2000 380 ac with 3126 cats, speed/ rpm and consumption questions

S

sea dawg

New Member
Sep 1, 2010
12
white rock bc
Boat Info
2000 380 ac
Engines
cats 3126
I just purchased a 2000 380 ac with 3126 cats. It is a great boat but i have a few questions that i hope more experienced owners can shed some light on....

At WOT, my starboard engine reaches 2900 rpm ( most of the time, this last weekend i could only get 2600) while my port engine barely pushes 2600 ( sometimes less .... ie 2300-2400)

assuming the 2900 /2600 wot, i barely get 19 knts.

I realize that speed is impacted by current, tides and winds but I have tested the wot at slack and no wind conditions and still get the same results....

I get a little bit of vibration on port side, the allingment was just done and the prop and shaft look true...

btw we tested it initially with no personal effects , 1/4 tank of fuel and 3/4 water so not over loaded.... in fresh water ( so no tide ) and no wind.. still only got 19knts

I seem to get an avg of 11-14 knts at 2400rpm seems pretty low for the fuel consumption....

so i have been cruising at 1500/1600 rpm with appx 7-9knts

any idea what is causing this?

I called Cat and they really could not provide any insight

am i kidding myself in being fuel efficient at running it at displacement speeds.... by my calculations, 1500/1600 seem to be the most efficient despite the fact that logically, it would be more efficient on plane..

talking about planing... i realize that it comes down to 'feel' and experience but i am having some challenges knowing the right 'planning' cruising rpm/speed. i have played with the trim tabs but do not really feel or see any difference.... hummm!
Can i rely on what the wake is doing? whether i get water no longer churning on my swim step???

I realize that i am asking allot of questions that are all over the map but any insight on any of the above would be appreciated.

Thanks



:huh:
 
In my boat, 2300 rpms and I'm doing about 22kts. Something is wrong here. What tachs do you have. How are you measuring speed?
 
Are you pushing the "bow down" buttons ALL the way down before you power up? You need to have full tabs then adjust them from there, to do this hold those buttons for 15 seconds or till you hear them stop. (with eng. off) Also you should feel NO vibration.
 
Did you have a survey completed? It could be several things, clogged fuel filters, dirty hull, growth on hull, etc. Do you have the right props on, do the engines turn suggested WOT in neutral? Something is definitely wrong...
 
SeaNile said:
Did you have a survey completed? It could be several things, clogged fuel filters, dirty hull, growth on hull, etc. Do you have the right props on, do the engines turn suggested WOT in neutral? Something is definitely wrong...
Click to expand...


Thanks Seanile, yes, had a survey, just had the filters replaced before buying it, the bottom was pressure washed. I will double ck the wot in neutral this pm....i get that something is wrong.... just not sure where to start looking... ;- (
 
katricol said:
Are you pushing the "bow down" buttons ALL the way down before you power up? You need to have full tabs then adjust them from there, to do this hold those buttons for 15 seconds or till you hear them stop. (with eng. off) Also you should feel NO vibration.
Click to expand...


I think so but i will try this with your your suggestion..... i will report back... thanks
 
Turtlesboat said:
In my boat, 2300 rpms and I'm doing about 22kts. Something is wrong here. What tachs do you have. How are you measuring speed?
Click to expand...

thanks for your response,... i have the tachs that are standard with the boat... i do not see a name brand.... I am using both a 3210 gps as well as a raytheon st 60 tri data.... hummm....:huh:
 
Absolute first thing to do is to verify that the tachs are correct using a photo tach. I'm guessing they're not but that ain't your whole problem.
 
I agree, phototach the engines but that is not the route of your problem. Are the turbos spooling up? Do the engines emit any smoke out of the exhaust? The color of the exhaust will be key in the diagnosis.
 
sea dawg said:
Thanks Seanile, yes, had a survey, just had the filters replaced before buying it, the bottom was pressure washed. I will double ck the wot in neutral this pm....i get that something is wrong.... just not sure where to start looking... ;- (
Click to expand...

The $million question is how did it perform at survey?
There were no issues at that time- reached max rpms/no smoke, no overheating? Speed?

I'm confoozed...
 
tobnpr said:
The $million question is how did it perform at survey?
There were no issues at that time- reached max rpms/no smoke, no overheating? Speed?

I'm confoozed...
Click to expand...


It did have have the difference in the port and starboard rpm but no smoke and no overheating. The surveyor thought it would be an issue with the alignment and fuel filter. I did both but it has not fixed the issue. im confused too! :huh:
 
SeaNile said:
I agree, phototach the engines but that is not the route of your problem. Are the turbos spooling up? Do the engines emit any smoke out of the exhaust? The color of the exhaust will be key in the diagnosis.
Click to expand...


the exhaust is clear as can be with the exception of a tiny bit of white smoke on start up. but this goes away almost instantly and there is very little.... could it be a possible injector issue?
 
Last edited:
By the way, the engines are very clean, the oil samples came back great, and i have a total of 530hrs ....
:smt100
 
SeaNile said:
Read the following.

http://www.sbmar.com/Maintenance/PDF/Low-Power-Troubleshooting.pdf
Click to expand...


Here is an update, you and a few others were right, the tachs were off by 300 on my port engine.
so this explains the low rpm... glad to find this out. Thank you!

I will be out this weekend and will try to get 20-24 knts. I will test this at at slack and hopefully minimal wind in order to get as true of a reading as possible.

thanks again for all of your help
mike
 
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