Building the Catalina Wherry - Part 5 - Lofting Bevels

Welcome back to Nomad Boatbuilding. I'm Mark Rutten and we're building the Catalina Wherry. Today we're going to get into some lofting. Now just a reminder that lofting is a process of taking a scale drawing of a boat and using a set of coordinates that we call the table of offsets, redrawing it full scale on the loft floor. The loft floor is literally that. It's either a wooden floor of a boat building shop or in my case I build a little platform in order to do this work on top of. Now I'm not going to cover the entire process of lofting because it is both lengthy and a bit tedious and very very difficult to shoot. So what I am going to do is show you just a few aspects of it that I think people struggle to understand. Now part of the footage here was taken from a live stream I did on Instagram and that's why you'll see me looking off in some oddball direction. I'm looking at my phone rather than the camera. So with that said sit back and relax and let's dig into a little bit about lofting. Yesterday I finished figuring out my mold reductions for the boat here and I've done it on my Mylar. So rather than do that live because it's a bit lengthy and boring and hard to show, I'm going to talk about the fundamentals behind doing that and how it works. So when we build a boat and we want to make molds for it we want to reduce the dimensions of those molds by the thickness of the planking and some people deal with that right off the bat by lofting to the inside of their planking surfaces and I've done that but I hate doing it because I get really screwed up when you get towards the the stem especially and around the transom trying to figure out how to lock to the inside not knowing exactly how the outside is going to look. My brain can't go there. I much rather just sort of think about the boat as the outside skin and then worry about how to build everything inside of it. So I locked that way and as a result I need to figure out the mold reductions in order to make that happen which is the payoff or it's the penalty. I'm not sure which one it is. If you've got a long skinny boat like a canoe or something you can pretty much just get away with reducing the molds by the thickness of the planking however the more shapely your boat is the more angle between the different stations the more the relative thickness of those things relative to the cross-section of the boat that dimension changes if you can imagine if you can imagine you've got a cylinder here we'll pretend this is a boat well the stations you know towards the middle there's very little difference in bevel between them but as you get towards the ends as that cross-section moves towards the ends it gets steeper and steeper and steeper and how thick that planking is relative to that cross-section changes so we need to figure out how to do that here's the thing that really helps to understand what's going on with bevels so we've got a body plan here so these are the the sections of our boat cross sections of our boat sacked on top of each other and working from this we can figure out what the bevels are and here's the best illustration I can come up with so I've got one section here and another section right here so if I take this square and I put it up against one of the section lines and then I go up the length of the square the station spacing so in this case it's two feet then add a straight edge to it and then we take that straight edge and we touch the next station and we're going square to the face of that station right here this is the angle the difference in angle between one station and the next right so I could take like a bevel gauge come on did I work one-handed again okay I want to open up there so so there you go so that angle right there is the difference between one station to the next station that's what we're trying to figure out but and you could certainly do it like this using a square and a pointer but that's kind of awkward to do as you can imagine you just saw me fumbling around trying to work one-handed and I thought about actually making a jig that does exactly this you could do it and as we go to the next station here that becomes steeper towards the midship of the boat there's very little angle as you can see it's getting closer and closer to plump as you would expect okay so how do we do this in a simpler way without farting around with this big construction here and be able to visualize this is the key to understanding how this next little step works so if you can visualize that and I could not visualize that for the longest time until I found a book that actually illustrated that very thing I just showed you this book by Ed Monk and you can see right there is the illustration of that particular little example with that in mind I'm going to direct you to another book and well I like Howard Chappelle for almost all things boat building related uh the Gujon Brothers boat building manual here actually has got one of the best uh lofting descriptions in there so the next thing we think have to think about is this little protractor so we call this a master bevel board and we would make one of these full size and so what I want you to look at here is this little this little stick right here so we call this a bevel board I make mine out of mylar they suggest you make it out of a piece of wood that is cut to the same thickness as the thing that you want to reduce so you're planking or maybe it's planking and battens and in the case of this boat I am reducing these lines by both the planking thickness which is this little quarter inch square here plus I'm going to be using a battens on my mold spanning like marking all the plank lines and they're going to stay on the mold through the planking process so they're 5 8 square so I got 7 8 of an inch that I need to reduce my molds I could have just reduced them all by 7 8 across the board because it's not a real beamy boat but for the hell of it I like to go through this process if for no