Boat Building Forum

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lofting question *PIC*
By:Paul G. Jacobson
Date: 1/5/2011, 11:27 pm
In Response To: Strip: lofting question. (Sean McGrath)

: Hello,
: I've recently been bitten by the bug to build one of these
: beauties, and I'm anxious to get started. I have a basic
: question

You'll have more questions. Feel free to bounce them off this panel. Just remember that free advice is worth every cent you paid for it--except here.

: and hope somebody can help. I bought Nick's book, and I
: wouldn't mind buying the plans to start my Great Auk, but I'd
: rather do it all myself, including the lofting.

Problem: where
: can I find the size graph paper required to do this, or is there
: another method used that is an option?

Forget paper. You need to cut the forms from either particle board or cheap plywood, so loft your lines directly on the plywood, and then cut them out. This saves you the time of setting up a drawing table to hold the paper, and later using carbon paper to transfer the lines, or gluing your paper to the plywood. (messy, and you gotta get some glue)

Some people use cheap 1/4" lauan plywood ( about $10 for a 4x8 sheet) and lay out the lines for just half of the building form. Then they cut these half-form templates from the cheap thin plywood. When they amke their building forms they trace around the template to give them one side of the final form, then flip it over, line up the centerline, and trace the other side. This ensures that both sides are symmetrical, but it adds an extra step and many hours of work. If you plan to make more than one boat from the same design, though, this is the way to go.

Generally small-boat lines are laid out on a grid of either 1 inch, 2 inches or 4 inches. For most of the kayak patterns around today the designers use a 2 inch grid. Getting a finely ruled drafting paper with a grid of 8 or 10 to an inch is good for making models, but overkill (and overly expensive) for making the final boat. You'll need to create a 2" grid pattern on the wood, and the easiest way I know to do that is to cut a piece of wood exactly 2 inches wide and about 36 inches long. alternately, find a yard stick, which is probably 1 1/4 inches wide, and attach some blocks which are 3/4" wide to one edge. Add scraps from strips to a common yardstick and get to work.

Draw a main line horizontally on the wood and call it the waterline. Your next horizontal line will be parallel to this and 2 inches underneath it. Lay your gauge on the waterline, so it just covers the line you drew, and trace tightly long the edge of your gauge to draw your second line. Move the gauge down to just barely cover the last line, and trace out the line which is 4 inches under the water line. That should do it for under the waterline.

Put your gauge on the waterline again, but this time trace out lines 2", 4", 6", 8" and 10" above the waterline. That should cover just about any building form. If you need to, you can always draw more lines.

Get a good, large, square and put one arm of it on the lowest line you've drawn (that would be 4" below the waterline). Trace along the other arm to give you a centerline which is perpendicular to the bottom line, and every other line, too. Reverse the square and double check that your line is indeed perpendicular to both sides of your base line. Sometimes things shift, or a square is not quite square. double check. Get your 2" gauge and again measure out lines to the left and right of the centerline. You'll need to go about 10 to 14 inches on each side. Again, it depends on how big the form will be.

I use a rafter square. One of the arms is already 2" wide. Tacking a straight edge to my board, I can just slide it along that rail and strike off the vertical lines accurately and quickly. The inch markings on the square's arm, and the previously drawn lines should always match up. It works great for the vertical lines, but I still need the longer gauge for my horizontal lines.

Get a small, clear plastic ruler. Once you have calculated the grid coordinates, make a mark on your wood. Later you'll drive a brad or small finishing nail into that point. 4d finishing nails, or 18 gauge 1-1/4" brads work fine.
These provide a strong series of posts around which you bend a flexible strip of wood. The finishing nails have enough strength that you can clamp the wood strip to them with bulldog clamps, or 1" spring clamps. Thecurved piece of wood (also called a spline by some) defines the shape of the curves for the boat form. Tre around it with a pencil on the side which touches those brads or nail. Then pull the nails and cut out the form. If there are depressions, or rough spots from the nail holes which are under the smooth edge of your form, don't try to cut deeper, or sand them out. Ignore them. your strips will go right over them with no problems.

