View Full Version : Using half model instead of full lofting?
03-10-2006, 12:27 PM
Ok I know some of you old timers and curmudgeons are going to get on my case for asking this but here goes anyway:
Can I skip the full lofting for a small flat bottom skiff and use a half model with a lofting of just the sections, stem and transom to build?
Iím going to build the half model in order to get my rough plank shapes so I can buy my stock ASAP and start it drying before getting to the spiling (you may have seen my other post about this). If the half model is good enough to tell me the offsets are fair then all I need from the lofting is the full size sections and the details of the stem and transom.
03-10-2006, 02:04 PM
the half model isnt going to show you much of anything at the scale youre going to be building it in.
if you want to try to save time skip the 1/2 model and skip the lofting except for dody plan and use as its given in the offset table. set it up on your strong back and fair it in place with a batten, shims, handplanes etc.
depending on the accuracy of the offsets, you may find that you have spent more time trying to save time smile.gif
lofting full scale cant be replaced with a gimmick
why are you so adverse to lofting? it aint rocket science
03-10-2006, 02:36 PM
I'm not averse to lofting, I rather enjoyed it with my first boat.
But the more I evaluate the construction of this skiff I can see that I'm not going to gain much by doing it. Because the design is so simple the full lofting isn't doing much more than confirming that the offsets for the stations are fair.
I'm making the half model to get the plank shapes prior to seting up the molds so I can buy my plank stock now and start it acclimating to my garage. I think your right, the half model won't tell me much about the lines unless there is a really bad error in there.
So what I've done (and this is another cotroversial idea for some) is to "loft" the skiff lines in Adobe Illustrator. I created a document that can encompass the full size drawings, about 200"x48". Illsutrator has a bezier curve function that acts as a batten (it's always a fair curve) and I just need to pass it through the points taken from the plans. Anyway, I've done all that today and it looks good, no obvious errors in the offsets.
03-10-2006, 02:56 PM
There is another alternative to full scale lofting that works well. Don't know the proper name but I call it foreshortened lofting. Get a sheet of 11X17 graph paper or even smaller for a small boat. Lay out the offsets vertically as large as the paper will allow. Lay out the longitudinal stations at a much smaller scale. Connect the dots with a batten. Any unfairness will jump out at you more dramatically that even full scale lofting will show. Works for me.
I use half models sometimes but follow those with the above lofting to get the final shape.
[ 03-10-2006, 03:58 PM: Message edited by: Tom Lathrop ]
03-10-2006, 03:19 PM
Yes, especially for simple shapes that really come off the station molds.
Edited to add - I'm describing a construction model, really a model boat, and not a traditional half model.
I built "Leeward" from Gardiner's Chamberlain Gunning Dory plans at 1-1/2" to the foot as that was a convenient with each 1/8" on the scale a full inch in life. I made the scale model with modeler's balsa for the planks in exactly the stages real construction would go.
This gave me excellent patterns, especially for the wierdly shaped garboard. I was able to play with layout and scarf plans for the seven major pieces of that boat - shear and mid strakes, garboards, and bottom - to determine the most economical way to use the plywood - saved me a whole sheet! Also it gave me a chance to make some construction errors on a cheap model.
I was able to easily expand the model's parts directly onto the plywood.
[ 03-10-2006, 06:21 PM: Message edited by: Ian McColgin ]
03-10-2006, 11:07 PM
how will you get your stem bevels and profile shape, expanded transom shape, and station bevels, etc etc witout a full scale lofting?
03-10-2006, 11:29 PM
is there a good reason why the edge of the deck gets so flat at stations 3 and 4? that is a bit of unfairness that doesnt make sense to me in the small scale drawing but possibly may do so full scale
03-10-2006, 11:51 PM
Originally posted by Dolly Varden:
how will you get your stem bevels and profile shape, expanded transom shape, and station bevels, etc etc witout a full scale lofting?Stem profile can be scaled up from the drawings but I also have offsets for it in these plans. If doing a two peice stem you can get the stem bevel with a simple trying batten on the assembled molds and stem. I'm doing a one peice stem and can get the bevels from my "lofted" boat in Adobe Illustrator. Expanded transom is given in the plans. The trying batten will also get the station bevels for you. A boat of this type does not have much that can't be fitted after the setup.
As for the flat spot, I think its got more to do with the online reproduction of the lines, my actual plans don't seem to have it. But if it is there, the full size Illustrator "lofting" will find it.
