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Old 06-03-2008, 17:39   #1
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Reverse Bow

Is this the shape of things to come and would this have any application on a cruising sailboat?

Feadship’s 72-meter Reverse-Bow "Predator"; new images… http://www.yachtforums.com/forums/yacht-news-builds-launches/8670-new-launch-feadship-72m-reverse-bow-predator.html

Blohm & Voss; Radical New Reverse-Bow 118-meter "SIGMA"… http://www.yachtforums.com/forums/yacht-news-builds-launches/8672-new-launch-blohm-voss-118-meter-sigma.html
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Old 06-03-2008, 18:28   #2
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WOW, those are INCREDIBLE!! It NEVER ceases to amaze me the amount of money out there for private mega/super yachts!!

Nice post, thanks!
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Old 06-03-2008, 18:28   #3
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I saw a ship on the drawing board with the same thing. It was in one of the trade magazines a few months ago...I wish I could remember which one.
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Old 06-03-2008, 18:44   #4
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I can't believe a reverse bow would be used on a sailboat. The whole idea of overhangs is to provide bouyancy when the bow digs into a wave. You could provide some bouyancy by flaring the bow with a reverse bow, but it still seems like it would not be ideal on a sailboat. However, I won't be surprised if Wally Yachts or one of the adventurous Italian naval architects employs a reverse bow even if it goes against rules of functionality.
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Old 06-03-2008, 18:45   #5
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I don't think reverse bows are necessarily new - a lot of vessels from early 20th century had a reverve rake (http://www.maritimequest.com/warship...efatigable.htm) Maybe not as pronounced as these new designs, but funny how these ideas seem to be recycled. What I find curious is that SIGMA's bow is purported to make the vessel pierce waves, but it has fairly significant rocker, which IMO is a design feature for vessels that ride over waves, not pierce them.

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Old 06-03-2008, 18:47   #6
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Found it, Ulstein calls it an X-Bow.

Here is a YouTube video of the difference between a standard OSV and one with the X-Bow:

Largest X Bow ship launched by Ulstein Verft - Offshore Shipping Online
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Old 06-03-2008, 19:35   #7
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You'd never see this in a 30 to 60 foot sailboat, it'd just be suicide. A sailboat larger than that? Maybe, but it would have to be a tall hulled ship (more than 1 deck), and even then it still wouldn't make sense because one of the key features of these designs is their underwater component, which I don't believe would translate to a hull that heels.

BTW: I believe the turn of the century warships with a similar bow were so designed to minimize the pitching on deck. This was an effort to provide a stable platform for the great guns. After all when you're a warship seaworthiness often takes a back seat to deadliness. Though the designs look similar their purpose is different, I wouldn't characterize this as an instance of "rediscovering" old technology.
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Old 06-03-2008, 19:40   #8
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There are considerations other than hydrodynamic considerations. For a sailboat, I just keep imagining how much kelp and other seagrass you would find on deck in the morning with a bow that is essentially shaped like a plow.
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Old 06-03-2008, 19:50   #9
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I wondered the same thing Lodesman but I will know more when I see the G-force test data at critical wave period for the bow and bridge deck.

I suspect that because of the narrow piercing entry of the bow, coupled with a reverse sheer and a wave swept bow design, the weight of a breaking sea will keep the nose down. The intent is to minimize the resistance caused by the bow climbing over the top of a swell, thus maintaining a faster but wetter ride in a head sea.

Don’t know much about sailing cats but I wonder if this would help in their head sea area of weakness in moderate conditions?
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Old 06-03-2008, 19:57   #10
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Quote:
Originally Posted by David M View Post
Found it, Ulstein calls it an X-Bow.

Here is a YouTube video of the difference between a standard OSV and one with the X-Bow:

Largest X Bow ship launched by Ulstein Verft - Offshore Shipping Online
Great shot of those two hull designs side by side in a head sea on YouTube. The X bow definately works better. Thanks David
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Old 06-03-2008, 20:22   #11
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I read an article where Schionnings were doing a sailing cat with reverse bows. From memory the only real advantage they could claim was a reduction in windage.
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Old 06-03-2008, 20:46   #12
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Actually, reverse bows (wave piercing) have been around for a long time.



I've have been considering building one on my vessel but fear the criticism
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Old 06-03-2008, 20:52   #13
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it looks almost like the reverse bow doesn't try to plunge as badly into each wave... perhaps because of the lack of flare?

(Either that or the same water flow goes up... it just stays in sheet form instead of exiting stage left at a high rate of speed! )
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Old 06-03-2008, 21:29   #14
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Quote:
Originally Posted by Hubec View Post
BTW: I believe the turn of the century warships with a similar bow were so designed to minimize the pitching on deck. This was an effort to provide a stable platform for the great guns. After all when you're a warship seaworthiness often takes a back seat to deadliness.
Wasn't just warships, but a lot of steamships from the turn of the century had this reverse sheer. Image:RMS Luisitania.jpg - Wikipedia, the free encyclopedia
Again, not very pronounced - just off of plumb, but the rake increases considerably below the waterline - sorry couldn't find a drydock photo.
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Old 06-03-2008, 21:56   #15
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The reverse bow was pretty much a signature of the Dreadnought type of Battleship http://en.wikipedia.org/wiki/Dreadno...ury.Apparently went out of favor with the more modern ships later in the century that went back to an overhanging bow.

The underwater bulb bow on most modern ships is kind of a throwback. Understand that the bulb increases efficiency over a limited speed range. Great for ships that will be steaming at a constant rpm 24/7 like a tanker or container ship. Not so efficient for ships/sailboats that vary speed constantly.

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