hull efficiency

70 Sunreef Power Cat Hull Mods Double Efficiency

Laurent Bourgnon family on Sunreef Yachts 70 Power JAMBO - Photo Courtesy of Sunreef Yachts

Laurent Bourgnon family on Sunreef Yachts 70 Power JAMBO - Photo Courtesy of Sunreef Yachts

Sunreef Yachts said last week that modifications it has made to the 70 Sunreef Power catamaran JAMBO have nearly doubled the yacht’s fuel efficiency.  The fuel consumption on JAMBO dropped from 13 liters/hour/engine at 10 knots at 2,300 rpm, to 7.5 liters/hour/engine at 10 knots at only 1,500 rpm.

The mods are a demonstration of one of the fundamental principles of the hydrodynamic laws that affect boat hulls.  Basically, Sunreef lengthened the hulls’ overall length, in part by added bulbous bows to each hull.  Swim platform extensions also added waterline length. Stated simplistically, the principle is that longer (waterline length) hulls can go faster than shorter hulls. 

View of bulbous bow on 70 Sunreef Power Cat JAMBO - Photo Courtesy of Sunreef Yachts

View of bulbous bow on 70 Sunreef Power Cat JAMBO - Photo Courtesy of Sunreef Yachts

In the case of JAMBO, additional efficiency is derived from the bulbous bow design, which “cancels” part of the normal bow wave by creating another bow wave exactly opposite in phase to that normal bow wave.  Bulbous bows have been used on commercial vessels, warships and many larger yachts for many years, but the decision to use them on mid-size yachts is complicated by such factors as expense and more complicated hull fabrication.

In any event, the improvements demonstrated on the Sunreef power cat are significant and obviously worth the effort for JAMBO’s owners.  You can read more about the Sunreef pwer catamarans in our earlier coverage here.

Copyright © 2011 by OceanLines LLC.  All rights reserved.

Posted by Tom in Boats, Cruising Under Power, Powerboats

A Closer Look at the New Krogen 52′

Stateroom with Office Accommodation Layout of new Kadey-Krogen 52"

Stateroom with Office Accommodation Layout of new Kadey-Krogen 52"

Kadey-Krogen’s recently announced 52′ is a classic example of a builder filling out a product line in specific response to customer demand. In this case, the company already had on offer its well-established 48′ and the new 55′ Expedition. The 55′ Expedition, however, is not really the “other” boat in this comparison — it’s the Krogen 58′ which was more of a model for the new 52′. In a recent interview, Kadey-Krogen Vice President Larry Polster talked about the boat itself and what kind of customer is the target for the new 52′.

With the first signs of the economic recovery beginning to emerge in the recreational boating industry, Kadey-Krogen is optimistic about the market for the new boat. “There’s clearly a market for bigger boats — upper 40s to mid-50s,” says Polster. He says the company originally had a hole in its lineup that stretched from the 48′ to the 58′ and originally started out designing a 53′. But input from the early customers on that design turned it into the 55′ Expedition, a significantly different design that the traditional Krogen. And the price wasn’t between the two original yachts, either.

Polster says the 52′ is better understood as a smaller 58′, rather than a larger 48′. And of course, he emphasizes, the new boat is designed fresh from the keel up. “It’s a purpose-built boat; not a stretched hull,” says Polster. The familial resemblance to the 58′ can be seen in details such as the Portuguese bridge, the Dutch door in the starboard-side galley, and the open office space below. So, the 52′ will appeal to those who like the design of the 58′ but might be intimidated either by the size or the price. And yet, it is substantially roomier than the 48′, not least because of the extra foot of beam (17′-9″).

Interestingly, all of the launch customers have chosen the same layout — master stateroom forward, twins to starboard, and a convertible open office to port. Kadey-Krogen has converted several of the initial letters of intent to firm contracts and construction is on schedule.

Starboard Profile Rendering of the new Krogen 52'

Starboard Profile Rendering of the new Krogen 52'

As a clean-sheet-of-paper design, the new 52′ is one of the few boats of her size that was designed from the outset for the baby boomers who started retiring last year. Manufacturers today — from the boat builders themselves to systems providers like KVH — understand that liveability aboard is key to success with the boomers. That liveability issue is directly related to keeping household standards. Not only do you see household-standard appliances and near-shore size beds and head fixtures, but even minor details like stair steps. “We’ve taken great pains to make all risers and treads house-standard,” says Polster. “The magic ratio is about 17 — rise plus run — but a tread of only 7″ is hard to stand on.”

Kadey-Krogen expects high efficiency from the 52’s hull. Predicted performance at a speed/length (s/l) ratio of 1.1 shows the requirement for 70 hp, moving the boat at 7.6 knots. The boat will displace 70,000 lbs at half-load. Standard engine is a 231 hp John Deere (all Krogens have JD power), and the genny will be a 12kW Northern Lights set.

The new 52′ has a competitive base price right now of $1.295 million. That compares to a base of $949K for the 48′ and $1.595 million for the 55′ Expedition.

One interesting side note: the question often arises — how big a boat do I need to live aboard? Obviously, there can’t be only one answer to that question, but in Kadey-Krogen’s experience, the answer is — “somewhere in the 40’s.” “We built 50 of the 39’s and as far as I know, only one couple lived aboard full-time,” says Polster. One size up, however, and it’s a different story. “The 42′ is a little bit longer, but a full 18″ wider in beam and tons of owners are full-time liveaboards.”

Copyright © 2010 by OceanLines LLC.  All rights reserved.

Posted by Tom in Boats, Construction & Technical, Cruising Under Power, Engines, Industry News, Passagemaking News, People, Powerboats, Technology