Operating A Twin Engine Boat: The Basics

Operating a twin-engine boat comes with its own set of challenges and advantages. One of the most significant benefits of a twin-engine boat is redundancy, ensuring that if one engine fails, the other can be used to get home. Additionally, twin-engine boats offer superior manoeuvrability at low speeds, making it easier to control the boat, especially when performing standing turns or making small directional changes. However, operating a twin-engine boat, especially when docking, requires understanding the dynamics of propeller torque, thrust, and steering. It is crucial to know how your boat handles on a single engine, as this knowledge can be invaluable in an emergency.

Operating a Twin-Engine Boat

Docking: how to back a twin-engine boat into a slip

Docking a boat can be a stressful experience for many boaters, but with the right knowledge and preparation, it can be done efficiently and safely. Here is a detailed guide on how to back a twin-engine boat into a slip:

Preparation:

Before approaching the slip, it is crucial to prepare your boat and yourself. Ensure that you have deployed the necessary fenders and lines, and always be mindful of wind and current conditions, as these factors can affect your docking manoeuvre. Check for any potential obstacles or hazards nearby.

Trimming the Engines:

Trim your engines slightly upwards using the tilt-trim switch at the throttle. This ensures that the propwash goes under the boat, where it has the most significant effect. If not trimmed correctly, the propwash may hit the transom, making the boat harder to manoeuvre.

Approaching the Slip:

As you approach the slip, maintain a 90-degree angle. When the middle of your boat is aligned with the middle of the slip, stop and centre your steering wheel. From this point onwards, it is easier to turn the boat by opposing the engines, i.e., shifting one engine into forward and the other into reverse.

Spinning the Boat:

To get the boat spinning, remember that the bow will move in the direction of the throttle shifted into reverse. For example, shifting the starboard throttle into forward and the port throttle into reverse will cause the bow to spin to port. In ideal conditions, with no wind or current, you can spin the boat until it is perfectly parallel with the finger pier.

Dealing with Space Constraints:

If you don't have enough room to spin the boat completely, you can remove all forward thrust by taking the forward throttle out of gear. This will cause the boat to start backing up while continuing to spin, allowing you to get closer to the slip. Remember that removing the forward throttle will reduce the spinning rate, so you may need to shift gears to find the right balance between backing up and spinning.

Final Adjustments:

As the boat moves into the slip, you can stop all spinning motion by briefly reversing both throttles as needed. Then, back slowly into the slip until you come to rest at its side. Make any necessary final adjustments by shifting the throttles accordingly to bring the boat alongside the slip.

Dealing with Wind or Misalignment:

If a gust of wind knocks the boat off course or you misjudge the current, don't panic. Use your judgment to apply more or less power to one outboard or the other to correct your course. If needed, don't hesitate to pull away from the slip and start over—there's no shame in a do-over, and it's better than causing any damage to your boat or the dock.

Remember, docking a twin-engine boat is a skill that improves with practice. Find a safe space to familiarise yourself with your boat's handling characteristics and the effects of wind and current. With time and experience, you'll become a docking pro!

Manoeuvring with twin stern drives

Twin-engine boats provide more manoeuvring control than a single engine boat. They give you the ability to push or pull from both corners at the stern, making it easier to manoeuvre in a straight line, perform standing turns, or make small directional changes with a single thrust – all without the wheel.

There are three types of propulsion systems to be found on propeller-driven boats: stern drives, inboards, and pods. Stern drives are an articulating steering system, meaning the wheel turns the twin drives which redirect thrust. However, unlike an outboard engine, you can’t see them from the helm, so you need to be careful that you don't accidentally shift into gear with the wheel turned.

When manoeuvring a twin stern drive boat, you can choose to use the wheel or not. Using the wheel makes things happen more quickly, while working with the shifters alone tends to slow things down. In windy or choppy conditions, using the wheel and one or both drives may be necessary. In calm conditions, it is best to use the shifters alone with a centred wheel. Either way, use short shifts and a certain amount of drifting in neutral to control momentum.

To learn the steering characteristics of your twin stern drive boat, take the boat into safe water and bring it to a stop in calm conditions. Shift the port drive into reverse with no throttle added. If the stern goes to starboard, then the opposite should happen when you shift the starboard drive into reverse with no throttle added. Try the same using a forward shift in relation to the bow. If one drive understeers, shift the other drive into the opposite direction to compensate. This is called a rotation or “bulldozer” shift.

When docking a twin-engine boat, it is generally easier to oppose the engines, putting one into forward and the other into reverse, which causes the boat to spin in place. Before approaching the slip, prepare by deploying fenders and lines, and check for wind and current. Trim your engines up slightly so the propwash goes under the boat where it has the greatest effect. Approaching the slip at a 90-degree angle, once the middle of the boat is even with the middle of the slip, stop and centre your steering wheel. Oppose the engines to get the boat spinning, remembering that the bow will move in the direction of the throttle you shift into reverse.

How to turn on one engine

Turning on one engine of a twin-engine boat is a useful skill to have, especially if one of your engines breaks down. Here's a detailed guide on how to do it:

Understand the Dynamics:

Firstly, it's important to understand the dynamics of a twin-engine boat. The boat's steering is affected by three factors: prop offset, prop walk, and the rudders. The prop offset refers to the distance of the propeller from the centreline, with a greater offset resulting in a greater steering effect. Prop walk is the sideways travel produced by propellers, especially when moving backward. The rudders are more effective when the boat is moving forward due to the increased water flow from propeller thrust. Knowing how these factors interact will help you turn the boat effectively with a single engine.

