legion050
30.05.2021 12:12:44
A lawn mower won't start without a blade on it. I doubt you could start an RC engine without a prop. Has anyone tried?[:o] here
See full version: Running the outboard without the prop
A lawn mower won't start without a blade on it. I doubt you could start an RC engine without a prop. Has anyone tried?[:o] here
A lawn mower won't start without a blade on it. I doubt you could start an RC engine without a prop. Has anyone tried?[:o] more
I smacked one inverted one time. The plane popped back up. The prop went from a 11x6 to a 2x6. The engine turned about 50,000 for about 1/10 of a second. I could not tell you if it died from overheat or no flywheel or what. I really thought it had thrown a rod or something. Once I fixed the plane it ran fine. more
The only time to run an engine without a prop is if you want a new engine. Running without a prop is a sure fire way to destroy the engine. more
Never ever run it without any load, unless you really need a new engine, also there is no way to tune an engine with no load applied as the tune will change with load.
A bent blade or nick will severely affect performance and could even damage the engine and transmission. Even worse, a bad prop may look fine to the eye. Larry Carlson at Black Dog Props in Stevensville, Maryland, which uses computers to diagnose and repair props, says that 80% of the propellers on his shop floor look healthy. But those otherwise "healthy"-looking propellers typically have differences in pitch of 1/2inch to 3/4 inch. [links]
Number of blades: More blades are smoother, but slightly less efficient. The typical compromise is three blades, although four blades are becoming increasingly more popular. more
With the prop out of the water, tap each blade in turn with block of wood. A different tone may indicate a serious problem.
The way your boat runs could tell you whether you've got the right prop or not.
Diameter: An important factor in thrust — the larger the diameter of the prop (everything else being equal), the more water that gets moved. As a general rule, when performance suffers, you change pitch and not diameter. Diameter is the first number listed in a prop size, such as 14 x 17.
Which material is best for a prop? A lot depends on where you do your boating. If your chances of hitting a submerged object are low, an aluminum prop is an all-around inexpensive choice. Aluminum props come standard from most boat and engine manufacturers, but they're less rugged than stainless-steel props. The latter are less likely to be damaged but are more expensive to repair. [links]
The more over-sized the prop diameter, the greater the wear you are placing on the motor. As the diameter increases, more power is required to achieve the same workload, resulting in abnormal stresses within the engine cylinders. In a worst case scenario, pistons or cylinder walls can be become damaged or the piston rings blown. Symptoms may include unusual engine tapping and reduced performance during acceleration. [links]
rpm gauge image by 76media from Fotolia.com more
The diameter of the propeller affects the engine speed and efficiency. Combined with pitch, the prop diameter affects how quickly the boat can move, the distance of travel for each revolution of the prop and the torque of the spinning propeller. It is important that your propeller is matched to the motor or serious engine problems could result.
Propeller diameter increases with the size of the boat. As the diameter increases, the blades of the propeller offer more resistance to travel through the water. This creates potentially damaging drag on smaller engines and boats. For larger boats, a larger diameter provides more propulsion power for the same reason. The larger boat presents more resistance to forward movement and needs a prop with a higher rotational reach. Diameter and pitch together determine the size of a propeller. To determine the prop size, measure the distance of forward movement for one complete rotation of the prop. This allows you to have two props of the same size but different diameter measurements. Higher pitches allow for greater speed and lower pitches reduce the drag on the engine.
A large diameter prop with a shallow pitch will have to spin more times to achieve the desired movement. To prevent the engine from over-accelerating, make sure that you use a prop with sufficient pitch for the size and weight of the boat. Larger diameter props offer the potential for higher speeds if the engine has the torque to push through the increased water resistance. Boating professionals such as Overton's or Dunnrite Propellers recommend matching your propeller diameter closely to the rated RPM of the engine.
marina fuel supply image by Christopher Nolan from Fotolia.com [links]
If you own a boat that has an outboard motor on it or boat with a sterndrive system, the propeller shaft must have what is called a thrust washer on it that is positioned on the shaft in front of the boat propeller. The thrust washer has two functions. The first reason why you must use one is it stops boat propellers from sliding forward on the prop shaft while being run in forward gear. That would cause damage to the lower unit housing from coming in contact with the rotating boat prop.
The propeller would also be damaged which would not be repairable along with possibly the lower unit housing not being repairable. The second reason is it centers and secures the front of the boat prop when the prop nut on the shaft is tightened to the proper torque spec. There are two thrust washer designs that achieve this. One is just flat on the side that contacts the propeller that makes it impossible for the boat prop to wobble once the prop nut is tight. The other design has a smaller diameter protruding inner shoulder to it that tucks inside the front of the prop that also centers and secures the front of the boat propeller.
You must use the correct thrust washer for your prop shaft to insure the propeller will be inside the lower unit housing at the proper depth so the exhaust gases will only exit out the center of the propeller instead of out over the propeller blades which would cause a huge loss of performance.