Re: Lofting

I want to thank everyone for replying to my post on lofting. I do not
know what my next project will be. There is a sharpie design in J.
Gardner's "Building Classic Small Craft" that is attractive, but
Bolger's Gloucester Yawl -- the sponson sharpie in "Small Boats" --is
one that I return to time and again to listen to the seductions of
its siren song. I have been warned that building small boats could
get into one's blood. I must admit that I have the fever -- and
badly. I may never use lofting techniques. But then again, there are
a lot of things that I know that I never use, but this does not
detract from the value of knowing and understanding them.

I share the sentiments posted by one of our colleagues, I can't wait
for Bolger to publish another book of designs and I certainly would
not turn down a reprint of "Different Boats."

Cheers, Dennis Marshall

I just took a two-day class on lofting, so I'm willing to take a shot
at it.

You mentioned a table of offsets. Set that aside for a moment.
Imagine that the boat is a loaf of bread poised a few inches above a
level table. We'll call the tabletop the "baseline." If you cut the
bread into standard slices, each cut is a "section." If you look at
the loaf from above, and slice it down the center from one end to the
other, that's the "centerline." Make more slices parallel to the
centerline cut, and those mark the "buttocks lines." Look at the
loaf of bread from the side, and make cuts parallel to the tabletop.
Those mark the "waterlines." (I'm going to omit the diagonals from
this discussion.)

The table of offsets describes the shape of the boat in relation to
the cuts. The table consists of two sections. One section has the
heights above the baseline for the sheer, buttocks lines, and
bottom. (The bottom of the boat may include points for the rabbet,
keel, etc. but I won't get into that.) The other has the half-
breadths (measured from the centerline) for the sheer, waterlines,
and bottom. So, for example, I'm looking at the offsets for the
lapstrake Chebacco from BWAOM, and they show that the "deck" (or
sheer) at station 5 is 2 feet 9-6/8 inches above the baseline, and 3
feet, 10-4/8 inches from the centerline. (Dimensions are typically
given as feet - inches - eighths, and a plus or minus sign means add
or subtract a sixteenth.)

When you loft a boat, you use the table of offsets to draw three
views of the boat (usually full size): a plan view (from below), a
profile view (from the side), and a section view (from the front and
back). You start by laying out the perpendicular lines in each
view: the sections, baseline, centerline, etc. Then you use the
offsets to draw in a series of long curved lines showing the shape.
For example, if you want to draw the sheer in the profile view, you'd
take the height at each section from the table, mark that on the
profile view, bend a wooden batten around the points (holding it in
place with nails or lead weights), and draw the line.

The goal is to draw fair curves -- with no bumps or flat spots -- in
each view. If, for example, the sheer looks flat at section 5 in the
profile, you may have to move the point a bit to get a fair curve.
But part of the trick involves reconciling the three views: if you
move a point on the profile view, you also have to move it on the
plan view and the section view.

The drawings show you not only the outline of the boat, but also the
shape of the boat: whether she's firm-bilged or slack-bilged, and so
forth. For example, on the plan view you draw the waterlines -- not
the real "waterline" but artificial lines a certain distance from the
baseline. Looking that those lines, you can see the width of the
hull at 12 inches above the baseline, 18 inches above the baseline,
etc. The plan and profile views are like two "topigraphic" maps of
the hull: one viewed from the bottom, and one from the side.

Once you're done, you make your molds from the section views. You
can also draw out the shape of the transom, stem, and keel; pick up
the bevels for the stem and keel, etc. What you're doing, really, is
using the table of offsets to make all the full-size patterns you
need for different parts of the boat. And to do that, you have to
draw the boat. (If a round-bottomed design says there's no lofting,
as in some of the plans offered from WoodenBoat, the designer has
done all the work for you, and has provided you with the necessary
full-size patterns.)

It's really an elegant system: who would have thought that you could
draw -- and build -- a boat from a simple set of numbers? It's also a
heck of a lot of work.

Hope this helps.
Steve Paskey

--- In bolger@y..., brucehallman@y... wrote:

> Would somebody please explain in a few paragraphs the process of
> lofting? TIA, Bruce Hallman

It is the drawing out full size (usually), and the
reconciliation (as to fairness and accuracy)in plan,
profile, and body view (at least) of the lines of the
boat, and any details necsary for its construction
(bevels, rabates etc..), or the sourcing of parts.

How did I do?

---brucehallman@...wrote:

<HR>
<html><body>
<tt>

> that fall under the general rubric "Lofting

for Dummies" would be 
 
I am not ready to buy a book, and I have no near term
plan to do any 
lofing, but for years I have read the term, and it is
never defined! 
 
What the heck is lofting anyway? [Actually I
have a clue that it is 
the process of expanding offsets from a table provided
by the 
designer, but in practice, what is involved to do
this?] 
 
Would somebody please explain in a few paragraphs the
process of 
lofting? TIA, Bruce Hallman 
 
</tt>

 



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- pls take "personals" off-list, stay on
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- add your comments at the TOP and SIGN your posts,
snip all you like 
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> that fall under the general rubric "Lofting for Dummies" would be

I am not ready to buy a book, and I have no near term plan to do any
lofing, but for years I have read the term, and it is never defined!