You will probably find it easier to cut your 4x8 plywood into smaller, more manageable pieces before you put lines on them. If none of your forms is going to be over 15 inches tall, I'd suggest you start by ripping the plywood into three long strips about 15 3/4" wide and 8" long. Many lumber yards have panel saws and will do one or two cuts for you for free, with additional cuts at nominal prices. Let them do these first cuts at the store. The cost is very reasonable, and it makes the wood much easier to handle. Plus it saves yo a lot of time. If you ask for 2 pieces about 15 3/4" wide, the remaining 3rd piece will be somewhere between that and 16". If you know how wide the biggest 3 forms will be, get them to cut that much, plus 2 inches, from these ripped pieces. Let's say your widest form is 22", and the ones on either side will be 21". Have them shorten your 8' pieces by 2' each. You'll end up with 6 pieces of plywood or particle board. The biggest will be about 6'long and 16 " wide. That should fit inside a compact car, so you can easily get it home and cut 3 or 4 more (narrower) forms from each one. If you have a VERY compact car, just have them cut the plywood into 12 pieces which can fit on the passenger seat. Or you can bungee the pieces to the sissy bar on your motorcycle.

If you screw up on laying out lines for a form, flip the board over and start again on the other side. No need to erase things.

If you are still thinking about going with paper, head over to an Office Max, Staples, Office Depot, or similar large office supply store. If you look in the area where they have the big flip chart pads, you'll find some which are already ruled with a 2" grid. Enough pages on one pad for 2 kayaks, and the $15 cost (roughly) is much cheaper that buying ruled paper in that size meant for drafting.

If you are located on a desert island with little more than an internet connection you can enter the coordinate points into a drawing program, like Adobe illustrator, or one of the many shareware programs. Then let your printer kick out 6 or 8 pages of standard-sized paper for each form. You can tape or glue these together to get your forms.

For sketching out ideas I've used the drawing functions, or the table functions from Microsoft Word to create a grid or table which fills my page with boxes that are 1" or 2" to a side. I create these with blue 1/2pt lines, and print out a dozen. As long as I can keep the lines straight when I join pages, tape gives me a bigger sheet to work on :) At one time I had a .pdf file of just those grid lines. If you are desperate, give a shout and I'll put it up on my website.

Hope this helps.

PGJ

Ilustration below gives an idea of what you'll do.

Messages In This Thread

Strip: lofting question.
Sean McGrath -- 1/5/2011, 4:22 pm
Re: Strip: lofting question.
lance buck -- 1/5/2011, 5:44 pm
Re: Strip: lofting question.
Kurt Maurer -- 1/5/2011, 7:14 pm
Re: Strip: lofting question.
lance buck -- 1/5/2011, 8:33 pm
Re: Strip: lofting question. *PIC*
Tony Olsen -- 1/5/2011, 11:15 pm
lofting question *PIC*
Paul G. Jacobson -- 1/5/2011, 11:27 pm
Re: lofting question
Clayton Plunkett -- 1/6/2011, 9:23 am
Re: lofting question *PIC*
Tony Olsen -- 1/6/2011, 11:44 am
Re: Strip: lofting question.
Bill Hamm -- 1/6/2011, 12:52 am
Re: Strip: lofting question.
BillPadin -- 1/6/2011, 12:19 pm
Re: Strip: lofting question.
Mike Bielski -- 1/6/2011, 1:49 pm
Re: Strip: lofting question.
Bill Hamm -- 1/6/2011, 1:54 pm
Re: Strip: lofting question.
John VanBuren -- 1/6/2011, 4:55 pm
Re: Strip: lofting question.
sean mcgrath -- 1/6/2011, 5:00 pm
Re: Strip: lofting question.
Tony Olsen -- 1/6/2011, 11:04 pm