How to Understand Boat Building Plans

When you first look at a set of boat plans it can be fairly confusing. There'll be some elements you can probably recognize but there'll be a whole bunch of stuff that you just can't make head or tail of. Pictures of the boat that look like they have spaghetti all over them for instance. Welcome to Snowmad Boatbuilding. My name is Mark Rutin and I'm a wooden boat builder on Vancouver Island. Today let's look at the basics of boat plans. So I got this set of plans from the Adirondack Museum at Blue Mountain Lake, New York and that's where the original boat that these plans are drawn from still resides. This set of plans was developed from an existing historic example of a boat built by John Henry Rushton. It's his Yugo canoe and I built an example of it for the Vancouver Airport Authority. You can still see that boat hanging at the Vancouver Airport in the international arrivals area. This is called a construction drawing and what it features really is just a bird's eye view of the finished boat as you would see it if you're taking a photograph of it for instance and a profile that is a cross section so a slice right through the center line of the boat. The idea is to show us all the bits and pieces that make up the construction. So the way the stem is constructed, the ribs, how often they're placed, the keel construction and so forth. Up here we've got some detailed drawings that show us sections through the keel and garboard which are the lowest most plank. So they're showing you how it's expected you might build that. There's usually another one it's more of a cross section through the mid midpoint of the boat and then a bunch of other smaller details such as floor boards here. They've got even a little full-size drawing of the stem head, the section through the stem, some details about fastening the planks at the laps and at the frames and again some details about doing scarf joints. They've got some drawings for the seats here and even a drawing for the stem band so this is rather complete. And then this last list of what they call scantlings. Scantlings are the name for any of the little pieces of the boat and the size of stock you need to create them. And so these numbers along this list here refer to all these different parts that are outlined throughout the rest of the drawing. Now this is great to have this is almost more like a serving suggestion on a cereal box. We don't really need this information to build that boat. It's helpful and it gives us a good indication as to how the person who designed the boat expected it to be built. But a lot of these details you can kind of work out on your own and often you change them to suit the materials that you have on hand. Now this is the really important part. This is referred to as the lines. So what we have here is we have an image of the boat drawn in three different ways in three different views and the lines you see represent slices through the boat in different orientations. The drawing on this half is really just showing you plank lines and this is not something you typically get on a set of drawings. But because they're giving you a set of drawings that were taken from an existing boat and it's a historic boat they're trying to make it as complete as possible. So that's that's a nice detail but we don't often get those in a set of boat plans. So here we have the profile, we have the body plan, and we have the half bretts. Half bretts meaning the shape of the boat from the central line out. And this portion is the half bretts. This portion is called the diagonals and they represent what would happen if you slice the boat along these lines right here. These long ones running this way, those are the water lines. They represent slicing the boat along these horizontal planes right here. And then up here you'll see these lines that say butt. So those are referred to as buttock lines and they represent slicing the boat along these vertical planes right here. So the combination of all these different lines or planes give you a good representation of the shape of that boat. And by having all those different lines it allows us to very accurately recreate this drawing full size. Now down here this is the really important part. This is the table of offsets and it's really just a set of coordinates that relate to this grid system that we've been given. The grid system is basically a baseline, a centerline, and this is also a centerline here. And so from those three different reference points, and there's really just two of them, we can recreate that boat very accurately. And so the designer has taken the time to very carefully try and measure off each of these lines and list them on this piece of paper. And that's important because from the original drawing to this copy we have there can always be little changes due to the camera, due to the paper, even swelling and shrinking. There could be all kinds of reasons that you couldn't really get an accurate recreation of those numbers yourself. Now over here this is really just the stem profile and so that allows us to make a mold for the stem over there. Now another important thing to note is over here there's usually a set of instructions and it'll tell you what these numbers represent. So in this case it tells us that these numbers represent feet, inches, and eighths of an inch, which is standard in a set of table of offsets. And more importantly it's to the outside of the smooth skin planking. So that means it's really to the outside surface of this boat. Now that's important because we need to create a set of molds that represent the inside surface of those planks. To do that we're going to do something called a mold reduction. This little piece of information also tells you how to set up your grid. It'll tell you how far apart these station lines are spaced. These are called, these refer to stations. It'll tell you how far apart the water lines are and the buttock lines are and they'll usually tell you how far up from the baseline the diagonals originate and how far out they go and so you can create this grid accurately. Now my job is to redraw or what we call loft that set of lines full size in order to build the boat. So what I'm after is basically this and this is again this is the body plan, difference being that I've done the mold reductions on this. Now to do those mold reductions I make this thing which is called a bevel board and what that does is it allows me to set this bevel board on this drawing. If I lay it across these molds or this body plan at any particular point I can determine by reading from one point to the next point what the bevel is between these stations. And I need to know that because as the planking wraps around the boat its thickness relative to these station lines changes. The plank doesn't change thickness but because of the skewed angle of the planking to the station lines it appears at different thicknesses and so we need to try and figure out what that is. It's not as critical in a very small boat but in a much larger boat it can make quite a bit of difference. So this little line I have drawn on here this represents the plank thickness and so the more skewed my angle gets or thicker the plank is compared to down here. Now the other thing we get off of the lofting is this. So this is my drawing for my stem mold so I've recreated the stem here and I've done a few cross sections through the stem and that allows me to pre-bevel the stem fairly accurately. That's something that's hard to do on the boat. I always leave a little extra to tune up once the stem is fastened onto the mold but it's nice to be able to get them away at the bench. Now if I was given no other information, this table of offsets, this information that describes the shape of the stem, and this information that describes how to lay out my grid, I could build this boat without seeing any of the other information. I wouldn't have to see a picture of it whatsoever because this will tell me what that looks like. That's one of the really cool things about lofting. So one more item on here and that is over here we have plank widths taken at the outside of the plank it says and that's kind of nice. That allows me to try and reproduce these plank lines on my finished boat. Now it does say here that these lines are not fared so you have to take these with a grain of salt and that means when we set up our mold we can use these numbers to help get the process of lining off started but we shouldn't adhere to them as gospel. We should try and tweak those lines until they look nice. Now this is a lot of information and that's what you're paying for. I never shy away from buying a good quality set of drawings. I don't believe in searching out free drawings necessarily just for the sake of economy because there's no saying that you're going to get good quality detail off of them and it could make your building process a lot more difficult. $75 for a set of drawings or $100 I think is well worth it in the scheme of things and as you get into larger and larger boats the price goes up. If the drawings are coming from a good well-known designer I've spent three four five hundred dollars on a set of drawings and you know what I guarantee it's always been worth it. I've never regretted that expense. So there's a basic rundown on the kinds of things you might find on a set of boat plans. Now this set of plans might differ from other ones that you might find. For instance if you're going to build a sailboat it's going to have a sheet that's dedicated to the sail plan. I made a separate video about reading plans like that right here. Now if you're interested in lofting and I highly encourage you to try it I made a separate set of videos that walk you through the very basics of lofting over here in my Bushi Dari series. Alright that's it for today folks we'll catch you later.