[Keith Pleas]

Bumping this – and reducing to the bare essentials – after splicing the RPM, PSI, and temp:

Is there any consequence of eliminating EVERYTHING else from the “Plug Instrument Module” entirely

[Keith Pleas]

Searching on a related topic I ended up with the diagram that shows the wiring connection to the tach: https://www.sbmar.com/wp-content/uploads/2015/11/B-C-Panel-wiring.pdf

That other thread also mentioned that it’s not just the key power, but there’s something in the tach having an RPM reading that turns on the hour meter.

Anyway, I ordered the Chetco interface today so I won’t be bothering to fix this.

[Keith Pleas]

Thank you guys! I hadn’t considered that the _gauges_ might have failed. But I was planning to replace them with a Chetco SeaGauge anyway – the plastic is a bit crazed, some of the backlight bulbs have failed, and the gauges just look old. The SeaGauge _outputs_ the Engine Hours in PGN 127489 Engine Params Dynamic that my dual 12″ Raymarine Axioms should pick up easily – I talked to the inventor and he said I could push starting hours into the unit and after that it would keep track internally. I was going to run that in parallel for a season and then replace most of the helm panel with a 3rd Axiom.

Is there a 12v+ pin on the back of the Cummins tachs that I should at least check for keyswitch power? My preference is to have things working _before_ swapping things out.

[Keith Pleas]

Thank you for the pointer Corey. I carefully compared your board with mine and can see all of the connections and mounting points match up.

Would you suggest swapping out both boards? I’m not sure how to evaluate those changed alarm points. Are there any other improvements?

[Keith Pleas]

Rob Schepis wrote:

Sounds like a bum PC board. Can try swapping the boards.

Ah – you’re saying swap P & S boards and see if the issue travels with the board.

Looking again at my board picture, I see that the board is…discolored…at that jumper J5 and resistor R13 adjacent to it. Is that a common failure point? I can see that there could be an intermittent connection with a bad solder point there. My solder skills aren’t great but I could try redoing that – or I could just put in a new board.

[Keith Pleas]

Tony Athens wrote:

Have you disconnected the 2-wire PINK/BLACK harness at the main instrument panel that goes back to the the engine? You could have a bum PCB board as Rob suggested.

Is that the “WATER IN” J5 in my 3rd picture? I think that’s a single PINK/BLACK wire – you can see it hanging free in that image. Like I said, it made no difference.

Searching on the PCB board…I see a post from you back in 2017 where you were considering running a batch of your own boards – did that happen?

[Keith Pleas]

EDIT: I fixed the original post, this had images but I cannot delete it. 🙂

[Keith Pleas]

@Shawn – I have the same engines – I’m not experiencing that issue but I’d like to spray some corrosion protection in those harness plugs. Can you tell me (an engine novice) exactly where these are located?

[Keith Pleas]

I’m not an expert, but there’s also a “water in fuel” sensor – and alarm. I have had that one intermittently on one engine at startup in the winter with RH in the engine space above 60% – but it goes away as the engine warms.

How do you know “temps are good”? I was going to say corrosion in the cooling system but your profile says Ohio so that’s freshwater, right?

[Keith Pleas]

Thank you @Tony for the detailed response! It’s going to take me a while to study those charts, but I’d like to explore your “during a 8 hours day”. What if that “day” is just Saturday and Sunday 10 times a year? I just ran across a mention of M1 through M5 (continuous duty to weekend and day trips) and believe these are M3 engines. And your fuel burn…I said that the consumption is relatively flat for a waterjet so that’s much less of a factor. I can easily hit 2800rpm but haven’t tried to go past that – I will do that next time I’m out in good conditions. But 1 hour at 30 knots gets me most places I’d want to go in a day and given the number of days I go boating, the engine would last for a long time. Right?

42 gallons (per engine), $3.50/gal, that’s…$294/ day. Maybe, just maybe, I’ll get one chance to take this boat to Alaska in my lifetime. But month over month, I’m not going to spend $300/month of fuel.

