X-bow warships?

[CJGibson]

This vessel pulled alongside us yesterday. Drew quite an audience of rail-leaners. These "X-bow" vessels are becoming quite common in the North Sea. Apparently the X-bow design is better in heavy seas.

This got me wondering if the X-bow was being or had been considered for warships? A rummage on the net suggests not, but perhaps a ship specialist might have a better idea.

Chris

 

[Hanse]

There are some pretty interesting videos on youtube of those types.

 

[Sea Skimmer]

I was looking at these a couple weeks ago and didn’t notice any naval projects. The focus on coastal operations in the world’s navies today probably downplays the value, and cruising efficiency may not be so great. Also just out of hand, having a tall bow is not desirable for most if not all types of warships. It will consume lots of precious top weight, while offering a less then optimal position to install large radars and other sensors. The value of the X bow also decreases with size, and warships tend to be a lot larger then most of these oil platform supply vessels that are using the X bow.
For military roles its best future would seem to be in the OPV role for European powers, but that's a very small niche.

 

[Hobbes]

AIU, the X-bow is used because it offers good seakeeping properties over a large draft range. For supply vessels, the draft varies considerably. For warships this'll be less of an issue.

 

[CJGibson]

Ah, that makes sense. we load them up, empty them and send them back. So thanks for that. I will now become the platform expert in X-bows.

Chris

 

[Arjen]

AIU, the X-bow is used because it offers good seakeeping properties over a large draft range. For supply vessels, the draft varies considerably. For warships this'll be less of an issue.

X-bow may offer better seakeeping properties over a large draft range, but the seismic research vessel Oceanic Vega also has an X-bow. Correct me if I'm wrong, I don't expect Oceanic Vega to be used over a large draft range.

 

[Jemiba]

AFAIK, the X-bow was developed by the Norwegian Ulstein shipbuilding company:

the advantages claimed the developer are:

- Higher transit speed in calm water due to low angles of entry and increased waterline length
- No bow flare, eliminating bow impact and slamming in foreship
- Lower pitch and heave accelerations due to foreship volume distribution and slender hull water line
- Reduced noice and vibration levels in foreship due to soft entry into waves
- Less spray
- Negligible occurrences of green water on bridge deck
- Working deck and deck equipment better protected due to hull extended to full beam in
accommodation area
- Higher transit speed in head and following sea, giving reduced power consumption and/or
higher fuel efficiency in waves and still water

(directly copied from the Ulstein homepage : http://www.ulstein.com/kunder/ulstein/cms66.nsf/doc/3A6662B6DEF379B3C12576C70031E17D

From what I've found it was first used on oncean-going tugs, which, I think, aren't used over
a large draft range either.

 

[Hobbes]

More info on X-bow:

http://www.stowmasters.com/xbow.htm

Apparently, it's a variation on a Dutch design meant for an OPV.

http://www.ulsteingroup.com/kunder/ulstein/mm.nsf/lupgraphics/ULSTEIN%20X-BOWlr.pdf/$file/ULSTEIN%20X-BOWlr.pdf

While my initial reading suggested the draft range to be a driving design parameter, this bow shape also offers advantages when the ship's draft is constant.

 

[Arjen]

I found the Dutch design Hobbes referred to (thank you, Sir!). It's not as extreme as the Ulstein X-bow.

 

[RP1]

That's an "Axe" bow, not an "X" bow, the two are different.

RP1

 

[Arjen]

That's an "Axe" bow, not an "X" bow, the two are different.

Well, they are different, but both aim to cut through the waves rather than bump over them. Hobbes' Stowmasters link points to an article which also mentions older designs that did the same:

While virtually all of these new designs are emphatically contemporary inside and out, the hull form calls to mind a number of precedents. Steam-powered Dreadnought-class battleships of the early 20th century offered a similar profile aimed at reducing resistance in order to achieve the tactical advantage of higher speeds than a more conventional flared bow shape would allow.
Power cruising purists will fondly recall early 20th-century plumb-bow designs from, among others, the Elco and Lake Union yards; many of these classics still cleave coastal waters, leaving a characteristically miniscule wake as just-perceptible evidence of their passage.

Not too sure about Dreadnought, because I always thought that owed much of its shape to ramming considerations.

 

[Hobbes]

That's an "Axe" bow, not an "X" bow, the two are different.

This article suggests they're related:
http://www.marineinsight.com/sports-luxury/cruise-industry/futuristic-shipping/features-and-benefits-of-x-bow-ship/

 

[Mike Pryce]

Talking of axes, this page suggests that the X-bow originated from warships full of axe wielding Norwegians crossing the North Sea:

http://gcaptain.com/a-viking-ship-redesigned-for-modern-use/?190

 

[royabulgaf]

That first photo vaguely reminds me of the Great Lakes whaleback ships from the turn of the last century.

 

[RP1]

This article suggests they're related:

I believe they are mistaken. This is very common. I have never seen anything, other than this mixing of paragraphs in a magazine article, to indicate that they are related.