03-11-2006, 08:26 AM
theres a lot of ways to build a boat. spending hours with a fairing batten attempting to discover bevels via chisel and block plane isnt one i care for. i prefer to do as much of the work as possible before setting up the molds. - much easier to use a rubber eraser on a lofting when something doesnt work out, than glueing shims and wedges onto mold stations
03-11-2006, 11:03 AM
I learned a lot from a cardboard model. The precision is up to your selection of the scale and how tight you want to work. For the Yankee Tender, I needed to know if the chine logs could be gotten out of straight pieces, and how much sweep there is in the garboards. It turns out that the garboards are straight on the bottom edge, and the chine logs only need to be beveled. http://www.imagestation.com/picture/sraid59/p7f4758dbfde22b023c251a2d74c93a1f/fc5a4e06.jpg
03-13-2006, 11:43 AM
Originally posted by Dolly Varden:
theres a lot of ways to build a boat. Hey you finally said something I truly agree with :rolleyes:
The trying batten is Walter Simmons prefered method for his fine crafts, so it's good enough for me and good enough for this little skiff. If I were building a more complicated boat I'd never skip the lofting.
[ 03-13-2006, 12:43 PM: Message edited by: dmede ]
03-13-2006, 12:08 PM
have it your way dmede, but get ready to do some fixin there at stations 3/4 smile.gif
03-13-2006, 02:03 PM
The best argument I can make for doing the lofting is practice for a future more complicated design. Since I already have several "next" boats picked out it's likely I'll build again, so I'll probably loft this one too.
But I'm still curious about how many people here build without lofting? It's the main theme in the latest issue of WB and seems to work fine for a lot of builders. All I know is that I lofted my first canoe and it served no purpose during the actual building, I made no changes to the molds. My next canoe (decked and far more complicated in design) was built wiith no lofting
The mold, frame and bulkhead bevels for these two boats were picked up with the trying batten and quickly faired out with a spoke shave. Semms to me this skiff would be similar, if not easier since it's sides are stright, not curved or multi chined like my previous two boats.
03-13-2006, 07:03 PM
I may be so caught up in the "answer" that I may be missing the question. Isn't this what the article titled Patterns for Extended Planks in the last WoodenBoat (188 Jan/Feb 2005)was discussing? The author, Walt Hansel, made a half model of a skiff and then took the lines off using mylar sheets.
03-13-2006, 08:37 PM
Originally posted by PaulC:
I may be so caught up in the "answer" that I may be missing the question. Isn't this what the article titled Patterns for Extended Planks in the last WoodenBoat (188 Jan/Feb 2006)was discussing? The author, Walt Hansel, made a half model of a skiff and then took the lines off using mylar sheets.Edited to fix the date.
03-14-2006, 05:44 PM
You'll still, occasionally, see a builder's model in shop somewhere. Rather than a method to avoid lofting it was fairly often used as a means to avoid drawing scale drawings. Carve the hull sweet to the eye, cut a series of narrow kerfs in the moulded dimension, insert paper and pull the station shapes. Fair on the loft floor...
Models have other uses, as mentioned, especially for initial fairing and pulling plank shapes off simple built-up models.
But except in the simplest shapes I don't think a model is going to obviate lofting.
03-14-2006, 05:59 PM
I cut the half model out last night. It needs a bit more fairing but I can see that at the scale I cut it to (1" : 1'), it won't be good enough to validate the offsets. It will however give me my flat plank dimensions, which is the next step in this infant build. After that, full lofting and on to building.
It's amazing how compelling even the simple shape of a skiff half model can be.
[ 03-14-2006, 07:38 PM: Message edited by: dmede ]
03-15-2006, 11:52 AM
Making a half-hull model is just right. Even though it doesn't, necessarily, cut down on later work you get the shape in your mind. You work the numbers, see what's what, with such a model.
The last model I built was of Atkin's "Pemaquid." His best dory. Lost now in three or four moves.
Poster board was the material. It's as fancy as you like.
I still might build that boat, its in my mind. smile.gif
Good luck, Dmede.
03-15-2006, 12:18 PM
I built a "Pemaquid" almost thirty years ago... modified a bit to incorporate curved sides, a full size "half model" mocked up with molds and battens to get it fair and then used the temp molds as templates for the frames.
It's a good boat, very capable and still in use, it has a one cyl Yanmar now.
03-16-2006, 05:45 AM
So you curved the sides. I'd like to hear more about your Pemaquid, and more to the thread, amplify just how you did it. I think see it, but it might be helpful.
With a simple shape like Pemaquid, or dmede's skiff, you can get away with going from a carefully built model to building. If large enough scale you work out the bugs that would be found out in full-scale lofting. Drawing it full size, however, is never a bad idea.
For that matter, with a skiff or a flat-sided dory you can go right from the scale drawings and the offsets. Bugs have a way of fairing out. There's a colloquialism in Maine, "skiffboards." White pine wide enough to bend around a center mould and you have a hull. Some good boats, and some not so good, have been made that way.
It's a great looking little boat, Pemaquid. What did you build it out of? I'm not likely to build one now, I've got the same basic idea in my shop, a Drascombe Lugger. But I'd love to hear more.
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