Basic Lofting

[Vern]

Hi all,
I did a search on lofting in this forum but didn't find quite what I need. What I'm looking for is a source for some basic procedural explanations on the process of lofting with some diagram examples.
Can anybody point me in the right direction?
Thanks,
Vern

[Todd Bradshaw]

There is a pretty good chapter on lofting (with illustrations) in the book "The Gougeon Brothers on Boat Construction". It's mostly a text about building wood/epoxy boats, but the lofting chapter has enough info to get you through most situations. To a certain extent, the best way to learn lofting is to try it. Find a set of offsets for a boat that you're interested in and even if you do it in a reduced scale on a big sheet of paper, you will start to get the idea.

Lofting complex elements like raking, curved transoms can get pretty tedious and require a lot of concentration, but most lofting is reasonably simple and straightforward. I think people are scared-off by the complexity of finished drawings, but when you actually do one, one line at a time, things seem to fall in place.

[Bruce Taylor]

Greg Rossel's (with an umlaut over the "o"...I'll bet Brian C. knows how to do that!) Building Small Boats has a very good chapter on lofting.

If you're building a lapstrake boat, I think Walt Simmons Lapstrake Boatbuilding has what you need -- if my memory is accurate.

Tom Hill's Ultralight boatbuilding has a little section on lofting that will get you off the ground (or on the ground, rather, since that's where most of the lofting is done).

Bud Macintosh addresses the subject in his wonderful Wooden Boatbuilding, but I doubt that you could learn to loft from that book.

THere are whole books on the subject (there's a blue paperback...I forget the title...probably available from Woodenboat) but you probably don't need that much detail.

Can't think of other sources just now...

[Syd MacDonald]

Allan Vaitses wrote a whole book on lofting. I read it through twice and still couldn't get started on my boat. Lots of detail about everything but no starting point. I finally got out Bud MacIntosh's book and everything I needed was there in the first chapter on three pages. Twenty distinct steps and I had everything I needed on the floor. Fun to read too. I think that now I could get something out of vaitses's book.

[Art Read]

Trust us... Just do it! It'll fall into place as you go along, and unlike expensive boat building wood you can use an eraser...

[NormMessinger]

Also, one need not loft full size to learn the technique. Especially if you're an old coot like me who doesn't like crawling around on the floor that much any more.

--Norm

[TomFF]

I've got to admit I'm struggling with the same issue. I'm reading Rossel's book and its mystifying. I appreciate the advice to just do it.

Just a question though. When describing lofting Rossel says plans will show a profile (heights), half breadths, and diagonals. But most the plans I've seen don't give diagonals on the table of offsets. Am I missing something or can you loft without the diagonals?

[noquiklos]

I'm no kind of a pro here, but as I understand them, diagonals are arbitrary, usually placed at intervals that cross the most extreme curves, and are useful for fairing the lines. Sort of a fine tuning of the lofted lines.
Roy

[Todd Bradshaw]

Diagonals, as seen from the bow and stern-view portions of the lofting drawing start at intervals along the vertical centerline of the hull and depict slabs of hull cut on an angle, mostly intersecting the bottom and bilges. On the front and rear views, they are just straight lines but on the top view, they should be flowing curves. Studying them is actually one of the better ways to judge how the boat will flow through the water.

If you are lofting a boat to build it (to use the drawing for cutting molds, frames and parts) they may not be very important to the project. On the other hand, if you are lofting to design the boat (especially a sailboat) and to fine-tune it's performance- making sure that there aren't any strange humps or shape abberations that might slow the hull down, lofting the diagonals can be very handy.

They may, or may not be listed on the table of offsets. If, for some reason, you decide that you would like to see them, you can always add them yourself by drawing diagonals on the bow and stern views, measuring their offsets, marking those on the top view and fairing-in the curves.

[duliano]

I have both Greg Rossel's (sp?) and Allan Vaites books. I read Allan's book first and finished it more confused then when I started. Then I read Greg's book and was able to understand the basics. This then enabled me to re-read Allan's book and start to make some sense out of this. I have now lofted two boats and although I am not very good at it yet -- I am starting to get more comfortable with it. The one thing I did learn though is that lofting is a lot harder to expain and read about than it is to actually do. So my advice to you is to not get caught up in just trying to read it but to use these books as a set of guides while you actually try to do the lofting.

If you are still stumped -- you can think about taking a class. I know that The Woodenboat School has a 1 week class on lofting and I am sure there are others.

Good Luck

Regards,
Dominic
Clayton, NY

[TomFF]

Okay so I draw the diagonals on the bow and stern views. No problem there. Then I measure their offsets. I'm suddenly lost. How is that done?

I would love to take a boat building class. Unfortunately time, money, and distance have allied themselves against me.

[NormMessinger]

I should leave the attempt to answer to someone who has lofted more than boat, but just in case Miller is reading....

Tom are you asking where the diagonal is measured from? That would be from its intersection with the center line to its intersection with the respective sections.

Where I had a heck of a time was determining the positions of the diagonal on the Farne Islander lines. The hull looks okay so what ever I did must have been good enough.

Best.

--Norm

[Bruce Taylor]

Measure out from the center line to the point of intersection with the station (measuring down the diag.) So, if station 1 at diagonal A is 4 1/8" in from the center line (in what you're calling the "bow" view, i.e. the "body plan") then on your "top" view (half-breadth, as seen from above) measure 4 1/8" from the center line, along the vertical line at station 1...and mark the spot.

Much easier done than said.

And for all your trouble you get a lot of long droopy lines, very much like the WL's but somewhat less useful (at least from this amateur's POV). If the plans don't provide diags. maybe you can get by without 'em?

What kind of boat are you lofting?

[This message has been edited by Bruce Taylor (edited 02-04-2001).]