I just bought a Catalina 30 with a Universal MX25 diesel. At what RPM should I cruise the boat at? Also, what temperatures should the engine run at?
RPM Question?
- Thread starter Bad Obsession
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Ross is only partly correct
on raw water cooled engines the thermostat should open at 140 F. Fresh water cooled or engines with an heat exchanger open at 180F. Most diesels run better on the hot side around 190 to 200 degrees. The engine should have a govenor that will limit your RPM to somewhere in the area of 3600 rpm. I really don't go by rpm that much but by engine temp. (assuming everything is correct, prop pitch etc) I cruise at about 190. Which on my engine is about 2600 rpm. If you can't get over 300rpm out of your engine then your prop is incorrect. Either to much pitch or diameter. If your at half throttle and the engine is turning 3300 rpm, the prop is to small. I have oversimplified the whole thing just to give you an idea of the big picture. You will not get into trouble with these rules of thumb Fair Winds Cap'n Dave
on raw water cooled engines the thermostat should open at 140 F. Fresh water cooled or engines with an heat exchanger open at 180F. Most diesels run better on the hot side around 190 to 200 degrees. The engine should have a govenor that will limit your RPM to somewhere in the area of 3600 rpm. I really don't go by rpm that much but by engine temp. (assuming everything is correct, prop pitch etc) I cruise at about 190. Which on my engine is about 2600 rpm. If you can't get over 300rpm out of your engine then your prop is incorrect. Either to much pitch or diameter. If your at half throttle and the engine is turning 3300 rpm, the prop is to small. I have oversimplified the whole thing just to give you an idea of the big picture. You will not get into trouble with these rules of thumb Fair Winds Cap'n Dave
I can't quarrel with that.
Your engine can power a small cruising power boat or a fairly large sail boat. The speed at cruise is the important factor. Remember that 1 inch of pitch at 1000 rpm is a theoretical 1 knot at 100 percent efficiency. Sail boats generally go slowly, so large pitches and small diameters and high rpm is not a good combination. A modest pitch, a large diameter and a slow turning shaft is the best combination.
Your engine can power a small cruising power boat or a fairly large sail boat. The speed at cruise is the important factor. Remember that 1 inch of pitch at 1000 rpm is a theoretical 1 knot at 100 percent efficiency. Sail boats generally go slowly, so large pitches and small diameters and high rpm is not a good combination. A modest pitch, a large diameter and a slow turning shaft is the best combination.
Cruise at...
approx. 80% of max. rating, usually around 2600-2800 rpm. Do NOT idle engine around alot or let idle under no load for extended times as it will "coke up" in the exhaust elbow. Warm it up good and run at wide open throttle frequently for awhile to keep it blown out. Let cool down a bit at idle before shutting down.
approx. 80% of max. rating, usually around 2600-2800 rpm. Do NOT idle engine around alot or let idle under no load for extended times as it will "coke up" in the exhaust elbow. Warm it up good and run at wide open throttle frequently for awhile to keep it blown out. Let cool down a bit at idle before shutting down.
Capt Dave
You are mostly correct. I like your explination of crusing by temp. But the Universal serise excluding the M3-20 and M50 are all 3000 RPM engines. Their best cruise is 2400-2800. The tach is a variable that can be tuned with an accuracy of 100rpm. Pat McCartin Inland Marine Diesel BUford, Ga imd_ga@hotmail.com
You are mostly correct. I like your explination of crusing by temp. But the Universal serise excluding the M3-20 and M50 are all 3000 RPM engines. Their best cruise is 2400-2800. The tach is a variable that can be tuned with an accuracy of 100rpm. Pat McCartin Inland Marine Diesel BUford, Ga imd_ga@hotmail.com
Cruising temp
I have been watching my crusising temp. I ran my engine for 4 hours the other day and it never got above 170. I was running at 2600 RPMs and I was going about 5.5 knots. I thought that my boat should cruise around 6 knots being it has a descent sized engine for the boat and it has a three blade prop.
I have been watching my crusising temp. I ran my engine for 4 hours the other day and it never got above 170. I was running at 2600 RPMs and I was going about 5.5 knots. I thought that my boat should cruise around 6 knots being it has a descent sized engine for the boat and it has a three blade prop.
Wind and waves
can easly account for the 0.5 knots. My Catalina 30 with 11HP engine could get to hull speed all the time if the waves where flat, but add a little wind and waves to 1 foot and might as well hoist the sails and dowse the iron spinnaker as the boat will go faster under sail. I used to run the engine WOT ALL the time and never had ANY problems. Diesels like to be run hard as I found out in the Army. WOT is the most efficient speed also if your prop is sized right. So WOT for everything except docking and put the sails up once the wind gets above about 7 kts relative.
can easly account for the 0.5 knots. My Catalina 30 with 11HP engine could get to hull speed all the time if the waves where flat, but add a little wind and waves to 1 foot and might as well hoist the sails and dowse the iron spinnaker as the boat will go faster under sail. I used to run the engine WOT ALL the time and never had ANY problems. Diesels like to be run hard as I found out in the Army. WOT is the most efficient speed also if your prop is sized right. So WOT for everything except docking and put the sails up once the wind gets above about 7 kts relative.
