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Author Topic:   DAUNTLESS 15 Propeller

jrjbooger3 posted 11-17-2008 02:20 PM ET (US)
I have a 1993 Evinrude 70-HP [mounted on a Boston Whaler DAUNTLESS 15]. I don't know the pitch of the propeller. I will try to find out. With two people about 400-lbs, [with the engine] trimed out, the engine speed will reach about 6,000-RPM [at maximum throttle]. I think this [engine speed] is too high. I would like to [change propellers]. Does anyone have the same set up? Or ideas.
jimh posted 11-18-2008 12:00 AM ET (US)
You can easily discover the diameter of your propeller by measurement. You can generally deduce the pitch by looking carefully for markings on the propeller of either the pitch or a part number. If a part number is all that is marked, just enter the part number into a GOOGLE search with the additional term "Propeller" and you will likely be able to find a listing that will mention the pitch.
jrjbooger3 posted 11-20-2008 08:18 AM ET (US)
I cleaned the prop up and swa that it said 13*10. The prop is pretty beat up so need to get a new one, but didnt know if i should change different size or pitch.
jrjbooger3 posted 11-25-2008 09:44 AM ET (US)
I cleaned the prop up even more and saw that it was a 13x19. not a 13x10.
jimh posted 11-25-2008 09:48 AM ET (US)
There is a rule of thumb that a decrease in propeller pitch of two inches will produce an increase of engine speed of 450-RPM, and vice versa. If you want to reduce the wide-open-throttle engine speed, increase the propeller pitch.
Tom W Clark posted 11-25-2008 11:24 AM ET (US)
The rule of thumb is that every two inch change in propeller pitch will produce an inverse change in engine speed of 300-400 RPM, but different propeller models are different as are outboard motors.
A 450 RPM change is possible, but would be unusually large.
It sounds as if you are well propped as it is. I would expect that boat and motor to make good use of a 13" x 19" propeller as the 70 HP OMC motors from that era had a 6000 RPM redline.
jrjbooger3 posted 11-25-2008 12:49 PM ET (US)
thanks Tom and Jim, i know the red line was around 6000 RPM, and that is what my bout will run at WOT, but is it ok to run the motor at that high of RPMs for few miles, or would it be better to run at like 5500RPMs.

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Author	Topic: DAUNTLESS 15 Propeller
jrjbooger3	posted 11-17-2008 02:20 PM ET (US) I have a 1993 Evinrude 70-HP [mounted on a Boston Whaler DAUNTLESS 15]. I don't know the pitch of the propeller. I will try to find out. With two people about 400-lbs, [with the engine] trimed out, the engine speed will reach about 6,000-RPM [at maximum throttle]. I think this [engine speed] is too high. I would like to [change propellers]. Does anyone have the same set up? Or ideas.
jimh	posted 11-18-2008 12:00 AM ET (US) You can easily discover the diameter of your propeller by measurement. You can generally deduce the pitch by looking carefully for markings on the propeller of either the pitch or a part number. If a part number is all that is marked, just enter the part number into a GOOGLE search with the additional term "Propeller" and you will likely be able to find a listing that will mention the pitch.
jrjbooger3	posted 11-20-2008 08:18 AM ET (US) I cleaned the prop up and swa that it said 13*10. The prop is pretty beat up so need to get a new one, but didnt know if i should change different size or pitch.
jrjbooger3	posted 11-25-2008 09:44 AM ET (US) I cleaned the prop up even more and saw that it was a 13x19. not a 13x10.
jimh	posted 11-25-2008 09:48 AM ET (US) There is a rule of thumb that a decrease in propeller pitch of two inches will produce an increase of engine speed of 450-RPM, and vice versa. If you want to reduce the wide-open-throttle engine speed, increase the propeller pitch.
Tom W Clark	posted 11-25-2008 11:24 AM ET (US) The rule of thumb is that every two inch change in propeller pitch will produce an inverse change in engine speed of 300-400 RPM, but different propeller models are different as are outboard motors. A 450 RPM change is possible, but would be unusually large. It sounds as if you are well propped as it is. I would expect that boat and motor to make good use of a 13" x 19" propeller as the 70 HP OMC motors from that era had a 6000 RPM redline.
jrjbooger3	posted 11-25-2008 12:49 PM ET (US) thanks Tom and Jim, i know the red line was around 6000 RPM, and that is what my bout will run at WOT, but is it ok to run the motor at that high of RPMs for few miles, or would it be better to run at like 5500RPMs.