Prop Selection/engine Performance

[JCG]

I have a 1975 Hatteras Sports Fisher, 46 ft powered by the original 871 TI detroit engines. Does any body know the original prop diameters and pitch for this configuration?
I have a problem with both engines loading up and blowing black smoke and only turning about 1800 rpm with throttles wide open. Some of you may remember my post about this problem. Originally about 1500 rpms was all I could obtain. I cleaned the intercoolers and cleaned props/bottom and got about 1950 rpms WOT with everything clean underneath, this was such an improvement I thought the problem was fixed but now I think rpms with a clean bottom should have been somewhat higher.
Will be pulling the boat this weekend and wanted to check props....... need to have a good idea of what the boat is really capable of doing with these engines and expected rpms if boat is propped correctly.
Talked to a local diesel mechanic and he thinks it's over proped.

 

[Sonny]

maybe just maybe your engines are just worn out and tired. detroits are legendary for running way beyond the call of duty and still running faithfully. i've seen them run with bent rods, completely absent valves, soft rings etc. point is despite their pedigree they do not maintain rated output indefinitely. they will slowly die. you have a sportfish which probably means the engines were run at the high end of their rating for most of the time on the hour meter.
cleaning intercoolers will not change available rpm, it will only change how long certain loaded rpm is available, but clean coolers are where any sort of engine tuning begins

 

[saltshaker]

You should be able to reach 2300 rpm at full load, 2500 rpm no load. 1950 is way too low. If the engines check out OK, then you either have a lot of excess weight, wrong props or both. What gears and what props do you have. I have 28x28 4 blades on my 46C but my engine package is different. I believe you should have 28x32 4 blades if you have 2:1 Allisons behind the 8V71TI's. You should be able to cruise 19-20kts@2100 rpm and 23-24Kts WOT@2300.

 

[aquacraig@shaw.ca]

JCG, I am not an expert but know that 8V71's should run WOT in neutral at about 2100-2200 rpm. Thet should also heat up to around 180F. If not, then you start looking at all the bits and pieces till they go. Overloading with props should not cause all that black smoke...unburned diesel.

Craig

 

[stormchaser]

You should be able to reach 2300 rpm at full load, 2500 rpm no load.

??? My 8v71TIs run up to 2200 and I'm fairly certain all is good. That's the spec in the manual.

 

[Avenger]

Craig, overloading most certainly will cause black smoke. Who told you otherwise?

 

[REBrueckner]

JCG... Sonny posts one possibility....plain old wear, but there are a lot of other possibilities...perhaps a common cause to a common symptom....have you changed fuel since this has been experienced??

So both engines are doing this....Have the engines been tuned up...properly? Are the engines missing? Have you checked exhaust manifold temps from each cylinder to assure combustion in each? (equal temps from each exhaust port).... I don't recall what checks may have already been done...Are you sure your manual engine shut offs are in the full open position (to admit intake air)??

Now, no one here will likely believe this: and I do not understand it to this day myself, but I noticed a prior log book entry when I was aboard my own boat last week....an entry I made about two years ago: "stb engine smoking black and running rough except at idle!!! vacuum (on fuel filters) normal"....this was a few miles from Nantucket Harbor on a calm day....so I proceeded at idle speed, anchored, and CHANGED both port and starboard fuel filters...never expecting THAT to solve my problem...but it did????

...all was normal after that and I did NOT drain the RACORS;the filters were NOT as dirty as usual at the end of a season.... likely the filters had only 40 to 50 hours on them....

So if you are using 2 micron fuel filters, take them out and try 10 or 20 micron filters....it's a long shot, I know, but it's cheap and then you'll know your fuel filters have been eliminated as an issue...but if your engines are running smooth, no miss, that's a different symptom than I have described here.

Also maybe someone can post a way to check if turbos are actually working... I don't know how to tell but a lack of intake air at higher RPM could sure cause your posted symptoms...would a failed turbo on each engine cause JCG's symptoms?? Seems possible....

At what RPM do you begin to notice black smoke?? The more details you provide on what you observe the better engine analysis experts can provide
Do you get about 2500 no load RPM without smoke;........if you get smoke under load at say, 1200 RPM and on up, that's not a prop loading issue....but if smoke only occurs at say 1800 RPM and up, it could be. So far, we who are reading your symptoms are pretty much in the dark....we are guessing....
tell us what else you know....

My 1972 48 YF was originally propped according to my Hatteras papers with 28 x 32 four blade props behind Allison 2:1 and 425 SHP 8V71TI's with N 90 injectors. My boat is about 13% heaver than a 45 sportfish according to my early 1970's Hatteras brochure. My boat was clocked at about 22.3 knots by Hatteras when first sea trialed. She is overpropped now and top RPM is about 2150 RPM and just over 20 kts but I never run anywhere near that.

