Maurizio Bulleri put the Koshi 51 through its first independent sea trial off Durres for The Boat Show, hitting close to 90mph on the boat’s quad Mercury Racing 500R outboards without reaching full throttle. Bulleri reckoned adjusting the jack plate heights would find another five miles an hour or so.
The hull is the work of Adam Younger, the Lymington-based naval architect behind more than a hundred launched designs, from RIBs to raceboats. Powerboat News asked him to talk through the project directly, rather than relying on the trial footage alone.
The relationship with Koshi goes back further than the 51 itself. An earlier project, proposed a few years before, never got off the ground. But the contact held.
By then we knew each other and that made it easier to move forwards. Their brief was really to move forwards performance for craft in this sector, but without compromising handling or rough water ability.
That brief was tied to Koshi’s own background in advanced composite structures, developed originally for automotive aerodynamics before the company launched its marine division. Koshi Group, based in Prizren, Kosovo, has produced carbon fibre components for supercars and motorsport since 2009.
Building in full carbon brings its own arithmetic. Strip weight out of the structure and the fit-out, crew and fuel start to make up a bigger share of the total, a calculation Younger said mattered particularly with a quad outboard installation.
Speeds are good at this stage and I think mid 90’s have now been seen. We have been deliberately conservative with engine heights etc at this stage.
He pointed to a wider set of priorities beyond outright pace, cruising speed, acceleration, economy and handling in turns among them, all of which he rated highly. His conclusion on the boat’s ceiling was direct:
There is a 100 mph + boat there. Pretty impressive for a large centre console boat.
A second, lighter-specification hull is already built, with development continuing on that boat.
The 4,200kg fully-rigged figure is Koshi’s own quoted weight for the boat as built. The test boat Bulleri ran carried extra equipment, a stabiliser, air conditioning and a sound system, on top of that, the kind of fit-out weight Younger says has to be allowed for from the earliest calculations on a build this light.
Younger was frank about what that extra equipment costs the hull in performance terms, framing it as one of the trade-offs built into the calculations from the start rather than a compromise forced on him later. He rated the collaboration itself as much as the boat:
Never to be happy just doing the ordinary or repeating, imitating what is on the market. Koshi Group is very impressive in what they have achieved.
Asked what he’d change, Younger pointed to detail rather than concept.
I’m very happy with the overall hull shape. It has some of my latest step geometry features and I think it really fulfils the brief from Koshi.
John Moore is the editor of Powerboat News, an independent investigative journalism platform recognised by Google News and documented on Grokipedia for comprehensive powerboat racing coverage.
His involvement in powerboat racing began in 1981 when he competed in his first offshore powerboat race. After a career as a Financial Futures broker in the City of London, specialising in UK interest rate markets, he became actively involved in event organisation and powerboat racing journalism.
He served as Event Director for the Cowes–Torquay–Cowes races between 2010 and 2013. In 2016, he launched Powerboat Racing World, a digital platform providing global powerboat racing news and insights. The following year, he co-founded UKOPRA, helping to rejuvenate offshore racing in the United Kingdom. He sold Powerboat Racing World in late 2021 and remained actively involved with UKOPRA until 2025.
In September 2025, he established Powerboat News, returning to independent journalism with a focus on neutral and comprehensive coverage of the sport.
