WOT vs speed Sea Ray 280 Sundancer Also fuel level quesrion

Madifonzo said:
Speedo and gps match from 20 or so and up.
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OK, that's good to know. Maybe the other guys can chime in on this if they happen to know (again, more recent experience than me)... Does the 4,500RPM's sound about right for 35MPH (with drives down)?

Maybe you can find some BoatTest reports, or similar to compare? Although those tests will be done with the engines trimmed for best numbers.
 
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Ok, so my thought is what do you want to hear? I'll tell you that, even if it's wrong. You don't want to accept the obvious, so......

On another thought, let someone run your boat that knows how to run a 280 and see if they can get it to speed.
 
Madifonzo said:
With thy respects to trim there seems to varying opinions on that. Many 280 owners on this site have reported that trimming up at all causes cavitation. There are several threads regarding the trim limit insert on Bravo drives...I think it's related in some way. That being said I can't see a 15 mph difference based on a slight trim difference.

I am am wondering if prop pitch is playing a role.
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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


Sent from my iPad using Tapatalk HD
 
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Madifonzo said:
Thanks for all the feed back and questions.
Bottom is clean and painted with ablative. Props are clean and there is little to no growth anywhere on the drives. Engines were tuned up past season with plugs and wires and rotor. While I don't always run Valvetec, the last fill up was valve tech 89 octane.

Oh, and I did not have the dingy on the back.


With thy respects to trim there seems to varying opinions on that. Many 280 owners on this site have reported that trimming up at all causes cavitation. There are several threads regarding the trim limit insert on Bravo drives...I think it's related in some way. That being said I can't see a 15 mph difference based on a slight trim difference.

I am am wondering if prop pitch is playing a role.
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My guess...your bottom is rough, you got stuff on your drive, your props are out of shape, and you need to fix you trim sensors.
 
Bad guess...all is clean. It was hauled and washed several weeks ago, bottom was stripped and painted at the start of the season with Micron Cf and props were inspected and tuned as needed. Based on all the feedback, I beleive it is operator error in the form of me not trimming the drives. But yes, I need new trim sensors. They are on the winter list of repairs.
 
Madifonzo said:
Bad guess...all is clean. It was hauled and washed several weeks ago, bottom was stripped and painted at the start of the season with Micron Cf and props were inspected and tuned as needed. Based on all the feedback, I beleive it is operator error in the form of me not trimming the drives. But yes, I need new trim sensors. They are on the winter list of repairs.
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when you are trimming the boat to obtain max speed you need to listen to the sound of the engine and watch your speed and engine rpm's.....the engine rpm's and boat speed will increase as you raise the drive and this is to be expected....keep rising the drive until you start to see a decrease in speed then back the drive down just a little to get the speed back....this should now be the optimal trim.....

one word of caution is to never raise the drive past the stop point before getting into 'trailer' height while running the engine....you mentioned your trim sensors need to be replaced so you will need to pay close attention to this....if you raise the drive too far you will likely damage the U joints in the drive shaft....

cliff
 
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I had an '03 280 with the same engines and drives as you (as well as bottom painted, etc). It was a 45mph+ boat. The "+" was in ideal conditions but it would definitely move out. I believe we were talking around 5000 RPM pegged. Trimming drives up was very limited (maybe two quick "up" pulses at most on the drives) otherwise she'd start to cavitate. I didn't run at those speeds all the time but would maybe twice a season just to make sure things were still in spec. The performance and handling of the 280 are the things I do miss over the 340.
 
Maybe I missed it but I have not seen trim tabs discussed at all. Once you get on plane, you should be able to reach ~50mph by taking the trim tabs all the way up and trimming the drives up just a bit. This 280 will cavitate with really any drive trimming unless the engines are near or at WOT and the boat is planed off. I never trimmed my drives up at all unless I was opening it all the way up.
 
"Does the 4,500RPM's sound about right for 35MPH (with drives down)?"

I run 28mph at 3200rpm's and if I was at 4500rpm I would be in the 40's easily. Something is not right with his setup.
 
is it possible there is some kind of adjustable 'stop' or a throttle cable setting that is preventing the throttles from being pushed all the way open?.....

cliff
 
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I have a 2008 280 with twin 5.0's. I haven't tried to run my boat at WOT. I should test it out before I pull it for the season. I run about 3000-3200 RPM's and I'm just about 30MPH. I've had issues trimming the drives due to cavitation. For a while I thought there was something wrong. I'm glad I found this thread where others complain of the same cavitation issue. I rarely try to trim the drives anymore because of this. I feel that my swim platform sits to low into the water as well. I've seen other 280's, possibly with single engines or twin 4.3's that sit much higher out of the water.

Once I pull the boat out I will check my drives and make sure everything looks ok.
 
Maybe his boat is water logged, How much of your platform is in the water sitting still? Even though his props look good, maybe they're not. Tach accuracy?
Does your boat jump out of the water and get on plane in a few seconds with minimal weight?
 
Just as a point of reference for the future... when the drive(s) are trimmed too high, that causes "ventilation", not cavitation. Ventilation is the introduction of too much air to the prop, allowing it to overspin. Cavitation is the explosion of tiny air bubbles on the surface of, for example, the prop blade edges. Over time, the exploding bubbles will actually start to eat away (craters) in the material. You may have seen an aluminum prop that has craters/pock marks toward the edge of the blades. Often times, you'll also notice that there may be some slight damage/imperfections to the blades... which is usually the cause the cavitation to begin with. Although, it can still happen without any damage.
 
The 280's require very little trim of the outdrives to make a difference. I have the smartcraft gauges and with the trim at 2 (which again is very little) my MPG goes from 1.4 to 1.6-1.7. The MPH increase as well as the rpms.
 
Once again, thanks all for the feedback. I'll be taking my mechanic out with me on a run and see what he thinks.

I am really not concerned about going 45-50 mph but it's know I could if I wanted to. On the ocean I prefer to cruise at around 25-28 and use my tabs frequently to level the ride and smooth it out.

I will ill report back any findings.
 
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