Scale

[chandler]

I have a question for the pencil and paper designers.
When creating offsets how do you come up with fractions of an inch when using say 1/2 inch scale?

[Wynand N]

why do you think so many countries uses the metric system:?: Simplicity at it's best and no fractions, only decimals;)

[chandler]

Ok Wynand
so how do read millimeters from a 1/2 centimeter scale??

[Eric Sponberg]

Chandler,

You have to buy an architect's scale (a triangular section one is best) which usually has divisions from 3" = 1' down to 3/32" = 1'.

An engineer's scale divides feet into 1/10th divisions, or multiples/fractions thereof, and generally goes 1/10 to 1/60 or 1/80.

A metric scale also divides meters in similar divisions to an engineer's scale from 1/10 down to 1/100.

Look in any artist/architect supply store, or you can look in the Charette catalog (online???) to see what would suit you.

Eric

[Poida]

G'day Wynand, it beats me why anybody would want to use inches, we had them at school bloody headache.

Anyway I reckon metric boats float better than the imperial ones.:rolleyes:

[boltonprofiles]

By just a fraction....................

[marshmat]

I see I'm not the only one with an SI preference.... now and then you come across an old (or in the case of Americans, sometimes new) steam plant or something, and it's all in imperial units... so many correction factors everywhere to fix the unit inconsistencies, etc... the same thing in metric often takes less than half the time to solve....
Chandler, it's well worth it to invest in the right type of scale rule for the plans you're working from..... the scale is about $9, and you'll likely make at least $500 of errors if you use the wrong one :)

[chandler]

Thanks guys
You're missing the point.
I have scales up the yin yang.
Someone please tell me how with a 1/2" scale you can determine 1/8ths of an inch in a table of offsets?
A 1/2' scale is divided into 24 parts in it's smallest portion. That gives at best a mark for each 1/2", I can see half way between 2 marks, that gives accuracy to 1/4", where do you come up with 1/8ths?
From the lofting? Sure, but how many boats are designed and never built, therefore never lofted? Most of them I'd bet.
Eric, is there a trick I'm missing?
Also Eric what scale would you draw a 34' sailboat on 24x36 paper?

[marshmat]

My 1/2" to 1' scale has markings for 1/2", but not 1/4" or 1/8". You can interpolate to the 1/4", but it doesn't seem feasible to go to 1/8" precision on a drawing done at 1/2" to 1' scale, that would be thinner than the thinnest lines on the drawing. If offsets are done to eighths, they might have been done from a bigger drawing or with mathematical interpolation methods. Not until I go to 1":1' do I see markings on the scale rule for 1/4", which would make interpolating to 1/8" reliable.

[longliner45]

ok im out of my comfort zone on this one but I think this might help,,,1 inch contains 1000,,,,,,,, 1/2 inch = .500,,,,,thousands,,,,,,1/4 inch = .250,,,thousands1/8 inch = .125 thousands this is machine shop lingo ,,,hope it does some good,,,,longliner

[jehardiman]

Thanks guys
Someone please tell me how with a 1/2" scale you can determine 1/8ths of an inch in a table of offsets?
A 1/2' scale is divided into 24 parts in it's smallest portion. That gives at best a mark for each 1/2", I can see half way between 2 marks, that gives accuracy to 1/4", where do you come up with 1/8ths?
From the lofting? Sure, but how many boats are designed and never built, therefore never lofted? Most of them I'd bet.
Eric, is there a trick I'm missing?
Also Eric what scale would you draw a 34' sailboat on 24x36 paper?

Yes, you are missing a trick. First, use a very sharp pencil. Second, when laying out the prime dimensions, measure from the edge of the CL and BL and use the divider points to prick them in the paper. Now draw your lines, ensuring that the lines just catch the prick to the inside. Now when you measure, measure from inside to inside you should be able to "read" to 1/8" +/- 1/16". But remember that at this scale, the drafting spline and/or lofting batten is more likely to be off than your measurement. I've done 60' shapes at 1/2"=1' with offsets to 1/16" (i.e. eights with a + or -) and the largest error was 3/8" where the body was rapidly tailing off. Even using CAD offsets to 4 decimal places, expect 1-3 eights errors when you try to run a batten through them depending on the b-spline method used by the program.

[tom28571]

I have a question for the pencil and paper designers.
When creating offsets how do you come up with fractions of an inch when using say 1/2 inch scale?

You can't but there are ways to get those fractions on paper. You draw length and beam in different scales. By compressing length scale, expanding beam scale and drawing only half breadths you can easily read 1/8" offset variation on 11" by 17" paper, even for a 30' boat. This is one method of lofting without doing it full scale. Unfair lines jump right out at you.

You don't have to draw the whole boat, only the line or lines you are interested in.

[longliner45]

you need to contact a real mathamatition ,,,,may I suggest dr holyoak of yellow springs ohio.I will see if it is possible

[Eric Sponberg]

jehardiman and Tom Lathrop answered your questions about reading a scale. The fore-shortening method by Tom is used frequently and produces fair lines.

As to scale, I like working at D-size, either by hand or by computer, and for a 34' boat, I would likely draw it at 3/4" to the foot. That makes 34' = 25.5" long on the paper. This gives you room for a body plan at one end of the paper. On my Moloka'i motoryachts, I have to draw them at 1/2" or 3/8" to the foot to get them on D-size paper.

