View Full Version : W.o.t.
Efldrifter
06-21-2009, 10:47 AM
Wide open throttle. I have a 16' ft alumaweld super vee with a 02 Mercury 2-stroke 90/65 jet. It also has a ss 4 blade impeller. My question is, dose it hurt anything to run the throttle wide open for extended time? I find that I seem to run the throttle w/o most of the time . I don't currently have a tach , so I'm not sure what rpm's i am running. It would seem to me that the thottle should be at maximum before reaching the reccomended maximum rpm. which I belive is 5500. Thanks in advance for your :twocents:.
Starfish
06-21-2009, 11:47 AM
It shouldn't hurt much other than your pocketbook. It's probably worth having a tach to be on the safe side, but typically your impeller will be sized to keep you out of trouble. Fuel consumption will be higher than if you backed off a bit, but 2-stroke outboards are pretty bulletproof when it comes to running wide open within their recommended RPM range.
The RPM that your motor runs at WOT is related to the size of the prop, weight of the boat+gear. WOT could be too much or not if you push the motor to the high side of the recommended RPM range.
cmb1998
06-22-2009, 03:13 PM
The RPM that your motor runs at WOT is related to the size of the prop, weight of the boat+gear. WOT could be too much or not if you push the motor to the high side of the recommended RPM range.
He is running a jet. Weight of the boat doesn't affect the RPM of the motor, although it may affect the speed of the boat.
Later,
Chris
Weight of the boat+gear will affect the maximum speed of the motor, and the principle is the same for the size impeller as well. The reason is the motor won't can't get to the higher speed if it is pushing more force. That is, if we assume the jet impeller isn't slipping. If it is, then all bets are off!
cmb1998
06-22-2009, 04:16 PM
Weight of the boat+gear will affect the maximum speed of the motor, and the principle is the same for the size impeller as well. The reason is the motor won't can't get to the higher speed if it is pushing more force. That is, if we assume the jet impeller isn't slipping. If it is, then all bets are off!
The motor always produces the same amount of thrust (assuming you have not damaged some componet of the pump). It's only a matter of how much thrust is required to push the weight of your boat, thus RPM's should always be the same at WOT.
Read here -> http://www.americanturbine.com/information/understand_jetboat.htm
Later,
Chris
Efldrifter
06-22-2009, 06:00 PM
I am still a bit confused. I guess the answer I am looking for is when outboard motors are set up. Is the maximum throttle rpm under the factory specified high limit? So you couldn't over rev. I tend to agree with Chris. The thrust you create at a determined rpm would always be the same. Thanks for your input. Guess I need to install a tach. And thanks for the link. Good information.
Read here -> http://www.americanturbine.com/information/understand_jetboat.htm
Yes, that is the same section they had 7 years ago, but I think you are making some assumptions. You are implying that a heavily loaded boat will follow the same RPM curve. In my experience, that is simply not the case.
olybirds
06-27-2009, 03:54 AM
Yes, that is the same section they had 7 years ago, but I think you are making some assumptions. You are implying that a heavily loaded boat will follow the same RPM curve. In my experience, that is simply not the case.
your thought process holds true for a PROP.. a JET is a different beast. THe jet impeller is internal to the motor and facing down, it will spool up no matter what the load, but a heavy load will cause more drag on the boat, thus slowing the boat, but the motor will get to max rpm..
THe jet impeller is internal to the motor and facing down, it will spool up no matter what the load, but a heavy load will cause more drag on the boat, thus slowing the boat, but the motor will get to max rpm..
You seem to be ignoring the flow into the intake. The flow velocity into the intake changes compared to the speed of the boat. The speed of the boat varies by weight in the boat. Changing the amount of pressure/flow into the pump/jet will affect the ability to reach the same engine RPM.