Hatteras 43C 1983 high performance

[giuseppe]

Dear friends the problem of my boat is that at full power the engines only reaches 2.000 rpm.I have 2 6v-92tac-2 high performance 500 shp?,allison marine gear 1.5:1,props 26x28 3 blades.I have checked the cilinder compression and they are ok.Do you have some suggestions.
Many thanks

[Genesis]

Any smoke at that 2000 RPM?

In order, check the following:

0. How clean is the bottom, including running gear? This is the obvious first start.

1. No-load RPM. If they don't turn up no-load to 2500 RPM, you will run into the governor. If you have no smoke at that 2000 RPM, this is a good bet. Note that you need the engines good and warm to do this test.

2. Airbox and airhorn pressures at idle, 1500 RPM, 1800 RPM, and WOT. Report back with them. You need BOTH airhorn (post-turbo) and airbox (post-BLOWER) pressures.

3. If neither of these shows a good cause, then you start with a full tune-up and injector short-out test.

DO NOT run the boat for significant amounts of time with this problem, if you are truly overloaded you could easily trash the engines.

I have these motors in my 45C, and know quite a bit about them.

BTW, 26x28 is a bit aggressive with that setup. My wheels are 26x26. You may need to have them repitched. It is important that you can reach 2300 RPM in gear and fully loaded, 2350 is better.

[George]

Agreed with Genesis, proping could well be the case, however how long have you run this gear and did it perform before? Another consideration that came to mind is a fuel restriction. I'll assume you change your filters on a regular basis, and all things remaining the same when you look at two engines performing exactly the same, I think fuel blockage. I recomend putting guages on your fuel system to measure if your getting a restriction. Also, disconnect your throttle cable from your govener, and manually raise your throttle to determine your WOT no load, reconnect your cable and make certain you get the same amount of travel and RPM. Lastly, have you checked your shaft RPM and does that coincide with your tach.?
You can either borrow or rent a strobe which will give you actual shaft RPM, simple to do. Set up with your partner a prearranged agreement to set the rpm at specific rpm's for a specific time and record actual vs. tach. This takes about 10 minutes per engine and be sure to check both.
Lastly, I think I said that allready, if one prop is out, that will put a load on the other engine and make it appear that they are both failing. If you have scuba, again easy to do a simple check. Get a 3' heavy thick aluminum strip and attach to your strut with a bar clamp at the closest distance to the prop blade so that the alum. strip barely touches, spin the prop and make sure all blades touch at the same point. Mark "Score" the aluminum bar so you can reposition it on the other strut equal or close to it's original position on strut #1. again, spin the prop and make sure all blades touch in the same way. That test can tell you alot about the health of your running gear.

[giuseppe]

Thanks for your answer.Yes i have some dark smoke at 2.000 rpm.The engine no load rpm is 2.500

[giuseppe]

thanks george

[Genesis]

You're overloaded.

Did the boat EVER turn up to full RPM?

26x28 is aggressive for that boat. I have a 1985 45C, which is the same boat basically, with the same engines. Roughly the same weight, etc.

I also have the original build sheets from Hatteras on the hull. It specifies 26x28, Michigan Wheel, 3 blade props.

I have those wheels, and a set of spares. Mine were repitched to 26x26, and that's as far as I'd ever want to go. I can just get to full RPM loaded. 26x28 would leave me about 200-300 rpm short, which is about where you are!

Since you have smoke, you are either overloaded OR you have an airflow problem. Black smoke = not enough air for the fuel being injected.

Thus, your first job is to verify the no-load speeds (you need a photo tach - DO NOT trust the bridge tachs!) and once you know the governor is happy, you need airbox and airhorn pressures at 1500, 1800 and full throttle. Note that when checking no-load you do it with the throttle linkage disconnected and your HAND on the throttle lever, so you can verify that it goes all the way to the stop. When you reconnect it you then verify that it goes all the way to the stop when you select full throttle at the bridge, and if not, you fix that too. You also need a fuel restriction gauge in the suction side of the fuel system AFTER all Racors but BEFORE the fuel pump - I want to know what your maximum vacuum reading is at full power, and whether the needle is jumping around at all (and if so, how much) or if the reading is stable.

With all these numbers I can give you a good idea where to start looking. Until you know if the engine is producing the right amount of boost, if the aftercooler is clear, and the fuel flow is ok you're guessing. You may just be overpropped, but you may also have a problem such as a bad turbo or fouled intercooler and without knowing what's going on you're going to spend a lot of time and money chasing this demon.

Let's not guess and instead diagnose.

[giuseppe]

Genesis,i don know if the boat ever reached full rpm because i just bought it.Speaking with the owner he told me the boat neve r reached the prescribed rpm but he also was not the first owner...I can give you some more data because i made some checking before i bought it:
eng sx: rpm no gear 2555;rpm max whit gear 1982;exaust gas temperature turbo sx 356 ° c turbo dx 349° c,cilinder compression left side 500,right side 500.
engine dx: rpm no gear 2548,rpm max whit gear 1950,exaust gas temperature turbo sx 276°c turbo dx 286°c,cilinder compression left side 480 right side 480.
What you think?
regards.

[Genesis]

Compression is good, but it won't be for long if you don't take care of this!

I still want those airbox and airhorn pressures, along with the fuel vacuum number. Before you repitch the props (which is what I think you're gonna have to do) you first must know that the engines are producing the correct amount of boost and getting fuel.

You are dangerously overloaded and if you continue to run the boat this way you WILL damage the engines.

This needs immediate attention.

[giuseppe]

Dear Genesis,actually my boat is on the ground and i will going to put back into sea next month so if you agree i think to change the wheels and once in the water proceed to the check you suggest me.

[Genesis]

If you're on the hard now, I'd repitch the props to 26x26.

That isn't terribly expensive to do. Just be aware that if the engines turn out to have a problem that you can correct (and need to), once you do then you'll be underwheeled and will have given up a couple of knots of speed. The good news though is that you'll have bought yourself a bunch of extra engine life doing it in that case.....

The boost numbers and such still need to be taken; aftercooler plugging is a major problem on these engines, and it needs to be monitored on a somewhat-regular basis.