Semi-displacement hull w/single 120hp Lehman. What Prop Size?

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https://www.flickr.com/photos/55428883@N04/sets/72157642644018403/

Here is a link to some photos of Portola, photos of the engine are in there. Air start, direct reversing, built in 1929. In the 1970's we dropped a Cat 3208 in it, on a separate shaft to assist in maneuvering since the direct reversing means you literally shut the engine down, shift the cams and then start it up in reverse. I put a vid on youtube years ago that you could probably search for as well.
 
...Now that's a Yacht.
Beautifull boat and I wish I had that anchor winch

Thanks for the post Rick
Fantastic
 
Andy G said:
My 36' is pretty much identical to Rich F's boat,except we have twins Lehman's and an aft cabin model.

According to the IG owners manual for 36' boats the standard issue for Lehman 120's on IG's is a gear box of 2:1 with 3 blade 24" props with a 16" Pitch. This is what my boat runs.

My boat seems to top out at about 2500 rpm.

At this wide open speed, you are enveloped in clouds of blue smoke, with a prop wash that makes Niagara Falls seem like a milk pond. Unburnt diesel chokes the life out of your nearest and dearest, your lungs turn to cinder The engine sounds like 1,000 Wasps have been poured into the cylinders, the wife is thinking of her options, and crew are crying and wanting to go home. You are a pariah.

Whereas at 1600 rpm, the soft calls of the Whippet birds float down, the light softly shimmers through the branches of the water gums, the fine spicy Shiraz awaits. The wife lovingly glances in your direction, the children smile and laugh, and all is good with the world.You are the captain of all you survey.

The difference, one Knot.:rolleyes:
Click to expand...

Bravo.
Wonderful post and pretty much my experience, though for me it's a two knot difference, but I'm not sure I'd live to see the extra two miles:nonono:

The one time I actually planned to run WOT for a minute or two, I couldn't take the stress of wondering when those bees where going to take off in all directions.

In the last year, I did have a few occasions where i had to ask Scotty for full power, in spite of his admonitions, the situation demanded speed:thumb:
 
Spoke with Bob at American Diesel

So I just got off the phone with Brian at American Diesel (VERY helpful and very nice guy) and this is what he tells me:

The 2715e Lehman (120hp) should turn at 2,500 RMP under load and 2,705 RMP with no load. He definitely thinks that it is NOT a prop related problem as he knows the IG design very well and I confirmed with him that this prop was similar as to what the rest of you guys have on your boats as well as being the original prop installed by Halvorsen.

My Lehman turns up to 3,000 RMP with no load and only 1,900 RPM with load. This, he said sounds like a fuel injection pump problem. There should only be the 250 RPM difference between load and no load.

He did tell me to confirm the gear ratio with the photo-tach (which I ordered one today and I'll try it out once it arrives). He said to confirm the ratio but its probably a calibration issue with the pump. Guess I better get to work, I'll post updates.
 
Hi, Rich. Glad you were able to narrow down the issue somewhat. Definitely keep us posted--I hope you get this resolved!
 
So the saga continues. I had my 4 blade (24x17) turned down and repitched to a (23x15-14). I was able to gain another 100 RPM only. My WOT RPM is now 2,000, better but still not there. Can't seem to figure it out. I had the injector pump removed and calibrated (at the suggestion or Brian at American Diesel). Turns out that the pump is exactly within spec and in perfect condition, what a waste of money, the only thing I gained from that was the knowledge that the pump isn't the issue. Something is holding this engine back and I cannot figure it out. By the way, I did get a photo tach and it is in fact a 2:1 gearbox. The repitch did take care of any smoke I was getting. I'm still steaming a lot so I ordered the new Lehman (single shaft) raw water pump, along with completely rebuilding the raw water system and new coolers, we'll see about the steam.
 
I wonder if the tach gauge is reading correctly? Have you checked that out? Alternator pulley size may influence the correct tach calibration? Just throwing stuff out there. I'm sorry about all of this!

Jim
 
I have calibrated the tachs with a mechanical tach on the flywheel as well as using a photo-tachometer (just to be certain). Its really puzzling.
 
Have you tried cleaning out the cooling water system with a proprietary cleaner, if it's nice and clean it will help with heat transfer.
It does no harm at all to run the engines up to full rpm every so often to burn away any unburnt fuel in the exhaust system, increase the revs gently until she's running at full chat, (ignore the thousand bees) the engine will smoke like hell but as the temperature of the exhaust gasses rise it will burn away any sooty deposits and after a while she'll start to run clean, let her run clean for five minutes or so then gently drop the revs to your 'normal' cruising speed.
To increase engine life, when shutting down your engine after running hard let her tickover for around 5 to 8 minutes to relieve the thermal stresses around the engine, this is especially important for turbo engines.
For prop calculations go to vicprop.com and feed in your details for a free calculation.
 
