View Full Version : How to build from the tables of offsets
12-22-2000, 12:25 PM
I would like to build an endeavour 17 using the tables of offsets with each set of ines but I don`t know how to use them. Can anyone help me?
12-22-2000, 12:39 PM
There are many sources that will answer your question. A good one is Allan Vaitses, "Lofting", available through WoodenBoat. Another is Walter J. Simmons, "Lines Lofting and Half Models," www.duck-trap.com. (http://www.duck-trap.com.)
12-22-2000, 12:46 PM
The offsets are coordinates of points on the surface (either outside or inside) of the hull. What one generally does is to draw the thing full size, then use this full size drawing to make the building form and parts for the boat. The process is called "lofting", supposedly because they used to do it in the lofts above boatshops. There's a really good book on it by Allan Vaitses, entitled (surprise) "Lofting", which will tell you more about it than you wanted to know. See below:
I think the Wooden Boat store sells it also.
12-22-2000, 01:38 PM
The offsets are use to describe the dimensions of the craft in three axis's (X, Y, & Z - height, width and depth) the building is saved for the construction plans. Having the offsets alone will not allow you to build without having an intimate knowledge of the construction methods and techniques intended by the designer. A set of lines intended for (God forbid) 'glass cannot be used for another material. Nor can a set of lines for plank on frame wood construction be used for cold molded wood construction. Though they may be of the same material, adjustments MUST be made by the designer or NA for a different method of construction.
If you have a FULL set of plans for your project and intend to stick to the plans for construction, then you'll need to educate yourself with on of the books available like "Lofting" which is very good.
12-22-2000, 03:09 PM
Check out the Gougeon Bros. on Boatbuilding. It's got everything you need for loft and subtracting planking thicknesses and everything.
12-22-2000, 04:59 PM
Oh, it isn't rocket science. The offsets are just measurements "up and over" from a baseline and a centerline. They give you points. You stick yer ruler on them and draw a straight line. Or you drive nails into several of them and bend a skinny long stick called a batten around those and draw a curved line. When you've done them all, you have a FULL SIZE picture of the boat plans, which you can use for patterns to cut the pieces you need to built it. You can't use a little plan because the tolerances aren't close enough. A pencil line on the plan in the book would be 2 inches wide if you just blew it up full size to make patterns for the real boat. The offset table tells you where the points are from which you can draw full size with skinny pencil lines. BUT, the offset measurements are taken off of a scale drawing by the draftsman. Usually, unless they have been corrected by someone else who drew the boat full size, they have errors in them. You have to correct these by eye. This is called "fairing" the lines. Bottom line, you have to draw (or "loft"... called that because that's where it was done) the boat plan full size before you can build it. Offsets are the full size dimension measurements. Now, you could get Vaites' "Lofting" book, which is really great, but I have a hunch you would glaze over pretty quickly trying to read it. Lofting is one of those things that is really boring to read about. It is a lot of fun to do, though. Since you are at the point where you are just figuring out what offsets are about, I'd urge you to slow down and do a little more research on building first. The plans are only part of the battle. Generally, there is a whole LOT of detail that the designer leaves to the boatwright. If you don't have that information in your head, the plans aren't going to do you much good. For the sort of boat you are contemplating, get John Gardner's "Building Small Craft" and read that. He has a good chapter on lofting in there and all the construction details you will ever need. That should answer your questions. Like I said, Vaites' book is the "lofting bible," but it is really a reference work and not what you'd call light reading! LOL
12-22-2000, 06:06 PM
The offsets for frames give you a "point" on the paper to draw a line between to make the frames. You put a line at the "height above base" and intersect it with a line at the "half bredth" for that item (say, a chine) and repeat for the other points the offsets give you (chine 2, top of beams, rabbet along keel, etc.) and you have the points for drawing the outline of the frame. But the dimensions are coded a little differently than you've probably seen, which probably stems from an attempt by the powerful boat building oligarch to discourage math-challenged folks like myself:
HEIGHTS ABOVE BASE HALF BREDTHS
Beams 3-7-0 1-9-7
Chine 1-8-4 1-3-1
The numbers given are "feet", "inches" and "eighths," so that the beam on this boat is 3' 7" above the baseline, and 1' 9 7/8" out from the centerline.
Not very clear. Try this: draw a vertical line on one side of a large piece of paper, and a horizontal line along the bottom, and measured up 3' 7" from the baseline and 1' 9 7/8" from the vertical line. Make a mark. You've just lofted the "3-7-0" and "1-9-7" numbers from the table of offsets onto the paper. Now look at the next set of numbers, and make a mark for them. You'll note that "1-8-4" really equals 1' 8 1/2" (4/8 of an inch equals 1/2.) Do the same with the final set of numbers, and you'll note that they do not extend out from the vertical line at all. But make a mark there, up 6 7/8" from the horizontal line. Draw a line between them, and you have a pattern for half of the first frame (build the half, flip it over to use it as a pattern to build the other half.)
