Overprop?

[dixiestriker]

I have an older 89 luhrs 40 with the 454s I bought the boat last year and used it for the summer in lake ontario. The problem i am having is i cant get the engines to rev over 3200 RPMs at WOT The engines run strong the buttom is clean , the props they came with the boat i dont think they are the originals. they are 4 blades 24x25s Do you think i am overprop and should lower the pitch on the props or just leave it the way it is? I usually run the boat around 2500 rpms and cruise around 17 knots

[T380fisher]

Your engines should top out between 4200-4400 RPM's (depending on amount of people/fuel/water onboard).

It sounds like you are way overpropped or there is something else going not allowing the engines to achieve rated RPM's. (ie overweighted, not geting enough fuel, etc...)

Did you have the boat surveyed when you bought it? How did it run then?

I have a 1990 Tournament 380 Flybridge. A much different boat than the 89 40', but the same engines....I am propped with 22x22 four blades, no cup and turn 4350 in the Spring (and 4200 in the fall thanks to growth)

[dixiestriker]

If it was one engine then i would say its engine problem but is both engines max out at 3200 rpms and both have their own fuel tanks I took compression test and all cylinders have between 155--160 pounds pressure And yes there was a survey and a sea trial done but i was not there at the time and the surveyor never mension any rpm problems..The boat is out of the water now and i will take those props to a shop to get them checked out ...Meantime i found the original props wich are 3 blades 22x23s i think i will use them in the spring to see if there is any difference

[T380fisher]

From the size difference of the origonal props to the ones currently on the boat, I would say you are overpropped. An old rule of thumb that I remember is 200 rpms per inch of pitch and per inch of diameter. That's about 800 rpms you should pick up by going to the old props. You may lose some speed, but in the long run your engines will love you.

Shame on the surveyor, that should have been an instant red flag for the performance of the sea trial.

Good Luck.

[Maximillion]

Hey Dixiestriker,

The original props for that engine set-up was a 22 x 22 3Blade with a light cup. That is what was specked for the boat. Hope that helps.

[dixiestriker]

Thanx for your reply, what i done i took the the 4 blade props to the prop shop and they pitch it down to 22x24 and the guy said i should gain a 400 to 500 RPMs... Mean time if i still am 400 -- 500 overprop and i cruise around 2500 RPMs is that big load for the engines? or doesnt make any difference because i dont push them hard?

[HisDoghouse]

Sounds to me like you're still overpitched at 24". Can the prop shop drop you to 22" pitch? Not sure about gas, but overloading a diesel is not a good thing to do.

On my last boat with twin 'rudes, I went from a 3 blade to a 4 blade prop, same diameter and pitch, and they worked great.

[dixiestriker]

The boat should be in the water by the third week of april...i will try the 4 blade props first with the minimum fuel and water on board and see how close i am to 4200 RPMs at WOT If i am still far away i will try the original 3 blade props and see what happens...

[Dave K S]

It does not matter at what RPM you run your boat, overloading is overloading. You should make sure that you can reach the max rated RPM when the boat is fully loaded with fuel and gear. If you can not reach the rated RPM then you will cause an overloading condition at any RPM. This can cause preignation in the cylinders. I had to replace my 454's because of this condition. The preignation burned a hole in the top of the piston and distroyed the engine. Overloading is bad at any RPM. I would start by following Maximillion's advice and use the 22x22 3 blade prop. Running an overloaded engine is like running your car up hill in high gear. You can hear the engine pinging even though you are not at a high RPM. You are overloading the engine and what you are hearing is the fuel igniting in the cylinder while the piston is still on the up stroke. This creates extreme heat and will melt the top of the piston if you do not decrease the load.

[dixiestriker]

Thanx for the advice Dave I will start with the 4 blade props and see where i stand and then switch to the 3 blade if the 4 dont work..Also need to check that the boat isnt overweight and the engines are running in full...last year the boat was new to me and didnt try a lot of things But this year hopefully will have the time to solve ther problem..I havent been able to talk to the previous owner but from my understanding hes been using the 4 blade 24x24 props for years when the boat was in maryland Also need to double check the throttle cables and make sure the 4 barrel butterflies open up all the way since the flybridge was removed to truck the boat to my location and maybe i didnt hook up cables right

[T380fisher]

Dixiestriker.....I agree with Dave K S....overloading can happen at any RPM if you are wrongly propped.

You should load the boat with the gear and supplies and people on board that you will normally run. Then for spec have at least 1/2 Fuel and 1/2 water (more the better). Then prop the boat based on this performace test. Getting perfomace stats without the normal operating conditions is pointless. Your range is 4200-4400 RPMs. Mine drop during each season due to bottom growth and the amount of "stuff" that keeps coming down to the boat each weekend. Try to get your WOT number in between since you know the bottom and props are spotless. You probably don't have the growth issues in Lake Ontario that I see in S. New Jersey, but being new to the boat you may end up increasing the load of supplies throughout the summer.

