Greg Ryan reports that the maximum width (tip to tip at the bottom of
the gunwale) of his section 10 template is 73 & 29/32 inches or 1876 mm.
My station 10 is 73 and 15/16 inches or 1878 mm.
Rob reports that his station 10 is also 73 and 15/16 inches.
The classs rules state, "the beam at the widest point shall be a
maximum of 1.934 m.
Bram says that station 10 should be 74 inches at the widest point, and
the beam will be about 2 inches wider than that because by the time you extend
the gunwale down below the tip of the station the proper amount, the boat
becomes the correct width less 1/4 inch for builder error.
Presumably then the correct width is the width specified in the maximum
beam rule minus the 6 mm tolerance. So, if we subtract the 6 mm (1/4 inch)
for builder error from the 1934 mm maximum width, we find that the designed
width is 1928 mm. If we subtract 6 mm for builder error from 1928 mm, we get
1922 mm as the minimum width within the tolerances.
I stapled one 1/4 inch thick strip to the outmost part of the topsides
on each side of station 10 of my jig, and 1/4 inch strips two layers thick to
each gunwale at stations 9, 10, and 11 so that the strips on the gunwale
formed a flush continuation of the strips on the topsides.
The widest point when I did this was at station 10 (the widest station)
because as the strips on the gunwales of the jig were bent inward towards
stations 9 and 11, they moved closer to the centerline. I then measured across
station 10 right up against each side of station 10, and the measurement I got
is 75 and 5/16 inches or 1913 mm, an increase of 35 mm.
In the case of Greg Ryan's jig, the measurement should be about 1911
mm, assuming an increase of 35 mm for planking the gunwales so that they form a
flush continuation of the topsides. Assuming the class minimum is 1922 mm,
that means Greg needs 5.5 mm of glass and resin on each side to come up to the
class minimum and I need 4.5 mm of glass and resin.
When I look at a ruler it seems to me that 2 mm is sufficient for the
amount of glass needed on the gunwale, and no question 2 1/2 mm is sufficient.
3 mm looks like an awful lot and 4 mm looks unquestionably unnecessary. 4.5
and 5.5 mm look utterly ridiculous.
Sorry Greg, but it looks to me like your boat is definitely out! You
cheater! Unless, of course, you start gooping and globbing fairing compound to
make up the difference. And let's hope (hee, hee, hee) your boat is not
below the tolerance over any large areas of its hull and by even more.
Otherwise
you are going to have to pile an awful lot of fairing compound onto your boat.
If your boat is too large in places, of course you can sand them down;
possibly through the glass and into the core. By the time you fix that thing
so it measures in it may be a worthless piece of crap. Hey, why didn't you buy
CNC in the first place? You dunce! What kind of doctor are you anyway?
Don't you know an unlevel playing field when you see one? What kind of fool
are
you to have bought those plans?
Of course, I do not mean to be a name calling, finger pointing, mean
spirited bickerer, but I do want to get a point across and obtain a solution
for
myself and others who may be in the same situation in which Greg Ryan and I
find ourselves. And now, early on, is the best time to do that while things
are still relatively easy to fix.
Converting 74 inches to metric we find that the station 10 template
should be 1880 mm at its widest point. Adding the 35 mm increase in width from
planking the gunwales down far enough to form a continuation of the topsides,
we come up with a width of 1915 mm across the gunwale topside intersections.
Adding 4 mm for 2 mm of glass and resin on each side, we get 1919 mm, 3 mm
below the class minimum. Therefore, at station 10 the template puts you 3 mm
below the minimum before it shrinks. In 3 out of 3 cases it has shrunk. Twice
by
1/16 inch and once by 3/32 inch.
Bram tells us, "I will be controlling who gets DXF files tightly and
those files will be held to the center of the measurement margin." So, where
in
practice someone building with CNC mold stations should end up at around 1924
mm before glassing and close to the designed 1928 mm after glassing, someone
building with templates ends up between 1913 and 1911 mm before glassing and
between 1917 and 1915 after glassing; 11 to 13 mm from the center of the
measurement margin after glassing in a class with a tolerance of 6 mm from that
center!
Admiditedly the shrinkage will not be as great at the smaller stations,
but it is there; and who knows where the templates we have place us with
regard to the tolerances in the first place?
I hate to come across as a malcontent, but from what I have seen I
could face problems come measurement time, and through no fault of my own.
Bram, you told Paul, "Don't have any fears of screwing up a station or
two. It has already happened at least once and I will send you a replacement
at no charge (except shipping)."
Bram, I would like you to send me another complete set of templates,
and I would like to pay you the cost of having them produced and shipped to me.
Will you do that assuming you have been paid?
I will glue the templates to mylar, draw new lines outside of the
existing ones to increase their size by the hull thickness, and carefully cut
along
the new lines thus formed.
I will bring these station templates and bottom templates with me when
my boat is being measured to demonstrate that I have built according to the
templates. I feel that then, if my boat does not measure in, I have a good
case
that it should be given a measurement certificate anyway. Wouldn't you agree?
Since we are to be ignorant of the designed dimensions of the boat we
are building to tolerances, I think this is the best someone without the CNC
produced mold stations that will be right "to the center of the measurement
margin" can do.
Bram, do you think my measurements and/or calculations, are faulty?
Bram, is my understanding correct that the maximum width of 1934 mm
minus the 6 mm tolerance equals the designed width of 1928 mm, and 1928 mm
minus
the 6 mm tolerance equals a 1922 mm minimum width?
Bram, are there any flaws to my reasoning?
Bram, do you find this an acceptable solution for someone facing a
potential measurement problem through no fault of their own? Worst, or maybe
best, case I would just be doing unnecessary work and spending some money
needlessly.
Please let me know.
Thank you in advance for the courtesy of a response.
Eldon
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