other reason just to remind myself how to go through it because it's so easy to forget how to do the little bits and pieces of it so this is a master bevel board and the whole idea behind this is we use this as a tool to figure out what the various bevels are on our boat and it's really just a very large protractor it's not something you can buy you've got to make it and there's a system of layout for making it which we're not going to get into right now the key to using it is laying off your station spacing on the master bevel board so we got a 24 inch spacing on this boat put a mark there at 24 inches and then it's just a of drawing a perpendicular up that line and these gradations of course go from zero up through 45 and a little bit beyond but we don't usually need to use them all that high it all depends on the boat you're building of course and so now we take a piece of mylar and you could do this with wood too if you wanted to I mean I have a a wooden master bevel board that I made back in boat building school that we use just as like a protractor to pick up bevels off of things and record them so this is kind of like that however we use this a little bit differently and use this in the locking process so with that done now I just have to spend a bunch of time drawing a whole lot of lines and we're basically tracing all these gradations and I like to use a different color at the five degree marks because I just find it much easier to figure out where I'm at quickly I've popped a nail in here at the center point or the fulcrum of this protractor now we're at 45 I'm not going to bother going any higher than that because I'm pretty positive I won't need it okay and now the next thing we do is you just fill in the rest of the gradations again I'll just switch to another color and use blue for these ones and I mean it should be understood which edge it is you've set your protractor at because that's the edge you're going to work off of I made this about three inches wide but that's just because it's a convenient width of material to use in terms of the piece of mylar but the width that we really are concerned about is the thickness of planking or the thickness of frames or the combination of the two in this case I'm going to be laying off the thickness of my planking plus the thickness of some battens that I'll be applying to my molds in order to line out my planks so I'm going to be using a battened mold for this project what that means is that we apply a little square batten at every plank landing on both sides of the boat and those battens both support the edge of our planking stock because it's light plywood so it has a limited range of stiffness and while we want it to be able to wrap around the boat what we don't want is we don't want it sort of buckling in ungainly ways and plywood is not always super cooperative that way I mean sometimes it has a natural bow to it in one direction or the other that can be fighting with you or as you're planning it may want to sag in between the molds so in order to combat that you got to have more molds which takes a bunch of extra effort to build so the battens is kind of a simple solution to that problem and it has the added benefit of giving us a method of trimming some of our planks to shape on one side of the planking as we after we've hung it so there's a bit of a time savings there and this little device doesn't need to be massively accurate but this will be fine so we'll just give ourselves some numbers and I'll write down what this is from so this is the Catalina Wary okay so the next thing we need to do is we have one edge that is our primary edge now we need to reduce our planking and mold thickness so or in this case it's combat thickness so we're going to do quarter inch planking plus I was thinking I'm going to do a 5 8 bat that's a a strong plank lap usually plank laps are about twice the thickness of your planking half inches feels a little bit skimpy maybe from the top here now my quarter and then mark my weights so now we connect those dots so what this is going to do is it's going to tell us what the true width of this combination of planking and batten is at any particular angle along the scale so while it's 5 8 plus a quarter inch at this end which makes 7 8 of an inch by the time you get up here towards 45 degrees the combination of those two comes up to an inch and a quarter so that's a pretty big jump so that's important to know because if we want to reduce our planking accordingly so that we keep the same finished lines we need to know how much that changes over the length of the boat now one thing I could do if I weren't using the battens I would probably be inclined to just go ahead and just reduce all the molds by one quarter inch and call it good but I'm not going to do that because I'm using the battens I want to make sure that I reduce it a bit more now the other flat side of the coin is you could just increase the size of your boat a little bit by adding battens to the outside of those finished lines of course you're going to have to increase the width of your transom to compensate and you got to think about the stem so the stem width would have to increase to compensate for that too and in order to get it to finish out at a nice fine point it means that you probably need to put in a heavier cut water or you need to do something to sort of compensate for that extra thickness that is our bevel board so I'll trim this down so it's a bit shorter we'll put away the master bevel board here so there's two ways you can you can lay these out one of them is laying them out from the the fulcrum of that protractor out the station spacing distance which I've done with this one the other method is you go twice the spacing station distance and the only reason to go twice is because you can get a slightly better relative angle on the thing that you're measuring so the way you use it is you basically take your little stick here and you lay it on your lofting you put the zero degree end of it on one station