How To Determine Propeller Slip

Propeller slip, also known as prop slip, is a critical statistic that directly affects performance. The simplest way to explain prop slip is to think of a screw. Each time a screw makes a complete turn, it has completed a “pitch.” Pitch is the distance the screw traveled during one complete turn. A propeller turns in much the same way and also has a pitch. The problem is that water produces drag against the boat and propeller, so the propeller never actually reaches its full pitch. The lost distance of the pitch due to drag is called the propeller slip, or prop slip for short. Reducing the prop slip results in enhanced performance and fuel efficiency.

There are many factors that affect prop slip including the actual pitch of the propeller, the condition of the propeller, the design of the hull, the condition of the bottom of the craft, additional weight on the craft, distribution of weight, height the engine is mounted at, engine trim angle and setback, jack plate mounting, speed of the craft, and more. Speed and hull type are two of the top factors that affect prop slip. For instance, a sailboat or barge traveling at 9 mph will have a prop slip of approximately 45%, while a hydroplane traveling at over 90 mph can have a prop slip as low as 7%.

How is Prop Slip Determined?

To properly determine prop slip, users must know several determining factors, including speed, RPM, drive ratio and propeller pitch. The professionals at Livorsi use this algorithm to determine prop slip:


For instance, let’s say a boat is traveling at 61.3 mph at 4300 RPM. It has a prop pitch of 24″, and the drive ration is 1:36:1. By using the equation listed above, and inserting the figures just stated, we can see that the prop slip equals 14.7%.

Algorithm (2)

In order to achieve maximum performance, prop slip must be determined at a variety of speeds. Additional factors such as RPMs, course over ground, and speed (in mph or Km) can be determined in real-time. Having access to these performance statistics in real-time allows users to determine if changes should be made to other parts or features of the craft in order to enhance performance. It is also useful to determine if a newly-installed part has a positive or negative influence on prop slip.

Just ask Teague

If this all seems a little much to perform each time prop slip is to be determined, Livorsi has developed a high performance marine line of gauges that will do the work so you don’t have to. Check them out or call the knowledgeable parts department at Teague Custom Marine for guidance. As one of the leading marine distributors of Livorsi products, they can talk you through a variety of Livorsi gauges including Mega/Race gauges, Industrial Series, Standard Gauges, Specialty Gauges, and Air/Fuel Mixture Gauges. If you are unsure of the correct part for your specific boat, they will make recommendations for parts, as well as styling, as gauges are available in different colors.

About Livorsi

Livorsi has been a leading manufacturer of custom marine parts for years. For over 25 years, Livorsi has continued to excel by producing innovative parts for performance boating enthusiasts. Teague Custom Marine has partnered with Livorsi due to the reputation Livorsi has for quality, reliability and value for custom performance marine parts.