RP1

 

[Mike Pryce]

There are several online references that imply the Ulstein X-bow evolved from the Damen Axe bow:

http://www.marineinsight.com/sports-luxury/cruise-industry/futuristic-shipping/features-and-benefits-of-x-bow-ship/

http://www.stowmasters.com/xbow.htm

but none of them explain how/why this happened in different firms/nations. I think it may well be an internet myth that becomes 'true' only by being repeated (as may the Viking link, nice though it sounds!).

I don't know much about ship design, but the two look like they will have different benefits/issues, although having been very seasick on the North Sea anything that reduces the causes is welcome!

Ulstein have designed a Coast Guard X-bow, which is para-military I guess, and could have a few automatic cannon etc. (fire hoses seem to be shown):

http://www.ulsteingroup.com/kunder/ulstein/cms66.nsf/pages/shipdesign.htm?open&qnfl=flash#shipdesign/s-series/ulsteinsx116/product/ulsteinsx116.itm

But I guess for a warship the loss of prime real estate for larger guns and missiles on a foredeck may be an issue. It is a cargo ship, basically, and warships have different needs/roles etc.

 

[RP1]

From a builder of the Axe-bow (Well, hosted by them anyway):

http://www.amels-holland.com/editor/assets/artikelen/TYR112_Sea_Axe_Amels_the_yacht_report.pdf

Having discussed this with employees of both organisations involved, I have learnt to be *very* exact. They are also quite different in shape, the "Sea Axe" having, for example, a keel with reverse sheer forward, which helps reduce slamming. X-bows are more conventional in this respect.

RP1

 

[Lauge]

the advantages claimedthe developer are:

[....]
- No bow flare, eliminating bow impact and slamming in foreship
[....]
- Reduced noice and vibration levels in foreship due to soft entry into waves
[....]

Speaking as someone with only the most rudimentary knowledge of ship design, could these two claimed advantages translate into greater acoustic stealth?

Regards & all,

Thomas L. Nielsen
Luxembourg

 

[Arjen]

Comparison of Axe-bow(442) and conventional bow(441) from Wikimedia:

 

[Hobbes]

Speaking as someone with only the most rudimentary knowledge of ship design, could these two claimed advantages translate into greater acoustic stealth?

Interesting question. Does a wave breaking on a ship's bow sound different from a wave cresting? I expect that both have a very noisy signature, i.e. lots of different frequencies in a random distribution.

Exactly the sort of noise you'd normally filter out so you can hear the regular and transient noises a ship makes.

 

[TomS]

Less slamming and vibration are good for sonar performance (keeping the sonar dome in the water is always good) and for habitability (all of those things contribute to crew fatigue). If North Atlantic convoy duty were still a primary driver for ship design, I think these hull forms woudl be very interesting. It may not be quite so important these days, though.

There is some similarity to the wave-piercing tumblehome configuration of DD(X)/DDG-1000, especially in terms of slamming and such like.

 

[Avimimus]

Talking of axes, this page suggests that the X-bow originated from warships full of axe wielding Norwegians crossing the North Sea:

Post deserves note

 

[TomS]

Worth adding that the X-bow design was offered for the USCG Offshore Patrol Cutter program but lost to more conventional designs.

Thread 'USCG Offshore Patrol Cutter (OPC)' https://www.secretprojects.co.uk/threads/uscg-offshore-patrol-cutter-opc.16907/

 

[apparition13]

But I guess for a warship the loss of prime real estate for larger guns and missiles on a foredeck may be an issue. It is a cargo ship, basically, and warships have different needs/roles etc.

It's quite high up, but there is room for a gun on the foredeck ahead of the bridge. The USCG OPC design shows a 57mm, but a 76 would work as well, and on a large ship 127 should too.

While it doesn't have as much room forward, it has more room amidships and aft. You could put a weapon deck amidships, with helicopter facilities aft. If you want to separate weapons in order to reduce the chance of having your armaments knocked out by one hit, you could put vls aft of the superstructure, then put in your helicopter hanger and pad ala Spruance, and have additional weapons aft of the helipad. Imagine a Tico with an X bow, the forward gun and superstructure moved forward, the forward vls moved between the hangar and the superstructure, and from the hangar back pretty much the same.

Or for a frigate, an Absalon/Iver Huitveld type with an X bow. The superstructure is already forward, with the weapon deck amidships.

 

[TomS]

Interesting video on the relative function of the X-Bow and Axe Bow, and both compared to a conventional bow and a wave-piercing bow. The interesting point, IMO, is that the X-Bow and Axe Bow are both intended to reduce pitch accelerations and hull deceleration in a head sea, which are hard on crew comfort. But they're sacrificing some degree of ability to keep green water off the bow, and possibly some roll behavior in quartering seas. Hence the incredibly tall forecastles on the X-Bow designs, which would manifest in large sail areas and more vulnerability to crosswinds. So, horses for courses. A warship is generally more concerned with absolute sea-worthiness even at the expense of some crew comfort, which is probably why you don't see a lot of X-Bow warships (and only recently some with something akin to the Axe-bow)

View: https://www.youtube.com/watch?v=5eepu_owFHI&ab_channel=DMS%7CMarineConsultant

 

[Grey Havoc]

Regarding a recent example of an Axe Bow design, a Damen Stan Patrol 6009 patrol boat for the Guardia di Finanza:

Guardia di Finanza takes delivery of new flagship