Feet-Inches-Eighths to mm

[rwatson]

I use decimal inches.
Measuring tapes with decimal inches are readily available, and it is easy to estimate 0.01 inches.
So one can think in American units (e.g. a plywood sheet is 48 inches wide), cut a sheet with a Festool saw blade 0.1 inches thick, and make further measurements with the same ease as in any other decimal system.

If you can 'visualise' " 0.01 inches", a hundredth of an inch, ( .254 of a mm) then you have really good eyesight, but no plans for boat hull offsets go to that degree. Its a rare plan that gets to 32/s of an inch (.75mm), though I have one set that does. By then it goes to a CNC machine for cutting. Even then, 1/10" ( 2.54 mm) is too coarse.

Decimal inches is a poor orphan in the measurement world, and nothing but precise metal engineering uses it, for jobs that rarely go over a foot.

For boatbuilding, metres, centimetres, millimetres seems to be the best way for my poor brain that shudders at feet and yards, and calculating displacement from non-metric volumes.

 

[daiquiri]

Ok I am reposting here, for you guys' convenience, my spreadsheet for the convertion of tables of offsets.
Cheers

 

[sprit]

rwatson:

If you place a millimeter ruler over a line, you will see that it is easy to estimate whether the line is at one or the next ruler marks. If the line is just between two ruler marks, then you can estimate 0.5 mm. If the line is nearer one or the other ruler marks, then you can easily estimate 0.25 or 0.75 mm.

Yes it is easy to estimate 0.01 inches (about 0.25 mm) when reading a tape marked in decimal inches.

 

[TANSL]

but no plans for boat hull offsets go to that degree.

Of course you get to that precision, even in boats 400.000 mm in length.

 

[motorbike]

we have a mix of two systems, for us oldies born before 1980 we often think in feet as it suits but act in metric. For example we say "that boat is 38 feet" no one says 11.6 metres, but working on that boat no-none uses inches, its just to hard after using multiples of 10.

 

[beernd]

I just copy the offset table into EXCEL
Then I make a second table where each cell has the number of feet inches and eights of inches added up an example (3*30.4)+(4*2.54)+(5*0.3175)
Please note that I convert to centimeters rather than mm, this is because it is easier to read centimeters from your tap messure than mm example 12.7 is 12 centimeters and the .7 the milimeters

 

[kilocahrlie]

As a matter of habit, I've always drafted my work, boats, aircraft, automotive, or other, in both SI and English units, tolerances and related data in GDT (Geometric Dimensioning and Tolerancing).

I usually leave the annotated, corrected, clarified, and finalized calculations pages attached right behind the drafting so that anyone wishing to challenge my work is free to do so. It is a slight, but usually welcome effort at transparency. The emphasis is on correctness of engineering and clear communication so that the technicians have little to question.

 

[SukiSolo]

The emphasis is on correctness of engineering and clear communication so that the technicians have little to question.

The real problems come when the tooling is made in the Far East and the toolmakers cannot understand the notation in English! Don't ask how I know.....

 

[OzFred]

…
Pity the main metric units were 'wrong'. I believe a nautical mile was meant to be 1Km but they got the circumference of the earth wrong.... In other ways such as density etc it makes things much simpler.
…

According to Wikipedia, a nautical mile is based on 1/60th of a degree of latitude and is now defined as exactly 1,852 metres.

The world is not a perfect sphere (it's more an oblate spheroid), so a degree of latitude is a different distance depending on where it's measured. Any such measure based on a physical object is only an approximation of the true value (as is any physical measurement).

 

[kilocharlie2]

Suki -

Don't worry, I won't ask - I know how you know. That used to be my job - toolmaker. I can hear Alabama playing Song of the South:

"...Gone. Gone with the wind - ain't nobody lookin' back again. "

Guess I'll go get a job with the TVA....

 

[Proflooney]

I like to use this handy dany lil prog been using it for years https://joshmadison.com/convert-for-windows/

 

[daiquiri]

It would be so nice to read previous replies before posting a duplicate link.