Lifting Keel
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Lifting Keel
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OVNI's are lifting-keelers, i.e. there is no ballasted, fixed
keel but instead there's a blade that can be lifted inside the hull, therefore
drastically reducing the boat's draft, from over 2 meters down to only 60 centimeters. The keel is
made in aluminium, therefore
its contribution to the ballast weight is negligible and the actual lead-ballast is
inside the hull. In smaller OVNI's, up to the old 385 (nowadays up to the 365),
the keel lifting is by means of a block-and-tackle, so the keel is free to lift in case of
impact, while in bigger boats the lifting is by way of an hydraulic pump: in
case of impact, a small safety membrane is blown, and needs to be replaced in
order to put the circuit back into pressure. No big deal, but it takes
time. Unavoidably, the keel's shape is dictated by the need to accommodate it inside the hull (with the corresponding bulk in the main cabin) and although it's quite deep, it's nevertheless rather small. The result is that performance close-hauled is not exceptional (to put it mildly...) but it's certainly comparable with many mass-production boats. Clearly, it's a boat which is at its best in long-distance voyages along the Trade Winds. Normally, the keel is kept fully down when close-hauled or reaching, and gradually lifted when running with the wind: frankly, I've made many tests and never found a big difference with the keel up or down, while I dislike the feeling of the boat being less responsive to the rudder when the keel is fully up. Maybe it's just a feeling, many sailing gurus advocate sailing in heavy seas with the keel up, to reduce the risk of the boat "tripping on its own keel" and rolling over, but I suspect they refer to seriously bad situations, when running with cables trailed from the stern or heaving-to. Frankly, when we chose the OVNI in view of our planned circumnavigation, our motives were mainly based on the hull's strength and durability (not surprisingly, used OVNI's are very expensive, as a well-kept hull is virtually indestructible!) and we were not very keen about the lifting keel, so much so that we would have chosen a fixed-keel alternative, if available. Our doubts concerned mainly the boat's ability to self-right from a total inversion, where the hull's form-stability becomes a liability and may keep the boat capsized (in an ocean voyage, one must think for the worst!...).
The stability curve of a fixed-keel boat The curve for the lifting-keel version of the same boat Without becoming too technical, the above curves ("stability curves") show the righting couple's values at the various heeling angles, from zero (boat upright) to 180° (boat fully inverted): in all boats the righting couple increases while the boat heels, up to an angle around 60° where the couple starts decreasing until the "angle of vanishing stability" is reached and then the couple becomes negative (the boat capsizes). The smaller the negative values and the greater the possibility that the rocking motion caused by the waves may bring the boat to the good side of the curve again, and the boats right herself up, but wide boats with the ballast high-up in the hull are very stable in the capsized position. This always worried us a bit, although we did not plan to sail in areas with extreme weather conditions. Then, in our readings we found out that many long-distance voyagers are strongly in favour of the lifting-keel as the ultimate heavy-seas solution, and in fact I found no record of an OVNI having capsized.
Shaula4 with the keel lifted Today, after nearly 40,000miles (and a knock-down in the Caribbean), I believe we can summarize pro's and con's as follows: PRO's: - possibility to let the boat rest on the bottom in anchorages which dry out at low tide, without the need of complicated contraptions to keep the boat balanced on its keel (this is in fact the main reason for the lifting-keel in France Atlantic shores, but the problem is nearly non-existent anywhere else) - possibility to access shallow-draft anchorages (and this is indeed a very handy capability, in coral atolls and reefs but also here in the Mediterranean) - possibility to sail in canals and internal waterways (useful for example to take the shortcut between Atlantic and Mediterranean via the Canal du Midi, which has a maximum draft in the range of 1.5 meters) - strong reduction of the risks of structural damage in case of impact with the bottom or with obstacles offshore, be it a fishing net or a floating object or - not at all as unlikely as it sounds - a whale! - great stability and gentle motion due to the heavy ballast in the hull (it must necessarily be very heavy to ensure self-righting capability) - (alleged) reduced risk of capsizing in very heavy weather CON's: - reduced close-hauled performance - mediocre manoeuvrability under engine when the keel is lifted, but this is a limited problem as normally manoeuvres in port are performed with the keel at least partially down! - dubious self-righting capability when totally inverted (due to the broad beam, the boat is very stable once capsized); we can only testify that in a 120° knock-down, the boat did right herself up! In summary, the
picture is that of a very solid boat, with good downwind performance in fresh
winds, particularly suitable to navigate poorly charted areas or tricky,
rock-strewn anchorages, as well as tidal waters: a long-distance boat, by any
means. Probably not justified to sail in places like the Mediterranean, also in view of the high price and of the modest performance in light winds.
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Webmaster: Gianfranco Balducci - email: gfbalduc@tin.it Last Update: 21/09/2014
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