48 Sundancer top speed WOT

M

Micj81

New Member
Dec 19, 2010
14
Lake Ozarks
Boat Info
2007 48 Sundancer
Engines
Twin Cummins 8.3
SeaRay says the boat should run 34 Mph. The boat is equipped with 5.8 Cummins HO, 540HP Each rated at 2600 rpm. I'm running factory recommended props 24 X 29. At WOT I'm lucky to hit 29 or 30 with GPS. Others in the marina have the same engine / prop state they run 32 -34 no problem at WOT. If I am turning the correct RPM with the correct prop's what could be causing me to not meet mfg recommended speed? I'm not going to run the boat that fast, I just want to make sure I don't have another issue going on that needs to be addressed. TIA - MJ
 
I have "tested" my 48 this summer and I feel as if I'm missing 1-2 mph. Here's what I learned:

Trim Tabs: Raise your Trim Tabs ALL the way UP!
Do not use the engine synchronizer. Pin the throttles on each engine "individually"
WOT: 2650 rpm....are you getting that? The engines are rev limited at 2680 (I think)
Being at LOTO, I'm guessing that there is no "tide" and perhaps even a very negligible amount of current. Either way, do your test run once going "up river" and once going "down river".
What is the condition of the bottom? My boat hasn't been out of the water since early 2022. I feel that I am dragging a carpet around.
What is your Boost reading on the Smartcraft? Is the Turbo performinng up to speed?
Lastly, but I'm sure that there is more, are your props in good shape? Have they been tuned? Are they dinged?

I'm sure others will chime in with other things to look at.

Jaybeaux
 
Micj81 said:
SeaRay says the boat should run 34 Mph. The boat is equipped with 5.8 Cummins HO, 540HP Each rated at 2600 rpm. I'm running factory recommended props 24 X 29. At WOT I'm lucky to hit 29 or 30 with GPS. Others in the marina have the same engine / prop state they run 32 -34 no problem at WOT. If I am turning the correct RPM with the correct prop's what could be causing me to not meet mfg recommended speed? I'm not going to run the boat that fast, I just want to make sure I don't have another issue going on that needs to be addressed. TIA - MJ
Click to expand...

What model year are you talking about? Not sure there were Cummins of that displacement in the mid-2000s 48DAs.

If you are talking about the 8.3s, I have those in a 2007, not HOs I don't think so closer to 30-32mph, cruise at 28.
 
Ericinmich said:
What model year are you talking about? Not sure there were Cummins of that displacement in the mid-2000s 48DAs.

If you are talking about the 8.3s, I have those in a 2007, not HOs I don't think so closer to 30-32mph, cruise at 28.
Click to expand...
My error, you are correct. QSC 8.3. 2007, 48.
 
A few things come to mind. How are you measuring RPMs -- digital or analog gages? Are you sure they are accurate? Prop may not be to exact spec. and needs to be checked? Boat is loaded with beer and women?
 
Micj81 said:
My error, you are correct. QSC 8.3. 2007, 48.
Click to expand...
I have the same engines in a 2007 44DB. I can get 32 WOT but with 375 gallon tanks, don’t have the range to do that for long. At 2200 RPM and 18 kts I'm burning 36 GPH.
 
Micj81 said:
SeaRay says the boat should run 34 Mph. The boat is equipped with 5.8 Cummins HO, 540HP Each rated at 2600 rpm. I'm running factory recommended props 24 X 29. At WOT I'm lucky to hit 29 or 30 with GPS. Others in the marina have the same engine / prop state they run 32 -34 no problem at WOT. If I am turning the correct RPM with the correct prop's what could be causing me to not meet mfg recommended speed? I'm not going to run the boat that fast, I just want to make sure I don't have another issue going on that needs to be addressed. TIA - MJ
Click to expand...
Are you sure you're measuring in MPH and not knots?
 
Golfman25 said:
A few things come to mind. How are you measuring RPMs -- digital or analog gages? Are you sure they are accurate? Prop may not be to exact spec. and needs to be checked? Boat is loaded with beer and women?
Click to expand...
RPM reading was from Vesselview. 1/2 tanks of fuel, 1/2 water tank, empty holding tank. The props are not tuned but were in good condition. Bottom paint is needed but had been cleaned two weeks prior. Do you think speeds would increase if I were to load it down with bikini clad women?
 
Jaybeaux said:
I have "tested" my 48 this summer and I feel as if I'm missing 1-2 mph. Here's what I learned:

Trim Tabs: Raise your Trim Tabs ALL the way UP!
Do not use the engine synchronizer. Pin the throttles on each engine "individually"
WOT: 2650 rpm....are you getting that? The engines are rev limited at 2680 (I think)
Being at LOTO, I'm guessing that there is no "tide" and perhaps even a very negligible amount of current. Either way, do your test run once going "up river" and once going "down river".
What is the condition of the bottom? My boat hasn't been out of the water since early 2022. I feel that I am dragging a carpet around.
What is your Boost reading on the Smartcraft? Is the Turbo performinng up to speed?
Lastly, but I'm sure that there is more, are your props in good shape? Have they been tuned? Are they dinged?

I'm sure others will chime in with other things to look at.

Jaybeaux
Click to expand...
Thank you for the info. I have not tried it without sync on throttles. I'll double check but yes, 2650 RPM. The prop's are not tuned but are in good shape, no dings. I am due for bottom paint but had it cleaned about 3 wks prior to testing speed. I dont know how fast the growth will grow on the bottom but possible contributing factor? I did not think about checking the boost reading in smartcraft to see if they are performing properly but will do so this weekend. Thank you very much for the input. Much appreciated.
 
I suspect Sea Ray's testing was done in very light load conditions and for sure was done with a perfect, possibly unpainted bottom. Doing a full bottom job can easily add a knot or two to top end. No point in speed testing unless the bottom is smooth and clean.

You also need to do two runs in opposite directions and average the speeds to overcome any wind or current effects.
 
if you’re hitting 2650 WOT it sounds like the engines are healthy and happy. The props could need a tune and bottom growth does happen very quickly late in the season with the water being warm

I always focus on WOT rpm vs boat speed, there are just too many contributing factors from hull to hull. For example, our boat is faster with full tabs down that it is with them up, but that’s not true for all.
 
I’d get the props checked on the next haul out. Pitch may have been changes at one time.
 
I’d get the props checked on the next haul out. Pitch may have been changes at one time.
 
swaterhouse said:
I suspect Sea Ray's testing was done in very light load conditions and for sure was done with a perfect, possibly unpainted bottom. Doing a full bottom job can easily add a knot or two to top end. No point in speed testing unless the bottom is smooth and clean.

You also need to do two runs in opposite directions and average the speeds to overcome any wind or current effects.
Click to expand...
Thank you for the input. Much appreciated.
 
Strecker25 said:
if you’re hitting 2650 WOT it sounds like the engines are healthy and happy. The props could need a tune and bottom growth does happen very quickly late in the season with the water being warm

I always focus on WOT rpm vs boat speed, there are just too many contributing factors from hull to hull. For example, our boat is faster with full tabs down that it is with them up, but that’s not true for all.
Click to expand...
Thank you for the reply. I appreciate it.
 
Micj81 said:
RPM reading was from Vesselview. 1/2 tanks of fuel, 1/2 water tank, empty holding tank. The props are not tuned but were in good condition. Bottom paint is needed but had been cleaned two weeks prior. Do you think speeds would increase if I were to load it down with bikini clad women?
Click to expand...


No question bikinis and alcohol makes any boat run better. That is settled Maritime science.
 
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