Axe Bow / Enlarged Ship Study

Err, how do they control bow steering in big swell with such a deep bow?

Kelly

Hi Evan, the Bourbon Orca has nothing to do with the Axe-bow concept. It's a completely different animal.

That said, it's possible that the Axe-bow also has merit for slower vessels, but that remains to be investigated. If you do the same design exercise - minimizing the vertical accelerations - for displacement vessels, maybe you come up with something like the Bourbon Orca?

Kelly, as far as I know,
1. they have quite sizeable rudders
2. outboard of the rudders are fixed fins (similar to the rudders)
3. the rudder actuators work faster

I know they have been investigating (or still are) the possible use of a bow rudder, but that's certainly not fitted on the 4 vessels produced so far (probably because it's not necessary).

Cheers,

Bruno

Thanks guys.

Note: I posted this in another thread, but thought it was applicable to this discussion as well...

In year's past, private yachts were quite a bit smaller then the behemoths being launched today. Most of them were destined for native waters, with only a few big enough (and brave enough) to cross the pond. Enter: Dockwise, but that’s another story.

As yachts have increased in size, so have our expectations. We want to travel far, but getting there isn’t always a pleasant trip. Recently, a few designs have bucked the aesthetic trend in favor of function, in search of a way to work with waves as opposed to fighting them. A most recent example of this would be the Craig Loomes designed Earthrace vessel and I’ll expand a little on this…

A conventional (flared) bow design attempts to displace oncoming waves. As a flared bow submerges into an oncoming wave, water is displaced outwards. This results in deceleration and vertical forces that add resistance to the hull’s forward motion. This also creates lift, raising the bow out of the water. As the wave passes, a trough follows and the hull looses lift and falls in search of buoyancy. This is called pitching and in extreme conditions it can be violent. Stabilizers can help reduce pitching, but only to a certain degree.

In contrast, piercing bows (aka: fine bows) favor silhouetting a wave, or submersion. By going “thru” a wave, as opposed to over them, deceleration and vertical forces are reduced. The result is far less pitching and ultimately… a smoother ride with more consistent speed. But… it’s a much wetter ride!

On yachts the size of yester-year, the amount of freeboard was simply not sufficient to overcome the drenching a fine-bow would create. But with the size of today’s super yachts, coupled with the trend toward high freeboard, expedition-like bows in recent years, a piercing hull form can produce better performance without the need to run windshield wipers 24/7!

Hi there everyone,

I used to work for damen and heard a lot of information about the axe bow concept. To get it straightened out, here some of the public information:
the axe bow concept is intended for high speed vessels operating in high seas. The vertical, narrow and downward extended axe shaped bow doesn't only cut waves, but also smoothens out any vertical movements. It does not stop these movements, but decreases the accelerations, which causes a smoother ride. To decrease the spray, the wheelhouse is placed a bit more to the rear, and also a number of spray rails are mounted.
Towards the rear the vertical frames go into a flat horizontal box shape frame shape for creating a planing hull shape. The outwards placed twin or more propellor arrangement makes up for any steering problem causes by the axe shaped bow. The high speed also makes this less of a problem. On lower speeds the bow thruster may have to work a bit harder for moving the bow sideways.
Also to make things easier: the bow desing from the norwegian Ulstein is called the X bow, opposed to the Dutch Damen Axe bow...

The increased buoyancy as the bow is pitching down was also the idea behind the famous "Clipper Bows" on the Tea Clippers.
They still look good hundreds of years later, but perhaps the pitching motion was a bit excessive..?

Hi,

After being involved in extensive tank testing of a boat with an Vertical Bow and a 4 Fin Stabiliser System it was proved that in order for the Stabs to have any noticeable effect on pitch a speed of 18 kts and above was needed and the forward fins were switched to purely pitch control.

Given the results of the Tank Testing the client didn't opt for that facility and just stuck with a standard 4 Fin install.

The Feadship 72m reverse bow yacht 'Predator' Captains report:

‘The yacht handles better
than any I have ever sailed. We
have been in 5m seas and Predator
throws no bow wake.’
Capt Drewes is equally
impressed with the comfort standards
in other ways too: ‘The specs
on noise, vibration, speed and
handling also surpassed our highest
expectations. We averaged 20
knots with two engines running at
1,500rpm, and at that speed
Predator is as smooth as other
yachts I have run at seven knots.

Couldn't agree more. Lightweight vessels with heavily flared, blunt bows 'stop' dangerously, leaving one few choices and, therefore, at the mercy of anything over three metres or so.
To be seaworthy, any vessel needs to be able to make reasonable controlled way with, at the same time, an acceptably easy motion.
Any vessel without a soft 'punch' is, quite simply, dangerous.
Young 'naval anarchists' (sic), even many in the commercial world, should be made to abandon their bloody laptops, go to sea for a few weeks in northern latitudes and stand a few watches in real seas.
The Norwegian Ulstein company, with their (unique?) team of sea-time educated designers, have finally made acceptable the 'X' bow and the Axe bow. We are making progress there, but elsewhere at about the same speed as the usual yacht trying to go upwind in a seaway.

Reverse Bow

Hi does anyone know of any reverse bow yachts currently under construction. I love 'a' and Predator and was lucky enough to see Predator in Palma. The photos i've seen do not do it justice.

Thanks Lara