Hi there Gary
Right, to plot the position of propeller shafts on your frames – it is quite easy to do.
But, bloody difficult to explain
so….we shall take it in easy steps.
Stage 1 – we need to put your main plan on a table; then you need a good steel ruler, plastic ruler, nice sharp pencil and a pair of drawing compass’ (you know the ones – they are used for drawing circles with.) So, the first thing we do is on the view of the side of the model; we will locate the propeller shafts and we draw a centre line through the very centre of the propeller shaft on the side view plan. This centre line goes well inside your hull. In other words, on your particular hull, the centre line should pass Frame I; when you have drawn that centre line in; we need to draw in the frame positions at right-angles to your keel. These are drawn in as dotted lines in my scribble to help you. These must be at right-angles to your keel.
Stage 2 - move over to the drawing which shows the frames, the ones you have traced off to produce the ribs. On this drawing you will see the position of the propeller shaft which has already been marked with a cross and a dotted circle to represent the propeller (on the plan).
You will see the distance between the centre of the cross and the centre of your frames – it is called the prop shaft centre line. This centre line runs parallel to your keel, at a set distance and in fact it never varies (on this particular model). So, now you have 2 dimensions – these 2 dimensions are equal on both sides of the frame, port and starboard. Now you have 2 plotting points from which to work, one from our side view plan and one from our frame plan.
Take your first frame, where the prop shaft begins to enter the hull; this looks as though it is frame K on your model. Take a dimension from the bottom of your keel to where K dissects the centre line of the prop shaft – on your side view model – with a pair of compasses. You move over to where you have drawn rib K on your plywood, on the centre line of Rib K you mark this height – from the keel up over. This marks the position of the height of where the prop shaft enters the hull – now what we need to plot is the distance from the centre line of the frame to your centre line of your prop shaft. This dimension comes from your frame plan which is marked with the cross. Mark this position on Rib K on the plywood.
Move on then to the next rib and do exactly the same on Rib J, same procedure mark your height from the keel and also mark your distance. This produces what is called a ‘plot’ of where your propeller shaft will pass through your frames and this in turn will give you an indication of where to drill holes through your frames for the position of your prop shafts.
I hope you can understand my above description. I am attaching a couple of scribbles – hey I hope you can understand them. If not give a yell and will have another go at an explanation for ya. Neee worries.
Aye
John e
Bluebird