Hydrofoil whistling? How to sand your hydrofoil and solve this problem

Have you ever, while on your hydrofoil, heard an humming sound that sometimes becomes a whistle? Fear not, there is a solution!

Why does the hydrofoil whistle?

As you know in hydrofoil there are leading edges (the front ones) and trailing edges (the rear ones) which are defined by the direction of march.

The leading edge is the one that slices through the water during the run, while the trailing edge is the one at the rear after which the water rejoins.

Highlighted in red you can see the trailing edges of the front wing and stabilizer, which are often the cause of hydrofoil whistling.

Regardless of the brand of your hydrofoil, it may happen that the trailing edges are not enough sharp and that a small 'step' remains at the end. The height of the latter is one of the main factors determining the scale of this problem.

In practice, when the water rejoins after the foil has passed, if this "step" is present, an empty space is created where inside the water creates whirling flows that produce the annoying noise of the foil, which can turn into a whistle and then into vibrations as speed increases.

In the drawing below this phenomenon is made clearly visible so that you can understand the dynamics, but actually this 'step' is almost imperceptible to the naked eye, and often even to the touch!

What should we do to solve the problem? Sand the hydrofoil!

How to sand hydrofoil?

To eliminate or reduce this problem, the solution is to sand the trailing edge of the front wing and/or stabilizer.

But be careful, this must be done following a very precise procedure!

As you can see from the side section of the foil below, the wing and the stabilizer have different profiles, in particular they are reversed, allowing the hydrofoil to 'fly' on the water in the correct way.

In order not to alter these characteristics, it is important to know which side and how much you can sand.

If done in the wrong way, you may risk worsening the situation and increasing vibration and hydrofoil whistle.

First of all, you need the right tools:

p220 water sandpaper (or similar)
p1000 water sandpaper (or similar)
1 rigid support for the sandpaper

The special feature of water sandpaper is that it needs to be wet before being used.

This is an important step, so make sure you have the right paper and remember to use a solid support for it and a stable base for the foil.

How to sand the front wing of your hydrofoil

Wet the sandpaper and place it on the rigid support. After that, you are ready to sand.

Before you start, we recommend that you read the instructions all the way to the end.

It is essential to sand the hydrofoil by making wide and uniform movements as shown in figure 4-A. Sanding with short, interrupted moves would risk ruining the profile of the foil, compromising its correct functioning.

The operation should be carried out maintaining a sandpaper angle of about 30° and continue until the "step" is almost eliminated.

Start sanding the hydrofoil with the coarsest sandpaper (p220) at the underside of the front wing trailing edge, as shown in figure 4-B.

Once this stage is complete, move on to finishing with the finer paper (p1000) and make sure to round a bit the trailing edge. The final result should be as in the last figure 4-C.

How to sand the stabilizer of your hydrofoil

The procedure is the same as for the front wing but the angle changes. Be sure to read the instructions all the way through before you begin:

It is essential to sand the hydrofoil by making wide and uniform movements as shown in figure 5-A. Sanding with short, interrupted moves would risk ruining the profile of the foil, compromising its correct functioning.

The operation should be carried out maintaining a sandpaper angle of about 30° and continue until the "step" is almost eliminated. Start sanding the hydrofoil with the coarsest sandpaper (p220) at the upperside of the stabilizer trailing edge, as shown in figure 5-B.

Once this stage is complete, move on to finishing with the finer paper (p1000) and make sure to round a bit the trailing edge. The final result should be as in the last figure 5-C.

Result

Now that you have properly sanded all the trailing edges of the front wing and/or stabilizer, you will feel the result of your efforts once in the water.

If you have followed the instructions provided precisely, the vibration and whistling of the hydrofoil will have decreased considerably or even disappeared.

WARNINGS

When carrying out these operations it is very important to take great care because once sharpened in this way the edges of the foil may become sharp and dangerous both during the operation and during use in the water.

When sanding, use work gloves and never go directly with your bare hands to feel the sharpening of the edges.

Sabfoil does not provide this type of service and anyone who decides to carry out these procedures on their hydrofoil is doing so aware of the risks and on their own responsibility.

We advise you to read the warranty policy carefully before starting.