5 July 2023
Less fuel needed thanks to Optima nozzle
Skipper Sieberen van Terwisga has been sailing with an Optima nozzle below his cement tanker MV Fenna for more than a year now. He knew what Damen Marine Components (DMC) says about its nozzle: better propulsion, less fuel consumption. But did he know that the savings would be so high? ‘Sometimes it can be as much as 30%.’
Van Terwisga apologises: he is a little hoarse. Has he been out partying? ‘No, racing’, he replies. This year he became a skipper for the committee that organises annual races of traditional Frisian sailing boats, known as ‘skûtsjes’, in the village of Eernewoude. ‘So then I sometimes have to do a lot of shouting.’
The sailing ship that he sails is a Frisian cultural heritage vessel built in 1930. The ship that Van Terwisga sails in his working life has also already reached a respectable age: the cement tanker MV Fenna dates from 1963, so has already been sailing for 60 years. Van Terwisga himself is still a young skipper, of 33.
He is also a mindful skipper, who keeps a close watch on the performance of ‘his’ Fenna and likes to compare all the figures. In the past year he has been able to do that to his heart’s content, after a DMC Optima nozzle was installed below the Fenna, in combination with a new tunnel. Would it really mean less fuel consumption?
After more than a year of sailing, he can confidently give a definitive answer to that question. ‘You bet’, he says. ‘In some situations, there’s a difference of up to 30%. On average, we realise fuel savings of 15% to 20%, which is still a great deal.’
A 60-year-old ship with a brand-new nozzle: how did that happen? ‘It started with the Hilda’, Van Terwisga explains. MTS Hilda is the other ship owned by the VOF H. Taekema, the company that Van Terwisga owns together with his wife and parents-in-law. The Hilda and the Fenna are tankers for shipping cement, sailing routes between Germany and cement plants in the northern Netherlands.
‘We came to the conclusion more than 10 years ago that the Hilda was a bit less profitable than it could be. My father-in-law responded to that by having a nozzle installed below the ship, and we were very happy with that. When we were facing the same problem with the Fenna, and gas oil price were also shooting up, we went looking for a nozzle for this ship too.’
Van Terwisga requested quotations from various suppliers, including DMC in Hardinxveld-Giessendam. ‘I’d almost say that was a natural choice, because DMC is a very well-known name in inland shipping, with a good reputation’, Van Terwisga says. ‘We were sent calculations, which we compared. The DMC Optima nozzle came out of that comparison as the best in terms of efficiency, returns and price-quality ratio.’
The Fenna is a relatively small single-screw vessel, 57 metres long and 7.28 metres wide, with a draught of 2.90 metres. For that reason, a choice was made for an Optima nozzle with a diameter of 1260 millimetres, considerably less than average. ‘But because of the small dimensions of our ship, we simply couldn’t fit a larger nozzle.’
That called for customisation, says Kees Oevermans, the Technical Sales manager who oversaw the process on behalf of DMC. ‘The nozzle has a length-diameter ratio of 0.4. 0.5 is more common, but there was so little space that we chose a shorter variant. A special, custom-made nozzle. Still smaller is also possible: we’ve even made ones of half a metre. And ones of up to 6 metres. There isn’t really a limit for the diameter.’
In comparison with an open screw, a nozzle requires more water while the ship is sailing. ‘With that, you actually increase pumping action’, Oevermans explains. ‘There is more thrust, so that you can either sail faster or use less fuel without changing the speed. We never make predictions about the expected fuel consumption, because that’s different for every ship. But a nozzle is certain to save you fuel.’
Van Terwisga can endorse that since the nozzle was built into the Fenna in February 2022. ‘I noticed right from the start that it makes a difference. We can now continue to sail at the same speed at a lower RPM. Sailing slowly and still maintaining thrust is what makes the difference. If we sail very stably at 10 to 11 kilometres an hour on still water, the fuel saving can go up to as much as 30%.’
On average, the Fenna realises savings of 15% to 20%. Van Terwisga would have signed up for that in advance too. ‘It means that you automatically sail more easily and calmly, because you always have the feeling that you are keeping up your speed, even when you pull back a bit on the gas. After all, you always have continual thrust. It does mean you have to adjust how you sail, but you quickly get used to that. You also have more comfort: it reduces the noise.’
An additional advantage is that it saves sailing time. ‘You remain at speed a little more stably, because you have more thrust and relatively somewhat fewer problems from situations where the speed is more restricted, for instance in shallow areas and on smaller canals or rivers.’
He can therefore recommend the Optima nozzle to other shippers, for both existing and new vessels. ‘If you are looking purely for better returns, then the nozzle is advisable’, he says. ‘We’ve demonstrably saved fuel in the past year, which is very welcome in these expensive times. The cooperation with DMC has also been excellent. They assisted us with the installation work, which we organised, and I can still always contact them for answers and advice.’
And, he says, there is another important reason for choosing an Optima nozzle. ‘Every litre of fuel that you save means fewer emissions. We all have to think about that too. And the engine now runs continually with a better load. That’s better for the environment too.’