I also believed no load throttle was about 2500 RPM on these engines...but I have no specific reference material for that; I have never heard of no load RPM spec less than full load spec....

 

[saltshaker]

??? My 8v71TIs run up to 2200 and I'm fairly certain all is good. That's the spec in the manual.

Unless you have commercial rated engines, I believe 2300 RPM is full load RPM. If you can't make that then you are overloading your engines.
http://goldcoastpower.com/brochures/DD 8V-71N&TI LOW PROFILE Brochure 1.jpg

 

[stormchaser]

Hummm...will have to double check when I go out next...maybe I am mistaken.

 

[saltshaker]

Dave,
I added a link to an 8V71 brochure. zoom in at the bottom right and you'll see max rated full load rpm is 2300.
http://goldcoastpower.com/brochures/DD 8V-71N&TI LOW PROFILE Brochure 1.jpg

 

[REBrueckner]

All the older 71 series recreational (pleasure craft) engines are rated at 2300 WOT....naturals and turbos....exception is the newer high HP conversion like 485HP 671TI's rated at 2500 WOT...

Workboat and crew boat engines have smaller injectors, lower rated RPM's and lower rated HP...

 

[JCG]

CRANKED THE BOAT THIS WEEKEND AND PUT HER ON THE HILL. DID THE WOT THROTTLE TEST AND GOT 2500 RPM WITH NO SMOKE. ACTUALLY HAD A DIESEL MECHANIC LISTEN TO THEM HE SAID THEY SOUND FINE NO MISSING ETC,. PROPS ARE 28 X 34 .

THE ENGINES RUN FINE UP TO ABOUT 1400 RPM WHERE THEY BEGIN TO BLOW BLACK SMOKE. tHEY WILL RUN UP TO ABOUT 1800 OR SO WITH SMOKE GETTING PROGRESSIVELY WORSE. SHOULD BE 2300 RPM ANY IDEAS?

 

[stormchaser]

over-propped.

 

[saltshaker]

Do you have 3 or 4 blade props? Any excess weight in the boat, has she been in or out of the water? Bottom and running gear clean and in good shape. Call Hatteras. They should be able to tell you what props came with your boat. If you have the original props on, then you should send them out to verify they are as stamped. Sounds like you are way over propped. Not sure you could take enough pitch out to get you were you need to be. Do you have spares that you could try?

 

[REBrueckner]

Storm MAY be right about overpropping, but I don't buy it....not with smoke present at only 1400 RPM....specs show only about 100 HP at 1400 RPM....my engines LOAF at 1500 RPM just getting turbo exhaust temps to proper operating levels..

This started with both engines at the same time? : my guess, a common problem: bad fuel? dirty bottom? lack of air in engine room??... if this started suddenly, my bet is FUEL..

the history of this problem will give the answer...DID you replace your fuel filters?????

I know you implied the bottom was clean, but did you SEE it yourself, or rely on a diver who SAID he had cleaned it...two very DIFFERENT situations..

good luck....

 

[saltshaker]

Rob,
If I remember correctly, his previous thread stated that he has never seen this boat reach rated RPM. Only hit 1500 RPMs when purchased. If this is correct, he needs to check that he has the right props. Fuel could very well be the problem, but I think he has had this problem for a long time.

 

[JCG]

Let Me Try To Clear Up The History As Well As Give You Better Details.

The Boat Is A 1975 Hatteras 46 Sport Fisher (displacement 46000 Lbs) With Detroit 871 Ti Engines Coupled To Allison M20c Transmissions With 28 X 34 - 4 Blade Props.

The Boat Was Formerly Used As A Charter Boat For Snapper Fishing Out Of Destin Fl. The Boat Was Damaged In Ivan, Primarily Cosmetic, Engines Were Running But Boat Was Not Able To Test Run. It Sat On The Yard For Two Years While I Reworked The Exterior And Interior, Engines Were Cranked And Run For About 30 Minutes Every Six Months.

The Previous Owner Said Both Engines Were Rebuilt On Top End One About Six Months Prior To Ivan And The Other About One Year. Meter Shows Only 450 Hrs On One And 1100 Hrs On The Other. I Have Put About 200 Hours On Them. One Has Obviously A New Blower Housing Judging From The Paint. When Purchased I Planned To Rebuild Both Engines But Because Of The Expense, Diffculty And Since They Appear To Be Ok I Decided To Stick With Them.

After The Two Years I Had All The Fuel Pumped Out And Polished/ Stained And Returned To The Tanks, Added About 150 Gallons Of Fresh In May Of 2007, Boat Was Splashed June 2007. On The Initial Run With New Paint/ Shiney Props As Clean As You Can Get It I Had The Problem.

