For many years now, owner of boats have debated the questions of 3-blades versus 4-blades .
Most outboards — 90 percent by some estimates — are equipped with three-blade propellers, and most offer strong performance. 3-blades props are popular because they tend to offer a performance compromise, a pleasing ( or at least satisfactory) blend of acceleration ,fuel efficiency , lift and speed . If you want to improve acceleration, fuel efficiency or lift ,a 4 -blade propeller might help, but just be aware that performance gains in one area can mean performance losses in another. It is all about what is most important to you. Also, before changing props, make sure there are no other factors adversely affecting performance, such as hull fouling, lack of adequate power, or improper weight distribution. Only after you are confident that the boat and power are well-tuned should you then move on to propping.
Decide which performance attributes you desire most. The captain of a flats boat, for example, might want to pop up on plane more quickly, and add lift for running in very shallow water.The additional blade area grips the water better, allowing for quicker acceleration.The greater blade area also lifts the hull more while underway, which minimizes draft. However, the additional drag generated by an extra prop blade can also reduce top speed.While speed is important to some saltwater anglers, others seek fuel efficiency and the fishing range that comes with it. “This is where a four-blade prop can really help.
Ventilation — the tendency of the blades to lose their “bite” — often occurs when props are immersed in aerated water, such as the wake of a stepped-hull boat. On other boats, aeration can be unintentional, caused by poorly positioned water intakes or large through-hull transducers.
A four-blade is less likely to ventilate in aerated water, simply because it has more blades to grab the water. That’s why you see some stepped hulls equipped with these props.
Four-blades can resolve other ventilation issues. If a helmsman elevates the jack plate on a bay boat too high, the prop tends to lose its bite and ventilates. The grip of a four-blade allows a bay-boat captain to maximize the height at which he can run the outboard, and cross flats that might not be navigable with a three-blade prop.
Two key measurements of a prop are diameter and pitch. Pitch is the theoretical distance (e.g., 19 inches) a propeller will move a boat with one revolution of the prop shaft. Generally speaking, the diameter of a four-blade prop is smaller than that of a three-blade prop with the same pitch.This helps a four-blade spin up quickly and allows the motor to rev as high as it would with a three-blade of comparable pitch. Nearly all saltwater props for outboards are made from stainless steel.