Seems to me you should have 2.5-1 gears or a 3 blade like the stock boat. Just a case of too much blade area or not enough torque to turn the prop w the extra blade on it.

The stock boat is supposed to have 2-1 gears and a 3 blade prop.

Wxx3 wrote;
"According to the IG owners manual for 36' boats the standard issue for Lehman 120's on IG's is a gear box of 2:1 with 3 blade 24" props with a 16" Pitch. This is what my boat runs."

Why is this still a mystery? Or have I missed something?

jleonard is getting his rpm and performance w a 4 blade but only 20" in dia. Three inches in dia is a huge difference in load.
 
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The most likely cause is over propping. The IP guy wasted your money.

Look at any engine curves and you will see a max output power curve and a prop demand curve. The prop demand curve is always lower on the graph than the max output curve. The curves meet only at max rpm. If the prop curve were higher than the max power curve the engine could not speed up. That is your condition.

Over propping means that you are loading the engine above the prop demand curve and probable hitting the max power output curve well below rated RPMs. The engine is putting out everything it can at that RPM. The problem is that the IP is set up to provide more fuel than needed by a prop curve at that lower RPM. That is the reason for more smoke. The engine is being given enough fuel to speed up but load wont allow it. Over fueling may cause hot combustion chambers and associated problems in addition to smoke. Smoke is good because it warns you that the engine is overloaded for its settings.

keep in mind that the same engine could be sold significantly derated HP to run at the RPM yours does but the fuel would be limited by the different IP settings to less than your current settings.

I suggest you take all your data to a good prop shop and ask their opinion on proper propping. You may find some calculators on the web but they are often for planning boats.

There will always be debate about over propping to save fuel but in reality each engine uses X amount of fuel to produce Y HP at any rpm it can reach within normal operating range. It is my opinion that over propping will generally use a bit more fuel at a particular load because the engine is being given extra fuel to allow increasing RPM that the load will not allow.
If you look at the fuel used on the two curves you can see that the engine can use the same amount of fuel at different RPM points on each curve.

Lower propping provides faster spin up which IMO gives quicker response when maneuvering and pushing through steep head seas.
 
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My Albin 40 has a 22L17 prop. I just tried a full power run and got 2300 RPM. Not sure of the gear...no plate that I see so I still have to do a little detective work there.

My cruise is around 1600-1700 rpm..and I've averaged 6.3 knots and 3.3NMPG at around 1.9 GPH over 5000 miles in the last 2 years.

No black smoke at full throttle...ran like it should...except what 200 RPM less than manufacturer max.
 
personally I would not worry about your propping. It will give a surveyor something to complain about if you ever sell. the OP is by 600 RPM or more depending on which number you accept.

How big is your engine, 120HP??
 
bayview said:
personally I would not worry about your propping. It will give a surveyor something to complain about if you ever sell. the OP is by 600 RPM or more depending on which number you accept.

How big is your engine, 120HP??
Click to expand...

If you are talking to me....

I'm not worried...in fact I prefer it.

Don't care what the surveyor thinks..

120
 
Based on my own experience many boat engines don't have an efficient air filter, dirty air will wear the engine.
When talking of props and rpm I notice no one has mentioned the all important toque curve of the engine.
Personally I would use vicprop.com to calculate your prop, they've never been wrong on any I've done but as someone pointed out it doesn't take account of all the 'extra's & boys toys' we pile on adding extra weight.
I over prop to drop the rpm by 250 rpm and if necessary can run WOT for a half hour if I need to get out of trouble.
Yes, Rolls-Royce did actually test to destruction in many ways, you wouldn't believe the abuse a diesel will take before blowing. it's phenomenal.
 
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Irish Rambler said:
Based on my own experience many boat engines don't have an efficient air filter, dirty air will wear the engine.
Click to expand...

Dirty air isn't that much of an issue for and engine in a boat. Unless you are getting a lot of salt spray in your engine space. Otherwise running an engine around in a boat is nothing like running it in a truck over the road when it comes to dirt in the air it breathing.
 
I agree completely as we do both, it's surprising the amount of dust the filter does collect. Naturally our coastal canal cruising has more chance of fine sandy dust off the North African desert with the Mistral.
 
