Loss of Power/RPMs

[WaterKnot]

Took the boat out the other day and noticed a loss of RPMs and knots. Had the hull cleaned by a diver two months ago. I typically get 15 knots at 3,700 RPMs and 19 knots at 4,100 RPMs running Wide Open Throttle (WOT). On this outing, I could only get 3,800 RPM WOT with a max of 14 knots. Boat was trimmed normal, no extra weight, four people on board, with almost no wind and current. Engine was warmed and we cruised for about 2 hours and saw no changes.

This is the first time I’ve experienced a loss of power/RPMs. I have a 2011 R-27 with a Yanmar 4BY2 diesel. The engine has about 1,300 hours on it. Has anyone experienced this before and how did you fix it? I’m thinking maybe the throttle cable needs to be adjusted?

Thanks in advanced for your help.

 

[lproulx]

Don't know if this applies to your engine, which is much bigger than the ones I am familiar whit, but consider some sort of obstruction in the exhaust elbow - carbon, rust, etc. When this happens, the engine can run fine, but just not make as much power as it's supposed to.

 

[Cutwater28GG]

two months in this warm summer weather can drive a lot of growth on the bottom.

proposing some possible options and Im sure someone more knowledgable will come along soon

could it be where the 4 people and gear was stowed?
restriction on fuel flow?
Did I read a while back about the yanmar restricting performance because of turbo and exhaust issues? (i dont know the yanmar well as I have a volvo)

 

[Severum88]

Bottom is dirty I bet. I have lost 3-4 knots and seen the same behavior as you on a dirty bottom of my C26. I am having to have my hull cleaned in Socal every 3-4weeks rt. now. YMMV.

Severum

 

[WaterKnot]

Thanks for the feedback. Same amount of gear and location, and everyone was sitting in the salon.

In regards to having the hull cleaned again, have any of you seen a loss of RPMs due to a dirty hull? I’ve see a loss of knots because of a dirty bottom, but never a loss in RPMs.

 

[ixlr8]

Thanks for the feedback. Same amount of gear and location, and everyone was sitting in the salon.

In regards to having the hull cleaned again, have any of you seen a loss of RPMs due to a dirty hull? I’ve see a loss of knots because of a dirty bottom, but never a loss in RPMs.

I had my 27OB in the salt water for 6 weeks with no protective bottom paint. I had so much growth that my WOT speed went from 40mph clean to 28mph dirty. Max RPM clean was around 5600, max RPM dirty was about 4800 rpm if I remember correctly.

 

[BB marine]

Thanks for the feedback. Same amount of gear and location, and everyone was sitting in the salon.

In regards to having the hull cleaned again, have any of you seen a loss of RPMs due to a dirty hull? I’ve see a loss of knots because of a dirty bottom, but never a loss in RPMs.

Load on the engine will reduce rpm. Bottom growth creates drag and increases load on the engine. The engine is working harder to push the boat and the rpm is lower. It doesn't take much to load these small displacement diesels down. I believe a good scrubbing of the bottom will leave you presently surprised of the recovery of speed and rpm.

 

[knotflying]

I agree with Brian. It does not take much growth to put load on the engine. I have seen similar numbers on my boat with a dirty bottom.

 

[doke01]

Dirty fuel filter.

 

[WaterKnot]

Having the diver clean the hull this weekend. If it ends up just being a dirty hull, I’ll be grateful while feeling dumb. Was at the marina the other day at -2 tide and notice the boat across from me sitting on the harbor floor. We just moved to this marina a few months ago and our slip is right off the ramp. Assuming that’s why it was available. The harbor is extremely muddy/dirty compared to our last marina. I’m thinking the harbor and being so close to the shore is resulting in the hull getting dirty twice as fast. If that’s the case, it looks like I’ll be cleaning the hull more often. Will also try to get a slip further away, in some deeper and cleaner water.

If that is not the case, the fuel filter and batteries are next on the list.

 

[TomFin]

I'm in Kingston just north of you and get micro barnacles growing on the prop. On several occasions I have had a vibration they cause and definite loss of RPM can have to get the diver out to clean.

 

[WaterKnot]

Got the hull cleaned and took the boat out this weekend, she runs like a champ! I’t must be the new marina. Growth develops significantly quicker here. Looks like I will be cleaning the hull more often. Thanks for the help!