Putting Down The Prop: Milan Boat Maintenance 101

Learning how to put the prop down on a Milan boat is a basic skill for every boater. A propeller, also known as a prop, transfers the engine's power to the water, creating thrust from its push-pull effects. Without a proper fit and top-quality propeller, the boat will move slower or won't move at all. To replace a propeller, you must first choose the right replacement propeller, taking into account the diameter and pitch, as well as the type of material and number of blades. Next, prepare the necessary tools and replacement parts, such as a prop wrench, needle-nose pliers, a cotter pin, and a new prop. Then, follow the steps of removing the old propeller and installing the new one, including tilting the engine, removing the cotter pin, loosening the propeller nut, and detaching the washer and nut. Finally, waterproof the new prop with grease, put on the new propeller, washer, and nut, and insert a new cotter pin to lock it in position.

Choosing the right replacement propeller

Boat Category and Purpose:

The type of boat and its intended use play a significant role in propeller selection. For example, boats used for fishing, water sports, or leisure cruising will have different propeller requirements. Understanding how you plan to use your boat will help determine the kind of propeller you need.

Engine Specifications:

The engine's horsepower and RPM range are essential factors to consider. Choosing a propeller that aligns with your engine's specifications ensures effective power transmission and maximizes propeller performance. The propeller should allow the engine to operate within its recommended RPM range while applying its maximum horsepower to the water.

Propeller Material:

The most common materials for propellers are aluminum and stainless steel. Aluminum propellers are usually more affordable and suitable for casual boating. They are also lightweight and resilient, making them a good choice for novice boaters or those navigating in rough waters. On the other hand, stainless steel propellers offer increased strength, efficiency, and performance, making them ideal for high-speed operations and heavy-duty use. They are more expensive but provide better acceleration and handling, making them a preferred choice for sports or serious boating enthusiasts.

Propeller Diameter and Pitch:

The diameter of the propeller refers to its size and influences the amount of water it can push. Larger diameters provide more thrust but may also increase pressure on the engine. The pitch of the propeller, on the other hand, determines how far the propeller moves forward in one complete revolution. Higher pitch results in higher speed but slower acceleration, while lower pitch increases acceleration at the expense of maximum speed.

Number of Blades:

The number of blades on a propeller affects its thrust, efficiency, and control. Three-bladed propellers typically deliver higher maximum speeds, while four-bladed propellers offer better turning and acceleration capabilities. For most applications, 3 and 4-blade propellers can be used interchangeably without a significant change in performance.

Cupped Propellers:

Cupped propellers have special curved trailing edges that maintain performance at higher trim levels and in tight corners. They can help achieve higher top-end speeds or the same speed at a lower engine RPM, resulting in improved fuel efficiency.

Wide Open Throttle (WOT) RPM Range:

When selecting a replacement propeller, ensure that it allows your engine to reach its optimal WOT RPM range. This range is typically between 5000 and 5500 RPM for outboards and 4200 to 5000 RPM for sterndrives, depending on the engine type. Refer to your boat's owner's manual for specific recommendations.

Elevation and Weight:

If you use your boat at different elevations, such as high mountain lakes and sea-level bays, consider carrying two propellers with different pitches. This will help compensate for the decrease in engine performance at higher altitudes and ensure optimal RPM at all elevations. Additionally, if your boat is used for various activities, such as towing skiers or carrying heavy gear, you may need a propeller with a different pitch to match the changing weight and engine performance requirements.

Ventilation and Cavitation:

Ventilation occurs when air or exhaust gases are drawn into the propeller blades, causing the boat to lose speed and the engine to over-rev. Cavitation, on the other hand, is the vaporization of water due to extreme low pressure on the back of the propeller blade. Both issues can lead to reduced performance and potential damage to the propeller and engine. When choosing a replacement propeller, ensure that it is designed to minimize ventilation and cavitation.

Preparing tools and replacement parts

Preparing the tools and replacement parts is a crucial step in fixing or replacing the propeller of your Milan boat. Here is a detailed guide to help you through the process:

Mount the Boat Properly:

Ensure you have a suitable boat mount that matches your Milan boat. The boat should be mounted in a dry area, elevating the propeller to eye level. This will provide you with easy access to the propeller and ensure a stable working environment.

Gather Necessary Tools:

You will need a set of tools to perform the repair or replacement. Here is a list of tools to prepare:

• Adjustable wrenches or crescent wrenches: You will need at least two adjustable wrenches to fix any dings or bends in the propeller blades.
• Mill bastard file: This type of file is useful for removing burrs or sharp edges on the propeller blades. It helps restore the blades to their original smoothness.
• Voltmeter: A voltmeter will come in handy for testing the wiring connections to the propeller. It can help you identify any frayed or damaged wires that may need replacement.
• Propeller wrench: In case you need to remove or install the propeller, a propeller wrench is essential for tightening or loosening the prop nut.
• Spare parts: It is recommended to have spare parts readily available, including a spare propeller, nut, thrust washer, and any other relevant hardware.

