Making a lines plan from an existing boat

Hello does anyone know of a method for making a lines plan from an existing vessel WITHOUT taking the boat out of the water? If it has been done how accurate was the resulting model?

A client requires a full stability analysis for regulation compliance however there is no lines plan available. I have experience taking offsets from a hull so I know what is involved in the normal procedure, but this is a 40m+ vessel that would require dry docking. Around the office we are discussing using a laser level to obtain points on each side of the hull and measuring from the inside of the plating at frame locations. Aside from the obvious difficulties involved with finding shell access in accommodation spaces, could this work?

My gut feeling is that it would be possible to create a hull but the accuracy would poor. The keel alone would have to be a complete guess.

The vessel is a round bilged, transversely framed, welded steel construction, motor yacht registered as a passenger ship.

 

Using a level on a floating boat is a landubber's idea. It will not work. It should be fairly straightforward to take measurments of bulkheads with a jogging/pickup stick and then transfer them. You can then use the bulkhead spacing to draw the lines. You just have to add the skin thickness and whatever appendages there may be.

 

Talk to a local surveyor, the land/civil engineering type, especially if you can find one who has experience with measuring equipment and piping in manufacturing plants, etc.

 

Talk to any shipwright or boatbuilder. It is a simple procedure that is performed on a daily basis.

 

If the purpose of this operation is just to satisfy bureaucrats and get a stamp and signature, take the lines plan from a lookalike and scale that up or down using just a few measurements made with a laser or an ultrasonic device.

Yes, the keel will be pure guesswork, but does that bother anyone?

 

I wonder what happened to the original lines. They should be filed somewhere with the original permits.

 

I would me more worried about how to make the weight analysis.. The only proper way to make this is to produce a similar hull (with delfship or similar softw) including all plate thicknesses, tanks, gear etc.. IMHO
That is off course if just a evaluation of Metacentric height and roll period isn't enough..

 

While the stability analysis is created to satisfy bureaucrats rules, it is also a verification of how safe this vessel is for the passengers. And David's head will role if there should be an accident...He is taking responsibility for the safety of those unsuspecting holidaymakers....he must be sure (doubly sure) of his data.

Yes, take all the measurements you can inside the hull. Find photos of the boat on the hard to correlate with. Then hire a diver to measure the keel and transom, locate the bow thruster, etc. You can even make a big aluminum adjustable square(adjust with c-clamps) of two pieces of angle bar. Hold this upside down in the water with a point against the hull, mark the waterline and distance off centerline....probably with the help of a diver (make sure the hull is clean at measurement points) and a couple of levels....a long days work.......but possible.......

 

Actually, it may be possible to use a software package and underwater photos to get the hull lines within a very high degree of accuracy. Photomodeler is the only software I'm familiar with, and it uses reflective targets on the "object", the focal length of the camera and a few known distances (as well as dozens, if not hundreds of photos), to produce a surface model. The more photos, the smaller the error, the higher the accuracy. You could do the same thing inside the hull too.

 

Presuming you can see through the water.......

 

In principle yes but .....
- The water would need to be sufficiently clear.
- The camera/lens would need to be calibrated underwater though with enough photos a "field" calibration might be possible.

 

For the interior it might be hard to get photos from enough different angles which share sufficient points.

 

Yes I've done it quite accurately measuring inside, but it depends what the access is like.
Use land surveyors tools, tapes laser levels, and an audio distance gauge is useful too. Photograph everything helps remember where they all relate, work from transverse frames and bulkeads and correlate everything with measurements of deck and topsides with plumblines from the sheer. Give it a full day and 2 people. Be prepared to go back a couple of times to check the apparent anomalies.

 

Any shipwright worth his salt can do it with a tape measure a few sticks, paper and pencil. There is no need for software, even though it may be made to work.

 

& put him in a wetsuit with a few clamps, sticks, datum wire, 2' square & a tape measure & a digi camera & you'll get the keel etc too.