Boat hulls are quite important when it comes to boating performance, ride comfort, stability and fuel economy. Deadrise is one of the more important metrics with respect to hull design. Deadrise is commonly used to determine how well a boat can cut through seas or how a boat rides. To fully illustrate the importance of deadrise, we’ll first look at the definition then look at why it matters in boating.
Deadrise Definition
The deadrise of a boat is the angle measurement between the boat bottom and a horizontal plane on either side of the center keel. The deadrise of a flat bottom boat is much lower (or zero) compared to a vessel with a deep-V hull. You’ll often hear deeper, or sharper V-shaped hulls referred to as having a lot of deadrise. These boats that are built to run offshore might have a deadrise of 20 degrees at the transom and 30-50 degrees at the bow (more on different deadrise values at different locations along the hull later).
Flat bottom boats might have less than ten degrees of deadrise, or even zero deadrise. These boats are built this way to be able to navigate very shallow waters but would be a nightmare offshore in any sort of seas. In such conditions, a flatter boat isn’t able to channel the water away as the hull meets the water and results in more “slamming.”
The deadrise of the boat can often be measured at various points along the length of the hull such as at the transom, at the bow and other points in between. The transom deadrise is the most commonly cited deadrise value, however, because most boats run on the aft 30-50% portion of the hull.
When shopping for boats, knowing the deadrise value is an important number to research. Some manufacturers may only note a single deadrise value and not make it clear at which portion of the hull this measurement was taken. Deadrise values will typically increase as you move forward toward the bow, so it’s important to know exactly where the deadrise was measured. Additionally, a deadrise value taken at a point on the bow that doesn’t even meet the water isn’t relevant to boat performance.
Why Deadrise Matters
The amount of deadrise is an important metric because it gives the boat owner an idea of how well the boat will run or cut through rougher seas. A larger deadrise value will cut through seas easier and generally provide a softer ride.
Is there a downside to a large deadrise value? The tradeoff of cutting through chop with ease while running the boat typically comes when the boat is going slow or is at rest. While the deeper-V hulls can cut better through water, a flatter bottom boat will be more stable at slow speeds or when not moving.
Many manufacturers attempt to find a happy medium where the boat will carve nicely through rougher seas but also maintain good stability while at rest or when trolling.
It’s worth noting that deadrise isn’t the only factor in stability and a soft ride. Beam width can also have an effect on both ride and stability. A wider boat, generally, will begin to “pound” on the water sooner than a more narrow boat with the same deadrise. Similarly, a wider beam boat will typically have more stability at rest.
As multiple characteristics of the boat can affect ride comfort and performance, the importance of sea trials is always worth mentioning. Getting out in the open water with a boat is the best way to compare how vessels in various conditions. Experienced boaters know that while specifications on each boat are important, assumptions based on such numbers can be mistaken once the boater gets a feel for the boat out on the water.
if you have any questions about deadrise, hull design or other boat performance metrics, please contact the Tom George Yacht Group at any time.