How Low Should a Motor Set on a Pontoon Boat? (Explained)


How Low Should a Motor Set on a Pontoon Boat

Pontoon boats are exciting vessels, famed for their stability and user-friendliness. They barely flip, thanks to their size and construction. Pontoons are appreciably spacious, making them excellent options for a family ride out. Driving pontoon boats doesn’t involve significant technicalities or experience either. This is courtesy of speed and shape.

If you desire your pontoon to perform optimally, the transom motor height should be a critical consideration. It can be set high enough provided there isn’t a notable drop in water pressure and possible ventilation complications. This is beneficial in enhancing the speed by cutting down the hydrodynamic drag’s impact while the pontoon boat is in motion.

What is the Outboard Motor?

Most watercraft – especially the smaller variants – leverage outboard motors as their motorized propulsion mechanism. The outdoor motor is made of the engine, jet drive (otherwise known as a propeller), and gearbox.

From its design, the transom’s exterior is outfitted with the outboard motor. Outboard motors are loved for their flexibility (a notable differentiator between outboard and inboard motors), in that you can readily remove them when you want to store them or for maintenance purposes.

Outdoor motors do more than just propelling your boat. They also play a crucial role in the maneuverability of your boat, specifically regarding steering control. Considering their design mechanisms, these motors can pivot over the mountings, controlling where the thrust is directed at.

Yes, an outdoor motor could hit the bottom. To avoid this scenario, you could tilt the motor up. This can be done either manually or electronically.

Such elevation is beneficial, especially when you are driving through shallow waters. Should there be debris in such waters and your motor isn’t elevated, you can expect it to be damaged, with even the propeller suffering damages too.

Several types of outboards are deployed in boats today. Below are the most prevalent types.

Electric-powered Outboards

Ray Electric Outboards first introduced electric outboards in 1973. They are propulsory units designed to be self-contained, which find application in boats today.

Electric outboards are distinct from trolling motors. The latter is not built to be a major power source.

Commonly, electric outboards have motors operating within a DC range of 12-60 volts, with a DC bandwidth of 0.5-4kW. Given this design, electric outboards can turnout at least 10kW, giving it the capacity to substitute a petrol engine of at least 15HP. 

With more recent advancements, however, we are seeing contemporary electric outboard motors being operated by AC.

Portable Outboards

Outboard motors with anywhere under 15HP are commonly portable. They have reduced sizes and can be readily attached to the boat.

Clamps can achieve this appending. What more, portable outboards can be moved across boats as you like.

Portable outboard motors weigh as little as 26 lbs, integrated with fuel tanks. This facility could power a dinghy at approximately 9.2 mph.

Most portable outboard motors are fitted with manual start mechanisms. This involves steering duties being catered for by a tiller, with the gearshift and throttle heaped on the motor’s exterior.

Aside from dinghies, portable outboard motors are used to power smaller watercraft like canoes and Jon boats. In some cases, portable outboards find use in supplying sailboats with auxiliary power.

In exceptional circumstances, portable outboards find use in trolling aboard bigger watercraft. This is possible as portable outboards are reputed for their efficiency when it comes to trolling speeds. 

When using these portable outboards for such trolling purposes, the motor should adjoin the transom, appended to the primary outboard. This will make it possible to maneuver the helm.

Considering the need for complete remote control, contemporary designs of portable motors are coming with electric starting and power trim functionalities.

Why Your Motor Needs to be at the Right Height?

The height of your outboard motor is a significant consideration when setting up your boat. The motor needs to be set at an optimal height because it causes propeller ventilation issues if it is too high. This reduces the power of the propeller, especially its push on water. 

On the flip side, if the outboard is set too low, it triggers enormous drag. This slashes fuel efficiency and even reducing your boat speed. Considering the need for engine height flexibility, most outboards today have their motor bracket fitted with a series of mounting holes aligned vertically. This allows you to raise the outboard height or drop it as needed.

There are cases where you can enhance your pontoon performance by installing the anti-ventilation plate on top of the boat bottom. In this arrangement, the outboard is placed higher than normal.

Another thing to consider when examining the optimal height for your engine is the propeller’s distance from the boat’s bottom. Now granted the intermittent rise in water flowing under your pontoon, you can mount your engine at a higher height if your propeller is reasonably spaced from the transom.

The propeller distance differs depending on the outboard design. Take, for instance, a comparison between Mercury OptiMax and Mercury Verado outboard motors. 

The Mercury Verado’s propeller’s distance from the boat bottom is about 6 inches further aft when measured against the propeller distance for the Mercury OptiMax.

However, the standard recommendation is that for every 8-10 inches distance between the propeller and the transom, the outboard motor should be elevated by an inch.

Determining Your Boat Transom Angle

The transom angle – commonly measured in degrees – is the transom’s vertical inclination. Commonly, the transom angle ranges from 0-30 degrees, with the average transom angle set at 14 degrees. Expectedly, when the transom angle is zero, it means it is flat.

The transom angle is notable because it determines how flexible the boat trimming capacity is. Of course, there are many ways to measure your boat’s transom angle.

One common way to achieve this measurement is via your regular carpenter’s square ruler. How do you get this?

Start by sliding the square ruler’s long side under your boat, precisely at its keel point. Here, you would keep sliding the carpenter’s square ruler forward until the ruler’s shorter side vertically aligns with the transom. 

