Boat lofting information required?

It used to be by building a solid wooden half model of one side of the hull , which was then subjected to scrutiny by other builders and seamen in order to achieve a final form that was most pleasing to most eyes , AND was optimised for it's intended purpose .

Modelling is still relied on today ( albeit as computerised images ) to get the " Bugs " out of designs , by a process of many people contributing amendments and improvements .

In the Old days the model was then sliced up in all three dimensions , and the " slices " scaled up to full size on the floor of the Moulding loft , a vast flat space , using chalk and string and bendy wood laths pinned to the floor . At that full-sized stage any " Unfair " errors of lines became obvious and could be put right .

Scrap-wood patterns were then made for the ship's frame-makers to start selecting and cutting and scarfing together the complex curved ship's frames .

And later , planking plans for cladding the hull .

It was then the Shipwrights job to fit it all together , with a lot of sawing and hammering and chiselling and adzing and bad language .

Later on steel ships ( as complicated as the big battleships ) would be made in a similar way ,chalk -lines on the floor transferred to a frame-making shop , where yellow-hot steel angle irons would be taken out of furnaces and bent between steel pegs set into a steel slab floor ( like a giant Pegboard ) and belted into shape by sweaty men with sledgehammers and a lot of bad language .

And hull plates set out as flat shapes to be cut ,and then bent to complex curves in roller presses .

You can actually still work off a hull model , but nowadays there are huge computer programmes that will do it all for you .

Brief history of lofting

The first real records of lofting being used date back to the 1600's and 1700's. It must have been used before this time for the ships to be built.

Ships were built by shipwrights and the master shipwright, a man of great importance had all the details in his head and in his personal note book. If it looked right then it was right was the maxim. The master shipwright would know what had worked before and he would follow this basic design.

The loft floor came into being as a place to bend the frames. From the shipwrights sketches an outline was drawn on a flat floor to full size. Pegs were knocked into place and the steamed oak timbers would be bent into shape and allowed to cool. These frames were then locked into the keel and hull timbers steamed and fitted, hot to the frames. Hull timbers were not bent or shaped at this time on the lofting floor.

The lofting floor got its name because it was usually in the loft of a building.

By the 1800's when steel ships came along greater expertise was needed. Steel would not take the inaccuracies that would could,. The improvement in mathematics allowed calculations and drawings to be made and from these more detailed plans were available. Also the skills of the shipwright were no longer in demand as they had been with wooden ships.

In the first instance the scale used was half scale. The outlines of frames were laid out in full scale from this on the lofting floor.and templates made for the various trades. By the 1900's the scale used was one tenth. By 1970s with the advent of computing power and CAD the demise of the lofting floor happened. Computer generated plans were available and computers could speak direct to machines which shaped hot steel into the required format

So in answer to your question the initial information came from each of your points at one time or another.

Common sense and guess work dating right back to the days of Noah and behond.

The plans used were called the half lines plan and these are still used and carried on todays ships. The name given was because only half the ship was shown on the plan, the ship being symetrica along the centre line.

Naval archiitechts still control the computerised drawings and necessary calculations.

It may come as something of a surprise but … you do it in exactly the same way as when you draw anything else for the first time.

Firstly, you will know from the start what kind of vessel is intended and its displacement because those are the first things the client will tell you. (Or, if doing it for yourself, will have chosen).

Then you will already have gone on to decide on a block coefficient for the type of vessel required, specified from this where the vessel's load waterline should settle from an appropriate freeboard v draught v beam calculation (initially at least) along with anticipated speed and prismatic coefficient. All of which things specify the kind of hull shape you're looking for.

So you will have a really very good idea in your head of what kind of hull shape is needed - just from what has worked well in the past - before you even start to draw.

So with all this in mind you take the plunge!

Simply start drawing the profile of what you have in mind and from which, by the time you get to that stage - ie: the drawing board (or screen) is as you can see, already a lot of information.

This 'profile' drawing would be the initial impression - like the 'front elevation' for something like, say, a house. In lofting you draw this profile inside a so-called 'grid' of evenly-spaced straight lines: Horizontal lines to show the 'waterlines' and 'level lines' (so-named depending on whether they are above or below the LWL) and vertical lines to define the positions of the 'stations': Like the 'slices' of a loaf of bread and the shape of which you will ultimately need in order to construct the actual vessel from.

Begin with the outer-most profile line of the vessel - usually comprising the stem, sheerline, transom and underside of keel - then add others inside this, thus defining the shapes you would get if you were to slice-up the 'solid' hull shape by running it along the fence of a circular saw, parallel to the vessel's centreline.

The more lines there are in your grid, the more accurate and 'fair' the vessel will be. (And the more work involved in drawing it).

When your profile looks good and meets these initial dimensions you are ready to move on to drawing the half-breadths: The curves which describe the shape of the sheerline, and each waterline and level line in the grid. As seen from above. Begin with the sheerline and the LWL. Then, as before, add the others, in between.

Since you are not asking for an in-depth explanation of the process - simply where the initial information comes from - that's about it. But I give you a link to a more precise account below, in case.

But the answer is that the information comes from human intervention. The designer draws it. How they want it.

Have a go!

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See Answers at: http://uk.answers.yahoo.com/question/index;_ylt=Ah...

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