Halfhull1.pdf

Building a Half Model

Russell Barnes

If you have ever had this problem you will know what I am talking about. What problem? Burn out.

Plain and simple. The model is there, but you cannot get yourself motivated. Something happened,

either you changed your daily schedule or you had an illness. Whatever it was, it just got you out of

your routine and now you do not feel like building. I got out of my usual habits over the Christmas

holidays and afterward, I could not get motivated.

I have often heard that one way to get out of the doldrums is to build something small and quick.

Not much time invested and there is a sense of instant gratification that gets you back in the mood

to build. I decided to try a half model to get me out of my doldrums. I have always wanted to learn

how to make them and now seemed the perfect time to try. The really good thing about a project

such as this is that it does not take much time, very few tools, and little in the ways of materials. On

my first half model, I spent about 15 hours of spare time over the course of one week, about $10 or

so in materials, and used only the most basic scratch building tools.

When I first decided to try my hand at building half models, I was not sure how to begin. But, then I

told myself it always begins with the lines drawing. This is where every model building project

begins. If you look at a given lines drawing, you will see that the waterlines in the sheer profile draw-

ing are at more or less regular intervals from the keel up. If you are building a half model, then the

layers of wood you use must match the thickness of the intervals between the waterlines on the

plan. The upper layer is always a bit thicker to account for the curve of the hull's sheer line or deck

line that has to be cut into the upper layer.

For the purposes of this description, let us lay out some terminology. The layers of the hull are called

lifts. This style of building is often referred to as a lift model or a bread and butter style model. The

layers are the lifts, or in the case of the second term, the bread. The glue is the butter, much like the

butter between two slices of bread (or wood in this case). The side view on the plan is called the sheer

profile drawing, but for the purposes of a half model, we will call it the profile. The waterlines on the plan

can also be called lift lines since each waterline corresponds with the shape of a given lift.

There will be templates needed to build this model. The profile

template is one, and then there are also the lift templates. The lift

templates are each waterline shape in the half breadth drawing of

the lines plan. There are also the section templates. These are

taken from the body plan of the lines drawing.

One other useful template will be the transom template. This one

is a little different and it takes just a bit of explanation. To illustrate

this, I will use the example of my Biloxi schooner half model's

plan. What you need is the expanded shape of the transom. You

cannot use the shape of the transom in the body plan because the shape given does not account for

the angle of the transom. The body plan shows you a foreshortened view of the transom. What you

need is the "full face" shape of the transom.

First, take a deep breath and do not panic. If you have a ruler, a scrap of paper, a sharp pencil, and

a little time, you can do this. I will walk you through the basics. Look at the sheer profile and half

breadth views of the plan. The sheer profile gives you the upper and lower extremities of the tran-

som and they correspond with the same extremities given in the half breadth. The top of the tran-

som is at the deck line and the lowest point of the transom is where the angle changes in the profile.

For each section template, there is a centerline. In the expanded view we will create, the centerline

for the transom is the aftermost angle of the profile also called the rake of the stern. Use that angled

line as your centerline. (Photo 1)

Next, use a T square to strike in reference lines from which you will measure the widths of the tran-

som curve. These measurements are taken on the half breadth, but we need those reference lines

to extend down to corresponding points on the angled line that is the centerline of the expanded

transom. There is no hard and fast rule about where these reference lines must be placed. The only

thing to keep in mind is that you want to get a couple of reference points to create the curved shape

of the transom. Locate your reference lines accordingly. (Photo 2)

Next, use a tick strip to measure off the width of the transom's shape in the half breadth along each

of those reference lines you just created as well as the half breadth width of the deck. Transfer those

lines down to the corresponding reference lines on the profile drawing, measuring out from that

angled centerline at right angles. (Photo 3)

With those reference points marked, you can use a French curve or a ship's curve to create the

expanded shape of the transom. Now, trace this shape onto a piece of tracing paper and then rub-

ber cement it to some poster board for use as a transom template for the model. The transom tem-

plate requires only the centerline and the shape of the transom. (Photo 4)

The rest of the templates can be gotten directly from what is already on the lines drawing. If you

wish, you can make multiple copies of your lines drawing and use each copy to cut out a different

template. Or, you can tape the drawing down on a flat surface and trace the templates using tracing

paper. Either way, make sure to take in all the reference lines needed for the template to work prop-

erly. For the lift templates, be sure to include the centerline of the hull as well as the station lines.

These are important for proper alignment of the templates on their corresponding lifts. The profile

drawing needs to have the station lines, the baseline along the top of the keel, and the horizontal

waterlines. For the section templates, you will need the centerline and the horizontal waterlines. If

you make multiple copies of the plan and cut out the various elements, then these lines are already

on the plan. You just need to make sure you do not cut them out of the template. If you are tracing

your templates, make sure to have a good straight edge to keep these lines nice and even and also

make sure to keep your pencil nice and sharp.

To complete your templates, I highly recommend rubber cementing them to poster board and then

cutting them out. You can simply rubber cement them to the wood, but it pays to have a template

Solid Hull Templates

that you can use at several points in the construction process to double check alignment and

shapes. This is particularly true of the section templates as they will be needed to check and re

check the hull as it is faired. Having a set of templates on poster board also allows you to reuse

them at a later date for making another model from the same plan if you choose.

The next step is to cut some timber for the lifts that will make up the model. The vertical spacing of

the waterlines in the plan will tell you how thick the lifts should be. In my case the lifts in the lower

part of the body wanted to be 1/8" thick while the uppermost lift was about ½" thick. The uppermost

lift will be thicker so the sheer curvature of the deck can be cut into it. You can either buy your tim-

ber to pre-milled specifications or you can mill your

own. Basswood will do, but since it is a soft wood,

staining might be a problem. I have had mixed results

using basswood. Sometimes it will stain well and

other times not. I always use a pre stain conditioner,

but even that does not always guarantee good results

with basswood. Basswood is easier to work, but it will

show every nick and ding. Whatever wood you use,

you will create a block made up of the various lifts.

Once you have your lifts sized for their vertical thick-

ness, make sure they are a uniform width. The length

can be approximated, but it is probably best to make

the lifts uniform in both length and width. The width of

the lifts should be about ¼" wider than the width of

the finished hull. The length of the lifts should be

about ¾" or so longer than the finished hull. (See

photo below left)

Solid Hull Section Templates

With the lifts ready, stack them to create a hull block.

Clamp the block at each end. I use miniature sliding

bar clamps for this. While you have the block

clamped up, decide which edge of the block will be

the centerline of the hull. Mark the edges of those lifts

to remind yourself where the centerline is. From your

plan, make a tick strip to create a template for the

station lines. Just mark those station lines with a

small tick at each point. Now, place your tick strip on

the back side of the block and align it so that there is

plenty of room at each end of the block. Transfer the

marks for the station lines onto the back side of the

block. Set that tick strip aside as you will use it later

on in the shaping process. (Bottom Photo) Those sta-

tion lines are a master guide to the alignment of the

model and now that you have that tick strip, do not

throw it away.

Lift Blanks

Next, use your machinist's square to draw the station

lines all the way across the back edge of the block.

Transfer the station lines all the way around the block.

To do this, I just made a small mark at each station

on the faces of the lifts once I had the stations

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