A Shipwright in Training

One of the good things about the 2nd year here is that we get to see how someone else handles a tricky task like lofting. Warren is a fan of not laying down your lines until you’ve gotten all your views to agree with one another. At that point, you lay it down in pen and treat it like gospel.

So, the question is, how do you look at all those lines you’ve taken off your boat (or taken from a table of offsets) all at once so that you can see where things are looking wonky? First, a couple of things to keep in mind:

• your long lines will show unfairness better than the relatively short lines in your body plan.
• You should work out from the bottom and center of the boat to the edges when fairing
• Trust the intersections that are close to right angles more than the more acute intersections

In case you haven’t already guessed, this little entry is not for everybody.

But here’s a quick refresher of the things I’m talking about. The body plan is a view of the boat sliced like a loaf of bread, the plan view is looking down on the boat from the top, and the profile view is just like it sounds, a view of the boat from the side.

Here’s the body plan we’ve been working out:

The plastic batten in the center left isn’t really the greatest looking thing, but a lot of that is because of how much of the batten runs out above the actual sheer line. All of these battens run out above the actual sheer line.
Think of these lines as outlining the edge of the boat as you slice it from side to side along its length (like a loaf of bread). The lines to the right of center show slices of the boat from the middle to the bow of the boat. If you put your hand over the left side of this view, it’s like you’re looking at the boat coming at you. If you blot out the right side, you’re looking at the boat sailing away from you. That clear plastic batten describes the shape of the transom. I think it’s a little off… here’s a photo where you can see the transom:

The guys who built these boats didn’t go from plans. They pretty much started with a stem and transom profile, a length, and then winged it from there. That thought comforts me when I’m working to fair out lines to within a 32nd of an inch.

So, here’s how we loft.

1. We use thin battens to lay out the body plan from the information we got by taking the lines off of the boat. We hold them in place with finish nails so they can be moved as we go.
2. We lay out the keel, rabbet, and sheer in the profile view. These are long lines, because they go the length of the boat. We get these lines fair.
3. Using the faired lines from step 2, we go back to the body plan and correct the points for the sheer and rabbet. We won’t change those points any more… they’re locked in because we know they come from a nice, fair line.
4. We use pickup sticks to get intersections of the stations in the body plan and the first water line. We then plot out that waterline in the plan view.
5. At this point, the negotiations begin. As we see unfairness in the waterline in the plan view, we make little adjustments to get it fair, as long as these adjustments don’t screw up the way the stations look in the body plan. It helps to have one person looking at the waterline and suggesting changes, and one person at the body plan saying whether or not those changes will work. Let’s look at what I’m talking about.

Here the pickup stick is laid across the 2nd waterline, called the LWL, or Load Waterline (the first waterline is the horizontal line below it). The end of the stick is on the red centerline. Each wooden batten lies along the points we took from measuring the boat, and each one represents a cross-section of the boat. These cross sections are called stations. We slide the pickup stick beneath these battens, and then make a little mark on the stick exactly where the batten crosses the stick. We then label these marks, “station 1, station 2, etc.” so that we know where the marks come from.

We now want to take those measurements and use them to draw the waterline as if you were looking at the boat from above (or below, it doesn’t matter… we’re assuming the boat is clear). Essentially, the shape we’ll get is the shape the water traces along the hull if we dipped the boat into water just to the level of the waterline.

So, we take that stick, and hold it up to each station mark on the plan view, and make a little tic mark on the lofting at the height of the waterline as you go from station to station.

Here, the pickup stick is at station 6. We put the base of the stick exactly on the baseline, since this represents the center of the boat as you’re looking down on it. There’s a tic mark on the stick that we made where the waterline intersected with station 6 in the body plan. We transfer that mark to the lofting, and label it “LWL.” We go along each station, making a tic mark that corresponds to the distance from center the LWL was at each station. We end up with a series of points that we connect together with a long flexible batten.

If that batten makes a nice, fair curve, we say “Woo Hoo!” and we don’t have to change any points on the body plan where the stations intersect the LWL.

If it’s not fair, we move the batten slightly up or down to create a fair line. Say we moved the batten at station 6 down 1/8″ to make it look more fair. On the body plan, we’d have to take the batten that defines station 6 and move it in towards the centerline by 1/8″ at the LWL.

Maybe that will make the body plan batten look awful. If so, then we know we have to fair things out somewhere else.

What I meant earlier about working from the bottom and center out was this:

1. Transfer and fair your lowest waterline
2. Transfer and fair in the first butt line
3. Transfer and fair in your first diagonal
4. Transfer and fair in your next waterline
5. Transfer and fair in your next butt
6. and so on, working outwards
7. Each time you fair in a long line and transfer any changes to the body plan battens, mark where those battens now cross the butt or waterline that you just faired. Those are now locked in. Any changes as you work out with have to happen between these locked points and the locked in sheer points.

In case you don’t know, the butt, or buttock, lines in the body plan go up and down, since they slice along the sides of the boat like you’d slice a banana for a banana split. The sheer lines on the body plan haven’t been drawn here, but you can see how the battens run out above the sheer. The arrow below is pointing to the mark that indicates the sheer line in this view. We just haven’t drawn it in yet.

See, I told you this entry wasn’t for everybody.

I’m really hooked on using the battens this way though. It makes it so much easier to work back and forth, adjusting multiple views as you change a point.

We had 2 teams, each working on their version of the same lofting.

It would have been too much trouble to have 7 people try to loft one boat together. This way, we each get to really get into the process.

Meanwhile, the other group of 2nd years are working on lofting the Bulldog, a 1934 boat built for junior sailors.

They didn’t take the lines off her, instead they used numbers from the original plans to generate their lofting.

She’s in rough shape. You can see that they’ve already taken her stem out to see how it was constructed.

This is the body plan they’ve generated so far (they’re a few days ahead of us).

Meanwhile, the 1st years have finished up their bench projects, have lofted their beetle cats, and are setting up the molds to place their boats on.

It’s starting to look like quite the production shop down there. We’re up in the room behind the balcony these days, where we remain mysterious and aloof… like monks.

This entry was posted on Tuesday, September 25th, 2007 at 11:10 pm and is filed under Classes. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.