Panel Discussion

A panel discussion

Many, if not most, small boat designs are made with stitch and glue building in mind. For that to succeed panels must be developed. There is software to do that however some of these programs are expensive, others are complicated or will not work with certain operating systems. Hulls and Windows 10 come to mind.

However there is a way to develop panels using simple geometry. To describe this method I will recreate my Sampram dinghy design.

Here are the lines,

The first panel we'll develop is the bottom. You can find the length of the panel by measuring the curve of the bottom and the widths come from the section half breadths. So we start by drawing a baseline and then transferring the distance between section lines to the baseline. I've used my computer program but all of it can be done by hand with compasses, rulers and squares.

Repeating the operation until we have all the section distances transferred. You'll notice that not all of the circles are the same size, this is how we determine the true length of the bottom.

The half breadth measurements are taken from the sections drawing and transferred to the section distance marks on the baseline. 

Draw a vertical line through each section distance mark and where that vertical line cuts the half breadth circle is an intersection on the edge of the bottom. Join all the intersections  in a smooth curve and eliminate the circles and vertical lines and you have a half panel developed for the bottom. 

Divide the length of the baseline by ten and mark off section lines for dimensioning.

You can infer that the same can be done for the sides however it is slightly more difficult. First thing to do is to develop the bow and stern transoms and from those developed panels you can measure the true length of the side of each transom. To develop the panels draw two lines perpendicular to the transom at the gunwale and at the chine.

From the lines plan get the half breadth of the top and bottom of the transom 

and apply those lengths to the perpendiculars. 

Join the intersections, eliminate all the unnecessary lines and you have a half panel of the transom. 

 

Now we're ready to start developing the side panels! Next Time!

The Thin Green Line

The Thin Green Line

In my last post I said that I would explain the use of the multiple waterlines. Firstly, why are they green? Because I like them green, as soon as I see a green line I know it's a waterline.

Why are there so many? Because we will use them to develop the 3D shape of our boat along with other reference lines.

So far we have our midsection, bow transom and stern transom. The thing that joins these entities is the water line, By transferring the location of the LWL on these three sections we can start to develop the shape.

First we draw in several waterlines. I will explain further later.

Next we locate the point of contact in plan of the LWL and the three sections thusly, note the red circles,

and join the points with a fair curve, very easy on the computer.

Then we do the very same thing for each of the other waterlines like this,

Until we have this,

You can deduce from what we have just done the reason for the many waterlines.

Now we can go back and construct the other sections using the waterlines we have just created.

The Tricky bit

The Tricky Bit

When we left off we had our boat in plan and profile. The job now is to see if those lines will match up in the third dimension and still have fair curves. This is done by drawing the sections.

In the cartoon the sections are drawn in the middle of the drawing about station 5 which is used to represent the centreline (CL). You can in fact draw it any where, the reason I chose that particular position was that I was doing this without most of the tools and no drawing board. So to lay off the sections I was using tick strips. You can read more about this method here (http://www.lackeysailing.com/daysailor/sidebars/tickstrip.htm)

In that application the person is using a large piece of wood as he is doing it full size, however you can use strips of paper to do the same thing on your scale drawing. In order to do this you must first draw in a waterline (WL) where you are going to put your sections drawing, in this case I put it mid way between the profile drawing and the plan.

In the following picture a small slip of paper is laid along Station 5 and ticks are made at the WL, the chine (the curve of he bottom) and the sheer.

This then transferred to the new WL and CL by lining the strip along the CL with the WL tick at the WL. Then the strip is laid out on the plan to take off the widths and the widths laid out in the same way along the WL. Lines are drawn from the ticks parallel to the WL and CL and where they intersect are the sheer and chine points. You draw lines through those points and you have a section. This is time consuming and prone to error.

There is another way. To the right, or if you prefer left, of the drawing extend the WL and draw an new CL perpendicular to the WL. Extend the plan CL to intersect with the new CL and from that intersection draw two 45 degree angles.

Then using your triangles transfer the plan and profile measurements. First the plan,

You will probably have to extend the line of the second triangle using a ruler, make a tick mark on the diagonal slide your triangle down and do the same for the chine line in plan.

Then slide your triangle along the yard stick and draw two perpendicular lines through the marks.

Now go to the profile and draw Two lines parallel to the WL from station 5 at the sheer and chine.

Join the intersections, erase all the unneeded lines and you have the half section at station 5.

Now do that for all the other stations with stations 0 to 5 on one side of the CL and 6 to 10 on the other. Draw a line parallel to the baseline from the bow to the CL. You end up with this,

And now for the tricky bit. Join the ends of the section lines at the chine and at the sheer to see if you have a fair curve. In most instances, when drawing by hand, you won't on the first try and will have to alter the lines in plan and profile to make the curves fall fair. That can be exceedingly time consuming.

Once that's done you have this,

In this case the curves fell fair on the first go and there is a reason for that, we'll discuss that next time.

More tools of the trade

More tools of the trade

In the last post I said to make a line parallel to the yardstick 6” up, that was six real world inches not scale inches and the same for the center line. All other measurements were to scale 1/2”=1'. In this post all measurements are scale unless otherwise specified.

We ended the last post with the following grid,

On this grid we will construct the lines in plan using the centerline (CL) marked in red and in profile using the waterline (WL) in green. From the cartoon we know that the proposed draft is 6”, and it appears halfway between station 5 and station 4. Measure down from the waterline 1' on stations 4 & 5. Draw a line from the intersection of the WL and station 4 to the mark on station 5 and vice versa, that will establish the point of maximum draft thusly.