A pretty savvy diesel mechanic told me that as much to filter the air the air filter was there on a boat was to cut down noise. He also said that unlike a road vehicle that a boat is going uphill all the time.
 
If boat is trying to climb over the hump at full power, and getting stuck there (trying to exceeed hull speed), then a repitch will be rather pointless. Best to prop for a comfortable and efficient cruise and not worry about full power rpm.
 
Well said Mule, your savvy mechanic hit the nail on the head.
It is also surprising when changing air filters just how much dust they do accumulate, even way out at sea.
 
I haven't done that yet, I too think running a cleaner through the system couldn't hurt. I know the hoses and heat exchangers are all clean as they are all new but the block, water jacket and tank could probably use a good chemical scrubbing.
 
manyboats said:
Seems to me you should have 2.5-1 gears or a 3 blade like the stock boat. Just a case of too much blade area or not enough torque to turn the prop w the extra blade on it.

The stock boat is supposed to have 2-1 gears and a 3 blade prop.

Wxx3 wrote;
"According to the IG owners manual for 36' boats the standard issue for Lehman 120's on IG's is a gear box of 2:1 with 3 blade 24" props with a 16" Pitch. This is what my boat runs."

Why is this still a mystery? Or have I missed something?

jleonard is getting his rpm and performance w a 4 blade but only 20" in dia. Three inches in dia is a huge difference in load.
Click to expand...

Eric, what kind of speed are you getting? Not that your hull will at all compare to my hull speed, just curious. I do think my prop guy was wrong and I intend on confronting him on the issue.
 
Irish Rambler said:
Based on my own experience many boat engines don't have an efficient air filter, dirty air will wear the engine.
When talking of props and rpm I notice no one has mentioned the all important toque curve of the engine.
Personally I would use vicprop.com to calculate your prop, they've never been wrong on any I've done but as someone pointed out it doesn't take account of all the 'extra's & boys toys' we pile on adding extra weight.
I over prop to drop the rpm by 250 rpm and if necessary can run WOT for a half hour if I need to get out of trouble.
Yes, Rolls-Royce did actually test to destruction in many ways, you wouldn't believe the abuse a diesel will take before blowing. it's phenomenal.
Click to expand...

The air filter is completely clean, I even ran it without just to be sure. I also have heard that a dirty filter will cause all of these symptoms. Thanks for the suggestion of vicprop.cm, I definitely give it a shot.
 
120

bayview said:
personally I would not worry about your propping. It will give a surveyor something to complain about if you ever sell. the OP is by 600 RPM or more depending on which number you accept.

How big is your engine, 120HP??
Click to expand...

Yes, its 120hp. I think the over propped load that it is causing thje engine is causing the exhaust to run hot (don't have a pyrometer to confirm) but a loaded engine will have hotter exhaust (you won't see it in your gauges so much) but this may be where the steam is coming from.
 
Prop

bayview said:
The most likely cause is over propping. The IP guy wasted your money.

Look at any engine curves and you will see a max output power curve and a prop demand curve. The prop demand curve is always lower on the graph than the max output curve. The curves meet only at max rpm. If the prop curve were higher than the max power curve the engine could not speed up. That is your condition.

Over propping means that you are loading the engine above the prop demand curve and probable hitting the max power output curve well below rated RPMs. The engine is putting out everything it can at that RPM. The problem is that the IP is set up to provide more fuel than needed by a prop curve at that lower RPM. That is the reason for more smoke. The engine is being given enough fuel to speed up but load wont allow it. Over fueling may cause hot combustion chambers and associated problems in addition to smoke. Smoke is good because it warns you that the engine is overloaded for its settings.

keep in mind that the same engine could be sold significantly derated HP to run at the RPM yours does but the fuel would be limited by the different IP settings to less than your current settings.

I suggest you take all your data to a good prop shop and ask their opinion on proper propping. You may find some calculators on the web but they are often for planning boats.

There will always be debate about over propping to save fuel but in reality each engine uses X amount of fuel to produce Y HP at any rpm it can reach within normal operating range. It is my opinion that over propping will generally use a bit more fuel at a particular load because the engine is being given extra fuel to allow increasing RPM that the load will not allow.
If you look at the fuel used on the two curves you can see that the engine can use the same amount of fuel at different RPM points on each curve.

Lower propping provides faster spin up which IMO gives quicker response when maneuvering and pushing through steep head seas.
Click to expand...

