Consuming less fuel also makes sense if the gas station does not have to pay the maximum price. Because those who drive economically also blow less CO2 into the troubled atmosphere.
Yes, to speed elegantly across the surface of the water in a well-tuned boat, leaving only a long white foam strip in the wake, is perhaps the greatest joy for those who have dedicated themselves to motor boating. If the boat has a well-balanced and clean hull and the helmsman also lets a little feel on the throttle, this pleasure can even be efficient. Well, at least a little. Of course, physics cannot be outwitted here. The fact is that it takes a lot of power and fuel to lift a boat out of the water enough to put it on a brisk plane. In an era in which ships and costs are getting higher and higher, but in which there is also far more environmental awareness than 10 or 20 years ago, every skipper can do a lot on his own to reduce fuel consumption and thus harmful emissions at least a little Keep frame.
The most important tips for saving fuel in brief:
- A clean underwater ship
- The right trim
- A soulful hand on the throttle
- A propeller that is matched to the engine and the boat
And here is the expanded list of our advice on how to run your boat more economically:
- If you are not driving long distances, avoid carrying a full tank with you. That is unnecessary weight, and even on smaller boats it can quickly add up to as many extra pounds as three or four full-grown men on board.
- Pay attention to the weight distribution so that your boat floats on the waterline and then runs stable on level gravel without plowing, stamping or heeling.
- Have the fuel flow displayed and calculate the speed at which you are most economical on the road, i.e. can cover the most miles per liter.
- Teach yourself to consciously refrain from accelerating at full throttle or to be on the road with more than 80 percent gas, because both of these increase fuel consumption radically and at the same time reduce range.
- The fuel consumption also goes through the roof as soon as the underwater hull has a beard, i.e. algae, mussels or other growth that drastically increases the frictional resistance. Therefore: keep the hull clean and, if possible, store the boat on land on the trailer or in a drystack storage facility.
- Make sure your boat is equipped with a propeller that is matched to the engine.
- Speaking of props: a damaged screw increases fuel consumption and reduces performance and comfort. Check the propeller regularly and, if necessary, have it serviced or repaired by a propeller specialist (e.g. remove nicks). Costs little, helps a lot.
- Be proactive when trimming your boat, either by adjusting the trim tabs in good time or by shifting your weight so that you are in a balanced way, which means that the water flows against the hull at the optimal angle.
- Don’t forget to do regular engine maintenance.
- Avoid constantly adjusting the throttle, unless the sea makes it necessary.
Fuel efficiency through design
If you haven’t bought a boat or are thinking of a new one, it is worth choosing one with an efficient design. While many yearn for a sports machine with a deep V-hull that briskly cuts through the waves, the shallower, multi-purpose hull is often the better choice for a recreational boat. Low weight and a neatly shaped hull allow the water to drain off faster, but there are also other shapes, such as catamaran hulls, ventilated stepped hulls and hydrofoils that minimize frictional resistance.
However, the combination of engine and propeller and their behavior with the boat is just as important. Make sure your engine is of the appropriate weight and power for the stern of the boat. Especially with outboards, it may be worth converting to a more modern and efficient model. Also make sure that you have installed a suitable propeller, i.e. one that fits the machine and with which the speeds specified by the engine manufacturer can be achieved. A wrong or damaged propeller can negatively affect both acceleration and top speed due to slip, if it should grip and pull. In fact, it is often worth trying different types of propellers because the differences can sometimes be quite astonishing.
Dirt on the hull
As mentioned earlier, weed and barnacles affect the performance of a boat like no other. How does the beard come about on the underwater hull? It starts with a base layer of microorganisms and bacteria that multiply quickly to develop a thin film of “bio-slime”. After that, algae settle and weeds form, a very attractive food source for larvae, which subsequently lead to barnacles. When such an overgrown boat sets off, the friction between the hull and the water is radically increased. According to the International Maritime Organization, regular cleaning can increase the efficiency of a commercial ship’s hull by up to 12 percent, although the benefits of a clean hull are significantly higher for planing boats.
I have already come across test boats that performed a good 30 percent worse both at top speed and at maximum efficient cruising because the hull was dirty. A 22-footer, for example, did not even glide, so strong was the frictional resistance from the aquacultures that had spread across the entire underwater hull. And that was by no means an isolated incident. Many cruisers notice the decline in efficiency over the course of the season, either through higher fuel consumption or lower top speed. Depending on the type of boat, this loss can amount to 15 to 50 percent of normal performance. Let’s be honest: Isn’t that a real burden on the wallet, apart from the increased pollutant emissions, not to mention the loss of fun?
