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    « It's done because I say it's done. | Main | The SS JOY has set sail! »

    August 23, 2010

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    Paulina

    The term refers to the prcseos both of producing (in the first place) the plans that you say you have, and more importantly the prcseos of reproducing these again in full size. Somewhere that is big enough to do it.Hence the term lofting' The term comes from the fact that, in boatyards, this prcseos is usually carried out in the boat-shed loft! Because this space provides the necessary large area, clear of clutter. Based on the reasoning that if the boat shed is big enough to build the boat in, then the boat shed loft should be big enough to construct the plans in!A small vessel like a kayak shouldn't present any problems. Your garage might be suitable, for example.The purpose of this is to produce a set of body plans' from which you can construct the vessel's hull. The body plan' is the end result. Your objective in the lofting prcseos.The prcseos is rather too technical to go into here in real depth but I shall at least try to summarise it so you can understand what is involved.I must necessarily assume quite a high degree of practical competence.You will notice from your plans that there are three elevations: usually referred to as the profile' (side view), half-breadth plan' (top view of half the vessel, from centreline) and body plan (end-on view).It is the end-on' shape of each of these stations' that you are after: like finding the actual shape of each slice of a boat-shaped loaf of bread! From which you can construct the boat. (Like trusses for a roof except that each truss is a different shape. Hence all the palaver!)The first step is to construct a grid' your drawing sheet in full size. Use a low-priced sheet material and form a single board that is big enough, on the floor. Reproduce this grid, exactly the same but full size: A grid box, large enough to plot and draw both the profile and half-breadth plans in, using common station lines. Most lofters paint the board with white emulsion first, for clear line drawing.Along with your plans you will have received a table of offsets'.This is a list of ordinates' for every single curved line on each of the two above plans. So two lists!One list will be the ordinates for the waterlines' as measured from the centreline, at each station the half-breadths'. On the half-breadth plan.And the other list will be the ordinates for the buttock lines' (and sheerline, etc) as measured from a baseline, at each station. On the profile plan.Draw each line as you plot it, using a flexible batten of clear (no knots) softwood, preferably of square section. For a kayak, I would suggest about half-inch. The best material is silver spruce silver Christmas trees! But any nice flexible material will do for a starter! Use small nails and a claw-hammer to position the batten in the drawing. Don't put the nails through the batten, just alongside it. Remove them as necessary with the claw. Try not to pepper' the board with unnecessary holes. There is some considerable skill in this prcseos, but everyone who is interested must start somewhere. You will pick it up quickly.Don't simply force the batten to follow each and every ordinate that you have plotted. Some of them will be a bit off'. This is why you do it full-size rather than just expanding a body plan from a small drawing: Expansion also amplifies inaccuracies and you will be ironing these out all through the lofting prcseos to produce, from a set of nice, fair curves, a nice, fair hull shape!When you have drawn all of the waterlines and buttock lines on your plan, you now need to check that both plans fair in' with one another fairing in.This means that at every single place where a curved buttock line on the profile plan intersects a straight waterline, the same, but curved waterline on the half-breadth plan should also intersect the straight buttock line!Got it? You will do! It's fun!When all the lines you have drawn fair in accurately with each other across the two plans you are now ready to construct the all-important body plan.Starting at station one, transfer all the ordinates that your fairing has produced, from both the profile plan (vertically, from base) and the half-breadth plan (horizontally, from centreline), to the body plan grid. For each station in turn, thus producing for each one, a set of COordinates! Work downwards, from the sheerline at the top end to the centreline at the bottom end, for each station in turn.When you have a last drawn all of the body plan lines to the coordinates plotted from the other two elevations you are done!And the next step is not really lofting. It is lifting' the lines from this body plan.You will need to lift' the full-size body plan lines produced and transfer them onto the material you plan to use for the frames for the boat. These are then set up', as with the trusses of a roof, and the boat built around them. In an open kayak (you do not say what sort you are building) this is usually done by producing molds, as for dinghies. To be removed from the finished craft and used again and again.There is loads that I have not gone into here regarding this detailed subject-area. It is a really satisfying, and elegant craft. Almost an art. But hopefully there should be enough to get you there if you are determined.[Edit / Note: this is a much shortened version of my first answer, which Y! Answers found too long to handle - my apologies on their behalf - Email me if you need any clarification.]-| ).

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