Excellent info, thanks. I do think it is still an over propping issue. The engine checked out perfectly. At the suggestion of Brian at American Diesel, I even had the injector pump removed and sent off for calibration (thinking it could be a fuel delivery issue or timing issue). Turns out the pump is PERFECT! They didn't need to do anything to it. Another huge waste of money. Fuel, oil filters al new, new cooling system including the new lehman raw water pump (just in case), new hoses, new coolant. Based on all this, the boat has too much prop.

Obviously the only way to confirm this is to turn the prop down again, I just need to get my prop guy to do it for free now since I completely relied on him to get the correct size the first time. $800 to him plus another $150 to my diver to take the prop off and then put it back on! Ahhh! I'm going crazy over this whole thing!!!!
 
RichF wrote;
"Eric, what kind of speed are you getting? Not that your hull will at all compare to my hull speed, just curious. I do think my prop guy was wrong and I intend on confronting him on the issue."

I get a max around 7 knots and cruise at 6.15. But I have only 40hp and a full disp heavy 30' hull. I do max out at 3000rpm at WOT. Run 2300 at cruise.

I think your problems would be over if you adjust your engine load to allow your Lehman to max at 2500rpm. Did you ever firm up the gear ratio? If you've got 2-1 you need 3 blade props IMO.
OK I read back and see you have confirmed the 2-1 gear ratio. Think 3 blade props. If you get real lucky you could find them used but ....

I went back all the way to your #1 post. It seems you have tried the 23" three blade prop and only got 2000rpm. Is that correct? And I gather you're a single engine boat. If that's so I'm not sure what to say and I'm not often speechless.
 
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manyboats said:
RichF wrote;
"Eric, what kind of speed are you getting? Not that your hull will at all compare to my hull speed, just curious. I do think my prop guy was wrong and I intend on confronting him on the issue."

I get a max around 7 knots and cruise at 6.15. But I have only 40hp and a full disp heavy 30' hull. I do max out at 3000rpm at WOT. Run 2300 at cruise.

I think your problems would be over if you adjust your engine load to allow your Lehman to max at 2500rpm. Did you ever firm up the gear ratio? If you've got 2-1 you need 3 blade props IMO.
OK I read back and see you have confirmed the 2-1 gear ratio. Think 3 blade props. If you get real lucky you could find them used but ....

I went back all the way to your #1 post. It seems you have tried the 23" three blade prop and only got 2000rpm. Is that correct? And I gather you're a single engine boat. If that's so I'm not sure what to say and I'm not often speechless.
Click to expand...

Yes, single engine and yes I did also try a 3-blade although it was a large 3 blade). I just talked to my prop guy and he is standing by his choice on the new prop size he gave me. (23x15-14; 4-blade) I told him to humor me and say he is wrong, what size would I need to get to 2,500 rpm if the one he made for me was only getting me 2,000 rpm. He said look for a 3 blade 22" x 14", 15" or 16" pitch. I just talked to the guys a Vic Prop too and here are their calcs. What do you know, calling for a 22"x15"-16" THREE blade, smaller size and pitch if I want a 4 blade but that's a pretty much impossible prop to find. So now I go prop hunting....

Could have bought a nice new electronics package with what I have wasted on money here....

I'll post back later with results (no doubt I am NOT the only guy out there having this issue). I sure hope this info. will help some other poor soul...
 
RichF,
Apologies I don't wish to be rude but time spent on reconnaissance is never wasted.
I'm glad the guys at Vic prop sorted your problem, they're very helpful.
Put a few ads out for the prop you want but bear in mind that any s/hand prop will need checked and balanced BEFORE fitting.
Like you I couldn't get a 4 blade so I got one made, don't discount it, shop around and you may just find one.
Good Luck.
 
Thanks

Irish Rambler said:
RichF,
Apologies I don't wish to be rude but time spent on reconnaissance is never wasted.
I'm glad the guys at Vic prop sorted your problem, they're very helpful.
Put a few ads out for the prop you want but bear in mind that any s/hand prop will need checked and balanced BEFORE fitting.
Like you I couldn't get a 4 blade so I got one made, don't discount it, shop around and you may just find one.
Good Luck.
Click to expand...

I know, its just super frustrating. I know everything I have done to the boat are good things to have had done and I know my engine better than ever, it would have just been nice to have resolved this months ago.

I may have already found a 22x16 3-blade for only $99 locally. I'll give it a test first and if it works I'll spend some money on it having it tuned and balanced. Fingers crossed!
 
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