Lofting

[DCockey]

Boatbuilding in Your Own Backyard has only 10 pages on loft/laying down/fairing, and does not cover expanding surfaces.

[BATAAN]

Ah good, thanks for clarifying my vague old memories. The Lofting book is required then I guess.

[philSweet]

Can you give us a peek at what you are up to? Nothing restricted from public viewing, but it is nice to know the scope of the project. You may find someone who has experience with the design if you give us a bit more.

[pamam]

Bataan,

I found his book "Boat building in your backyard..." on Amazon, I might get that. However I found Delfship and entered all my coordinates for a chines.txt file and the solution looked like what I was expecting: the free version won't let me save or print the results. Anyway it looks good that I might put out the bucks if it is not to expensive, th at I have not checked out yet. I also found Freeship and will try that next. I have Rhino, but from the documentation that I could find on their site, ( non existant ), tons of tutorials etc but no users manual, it appears that they don't provide plate files of the results. Also their cheapest version is ~$800.00 so no thanks to that one.
Thanks, all

Mel

[BATAAN]

Yes, we never had to pay for Rhino as it was on the machines at work. BBIYOBY is a very good book to have and you will fall in love with PICAROON and all his designs.
I often save screen grabs on my hi-rez mac as it's the easiest way to keep things you can't get any other way.
Lofting is just 3d mechanical drawing. You carefully layout and check your baseline and all perpendiculars and measure exactly. A computer in not needed really.

[DCockey]

Rhino has the UnrollSrf command which unrolls developed surfaces. There is also the Squish command and related for flattening arbitrary surfaces. Squish has to be downloaded separately for the current version 4, but will be included in version 5. http://wiki.mcneel.com/labs/advancedflattening

You can download Rhino for a trial http://www.rhino3d.com/download.htm There is a Users Guide and the Level I and Level II Training tutorials are excellent. http://www.rhino3d.com/tutorials.htm There is also a list of commands available which I believe I have printed out.

The Rhino interface and method of working is somewhat different than AutoCad. Anyone who is experienced in AutoCad and expects to be able to jump into Rhino and immediately use it will be disappointed.

[BATAAN]

Rhino was used there generally, and some (not me) were very proficient as it was used to pass around and process plans of many different things from Department to Department. You can do a pirate ship or a fantasy castle.

[pamam]

I tried Rhino, but it was too much for me at this time. I don't have the time to learn a completely new setup. Besides I'd never buy it anyway. Freeship worked great, it let me save the dxf file of the plate results and then I was able to print it full scale using ABViewer so I could lay it out on my plywood and cut it out - great. So my problem is solved and the Free does not run out ever in freeship. The Freeship and Deltaship were almost identical in features and layout. It looked like someone has done a lot of reverse engineering or an employee jumped ship and took the designs with him. So I have what I need to further my building of my sail boat. I'm still contemplating BBIYOBY.

Thanks again for all your help.

Mel

[nyloftsman]

lofting is the most important aspect of building any sort of boat. the first reason to loft the hull is to prove the naval architect`s drawings-that the dimensions he gives are accurate and the shapes shown can be built as shown. the second reason is the designer is drawing if by hand is drawing at a scale which is not accurate enough to make pieces accurate to a small fraction of an inch. the third reason is lofted plans are used to create complicated templates for bow radiuses, keel castings and their bolt holes, engine mounts, tanks, piping clearances, winch bases, propeller shaft layouts, finding true lengths for standing rigging, determinging exact sheeting angles for the specified sails which determine winch base locations.
the forth reason is that for metal vessels the plating plan can be developed to accomodate plate sizes, and the seams aligned to avoid backset or plates which curve to two directions and so cannot be rolled-wooden planked vessels use lofting to set up the planking plan for plank taper, shape, length, hollow, butt blocks, and so on. in commercial construction, lofting permits the vessel to be built all at once and assembled rather that sequentially. the most important reason to loft a vessel is that the process requires the brain to develop its graphic and spatial imagination which enables the loftperson to "see" or have some clear idea of the finished vessel before it is built.
as i recall your boat has plywood frames or bulkheads. when you loft the hull using the offsets to the finished hull surface and setting up horizontal sectiong (waterlines), vertical longitudinal sections (buttocks), and vertical
athwartship sections (stations) and change some of the offsets so that all the sections agree and then draw the frame lines-you will have to decide whether the frame material thickness will be on the fore or aft side of the frame line and is the frame aft or forward of the midship section. if the frame is aft of the midship section and the frame material packs aft of the frame line the frame will have to be cut on a bandsaw with an adjustable table which will be changed for the bevel of the inside of the hull planking angle to the frame aproximately where the saw cuts the frame. however on metal and some plywood boats the hull material bears on the corner of the frame which was cut square or at 90 degrees to the frame surface which is to say that aft of midships the frame material packs forward of the frame line and the frame is not bevelled, but the hull surface thickness must be deducted from the frame line and the angle of the hull plating accounted for. when the hull plating crosses the frame line at an angle, the thickness is greater than the nominal thickness. if the same thickness, say one half inch is deducted from all the frames, either all the frames will not bear on the inside of the hull, or the hull will not be fair.

[pamam]

nyloftsman,

Thanks for all that good info. My boat is a 3.5 meter sail boat, just a small boat. I have half the frames made according to the plans that I have gotten from the yaught club in Autralia. I used FreeShip to do the lofting of the plywood sides and bottom. The plate plans turned out to be OK. I have a question about what their 3D diagram showed up was that for a fair curve my second frame needed to be narrower because the curve, generated from the coordinates of the gunwhale and the chimes and keel, looks like it goes through the frame instead of on the outside edge of the frame. Does that mean that I need to make the frame smaller or the plywood will need to bend in 2 directions? These plans were drawn up by a naval architect in 1954. The plans do leave something to be desired.
Thanks,

Mel

[cthippo]

This site had scanned images from old boat magazines including a decent how-to article on lofting. I found it useful and you might as well.

http://www.svensons.com/boat/?p=Other/Lofting

[pamam]

Thanks cthippo,
Printed the article and am reading it. So far so good.
thanks,

Mel