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Old 27 September 2005, 14:16   #41
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Quote:
Originally Posted by hard1
.....Basically, the twin rudders were cranked inwards by 5 degrees at speed..... Far from creating drag, it created a high pressure area and thus created lift and enabled the hull to gain another 5 knots or so. Clever.
I would expect it to create a low pressure area between the rudders. Are you sure it wasn't a slightly different effect?

----------------------
Just googled it. Apparently, the rudders turn out rather than in and they’re special trim rudders. Interesting, I’ll read on.

http://www.modelwarships.com/reviews...2-S-100-p2.htm
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Old 27 September 2005, 14:29   #42
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Quote:
Originally Posted by jwalker
I would expect it to create a low pressure area between the rudders. Are you sure it wasn't a slightly different effect?
Hmmm, I think you may well be right. I'll creep down to the the archives and dust them off. The net result was the hull kind of running on what was tantamount to an air bubble with resulting increase in speed. One would like to imagine that this was entirely coincidental, with the dockyard guys getting the rudder alignment wrong, and just before they were about to shoot him, the delighted skipper yelled "Nein nein, nix schotten! it mit fasterwerker! Ach! too late..."

Apologies
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Old 27 September 2005, 14:40   #43
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Just found this on a great site

http://www.bmpt.org.uk/boats/S130/index4.htm

Another key innovation was the addition of a special rudder arrangement beginning with S-2 (1932). Port and starboard of the main rudder were two smaller “rudders” that could be angled outboard to 30 degrees. By generating what became known as the “Lürssen Effekt," at high speed, the angled “rudders” drew a ventilation air pocket slightly behind the three screws, increasing their efficiency, reducing the stern wave and keeping the boat at a nearly horizontal attitude.


Three shafts, main rudder and “effects” rudders


A wedge was added to the lower stern beginning with S-18 (1938). This deflected the water flow slightly downwards, counteracting any tendency for the hull to settle into the water as speed increased.
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Old 27 September 2005, 14:56   #44
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Quote:
Originally Posted by codprawn
Just found this on a great site

http://www.bmpt.org.uk/boats/S130/index4.htm

Another key innovation was the addition of a special rudder arrangement beginning with S-2 (1932). Port and starboard of the main rudder were two smaller “rudders” that could be angled outboard to 30 degrees. By generating what became known as the “Lürssen Effekt," at high speed, the angled “rudders” drew a ventilation air pocket slightly behind the three screws, increasing their efficiency, reducing the stern wave and keeping the boat at a nearly horizontal attitude.


Three shafts, main rudder and “effects” rudders


A wedge was added to the lower stern beginning with S-18 (1938). This deflected the water flow slightly downwards, counteracting any tendency for the hull to settle into the water as speed increased.
Ach, so!

For "wedge" read QL Boat Trim System, a trim revolution!!! Which conclusively proves that there is nothing, but nothing ever new under the sun...
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Old 27 September 2005, 15:12   #45
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Yes I always say that!!!

I quite like the look of the QL tab indicator
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Old 27 September 2005, 15:39   #46
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Quote:
Originally Posted by jwalker
So, at high speed, (and they emphasise high speed) the turbulence created be the protrusion becomes vigorous enough to form a firm, virtual wedge considerably larger than the protrusion itself, which gives the effect of a hooked hull. I knew the turbulent effect a protrusion would cause but I never imaged the forces to be so high.
Fantastic, you have explained that very well. The ex-Volvo chap over here said the same thing in a much more complicated way. I also asked what I thought a reasonable question and that is one of the principles of Bennett or traditional tabs i.e.they also 'add' to the hull length which obviously greatly assists trimming the boat more effectively - would the QL's not 'lack' in that department as they clearly do not stick out horizontally. The answer was to think outside the box as the principle is not the same?!
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Old 27 September 2005, 19:36   #47
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I've been back to Cod's link for a bit of swatting and this PDF is just the info we need. It's based an a 7mtr model...spot on!

http://www.maritimedynamics.com/products/trim_tabs.htm

click on; View the MDI Data Sheet on Trim Tabs (pdf) at the top of the page.
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Old 28 September 2005, 03:41   #48
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Quote:
Originally Posted by hard1
.......For "wedge" read QL Boat Trim System, a trim revolution!!! Which conclusively proves that there is nothing, but nothing ever new under the sun...
Aaaah but it is a virtual wedge so maybe it is new everything is virtual these days what worries me is when someone comes up with the idea of a virtual salary Des
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Old 28 September 2005, 04:04   #49
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Basically back to smart tabs then... ?
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Old 28 September 2005, 04:09   #50
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Quote:
Originally Posted by Scary Des
a virtual salary Des
I've virtually got one of those.

Des. I think your hat is safe. Mr Cods boat is going to have so much clobber on it, it will carry on down the ramp after it has left the trailer, never to be seen again. Virtual certainty.
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