Taking lines off a boat (again sorry)

Sorry to bring this up again!, but I have several specific questions regarding the process of taking the lines off a fairly taditional sailing yacht.

- Can a Laser measuring hand tool be used on a curved surface ie, a yacht hull as I have seen on a lot of them for sale that they can be only used on surfaces normal to the laser- or are they the cheap ones which use ultra sonic measuring and a laser pointer?!

- Once I have all these offsets for each station from whatever method, can MAXSURF be used to model the hull? I am not familar with developing a surface from offsets, rather than just developing it from scratch.

Cheers,
Sotondesign

 

If you're talking about those laser measuring tools as sold for measuring rooms in a house, then no, they won't work. (Even the true laser ones aren't that accurate on anything other than a perfectly normal sheet of drywall.) You may get offsets but there would not be enough precision to build the hull model. Maxsurf can probably do what you want; you might find it helpful to try a few practice models or tutorials first to figure out the best way to input such data.
Keep in mind that 'splashing' the design is a bad idea- I presume you're taking the lines either as an aid to the rebuilding of the hull or for historical/archival purposes.

 

Mystic Seaport in Connecticut uses a surveyor’s total station. It measurers the shape with a laser and downloads the measurements to a computer. They have published the method and if you get in touch with the Dupont shipyard at Mystic they will send a copy of the instructions. In the United States we can rent a total station and use that.

The low tech way is to use a sheet of plywood and a tick strip. You square up the boat and establish a center and a base line outside of the hull. Then place the plywood next to the boat at the stations keeping it square to the centerline and on the base line. Measure with the tick strip to the plywood as if you were making a pattern for a full bulkhead and then move to the next station. Lay the plywood down next to your lofting and transfer everything to that and fair the lines, as you would do a normal job. You can put the offsets into MaxSurf as marker points and make a surface that way.
Robert Gainer

 

Yes I need to take the lines off a boat to do an RCD stability assesment of the vessel- the origional lines are not unfortunatly available.

The "cheap and cheerful" £6 laser measurer devise clearly is not the way forward. Does anybody have a laser measurer or similar device which they have used with a reasonable degree of accuracy (+/- 40mm), rather than the rather long drawn out process of using plywood sheets etc....

Cheers
Sotondesign

 

Unfortunately, the only way to shortcut the old fashioned lofting process is with "MONEY". The devices and software available today can give you a perfect computer model duplication but it will COST bigtime.
Hard to believe but my uncle started his shipbuilding career in the lofting loft for Sun Shipbuilding div. Standard Oil in Penna. This was for oil tankers. They actually created templates for the ribs, bulkheads etc. (he ended up Pres of it.) not bad!

 

Oh yes, forgot to mention, I am now near 77 years old. Does that date the process, GRIN ?

 

Man why all the high teck, In the lifeboat/surfboat to motorsailer conversions i have done i simply level the hull using the keel as the longitudional reference to be leveled. Next I level up the hull twartship. In my case these hulls have no superstructure so i find it easier to do it with the hull inverted. Next i fasten a long piece of boxed aluminium along the keel bottom so the facing edge (of the hull side you are working from) runs along the centerline of the keel. It should be long enought to extend out past the bow and stern. On this facing surface i mark off stations about 20 in apart where there are fairley gentle beam curvitures and 10in. stations where there are more abrupt changes in beam curviture. (In this case closer to the bow and stern in these double enders.)( this to give me more accurate takeoffs) Then i welded up a big box aluminium square(1x3in box alum.) whose one leg exceed 1/2 the beam of the hull (use the 3-4-5 ratio to build your square). On this leg of the square i install two peel and stick measuring tapes.(one each side, along the outside edge). On the very end of this same leg i drill a 1/2 hole to receive a full threaded rod that is welded to a pipe that has a 2 in. square plate welded to it's bottom.(leveling leg) Next using double edge tape, fasten two (one each side) 3 foot levels longitudionally centered on the top and bottom faces of this long leg of the big square.The only other tools needed is a good heavy plum bob, an old style folding carpenters rule or equivalent and a couple of fine point permanent markers a few cold beer and a good friend. The idea is to clamp the shorter leg of the square to the piece of box aluminium placed along the centerline of the keel and down on the bottom of the keel face so the squares outside 90 deg. corner is lined up with a station mark. Then using your double edge taped on level and your leveling leg/ threaded rod, adjust the rod nuts (one top, one bottom) to level up the leg. then using preselected equal spaces(4 to 6 in) using the self stuck on measuring tape drop down you plum bob from these points and mark an x on the hull surface. Using the carpenters rule measure these respective distances as you work out along the leg of the big square. Transfer these measurements to a full or scaled grid.As you work along the hull, you'll realise the purpose of levels and measuring tapes on both sides of the long leg of the big square. If the hull is not inverted your leveling leg will be alot shorter and the plumb bob will have to be used in reverse. Hey it's old time low teck but any backyard boy can build and use it. Worked for me.

 

"Boats: a Manual for Their Documentation" has detailed discussion for several "low tech" methods for taking the lines from a boat. It's available for free download at www.museumsmallcraft.org and the WoodenBoat Store.

 

I use some strings and sticks to take the lines. You need a few points and then lay them on paper or a loft board and fair them. If you need help, send me a PM. I am in Devon.

 

I hope you meant +/- 4mm. We have hull molds scanned often. We have subcontractors perform the work and it is expensive. For small uncomplicated projects we use RhinoPhoto which is a reasonably priced photogrammetry program which runs in Rhino. It might work quite well for your project. There is an example video of scanning a sailboat hull at:
http://www.rhinophoto3d.com/index.php?option=com_content&view=article&id=55&Itemid=43

Good luck on your project.

 

That RhinoPhoto system looks pretty cool ...are there competitors to their system that are worth checking out too?

Thx,
Brian

 

Woodenboat has an extensive article on taking lines off. Just do a search of their online index. Very good stuff.
F

 

Frank ...Thanks ...But do you have any hints, links, or references to the article in question? I tried searching the magazine back-issue index with "lines" (zillions of results", "take lines", "taking lines", etc and am coming up with empty search results. What search term did you use? Thanks...

Brian

 

OK ...the key search phrase is "taking lines off" and here are the results. Which article were you referring to?

Bray, Kathy, illustrator: "Taking the Lines Off a Boat," 115:71

Dillion, D.W. (Dave), author and illustrator: "Taking Lines Off Small Craft," 107:70

Dow, Eric, builder: technique/taking off lines, 210:70

Laurent, Bret, Barry Thomas, and Clark Poston, authors: "Taking the Lines Off a Boat," 115:71

Lincolnville wherry: photos, taking off lines, 19:42

Lines: taking off/Bangor Pool peapod, 212:13

Poston, Clark, Barry Thomas, and Bret Laurent, authors: "Taking the Lines Off a Boat," 115:71

Thomas, Barry, Clark Posten, and Bret Laurent, authors: "Taking the Lines Off a Boat," 115:71

Tools for boatbuilding: for taking lines off small craft, 107:70


Thanks,
Brian

 

PhotoModeler www.photomodeler.com has all the capabilities of RhinoPhoto plus much more. It is a separate program (not a plug-in) which exports the results in several formats including .3dm which is the Rhino format.

I have been using PhotoScan www.agisoft.ru for boats with some "visual texture". It works slightly differently than RhinoPhoto and produces point clouds and meshes similar to the results of laser scanning.