Inspect and Remove the Propeller:

Before beginning any work on the propeller, cut off all power to the boat to ensure your safety. Remove the propeller entirely by taking off each small part that holds it to the boat. Place the blades in a safe area as they can be heavier than expected.

Check and Test the Propeller:

Inspect each part of the propeller for any issues, including bent or damaged blades. Even minor damage, such as nicks or burrs, can affect the boat's performance. If the propeller is repairable, you may need to test it by connecting it to the boat and performing a simple test.

Prepare Replacement Parts:

If the propeller is beyond repair, it's time to prepare replacement parts. Purchase a replacement propeller that matches your Milan boat perfectly. Ensure that you have all the necessary hardware and parts needed for the replacement.

By following these steps and preparing the required tools and replacement parts, you will be well-equipped to tackle the task of putting the prop down on your Milan boat.

Removing the cotter pin

First, tilt the engine to a comfortable position for you to work on. Next, use a pair of pliers to uncurl the cotter pin. Then, gently pull the pin out.

It is important to note that the proper way to secure a propeller is to have a thin nut against the prop, followed by a thicker nut locked against the thin nut, and then the cotter pin. If the cotter pin is hammered into the keyway, as some boat yards have done, this is incorrect and can cause damage to the shaft and prop nut.

Loosening the propeller nut

Propellers can be challenging to remove, so it is important to know the correct procedure for loosening the propeller nut. Here is a detailed, step-by-step guide:

Firstly, before starting any work on the propeller, it is crucial to prioritise your safety by tripping the boat's kill switch. This will prevent any accidental activation of the propeller while you are working on it. As an additional safety measure, you can also put the gear in neutral.

Now, let's begin the process of loosening the propeller nut. Using needle-tip pliers, carefully remove the cotter pin. This step requires precision and caution, as the cotter pin is delicate and prone to damage. Once the cotter pin is removed, place it in a safe location.

Next, we will address the nuts. Start by loosening both nuts with a piece of wood to prevent the propeller from spinning. It is important to keep the propeller stable during this process. Remove the half-height nut completely, and replace it with the full-height nut on the shaft's tail. Ensure that all the threads on the full-height nut are engaged. This step is important because removing a propeller often requires force, and having the full-height nut in place will protect the propeller from falling and causing damage or injury.

At this stage, you can attempt to pull off the propeller by grasping it firmly at the base of two blades and pulling in a straight line. Make sure you have a firm grip to avoid slippage, as a spinning propeller can be dangerous. If the propeller comes off, be cautious, as the shaft key may slip out. If this method is successful, you can proceed to install a new propeller after packing and reconditioning the old one.

However, if the propeller does not come off with this technique, there are other methods you can try. One approach is to use a tool called a prop knocker or harmonic puller. Before using this tool, you may need to tilt the rudder slightly to create clearance. Remove the nut and screw the prop knocker onto the shaft. Tighten it by hand, then use a hammer to rap the prop knocker four to five times. Be careful not to miss and hit the propeller. The vibration from rapping should help loosen the propeller from the shaft taper. After this, grasp and remove the propeller, then take out the knocker. If the propeller does not come off after several attempts, you may need to try a different method or seek professional assistance.

Another option for removing a stubborn propeller is to use a prop puller, a tool commonly found in repair shops. A prop puller utilises the principle of the inclined plane, employing screw threads to exert controlled and significant force between the propeller hub and the tail end of the prop shaft. Remember to have the large nut threaded onto the shaft's end to catch the propeller when it comes loose.

In some cases, you may encounter a frozen or extremely tight propeller nut that requires additional techniques to loosen. One suggestion is to reattach the propeller blades and use a piece of wood to prevent the propeller from turning. This setup will allow you to apply torque to the nut. You can also try using a breaker bar or an impact wrench to deliver more force for loosening the nut. If the nut is corroded, you can apply penetrating oil or a similar product and leave it overnight to facilitate the removal process. In extreme cases, you may need to use a small propane/butane torch to heat the nut and follow up with a few whacks using a ball peen hammer. This combination of heat and shock can break the bond formed by corrosion.

Remember, when working on your boat's propeller, it is essential to prioritise safety, take your time, and apply the appropriate amount of force gradually. Each boat is unique, so you may need to adapt these general guidelines to suit your specific vessel. If you encounter significant challenges or feel uncomfortable performing these tasks, it is advisable to seek professional assistance from a qualified marine mechanic or boatyard.

Detaching the washer and nut

To detach the washer and nut, first, remove the nut and washer by pulling the propeller off the shaft. If the propeller is well-lubricated, it should just slip off. If it's harder to slide than expected, you may tap it gently with a piece of wood. Then, slide off the thrust washer.

Next, check for any signs of damage. Look for chips and cracks. If the new propeller has any damage, replace it accordingly. Then, use an unsoiled cloth to clean the shaft. Inspect the threads for any fishing lines that may be tangled around the shaft. Use a sharp knife to carefully remove any tangled lines.

Frequently asked questions