That gets you started. Try it with graph paper and see where you get stuck. Then ask again.
12-22-2000, 06:41 PM
Frank - you forgot to tell him about the "+" and "-" for adding or subtracting a 16th. http://media4.hypernet.com/~dick/ubb/smile.gif
Your 1-8-4 could well be 1-8-4+ or 1-8-4- meaning 1 foot, 8 inches, 4 eights plus / minus a 1/16th.
12-22-2000, 07:10 PM
All that advice come down to loft it - Chappel a bit incompresensibly and (can't spell it but phoneticly) - Vatzy's book will do it.
12-22-2000, 07:24 PM
Offset lines are to the inside of the planking on the several boats I've messed with. Is this standard practice or does the designer specify?
12-22-2000, 09:18 PM
normal to the inside of the planking. The designer can't know exactly how thick the planking will be.
12-23-2000, 01:42 AM
If you are refering to the endevour 17 kayak from Ted Moore's Kayakcraft, there are a couple of books that would be useful to you. Ted Moore's Canoecraft covers the lofting process, probably adequately enough to get you through it, since what you are really needing is the proper mold shapes. This is another $20.00, but you'll have several canoe offsets to ponder. Additionally (bit of fyi here...), the tables of offsets in Kayakcraft do not include the numbers (offsets) for the stem profiles. Steve Killing had them posted on the bearmountain website though, so you should be able to get them from there. www.bearmountainboats.com (http://www.bearmountainboats.com)
The endevour is a nice looking kayak. Another book that may be of interest to you is Nick Schade's book on building a strip built sea kayak. There are three designs in there (offset tables). Some good information on building too, especially if you are new to the strip/sheathed methods. He has a vast web site on kayak building (strip, stitch and glue, skin on frame, etc.),with a very active builder's forum. The builders there are pretty much interested in kayaks only...canoe builders are tolerated. they are very helpful, but their focus is quite narrow.....they like kayaks. Hope this helps. Do email bearmountain as well. They will answer your questions too.
BTW....if the boat you desire to build is not the endevour 17 KAYAK........oops!, sorry.....just disregard this here post.
Have a joyous Holiday Season! garland
12-23-2000, 02:11 PM
C e, I did neglect to mention the "+" and "-" a 16th ... and not only that, but my nicely spaced post (using the space bar) ended up looking like a mish-mash. All those numbers are supposed to be separated and lined up below the "HEIGHTS" and "HALF BREDTHS" colums. But alas, I didn't check it after I posted it, and may have created more confusion than clarity.
I've always wondered about that 16th, though. You loft it out, and then "fair" it, so is that 16th really necessary? And why the weird way of saying 42 1/2"? Surely putting that in a box is clearer than 3-6-4?
There is a reason, though. I just don't know it.
12-23-2000, 11:16 PM
I'm not familiar with the Endeavor 17 or its designer. Apparently full-sized station mold patterns are not supplied, as they are with many small boat designs these days. My suggestion is to select a boat similar to the one you like, for which the designer supplies the appropriate patterns. Building the boat will give you insight into some of the lofting procedures without all the detailed study that it will take for you to understand it fully. I know people who have become discouraged about boatbuilding when they come up against lofting. To reiterate, first build a boat for which the designer has done the lofting for you. Then take on lofting for the next one.
I don't find a chapter on lofting in the John Gardner book referred to: "Building Classic Small Craft." However, this and his other books are highly recommended for construction details, and there are references to "laying down" and lifting from lines in the chapters on individual boat types. This book was first published as volumes 1 & 2, then they were combined in a memorial volume. There are good sections on lofting in Greg Rossel's "Building Small Boats," and in Bud MacIntosh's "How to Build a Wooden Boat." Also in Howard Chapelle's "Boatbuilding," where it's a bit harder to follow. These are all briefer treatments than Vaitses', which is recommended if you really want to get into it. The alternative is Walt Simmons's book, referred to in my previous post. Reading about lofting is only boring if you're not interested.
Most designers give you offsets to the inside of the planking, some give them to the outside, in which case the thickness of the planking is specified. Any designer worth his salt will tell you to which his offsets pertain.
Most designers use foot-inch-eighths. Some use + or - for sixteenths. Once in a while you come across foot-inch-sixteenths,; the designer will tell you which it is, usually right on the table.
[This message has been edited by Bayboat (edited 12-23-2000).]
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