Lack of power from engine

Manureva · Apr 17, 2014

Is your prop slipping in the flange behind the transmission, or the key way broken on the shaft? Or is the fuel rail going all the way to full trottle? Try removing the cable for fuel and see if it goes farther.

Don S/V ILLusion · Apr 17, 2014

That may not be the ideal prop for that engine but it's in the ball park. I'd look elsewhere for the problem -I assume you have a clean bottom and prop and the engine revs up properly in neutral?

Steve Dion · Apr 17, 2014

Our 2GM20F used a 2 bladed 15 x 9 prop.

I would contact a Prop Shop and have them size one for you. I do not think you can use a 15" prop on that model because of tip clearances. 17deg of pitch seem steep but I am not a prop guy. The rule of thumb is that 1 deg of pitch or diameter is worth about 200-250 RPMs. I think that the 3 blade will also take another 200-250 rpms.

You may also want to check to see that your tach is correct.

Richard Bryer · Apr 17, 2014

Hmm- That sounds like a pretty high pitch for that engine/boat combination. I found I was overpitched with a 3 blade Campbell Sailor 14X9 on my h34 with a Yanmar 3gm 22 hp

I found I could not get my rpms up to a cruising range of 2700 as I reached hull speed first. Are you getting any black smoke at that rpm?

Ted · Apr 17, 2014

Definitely over pitched for that motor. I've got a Yanmar 2gm with a 14" diameter x 10 pitch two blade folding prop which seems about right for my 29' boat displacing 6700 lbs. Does your engine come up to proper rpm's with no load? While you have owned the boat, did it ever run properly?

seadaddler · Apr 17, 2014

Neutral

What are the RPM"s in neutral at the dock,start with checking the easy stuff
before spending money.
Nick

Scott T-Bird · Apr 17, 2014

More info would help ...

I think the answer is Yes, the wrong prop could be the cause of the poor performance. But at this point, changing the prop probably won't bring the engine back to correct performance.

First of all, did you witness this performance when you purchased the boat recently? I suspect that this problem didn't happen overnight. Did the PO also suffer this piss-poor performance? I would question the re-build within 100 hours ... are you just taking their word? When you did your check-out sail did you run the engine under load? What did you find then?

I'll relate my experience and maybe you can relate. Our boat came with a Yanmar 1GM and we were told that it had been re-built in the past but no date or record was provided. It ran fine when we purchased so it wasn't an issue to worry about even though we were also told that the boat was slightly "over-propped". This made sense because we could achieve approx. hull speed (approx. 6.3 knots for 22' waterline) at 2200 rpm. At 2400 rpm we had some black smoke while the boat reached its max speed. At idle, max rpm was 3600 to 3800 rpm. The characteristic that I did notice and fret over to some degree was the way the engine labored to get up to speed. But I also thought the engine was a little underpowered for the boat (5700 lbs approx.)

All in all, I thought no big deal, we hardly use the engine, and when I did give it exercise I would run at 2200 for miles with satisfactory performance. We used the engine that way for about 25 to 50 hours per year from 2004 to 2011 (8 seasons). But at the end of 2011, I noticed the appearance of gray smoke ... since it was cold, I thought it was more like steam, but hindsight now tells me different.

Performance in 2012 sucked. Noticeable gray smoke, rpms and speed dropped off steadily thru the season. It wasn't nearly as bad as yours, but I think it was around 2000 rpms and maybe 5.5 knots top speed and getting worse as gray smoke persisted no matter how many remedies I tried.

I wanted a new engine so I re-powered with a new 2YM15 prior to 2013. I decided to keep the prop (2-blade) and I think it is matched correctly because max rpms under load can exceed 3600 rpm, top speed is close to 7 knots (surprisingly higher than hull speed). She cruises easily at 6.5 knots at 3200 rpm. This is all based on GPS speeds with no current (in a lake). We don't have black smoke at any power-setting. I'm a happy power-boater!

You've provided no information on the nature of your purchase. Hate to say it, but the PO possibly had it over-propped (Don could be very correct in saying it's in the "ballpark" ... it probably is) and the cumulative neglect caused a recent drop-off in performance that could possibly be pretty steep. Maybe the PO said he did a "re-build" when all he really did was try some remedies to get the boat in decent shape to make a sale. If he saw the hand-writing on the wall, it's possible he thought it would be best to get out quick before the solution gets really expensive ... which it might be now.

If I'm way off base on this speculation, I apologize in advance. But your description is very light and it leads to speculation. I would look at all the symptoms (and describe them). Do you have smoke? What color? Black, gray, white? Gray was described as a potential problem with the seals. They fail more readily when the engine is persistently run at low rpms. The injection can also be a part of the problem. I have very little diesel knowledge so I can't speak intelligently about that.

Your engine may be a good candidate for repairs or even a re-build. Get some opinions based on all the symptoms, not just the comments you here about the prop. It might be wrong but I have a hard time believing that it is so dramatically wrong that the PO suffered with this lousy performance for years. It sounds like a problem that you inherited with the boat, not something that suddenly appeared. I doubt that somebody suddenly just put on a ridiculously over-sized prop and expected you not to notice.

Kings Gambit · Apr 17, 2014

Fuel filters too old?

This may sound odd, but the one and only time I experienced a similar problem with my Yanmar (i.e., could not get the engine to full RPMs) I fixed it by changing both fuel filters. The boat had been sitting idle for a number of months, and I suspected some fouling [microbial critters] inside the filters. That was it; nothing else. Also, might try having your fuel polished or swapped out to prevent a re-occurrence.

jibes138 · Apr 17, 2014

I agree with checking your fuel system. A clogged fuel filter will choke off the fuel supply, it may run under no load OK but the minute you load it up it will bog down and possibly stall out due to lack of fuel. Also if you have an electric fuel pump it may have a built in course filter that can be replaced, so check that also, especially if the pump is upstream of your primary fuel filter.

