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Old 12-15-2015, 03:59 PM   #1
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Mainship 30 Pilot prop size.

I am hoping someone can help me resolve this issue. I purchased a 2000 Pilot 30 this spring. It has a 5.9 Cummins rated at 230 hp. Flat out I can only turn 2200 rpm as indicated on the tach with a top speed of about 15 knots. reading the engine specs I should be turning 2800 rpm wide open. I have been waiting to pull the boat for the winter to check the prop size. I expected it to be over propped. I knew the prop had been changed once and the original prop was given to me in the sale. The original prop is a 22x27 so I expected to find the installed prop to have a much higher pitch. What I found after calling Michigan propeller with the part number is that the installed prop is the same pitch as the original.
Are there other owners of a pilot 30 with a 230 hp Cummins in this group that can tell me what prop size they are running and what rpms they are turning at WOT at what speed?
If this was the original prop size I am at a loss as to why I can't achieve 2800 rpm. I have changed the primary and secondary fuel filters. The engine seems to run strong with no excessive smoke. This has been the same since I put the boat in the water with a clean hull. I purchased a handheld laser tach but never got a chance to use it to validate the installed tach reading. That will have to wait until spring.

Any help would be appreciated


Mike
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Old 12-15-2015, 04:58 PM   #2
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Mike:


Glad you made it over here. I think you will like it. So on to your problem:


First I suspect that very few Pilot 30s were delivered with that engine. Most were Yanmar 240s and 315s. So that in itself makes me suspicious. Maybe Mainship put the same prop on your boat that they would put on the Yanmar 315 and with less hp you can't achieve your rated rpm.


But there is absolutely nothing wrong with that engine in general. It is a great, bullet proof marine engine.


Secondly any discussion of rpm needs to be real rpm. Beg, borrow or buy (about $50 on Amazon) a phototach and check it. Dash tachs can be a couple of hundred rpm off.


But you are offa lot . You said 2,800 rpm but I am pretty sure that engine is rated for 2,600 rpm, but nothing wrong with propping a hundred or more higher. But your engine clearly isn't getting up to speed.


The first thing to look at is the bottom, prop and any excessive weight you have added. Any of these will drop rpms.


Then if those are ok then either the prop has too much pitch and won't let the engine rev or the engine isn't putting out the power it was designed for. So let's look at the latter.


You say you are not seeing significant black smoke. That is also an indication of the engine not getting enough fuel. The other thing that can affect power is not enough air, but with no black smoke that isn't likely.


The most common reason for an engine to run fine but not produce the power it should is that the throttle isn't opening all of the way. You would be surprised at how often this happens. So with the engine off, open the throttle all of the way and go down in the engine room and look at the throttle stop. It needs to be up hard against its stop. If not adjust the linkage and that might just solve your problem.


The other fuel issue is a restriction. The engine can get enough fuel at lower rpms but at some point the restriction just won't pass enough fuel. You have changed the filters though. So for this to be a problem it would have to be the fuel pump or a restriction in the pickup line to the top of the tank. I don't have a good test for the fuel pump. You can disconnect the fuel line back to the tank and blow back until you hear bubbles which should clear that line.


I am going to skip all of the things that can reduce power due to too much fuel or not enough air. If you don't have black smoke at wot then you probably don't have a fuel problem.


So after checking for all of these things you are convinced that the engine is putting out all it was designed to put out, the final solution is a flatter pitch prop and since you typically can not make more than a 200 rpm change with an existing prop it probably means a new prop.


And FWIW the gurus on boatdiesel (a great forum for marine diesel owners) tend to jump into a prop change first. But I believe in checking that the engine is doing all it can first.


But you can get some first class help there. After checking the couple of things mentioned above and you still haven't found the problem, consider posting to boatdiesel.


