Vertical Bow vs. Sloped Bow - What's the Difference and Why Does it Matter?

Bill Jennings
Aug 12
4 min read

Updated: Aug 19

The Fjord 39 XL / Original Photo - Fjord Yachts

Vertical bows are back in style. Since I last wrote about vertical bow designs four years ago, we have seen considerably more of them appearing on new boats.

But why?

A vertical bow is referred to as a “plumb” bow -- logically named because it runs straight down. That being said, over the past few decades boats designs have generally favoured a bow line that tapers backwards under the forward section of the boat. A vertical, or plumb bow, more closely matches the type of bow line we saw on the older wooden lake boats. It was typically covered with a stainless bow piece called a “cut-water." The vertical design marks a significant visual departure from what we are accustomed to seeing.

Lets look at the reasons behind the return of vertical bows and determine if it is a feature that we should be looking to include in our next boat.

A plumb bow makes several significant changes to the way a boat runs. One of these is an increase in waterline length. With the traditional sloped bow, as seen in most boats today, the forward section of the boat that is actually in the water is behind the forward tip of the bow. Changing to a plumb bow fills this space and increases the boat’s actual waterline length. The longer ‘waterline’ length increases the maximum hull speed. While this may be only noticeable at idle speeds, it is still an improvement. With a boat that is able to travel a little faster in its displacement mode comes better efficiency, meaning better fuel economy. The increased waterline length at the bow can also make for greater stability at rest.

With the added bow space of a vertical design, you also get more interior volume with the same boat length. It won’t be large enough for another stateroom, but added space is always welcome in any boat.

While these vertical bow advantages are significant, what I consider to be the greatest benefit is the better ride that it delivers. It can be very smooth, but it is understandable once you dissect the detailed action of a boat bow striking a wave. Because there are an endless number of wave types and sizes, I will look at the shape of the fresh water waves we generally encounter on a standard boat outing. The Bureau of Meteorology, in Melbourne, Australia, labels these most common waves as “small," 0.1 to 0.5 meters in height (4" to 18") and “slight," 0.5 to 1.25 meters in height (18" to 48"). Their shape is, generally speaking, much like a small hump on flat water. A slight curve exists on their leading edge, but again for the purpose of explaining affect on different bow configurations, I will choose an example leading edge wave slope of 45 degrees.

What happens when a traditional sloped bow, as seen in most boats today, strikes one of these slight waves? The entire 45 degree forward sloping bow strikes the 45 degree leading edge of the wave at the same time because the wave and bow are close to or exactly the same angle. This impact will be felt by passengers in the boat. The closer the wave and bow angle are to each other, the greater the impact. Next, the forward motion of the boat will push the sloped bow up and over the wave. The larger the wave, the higher the bow will rise with each wave. The up and down motion of the bow will be felt throughout the boat (smaller boats more so than larger boats).

Now let's compare what happens when a vertical bow encounters waves. The vertical bow projects straight up (90 degrees), and I’ll use the same example of a 45 degree leading edge wave. In this case, the base of the vertical bow enters the base of the wave first and more gradually enters the higher portion of the wave. With this sequential wave entry, there is less impact, meaning a softer ride. But there is more: the vertical bow slices into the wave while the sloped bow performs a combination of entering the wave and climbing onto it. With a larger portion of a sharp vertical bow slicing into the waves, there is greater stability, less bow movement, and no pounding. To a point.

If a vertical bow is superior, why in the evolution of boat design did they get replaced with sloped bows? Simple. Early pleasure boats did not have the higher horsepower capability of today’s boats and therefore spent most of their running time as a displacement hull, with no need to lift the bow for faster travel. Being an astute boater you may ask: “Does the lack of a sloped bow on vertical bow boats make it more difficult to come onto plane?” The answer is: yes, a little. But, because contemporary vertical bow boats have incorporated into the bottom of the bow a sloped section that, along with strakes, brings the boat handily onto plane, the new designs are intended to offer the best of both worlds. They cut better through chop yet still retain the ability to plane easily. So if you are looking to reduce bumping and pounding, a vertical bow is the answer.

Are there any major concerns with a vertical bow design? Not for most 'flatwater' boaters, but some will complain that raising their anchor without smacking it into the hull is more difficult. Others have noted that in big enough swells, their vertical bow boat has a greater tendency to bury itself and dive under waves. Under big enough conditions, this is certainly possible. This also then brings up issues like visibility and safety. It also brings up considerations for where you boat, the type of water, and how comfortable you feel in adverse conditions. Perhaps the most practical disadvantage is price. With new designs and new features, vertical bow boats are mostly showing up in luxury or higher-end categories. But, as boat builders find ways to incorporate changes to their existing plugs, prices will come down and we will likely see them offered across a broader price range.

The bottom line is this: a vertical or plumb bow generally results in a smoother, softer ride, albeit within certain conditions.

Expect to see more of them in your boating future. #tips