Diesel Duck 382

Diesel Duck 382
Diesel Duck 382 with the "get home" steadying sails up.

Tuesday, March 7, 2017

Lofting frames: Connect the dots carefully

To spin this past weekend in a positive light, I'll say that it was a great practice run.  I got started lofting the frames on our framing table.  Essentially you use the measurements from table of off-sets to plot out the various points for the chine, sheer and raised sheer (aft end) and then connect the dots. If you think of your framing table as a sheet of graph paper with an X and Y axis it's a little easier to understand.

The table of off-sets has the heights above the base line and the half widths.  You simply take the measurements for the designated part of the boat, at a specific station, from each part of the table of off-sets and plot them out on the framing table.  After you connect all the dots you'll have a representation of the boat frame for which the measurements came from.

It's important to note that these lines represent the outside of the hull.  When actually building the frames you need to set the timbers for the frame back from this line the distance that equals the thickness of your hull.

Station 26

I started with station 26.  I chose 26 because it was the largest frame and the first frame with the raised sheer.  Doing this one first would ensure that my lofting table was big enough.  Things went really well and this frame came out perfect.

The only challenging aspect of the process is doing mathematics in this peculiar boat building measurement format of Feet, Inches and 8th's of inches.  The math comes in to play when you subtract the height of the rabbet from all the other measurements.

Subtracting the rabbet is required because you don't want to have to draw out the size of the entire keel on your framing table.  This allows you to keep the size of your framing table manageable.  The process begins by laying out the thickness of your keel in the center of the framing table along your base line. You need to be precise.  If your keel is seven inches wide then you need to measure out 3 1/2 inches from the center line.   The bottom of these marks will act as the new baseline without having to draw out the entire keel.  In order to remove the keel you must subtract the height of the rabbet from the other measurements.  This allows you to use the bottom of your framing table as the base line instead of the arbitrary base line provided in the profile view.

I'm not going to get into it to much here, you can read Georges book for a much better explanation than I could ever give or you can check out Episode 7 of the Sea Dreamer Project on YouTube for a video tutorial.  In sum and substance you must subtract 12 inches from the feet measurement and added it back in to the other measurements in inches and 8th's of inches before you do the math.  However this is only required when necessary to do the mathematics and avoid negative integers.  In some cases you'll be able to just line up the 3 measurements for each point and do the simple math that will give you your final measurement.

The simple way will be obvious when you see it, for example;  lets say you want to subtract 3-3-4 from 5-5-4. Well if you try to convert 5-5-4 as described in Georges book you get 4-16-12.  When you attempt to subtract 3-3-4 from 4-16-12 you get 1-13-8.  Remember the 8 represents 8th's of inches, so if you have 8 8's that equals 1 inch so you would add that into the inch column and your 8th's column becomes zero.  The inch column then becomes 14, which is over a foot.  By subtracting 12 inches and adding that back into the foot column you get 2 feet 2 inches and 0 8th's or 2-2-0.  If you were to have just lined up the 2 original measurements, like in the good old fashion math way, you could just have subtracted each column and gotten the same answer.  You'll only need to convert the measurements as described in the book when you have a situation like trying to subtract 2-11-5 from 5-2-4.  You quickly see that your going to need to borrow from another column to avoid negative integers and that indicates you must convert the measurement by subtracting a foot from the foot column and add those 12 inches back into the inches and 8th's of inches column.

It sounds way worse than it is, and if you read Georges book and practice a few times it quickly becomes very clear.

My problems occurred when I accidentally used measurements from two different stations.  I was using a piece of paper to cover the columns I was not using for the express purpose of avoiding confusion.  However I was just not being careful enough and accidentally moved the papers to the wrong station and that sent everything to hell.  I quickly noticed my error when the station I was working on was not a mirror image of itself.  Unfortunately I had already drawn in the lines in marker.  I felt that I could not make the changes and draw in new lines and still have each station be clearly observable.  So I painted over it all and will try again.

The pictures below are where I stopped before painting over.  You can see the size and scale of this boat very clearly.  You can also get an understanding of the process of connecting the dots.

My 6' tall son giving scale to the picture.
My overall impressions are that this is a time consuming process, but not difficult.  You need to have rigid attention to detail and double check each measurement before drawing the lines in.

Additionally, when I start over, I am going to spread out the stations out more.  I started doing stations 26, 28, 30 and 32.  However, as a I drew them in, the bottom planking lines overlapped each other very closely.  Not really a big problem but I don't want to give myself an opportunity to make a mistake by being confused by lines that are so close together. I was using different colored markers for each station but still, the possibility for error is to great, at least for me.

So next time I'm going to start with stations 2, 8, 16, 24 and 38.  Each station is very different in size so I think they will be more clear to the eye.  Once each frame is assembled I'll paint over the table in white paint and lay out stations 4, 10, 18, 26...etc. repeating the process until all the frames are built.

I set up my Ipad to do a time lapse of my work day and have posted it here.

Thanks for checking out our project, hopefully next time I'll be able to report some success lofting the frames.

Be sure to check out our Sea Dreamer Project YouTube channel,  as we'll be having a little give away contest posted soon to thank everyone for putting us over 200 subscribers.  I know it's not much in the grand scheme of YouTube, but hey, it's a start!

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