What the heck is lofting anyway? [Actually I have a clue that it is
the process of expanding offsets from a table provided by the
designer, but in practice, what is involved to do this?]

Would somebody please explain in a few paragraphs the process of
lofting? TIA, Bruce Hallman

There is a lot more there than lofting, buy the book.

hal

On Friday, October 19, 2001, at 05:10 AM,garth@...wrote:

>
> George Buehler's "Backyard Boatbuilding"

Stuff deleted
>
> I'd be happy to fax you the pertinent pages -- but buying the book is
> worth every penny.
>
> All best,
> Garth

I'm quite sure that series of Lofting articles carried in WoodenBoat
a few years back was written by Greg Rossel. He teaches at WB, and
other places, and has authored a recently released book which I've
heard contains the whole series of those WB articles as well. I
forget the book's exact title, something like Building Traditional
Small Boats, but you can find it by searching for the author on
www.woodenboat.com, or amazon.com, etc. I'd imagine it's a very well
done book which would be worthwhile for many other purposes too--I've
come close to buying a copy for myself.
-- johannes

--- In bolger@y..., thomas dalzell <proaconstrictor@y...> wrote:
<snip>
> If I recall correctly there was an excellent article
> or series in some recent issues of Wooden Boat, which
> were also designed to cut through what is often
> regarded as the complexity of lofting. My
> recollection is that this article was excellent, from
> the perspective of someone interested in making the
> average personal boat.

I read this book and found it useful. The technique I learned was a
slightly different method, but this text was a good reference.

Mike

--- In bolger@y..., vcgraphics@t... wrote:
> "Lofting" by Allen Vaitses has a good reputation, but this is
> hearsay on my part

The clearest and simplest explanation of lofting I've seen is a short
section in George Buehler's "Backyard Boatbuilding." I don't have it
near me right now, but I think it was just 4 or 5 pages. It was the
first explanation of lofting that made me feel I could just go out
and do it.

I'd be happy to fax you the pertinent pages -- but buying the book is
worth every penny.

All best,
Garth

--- In bolger@y..., PseudoDion3@a... wrote:

> Hey, Folks! Any recommendations for books on lofting? Perhaps those
> that fall under the general rubric "Lofting for Dummies" would be
> appropriate.
>
> Thanks, Dennis Marshall

Hi Dennis, by all means Allen Vaitse's book on lofting. If you go to
the search function on the www.woodenboat.com you will find a ton of
articles and references for specific lofting problems. Also a short
exposition in Robert Steward's "Boatbuilding Manuel" is very good. You
might also refer to the Gougeon's epoxy construction manual which has
several pages on lofting with I found helpful. Some of the articles in
Woodenboat I find overwhelming and more than I want to know.

Bob Chamberland

What do you need to loft? If it is just lines, you
might consider getting a simple student level CAD
boatdesign program. I use an upper version of David
Vacanti's Prolines. You might want to use their
student version, or one of the free programs on the
WEB. I think there are some. In some cases one can
go direct to a fabrication plant with the output, and
they can plasma cut or something. I am not
knowlegeable enough about aluminum to know what you
can get away with. Also what about one of these other
builders, perhaps they already have done this work.

--- Phil Smith <pbs@...> wrote:

<HR>
<html><body>
<tt>
I'm about ready to start lofting a Bolger design, an
aluminum runabout 
that I've never seen published. According to PB&F
a dozen or so were 
made in New Zealand for a World Champion series of
some one design or 
another. PB&F say that the runabouts were
evidently well received but 
production runs did not follow. 
 
I've read that the instructions on lofting in
Chapelle's "Boat Building" 
is supposed to be really good. The process doesn't
appear to be overly 
complex but it will require a lot of care and careful
thinking about 
what it is that you are measuring (i.e.: am I
measuring to the inside of 
the planking or aluminum or to the outside.) 
 
I've rented space and need to construct a lofting
floor that I can 
dismantle later. 
 
I need to get on this. 
 
Phil Smith 
</tt>

 
<tt>
Bolger rules!!! 
- no cursing, flaming, trolling, spamming, or flogging
dead horses 
- pls take "personals" off-list, stay on
topic, and punctuate 
- add your comments at the TOP and SIGN your posts,
snip all you like 
- To order plans: Mr. Philip C. Bolger, P.O. Box 1209,
Gloucester, MA, 01930, Fax: (978) 282-1349 
- Unsubscribe:
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My favorite is "ship and aircraft fairing and
development" by Sam Rabl. It is reprinted from time
to time, and in my opinion is the most useful text for
the modern world. The major texts on boat lofting
like Vaites excelent work, are designed to loft far
more than lines, but to allow one to understand the
process in a way that might lead to a full skill in a
boatyard, where all manner of things like rabbets may
need lofting. In the modern world, Rabl's text breaks
the code on a number of "new" ideas like constant
camber, developeable surfaces etc... is prety useful.
His description of fairing lines is about as concice
as it gets.

