what is proper cruising rpm and max rpm for diesel in CD31

[RAJ]

just bought a CD31 and I was wondering what engine speeds the boat is designed for - the boat has a 3 cyl Universal 25hp w/ 3 bladed prop. What should the idle rpm be? What is the crusing rpm? What is the max rpm when she needs to be pushed?

thanks

Russell



rajarch@bellsouth.net

[Tom]

just bought a CD31 and I was wondering what engine speeds the boat is designed for - the boat has a 3 cyl Universal 25hp w/ 3 bladed prop. What should the idle rpm be? What is the crusing rpm? What is the max rpm when she needs to be pushed?

thanks

Russell

According to the manual the top of the power curve is at 1800 rpm. That is the spot where you will get the best fuel economy. However you probably won't make hull speed at that rpm (depending upon your prop.) Books on diesels say that you can cruise at 80% of the rated rpm. I don't have my manual at home here but I think our rated rpm is 3200 rpm. 80% of that would be like 2500. On mine if I try to run it at that speed it seems to really be working hard and vibration and noise go way up and the fuel efficiency goes down. I usually cruise at 2000, when really pressing go to 2200, in a boat threathening emergeny, of course, you "floor" it, but I've never had to do that. BTW Model 25 does not mean 25 horsepower. Model 25 was originally 18hp but Universal reworked it to get it up to 21 hp. I got this from the man at Universal personally. In calm water with no wind you should be able to get the rated rpm and not blow black smoke out the exhaust, otherwise you are over-propped. The engine originally came with a 2 blade prop.

Tom
CD 31 "Heiress" #15



TomCambria@mindspring.com

[Russell Johnson]

Tom

thanks for the info - when you are cruising in calm water @ 1800 - 2000 rpm, what would your hull speed be +-, given a clean bottom?

thanks,

Raj

just bought a CD31 and I was wondering what engine speeds the boat is designed for - the boat has a 3 cyl Universal 25hp w/ 3 bladed prop. What should the idle rpm be? What is the crusing rpm? What is the max rpm when she needs to be pushed?

thanks

Russell

According to the manual the top of the power curve is at 1800 rpm. That is the spot where you will get the best fuel economy. However you probably won't make hull speed at that rpm (depending upon your prop.) Books on diesels say that you can cruise at 80% of the rated rpm. I don't have my manual at home here but I think our rated rpm is 3200 rpm. 80% of that would be like 2500. On mine if I try to run it at that speed it seems to really be working hard and vibration and noise go way up and the fuel efficiency goes down. I usually cruise at 2000, when really pressing go to 2200, in a boat threathening emergeny, of course, you "floor" it, but I've never had to do that. BTW Model 25 does not mean 25 horsepower. Model 25 was originally 18hp but Universal reworked it to get it up to 21 hp. I got this from the man at Universal personally. In calm water with no wind you should be able to get the rated rpm and not blow black smoke out the exhaust, otherwise you are over-propped. The engine originally came with a 2 blade prop.

Tom
CD 31 "Heiress" #15

rajarch@bellsouth.net

[Tom]

Tom

thanks for the info - when you are cruising in calm water @ 1800 - 2000 rpm, what would your hull speed be +-, given a clean bottom?

thanks,

Raj

It depends on the specs of your prop, but probably in the 5 to 6 knot range.

just bought a CD31 and I was wondering what engine speeds the boat is designed for - the boat has a 3 cyl Universal 25hp w/ 3 bladed prop. What should the idle rpm be? What is the crusing rpm? What is the max rpm when she needs to be pushed?

thanks

Russell

According to the manual the top of the power curve is at 1800 rpm. That is the spot where you will get the best fuel economy. However you probably won't make hull speed at that rpm (depending upon your prop.) Books on diesels say that you can cruise at 80% of the rated rpm. I don't have my manual at home here but I think our rated rpm is 3200 rpm. 80% of that would be like 2500. On mine if I try to run it at that speed it seems to really be working hard and vibration and noise go way up and the fuel efficiency goes down. I usually cruise at 2000, when really pressing go to 2200, in a boat threathening emergeny, of course, you "floor" it, but I've never had to do that. BTW Model 25 does not mean 25 horsepower. Model 25 was originally 18hp but Universal reworked it to get it up to 21 hp. I got this from the man at Universal personally. In calm water with no wind you should be able to get the rated rpm and not blow black smoke out the exhaust, otherwise you are over-propped. The engine originally came with a 2 blade prop.

Tom
CD 31 "Heiress" #15

TomCambria@mindspring.com