New engine still no power

I checked the SOG on GPS with no tide. I also checked against a measured mile just to be sure.
 
I was interested in the tiny prop. My ratio is 2.14 on 3600 rpm. The supplier is offering a selection of blades. It's easy to change the folding prop blades but I don't have anywhere to dry out so need to pay for a lift. I only want to do it once if possible. From what you are saying a 14 x 9 would not be unreasonable.
 
Just read the previous post that it only revs to 2200 RPM. I seem to remember that 1" of pitch reduction = 500 RPM so you would have to reduce by at least 2" which seems drastic. If you can find a place to dry out and fit a 16x8 prop(if available) and it then revs to over 3000 RPM your problem could be solved. Regarding the small 11" prop originally fitted to the M33, it was apparently fitted with a 1: g/box and revved to 2500(35HP BMC diesel) When I got the boat a new 13x8 three bladed prop had been fitted but never used. When I launched the boat it would not rev higher than 1500 RPM. The engine had big problems so I re-engined with a Beta 25HP but didn't go for a larger engine due to the tip clearance problem.
 
There is something wrong here KAM
My calculations indicate that the prop should be about 15 X 10 or even 11. When looking at diameter you have to recognise that this is a folding prop though so because of the large hub diameter your 16 inch dia is about right for blade area.
In my calcs I allowed for a waterline length of 29ft, 4 tons displacement and a gearbox ratio of 2.25. Can you check this and tell me you agree this is OK?
By the way the speed came out at 7.5 knots.
If this engine is rated at 28HP I think it should easily drive the prop you have and you should be asking other questions.
1. Is it getting enough fuel?
2. Are filters clean?
3. Is there air in the system?
4 Is the pipework adequate?

I have seen several installations where the engine appeared to be running OK but there was either contamination of the fuel or it just was not getting through fast enough. Before changing props check. I don't think you are developing maximum power.
If I compare with my own boat it is 32 HP and 3600RPM but through a 1.85 reduction and mine is a 36ft cat so different hull configuration entirely but I drive a 16x10 conventional prop and get about 7 knots. Last year I had a fuel contamination problem and could not reach maximum RPM which knocked me back to 5 knots before I cleared it... Worth checking don't you think?
 
Yes. If my other post is correct and it's fuel restriction of some kind you would not get any. If you were over propped, you probably would.
 
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Anybody got any thoughts on the lack of black smoke?

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depends on the injection system. if that is mechanical then you will get black smoke if overloaded but if its electronic like modern cars you might well not. all depends on whether fuel input adjusts to throttle lever or air flow into the engine.

I think /forums/images/graemlins/grin.gif
 
Black smoke is not always present on overpropped engines. If the governor is working correctly there should be very little if any. Contact a prop specialist and get them to do a prop' calc'. The prop' needs to be matched to the engine power, revs and gearbox ratio as well as length and displacement of the boat.
 
Re the replies about lack of fuel and lack of black smoke. I did have a feeling that when I first ran the engine that the power was OK. I did a short full power run after the first week and thought I got decent speed but was single handed so did not check the revs or speed in detail but I thought I heard the prop cavitating slightly which I have not heard since. A couple of weeks later I misjudged the tide in the Sound of Jura and the wind fell light It was only when I opened up the engine that I realised I had a serious lack of power and nearly ran onto some rocks. So my main thought had always been lack of fuel. I spent the rest of last season assuming it was lack of fuel. I had the fuel system apart many times. I even ran the engine from a bucket of fuel straight into the engine. I took the governor apart and found that the torque pin, which is a spring loaded pin which opens up the fuel rack when the governor senses load, was only moving 0.2mm. This did not seem very much to have any effect. The engine manual indicated a dimension labelled "a" for the movement of the pin but the supplier could not tell me what "a" should be. They sent me a new governor lever assembly which measured the same. I fitted it but it made absolutley no difference as expected. There has been no variability about the lack of power. The max revs in gear is always the same. The only thing I have not had apart is the lift pump but I have run the engine with only the fuel in the filter and nothing else connected so I dont think this is at fault. I assume if there is fuel coming from the spill off pipe then there is enough fuel to the injection pump. I was starting to wonder if there was a fault in the injection pump but it starts and runs perfectly. Over the winter I took out the fuel tank and completely cleaned it and changed all the fuel pipes and filters and refilled with white diesel but it made no difference. Boatmike waterline length is 8.3m, displacement 5000Kg. Box ratio 2.14. I would appreciate a prop estimate on your program. I see what you mean about the folding prop hub. Thats why I don't want to reduce the diameter too much as the blades are starting to look very small. Whether or not the engine can swing it at the right revs must depend on the moment of the centre of pressure of the blades about the shaft so I am not sure if a big hub will have any effect. I have a 15 x 9 to try this weekend but would love to find a fuel problem first if possibel.
 
on those figures the program says 15 x 11 prop which is very near what you are using. So near that the change surely couldnt account for the problems you have. It has to be something that is making the engine down on power. What make of engine is it?
 
Its something I have not checked its only done 100 hours. I only appear to be getting half power. Could it make that much difference. If it is the problem it happened within the first 20 hours.
 
Yes, but even Jap engines arent totally fault free. I guess you have to go back to Beta themselves because if the prop is in the right territory (which it is) then it has to be something to do with the engine or box. Have come across a Beta with a dodgy as supplied gearbox - they promptly replaced it.

Are you sure the ratio is what you say - have you taken the ratio off the box itself or off the engine spec?
 
I took it off the plate but also checked it manually when out of the water. I also double checked the prop hand was correct. Its a saildrive unit. When supplied the prop spacer was missing. With the spacer fitted it seems very free but I have wondered if there is something wrong with the thrust race. The revs pick up a bit when motor sailing which hints at the prop size again.
 
No it doesnt show prop size cause you go faster motor sailing, it shows lack of power to swing the prop, either by oversize, but all the calcs say no, therefore lack of power by engine, therefore something wrong with engine. If no resistance in the drive train then fuel supply restricted or slight red herring tappets tight.
If tappets tight then lack of compression and hesitant starting, no mention of that therefore ITS GOT TO BE FUEL supply restriction
Stu
 
It does seem to keep coming back to fuel but it is not someting which has any intermittancy. Not sure what else to check or what could have changed. There is a fuel limitation adjuster on the fuel rack. It has an anti tamper device. I have been tempted to try adjusting it but Beta keep telling me it is not the problem. I had wondered if the lock nut had not been tigntened and it could have moved. The screw is vertical and screwing down would restrict the fuel flow but should not affect max revs off load. I have tried the torque limiter but this had no effect.
 
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