[Keith Pleas]

@billd – thank you for your reply. I’ve read Tony’s article on “Continuous Duty” https://www.sbmar.com/articles/continuous-duty-a-different-perspective/ and – if I understand correctly – would yield 55.9 hp/liter for my engines, and if I do get the 1nmpg expected at WOT would mean about 2.54 gal/liter of fuel (per engine). So…running at WOT I might get that 2500 hours, subtracting my 500 hours and going out 20 years…that’s coincidentally exactly the 100 hours/year that I’m looking for. So if I run only maybe 1/4 of those hours at that load, then that would leave me a good margin on the tail end. Does that sound reasonable?

[Keith Pleas]

Does anyone have guidance about max RMP versus longevity tradeoff? I was also thinking of putting in pyrometers to measure load – that would help account for differences between the waterjets and conventional propulsion.

[Keith Pleas]

Hi @Shawn – I don’t have fuel burn figures for my boat, but I do have them for a 37 Hinckley and a 36 Hunt Harrier – slightly different Hamilton / mains configs, but the nmpg is surprisingly flat once you get above about 13 knots. 2600 for the 5.9s sounds reasonable, but I’m hoping that I hear that running at 2700 is fine, or even 2800 for a period (not like 8 hours straight).

I came through the Ship Canal next to a Comitti Venezia 28 (http://www.turnermarinegroup.com/showroom/venezia-28/) and we bumbled along at 7 knots for like a half hour till we hit Lake Washington – I spooled up to 26 knots and then he carved a big arc around me and went down the lake at 30+. OK, no way I could keep up – that’s a 50 knot boat – but could I run at 30 for 15 minutes? 28 for an hour? What is the engine longevity tradeoff curve?

[Keith Pleas]

And an update. When hauled the boat had barnacles “from one end to the other”. The yard manager told me like it was a bad thing, but I told him I was thrilled to hear that. They pressure washed most off for the cross-country trip, and I had a very thorough bottom prep and paint on my end. On my first trip, 1/2 fuel and full water, 2 passengers, I hit 30 knots at 2800 into a light chop and breeze. Plus the hauler was able to give me a net weight of just under 17,000 pounds – working out to a dry weight of 15,500 which is what the literature of that era suggested was the dry weight. So problem solved.

I had Hatton do a complete service of the motors (I think I’m going to spring for the water pump relocate next time!) but I haven’t been back out yet to see if I picked up anything (the fuel filters were a decade old).

And now my next question – what would be a good “cruise” rpm for this boat? From a fuel consumption basis I expect 1nmpg from 2200 to 2800, and on an overnight trip on Puget Sound I was running about 26.5 knots at 2700. Keep in mind these engines are 20 years old, 600 hours, and I’m probably going to put 100 hours a year on them – so I’m not going to need 10K hours, but I also don’t want a premature failure. So, what would be the max RPM that YOU would run for, say, an hour?

[Keith Pleas]

Hi Dennis – I don’t have anything to say about your engines but I will note the amazing coincidence that both your boat (1989 Black Watch) and my new boat (1999 Little Harbor, see adjacent thread) were both built by the legendary Ted Hood. Ted acquired Black Watch in 1987 – you can read more about him (and a bit about Black Watch boats) in Ted’s autobiography “Through Hand and Eye”.

[Keith Pleas]

Thank you Rob! Those were exactly the answers I was seeking. 🙂

Well…there are 4 possible factors to explain the significant under-performance – engines, jets, bottom condition, and over-weight. That’s after we factor out the measurement error(s). One of the jets is essentially new, and – absent the other impeller being significantly dinged up (as in operating over gravel a lot) – they turn at an RPM dictated by the engines. Effectively these are the props and unless someone substituted non-standard impellers (which would have been caught with the factory rebuild 6 months ago) there really isn’t much variation from the jets.

But weight will be interesting. I’ll have a net weight from the trucker to compare to the (nominal) factory spec, but I’m not expecting anything un-expected (you’ll see what I did there).

Which leaves me with engines and bottom growth.

Dirty / fouled – I hadn’t really considered that distinction, but the yard manager thought it was likely to have barnacles by now. So I’m not talking about a coating of slime but something truly significant.

And now I’m left with the engines. It honestly won’t change my life much if I end up with 23 knots or 28 knots, but I do want to know what I should get. 1K RPMs is actually quite a lot for a jet, they have a very different efficiency curve than regular props and that’s probably 2 knots right there. Add in the other randomness and I feel comfortable with my “buy it now” gamble. Fingers crossed of course…

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