[C320-list] UK Halsey Mast Centering Method

[warren updike]

I did allow for such an offset in tuning my rig last year in an effort to
see how much the port list might resolve.  The answer is not enough to
notice.

It's an interesting exercise, Scott.  Thanks for the effort.

Warren & Pattie Updike
Catalina 320, #62, "Warr De Mar"
Middle River, Chesapeake Bay



-----Original Message-----
From: Scott Thompson [mailto:surprise at thompson87.com] 
Sent: Tuesday, June 09, 2009 6:11 PM
To: C320-List at Catalina320.com
Subject: Re: [C320-list] UK Halsey Mast Centering Method

Irv, I think your estimate of the offset is way off.  I think it's 
closer to 1/2 an inch.  See this picture on the web site:

http://www.catalina320.com/mediagallery/media.php?f=0&s=20081116101559509&i=
0&p=0

or here

http://www.catalina320.com/mediagallery/media.php?f=1&s=20081116101601205&i=
0&p=0

Note that the sheaves are separated by a distance that appears to be 
about the same as a halyard diameter.

If you really want to calculate a correction for this you can do so 
through a simple application of the Pythagorean Theorem.  Using this 
method, when you set one of the tape marks, the halyard forms the 
hypotenuse of a right triangle with a peak at the halyard sheave and 
with another corner at the tape mark.  There is a different triangle on 
each side of the boat, but they have the same hypotenuse length -- 
namely the distance from halyard sheave to the mark above the bosun seat 
on the halyard.  If you can measure the common hypotenuse, and the bases 
on each side (which should differ by about twice the sheave offset) then 
Pythagoras will give you the difference in height between the two tape 
marks when the mast is centered.  That is, calculate X=sqrt(H*H-B*B) 
where H is the common hypotenuse length and B is the base length.  B 
will be different on each side, and the difference in X between the two 
sides that this produces is the correction that you are looking for. 
Notice that B should vary from one side to the other by about twice the 
centerline offset of the sheave.

I did the calculation using H=40' and B=5' or 5'4" and found a 
difference of almost exactly 1/2 inch in the vertical dimension. 
However, these are guesses about actual dimensions, which will depend on 
how high you make that mark on your bosun chair among other things.

Scott Thompson
Surprise, 653


Irving Grunes wrote:
> UK Halsey has a video on centering a mast. It uses a person in a bosuns
> chair with a tape just above the seat. Then moving from side to side
placing
> a matching tape on each shroud.  Then its a short measurement from the
tape
> to the deck on each side to determine mast straightness.
> 
> This presupposes that the halyard exits the mast at its center.
> 
>>From the UK reply below, the answer was that there is insignificant
> difference if halyard does not exit from the center.
> 
> What correction should be made to compensate for the  2 inch or so offset
> that I think the C320 main halyard has from the mast centerline.
> 
> Irv Grunes
> #851
> 
> ---------- Forwarded message ----------
> From: Butch Ulmer <Butch at ukhalsey.com>
> Date: Tue, Jun 9, 2009 at 11:17 AM
> Subject: Re: UK-Halsey 'Contact Us' Email from: Irv Grunes
> To: igrunes at gmail.com
> 
> 
> It does not compensate for a difference such as you described however, I
> suspect that the differential would be so small as to be insignificant.
> 
> Charles "Butch" Ulmer
> UK-Halsey International
> 175 City Island Ave.
> Bronx, NY 10464
> Tel: 718-885-2028
> Fax: 718-885-9236
> 
> 
> 
> On Jun 4, 2009, at 5:53 PM, <igrunes at gmail.com> <igrunes at gmail.com> wrote:
> 
> Re video-Center mast over the boat using a bosun chair and tape. Usually
the
> Halyard does not exit the mast at its center but from a sheave on one side
> or the other. How does one compensate for that difference? The video was
> excellent in that the system of measurement quite simple and accurate. Irv
> Grunes

-- 
Scott Thompson
Surprise, #653