STANDING THINGS UP
February 28, 2021
Opening up the stitched bottom panels and raising them towards the ceiling gave us our first look at the boat coming together in three dimensions. This was extremely satisfying, but the result was a somewhat abstract, boat-like shape; is that the bottom of an upside down boat, or is that the beginnings of a life-size whale sculpture? In contrast, erecting the bulkheads on our building frame, or "standing things up" as Burnett's designer Sam calls this step, resulted in something that was unmistakably the skeleton of a boat. Seeing the bulkheads positioned in relation to one another as they will be in the finished boat gave us a true sense for the size and shape of the vessel we are building. Along with that came a true sense of panic when we realized how relatively small our workshop suddenly seemed!
Once standing up on the building frame, Burnett's bulkheads filled the shop and turned a spacious workspace into a cramped one.
Erecting a bulkhead and attaching it to the building frame is simple: attach two upright members (posts) to the bulkhead, stand the bulkhead up, and fasten the upright members to the corresponding cross member on the building frame for that bulkhead. The challenging part of the task is fine-tuning its position so that it is precisely where it should be in relation to the rest of the bulkheads. To do this we made use of the two reference lines that were marked on the bulkheads when lofting them: the design water line and the center line. We also used our string line on our building frame.
The string line on the building frame runs down the length of the frame at the center of the cross members, and this line is in the same plane as the center line of the boat. Positioning the bulkheads so that the center lines marked on each bulkhead are directly above the string line therefore ensures port-to-starboard symmetry. The design water line, which marks where the boat will sit in the water, can be used to set the elevation of the bulkheads; the vertical distance from the string line to the water line should be the same for each one.
I suspect that's clear as mud (I decided I better crank another pot of coffee when writing this paragraph), so let's use some photos to walk through the process we used for standing up and positioning each bulkhead.
Preparing the Bulkhead
First, we drove a nail into the bulkhead at the intersection of the center line and the design water line. The significance of the point defined by this intersection is that it is an identifiable point on the bulkhead that needs to be lined up with the same point on all other bulkheads. Once the bulkheads are lined up in position, an imaginary line formed by connecting the tip of each nail with the head of the nail on the next bulkhead it points towards should be a perfectly straight line.
The star on the dimensioned drawing is the intersection of the design waterline and the center line. A nail was driven into this intersection on each bulkhead and used to line them up on the building frame.
Attaching the Plumb Bob
Next, we got out our plumb bob, which is essentially a weight that comes to a point on one end and has a string attached to the other. We adjusted the length of the string so that the distance from the pointy tip of the plumb bob to the end of its string matched the vertical distance we wanted the design water line to be from the string line on the building frame. This distance is somewhat arbitrary; to get the bulkheads in the right place in relation to each other all that matters is that the distance is the same for all the bulkheads. We picked the distance that would be the most comfortable working height for hull construction. After attaching the upright members to the bulkhead, we clamped the uprights to the corresponding cross member of the building frame. This got the bulkhead approximately in the right spot. We then attached the plumb bob to the nail on the bulkhead.
We attached a twist tie to the end of the string on the plumb bob so that we could easily adjust its length. Fine-tuning the length by twisting the twist tie was a lot easier than trying to tie a knot in exactly the right place!
Tweaking the Bulkhead's Position
Once the pendulous plumb bob settled, the string and the tip of the plumb bob were oriented parallel to the force of gravity, which is perpendicular to the string line on the building frame (the string line was positioned using a laser level). The next game we played was tweaking the bulkhead's position so that the tip of the plumb bob just barely touched the string line, and the string attached to the plumb bob was parallel to the center line marked on the bulkhead. For those of you who have played Whack-A-Mole, imagine a very slow version of that game which requires considerably more precision.
To become correctly positioned, the entire bulkhead in the above photo needed to be moved to the left so that the tip of the plumb bob just barely touched the string line. However, the bulkhead also needed to be rotated counter-clockwise so that the string attached to the plumb bob covered up (and was therefore parallel to) the center line on the bulkhead (pencil line left of the white string).
The best method we came up with to tweak the position of the bulkhead was to loosely clamp the upright members to the cross members of the building frame and make adjustments by tapping wedges underneath the uprights to raise them as necessary.
Quick-grip clamps applied enough pressure to hold the bulkhead stationary, but had enough play to accept the subtle movements driven by the wedges that were needed to get the bulkhead right where we wanted it.
Locking Things in Place
Once we were happy with the position of the bulkhead we secured it to the building frame with some hefty screws. Each of the twenty-four uprights will be bearing approximately 400 pounds once the hull is ready to come off the building frame, and we don't want the entire project to literally come crashing down on us!
Screwing the upright members holding up a bulkhead to the cross member of the building frame after it has been tweaked into position.
The next step was to make sure the bulkhead was plumb (vertical). To make these adjustments, we secured angled braces from the upright members to the building frame once the spirit level told us the bulkhead was vertical.
Using dry cedar 1x4's to brace the plumbed bulkheads.
That's essentially it! One of Burnett's twelve athwartship bulkheads is positioned. Repeat the task for the eleven other bulkheads and we have the skeleton of a 39' sailboat.
Do you remember those two longitudinal bulkheads that run parallel to the center line? Of course you do, how could one possibly forget such an important component of the boat. Once the two athwartship bulkheads furthest aft (stern of the boat) were in place we interlocked the longitudinal bulkheads with them using the 3/4" wide slots that had already been cut.
Testing the width of a slot cut into Bulkhead #11 by running a scrap piece of 3/4" plywood the length of the slot. This slot is where Bulkhead #11 interlocks with the starboard-side longitudinal bulkhead. This was another case of us opting for slightly too snug of a fit, resulting in a bit of sledge hammer work. Classic.
Dry-fitting (no glue) the port-side longitudinal bulkhead to check its fit.
Notches for Sheer Clamps
The carefully positioned bulkheads on the building frame make up the bulk of the skeleton required to form Burnett's hull. However, a few more pieces of internal framework were needed. The notches cut into the corners of the bulkheads are there so that the scarf-joined Douglas fir sheer clamps can be bent around the bulkheads and glued in place. Installing those as well as harpins and breasthooks is the next step in the build. So you can look forward to adding a couple more specialized nautical terms to your repertoire in an upcoming post!