If I recall correctly there was an excellent article
or series in some recent issues of Wooden Boat, which
were also designed to cut through what is often
regarded as the complexity of lofting. My
recollection is that this article was excellent, from
the perspective of someone interested in making the
average personal boat.

---vcgraphics@...wrote:

<HR>
<html><body>
<tt>
"Lofting" by Allen Vaitses has a good
reputation, but this is 
hearsay on my part (I have read Chapelle, but not
Vaitses). 
WoodenBoat has reprinted it and it is available on
their website. 
 
<a
href="http://www2.mailordercentral.com/wbstore/Prodinfo.asp?number">http://www2.mailordercentral.com/wbstore/Prodinfo.asp?number</a> 
=325-114&item=1 
 
Careful, the link wrapped, you may have to cut &
paste to your 
browser. 
 
Sounds like an interesting project. 
Good Luck, 
Vance 
 
--- In bolger@y..., Phil Smith <pbs@w...>
wrote:

> I'm about ready to start lofting a Bolger design,

an aluminum 
runabout

> 
> I need to get on this. 
> 
> Phil Smith

</tt>

 
<tt>
Bolger rules!!! 
- no cursing, flaming, trolling, spamming, or flogging
dead horses 
- pls take "personals" off-list, stay on
topic, and punctuate 
- add your comments at the TOP and SIGN your posts,
snip all you like 
- To order plans: Mr. Philip C. Bolger, P.O. Box 1209,
Gloucester, MA, 01930, Fax: (978) 282-1349 
- Unsubscribe:
bolger-unsubscribe@yahoogroups.com</tt>
 

 
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Dennis,
I'll jump in and join Johannes and Vance in their recommendation
of Vaites book on lofting.Excellent book,especially if you're the type
that can teach your self things through books(autodidacte).
To get a feel for the craft and Vaites' style ,I found it helped
me alot to actually loft,full size,the skiff illustrated in the first
part of his book.
Once you get the hang of things,you'll soon be seeing the lines
in three dimensions,literally bulging off the loft floor.
I cannot recall whether Vaites mentions this but a handy trick
to help keep things rational is to use different coloured
pencils/markers/pens for the principal lines eg;black for the
waterlines,red for the buttocks,green for the diagonals etc....
You soon see the perfect logic of the whole process and how each
view must match the other.
The beauty of the while thing is that you end up with full size
plans to your boat from which you can actually pick out any
part,perfectly scaled,and build it before actually installing on the
boat.Really neat!
And yes,a fair line(curve) will take precedence over the
designers offsets.......within reason! Found three"errors" on a
couple of stations several years ago while lofting a Herresoff(sp) 12
1/2 for a friend.
Anyway,get this book,study it,practice it and then use it!
You'll be glad you did!
Good luck with your new project!
Sincerely,
Peter Lenihan,forced to strip my boat for haul-out,as the temperatures
dip to + 3 Celsius with a chill factor of - 7 Celsius,on the blustery
shores of the St.Lawrence.............

--- In bolger@y..., PseudoDion3@a... wrote:
> Hey, Folks! Any recommendations for books on lofting? Perhaps those
> that fall under the general rubric "Lofting for Dummies" would be
> appropriate.
>
> Thanks, Dennis Marshall

"Lofting" by Allen Vaitses has a good reputation, but this is
hearsay on my part (I have read Chapelle, but not Vaitses).
WoodenBoat has reprinted it and it is available on their website.

http://www2.mailordercentral.com/wbstore/Prodinfo.asp?number
=325-114&item=1

Careful, the link wrapped, you may have to cut & paste to your
browser.

Sounds like an interesting project.
Good Luck,
Vance

--- In bolger@y..., Phil Smith <pbs@w...> wrote:
> I'm about ready to start lofting a Bolger design, an aluminum
runabout
>
> I need to get on this.
>
> Phil Smith

Dennis, "Lofting" by Alan Vaitses is one of the classic sources on
the subject, and is now back in print.
-- johannes

--- In bolger@y..., PseudoDion3@a... wrote:
> Hey, Folks! Any recommendations for books on lofting? Perhaps those
> that fall under the general rubric "Lofting for Dummies" would be
> appropriate.
>
> Thanks, Dennis Marshall

I'm about ready to start lofting a Bolger design, an aluminum runabout
that I've never seen published. According to PB&F a dozen or so were
made in New Zealand for a World Champion series of some one design or
another. PB&F say that the runabouts were evidently well received but
production runs did not follow.

I've read that the instructions on lofting in Chapelle's "Boat Building"
is supposed to be really good. The process doesn't appear to be overly
complex but it will require a lot of care and careful thinking about
what it is that you are measuring (i.e.: am I measuring to the inside of
the planking or aluminum or to the outside.)

I've rented space and need to construct a lofting floor that I can
dismantle later.

I need to get on this.

Phil Smith

Hey, Folks! Any recommendations for books on lofting? Perhaps those
that fall under the general rubric "Lofting for Dummies" would be
appropriate.

Thanks, Dennis Marshall