Prop, Tach or Engine?

[Richman]

I have a problem that maybe you all can help me with. Here is what I can tell you:

o 23ft. walkaround listed at 2700lbs dry and about 4000lbs w/engine,fuel,gear and me.
o Bottom is not painted, and there are no trim tabs
o Engine is a 1998 200hp Johnson with a 14.5 x 19p, 3 blade aluminum, 1:86 ratio
o WOT is 4300 rpms, yes 4300, speed is 37mph on GPS
o Engine runs very well, or at least sounds like it does
o Boat planes easily although I don't recall at what rpm or speed
o Tach is set to position "6"

I removed the prop recently and found the thrust washer cracked in two. Motor had not vibrated to any degree though. I purchased a 15 x 17p prop but that will only give me about 300-400 rpms. Any thoughts would help on how to get this engine in its optimal range of 5600-5800 rpms. Thanks to all.

 

[steelespike]

Re: Prop, Tach or Engine?

Do a compression check.Be sure throttle opens all the way.Be sure it is in proper tune.Fine tune the height.A good starting point is the antivent plate(just above the prop)approximately even with the bottom of the boat. raise it a hole at a time until just before venting becomes a problem.Be sure it pumps water. adjust trim carefully for best rpm and speed.Once you have all this set you may be able to fiddle with the prop for a little more height, rpm and speed.

 

[Richman]

Re: Prop, Tach or Engine?

Thanks Steelespike,

The antivent plate is level with the bottom of the V on the hull. Compression is 95-100 on all cylinders. Plugs came out after 10 hours of use looking normal; blackened but not fouled. I have only owned the boat for one year and it always has run like this. It sounds liek it's running fine but I am worried that if the engine is really turning only 4300 rpms, it's shortening its useful lifespan by laboring too much.

I will check throttle plates once the weather breaks a little and I can get it in the water. Any other thoughts folks? Is it possible the tachometer is just faulty?

 

[walleyehed]

Re: Prop, Tach or Engine?

All instruments appear to be correct, showing a slip ratio of 13% calculated.
I can tell you up-front, 19P is way over-propped for that rig, and after engine weight, you have 900lbs of fuel and gear??
First place to start is raising the engine a hole and test....you should be able to raise to third hole with no water pressure issues, and you could possibly expect 150-250 more with the engine raise, but that ain't gonna catch it....
Your '98 200 has a bit more punch than my older 200, but I'm on a 2400lb total weight 18ft aluminum deep-V. I operate between 3000-4000ft above sea-level and it costs ya about 1" of pitch for every 1500ft up, and at 3600ft, I can only hit 6K plus a few with a 17P (with a jackplate and low-water pick-up), so at sea-level, my best-use prop is a 20P Raker worked to have a bit more cup-"just slightly" more.
200 is not much engine for a 4000lb.+ boat, and I would "expect" to see a 15P in use there, but it still will need to come up(the engine).
I would follow the above advice and make sure the throttle plates are at 90 degs with full throttle-ENGINE OFF. Compression looks great at 95-100...I just hope the 4300RPM has not damaged the engine any...the comp check says it's good, but the plugs may show the results of low RPM lugging being black.
I would have a competent tech set the timing, or check to see it's not retarded.
Your fuel line is 3/8", right?
Last but not least, run good quality 87 octane and a good TC-W3 oil.

 

[dcg9381]

Re: Prop, Tach or Engine?

I'd use an inductive tach. Most tachs are designed to be generic and have to be dialed in to be accurate.

I don't know what to tell you in regard to the thrust washer.

I'd do some calculations of prop slip. You want to get down near 10%.

Post mph, rpm, prop slip, and prop pitch.

Your boat sounds heavy and pretty over propped to me also. I've got a 23 foot boat, about the same weight - 4000lbs. 385 hp. It came with a 23P prop, but slightly smaller diameter than what you're running.

 

[Richman]

Re: Prop, Tach or Engine?

Thanks to all - I think I will have a mechanic just give it a tune up, check the throttle plates and lift the engine a hole and see how it shakes out. I will try the 17p prop.

My weight calculations are as such:
2700lb boat + me @200 lbs + 678lbs of gas (113gal) + 300lb motor + 100 lbs gear = @4000. Or does the listed dry weight usually include the motor? Max rated horsepwoer is 230 so I am not convinced it is underpowered by any great amount.

Not to derail my own thread but what harm would there be if a motor never was run at WOT? I guess the answer is it would depend on if it was laboring and not able to achieve optimal rpm as compared to a motor that was not laboring. Correct?

Anyway, I am looking forward to more rpms and a bit more top end. Thanks

 

[Silvertip]

Re: Prop, Tach or Engine?

You underestimated engine weight by about 100 pounds.

 

[QC]

Re: Prop, Tach or Engine?

Not to derail my own thread but what harm would there be if a motor never was run at WOT? I guess the answer is it would depend on if it was laboring and not able to achieve optimal rpm as compared to a motor that was not laboring. Correct?

If it will not reach recommended WOT RPM range at WOT then it IS "laboring" . . .

In other words, you can run all day, every day for the rest of the engine's life at less than WOT, that's good. However, if it didn't get to WOT RPM range when run at WOT at least once, then it could be over or under propped and not good at your cruise RPM that you have ended up at . . . The WOT test ensures that you are propped right for most, if not all, operating conditions

 

[Richman]

Re: Prop, Tach or Engine?

QC - what if an engine (mine) was not reaching optimal rpm range at WOT because the throttle plates were not opening fully? In other words, I never "floored" the accelerator. Would that be as bad as an engine that had lugged all its life due to propping or other issues?

 

[QC]

Re: Prop, Tach or Engine?

No. Same as running part throttle which you would be if it was right and you backed off a little to cruise . . . Throttle opening percent roughly equals percent of available horsepower . . .

Plus, don't let this make you crazy. Once it's right you'll never know if the motor's life has been shortened, lengthened, or not affected. You just won't . . .