Homemade: Owner builds bulbous bow from ball fender

Mr Kropp, what is your fender doing at the front of the bow?

This actually has old roots. I've been a glider pilot since 1971, and aerodynamics is of course a key issue. Basically, it's always about efficiency. Small changes to the profile can have an enormous impact, even if you hardly recognise them visually. It is precisely this idea that has never let go of me: How can you utilise flow more efficiently? At some point, I saw a small bulbous bow on a boat. The owner told me that he had been measurably faster on his standard route, by around five per cent. I did the maths and thought: that could work.

Why a Fender of all things?

Because the conversion was surprisingly simple. The tube was adapted at the front and fixed with Sikaflex. It was important that the surface was properly prepared, i.e. that there was no more antifouling underneath. The biggest challenge was the position and size of the ball. It had to protrude slightly from the top of the tube, but not from the bottom. Otherwise the desired wave effect would be cancelled out. In the end, it took three winters to find the final shape.

Was it really worth it?

Measurements on longer tours show around three to five per cent less consumption. We also reach our cruising speed at around 200 revolutions per minute less. And even if it's only five per cent: That adds up over longer distances. But to be honest, I was less interested in the money. I'm just happy when a technical idea works.

Was it just an idea at the beginning or did you quickly realise that you wanted to implement it?

I have a certain obsession with optimisation and have already optimised the consumption of cars and tuned engines more efficiently. I just like to try things like that out. So I realised relatively quickly: I'm going to test it. Simply out of curiosity. I was interested to see whether the idea would work in practice.

Were there imitators or interest from others?

Interest yes, but many boat owners prioritise looks over efficiency. However, some have literally asked: "If it saves money, why doesn't anyone do it?" I have even considered offering the concept to a shipyard. It would be even easier to integrate something like this into series production.

If you could give a central message, what would it be?

There are many small adjustments you can make. Not just on the boat, but everywhere. If everyone optimises three or five percent - in terms of consumption, energy, technology - then that is enormous in total. I believe that innovation doesn't come from bans, but from clever improvements. And sometimes that simply starts with a tube and a ball on the bow.

Sitting around at home would never occur to 70-year-old retiree Gerhard Kropp. Whether boat, car or plane, everything is constantly being scrutinised and optimised. Even his former motorboat.