21 Pitch Prop vs. 19 Pitch Prop: Which Do You Need?
Your boat is very much like your car; without proper maintenance and the right parts, it will give you issues and might leave you stranded while out fishing for bass. The difference between your boat and your car is that the parts aren’t quite the same.
While it will do you well to know how to change a flat on your car, when it comes to boating, propeller diameter and pitch are some of the most important terminologies. This is because it’s your propeller that actually drives the boat. So understanding a bit about it could save you a whole lot of headache down the road.
What Is Propeller Diameter and Why Does It Matter?
Any time you want to buy a new propeller for your boat, you need to understand what the specs are and what all those terminologies mean. Propeller diameter and pitch are two of the most important specifications that directly translate into real-world performance.
Let’s start by defining what they mean.
The diameter of a propeller is the distance across the full circle being made by the blade tips. It’s primarily determined by the rpm at which the propeller would be turning as well as the amount of power being delivered to it. This diameter tends to increase on propellers typically used on slower boats while increasing propellers used for faster boats.
What Does “Prop Pitch” Mean?
Propeller pitch typically referred to as “prop pitch,” is essentially the distance a propeller would move in a single revolution through soft solid. Kind of like the distance a screw would move through wood in one rotation. So, in this case, a “21 pitch prop” would move 21 inches forward in one revolution, and a “19 pitch prop” would move 19 inches forward in one revolution.
So what does all this mean to your boat?
Think of your propeller as if it were the axle on your car. The lower the ratio, the more pulling power it has from a standstill. This is the same physics that is applied to a boat propeller. A boat with a lower pitch propeller could accelerate much faster from a standstill position than one with a higher pitch propeller. Unfortunately, this lower pitch would make your engine reach maximum rpm at much slower speeds, albeit faster acceleration.
On the other hand, a higher pitch propeller will give you better top speeds but much slower acceleration. It should also be noted that simply fitting a high pitch propeller to a boat with a lower horsepower engine doesn’t mean that you will make your boat faster.
While the boat will achieve higher speeds, it will do so for a short while before getting bogged down. The propeller’s higher pitch and diameter will eventually overwork and wear down the internal engine parts that just aren’t built to withstand that kind of stress.
Pro tip: Remember that each inch of pitch is equivalent to about 200 rpm. So if you are going to be changing the propeller on your recreational boat and decide to go from a 21 pitch prop to a 19 pitch prop, you will be essentially increasing the engine rpm by around 400 revolutions.
The idea is to find a boat propeller that will give you the kind of speeds you want with the right kind of acceleration, and that’s why most people get stuck between a 21 Pitch Prop vs. 19 Pitch Prop.
21 Pitch Prop vs. 19 Pitch Prop – Which One Should You Choose?
As is the case with pretty much everything else, the answer to this question is highly subjective; it depends on what it is you need in particular. As such, here are some tips that will help you determine which one between 21 pitch prop vs 19 pitch prop you need.
What Are the Problems You Are Looking to Solve?
What are some of the issues you are facing?
- Is your boat sluggish when coming out of the hole, or are you having issues hitting the kind of speeds you want?
- Is it a fuel consumption issue?
- Do you want better all-around performance?
- Maybe your current prop is ventilating excessively?
As soon as you define the problem, you will be in a much better position to find the perfect solution.
Are You Under or Over Revving the Engine?
Your boat owner’s manual will include specs that tell you within which range your boat engine was designed to rev. It’ll look something like this: “4200-5000rpm for sterndrive” or “5000–5500rpm for an outboard.”
Under revving or over-revving, your engine will damage it faster than you would like. If you find that your boat engine is either under revving or over-revving in contradiction to the specs, the simplest solution is to buy a propeller with the appropriate pitch for your specific boat, which leads us to the next point.
To Pitch Up or Pitch Down?
This is an integral question that must be answered before you buy the new propeller. As explained, by increasing your prop pitch, you will be effectively decreasing the engine’s rpm and vice versa.
Since the general rule of thumb is that every two-inch increase in pitch decreases the engine’s rpm by about 400 revolutions, if you find that your boat is under revving, then you might want to consider getting a propeller with a lower pitch and vice versa. If your boat’s issue is that it’s over-revving, then getting the 21 pitch propeller might be the best solution.
Also Read: Best Bass Boats – Top 7 Picks
The beauty of all this is that your boat manual will have the desired specifications, but you could also ask your mechanic or even your dealer to advise which prop pitch would be the perfect solution for your specific boat. Just remember, one of the most important considerations here is your performance goal. What is it you want the boat to do exactly?