and then you look over to the next station and you see where the angle crosses it and of course you've marked out the numbers here and so for instance from my station three to station two at this point I get what looks like roughly 10 11 12 say 13 degrees that's the bevel between those two stations using the other method the longer the double the station spacing I would go from station four to station two read that dimension and that actually tells me the slightly more accurate dimension for station three so in this case it comes out at like 10 degrees so the difference is that when you use the single station spacing I'm getting the distance between one station the next but when I use the double station spacing I'm getting the sort of a mean or an average result between the three stations gives you a more accurate triangle let me try and clarify that a little bit better so here's some lines for the one section of a boat we'll just say the first method where we're measuring a bevel between one station and the next we create a triangle that looks like this so it's telling us what this angle is right here the other method is where we go with double the station spacing and it's giving us this angle here so you can see how while this is accurate to a certain degree this is giving us a better idea as to what this shape is relative to these two stations because we're trying to create a bevel that allows planking to lie across there and so for that reason using this double station spacing is slightly more accurate in some ways it doesn't give us as accurate an idea as to what this individual triangle is but this larger overall triangle is a little bit more accurate we can do it mathematically by measuring this angle and that angle and then figuring out what the mean is but this is just a fast simple way to get something that's close enough so what those bevel boards are doing is they're measuring in the case of the single station spacing they're measuring this distance right here and then telling us what the what this angle is between the two in the case of double station spacing it's measuring this distance right here and giving us what this angle is over here so you can see they're relatively similar i do use both methods and what i'll do is when i've got stations that are where i don't can't span three of them like station four here is my outer board station i don't have one further out to compare it to i'll use the single station spacing and where i can span three of them i will use the double station spacing there's a fudge factor involved because we're going to fare these things out once all is said and done so getting those angles a hundred percent perfect isn't a hundred percent necessary now why would you need the angles well if you're doing uh say sawn frames from these body stations instead of temporary molds you'd want those angles you want to know exactly what those angles are if you want to be able to apply heavy battens onto them and not have them just bearing on one corner of your mold then you want those angles as well i'm going to just do squared off edge molds it's going to be faster and easier and it's a pretty light boat and i'm not too worried about it but knowing those angles can be important if you have an application for cutting all those molds to those angles all the way through the length of them and we record those angles as we go this kind of bevel board is something that we make when we're in boat building school and we make it the same way we have that big master bevel board we lay a piece of stick across there and we draw a bunch of lines and i don't even remember what station spacing this one was done at it's a bit irrelevant what it's done at you do it whatever distance is convenient for the length of the board and of course the shorter the board the closer you've got to come to zero in order to fit the widest range of angles on woodpecker here has made a really nice little bevel board i don't i don't know that these are still available but they split the the angles from zero to 30 degrees on one side and then went from 30 to 45 or so or 55 on the other side and they've given you uh half degrees and quarter degrees in there in their markings so that's pretty nice i don't use this one as much as it's a bit heavier and bulkier but um but you know it's a great little tool and so in fact i don't even use these much at all because i don't really record angles myself very much recording numerical angles is something that works great when you're working in a team and you want to call out an angle for something to somebody else or you've got saws that are set up with retractors on them so you can reuse those angles numerically but i don't do that i tend to just sort of do it by eye or i bring my my my square over to the bandsaw and i set the bandsaw whatever the square is saying so i don't use that stuff as much i think it's important to explain how we use this bevel board for reductions so i've mentioned how to use it to determine what the angle is between one frame and the next but to do the reductions what we need to do is use these other lines that we've drawn on here the first line we've drawn on is the thickness of the planking and the second line we've drawn on is the thickness of the batten that i'm going to be putting over the molds so we want to reduce the molds by this combined thickness of batten and planking for instance right here on this mold we have angles of 15 16 degrees so we take our bevel board here and what we're essentially doing if i pick up this angle here say at 15 degrees take that dimension we carry it over here that's our reduction i don't use dividers to do this i use the bevel board itself i simply take this bevel board lay it on my mold wherever it might be the blue marks here put the 15 degree on intersection on there and i swing this line until it's perpendicular to the face of the mold up here it's 16 degrees so i go to the 16 i line it up there and i make sure this line again is perpendicular to the mold