This should be at 16″. Now, calculate the distance from the ruler’s inside corner to the keel point. For every 1/4″, you get a degree. This means 4″ equals a transom angle of 16 degrees.

Using the Yardstick Measurement Method

It is thrilling that you can quickly gauge your outboard mounting height with something as simple and ready as a yardstick. With this yardstick method, you should get the appropriate mounting height to realize the best speed when your pontoon is underway. 

This is easy. First, you would rest the yardstick along the keel situated at the pontoon’s bottom. The yardstick should be placed such that it aligns perfectly horizontally with the outboard.

Getting the keel parallel to the propeller shaft (which is achievable by trimming the motor), the straight edge should be simultaneously even with the anti-ventilation plate and keel’s bottom.

Why the Length is an Important Consideration?

The outboard length is critical to the overall pontoon performance. Typically, the outboard’s length is calculated by measuring the distance between the anti-ventilation plate and the clamp bracket’s upper edge. The outboard length is alternatively referred to as the motor shaft length.

Commonly, we see outboard lengths divided into four categories. These are the S, L, XL, and XXL categories. As you may easily infer, S denotes 15 inches, L going for 20 inches, XL going for 25 inches, and lastly, XXL denoting outboard lengths of 30 inches. We will touch on this consequently.

Now, it is right to be keen on the outboard length because the motor’s shaft length determines how well it submerges below the waterline. 

More importantly, the optimal outboard length prevents cavitation. This is when the propeller intermittently pulls out of the water when underway, hurting your boating or fishing experience.  

What are the Standard Shaft Sizes?

The truth is that the outboard motor shaft length for your pontoon boat depends majorly on your pontoon’s engine size. Pontoon boats with smaller engines are expected to go with shorter shafts.

On the other hand, if you have a high-powered boat, you would need longer shafts (possibly extra-long). In the case of sailboats, you will need significantly long shafts.

By industry standards, shaft lengths predominantly range between 15-30 inches. Therefore, while short shafts can be somewhere around a length of 15 inches, long ones can be around 20 inches, while extra-extra long shafts can be approximately 30 inches in length.

To determine the appropriate shaft length, you should consider your boat type. Do you have a fast boat or a slow boat? 

Other than this, you should also consider factors like the type of water, clearance, and placement when choosing your shaft length.

Why You Consider the Propeller Diameter?

The propeller diameter is essential when choosing propellers for your pontoon. If the size of your propeller blades is disproportionately bigger, it can strain a small engine.

Ultimately, this will reduce the engine’s speedOpens in a new tab.. On the flip side, if the propeller blade’s size is too small, the engine may spin at an excessive speed, consequently damaging it.

When choosing propeller diameter, you should rightly watch out for your boat size, weight, and cruising speed bandwidth. Commonly, you see manufacturers labeling their propellers by the diameter and pitch.

The diameter comes first and then the pitch. Therefore, an imaginary propeller label of “14×17” means that the propeller diameter is 14 inches while its pitch is 17 inches.

There are different types of mounting practices for outdoor motors. There is the standard, lower, and higher mounting. Let us learn about them. 

What You Should Know About Standard Mounting

Best practices always win, making the standard mounting practice the most ideal, especially for new boaters. In the standard mounting, the pontoon’s bottom is aligned with the anti-ventilation plate. By this, the pontoon’s bottom should be parallel with the propeller shaft.

As we have earlier established, the outboard is outfitted with vertically aligned brackets and mounting holes to realize such adjustments. 

What You Should Know About Lower Mounting

Unlike the standard mounting that beginners can easily achieve, the lower mount requires a bit more experience for proper handling. In this mounting method, the engine is aligned at a lower height than what you had for standard mounting.  

Of course, there are possible disadvantages that go with this. First, lower mounting can reduce your fuel efficiency, also decreasing your pontoon speed.

What more, when the outboard motor is mounted at a lower height on the boat transom, there is a significant possibility of excessive spray. More than this, your boat could experience inadequate underwater clearance, amplified case drag, and make an otherwise fast pontoon ridiculously slow.

To know whether you are correctly mounting your outdoor motor (at the appropriate height), start your boat with the engine in idle state. The next thing is to trim the motor by one-half or even a full trim. 

Consequently, quickly accelerate and analyze the performance. How is the propeller ventilation? In case of any failure, then it is apparent that the outboard was mounted too low.

Depending on your pontoon design, it may adequately handle lower mounting, especially for boats with no problems when the motor is submerged. However, this is not always the case.

What You Should Know About Higher Mounting

Just like lower mounting, higher mounting (for outboard motors) is best suited to professional or expert boaters. Overheating of the engine is a crucial consideration when going for higher mounting. This is because water scarcity (being that the motor is too elevated from the waterline) can affect its cooling.

More than overheating, another primary consideration is the design of the boat transom. From its make, can it handle the weight of an over-elevated outboard? This is crucial to preventing unnecessary breakdowns. 

Of course, higher mounting often corresponds to higher cruising speeds. This makes it more enjoyable driving your pontoon at a higher speed. 

This is because the horsepower and rotation per minute are amplified when the outboard is mounted significantly upwards.

Nonetheless, when going with higher mounting, bear in mind that the higher the outboard is mounted, the harder it is to steer your boat adequately.

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