Mounting An Outboard On A Jon Boat: Easy Steps

Putting an outboard motor on a Jon boat is a tricky task. The flat-bottomed boat can go faster with less horsepower, so the wrong motor setup could be dangerous. There are a few steps to follow when mounting an outboard motor on a Jon boat. Firstly, measure the height of the boat transom. The mounting height of the outboard affects the running speed. If it's too high, cavitation may occur, leading to a speed slowdown and propeller damage. If it's too low, water resistance will reduce speed and energy efficiency. Next, find the right shaft length for your boat transom height. Finally, place the outboard on the centre line of the transom and tighten the transom clamp bolts firmly. It's important to check the screws or clamps before use, as they may be loosened by mechanical vibrations.

Measure the height of your boat transom

To measure the height of your boat transom, you will need a measuring tape. The transom is the flat, vertical section at the rear of your boat, where the outboard is mounted. It is important to get the right transom height as this dictates the size of the outboard motor.

Ask a friend to hold one end of the measuring tape at the top, outer edge of the transom. Then, pull the tape across the width of the transom to the opposite outer edge. This measurement is the 'length of the taffrail', which is the width of the boat across the top edge of the stern. Mark the centre of the width with a grease pencil, as this is where your outboard motor will ideally be located.

Next, hold the tape on the top centre of the taffrail and measure straight down to the point where the transom joins the bottom of the boat. This is usually a sharp angle. This measurement is the dimension you'll need to decide between a short, long, or extra-long shaft for your outboard motor. The industry standard for a short shaft engine is a transom height of 15", a long shaft engine requires 20", and an height of 25" is needed for an extra-long shaft engine.

Additionally, you can set the end of the tape on the outer edge of the taffrail at the centre and measure inward to the inner edge. This measurement will be needed when selecting a mounting bracket for your outboard motor.

Find the suitable shaft length

Different heights of boat transom require different shafts on the outboard motor. Here is a simple chart that will help you find the suitable shaft length for the range of outboard transom height.

| Outboard transom height range | Shaft length |

| --- | --- |

| 15" to 20" | 20" |

| 20" to 25" | 25" |

| 25" to 30" | 30" |

Pro Tip: If your outboard motor is still hard to reach the water, you may need to install an outboard motor bracket first.

For more information about the selection of shaft length, check out our previous post: How to Find Your Shaft Length.

Check your capacity plate

When deciding on the motor size for your Jon boat, the easiest way to determine the ideal size is to check the capacity plate on the transom. The capacity plate will tell you the maximum HP rating for your boat. For example, if the capacity plate says "4 persons or 470 lbs, 25 HP motor", then the biggest motor you can fit is 25 HP.

It's beneficial to have reserve power, as this allows you to carry more weight if needed. You can always slow it down or set a throttle stop to keep you safe, but you won't be able to get a 10 HP motor to reach 60 mph. This is a good way to determine Jon boat motor sizes if cost is not a concern.

However, it's important to note that using an outboard motor that's too large for your Jon boat can be dangerous. On the other hand, a motor that's too small will make it difficult for your boat to get on plane. Generally, a 6 HP outboard motor is sufficient to move a Jon boat under 6,000 lbs at a decent speed, while a 9.9 HP outboard is suitable for a Jon boat under 1,2000 lbs.

Therefore, a 9.9 HP motor is a popular choice for Jon boat owners as it can accommodate a majority of Jon boat models (10 ft, 12 ft, 14 ft, and even larger sizes), as long as the weight is within the limit.

It's worth noting that the information above is just a rough guide, and the best Jon boat motor size will depend on various factors such as hull shape, weight placement, and propeller.

Place outboard on the centre line of transom

To place an outboard on the centre line of a jon boat transom, you must first understand the basics of a boat transom. The transom is the flat vertical section at the rear of the boat, where the outboard motor is mounted. The height of the transom is measured from the bottom of the hull to the top of the transom, using the centre line. This height is crucial as it dictates the size of the outboard motor that can be used.

When placing an outboard on the centre line of a jon boat transom, it is important to ensure that the motor is mounted at the correct height. Industry standards specify that a short shaft engine requires a transom height of 15 inches, while a long shaft engine requires 20 inches. The height of the transom can be adjusted to accommodate the motor, but it is crucial to ensure that the cavitation plate is level with the bottom of the hull.

Additionally, the transom angle, which is the vertical incline of the transom measured in degrees, plays a pivotal role in the boat's trimming abilities. The average transom angle is around 14 degrees, but it can vary from zero to 30 degrees.

When placing an outboard on a jon boat transom, it is also important to consider the material of the transom. Some jon boats have wood transoms, while others have aluminium transoms. The wood provides a better grip for the outboard motor clamps, but it is prone to rotting over time. Aluminium transoms, on the other hand, are more durable and lightweight but may require additional measures to ensure a secure clamp attachment.

Overall, placing an outboard on the centre line of a jon boat transom requires careful consideration of the transom height, angle, and material to ensure a secure and functional fit.

Tighten the transom clamp bolts

To tighten the transom clamp bolts, start by placing the outboard motor on the transom, positioning it as close to the center as possible. Next, evenly and securely tighten the clamp screws. It is important to ensure that the clamp screws are tightened securely to prevent the outboard motor from falling off or moving on the transom, which could result in a loss of control and serious injury.

It is recommended to use stainless steel bolts as they will not rust. Be sure to check the clamp screws for tightness during the operation of the outboard motor, as engine vibration can cause them to loosen over time.

For added security and to prevent complete loss of the outboard motor in the event that it falls off the transom, consider using a cable to secure it to the boat.

Frequently asked questions