Choose the right prop



When vessels don’t perform, or an owner wishes to improve performance, one of the easiest ways to drastically change the vessel’s overall performance is by changing the propeller. But how do you do that without messing things up?

Though we are an engine manufacturer, we sell many engines complete with the customer’s desired propulsion as a package. In these instances, we usually ask our partners or the propulsion makers to make calculations.

Critical to performance is the proper calculations. Any major propeller maker can make calculations for their props. It is a balance between hull, engine, and propeller. For propellers, you can always contact our partner, France Helices, though any manufacturer that makes quality can design you a good prop.

In order to make calculations, a minimum of information is required: Vessel specs (LOA, LWL, Beam, Disp, etc.), Engine specs, and at minimum, a GA drawing of the hull since these have different efficiencies (or, items like foils or spray rails can alter performance).

There are several important factors that impact a propeller design:

1. Diameter

2. Pitch (how the blades are “twisted”)

3. Skew (the degree of transverse offset of the blade from the hub)

4. Rake (The degree of angle of the blade from 90 degrees perpendicular to the center of the hub)

5. Camber (sometimes referred to as the “cup”)

6. Blade Thickness (Thicker blades result in less vibration, but can give greater cavitation).

If the propeller is not designed correctly, or is installed with incorrect parameters, then cavitation, which causes prop damage, engine strain, and gearbox strain among other things, is sure to result.

This is why you should always input bona-fide data into any calculations: Especially the correct displacement, which is the most common error made in calculations.

Should you not have a propeller manufacturer make calculations, there are several tools online:

From (Requires Membership)

I-Phone App from Roth Company (Inexpensive)



Celebrate Industrial Engine Week! Airboats



Today is the final day of our industrial engine week, and we focus on a niche market that has been up-and-coming for MDPT over the last couple of years: Airboats. Hmmm…


Correct. Airboats are a special case that is handled by MDPT rather than the larger MarineDiesel group because airboats are a hybrid of sorts. They are boats, but they use engines that are engineered for use on land. This makes them unique in the marine world.

Traditionally, airboats were simple vehicles: A shallow, flat bottomed boat with a (usually) used aircraft engine mounted astern that featured a direct coupling to an aircraft propeller straight off the flywheel. Ratios were inexact, with propeller pitch largely used to control performance levels.

Modern airboats bear little more than a casual resemblance to these old vessels. Modern airboats can now be equipped with climate controlled cabins, gun positions for military use, and are always equipped with modern, compact and high powered engines. Propellers are designed with lightweight composites, and there are complex gear or belt drive systems that can include variable gear ratios. Indeed, some airboats are now equipped with contra-rotating dual props that provide huge amounts of torque and extremely high speeds.

Airboats are often commonly seen in the Everglades, or on TV shows like “Swamp People”, and so on. They handle conditions in swamps quite well, being shallow draft and not having any propeller to run aground or get snagged. However, there are many other applications for airboats, and this niche market is booming: Military use for patrol, rescue, use on ice. All of these uses are now common.

For more information:

Leppek, Adam P., “Optimization of an Airboat Design” (2012). Honors Theses. Paper 2180. offers a good and interesting overview of modern airboat design and why airboats are well suited for their application.

MDPT is at the forefront of powering some of these cutting-edge designs. Our marine heritage serves us well in providing specialized engines for airboats. As we mentioned earlier, airboats are a hybrid of sorts. They use engines designed for use on land, but they are exposed to the harsh marine environment. We have the ability to combine these two fields of expertise into a single, customized and application-specific product, with appropriate injectors, connectors, and cooling systems. We also work very closely with the drive manufacturers, propeller manufacturers, and designers to offer complete airboat propulsion packages.

We have completed airboat projects in Russia, Finland, the USA, Australia, and Thailand, and this market segment is becoming a specialty of MDPT. Contact us today on your next project, but please see below for some previous MDPT installations.

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