[MHml] Cat Rudders Toed In?

[Peter Southwood]

Paul, a lot depends on how you measure.
Using a tape over 5m is tricky, even if you use a spring balance or some 
other form of tensioner, and wind can wreck your accuracy, but if you use a 
rigid device like an aluminium tube with a tape ot ruler fixed to it you can 
get far more reliably repeatable results. After all, what you are looking 
for here is a precise difference, where the basic dimension is of less 
importance.
However your point seems to be that the angle is not significantly different 
from zero, with which I will agree.
cheers,
Peter
----- Original Message ----- 
From: "Paul Nudd" <paulnudd at actionpotential.com.au>
To: "Informed discussion of multihull issues" <multihulls at steamradio.com>
Sent: Monday, September 04, 2006 8:38 AM
Subject: Re: [MHml] Cat Rudders Toed In?


> Glenn Brown wrote:
>> Paul Nudd wrote:
>>> Half a degree? You can measure that accurately?
>>
>> Sure, with 2 people: Just line up one rudder roughly fore-and-aft and
>> measure the difference between the center of the leading and trailing
>> edges.  For rudders that are 6" (254mm) front to back, 1 degree is 1/8"
>> (just over 3mm)
> -------------------------------------------
> So half a degree is 1.5mm, quarter of a degree is 0.75mm"
> Accuracy required for half a degree to be meaningful is +- 0.75mm
> If this is not possible then it is either 1 degree or 0 degrees.
> Best I can measure over short distances is +- 0.5mm
> over 5 metres I would be happy with +- 2mm
> First find centres of leading and trailing edges of both rudders,
> accurate to +- 0.5mm 4 measurements resulting in +- 2mm then measure the
> 2 distances accurate to +- 2mm each
> Cumulative accuracy of the difference (after 6 measurements) is +- 6mm
> So, if I measure 1.5 mm difference it may be anything between 7.5 mm and
> negative 4.5 mm
> Am I right?
> I think I'd do better 'eyballing' it.
> I think the best way is to set it on the move, motoring in flat water,
> adjust crossbar until both rudders show best flow.
> PN
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