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Posted by: Tom Daniels 6/9/2008 11:44 AM
We've begun working out the lines of the body plan, the view that slices the boat like a loaf of bread. The separate lofting floor that we're using for this view is also drawn as precisely as possible.



The closer we can get to laying out the grid absolutely perfectly, the less we'll have to worry about tiny errors adding up over time.



It's very satisfying to draw your diagonals and see that they exactly bisect the corners of each of the squares you've drawn before.  

This is the stage of building where having a little obsessive compulsive disorder is handy.  

We use a series of thin battens to connect the points that we previously laid out on the lofting.  Connecting these points gives us the shape of each section of the boat.  We use thinner battens for sections with tight curves, and thicker battens for sections with less curve.  The rule of thumb is to use the thickest batten that can make the curve without breaking.



We hold the battens in place by driving finish nails into the lofting floor next to the batten.  We try to use just enough nails to hold the batten on the points, and no more.


We know that some points that we put down earlier won't make a fair curve if we were to connect them with the batten, so we want to make it as easy as possible to pull a nail and let the batten spring into the smooth curve that it naturally wants to make.  

In other words, all the points that we so carefully laid down before are not necessarily correct.  Yes, I'm sorry to say, but it's true.  Even great designers make mistakes when transferring the measurements from their drawing to the table of offsets.  In the old days, sometimes the only thing that the loftsman would get from the designer would be a carved half-hull model of the boat, and he was expected to take his measurements off of that, and scale them up to the full size drawing!  

So, lofting involves a certain amount of interpretation from the loftsman.  He has to be able to look at the lines generated from the table of offsets and make judgements as to what is fair and unfair, what measurements were probably inaccurate or written down wrong, and what the designer wants the boat to look like.  This is where the art comes into lofting.  This is also where having a little obsessive compulsive disorder doesn't help you at all.  

At the end of the day we had the body plan in good shape, but we'll wait until we've finished the long lines to trace our batten lines in ink and call them permanent.



This gives a good idea of the boat's shape at various points along her length.  Since a boat is symmetrical, you only have to loft one side to get the shape.  The right side of the body plan is the forward half of the boat, the left side is the aft half.  So, the boat is coming at you on the right side, with the bow up at the top, and the left side is the boat leaving you with the transom at the top.

Tomorrow we'll make up some more long battens to lay out the long lines, probably 1/2" - 5/8" square and about 35' long.  Pure spaghetti.  
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Re: Working on the body plan    By Basil Carmody on 11/19/2008 8:22 AM
I'm already learning from your blog.

None of my many books on wooden boat building suggest your approach of 1.) lofting the body plan on a separate surface and 2.) using as many battens as there are stations and 3.)keeping them in place so that alterations from the long lines a.) can be made to the body plan without erasing a line already drawn on the body plan and 2.) by altering the batten's position (rather than a drawn line's) it is the batten itself (rather than the eye of the lofter) that determines the overall modification to the body plan line at that station.

I had planned to loft the long lines first, but it seems preferable to do the body plan first as you do, so that one fairs its lines first before attacking the long lines.

Go going.

Basil

Re: Working on the body plan    By TomDaniels on 11/19/2008 11:16 AM
I like using the multiple batten approach very much. Warren Barker, an instructor at IYRS, first showed me this technique. Keep in mind that we don't commit the body plan lines to ink until we've done quite a few negotiations with the long lines.

I'm glad this is useful for you!


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