# Props



## rickles23 (Oct 13, 2006)

Hi,
I was watching a program on LPG carriers and it showed the ship in dry dock.

On the single screw where the boss(?) is found there seemed to be a mini prop instead.

Is this to reduce cavitation?

Regards


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## chadburn (Jun 2, 2008)

I did not see the programme but there was a system known as the Contra Prop although the smaller blades were fitted to the Stern Frame. The main Propellor creates a spiral flow of the water acted upon, which involves a continuous expenditure of power for it's maintenance. With the ordinary arrangement of Screw this power is entirely lost, but with the Contra Propellor attached the water stream is again directed into a straight path. There was quite a gain claimed in efficiency in the order of 12%. Over the year's various vessel's were built with this system including Hamburg- American's steamer "Andalusia", the system also reduced vibration. When hand steering was the norm the straight propellor stream created by the Contra Prop meant that Rudder did not have to be turned a little to one side to maintain a straight course.


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## Ian J. Huckin (Sep 27, 2008)

chadburn said:


> I did not see the programme but there was a system known as the Contra Prop although the smaller blades were fitted to the Stern Frame. The main Propellor creates a spiral flow of the water acted upon, which involves a continuous expenditure of power for it's maintenance......QUOTE]
> 
> Is this what QE2 had on her when delivered but they fell off??? Was it called a Grimm Wheel or Grimm Vane???


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## Mad Landsman (Dec 1, 2005)

Ian J. Huckin said:


> Is this what QE2 had on her when delivered but they fell off??? Was it called a Grimm Wheel or Grimm Vane???


A picture of them HERE - just scroll down a bit..


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## Ian J. Huckin (Sep 27, 2008)

Mad Landsman said:


> A picture of them HERE - just scroll down a bit..


I think they broke up when she made her run from re-fit to her first passenger loading port. A fortune in scrap somewhere on the ocean floor....


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## randcmackenzie (Aug 31, 2005)

*Astern?*

I believe they destroyed themselves on the trials, but during what might have been called a somewhat excessive astern speed trial.

Well known contractors in the skills of boiler making often migrated from QE2 to other more mundane boilers, and kept us all regaled.


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## 5036 (Jan 23, 2006)

randcmackenzie said:


> I believe they destroyed themselves on the trials, but during what might have been called a somewhat excessive astern speed trial.
> 
> Well known contractors in the skills of boiler making often migrated from QE2 to other more mundane boilers, and kept us all regaled.


I was told that the technical director wanted to see if the old lady could still do her record astern speed with the Grimm wheels, they were never designed for that level of stress and thus a very clever fuel saving device was destroyed. They did one Atlantic return crossing during which time they completely disintegrated to the hubs which were subsequently removed in an unscheduled dry docking. No doubt the technical director got a further promotion above and beyond his level of incompetence.


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## rickles23 (Oct 13, 2006)

Hi,
Similar to the Queen's prop but the one on the boss was not much bigger than the boss.
Regards


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## chadburn (Jun 2, 2008)

The series of blade's that I was referring to were attached to the Stern Post and in front of the Rudder although the system was called Contra Prop the blade's did not move as with the Grimme Wheel. The system was invented as early as 1905. They did have various problem's but like most Engineering equipment improvement's were made to the system, in particular if "foreign matter" managed to get between the blade's and the Prop they were designed to shear off in order that the Prop would not be damaged and the vessel could "Carry on Steaming" until new blade's were bolted on.


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