Ship wave-making resistance

marcelo_malara · Post by **marcelo_malara** » Mon Mar 27, 2006 4:53 pm

I am in the process of reading an article by D. K. Brown titled Powering of warships (W.I. 3/1994).
He states that:

The high pressure areas of the bow and stern forms two sets of diverging waves, one originating at the bow and one at the stern.
The motion of the ship creates two sets of transverse waves, starting with a crest at the bow and a trough at the stern.
The combination of the transverse waves at the stern produces a lot of resistance if both waves come in phase.

On the other hand I downloaded a ppt file about the same subject (don´t know from where but I will send it to anyone on request) where on the slide 30 it states that it is the combination of the DIVERGENT waves which produces the rise in resistance if they come in phase.
So, which is the true?

ontheslipway · Post by **ontheslipway** » Tue Mar 28, 2006 9:01 am

I think they mean more or less teh same waves. You have bascially two wave systems:

A transverse wave sysmte trailing the ship and a diverging wave pattern. The fast you go, the mroe dominant the wave pattern will be toward being transverse. (This depends on you own speed, devided by the square root of your ships length. This means that this speed is relative).

Either way, waves have a tendency to superimpose. This means that if two wave crests meet, they join and combine into their combined wave height. If troughs and crests meet, they can cancel. Now, the energy that the wave needs to keep this up depends on the square of the wave height. This means that any ship producing a wavesystem combining into wave crests will have a way higher wave resistance than a ship with canceling waves. Of course, it's not as easy as trying to determine a bow and stern wave, you'd have to do the entire ship. These calculations are common (not easy)

BTW, a bulb is a device that purposely generates a hugh wave to interact favourably with the bow wave. Note that if you design it poorly or sail at a different condition, it may work against you!

Some images from MARIN, the Maritime Research Institiute of the Netherland (commercial break

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_Derfflinger_ · Post by **_Derfflinger_** » Wed Mar 29, 2006 12:59 am

foeth - Neat stuff! Thanks.

Derf

Ulrich Rudofsky · Post by **Ulrich Rudofsky** » Sat Apr 22, 2006 9:40 pm

This is the ultimate bulb, right? FREEDOM OF THE SEAS (and sailors rights!) Is that round opening a side-thruster?
http://www.spiegel.de/fotostrecke/0,553 ... _3,00.html

ontheslipway · Post by **ontheslipway** » Mon Apr 24, 2006 8:54 pm

Yes, most ships are fitted with one or two (or three) bowthrusters, making manuevring in harbours easier (Some ships have stern thrusters as well) Some ships have hatches to close the trhuster tube during sailing to reduce resistance.

Captain Morgan · Post by **Captain Morgan** » Fri Jul 21, 2006 1:54 pm

The new liner QMII has her engines in pods that can rotate to push the stern sideways also. It save a lot of money to not pay for tugs.

ontheslipway · Post by **ontheslipway** » Fri Jul 21, 2006 2:18 pm

Cruiser ships also go places where there are no tugs! You can fit stern thusters work as well, but podded propulsors work better! Still a fairly new and fragile technology with a sad 50% failure record so far.

Ulrich Rudofsky · Post by **Ulrich Rudofsky** » Tue Sep 12, 2006 12:57 am

Remember the bulb!? http://members.boardhost.com/jacobs1250 ... 87468.html