Low RPM at WOT during survey

[roger275]

I had a survey done on a 380DA Sundancer with twin 3126 Cats today. Top spec for RPM is 2800. One reached 2725 and other 2743. Weight of the boat should have been light since low fuel and water and only 2 people. Hull is very clean.
Is this a problem or is it close enough to 2800 not to worry about it? Temps were good. Thank you!

 

[kevin27]

How long has it been that way? How many hours on engines? Should be ok if it has not been that a long time and run hard. Your WILL need to repitch props to get in the correct range. My Cummins WOT is 2800 and I can turn 2875 with the sticks full fwd.

 

[fwebster]

When you get the boat loaded and she picks up some normal slime on the bottom, the rpms are going to drop, probably as much as 150-200 rpm. That will put you too far below 2800 and you will be overloading the engines. If you are correct about the loading and the bottom condition, then you will need to have the props adjusted enough to get you to 2800 when you are fully loaded. Just truing the props isn't going to do it....on some boats you can remove a little pitch on others removing a little cup works. Leave the what to do and how much to your prop pro.

The 380DA diesel is a great boat.....I know you will enjoy her.

 

[roger275]

When you get the boat loaded and she picks up some normal slime on the bottom, the rpms are going to drop, probably as much as 150-200 rpm. That will put you too far below 2800 and you will be overloading the engines. If you are correct about the loading and the bottom condition, then you will need to have the props adjusted enough to get you to 2800 when you are fully loaded. Just truing the props isn't going to do it....on some boats you can remove a little pitch on others removing a little cup works. Leave the what to do and how much to your prop pro.

The 380DA diesel is a great boat.....I know you will enjoy her.

Thanks Frank,
Turns out, it was 5/8 fuel and half water. Boat was in lift when I saw her and hull was clean. Surveyor says fuel in the Racors was "a little dirty"and might get the 100 rpm back with clean filters". Do you agree?

 

[CV-23]

Thanks Frank,
Turns out, it was 5/8 fuel and half water. Boat was in lift when I saw her and hull was clean. Surveyor says fuel in the Racors was "a little dirty"and might get the 100 rpm back with clean filters". Do you agree?

Have them changed and take another ride! Your spending big money and won't want to spend more on repairs.

 

[trit21]

Thanks Frank,
Turns out, it was 5/8 fuel and half water. Boat was in lift when I saw her and hull was clean. Surveyor says fuel in the Racors was "a little dirty"and might get the 100 rpm back with clean filters". Do you agree?

I don't think changing Racors is going to do anything for WOT unless they were really clogged at which point I think you would notice that with it staving for fuel. Listen to Frank on this one as he is the CAT expert on this site. If the boat ran strong, temps good etc, then it sounds like a simple adjustment of props can bring back the RPM's to spec or even over spec if so desired for longevity.

 

[markrinker]

Thanks Frank,
Turns out, it was 5/8 fuel and half water. Boat was in lift when I saw her and hull was clean. Surveyor says fuel in the Racors was "a little dirty"and might get the 100 rpm back with clean filters". Do you agree?

I would go as far to say that the ONLY accurate test would be with a fresh set of RACORs, and ideally, fresh 2m filters at the engine, too. I'd ask the owner to spring for a fresh set, and take it for another run. I bet your RPMs and top end come up...I know my 2000 410DA with 3126s drops off quickly as the RACORs load. If you can see it through the glass, its likely the culprit, and you may have some algae problems in the tanks that will need to be addressed...

 

[roger275]

I would go as far to say that the ONLY accurate test would be with a fresh set of RACORs, and ideally, fresh 2m filters at the engine, too. I'd ask the owner to spring for a fresh set, and take it for another run. I bet your RPMs and top end come up...I know my 2000. If you can see it through the glass, its likely the culprit, and you may have some algae problems in the tanks that will need to be addressed...

How do you detect and address tang algae? Thanks.