and where the edge of this bevel board crosses this line i've drawn that's perpendicular that's the reduction so you can see at this end of the scale the relative reduction is pretty straightforward or zero degrees come up to the 15 and we make a comparison and there's a little bit of a difference not a lot it's about six sixteenth of an inch perhaps but as you can see as you go higher and higher that gets greater and greater and if we're working on a very large boat this reduction might not be seven eighths of an inch collectively it might be an inch and a half or two inches if we're using heavy planking and big battens that wrap around the molds so rather than just reducing all these molds by seven eighths of an inch which i could do i like going through this process because it helps remind me how to do the process if i don't use it i will lose it now once you've got your molds figured out and your mold reductions done then you need to try and transfer those shapes to some finished wood now i do mylars because i find it convenient and i like having the mylar to do the assembly on top of but there's another method there's two other methods really one of them is just taking common nails and laying them flat along the board here i don't use this method because it just feels a bit crude to me but it's certainly doable so you would take common nails and you would stack them up and tap the heads into the lofting board so that they're all sort of smushed in there with one edge of those heads protruding and you take a piece of wood and you drop it on top and you stomp on it or tap on it with a hammer and you pull it off and there's all your markings and i should probably try that i don't know why i don't do it but i just never got into the habit of that the other method is using lifting sticks so with lifting sticks you would take a mold here you take a batten i'm going to just knock together this real quick it helps to call the same line mark so you have your bundle batten you wrap that around and then we have a there's not much to them they got a little bit of a shape to them and they've got to have a little throat here you can see this and it's got a little see that hole and a cut that's to allow these to spring open a little bit so you want a really nice snug fit onto your bundle batten and this these two don't have the greatest fit they're okay they're just they're just there but it could be a little tighter so you would take a whole series of these and i got i don't know a dozen of them or something like that and you set these up like every four or six inches along that batten okay then the other end has got a little hole in it so you take a common nail and you lock in that tail end there and once you've got a whole bunch of these it usually will hold the shape really well you can pull these battens out you can pull these nails away from your batten and then the whole thing is liftable i tried it on here i think my shape is just a little too small these sticks are fairly long and once i had it all sort of set up this whole thing could sort of shift a little too much and i had no way of sort of locking in the registration mark that i wanted and so i lost my confidence that i was going to get a good job out of it so i abandoned it and decided to just stick with my mylar system but in theory you would take a chunk of wood you know like so you lift up that whole little affair you slide that under okay and this is being held in shape and then you just mark that piece of wood out right there and that's your finished mold material you take that away and cut it on the bandsaw and that works great on a larger boat it's a really good way to go and in fact what you can do is you can take all your little sections of material that are going to be used in the final mold and you can stack them up with all the edges mitered together so that they fit nice and tightly and then drop that on there mark them all out cut them all out and then reassemble them later on i've certainly used it before but depends on the size of the boat maybe i should probably just make some smaller lifting sticks if i had lifting sticks that were like half this size probably that would have worked better as it was all of these guys were basically trying to crisscross right at the fulcrum here of these guys and it just it didn't work it didn't work at this scale uh so i finished doing the lofting on the catalina i was going to do sawn frames at first i decided i'm just going to plank this thing and worry about framing afterwards i'll probably put them in at every station i think now we'll laminate those frames up but then we'll fit them into the boat so they'll go square to the planking face they won't go square to say a uh the station spacing uh so they're not going to be like one's not going to be totally like parallel to the other they're going to be uh kicked over at a slight angle relative to the lay of the planking uh so we've got our patterns made for the stem and the stern knee we've got our pattern made for the stations and i've got our tramps and expansion done down there that's all ready to go i've got some nice materials for doing our molds we got this i found on my local uh hardwood supplier actually they had a whole pile of this um this knotty pine this tight knot pine 12 inch width a lot of it was dead clear or very close to it it's not pretty stuff though it's got all this blue stain in it so it's probably ponderosa pine judging by the size that's something we have a um so i'm gonna i'll be using that for our stations i've used it for the rib bands too although the bands are i was having a hard time getting the rib bands dead fair so there's a chance i might have to bite the bullet and buy some different material for those rib bands i cut a bunch out hopefully it works out okay i think it probably will anyhow so that's it for uh we will be back with some probably some mold making and some uh making some stems and knees and all that sort of stuff so ciao for now folks we'll catch you later