just wanted to update. Took the boat out today. Perfect day...little wind and seas were like glass. Had my wife, my dog and my tender on the back and 3/4 tank of fuel and full water tank. Pushed the throttle wide open. Once on plane I started to trim up. Could instantly see a difference in speed. Trimmed enough to see 42 mph and RPms at around 5000. I think with a lighter load and little more trim I could see mid 40's...maybe more.

quesrion about ventilation- how do I know if I have trimmed enough or too much? Does trim come into play at any speed or only at top speed. I have never really used the trim...only the tabs. But if I am understanding how trim works I should be able to trim at my cruising speed and decrease rpm this increasing efficiency? Am I right on that?

Did you put your trim tabs up after you were planed off? I mentioned this in an earlier post but it seemed to get lost as I never saw it mentioned in the following posts. This will make a difference.
 

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