Reverse Bow - Fad or Function
Evaluating Bow Shapes - How and Why Relationships are critical in Yacht Design
115m Megayacht concept from Oceanco.
Everything in yacht design is relative to something else. The form of a bow is relative to the total length and weight of the vessel. It's also relative to the speed, the cost, the aesthetics, the windage, the motion in waves. To make judgements about the characteristics and the effectiveness of the bow form we need to understand its relationship to a myriad of other factors.
To clarify what I mean by "relative"; put two similar vessels side by side. Let's say they share the same length overall. Vessel one has the bow raked aft so its waterline is the full length of the vessel. Vessel two has a conventional or forward raked stem so it's waterline is shorter.
We can posit the argument that vessel one will have a lower displacement to length ratio (be more easily driven), will have less weight and windage and will pitch less because it carries its reserve buoyancy close to the waterline.
Vessel two has to pitch before its reserve buoyancy can take effect, and this motion can induce more pitching, having a negative impact on performance and comfort. It is also more susceptible to down force from waves because the deck is wider at the forward extremities. It might deflect more spray than the reverse bow but it might also might throw up a lot more spray due to the pitching action.
We've built these arguments on the premise that we can make judgements by comparing two vessels of the same length overall. But we could have chosen any number of other parameters to compare the two vessels. These might include the length of the waterline, the displacement, the displacement to length ratio, the speed to length ratio, the number of double cabins with en-suits, and so on…
If we switch to making the comparison by using another set of parameters, the outcomes will changed depending which parameter we've chosen.
To further illustrate the point let's take a hypothetical look at a yacht with a reverse bow and let's say it is 50' long overall. Are we looking at a 50' yacht that has had the deck line pared back at the bow to create a reverse bow, or are we looking at a 46' boat that had the bow extended at the waterline to create a fine entry and a longer waterline? It's not the right question. The metrics are not the point. The point is the relationships that we've created including the amount of buoyancy we have in the bow and the relationship of that buoyancy to the centre of gravity of teh vessel.
Reverse bows are not a fad. For planing hulls the arguments are different but for displacement hulls reverse bows are the state of the art in our technological quiver where performance is paramount. They can be beautiful and those that are will endure just as many of the classic sailing yachts of the past have endured for their beauty.
The important thing is not whether the bow points forward or aft, the important thing is whether all of the design features work cohesively in style and in function.