Stations

From: David L. Stetson
Sent: January 28, 2002 17:22
To: [email protected]
Subject: 505world: Stations

For those who are still playing with the sections drawings and the offset table, the distance between stations are:

11 to 10: 600 mm
10 to 9 through 2 to 1: 460 mm
1 to bow: 310 mm

By the way, the drawings of the hull in the rule book and reproduced on the
website with the class rules are scale drawings, and reasonably accurate
measurements can be taken from those drawings. The diagonal, the buttocks,
and the waterlines can be determined. It sounds like some of you need to
refer to a book on hull design and lofting lines to get the full benefit of
the drawings. Just a suggestion...

Dave

David L. Stetson, PhD
Evolution, Ecology, and Organismal Biology
The Ohio State University
1735 Neil Avenue
Columbus, OH 43210

From: John Dean
Sent: January 26, 2002 04:22
To: Rob Napier
Cc: 505world
Subject: 505world: Re: 505 offset table

Rob

I have been following this thread with interest. I have always wondered
about the lines as shown on the 5o5 web pages... and now it seems to me that
we might not have an unambiguous definition of just what is a 5o5. It seems
odd that we can not easily answer the question as to how far apart are the
cross sections, waterlines and buttlines. How do the measurers do their
job? There must be some private knowlege thay have that tells them just how
to set the master templates on the hull. If they did not know the distance
between the sections, then they could not correctly or consistently put the
templates of the sections onto a hull for measuring it.

Is it possible that the real standard definition of what is a 5o5 is some
common understanding between Rondar, Waterrat and Kyrwood (et.al.)?

It might be a really good idea to have an accurate master hull drawing with
full dimensions and tolerances so that any of us could reproduce templates.
I know that I needed a template during my initial repairs of US5518, could
not come up with anything and finally just gave up. US5518, when I got it,
had been sadly abused and both bilges had been turned to mush by someone
leaving it tied to a dock where the "lake chop" constantly banged it against
the dock (apparently alternating the side tied up, since both were ruined).
I repaired it with fiberglass and epoxy resin and faired it by eye... but I
really wanted to know that ir was the right shape. I repaired about three
square feet on each side and that was too big an area for me to feel
comfortable that it was exactly restored.

So, I would support a decision to have the drawings made and published; and
made part of the rules.

Regards

John Dean


----- Original Message -----
From: Rob Napier
To: Tom Bojland
Cc: 505world
Sent: Friday, January 25, 2002 9:27 AM
Subject: Re: 505world: Re: 505 offset table

> Yes, but they were from the wrong templates!! And they were re-faired.
> What I believe we need is a straight copy of the Master templates we have.
> Otherwise we getinto no end of trouble.
>
> - Rob
>
> > Hi All
> > For your information
> >
> > I think that Hartvig Friederichs from Germany made some autocad drawings of
> > the hull some years ago.
> >
> > Regards
> > Tom

From: Richard Knott
Sent: January 25, 2002 15:17
To: Rob Napier; 505world
Subject: Re: 505world: Re: 505 offset table


Hi Rob
The quickest and most accurate means of measuring up any complex part is a
3D coordinate measuring machine. My employer uses two types: the one has a
sturdy cast-iron bed with an overhead arm supporting the remotely guided
measuring head; the other is portable and consists of a heavy magnetic base
which is clamped to any convenient base while the measuring head is manually
moved over the surface being measured. I believe the degree of accuracy of
this portable type is sub-0.01mm. It would take literally 15 minutes to
measure up the templates you described, once set-up. Output is in a variety
of CAD formats. (Sorry if I'm trying to tell you something you already
know!)

The cheapest & quickest means of reproducing the templates once measured
would be with a CNC laser profiler, which most of the larger steel
cut-and-supply shops now have. (we have three!) Accuracy is 0.01mm or
tighter. The most 'stable' material would probably be glassfibre PC board.
Aluminium and steel distort slightly.

Regards
Richard Knott SA6714 "The Hon. Hercules Gryt-Pype-Thynne"
BELL Equipment Company South Africa
Wheeled Loader Attachments & Specials

From: Rob Napier
Sent: January 25, 2002 12:23
To: Dave; 505world; Ian Gregg
Subject: 505world: Re: 505 offset table

Dave, Ian and All,

I may be able to shed some light. I am not sure of all the details, but this
is roughly the story.

