[Alex F]

I follow your logic, Tony. But my bottom was in decent condition and even though the running gear was due for cleaning, I’ve ran in this shape before and had no issue.

I’m having a concern that it could be some sort of a fuel restriction (either supply to the engine or on the engine side) for the following reason. Since both side had the same amount of growth generating extra drag, why would STBD perform as expected and get to 2600+RPMs. I dove under the boat, shortly after the test run and didn’t see any difference between the running gear growth. I spun each prop freely by hand. There was also nothing on any prop/shaft that could lead to extra drag on the PORT side.

I understand that in order to get closer to the valid conclusion, I need to check few things and produce more detailed data. I’ll report back as soon as I have something.

Quick question, which pressure tester would you recommend I use and where do I connect it in order to validate fuel flow to the HP pump? Maybe you have a link to an article, with pictures, you posted some time ago?

[Alex F]

My boat is not efficient in the 2200-2300 range, so I avoid it. My normal cruise on plane is at 2350-2400RPMs.

As per my older record, very light wind behind me and .25kts current, 1/4 of fuel, 20-21kts @2300RPMs.

I don’t have exact numbers from my last run on 2200. If my memory serves me right I was at around 15-16kts at 2300, but I’ll have to do another run to verify that.

Since my bottom/running gear was close to the time of being serviced, I was expecting to loose couple knots.

[Alex F]

Tony Athens wrote:

Exactly when did this Lower RPM occur? Last run or?

What the history of the past RPM vs. vessel speed?

Hi Tony,

Thanks for your reply.

I’ve owned the boat for the past 10 years. It never had an issue operating to the specs (both engines). Shortly after the purchase, I tuned the props to be in 2650-2680 range, so I can keep my engines happy.

Yes, the issue was observed during the last run. In the past couple months, due to covid, we did only short trips to a local anchorage and those were done running at low speed (my usual trawling speed is 8.5-9kts @1300 RPMs).

Even though I do WOT test on rare occasion, I usually advance throttles gradually to about 2500RPMs to get out of the hole and then settle her at around 2350-2400RPMs for normal cruise speed. Since my boat is super loaded with lots of stuff, heavy tender on a hydraulic lift and I usually have good load of fuel and water, I’m cruising in the range of 19-20kts. With freshly painted bottom and light fuel load she tops out 27kts at 2650RPMs.

During my last test run, when I observed the issue, my bottom was not ideal (a bit of slime, but not too much and few barnacles sprinkled around), and running gear had some growth. I have a diver doing routine bottom cleaning, so this was about 2-3 weeks after the bottom was serviced last. I wasn’t expecting to break any speed records, but just wanted to put her under normal load, exercise the turbos and clean blow by. If my memory serves me right, with PORT side just over 2300 and STBD at 2400RPMs she could only do in the range of 16.5-17kts. When I saw the PORT side struggling to go past 2300 I decided to do a WOT test on both sides. But, as soon as I saw the temp climbing up on the PORT side, I throttled back to avoid harming the engine.

Summary of the last test run:
PORT side:
1. Max RPMs observed was around 2350. Advancing the throttle forward (there was more room to go) didn’t increase RPMs.
2. Water temp was rising to unacceptable level. When it got close to 200 degrees, I pulled the throttles back.
3. Oil pressure registered at around 80PSI at 2300RPMs.

STBD side:
1. Don’t recall exactly how much above, but it definitely hit 2600RPMs.
2. Water temp remained in normal range 180-185 degrees.
3. Oil pressure was at 60PSI, which is where it always was at 2400RPMs.

I do all my regular maintenance, so I highly doubt that there’s a fuel restriction at the filters level. The fuel side (all filters) were changed in spring. I do it annually and as per my observation, the racors were in pretty good shape.

Plan of Action:
I’ll be treating loss of RPMs and high water temp as two separate issues.

On water side
1. I’ll double check the intake flow. I have screens on the bottom covering the scoop strainers, so I’ll double check that there’s no restriction in the flow and will compare it to the STBD side.
2. I plan on doing a quick test to see at what point the temp starts rising. I’ll run it at different ranges 1500, 2000 and finally 2300RPMs.
3. I doubt it’s an issue on the impeller side, b/c I replace mine annually and it’s just approaching the time to replace them. They always look like new when I take the old ones out. But, if all checks out before the impeller pump, I’ll replace the impeller as the next logical step.
4. Finally, if no improvement, I plan on descaling the system by running barnacle buster through it.

On Loss of Power side
1. I’ll do no load WOT test and expect to see 2920-3020RPMS.
2. I’ll check the throttle linkage to make sure it’s not something simple as loosened or stretched cable or something else preventing for lever to move the rack to WOT position.
3. I’ll replace the racor and the secondary filter on the PORT side, just to get this simple stuff checked off, but I’m not expecting it to solve the fuel restriction problem (assuming that’s what this is).
4. Using an air compressor, I’ll blow the fuel feed line from the racor to the tank. I’m thinking that if there’s any sludge it’ll clear any potential blockage in the hose or the tank tube.
5. If all above doesn’t solve it, I’ll have to shift my focus on the engine components. At this point I was thinking to use fuel pressure gauges to check if the fuel flow is to the specs. I was hoping to get some help on what fuel tester I need to get and where to connect it.

Please let me know your thoughts.

[Author]

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