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!

Beyond the lines

The Drawings

The lines drawing that we have just completed is just the start of the process. To make a complete set of drawings several more are required. The list can vary depending upon the design. The following are the basics for small boats.

Lines drawing

Table of offsets

Construction plan

General arrangement plan

Out board and inboard profile

Deck plan

Machinery

We'll move on to the construction plan and come back later to the table of offsets.

Before starting the construction plan a few things need to be decided. First off, are the lines drawn to the inside or outside of the planking? What material will you recommend for construction? And what construction method?

Inside or Outside

This question is not very important in a small boat but in a larger vessel it makes a great deal of difference in the displacement. If the lines are drawn to the inside then the actual hull will be wider and longer increasing the displacement. If the lines are to the outside then care must be taken in drawing the frames because where the planking has a bend in it so that it meets the frame at an angle the width of the planking is different,

it has the same thickness but the width is at an angle. This makes very little difference on a boat that is planked with 3/8 ply but a lot on a vessel where the planking runs to two layers of 2”. I draw all my lines to the inside.

Material

Will the planking be plywood or structural lumber? In a boat such as this one, which will  be utilitarian, I would use plywood and epoxy cloth over the outside, we're designing a work boat not building a piano.

Construction

Plank on frame, plywood on frame, stitch and glue, these are the choices for a hull of this size. Plank on frame is traditional but may require skills not possessed by your client, in this case you. Stitch and glue uses modern methods and materials but it requires you, the designer, to lay out the panels, not always easy to do. There is a program, Hulls, which will do it for you but it doesn't work well with Windows 7 for some reason. So for this project we will select ply on frame.

The last thing you need to decide before doing the drawing is scantlings, the sizes of the materials you have designed the boat to be built from.

There are many scantling rules to choose from. Since I did the Westlawn course I use their rules. I do like Goerge Buehlers rules which are very simple, build it big, build it strong.

So we'll end here and next time start the drawing.