John Westell designed the 505 in 1953. He lofted the lines on tracing paper
at half scale. This drawing showed the sections at 11 stations, plus the bow
profile, etc., at half scale. He lifted the offsets and tabulated them, but
unfortunately there were one or two discrepancies. Nevertheless, for a
while, for ten years or more, copies of the tracing and the offsets sufficed
for building and for creatuing templates for measurement purposes. With
+/-7.5mm tolerance permitted, there was some latitude for building error.
However, as time went on, different templates in different parts of the
world were found to be different. From a half-scale drawing, by then getting
old, it was impossible to be strictly precise as to which were correct, and
the offsets were of only limited help. I guess part of the problem was that
builders were starting to use the permitted tolerances to improve the hull
shape; when people are deliberately pushing to the limit of the tolerances,
the shape needs to be defined very accurately.

I think it was then that the rules committee was formed, to sort out the
problem. They took a pragmatic view, and selected or made a Master set of
templates for sections 3, 6 9 and 11, and the bow template. From that date,
the Master templates have defined the 505 sections for all practical
purposes. They are female measurement templates, 7.5 mm oversize, and when
fitted over the hull, the hull must lie within 0 to 15mm of the template.
Exact copies of the Master templates are supplied to national authorities.

I believe the Master templates match the original drawings and offsets
pretty closely except in the region of reverse curvature under the gunwale,
where they are noticeably more curved. This is well above the region of the
offsets, and not significant to the performance of the boat, but should be
borne in mind if using the drawings for making a trailer cradle.

I have had in mind for some years to get the shape of the Master templates
defined in digital form. To get it done professionally would be very
expensive. If anyone has access to a numerically controlled machine (or
whatever) that might do it at minimal cost, please let me know. I would need
advice also on the format to be used. It would not be any use unless it
could be used to replicate the Master templates with no discernible
differences, say within 0.1 mm.

Rob Napier
Chairman, International Rules Committee

From: Brent Benson
Sent: January 22, 2002 22:20
To: JOHN BARRY
Cc: 505world
Subject: Re: 505world: 505 offset table

Hello John,

This is in the "any help..." catagory. i.e incomplete help.

Take the axes to be:
x-along centerline in direction stem to stern
y-abeam from centerline
z-vertical from waterline.

The X and Y used to label buttocks in the table have nothing to do with
an axis system.

The stations are a set of cross-sectional yz planes that conventionally
divide the waterline into 10 equal spaces along the x axis. One
critical number that is not given in the table is the distance between
stations, and I didn't find it elsewhere in the site.

The LWL , A, B, C are conventionally xy planes [all called waterline
planes] where LWL is at the designed waterline z=0, and the others
parallel to it at specified values of z, also numbers I couldn't find.

Buttocks and Centerline are vertical xz planes where the y distance from
the centerline should be specified; numbers again not found except that
y=0 for the centerline plane.

There is one set of data for a Diagonal plane...unspecified angle.
Don't worry about this.

To plot out the hull shape, you would normally plot a set of 10
corss-sections, each with constant x, and with y=breadth from table for
each z=0, A, B, C. Also at each cross-section you could put in the
point of y, z = [deck edge],[gunwale]. Then you can add points
y,z=[buttock dist from centerline],[heignt from table]. Finally you can
put in the height of the centerline [negative means below waterline] at
y=0 of each section.

You will need additional data, not on the offset table, to define the
arc on the stem. Then you can take the breadths from the table.

Don't worry about the diagonal plane, it is just a refinement when it
comes to designing a trailer.

Once you draw the section lines, you need to add the skin thickness to
get the outside shape of the hull.

To get started you just need to get the missing numbers described above.

Brent
Benson Sails

From: JOHN BARRY
Sent: Januari 22, 2002 19:59
To: 505world
Subject: 505world: 505 offset table

There is an offset table on the 505 web page. I am looking for an explaination
of what it means, i.e. A, B, C, buttock x, buttock y.
I assume there is some sort of coordinate system that this is based on.
How can I convert these numbers to an x,y,z coordinate system that I can plug into my CAD system? What is the distance between the stations?
Why does LWL get larger and then smaller?
I have already made a 3D surface using the line drawings but I guessed at the station positions.
My goal is to make a launching dolley that fits on my existing trailer which I am rebuilding.
The current budget is $56 worth of steel. All other parts I hope to scrounge from available materials.

Any help will be appreciated,

John Barry
Parker 505, XTC
Seattle WA