The Problem Is That The Engines Both Begin To Show Black Smoke At About 1200 - 1300 Rpm Which Gets Progressively Worse Up To About 1800 Rpm Where It Is Deep Black At Wot. Both Start Immediately When Warm And Usually Within Two Or Three Revolutions When They Have Been Idle. The Longer They Have Been Sitting (months) More Cranking Is Required. As For Temperature The Are Somewhat Difficult To Start When Below 50 Degrees. When Cold, White Vapor Does Come Out The Exhaust. On Initial Start Ups After Sitting For Weeks They Do Blow Smoke/blue For About 3 Minutes Which Completely Goes Away Once They Reach 150 Degrees. Both Turn At 2500 Rpm With No Load Witout Any Significant Smoke.

During The First Summer 2007 The Boat Was Run Numerous Times But Never For Extended Times With The Smoking Conditon/ Speed Was Held Around 1200 To 1300 Rpm. Performance Became Worse Which I Think Was Directly Related To Bottm Build Up

Same Thing Continued In 2008, But I Personally Spent About Three Hours Under The Boat Cleaning The Hull/running Gear. I Also Pulled And Cleaned The Intercoolers. Took The Boat Out With A Light Load And Got 1900 Rpm. Boat Actually Got Up On Top Of The Water And Speed Was Around 17 Knots. This Is The Best Speed /rpm I Have Obtained But Smoke Was Still There But Didn't Seem As Bad. I Thought Maybe I Had Resolved The Problem, Took The Boat Out A Few Weeks Later Fully Loaded And Could Not Get It On Top With Smoke Present.

Obviously The Props Are Suspect, So I Have Tried To Verify Correct Props But Can't Seem To Get Hold Of Hatteras Nor Can I Get Much Information From Prop Shops. Everyone Wants To To Test Them. There Is Nothing Significant Wrong With Them Other Than The Size/pitch Parameters.

I Belive That The Engines Are Either Trying To Burn The Fuel With Out Enough Air / Rich Or They Simply Are Overloaded.
So I Cleaned Intercoolers And Checked Turbos...air Supply/// Now I Am Looking At The Load. How Do You Try Out Differnt Props Without Spending A Fortune????

 

[Sonny]

Black smoke usually indicates incomplete combustion, which, as noted can be brought on by overloading by overpropping, seriously excessive weight (unlikely) or not enough air. Since both engines seem to be doing the same thing at the same time it might not be internal engine issues. Check air filters and air supply. Have the air intakes on the hullsides been blocked for some reason like winterization? The engines can draw enough air to run normally at low rpm through the bilges and gaps around hatches and doors, but when they need to start gulping massive amounts of cubic feet of air when they really start to make torque around 12-1400rpm they will strangle. I would also check to see if the turbos are spooling up. If you shut down a ti engine without letting it cool at idle first, the super-hot turbo bearing can cook the lube oil inside it and prevent the turbo from spooling up or stop it from spinning at all. You would need to fit a boost guage for this, and remember to check boost under load, not revving in nuetral. You should see a smooth curve. Any spikes in boost would indicate a stuck or slow bearing becoming unstuck. A pyrometer won't be useful because you aren't burning the fuel properly to check turbo performance by exhaust temperature.

 

[saltshaker]

Have you tried running with the hatch open or ER room door open? Try to open the ER door or hatch while running at higher RPM. If the hatch or door are hard to open, and feel as if they are being sucked shut, you have restricted air flow.As Sonny stated, make sure the hull side air intakes are clear. Do you have vacuum gauges on your fuel filters? If not you may want to get a set to see if you have any restriction in the fuel system. Check all the mechanical, fuel and air stuff first. How does the boat sit with regard to the water line? If she is heavy, she will sit low in the water. When fully loaded, the exhaust ports should only be about 1/3 submerged. If nothing changes you should get the wheels checked to see what they really are. I have a set of 28x28 4 blades from my 46C that are for sale if you need to go that route.

 

[REBrueckner]

I like the ideas in the prior two posts.....My 1972 8V71TI's have been sluggish starting below 60 or 65 degrees ever since I owned them...so I'm guessing your cylinder compression is just fine based on the start characteristics you posted....

Why did you have the fuel polished??/ was it dirty and ugly or did you do that as a precaution even though the fuel and fuel system looked clean??
What did you find when you cleaned the intercoolers??

Do you have new/fresh PRIMARY and SECONDARY fuel filters installed?? Are the filter bowls clean and clear since polishing, or really dirty and crummy???

How about drawing off a sample of fuel, maybe off the top of one of your RACORS and getting it analyzed???
My bet is still lousy fuel or dirty fuel filter or both. As I previously posted, I swing the same size four bladed props w/o cups as you on my 48YF (same engines, transmissions) which apparently weighs about the same as your boat and turn up about just over 2100 RPM....so I have trouble believing prop size alone is your problem, especially causing smoke at 1400 RPM...but it's possible...Your props are NOT cupped I assume...