Design


The latest concept from Aeolos Composites’ Hans Genthe is this ultra-light 45-footer, offered in cruiser/racer and pure racing versions


Breathtaking stuff I


The stunning and stunningly affordable Aeolos P30 is about to get a big sister... Hans Genthe introduces us to his latest concept, the new P45


n various forums the question arises again and again: which cruising yachts can plane? In 1982 I had already dealt with this question for the first time and


found a well-founded answer in the first edition of Konstruktion und Bau von Yachten by H. Dieter Scharping. I was then able to learn a lot more in the towing tank of the Hamburg Shipbuilding Research Institute during my shipbuilding studies – and to now see things more practically: The more curve in the underwater hull (rocker), the more difficult it is for the boat to detach itself from the wave system and leave its transom wave behind (planing). Roughly speaking, with any rocker angle of 15 degrees or less in the last 20-30 per cent of the craft, a boat can start surfing and eventually also plane. The more weight a boat has, the more


buoyancy it needs, and the more curved the lines underwater, the worse it can plane or surf. The planing ability therefore depends less on the beam and more on the weight. Wide-beam yachts can carry more weight with flatter lines. The BB10 can plane with only 2.3m of beam, but the boat weighs only 2.2t. But


76 SEAHORSE


you have to mind the weight of your luggage – more than 30kg/person is not allowed! Weight influences the shape: the lighter the boat, the flatter the underwater hull form. Then you just need to have enough sail area, and off you go. You can save weight by building lighter and/or leaving some comforts ashore.


The build improvements can include: • many large stringers that divide and stiffen the space inside (leaving little space for accommodation or stowage)


• high performance materials (expensive) • install less stuff/comfort • super light construction of any comforts you do have (very expensive)


A typical low-cost cruising yacht from a production shipyard has flat, shallow stringers, a thick (heavy) hull, cheap (heavy) equipment and is therefore overall heavy, round and not particularly buoyant. The opposite example is the ASSO 99 with zero degrees stern rocker angle and a displacement of just 1.1t at 10m length. Since a keelboat cannot plane upwind, one could simply increase the sail area by


using large downwind sails. But with heavy boats, this only helps in light winds. So it becomes clear where to put the


weight. Here are a few key figures about boats that I have sailed a lot and that can regularly plane.


All boats have an aft rocker angle of less than 10 degrees at the stern: • BB10: 10m, 2.2t, 1.2 ballast, planing starts at Force 5. Surfs at Force 4


• Farr 280: 8.7m, 1.35t, 0.65t ballast, planing: Force 3-4


• ASSO 99: 10m, 1.1t , starts planing at Force 3


• Rainbow 42: 12.7m, 3,6t, 1,6t ballast, planing: Force 4-5


• Rogers 46: 14m, 6t, 3t ballast, planing: Force 4


For comparison, some cruising yachts I have sailed: • Dehler 35 SQ: 10.5m, 5.5t, ballast 1,8t, does not plane, can surf


• Hallberg Rassy 41: 12m, 12t, lots of ballast, never planes


• Swan 48: 14.6m, 16.7t, never planes, but is nice upwind


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