What Engine Crankshaft Speed for a 13-foot Whaler Hull?

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Author Topic:   What Engine Crankshaft Speed for a 13-foot Whaler Hull?

blade posted 05-27-2005 01:49 AM ET (US)
I have a 13-foot Boston Whaler boat with a Evinrude outboard motor that was made in 1995. At what engine crankshaft speed should the engine be run? I find myself trying to run at 5000-RPM or more, but I think I should probably run at 4000-4500 RPM. What do you think? Will I cause damage to the engine running at 5500-RPM for very long?
Thanks, blade
Liteamorn posted 05-27-2005 10:56 AM ET (US)
To much info is missing here. What is your red line? Are you underpowered? If 5500 is the red line you are running the dog snot out of that engine.
Liteamorn posted 05-27-2005 11:06 AM ET (US)
Yes 4000-4500 is fine for almost any engine.
blade posted 05-27-2005 10:38 PM ET (US)
Sorry it is a 40 hp. And it does not have a red line on the tac. It must be after market. What would be the average speed at 4500-RPM?
jimh posted 05-27-2005 10:57 PM ET (US)
I do not recall ever seeing a red line on a marine tachometer. They are normally a universal tachometer and are not produced for use with a specific engine, thus they are not made with a particular red line region on the dial face.
Sheila posted 05-28-2005 01:09 AM ET (US)
Blade, your owner's manual, if you have it, or a dealer, should be able to tell you the maximum RPM for your motor. It varies from motor to motor.
Liteamorn posted 05-28-2005 07:44 AM ET (US)
Sorry change red line to MAX RPM. If your max rpm is 5500 4000-4500 should be a nice cruising speed
jimh posted 05-28-2005 08:43 AM ET (US)
Most two-stroke outboard motors are not run continuously at maximum rated engine speed. They really are not designed for that. Typical use of an outboard motor is to run at a cruising speed which is around 60-70 percent of the maximum rated speed. A typical maximum engine speed is 5500-RPM. Using the 70-percent guideline, your cruising speed would be
5500 x 0.70 = 3850-RPM
The speed of the boat through the water varies as a function of the engine speed, the lower unit gear ratio, and the propeller pitch. If you tell us this information we can help you find what boat speed you should be getting.
In most cases the sea state determines the engine speed, and, except in extremely calm conditions, maximum engine speed is not often used.
Liteamorn posted 05-28-2005 09:48 AM ET (US)
I usually cruise at the speed that the engine sounds the least labored. As Jim said if varies in different conditions. I have run all my outboards in the 4000-4500 range. My Old Yam on a Wellcraft topped out at 5000, it sounded the best at 4000 rpm. My Evinrude tops out at 5500 rpm, I cruise between 4200 and 4500. When I run them higher than that they sound like they are working a LOT harder than they need to. I found that they tent to labor when I run them lower also. When seas are less than optimal I run accordingly.
Ed
Liteamorn posted 05-28-2005 10:22 AM ET (US)
Make that TEND to labor.
blade posted 05-31-2005 03:22 AM ET (US)
Thanks for the replies!
I try to keep it under 5000 with the occasional push over the top. 4500 sounds good for the motor but I think I will talk to the mechanics about best speed for the engine without pushing too hard.
Your responses are VERY appreciated!
Thanks again,

blade

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Author	Topic: What Engine Crankshaft Speed for a 13-foot Whaler Hull?
blade	posted 05-27-2005 01:49 AM ET (US) I have a 13-foot Boston Whaler boat with a Evinrude outboard motor that was made in 1995. At what engine crankshaft speed should the engine be run? I find myself trying to run at 5000-RPM or more, but I think I should probably run at 4000-4500 RPM. What do you think? Will I cause damage to the engine running at 5500-RPM for very long? Thanks, blade
Liteamorn	posted 05-27-2005 10:56 AM ET (US) To much info is missing here. What is your red line? Are you underpowered? If 5500 is the red line you are running the dog snot out of that engine.
Liteamorn	posted 05-27-2005 11:06 AM ET (US) Yes 4000-4500 is fine for almost any engine.
blade	posted 05-27-2005 10:38 PM ET (US) Sorry it is a 40 hp. And it does not have a red line on the tac. It must be after market. What would be the average speed at 4500-RPM?
jimh	posted 05-27-2005 10:57 PM ET (US) I do not recall ever seeing a red line on a marine tachometer. They are normally a universal tachometer and are not produced for use with a specific engine, thus they are not made with a particular red line region on the dial face.
Sheila	posted 05-28-2005 01:09 AM ET (US) Blade, your owner's manual, if you have it, or a dealer, should be able to tell you the maximum RPM for your motor. It varies from motor to motor.
Liteamorn	posted 05-28-2005 07:44 AM ET (US) Sorry change red line to MAX RPM. If your max rpm is 5500 4000-4500 should be a nice cruising speed
jimh	posted 05-28-2005 08:43 AM ET (US) Most two-stroke outboard motors are not run continuously at maximum rated engine speed. They really are not designed for that. Typical use of an outboard motor is to run at a cruising speed which is around 60-70 percent of the maximum rated speed. A typical maximum engine speed is 5500-RPM. Using the 70-percent guideline, your cruising speed would be 5500 x 0.70 = 3850-RPM The speed of the boat through the water varies as a function of the engine speed, the lower unit gear ratio, and the propeller pitch. If you tell us this information we can help you find what boat speed you should be getting. In most cases the sea state determines the engine speed, and, except in extremely calm conditions, maximum engine speed is not often used.
Liteamorn	posted 05-28-2005 09:48 AM ET (US) I usually cruise at the speed that the engine sounds the least labored. As Jim said if varies in different conditions. I have run all my outboards in the 4000-4500 range. My Old Yam on a Wellcraft topped out at 5000, it sounded the best at 4000 rpm. My Evinrude tops out at 5500 rpm, I cruise between 4200 and 4500. When I run them higher than that they sound like they are working a LOT harder than they need to. I found that they tent to labor when I run them lower also. When seas are less than optimal I run accordingly. Ed
Liteamorn	posted 05-28-2005 10:22 AM ET (US) Make that TEND to labor.
blade	posted 05-31-2005 03:22 AM ET (US) Thanks for the replies! I try to keep it under 5000 with the occasional push over the top. 4500 sounds good for the motor but I think I will talk to the mechanics about best speed for the engine without pushing too hard. Your responses are VERY appreciated! Thanks again, blade