How to keep the hull clean
If you have your boat in the water, antifouling is still the easiest and cheapest solution. Fortunately, there are now numerous effective and eco-friendly products as an alternative to chemical warfare of the last decades, with aggressive biocides such as Tributiltyn, which were used in self-renewing paints. There are now numerous paints with low volatile organic compounds, as well as paints that have been mixed on an oil and water basis.
In recent years, so-called ultrasonic antifouling has also become a very realistic alternative. It works by emitting pulsed ultrasonic frequencies through transducers on the inside of the torso. This creates a layer of mobile water molecules on the entire underwater profile of the hull, which is supposed to prevent a colonization of microorganisms and thus fight the evil at the roots. For a large boat, however, this will be more expensive fun because multiple converters have to be used and you need a reliable power supply. But in terms of fuel savings when operating your boat, not to mention the crane bills and the costs of properly cleaning the underwater hull and properly disposing of the sewage, ultrasonic antifouling is still a very clean, modern and attractive solution.
Proactive behavior of the skipper
When a planing hull boat is calm in the water, it is buoyancy that keeps it afloat. But when it begins to move forward, it becomes (at least initially) a displacer. In other words, to cover the length of a boat, it has to push aside an amount of water equal to its own weight. With increasing speed, the shape of the hull produces more and more buoyancy, which lifts the hull above the surface of the water and radically reduces the displaced water volume. This buoyancy finally reaches a hydrodynamic equilibrium, with the boat gliding on a small section of the aft part of the hull and thus only having to accept very little resistance.
However, this balance can be quite unstable. If you trim the boat too much, it will be lifted too much out of the water, reducing the surface area of the hull in the water to the point where it can no longer support the weight of the boat. The result: the bow goes up and down, the boat begins to pound even without the influence of the waves. On the other hand, if there is too much hull in the water, the frictional resistance increases, hindering or interrupting planing, causing the boat to slow down and instead plow through the water like a semi-glider. The optimal compromise between control and efficiency is nothing more than the continuous balancing of hydrodynamic lift, speed and trim. And this is exactly where you as the skipper are required.
The ideal is to be on the move with a clean, well-trimmed boat and only have to accelerate enough to achieve optimal performance. Each boat has a different “sweet spot”, which depends on weight, choice of propeller, the ratio of length to width, hull shape, close-up, trim and many other factors. Fortunately, all of this can be determined relatively easily on your own boat. You only have to spend a few minutes while driving, gradually increasing the revolutions per minute, starting at 500, up to the very end of the scale, constantly checking the fuel consumption on the flow meter and the speed above ground on the GPS. If you know the tank capacity, you can calculate the optimal range from these values. This creates a pattern that can be visualized with a curve that most likely drops dramatically between 80 percent and full throttle, and shows a bandwidth for the ideal speed that should be between 60 and 75 percent, or between 3,600 and 4,500 U for modern outboard motors / min. If you move your boat within these parameters, you’re pretty well at it.
However, the speed range is only part of it. You also need to fine-tune the optimal trim of the boat, not only with the angle of attack of the engine (on outboards) and the trim tabs, but also with the correct weight distribution, in which most of the pounds should be stowed low and centrally (similar to the keel in a sailing yacht). Avoid bringing excess luggage and large reserves of fuel with you when you don’t really need them. Steer with concentration and take a look over the side to see from the waterline how far the hull rises out of the water when you are on plane. Listen to the sound of the engine revolving, get an idea of the boat’s swimming position and develop a feeling for the “sweet spot” of your boat. Good skippers try to increase efficiency on every trip.
On longer passages, when it’s about miles and not about sailing around, it’s worth keeping the tides on your side. Choose in a favorable weather window so that you are not forced to drive a defensive zigzag course. In addition, it is recommended to navigate between the individual waypoints as precisely as possible. All of this is actually trivial, but spread over an entire season, the positive effects achieved can help save quite a bit.
Minimize the distance
Also use other electronic instruments on board, especially your navigation software. The old geometrical rule of thumb that was ingrained in school, namely that the shortest connection between two points is a straight line, also applies to water.
If you deviate from the ideal line by only one or two degrees on longer stretches, you will be taking a detour that costs both time and fuel. A distance of 10 additional miles can, depending on the boat and the conditions, mean 80 liters more fuel consumption. You can also use the chart plotter to set the shortest course and look forward to the savings that you will generate.