How to make a better yacht bow
Types of bows (continued)
The opposite of the flared bow is the Axe bow, such as the scimitar bow on the Amel 199. Here where instead of increasing the flare above the water, a very narrow half-angle of entry is maintained from hull bottom to the deck, but extra buoyancy is built in below the waterline with a deeper forefoot, and the sheerline forward is raised against green water on deck.
This type of hull has with lower resistance and creates less pitching in a seaway than a flared bow. Although this shape of bow cleaves waves, it is wet in a seaway.
Experiments in The Netherlands have shown that instead of increasing buoyancy by flaring the bow above the water surface, axe bows increases buoyancy by bringing the underwater bow profile downwards and raising the sheer at the bow.
Not only do these features lengthen the vessel considerably, but they also make it easier to drive into head seas, requiring less power. In addition, it has been suggested that up to 20 per cent lower fuel consumption in head seas can be achieved because the bow does not have the vertical accelerations of a flared bow.
A relatively new trend for larger craft is the scow bow. It has been a fixture on Great Lakes A and C class sailing scows for many years, but its potential was suddenly realised when a Mini-Transat boat with a scow bow handily won the race. Now, designers Reichel-Pugh have designed a 27.4m sailing yacht with a scow bow.
This type of bow carries beam well forward with the intent that the waterline length is increased as the boat heels. The major drawback of scow bows is they slam when upright and on a large yacht, that might be more than the owner is willing to accept.
The totally opposite look to the Apple Cheek bow is the Wave Piercing bow as used by Craig Loomes Design of New Zealand and others on several superyacht and fast ferry designs.
The idea behind this bow is that the extended sponsons on each side of the catamaran or trimaran hull pierce the waves to reduce pitching in heavy seas. In this style of yacht, the main hulls have less buoyancy forward to allow it to slide through the wave rather than slam into it. By sliding through the waves, less engine power is required and the pitching of the yacht is lower.
The bow is an essential feature of any modern yacht. Elongated bows such as the wave-piercing bow, reverse or axe bow lengthen the waterline and make the angle of entry finer, decreasing the hull resistance of faster vessels and reducing pitching in a seaway. However, the longer waterline can make it harder for the vessel to turn. Meanwhile, bulbous bows decrease the size of the bow wave and consequently reduce hull resistance for vessels that operate at a set displacement speed and load.
A designer should pick the bow shape that is best suited for the desired speed, shape and pitching characteristics in a seaway.