We replaced the standard two-blade sailor's prop with a fixed 3 blade from a reputable propeller shop in the East Bay. I would have thought that they would correctly pitch the prop for such a common boat with the standard Universal 25. We now top out at approximatley 400+ rpm short of redline where the 2 blade had no problem achieving it. The new prop is a 15x9x1. Any similar applications with a suggestion for proper pitch? Or a suggestion for the best overall cruising prop for this boat. We noticed a side effect of excessive soot on the transom after the prop change, presumably as the diesel struggles to burn efficiently. Thanks, Jim P.
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Check with Kilian.
Jim: Check with Kilian Prop. I do not know where they are now but it is somewhere in the east bay. You may be able to contact Bay Prop and they can give you their new phone/address. They are first class and stand behind their products. You can try this number and see if it works. Kilian Propeller Tel: 510-614-0596
Jim: Check with Kilian Prop. I do not know where they are now but it is somewhere in the east bay. You may be able to contact Bay Prop and they can give you their new phone/address. They are first class and stand behind their products. You can try this number and see if it works. Kilian Propeller Tel: 510-614-0596
thanks for the comments
I'll advise what we come up with. My concern is mainly that we may be putting a strain on the engine with too aggressive a pitch on the prop. Other than that, we like the bite that the prop has. Jim
I'll advise what we come up with. My concern is mainly that we may be putting a strain on the engine with too aggressive a pitch on the prop. Other than that, we like the bite that the prop has. Jim
Overpitched
The soot tells me that the engine is overloaded and the pitch is too deep. You should have the prop company re-set it for you at their expense.
The soot tells me that the engine is overloaded and the pitch is too deep. You should have the prop company re-set it for you at their expense.
Try the C36 Association website
they're experts on your boat, and I'll bet their Tech Tips already has that information.
they're experts on your boat, and I'll bet their Tech Tips already has that information.
thanks Stu, we're new to the boat
New partnerhip on the Catalina, I'll link up with C36 for sure.
New partnerhip on the Catalina, I'll link up with C36 for sure.
Correct Prop?
Each inch of pitch will change the RPM about 150-200 RPM. This means you would have to go with a 15X7X3 to hit max RPM. Frankly this doesn't sound right to me. For example I am using a 15X10X3 folder on my 35' boat and can just hit top RPM. I wonder if your prop is mis-marked and you really have a 15X12X3 or something like it. At any rate the prop should be taken back to the shop for a checkout.
Each inch of pitch will change the RPM about 150-200 RPM. This means you would have to go with a 15X7X3 to hit max RPM. Frankly this doesn't sound right to me. For example I am using a 15X10X3 folder on my 35' boat and can just hit top RPM. I wonder if your prop is mis-marked and you really have a 15X12X3 or something like it. At any rate the prop should be taken back to the shop for a checkout.
I don't think you have a problem
It sounds like you may have the right prop sized to work your engine at a reasonable rpm. Soot is unburned fuel. Not neccesarily a bad thing. Lots of truckers "black stack" when they climb hills or go fast. Soot means you have enough load on the engine to work it to its capacity. There is no need to run up to red line rpm. If you could get to red line on the old prop, it was probably too small. That's why you went to a 3 blade; to get more of the engines power working to move the boat. If your engine performs well with this prop, back off a little when she blows black, and be happy!
It sounds like you may have the right prop sized to work your engine at a reasonable rpm. Soot is unburned fuel. Not neccesarily a bad thing. Lots of truckers "black stack" when they climb hills or go fast. Soot means you have enough load on the engine to work it to its capacity. There is no need to run up to red line rpm. If you could get to red line on the old prop, it was probably too small. That's why you went to a 3 blade; to get more of the engines power working to move the boat. If your engine performs well with this prop, back off a little when she blows black, and be happy!
I would love to think that we don't have to change
Thanks Tom and Fred. I'm not yet familiar with the vagaries of diesels but I was under the impression that the constant load of the high-pitch propeller would be detrimental to the engine. At least with a truck there are periods of flat and downhill to allow the motor to run with a minimal load and "clean itself out". Our prop pulls like a tugboat so if it's not hurting anything I would just clean the transom more often.
Thanks Tom and Fred. I'm not yet familiar with the vagaries of diesels but I was under the impression that the constant load of the high-pitch propeller would be detrimental to the engine. At least with a truck there are periods of flat and downhill to allow the motor to run with a minimal load and "clean itself out". Our prop pulls like a tugboat so if it's not hurting anything I would just clean the transom more often.
