21 Pitch Prop Vs. 19 Pitch Prop – How To Know Correct Prop?

Last Updated: May 11th, 2021 | By: Gina

Like you use and maintain your car, similarly you need to take care of your boat. Using the right parts will keep you away from any troublesome issues and prevent you to land up in an abandoned situation while you are on the go for fishing for bass.

When it is about boating then the two most important terminologies are:

  1. Propeller diameter
  2. Pitch

The propeller is the main part that is responsible for driving your boat. Understanding it in the right way will actually save you from a lot of hassles.

Let us understand this better…

Propeller Diameter – What is it and why it matters?

When you are thinking of investing for a new propeller for your boat, you will need to know about the specs and the terminologies properly. Pitch and propeller diameter are the two most important specifications that are directly relatable to real-world performance.

Let us start knowing them properly:

The distance which is made blade tips across the full circle is known to be the propeller diameter. Essentially, the rpm will determine the propeller turns and the amount of power which would be delivered to it. When it is about slower boats, the diameter tends to increase on propellers.

What do you mean by a “Prop Pitch”?

‘Prop Pitch’ or ‘Propeller Pitch’ is primarily the distance with which your boat propeller will move in one revolution through soft-solid. This is similar to the screw that is made to move through wood in a single rotation.

If you have a ’21 pitch prop’- it will move 21 inches forward in one revolution whereas the ’19 pitch prop’- it will move 19 inches forward in one revolution.

what does prop mean

How does this matter to your boat?

Just assume your boat propeller to be the axle on your car. The more pulling power occurs from a standstill with a lower ratio. Same physics is related to a boat propeller. If your boat has a lower pitch propeller then this will accelerate more quickly from a standoff position in comparison to a higher pitch propeller. Sadly, the lower pitch will let your engine reach to a max rpm at a slow speed, even though at a fast acceleration rate.

Better top speeds will be offered by a high pitch propeller but acceleration will be quite slow. Just keep one thing in mind that, by just fitting a high-pitch propeller to your boat along with a low horse power engine in any case does not refer that you will make your boat faster.

Your boat will achieve high-speed but for a short time span before it gets bogged down. Eventually with the high-pitch and diameter of the propeller they will over work & wear down thereby effecting the internal parts of the engine that are not designed to tackle this much stress.

Pro tip:

Note that every inch of the pitch is equivalent to – 200 rpm. If you are on the go of changing your recreational boat propeller from a 21 pitch prop to 19 pitch prop then you will have to increase the engine rpm by 400 revolutions.

The primary idea when you find a boat propeller is to go for the speeds that will give you the suitable acceleration and this is the reason why people stick between a 21 Pitch Prop vs. 19 Pitch Prop.

Boat Propeller

Which one should be your choice? 21 Pitch Prop or 19 Pitch Prop

The answer for this is quite subjective as this is completely dependent on your personal choice and need.

Some tips are listed below to help you determine which one you need- 21 Pitch Prop or 19 Pitch Prop

What Are the Problems You Are Looking to Solve?

What kind of issues you are facing?

  1. Is your boat moving slowly or you are facing any problems with the speed type you desire?
  2. Is the problem related to fuel consumption?
  3. Are you looking for a better all-around performance?
  4. Is your current prop ventilating excessively?

Once you are clear with the problem then it will be extremely easy for you to find the solution.

Are you revving the engine under or over?

The manual provided by the manufacturer will help you know about your boat engine specs and for which range it is made to speed-up.

It will be like this:

  1. 4200-5000 rpm for sterndrive
  2. 5000–5500 rpm for an outboard

Any condition such as over-revving or over-reeving will damage your engine much faster. If any of the case exists (under revving or over-revving) then the best solution is to purchase a new propeller that will work according to the specifications for your specific boat.

Pitch Up Or Pitch Down

This is probably the basic question that needs an answer before you invest in a new propeller. We have already discussed above, by increasing your prop-pitch the engine’s rpm will drastically decrease and vice-versa.

Going by the general rule, for every 2-inch increase in pitch the rpm of the engine tends to decrease by roughly 400 revolutions. In case your boat is over revving then you will need a propeller with a higher pitch and vice-versa. In the former case get a 21 pitch propeller for best results.