Q: Can I make my boat faster by changing the pitch of my prop?
A: This depends on what your present prop is doing. If you are getting
into the rated RPM range when you are wide open, then you are probably
not going to help yourself. If you go up in pitch, this will lower your
top RPM, and if it falls below what you should be turning, you will usually
lose speed. Conversley, going down in pitch will cause RPM to go up, which
can result in lost speed and possibly damage to the engine. The ideal prop
will put the RPM where it needs to be.
Q: What can I do to increase the pulling power on my boat?
A: You can always gain pulling power by going down in pitch. Most of
the time a drop of 2 inches is common. This will help quite a bit on the
low end, and will usually increase top RPM by about 4 to 5 hundred. If the
engine is already running close to red line, you might have to back off
the throttle with a light load to keep this RPM in line.
Q: What is the advantage of a 4 or 5-blade prop as compared
to a 3-blade?
A: Most boats are equipped with a 3-blade prop from the factory. A
4-blade prop will usually give a boat a little better low-end power and
handling, but often results in some loss of speed. A lot of bass boats
with high horsepower will do fairly well with a 4-blade prop, especially
with the new designs that are out now. Most inboard/outboard boats do just
fine with a 3-blade prop, unless they are lacking on horsepower. 4-blade
props do better when running close to the top of the surface, and most I/O's
are running deep enough that a speed loss is common because of the extra
drag. The 5-blade props are almost strictly a ski prop, where the low to
mid-range pull is of main importance.
Q: Can my present prop be modified, or do I have to purchase
a new prop?
A: Most props can be changed in pitch up to two inches of pitch from
the original size, either up or down. Cupping can be added or taken away.
What might help depends on what a person is trying to gain with their boat.
Q: What are the important aspects of the dimensions of a
A: The pitch of the prop is the most important dimension. This usually
determines the power and speed of the boat. Pitch is measured in inches
and refers to the number of inches a prop would move through the water for
every revolution. Of course, since water is a very fluid environment, there
is always some percent of slippage involved. The diameter of a prop is usually
a set dimension depending on the pitch and make. Most line of props will
go down slightly in diameter as the pitch goes up. The reasoning behind this
is that the lighter boats that can run higher pitch props don't need quite
the diameter as do the heavier boats. If a boat is using a 14 inch diameter
prop, and a 14 1/4 inch prop is available in another brand, as long as
the pitch is the same, the performance will probably not change.
Q: What is the advantage to a cupped prop?
A: A cupped prop can be run higher to the surface, as it holds the
water better and slips less than an uncupped version. A cupped prop is
going to run less RPM when wide open as it is pushing more water. It is
like running a higher pitched prop. If a boat is running a 21 inch uncupped
prop, a 19 inch cupped prop will usually turn about the same RPM, but will
have better power out of the hole, and might even run a little faster as
the engine or drive can probably be trimmed up higher.
Q: What are the pros and cons to stainless props versus
the aluminum version?
A: The stainless prop, if it is exactly the same dimensions as the
aluminum, will usually perfom a little better because they are a little
thinner and are more effecient as they don't flex as much under load. A
lot of the stainless props are designed for better top end than the aluminum
props by having a higher rake angle and better cupping. Of course, the cost
is higher, but the durability is a lot better. A concern with a lot of boaters
is whether or not a stainless prop will cause drive damage if a strike occurs.
If the prop hits a large rock or immovable object, then drive damage might
occur. Usually the blades will bend or the hub will slip before this happens,
but once in a while a shaft gets bent or gear tooth breaks. Most boat insurance
will cover any of this damage above the deductable.