Lining out the planks - Week 7

To start off the week we decided to take a break from fairing and bore the hole for the propeller shaft. The hole will go from the aft face of the sternpost through the deadwood and come out through the inner keel just forward of the floor timber at station 16. It's only about 24", but if you remember from a few weeks ago when we were assembling the backbone, there are two bolts through the deadwood that we'll have to avoid. When drilling for these bolts, we angled them so that we would leave enough room to bore the shaft between them. Now we'll find out if we left ourselves enough room.

To start we lay out where the shaft is going to go. Here we've drawn the centerline of the shaft on the side of the deadwood and marked where the shaft will exit through the sternpost.



Using a guide block similar to the ones we used when drilling for our keel bolts, we'll bore our hole using a barefoot auger that should make a nice straight hole.



The end of our guide block is cut to match the angle of the shaft. You can see that the centerline of the shaft matches perfectly with the centerline of the guide block lead hole. Once the guide is securely clamped to the sternpost, we're ready to go.



Even though we've taken our time making sure all our marks line up, it doesn't hurt to sight down the auger just to make sure everything looks as it should.



Now there's nothing left to do but start drilling.



Even though the hole is only about two feet long, it still takes a while since we're going through the end grain of the deadwood.



After we're about ten inches into the keel, we can remove the guide block. The hole we've got in the keel is more than enough to guide the auger the rest of the way.



On the inside of the boat, the auger came out right where we wanted it. But what about those bolts you ask? Well we did end up nicking them with the auger, but only very slightly. In the end we've got a nice clean hole through the bottom of our boat. It may sound counter intuitive, but we couldn't be more pleased.



With the shaft drilled, it's back to fairing. We're working on the port side cheek blocks now. To begin with we're concentrating on fairing the cheeks at each of the frames.



Once we can see that the plank will lay flat at the frames as in the picture below, we'll fair the cheeks between the frames and adjust our rabbet if necessary.



While we've still got some fairing to do over on the port side, the starboard side is ready for us to start lining out our planking. Regardless of whether you're building a carvel (like our catboat) or a lapstrake hull, before you can start planking you first have to line out all the planks. Lining out the planking means literally marking the top of each plank at the stem, the transom, and every frame between. To ensure a fair line we use battens so that we can easily see the plank lines.

The first batten is the top of the sheer strake. The sheer is one of the lofted lines of the boat, so we marked it on each of the frames back when we were assembling them. With a batten we connect these marks to verify that we have a nice fair line for our sheer.



Once the sheer has been established and we're satisfied that it's fair, we measure the girth at each of our stations. This is the distance from the rabbet to the sheer. Since the girth is greater at the middle of the hull than it is at either the transom or the stem, the planks will be widest at the middle and taper at both ends. Once you know the girth at each of the stations, it's possible to establish the taper based on these ratios, and the number of planks.

The second batten will mimic the sheer, tapering at each end. This batten is important because it establishes the lines of the topside planking (the next four or five planks most visible above the waterline).



With the sheer strake established with these two battens, we step back to see how it looks. Measuring the girth at each of the frames, we found that there wasn't much difference between the biggest and smallest, so the sheer plank could have been a uniform width over it's whole length, but we opted to taper it at each end. Why? Because it looks good. Sometimes it's as simple as that.



Each of the next planks parallels the bottom of the sheer, though these topside planks are a little narrower than the sheer strake. This is because the top of the sheer strake will be covered by a guard 1 1/2" wide. Once the guard is attached all these planks should look uniform.



While the planks taper at the ends, we kept the taper to a minimum to ensure that we would have room for fasteners. At the stem this is especially important since the planks will be under some pressure from the bend they're taking.



Similarly, the planks at the transom have a bit of twist to them, so maintaining enough room for fasteners is important here too.



As more battens go on, the shape of the hull starts to emerge. I think we were all a little surprised at just how shapely our little catboat is.



Once we have all the battens on, it's time to step back and make sure everything looks right.



At this point we're considering the shape of each of the planks, especially the garboard and broad strakes. The garboard is the plank next to the keel and the broads are the next two. In order for the topside planks to look uniform, the difference in girth is made up in these planks. In the case of the catboat, these planks are also forming the forefoot where the horizontal line of the keel rabbet meets the vertical line of the stem rabbet. These planks must be carefully lined out to create that transition. Remember that we've using 3/4" planking, and even with steaming there's only so much twist the red cedar will take before breaking.



At this stage we spend a lot of time looking at the plank lines and making small adjustments.



We look at the hull from every angle...



Visualizing the shape of the planks.



With a crowded shop it can be difficult to step back far enough to see the whole boat, so you improvise.



See what I mean about a shapely hull.



Too bad all that shape is going to be below the waterline.



It's important to remember too that we're building the hull upside down. So what will it look like right side up?



In the end you just have to stand back and say, "good enough." You could literally spend weeks lining out the planking if you kept fretting over little adjustments that in the end won't make any real difference. It's better to get things looking good, and call it. Otherwise you'll never get to hanging the planks.



Once we were pleased with the lines, we marked them on each of the frames, the stem, and the transom. While we've got the battens attached, we also marked with chalk anywhere on the frames that might need a little more beveling.



It's certainly been an exciting week, seeing the shape of the hull emerging. The only thing more exciting will be hanging that first plank.