Another C30 Owner Says
It is a 3000 maximum rpm engine. 80-85% of LOAD is the sweet spot. Rpm is not the same as load, but it is the most practical gauge we have. That makes 2400-2500 rpm the "deducted" preferred operating range. Caveat: don't put blinders on, and adopt a mindset that this is the only acceptable way to use your engine. Yes, your diesel likes to run under load, and will give a longer life if it gets to do it for a large percentage of its clock time. But practical considerations in the real world mean there will be plenty of accumulated hours on your motor that were not in that optimum range. Marinas have speed limits/wake restrictions for a reason, and if the argument "I have to keep my engine running at 80% of its max" informs all your motoring, you will become a discourteous and dangerous boater when steaming. And there are plenty of other reasons to operate your MX25 outside that range. Sure, it's less than "optimum," but out of the thousands of hours of potential service of your engine, you will only be taking off a small percentage. Diesels are rugged by design. When you're out in the open, find that sweet spot range. But know that your engine will forgive you for having to live in the real world. Fair Winds, Jeff
It is a 3000 maximum rpm engine. 80-85% of LOAD is the sweet spot. Rpm is not the same as load, but it is the most practical gauge we have. That makes 2400-2500 rpm the "deducted" preferred operating range. Caveat: don't put blinders on, and adopt a mindset that this is the only acceptable way to use your engine. Yes, your diesel likes to run under load, and will give a longer life if it gets to do it for a large percentage of its clock time. But practical considerations in the real world mean there will be plenty of accumulated hours on your motor that were not in that optimum range. Marinas have speed limits/wake restrictions for a reason, and if the argument "I have to keep my engine running at 80% of its max" informs all your motoring, you will become a discourteous and dangerous boater when steaming. And there are plenty of other reasons to operate your MX25 outside that range. Sure, it's less than "optimum," but out of the thousands of hours of potential service of your engine, you will only be taking off a small percentage. Diesels are rugged by design. When you're out in the open, find that sweet spot range. But know that your engine will forgive you for having to live in the real world. Fair Winds, Jeff
Yours is a fresh water cooled diesel engine...
Cruise at 80% of max RPM and is the benchmark NOT engine temperature. Proved you have the right prop this is the way to go. Fresh water cooled engine should run at around 160 - 165 degrees Raw water cooled engines should run at around 145 degrees. An engine that runs hotter than 170 would most likely suggest a partial blocked heat exchanger or some other component that's not functioning properly in the raw water circuit. A 170 degrees, the salt in the salt water begins to agressive separate from the water and thereby coat the coolant chambers making it harder for the fresh water chambers to cool. This is why fresh water systems run hotter than than raw water cooled ones. Incidently, Catalina 30's build between 1983 and 1989 left the factory with undersized heat exchangers... many of which were never changed out. I also would consult with an engine propeller company such as Michigan Wheel to confirm that you have the right prop for your engine.
Cruise at 80% of max RPM and is the benchmark NOT engine temperature. Proved you have the right prop this is the way to go. Fresh water cooled engine should run at around 160 - 165 degrees Raw water cooled engines should run at around 145 degrees. An engine that runs hotter than 170 would most likely suggest a partial blocked heat exchanger or some other component that's not functioning properly in the raw water circuit. A 170 degrees, the salt in the salt water begins to agressive separate from the water and thereby coat the coolant chambers making it harder for the fresh water chambers to cool. This is why fresh water systems run hotter than than raw water cooled ones. Incidently, Catalina 30's build between 1983 and 1989 left the factory with undersized heat exchangers... many of which were never changed out. I also would consult with an engine propeller company such as Michigan Wheel to confirm that you have the right prop for your engine.
Whats in a name?
Bad Obsession? You must mean racing, not cruising; a 'friendly' name that. Just returned again here mates, unlike you boys I have 'a life' such as it is...;-) Have to add a nickles worth here, with my experience, done lotta motoring, politely called "motor sailing" up & down the coast and I think 'Capn Dave of G. Springs is the closest, the other Dave M Del Rey, toughest marina to enter Sunday afternoons, Has the temp a bit low.Would be great if it WOULD stay at 140f but 190f is the practical temperture and doesn't hurt the engine any. BTW what do any o youse motor heads think of this "Pro-long"? I heard some positives, put som in my 'Vette when I changed the oil seems to LOWER the operating temp, in fact it does. How would this, meaning the "
Bad Obsession? You must mean racing, not cruising; a 'friendly' name that. Just returned again here mates, unlike you boys I have 'a life' such as it is...;-) Have to add a nickles worth here, with my experience, done lotta motoring, politely called "motor sailing" up & down the coast and I think 'Capn Dave of G. Springs is the closest, the other Dave M Del Rey, toughest marina to enter Sunday afternoons, Has the temp a bit low.Would be great if it WOULD stay at 140f but 190f is the practical temperture and doesn't hurt the engine any. BTW what do any o youse motor heads think of this "Pro-long"? I heard some positives, put som in my 'Vette when I changed the oil seems to LOWER the operating temp, in fact it does. How would this, meaning the "
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