Now we need to construct a fair curve from the intersection of Station 10 and WL through the point of maximum draft to the intersection of station 0 and WL.

This brings into play new tools, french curves, ship curves and splines and ducks otherwise known as spline weights. The basic drafting set contains french curves but in order to get long fair curves you really need ship curves or a spline and ducks.

A spline is a narrow sectional piece of wood or plastic which can be bent through several points to construct a curve. The spline is held in place by lead ducks,

These things are hard to find and when you do find them they are expensive. When I was doing the Westlawn course I carved two male molds and took then to a local foundry and had them cast ten for me which was way cheaper than trying to buy them, Or you can try to make them yourself, there is a good article at Duckworks on how to do this. (http://www.duckworksmagazine.com/06/howto/splineweights/index.htm)

Once you have all your ducks in a row then you can use the spline to draw the curve of the bottom.

And then remove the X from between stations 4 and 5. Which brings up another tool the eraser, get a good one you'll be using it a lot and you'll also need an eraser shield to protect the parts of your drawing you don't want erased and a drafting brush to sweep all the eraser bits off the drawing so it doesn't smudge.

Once the bottom curve is drawn turn your attention to the bow and stern. From the cartoon we know that the top of the transom is 1' aft of station 10 and 2' above WL, using dividers mark out those points.

Problem! The cartoon length over all (LOA) is 17' but we only want 16'. If we whack 1' off the LOA will we still get the sheer (the curve of the gunwale in profile) that we wanted? The only way to find out is to draw it in and look at it. So, again using the dividers, mark out a point forward of station 0 3' up from WL and 2' forward of station 0. Then draw a line from the mark aft of station 10 to the intersection of station 10 and WL. Do the same at the bow.

From the cartoon we know that the sheer is at it's lowest point at station 7, 1' 9” above WL so using the spline and ducks we'll construct a curve from the bow to the stern through that point on station 7.

Now take a good look at that line from all directions, is it fair, does it look good. I think so, in fact I think it looks better than the cartoon. So 16' is good.

Using the same process of taking measurements off the cartoon and using our spline and ducks we can draw in the sheer and bottom line in plan.

So far so good but the real test of all this will come when you draw the lines in section like the center portion of the cartoon. We'll discuss that next time.

Tools of the trade

Tools of the trade

Before launching into a discussion of how to go about transforming your cartoon to something resembling an actual design, we should talk about what you need to begin.

There are two ways to approach this question. The first is the traditional way with pencil, splines, french curves, triangles, a drawing board and lead ducks and the second is a computer and appropriate drafting programme.

How to proceed is a personal decision. Jim Michalak prefers the pencil and drawing board, others prefer the computer. I do most of my work on computer and some with pencil and drawing board but less and less all the time.

Lets start with the basics, a drawing board. A perfectly serviceable drawing board can be made out of a 2x3piece of half inch ply to which you can glue a similar sized piece of masonite or similar smooth material. On the edge of the board which will be closest to you fasten a yardstick. On the back of the piece of plywood, on the edge furthest from you, fasten a 3' 1x1 piece of any wood from your scrap bin, if you have a scrap bin. You now have a drawing board that can be placed on any table,with a slight tilt to make drawing comfortable.

You can get a basic beginner's drafting kit from Staples for $55.99, it does not contain T-squares but it does contain two triangles and with these triangles and the yardstick you can start to build the basic grid on which your design comes to life.

You will recall that first cartoon,

This is the basic grid, that one was drawn using grid paper. However we are going to draw one from scratch.

From the cartoon determine the scale, 1/2”=1ft, the water line length, in this case 13', and you're ready to start. Stick a piece of paper on to your drawing board, securing the corners with drafting tape, or painters tape, it works just as well and is cheaper. Don't use regular tape it tears the paper, what paper you might ask. I used to use paper banquet tablecloth, it comes in rolls 40”x300' and cost. between $25 and $55. That's a lot of drawings.

Using the ruler provided in the drafting kit measure up 6” from the yard stick at either end of the paper and join the two points.

This is your waterline (WL), I like to use a different color for the waterline , green, and centreline (CL), red, on the computer to avoid erasing them by mistake. However on the drawing board it doesn't matter all that much.

The WL needs to be divided into 10 equal parts, for this use the architects rule provided in the drafting kit. You can start at either end of the WL. But what length are the parts? We're going to draw 11 parallel lines, numbered from 0 to 10 so there are 10 spaces and 10 into 13' equals 1.3' which gives us a space of 15.6” (this is all way easier in metric), .6 of an inch is 9.6 sixteenths all of which is going to be headache making doing the measuring so now we need to make some changes to our cartoon design. If we round up the space would be 1-3-5 which is short for 1 foot, 3 inches and 5 eights which would give us a WL length of 13' 1/4”, on the other hand rounding down the space would be 1-3-4+ (the plus indicates add a sixteenth) and that would reduce the WL by a 1/4”, not much to choose between the two of them but 1-3-5 is easier to mark so we'll go with that. You can change the scale at this juncture so the drawing is larger and easier to work with.

Once the marks are made put your triangle on the yardstick and move it to the first mark. Draw a line, you can extend the line to the top of the paper by using the second triangle. Do this for all 11 marks.

 

Then number the vertical lines from 0 to 10, I like to work from right to left with the zero or bow end to the right, you might want to work the other way. Now draw another line 1' up from the yardstick and parallel to the WL, that will be your centreline.

You will end up with a grid something like this,

And there we will end for today.