Even though you are running at a lower than WOT (wide open throttle) rpm, doesn't mean you are running your engines easier. Overloading (or underloading, just as bad) can happen as described by others above. Running at WOT for very brief periods (ie. 30 secs) throughout the year can give you evidence on any oncoming engine/prop/bottom growth issues.

Good Luck. Isn't boat ownership fun?:)

[dixiestriker]

Thanx for the advice...boat should be in the water by the end of the month Like you said i will give it a test run in WOT to see where i stand with the 4 blades 24x22s and is iam not close to the 4200 rpm i will replace the 4 blade with the 3 blade props... But still cant undestand..boat came with 2 sets of props 4blade 24x24s wich over this winter the prop shop cut them down to 24x22s and a 3blade 24x25s I cant get hold of previous owner but both props sound oversize to start with for that boat..The boat spend all its time in kent island in maryland and it has almost 900 hours

[jerseyluhrs]

I am looking at purchasing the 40 Tournament (1989). Any words of wisdom?She has 454's.

[logadmin]

You may want to start a new thread to get a better response on that... :)

[dixiestriker]

Lattest report on overproping on the 40 Luhrs...over the winter i installed the flowscan 9000 - 20B on the 454s...i had the the 4 blade props machined from 23x24s to 21x24....Took the boat for a spin 3 people on board gas tanks 3/4 full..at WOT the tachometers registered 3300 RPMs the flowscan showed 4200 rpms I had no idea what gauge was correct...back to the dock put timing light on engines , this light shows rpms also and i see that both tachometers are wrong and flowscan was correct...I couldnt believe that both tachs were 900 RPM wrong.. So the last season wich i thought i wasnt hitting the right #s on WOT i was wrong ,,the tachs were defective..i think there is a adjustment screw in the back i will try to adjust if its possible ...Thanx again for all the help have a safe boating season

[Maximillion]

dixiestriker,

Where abouts in lake Ontario are you located?

[T380fisher]

dixiestriker...I also use my Floscan tach to run my engines. My boat is 18 years old this year and the faria tachs are just not dependable anymore (on my boat). My Port tach reads 300 rpms higher than my starboard tach. I have used a timing light on my engines and the Floscan is dead on...so I use it in conjuction with my syncronizer to judge engine rpm. This is one of my "winter" projects that never seems to get done. The center console on my T380 is a "b" to get to the back of the gauges (upsidedown & backwards), so it hasn't gotten done yet.

Good Luck with your season....glad you figured out your issue.

[dixiestriker]

Lakefront Promenade Port Gredit.....

[davebanks]

Ive got a T 380 with 425hp 671t detriots what props are specd for her
cheers dave

[Chasin waves]

Hey Joe,
Hope all is well. This is your old c/s rep.

[HisDoghouse]

Hey Joe,
Hope all is well. This is your old c/s rep.

Hey! I'm doing fine and would LOVE to hear from you!

The boat still has both wheels attached, but due to much higher fuel prices, my operations have slowed down significantly.

I'm still doing the contractor thing but have also started a NEW business that I'm going to use to allow me to retire from this full-time employment in the VERY near future. It's helping me to allow my wife to transition to part-time consulting in the spring next year.

Please give me a call at (757) 572-9236 when you get a chance.

Joe

[WILLOWBROOK]

I have a 1989 40" Luhrs also with twin 454's and 2.91:1 trans that turn 24x25 3 blade props and I only get 3200RPMs also. I am down here in the Carolinas and I too had the boat surveyed, and nothing was said about the props. I just replaced all 4 cutlass bearings thinking they were bad, and only one was, all others looked new, but I still replaced them all. both props were tuned and balanced and replaced on the shafts. There is no paper work from the previous two owners indicating a transmission and prop change while they had it. Luhrs responded back to me today, stating it had 1.75" shafts and smaller 22x22 3blade with light cup.:banghead:

[dixiestriker]

Double check your tachs willowbrook make sure they are showing correct. Mine were showing 3000 RPMs but actually the engines were reving around 4000, It took awhile to figure out cause the tachs were not faroff at idle but really of at high RPMs

[WILLOWBROOK]

I bought 2 of every gauge for my helm. and they are Fariar gauges. Could they be off also?? I will check them tomorrow with a different tach. They go to 4000rpm without a load but when I cruise they only go to 3200 rpm. I will check tomorrow. thanks for the reply, Dixiestriker, I will see if there is an adjustment on the back of the tach's.

[WILLOWBROOK]

dixiestriker, what gear ratio do you have and what size shafts came with your boat, I have 2.91 trans, 1.50 shafts
MAY 30,2009, I was cruising the river tonight and I went below to look at my carb's to see where they were at full throttle, to my amasement, both carb's were at less then 3/4 throttle and the back two barrels were not even close to being open. No wonder I never went passed 3200 rpm's. Carb's not going to full throttle. I will reset them tomorrow to see where I go then.

[dixiestriker]

Same as yours..As per the tachs there is an adjustment in the back..