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What the Hull! – Alexandros Stavroulakis

Writing the article ‘How to buy a RIB‘, I mentioned that the hull is the most important part of the RIB. It defines the RIB. So what makes a good hull? I found it of interest to you to hear the experts on this matter. So I contacted a top RIB hull designer to tell us more on this subject.

  1. What makes a great planing hull?
  2. What is the function of the horizontal “ribs” on the hull?
  3. What is the importance of the “dead rise”?
  4. How do you test the hull?
  5. Steps or no steps: what is the main difference?
  6. Foils on a RIB: what is your opinion?
  7. Which hull is your biggest success?
  8. Anything you want to share with our RIBs ONLY members?
Alexandros Stavroulakis

The first architect I contacted was Alexandros Stavroulakis. Alex is a Greek Naval Architect, R&D Director and co-owner of Skipper-BSK, a Greek RIB shipyard. BSK Marine is a company that has years in vessel constructing and her rapid progress creates a remarkable history and makes Skipper boats synonymous to quality and seaworthiness. Designing a Skipper Boat is a new challenge every time. Having studied naval architecture and industrial design and also being working in the boat industry from an early age, he knows each detail and every step of the boat construction from the inside to the outside and has the ability to make a supreme design from inside out.

1 WHAT MAKES A GREAT PLANING HULL

As I am travelling in Aegean Sea and most of the times I meet short and big waves, I need to have hulls that have the ability to plane in very low speed without pushing the bow up very high. This spec combined with steps to have a high performance is a great hull.

2 WHAT IS THE FUNCTION OF THE HORIZONTAL RIBS IN THE HULL

These are called “spray rails”. They are especially designed to interrupt the flow of the water to the upper level of the hull. The water line when a boat running is a triangle with the one corner at the bow. The deeper the hull the bigger the water line. This also means a bigger surface touching the water. So resulting in higher drag and more consumption.
The spay rails, interact with that flow making the hull riding in higher level. This delivers a smaller water line and lower drag. Therefore these horizontal “ribs” are very important and contribute massively to a better return.

3 WHAT IS THE IMPORTANCE OF THE DEAD RISE

The dead rise is the angle from the hull to the “floor” on the end of the hull (stern). The bigger the deadrise the smoother the landing after a jump. And also the stability could be not so good, the fuel efficiency and the top speed. The combination of a deep V and steps in a golden ratio gives the hull the best characteristics and efficiency. Furthermore, slow or big boats are not jumping and therefore the angle of the bow is more important than the dead rise.

4 HOW DO YOU TEST THE HULL

After a lot of calculations and flow simulations, the final test of a hull is a real size hull with real weigh/loads and engines on our Aegean Sea. It is extremely important not only to test the hull in a “laboratory” environment but even more so in real life. There is no match for testing on the sea as it changes every second as are the meteorological conditions. We do more than one test out on the sea so as to study the behavior of the hull in as many different conditions as possible. If this hull passes our severe tests only then we proceed on the deck design and construction to launch the RIB in the market.

5 STEPS OR NO STEPS: WHAT IS THE MAIN DIFFERENCE

For boats longer than 7 meters the steps are the only way for comfort and performance. The main defense is the lower drag that the water making on the hull, so more performance and more comfort as the boat is moving on an air bubble skin so to speak. The steps suck air right under the exactly defined place of the hull. More steps amplifies the effect and the RIB comes into plane in seconds. The calculation of where the steps will have the most efficiency on the hull is a secret.

6 FOILS ON A RIB: WHAT IS YOUR OPINION

I personally don’t like it. There are two big difficulties with foils on a RIB.

  1. The distance from the hull to the water is bigger (higher) so it needs extended (longer) engines to have the propellers in the water.
  2. Foils are not for rougher seas as it needs a minimum speed and if the waves are higher than the foils height, there is a problem.

7 WHICH HULL IS YOUR BIGGEST SUCCES

All my hulls are based on the same idea and technology. Our biggest success is the hull of the Skipper NC100s with the 4 steps designed back in 2004. For the first time a design like that was a world premiere.
This RIB is designed with proportions that give the boat a strong, expressive character and skillfully reflect her fast, seaworthy hull. The boat’s appearance and construction with emphasis on every detail, perfectly matches the high-grade materials. Skipper NC 100s is the first Skipper boat with reverse collar arch and the highest point in the middle of the vessel. Nowadays this arch is a trademark for Skipper boats, as all models have the same style. The Desire 120 models have the same hull but scaled up.

8 ANYTHING YOU WANT TO SHARE WITH OUR RIBS ONLY MEMBERS

Yes. When you want to buy a boat, you must define what will be the use of the boat and which are the personal key features. Furthermore, I would like that you to consider this. There’s no point in comparing non-similar boats and brands. As in the car industry, no one is comparing a Porsche to a Fiat or an SUV to a sports car. It is necessary to understand that also in the boat industry there are categories and qualities. And remember that everything affects the price.

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About the author

Karel Overlaet is a family man, Business Development Manager, creator of bingel (European market leading e-learning platform), owner of Medianaut, chairman Varen voor Autisme vzw (npo), nautical journalist and photographer, passionate about RIBs. karel@medianaut.be – Berchem – Belgium
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