Good luck, David
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Old 12-16-2015, 01:30 AM   #3
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I know what Tony would say....phototach it....and go from there. You absolutely have to know if your tach is correct. If it is, I would go straight to repitching the prop. But Like David said, you are pretty far off. So maybe take his advice. But 27 on the pitch is a LOT My boat has the 6BTA 330B and it came stock with a 23x27. So a Very similar prop with SIGNIFICANTLY more power and load(24k pounds....but 2 engines). So I do think you might be significantly over propped. BTW, my current props are 23x24 as I stepped down. I get 3050rpms on a 2800rpm engine. While my equipment does not really matter much...I think it is relevant since the prop size is so close...and your engine is much less powerful... I would consider 22x23 or 22x22. But talk to a prop shop and give him all of your parameters. They should be able to help you out. My pilot 30 had a 240hp Yanmar and a 5 blade prop so I do not think it would be relevant...and even if it was, I do not remember the dimesions.
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Old 12-16-2015, 02:38 AM   #4
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Your boat is very likely overpropped.
When you get around to the phototach thing, the first number you want to check is WOT rpm in neutral, then WOT rpm in forward gear.
Ideally, these numbers will be at least 100 rpm above specified revs, with very little difference between in and out of gear.
The red line specification should be printed on the tag located on the timing cover just forward of the fuel injection pump.
If it fails this test, post the numbers you get, and we can move forward from there to help you identify the problem.
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Old 12-16-2015, 07:34 AM   #5
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What RPM is the boat cruised at?

If you are wide open all the time , up on the plane or towing water skiers , after a real RPM check , you might want to resize.

If like most you put along at a K under "hull speed" to avoid the fuel burn and noise your prop may be excellent.

The first thing after splashing in the spring and doing a couple of hours would be to use a proper tach and discover the WOT RPM out of gear.

Then go back out and see the WOT in gear.

Then run at your normal cruise RPM, and note how many RPM down from max you are actually .

Post the results , and your speed desires.
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Old 12-16-2015, 09:50 AM   #6
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Tach bench test

Does anyone know of a way to bench test the tach to check accuracy?
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Old 12-16-2015, 09:56 AM   #7
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Not clear what is the problem you are trying to fix..... do you want to go faster ?
i have 2 x 300hp Cummins engines and 31 ft boat so maybe something similar ?? but no point comparing propeller sizes and engine rpm without knowing propeller rpm ??(transmission ratio).
are you single engine or twin ?
if you dont have any significant smoke you are not load limited so should not be looking at the propeller. at this point.
do your engine(s) have mechanical or electronic fuel control?
I am assuming you have "mechanical"
you must get a proper tach to get anywhere with this, cant go off the panel dials.
with a proper tach what is your max rpm when in neutral ?
at that point is the speed control arm on the governor, (the thing that the cable is connected to) pushing hard against the max speed adjusting screw ? if it is not then fix whatever is wrong with the cable.
what are the hp & rpm details from the plate on the engine ?
you should adjust the max speed adjusting screw to give around 250 rpm (in neutral) more than the rated full load speed from the data plate.
then sea trial again with your normal full loaded condition, fuel & water tanks as full as you will normally have them, clean bottom and clean prop rudders etc, this is very important. report back full speed rpm, exhaust condition, ship speed, weather / sea condition and i can tell you what is the next step.
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Old 12-16-2015, 09:58 AM   #8
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My two pennies worth is to take an old fashioned pen and paper, go down in the engine room and get the détails off the gearbox makers plate, then count how many bearings between the gearbox and stern gland.


Go to boat builders site and determine the hull shape.
With that information go to www.vicprop.com and calculate your optimum prop size.
Job done, no drama.
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Old 12-16-2015, 09:59 AM   #9
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best way to check the tach is on the engine.
photo tach speed versus dial speed throughout the rev range written in your note book is very useful for the future
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Old 12-16-2015, 10:19 AM   #10
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Mike:


Photo tachs have gotten so cheap, every boater should have one to check his dash tachs with. Or buy one and share it with your friends. Here is a list from Amazon, most under $20: Amazon.com: photo tachometer


When you get it, most come with white tape strips that you place on your engine's flywheel. Then start the engine and run the dash tach up to a steady 2,500 rpm and measure the real rpm with the phototach by pointing it at the white strip.


