Designing high performance vessels is both an art and a science. Performance is one of those terms that can be defined in many different ways. However, when dealing with vessel design, performance is measured in terms of a customer’s expectations when a boat is designed. On recreational boats, built by large yards as a production run or as a specific model, performance means a standard that can be advertised to potential buyers. On military, commercial, or government service boats, performance is strictly defined in terms of expected speed, vessel load, and vessel use.
So, what happens when a boat is built and it does not perform up to expectations?
Enter the blame game.
- The yard will blame the engine manufacturer.
- The engine manufacturer will blame the propeller manufacturer.
- The propeller manufacturer will blame the yard.
- The yard will blame the naval architect.
- The naval architect will then say that the customer’s demands were not realistic.
A cycle that is common, and usually is completely unproductive when solving the problem: WHY is the boat not performing?
Vessel design is a question of balance and the laws of physics. Numbers do not lie, and the laws of physics apply to everyone. What happened?
In our experience, the vast majority of performance issues are related to lack of communication between all of the different manufacturers of the vessel systems. In general, the following items are performance critical:
Vessel Weight / Displacement. This is the most common problem. It is either calculated incorrectly, or different materials were used than specified in the design (usually for cost reasons). Sometimes, it is not the yard’s fault. The vessel owner will often make changes after construction was started, sometimes ignoring the advice of the yard. This will put the builder in a delicate position of keeping the customer happy or achieving performance. It is not just with recreational vessels, either. MarineDiesel has seen many projects fail when a military commander decides to change the weaponry or vessel mission without any understanding of the physics involved, sometimes to comical results.
Bad Propeller / Propulsion Design. This is also not always the fault of the manufacturer. Propeller makers (or drive makers, or jet makers) can only make calculations based on the information that they are given. If they are given incorrect information, then the vessel performance will not be correct.
Bad Engine Selection. Engines cost money. Power costs money. As an engine manufacturer, the guarantees we make are based on the power of the engine we provide. So, if you buy 500 horsepower, we guarantee that the engine you buy will produce 500 horsepower. We do not make guarantees based on a project’s performance. Why not? How can we guarantee a performance level when we did not design or manufacture the hull, propeller, or drive? In some cases, a customer will try and save money by buying an engine that is under-powered for an application in order to save money. This returns us back to the laws of physics. There is no such thing as a free lunch.
Bad Hull Design. This is also quite common, especially on new, or prototype, hulls. On high speed or high performance vessels, design mistakes are often magnified, due to the increased forces on the hull at high speeds. We have seen such mistakes in water intakes, spray rails, steps (especially), foils, and simply bad designs. This is also why many yards insist on having designs that are proven, with other customers using the vessel.
It has been our experience that when vessels do not reach their required performance levels, it is usually a case of “all of the above” to varying degrees. It is important for vessel buyers to understand what they are buying and for everyone to be upfront and honest with all information. Unfortunately, in the competitive marketplace, costs are often the driving criterion on projects, and the ever present desire to reduce costs oftem is the real culprit, leading to bad decisions and poor engineering.