I'm commissioning my Beta 14 and have not been able to get the engine above 2750 RPM.
Raw water supply is 19 mm, functioning well, no signs of overheating (temp gauge ~60)
The engine runs up to 3700 RPM under no load (suggesting the engine and Tachometer are functioning properly over all.
The logical cause would be a propeller with too much pitch. I have consulted one of the top ten propeller shops in the US, and the largest on the West Coast (Mukilteo Prop Shop). Their determination is that my propeller (a two-bladed 12 inch, 12 pitch sailer prop) is NOT oversized (at least not enough to cause a 900 RPM shortfall), and that if I want a three bladed prop (I do), I should be swinging a 12-8 3-bladed propeller (supporting numbers at the end of this message).
When the throttle is advanced sufficiently to reach that 2750 or so, there is still room for further advancement, suggesting to me that it is not a problem with the throttle linkage not being able to advance far enough. There does not seem to be much in the way of engine-overload black smoke, though I may try harder to determine this.
Air supply to the engine is unobstructed.
One unresolved issue: could it be fuel starvation?
Fuel lines are 5/16", and I've heard that even 1/4" lines are enough to feed a Beta 20 (mine is the smaller Beta 14)
There is an inline shut off valve in the fuel circuit that I measured as 4mm in diameter. The hose-bibs for the 3/16 id fuel hose measure 5mm. If my geometry is on the mark, the cross sectional area of the valve is 12.6 square millimeters and the cross sectional area of the hose bib is 19.6 square mm. Is it plausible that this difference might be sufficient to cause fuel starvation?
Some questions for you before I can provide any answers.
1) is your boat a full keel boat with the prop in an apeture or is it a fin keel boat?
2) What make of sailor propeller do you have?
The boat is a full-keel boat with an offset prop (see photo attached)
The sailer prop is a Michigan Wheel 12 inch, 12 pitch, two-bladed prop. Please note I did not (do not) expect that that particular propeller would be suitable for the new engine configuration, but have been very surprised that the prop seems to be holding the engine back as much as it it.
One detail I neglected to include in my original post is that the exhaust system is 50 mm from an 8 inch high-rise exhaust manifold through to the through-hull exit. I have installed a Vetus NLP50-S water muffler (the S designates 'super' capacity... 2.6 gallons. The entire run from exhaust manifold to the exhaust through-hull (including a gooseneck) is approximately 8 feet (Vetus 50 mm exhaust hose)
In theory everything appears ok but there is obviously a discrepancy.
I have two more questions;
1) how does the boat perform under power? What boat speed do you get at 2,000 and at 2,700?
2) where is the fuel tank in relation to the engine?
The fuel tank is above the engine on the starboard side (it is a 10 gallon stainless steel tank under the seat). I have experienced no issues with the tank prior to now, but in the process of checking the fuel cut-off valve, I blew through the fuel outfeed tube to be sure that it was open (it was). I have since run the boat under load and its behavior is the same, so my hope that a partial blockage there might account for the problem seems unfounded.
The engine shows no signs of untoward behavior. It starts easily and quickly, idles smoothly, and responds to the throttle smartly, both accelerating and decelerating.
I haven't carefully calibrated a speed versus RPM curve, but I will do so. I ran for at least a half hour at 2000, and boat speed was on the order of 4.5 to 5.0 knots, and at 2700 it tops out at 5.5 or perhaps a bit more, but there was wind. I will take her out and do a more systematic assessment tomorrow.
My previous transmission was a 2.62:1 (Yanmar/kanzaki), so I'm turning roughly 25 % faster with the 2:1 transmission on the B-14
My prop calc program comes up with 12'x8" three blade with 50% BAR For a 2 blade it comes up with 12'x11" Waterline speed is 5.8 knots
The estimated max boat speed with the 2 blade shows a full 1/2 knot less for the 2 blade. I suspect that the extra twist of the current propeller is causing more grief than anticipated because of the props position. When you get your new propeller please let us know how she performs.
One thing that I did not answer before after re-reading your earlier post. You state There does not seem to be much in the way of engine-overload black smoke This does not surprise me at all as these new engines run much leaner that the older series of diesel engines. They have to be to meet the new EPA requirements so the only time that you will see a dirty exhaust is when there is a faulty injector or some other fault which is very rare indeed.
Have fun this weekend.
-- Edited by Stanley on Friday 28th of July 2017 05:18:28 PM
-- Edited by Stanley on Saturday 29th of July 2017 12:09:38 PM
Just to close off this topic, the new 12" x 8" propeller is close to perfect.
I can now run the engine up to full rated RPM, and the 3-blade prop is smoother and quieter than the old 2 blade.
The additional prediction of better maneuverability at low speeds is very welcome as well.
I am very pleased with the outcome.
thanks for your advice.