Some dash tachs, such as Farias that Mainship used on many of their boats, are adjustable. Use an allen wrench or small screwdriver (can't remember which) in the back hole to adjust it to match the phototach reading. If it is not adjustable, make a note of the difference and apply it for further discussion.


As others have noted above, and I neglected to mention it, seeing if your engine will reach about 200 rpm over rated which in your case is 2,600 + 200 in neutral at the dock is a first step once you have a correct tach reading. Then move on to the other tests if it makes that rpm. If not the throttle is not hitting the stop in all likelihood.


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Old 12-16-2015, 10:26 AM   #11
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Quote:
Originally Posted by djmarchand View Post
Mike:


Photo tachs have gotten so cheap, every boater should have one to check his dash tachs with. Or buy one and share it with your friends. Here is a list from Amazon, most under $20: Amazon.com: photo tachometer

Thanks David...I had no idea they were that affordable now.
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Old 12-16-2015, 12:03 PM   #12
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Originally Posted by stone beach View Post
if you dont have any significant smoke you are not load limited so should not be looking at the propeller. at this point.
I would be very cautious of this statement. It may be out of context just sitting there all by itself. I may have misunderstood. But just because your engines are not producing black smoke does not mean they are not overloaded. I know a lot of negatives there. To put it another way, your engines can be overloaded(by improper prop pitch) without producing black smoke. They will be "happy" to do that while providing you almost "euphoric" performance...but they are slowly dying on the inside. Prop overloading is the number 1 killer of Cummins engines....or any highly boosted engine. And it is not because peole are driving around with black smoke pouring out of their exhaust pipes. Now this particular engine is not as heavily "squeezed" as the higher powered aftercooled versions so maybe overloading is not as big of a deal. But if you want to cruise that boat up on plane and the prop is overpitched, you are doing damage to your engine....PERIOD!!!!...regardless of what the smoke is doing. The heat being generated over time(they usually die around 1200-1500 hours) will destroy your engine. If you are completely ignorant, you will notice nothing until the day they die.

Having an overpropped boat is kind of like dragging anchor. Nobody wants to admit that is what the problem is. I don't know how many people I have told they were dragging as they go by me at 1.5 knots and swearing they are not dragging....same goes for overproppers. They always go chasing something down some other rabbit hole. Everyone on this thread has provided you many rabbit holes. And all their points are very valid and something to look into. But checking your neutral RPMs at the stop would be a good start....if it makes it to the fuel cutoff, then you are likely overpropped. ANd it is something that needs to be dealt with BEFORE YOU DO ANYTHING ELSE!!!
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Old 12-16-2015, 02:18 PM   #13
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Baker's points are quite valid. If Mike's tach is anywhere correct, he is between 4-500 rpm overpropped and that is huge. Maybe Mainship made a big mistake and installed the wrong prop at the factory. Or maybe the PO replaced it with a very different prop. Who knows.


That engine should smoke like a chimney at wot with that much over pitch if that is what it is. If it doesn't then that is a strong indication that it isn't getting enough fuel, enough of an indication to do some diagnostics before jumping into a new prop which might mean that he will be stuck with much less than the rated 220 hp.


Do some basic checks like wot neutral rpm and the throttle hitting the stop. Then make sure that the fuel line is clear all of the way back to the tank. Maybe even replace the fuel pump. They aren't that expensive.


He can also follow the low air path as well down its "rabbit hole". A boost gauge which can be purchased for about $15, temporarily hooked to the intake manifold will tell that story. Post on boatdiesel to get the wot boost spec. This gauge should work- http://www.amazon.com/Glycerin-Fille...pressure+gauge


If he does all of the above and that doesn't fix it, then I agree it is probably time for a prop with about 4" less pitch. But do the simple stuff first and maybe he can get back his performance without replacing the prop.


But as Baker notes, you are harming the engine if you run it anywhere near 2,200 rpm if it really is over propped.


