How it works
Generally the resistance of a boat is made from the following components: Surface friction, Form resistance, Surface roughness, Wave resistance, Air resistance & Appendage drag. Obviosly, these will also change with the speed of the boat.
The graph below shows the general resistance components for different type of hulls.
As can be seen, in a planing or semi planing hull the wave resistance is around 50% of the total resistance. By changing the trim of the boat, the wave resistance can be significantly reduced.
The trim of the boat can be adjusted with different devices:
- To add a hull extension– As a result of the added hull area, the surface friction increases as well as weight
- Traditional Trim tab– As a result of the area from the trim tab, the surface friction increases
- Wedge / Hook added to the hull – Adds very little resistance, however these are not adjustable giving optimal performance at only one speed and one load condition, not so effective!
- Fixed Interceptors– Adds very little appendage, but without the possibility to adjust, performance can only be optimised at one speed and one load condition, not so effective!
- Adjustable interceptors– All benefits from the fixed Interceptor with the addition that the resistance of the hull can be optimised for every speed and load condition. The most efficient way to trim the boat in order to minimize the total resistance resulting in increased speed and lower fuel consumption!
The picture below shows a typical resistance curve for a planing boat around 50 feet with a high hump resistance.
Typically this would also mean a high trim angle at hump speed with high fuel consumption and it may also limit the visibility for the captain. A high trim angle is generally causing a high wave resistance as explained above. This means that if the trim angle of the boat can be modified, the wave resistance and total resistance can be lowered. Using Interceptors is the best way to adjust the trim of the boat to achieve a lower wave resistance saving fuel and environment. Visibility and acceleration can also be improved at the same time.
With ATOS, the lowest possible resistance is achieved for each speed as the interceptors are continously adjusted when the speed of the boat is changed.
The basic principle of the interceptor trim tab is to create preasure underneath the hull, at the stern of the boat. The pressure is created when the blade is deployed into the waterflow underneath the hull. Dispite what you first might think there is only a minor deployment needed to create a large lift force under the hull. This lift will change the running trim of the vessel resulting in a lower wave resistance.
The Humphree system is all electric powered by 12-24 Volt DC. Thanks to the design of the Interceptor it only requires a small amount of power to move the blade up and down, even under high speed operation. The Interceptor blade is controlled by our special develop Servo unit (electronic actuator).
The Servo unit is designed,
- To move the blade a full stroke as fast as 1 second
- With very high precision, up to 100 steps within one stroke
- With real time feedback to the control panel
This means that you always know where the Interceptors are positioned, or you can just let any of our automatic systems control this for you.
As it doesn't require an advanced hydralic system to move the blade up and down, you can forget all added weight for this and also the maintanence cost.
Interceptor vs. Traditional Trim tab
The Humphree Interceptor is by its design in total a lighter construction than the trim tab, it can also integrate easier to the transom and can be custom shaped with a curve to follow any shape of the hull bottom. The later means that it is possible to fit a trim system over a propeller tunnel or partly over the chine, as the shape of the Interceptor can follow almost any hull curvature. Please contact us for more information about customized Interceptors.
In difference from most trim tab designs, the Humphree interceptor is constructed out of composite materials. This means that you get a light construction that has almost zero added mass at dockside and it also leaves out all worries regarding corrosion problems and the need of zink anodes.
To find out more about our interceptors, please see our Interceptor Guide.