Choose the Turning Direction:

If your port engine is not functioning, and you only have the starboard engine running, turning the boat to port (counter-clockwise) will initially have all three factors working in your favour. However, when you need to go backward, these factors will work against you, making it challenging to complete the turn. Therefore, it's generally recommended to turn the boat to starboard (clockwise) against the working engine.

Use the Rudder and Throttle:

When turning to starboard, the offset and prop walk will be against you, but you can overcome this by increasing the throttle to boost water flow over the rudders. Use the rudder to counter the opposing forces and keep the boat turning.

Complete the Turn:

Once you've turned about 50 to 60 degrees, take the boat out of gear. At this point, there will be no prop walk or offset to fight against, and the water flow over the rudders will continue turning the boat. When you need to go backward, engage astern, and the prop offset and prop walk will now work in your favour to complete the 180-degree spin.

Prepare for Docking:

When approaching a dock or slip, prepare in advance by deploying fenders and lines. Check for wind and current conditions to anticipate their effects on your manoeuvring. Trim your engines slightly upwards using the tilt-trim switch to ensure the propwash goes under the boat, making it easier to control.

Oppose the Engines:

When docking, approach the slip at a 90-degree angle and centre your steering wheel. To turn the boat, oppose the engines by shifting one into forward and the other into reverse. Remember, the bow will move in the direction of the throttle shifted into reverse. Avoid touching the steering wheel and use only the engines for manoeuvring.

Adjust as Needed:

Depending on wind, current, and space constraints, you may need to adjust your manoeuvring. If you can't spin the boat completely, take the forward throttle out of gear to remove forward thrust, allowing the boat to begin backing up while continuing to spin. Adjust the throttle to find the right balance between spinning and backing up.

Stop the Spin:

As you move into the slip, briefly reverse both throttles to stop the spinning motion and back slowly into the slip. Make any final adjustments by shifting throttles accordingly to bring the boat alongside the slip.

What to do if one engine breaks

If one engine of a twin-engine boat breaks, the first thing to remember is not to panic. Twin-engine boats have redundancy built-in, so if one engine fails, you can still get home. However, it is important to act prudently and head for port as soon as possible, as the problem affecting one engine could subsequently affect the other, possibly leaving your boat dead in the water. Here are some steps to follow if one of your twin engines quits:

Plane Test

Find out ahead of time whether your boat can plane on just one engine. This is especially important if you are buying a new boat or repowering an existing one. Make sure to test the boat's ability to plane on a single engine and, if necessary, boost the horsepower to ensure adequate performance.

Tilt and Trim

When running on just one engine, tilt up the non-operable motor to eliminate as much drag as possible. At the same time, keep the running outboard trimmed in to enhance its ability to lift the stern and keep the boat on plane. Trim in all the way to get the boat moving, then adjust in small increments to maintain speed without falling off plane. Avoid sharp turns with one engine tilted up to prevent the tie bar from bending.

Weight Forward

To get the boat on plane, move weight towards the bow. Outboard boats tend to squat in the stern and rise in the bow as they accelerate, so shifting weight forward helps the boat climb on plane. Once underway, crew members can move amidships to maintain balance.

Lighten Up

The lighter the boat, the easier it is to plane. You can reduce weight by draining livewells, tossing ice out of fish boxes, or emptying the freshwater tank. Water is heavy, so removing it from the boat can significantly reduce weight and improve performance.

Use Trim Tabs

Trim tabs help to lift the stern and keep the boat level when running on one engine. They can correct the boat's tendency to heel over due to unequalised propeller torque. Apply down tab to the lowest side to level the boat and keep it on an even keel.

Turning the Boat

Twin-engined boats have offset engines and smaller rudders, so turning in one direction will always be easier than the other. If you have enough space, turn in the direction the boat wants to go, with the engine on the outside. If space is limited, steer against the working engine, using extra revs to increase water flow over the rudders and turn the boat.

Remember to practice these techniques in a controlled environment, preferably on a calm day with plenty of space, so you are prepared in case of an actual emergency.

How to plane a twin-engine boat with one engine

Operating a twin-engine boat with one engine can be challenging, but it is possible to get home safely if one of the engines quits. Here are some detailed steps to help you plane a twin-engine boat with a single functioning engine:

Plane Test:

Before encountering an engine failure, it is essential to know whether your boat can plane with just one engine. Test this ahead of time by running the boat on a single engine as if one had quit. This is crucial when buying a new boat; if it won't plane with one engine, consider a model with more powerful twins or boost the horsepower when repowering.

Tilt and Trim:

When running on a single engine, tilt up the non-operable motor to lift the lower unit out of the water, reducing drag. At the same time, keep the running engine trimmed in substantially to enhance its ability to lift the stern and maintain the plane. Trim it in all the way initially, then adjust in small increments to find the optimal trim for efficient planing. Avoid sharp turns with one engine tilted up to prevent bending the tie bar.

Weight Forward:

To get the boat on the plane, move weight, such as gear and crew members, towards the bow. This helps counter the tendency of outboard boats to squat in the stern and rise in the bow during acceleration. Once the boat is fully planed, crew members can move off the bow but may need to stay amidships to maintain the plane.

Lighten the Load:

The lighter the boat, the easier it is to plane. Reduce weight by draining livewells, emptying fish boxes, and even consider emptying the freshwater tank if necessary. Water is heavy, so removing it can significantly reduce weight on the stern, making it easier to plane.

Use Trim Tabs:

Trim tabs are essential for lifting the stern during the initial hole shot and while underway. They help keep the boat level and prevent heeling over when running on one engine due to unequalised propeller torque. Apply down tabs to the lowest side to level the boat and keep it on an even keel.

Remember, if one engine quits, it is prudent to head for port as soon as possible. Don't continue your day on the water, as the issue affecting one engine could also impact the other, leaving you dead in the water.

Frequently asked questions