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Old 12-16-2015, 09:57 PM   #14
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New information

So based on some feedback from members I did some additional research. I found that some of my basic assumptions were incorrect. I signed up to the Boat Diesel site and got the actual engine specs. The engine curve indicates a max RPM of 2500 at 180 hp. That's quite a bit different than what I had for data. I also went to a few different prop calculators and then called Michigan Propeller. Based on the original data I gave them, which I got from data handwritten into the manuals I received from the previous owner, they told me the prop I have on the boat (22x27) is correct. So that's how the previous owner came up with that prop which he purchased from them several years ago. Over the summer I brought the spare prop (which was the original installed on the boat) to a prop shop to have it checked out. The original was a 22 inch prop and stamped 27 pitch. The prop shop measured it out and told me it was closer to a 26 pitch. So I think if I put the original prop back on the boat in the spring it should get me closer to the 2500 RPM max value for this engine.
I will also find a way to bench test the tach over the winter or send it to VDO for calibration. The hour meter stopped working (built into the tach) so I will ask them to do a repair.
Thanks for the help thus far, very appreciated.
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Old 12-17-2015, 06:33 AM   #15
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Only a tach that is driven by an impulse counter which is mechanically driven , or a tach that is cable driven can perhaps be made somewhat accurate.

Most that are alt driven are no where near accurate.

Alt temp,alt load , belt age and load , pulley temperature all vary , as will the tach reading.

Best you can do with one of these is to use a photo tach at normal cruise and set the electric toy to match it.
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Old 12-17-2015, 10:06 AM   #16
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Mike:


Now that you are a boatdiesel member, post your CPL number and ask for the horsepower and rpm rating.


Cummins engines (and many others) are rated at various rpms to meet commercial vs recreational use. Your engine may be rated for 180 hp at 2,500 rpm but may also make 220 hp at 2,600 rpm. Also Cummins used two rating systems. One will give 210 hp and another will give 220 hp for the same engine, due to fuel temp I think.


The CPL number will tell the story.


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Old 12-17-2015, 11:36 AM   #17
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Stupid question

Where do I find the CPL number?
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Old 12-17-2015, 11:56 AM   #18
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Mike:


There should be a data plate, near the injection pump I think. It will give the CPL, horsepower rating, etc.


If Ski is following this thread he can give you more specifics as he knows these engines well.


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Old 12-17-2015, 12:24 PM   #19
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I found spray painting the flywheel with flat black paint, then add the shiny sticker, helps the phototach get a consistent reading. Pretty easy when the engine is warm and running to hit it with a rattle-can. Dries fast too.
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Old 12-17-2015, 02:39 PM   #20
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Originally Posted by Capt Mike View Post
So based on some feedback from members I did some additional research. I found that some of my basic assumptions were incorrect. I signed up to the Boat Diesel site and got the actual engine specs. The engine curve indicates a max RPM of 2500 at 180 hp. That's quite a bit different than what I had for data. I also went to a few different prop calculators and then called Michigan Propeller. Based on the original data I gave them, which I got from data handwritten into the manuals I received from the previous owner, they told me the prop I have on the boat (22x27) is correct. So that's how the previous owner came up with that prop which he purchased from them several years ago. Over the summer I brought the spare prop (which was the original installed on the boat) to a prop shop to have it checked out. The original was a 22 inch prop and stamped 27 pitch. The prop shop measured it out and told me it was closer to a 26 pitch. So I think if I put the original prop back on the boat in the spring it should get me closer to the 2500 RPM max value for this engine.
I will also find a way to bench test the tach over the winter or send it to VDO for calibration. The hour meter stopped working (built into the tach) so I will ask them to do a repair.
Thanks for the help thus far, very appreciated.
Mike, not to beleaguer the point, but it is incredibly inexpensive to acquire a phototach and incredibly easy to use it. Even if a shop does calibrate it, I would still only believe a phototach. It is a REAL number. There is absolutely no question what it is reading.
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