David in Sandusky · Apr 18, 2014

Call a prop shop

If your prop is a Campbell, you could easily be simply over-propped. (A Campbell requires less pitch than a standard design for the same thrust.) Call a prop shop that has experience with Campbell's. They will be able to determine what type of prop you have, and then (Campbell or not) whether it's the right size for your engine. If you are over-pitched, they will be able to address the problem. If not, you have eliminated that issue with quick, free support.

seadaddler · Apr 18, 2014

Mixing Elbo

Have you checked the mixing elbo.

Benny17441 · Apr 18, 2014

One word of advice, never jump to possible solutions before properly diagnosing the problem. First of all check the RPM in neutral like Nick indicates. They will either be normal or low. Normal RPM and acceleration in neutral will point to the drive train but low RPM will point to an engine problem. Most engine problems are fuel related so check the quality of the fuel in the tank, drain the water separator and replace the primary and secondary fuel filters. Bleed the system to remove any air and check for any fuel leaks specially around the pump. Wherever fuel leaks out air can get in. A punctured diaphragm in a fuel pump may prevent adequate fuel flow to sustain high RPM. If the fuel system checks out and the problem persists move to make sure the air intake is clear and the mixing elbow and muffler are not blocked. I believe your exhaust port is above the water line so check that the opening through the hull is not partially blocked by marine or critters growth. At this point if the engine continues to falter then check the valve lash and remove and clean the injectors. Checking compression and governor timing are best left to a professional but you can check crankcase pressure by removing the oil fill cap with the engine running and placing your hand over it. Excessive pressure caused by blow-by compression could indicate worn rings. This is unlikely as you indicate a recent engine rebuild but I have seen jobs less than adequate and unsupported claims of jobs never done. When reading RPM use your ears to gauge what the tachometer is telling you, marine tachometers are famous for going afoul and providing incorrect readings. If the engine checks out and is running strong in neutral then move on to the transmission, the best indicator about its health is the condition of the fluid, it should not have changed color, be clean and free of metal shavings. A slipping clutch would leave tell tale signs in the oil. Check the shaft for any undue vibrations and listen at the stern of the boat for any grinding noises. Finally you get to the prop and check that it is firmly attached with the holding nut and key firmly in place. I don't see the boat being over propped with the prop you indicate but verify the numbers stamped on it. Hopefully this will give you ideas on where to get started and don't take anything you have not verified for granted. Good Luck.

Scott T-Bird · Apr 18, 2014

Benny gave a great summary. I second his recommendation to check for blow-by. That will be an indicator if the engine was truly re-built or not. When I checked mine during my troubles, blow-by was VERY noticeable (if you have blow-by, you will feel sharp bursts of air as you hold your hand over the oil fill). It led me to believe that worn rings were the problem - which can result from being over-propped for a long period. But being moderately over-propped for a very short duration (as you indicate) isn't going to wear your rings that quickly. I have a hard time believing that the prop installation could have been so extremely off that the performance is as bad as you describe. The slow speed is a good indication that it isn't merely a problem with the tach reading incorrectly. Your speed is extremely slow and power is way off, so the rpm's are definitely way too low.

I also agree with the folks who say to check the filters first. Like Benny says, fuel problems are most often the culprit. Hopefully, that is your case, and an easy fix.

centerline · Apr 18, 2014

it is definitely over propped....on a 12hp engine, a 13x17 prop grabs too much water to allow it to be spun at the speed the engine needs to turn at... the thing to remember is its only a 12 horsepower engine, not a 25hp....
its a three blade prop you have. even a 2blade of that dia and pitch would be a bit much for your HP rating. that 3 blade prop is way more suited for use on a 24-30 than it is on a 12....

all things being equal, as a prop gets bigger in diameter, the pitch can go down in size because the tips are turning faster thru the water with less slip and in turn, propelling you just as fast....
but as you increase in diameter or pitch, you need the power to be able to overcome the additional leverage/force factor to allow the engine to rev up....
that prop is simply pushing too much water for the HP and as you try to turn it faster to get your RPM's up, it is trying to push even more.
too much prop is like lugging your truck around in too high of a gear with a load on....it physically cannot rev up and wont, no matter how much fuel you give it, or how well tuned it is, and its extremely hard on the engine.

but there is a balance where it will turn and move the boat along without stressing the engine, as it takes less HP to turn the prop slow.... but you just done have the power in the engine with it being mated to that prop to run either the engine, the prop or the boat to their respective potentials... individually or collectively. with the correct prop all three will come together nicely at the correct rpm for the motor.

as for the number of blades, adding more blades only decrease the amount of slip it has in the water, as does the width of the blades. not enough slip and you can experience a "lack of power" from on otherwise properly sized prop... too much slip and you will not be able to utilize all the power you have available....

sizing a prop is a science on a race boat, but a bit of understanding and experience will get us to where you need to go on slow boats like ours. Good Luck!

tcwaltz · Apr 18, 2014

I just recently put a Campbell sailor on my oday 28. I have Yanmar 2Gm20f. 13x7 cupped. We ordered one for someone else in the marina with a 2gm. His was also a 13x7 with light cupping. Performance is great on both boats. Sounds like to much prop but also agree you need to check out fuel filters as well. Ive had occasions when I first got the boat were performance went south due to clogging filters. Fortunately also have an electric fuel pump I can use to help get by until I can get to shore and change a filter

Steve Dion · Apr 18, 2014

I would not compare a Campbell Sailor to any other prop for sizing. They are really completely different.

The Campbell is an excellent alternative to the standard OEM props.