Understanding Pounding in a Catamaran

Hello, fellow sailing enthusiasts, and welcome back to Sailing In Style. Today, we're tackling an important topic that every sailor needs to understand - how to prevent your catamaran from pounding. Navigating the waves with style is all about knowing your boat and understanding the forces at play. So let's dive right in!

Understanding Pounding

Firstly, let's discuss what 'pounding' or 'smashing' means in sailing terms. This phenomenon occurs when a boat hits a wave with significant force, causing a loud 'bang' or 'thud' and a jarring motion. This not only results in an uncomfortable ride but can potentially cause structural damage to the vessel over time. In the case of catamarans, pounding usually happens when waves strike the underside of the bridgedeck, the section of the boat connecting the two hulls.

The Bridgedeck Clearance Formula

The key to reducing pounding in a catamaran is to have a suitable bridgedeck clearance. The 'clearance' is the height of the bridgedeck above the waterline. This is vital for smooth sailing and is often calculated using a simple formula:

Bridgedeck clearance (in inches) = 1.5% of Load Waterline Length (LWL, in feet)

The Load Waterline Length (LWL) is the length of the hull at the waterline when the boat is fully loaded. This formula gives you the ideal bridgedeck clearance for preventing pounding. For instance, a 40-foot catamaran with a LWL of 38 feet should have a bridgedeck clearance of approximately 7 inches. 

These are general guidelines and the actual clearance needed can depend on factors like the shape of the hulls and the bridgedeck, weight distribution, and sea conditions.

Practical Tips to Avoid Pounding

Load Management

Heavier loads can lower your catamaran in the water, reducing bridgedeck clearance. Be mindful of your boat's weight and how it's distributed. Lighten the load where possible and maintain balance between both hulls. As example, we would never add a microwave, dishwasher or dryer into our vessel configuration. As nice as they are for a luxurious travel experience, they also add more weight, reduce the storage capacity and more importantly, add more energy consumption. 

Speed Control

The faster you sail, the greater the impact when you hit a wave. In rough conditions, reduce speed to soften the blows. There are several possibilities to reduce the speed: 

Reefing Your Sails

One of the easiest ways to reduce speed is by making your sails smaller, a process known as reefing. This reduces the amount of wind that is able to push against your boat. Most modern sailboats have a built-in system for reefing the sails quickly and easily.

Change Sail Configuration

Another option is to change your sail configuration. Instead of sailing with a full mainsail and genoa, you could consider using just the mainsail or just a headsail (like a smaller jib or staysail). 

Heave-To

This is a sailing maneuver that allows a boat to essentially park in the water. It involves positioning the sails and rudder in such a way that they counteract each other, creating a balancing effect that results in the boat coming to a near standstill. It's a useful technique for reducing speed or for taking a break.

Deploy a Drogue or Sea Anchor

These devices are dragged behind the boat to create drag and slow the boat down. A drogue is typically a small parachute or cone-shaped device that is trailed from the stern, while a sea anchor is a larger device that is deployed from the bow. Both can be effective for controlling speed, particularly in strong winds and large waves, but they require careful handling.

Course Selection 

Alter your course to reduce direct impact with waves. Sailing at an angle to the waves rather than straight into them can help avoid hard hits to the bridgedeck. Often a small course change, especially when sailing large distances at once, makes a big difference, especially to reduce the pounding.

Weather Forecast

Always keep an eye on the weather forecast and plan your routes and sailing speed accordingly. Avoid rough seas when possible to minimize pounding, use multiple weather models and include the wave height, direction and pattern in your planning.

Boat Selection 

If you're in the process of choosing a catamaran, consider the design and dimensions carefully. Some designs are more prone to pounding than others. Here are some points to consider when selecting a catamaran:

High Bridgedeck Clearance

A higher bridgedeck clearance minimizes the chance of waves hitting the underside of the bridgedeck, hence reducing pounding. As we've previously mentioned, the formula to calculate the ideal bridgedeck clearance is Bridgedeck clearance (in inches) = 1.5% of Load Waterline Length (LWL, in feet). 

Curved Bridgedeck

A boat with a gently curved or arched bridgedeck can reduce pounding by allowing waves to more easily pass beneath the vessel.

Narrow Hulls

Narrow hulls cut through the water more efficiently than wider ones, helping to minimize resistance and thus reduce pounding. However, this may compromise on interior space.

Wave Breakers

Some catamarans come with wave breakers, small protrusions underneath the bridgedeck designed to break up waves before they hit the bridgedeck. 

Catamarans that incorporate these features into their design are likely to experience less pounding. A few models known for their sea-keeping abilities and reduced pounding include the Lagoon 52, Outremer 51, and the Neel 51 trimaran. But, very boat design involves trade-offs and what works well for one person might not work as well for another. Therefore, it's crucial to thoroughly research and possibly test sail different models before making a decision.

By understanding the mechanics behind pounding and implementing these strategies, you can enjoy a smoother and more comfortable ride on your sailing adventures. After all, sailing in style means sailing with skill and knowledge.

Remember, our journey on the sea is not just about the destination, but about mastering the art of sailing. Smooth seas never made skilled sailors. So, keep learning, stay curious, and continue to grow on your sailing journey.

Fair winds and following seas, until our next post!