Overload will hurt the engine
According to Nigel Calders book. The engine feels the total load of the engine. You might have an oversized alternator or something else adding to the load. I foget all of the bad things that are supposed to happen to an overloaded engine. An engine ran without a load also suffers but not as much. You might want to check that your transmission is full of oil and that there isn't anything wrapped around the prop etc. Also a dirty hull will load up the engine. My boats prop was overpitched and wouldn't let the engine reach full rpm's of 2500 (VOLVO MD11C) it would get up to 2250 or so. After being repitched it goes to 2500 and runs cooler. If the engine is fully loaded under flat water no wind conditions what happens when you have to motor into a 30 knot headwind and seas??? That's the problem in that to develope full horsepower you have to have so many RPM's with most engines developing maxiumum horsepower at high RPMs. Horsepower is from torque and RPMs. The sweet spot or power band is where you have a good combination of the two. Torque usually falls off at higher RPM.s and at lower RPMs you don't have enough horsepower. Most of us have noticed that going up a steep hill the engine will slow down and then just chug along at that speed to the top of the hill. What happened is the engine was above it's power band's RPM range and dropped back RPM's until the torque improved. IMHO
According to Nigel Calders book. The engine feels the total load of the engine. You might have an oversized alternator or something else adding to the load. I foget all of the bad things that are supposed to happen to an overloaded engine. An engine ran without a load also suffers but not as much. You might want to check that your transmission is full of oil and that there isn't anything wrapped around the prop etc. Also a dirty hull will load up the engine. My boats prop was overpitched and wouldn't let the engine reach full rpm's of 2500 (VOLVO MD11C) it would get up to 2250 or so. After being repitched it goes to 2500 and runs cooler. If the engine is fully loaded under flat water no wind conditions what happens when you have to motor into a 30 knot headwind and seas??? That's the problem in that to develope full horsepower you have to have so many RPM's with most engines developing maxiumum horsepower at high RPMs. Horsepower is from torque and RPMs. The sweet spot or power band is where you have a good combination of the two. Torque usually falls off at higher RPM.s and at lower RPMs you don't have enough horsepower. Most of us have noticed that going up a steep hill the engine will slow down and then just chug along at that speed to the top of the hill. What happened is the engine was above it's power band's RPM range and dropped back RPM's until the torque improved. IMHO
If you're getting soot from the exhaust at normal
cruising speed, say 1/2 to 2/3 of red line RPM. then the engine may be overloaded, or you may have a fuel system issue. If you have to run it up to 400 RPM below red line to get soot, that's different. It is not normal to have unburned fuel in the exhaust except at full throttle. You should not run at full throttle all the time. Does the soot stop if you back off the throttle? If the engine is not overheating, it's probably not overloaded. I have never had a diesel that I ran at full throttle or even close to red line RPM, even bucking into big seas. I have run 20 or 30 different diesels from 8 to 400 hp. Most sailboat diesels are also used on things like compressors and gen sets, where they run with a heavy load for thousands of hours. The soot may be a different issue. Have your injectors been serviced lately? Soot is unburned fuel. A poorly adjusted injector or a clogged tip could cause poor combustion. Or a burned valve, or a cracked compression ring. A talk with the prop folks and a good diesel mechanic is certainly a good idea. It's possible that the prop is too big, but it's also possible that it's just fine, and you are now working the engine hard enough to see an injector problem.
cruising speed, say 1/2 to 2/3 of red line RPM. then the engine may be overloaded, or you may have a fuel system issue. If you have to run it up to 400 RPM below red line to get soot, that's different. It is not normal to have unburned fuel in the exhaust except at full throttle. You should not run at full throttle all the time. Does the soot stop if you back off the throttle? If the engine is not overheating, it's probably not overloaded. I have never had a diesel that I ran at full throttle or even close to red line RPM, even bucking into big seas. I have run 20 or 30 different diesels from 8 to 400 hp. Most sailboat diesels are also used on things like compressors and gen sets, where they run with a heavy load for thousands of hours. The soot may be a different issue. Have your injectors been serviced lately? Soot is unburned fuel. A poorly adjusted injector or a clogged tip could cause poor combustion. Or a burned valve, or a cracked compression ring. A talk with the prop folks and a good diesel mechanic is certainly a good idea. It's possible that the prop is too big, but it's also possible that it's just fine, and you are now working the engine hard enough to see an injector problem.
Air Starvation or overload
You didn't mention speed. It might be possible that you are getting to hull speed. Once you reach hull speed the load on the engine goes up dramatically. With the 2 blade you weren't going fast enough to reach hull speed. My boat will reach WOT at near hull speed. The stern is really squated down at WOT with not much added speed.
You didn't mention speed. It might be possible that you are getting to hull speed. Once you reach hull speed the load on the engine goes up dramatically. With the 2 blade you weren't going fast enough to reach hull speed. My boat will reach WOT at near hull speed. The stern is really squated down at WOT with not much added speed.
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