Eric

[longliner45]

sorry gentlmen ,,I re read my last post and it looks a little wrong ,,I did not mean to take anything from anyone buy using the word (real mathamatition) please dont conscrew this into anything ,,just trying to be helpfull ,,thankyou ,,longliner

[chandler]

Thank you everyone
I've already drawn this hull at 3/4" in several revisions, done offsets twice and never been able to get dimensions closer than 1/2" for offsets.
I've lofted it once and it seems pretty close to the offsets, within 1/4 of an inch.
One of the problems with 3/4" scale is that the sail plan won't fit on 24x36" paper. I'd hate to change scales for different perspectives.
The other problem is I have several plans from Atkin and Alden drawn in 1/2" scales with offsets in 1/8 ths +or-. How did they do it???

[jehardiman]

Thank you everyone

The other problem is I have several plans from Atkin and Alden drawn in 1/2" scales with offsets in 1/8 ths +or-. How did they do it???

As I said before, measure inside to inside. If it exacty splits the white space between the 0 and 1/2" ticks, it's 1/4". If it is real close to the 0 but beyond the mark it's 1/8-, a little bit further out 1/8, not quite to the exact middle 1/8+. It is easy if you do it enough and understand that the last 1/8th is going to be covered by the paint anyway....;)

[tom28571]

Thank you everyone
I've already drawn this hull at 3/4" in several revisions, done offsets twice and never been able to get dimensions closer than 1/2" for offsets.
I've lofted it once and it seems pretty close to the offsets, within 1/4 of an inch.
One of the problems with 3/4" scale is that the sail plan won't fit on 24x36" paper. I'd hate to change scales for different perspectives.
The other problem is I have several plans from Atkin and Alden drawn in 1/2" scales with offsets in 1/8 ths +or-. How did they do it???

I can loft in the method that I described (foreshortening) and read 1/16" on 11" by 17" paper easily. You just have to be open to the suggestion.

[chandler]

Chandler
The answer you are looking for is to take your offsets to a tick strip. Take the tick strips and measure them with a verniers micrometer. Take the readings and convert them to scale....This should easily give you accurate readings to 16's or 32nd's if you desire. Hope this helps.
I know what you mean, it's impossible to try and determine 1/8ths of an inch from any type of scale.
Chandler

[zigzag]

I have a similar problem as imperial scales appear unvailable in HK. I was planning to use a computer conversion program and translate into metric or buy a conversion calculator. I believe I saw one advertised on the internet. does anyone see any problems in this Idea as I am more at ease with metric when scaling even though Aussie education taught me in imperial? I still use a dual measuring tape and if a measurement is exact in inches my eyesight prefers to use inches. I guess I should buy a digital tape measure sometime.

[chandler]

You can buy a pretty basic scientific calculator for $ 10 or $20 that has some memory ie. store reclaim that makes any type of conversion pretty painless.

[apex1]

I have a similar problem as imperial scales appear unvailable in HK. I was planning to use a computer conversion program and translate into metric or buy a conversion calculator. I believe I saw one advertised on the internet. does anyone see any problems in this Idea as I am more at ease with metric when scaling even though Aussie education taught me in imperial? I still use a dual measuring tape and if a measurement is exact in inches my eyesight prefers to use inches. I guess I should buy a digital tape measure sometime.

Download it here:

http://www.consoft.de/Default.aspx?art=multicalc

Do´nt use the currency converter, is never up to date. But Multicalc is very handy for SI unit conversion.

Regards
Richard

[webbwash]

In light of all that has been said --- it still comes down to the loftsman to complete the design process and the nav arch to confirm what was done meets the requirements of the design.
Sooo - it doesn't matter what scale you use, when it comes time to fair the boat, draw it full size on the loft floor and if you need to, re-input the values back into the computer for your nesting of plate or correct sizing of carbon fiber fabric, etc., etc., etc.

[ancient kayaker]

... if you need to, re-input the values back into the computer ...

It gives me a warm fuzzy feeling to think that people were using pencil and paper that recently.

[chandler]

People are still using paper and pencil :)

[kroberts]

If you have an Internet connection near where you are doing your paper work, you can look here:

http://www.onlineconversion.com/

As a computer programmer, at one point I was deeply offended by the fact that people used pencils at all. Even worse, I found myself using one constantly. Not even a pen, mind you.

Now I use that as a measure of application usefulness. If you turn the computer on in order to solve a problem, then FINALLY the computer program is more useful than a pencil.

It seems to be such a humble measure of success.

[netjaws]

why do you think so many countries uses the metric system:?: Simplicity at it's best and no fractions, only decimals;)

fractions are exact 1/1 of the time. you can't say that about decimals.

[ancient kayaker]

Poida, on metric vs Imperial:

There's little difference between the metric and Imperial systems and I use both. It is easier to do calculations in metric. Boat designers do lots of calculations, boat builders not so much.

I have a foot (sorry) in both camps; when designing I may think and calculate in either decimal feet and pounds or meters and tonnes. I'll draw at a scale of 1 cm to the foot if it suits my purpose. But I (have my computer) convert to feet-inches-sixteenths to build, every time.

There's a good reason for that. I'm less likely to make a mistake finding the mark in Imperial measure. In metric I have to find the meter mark, then the centimeter mark, before I can tick the millimeter. In Imperial I have to find the feet, then the inches, then the sixteenths. So far so good, no functional difference. On a short rule on a sheet of paper, who cares?

But take a look at the scales on a tape measure! Because there are 2.5x as many numbers on the metric scale the letters are smaller, the nearest meter number is 3x further from the mark than on the imperial scale and I can have trouble spotting it. Then it's harder to find the decimeter with 100 to chose from in each meter than with only 12 inches to the foot.

The Imperial system is based on the practical needs of folk who make stuff. The metric system (SI if you must) is based on the practical needs of folk who work at a desk working out taxes and scientific stuff.

Them neat digital readout tapes might solve the problem, haven't tried one yet but that might get me to shift to the metric system exclusively. It's nothing to do with being an ex-Brit!