Boatbuilding Page

'Thought we'd try something new...We spend a lot of time fielding questions about boatbuilding topics, and we're glad to help out when we can, but a lot of the questions asked have already been answered in our books. What you'll find on this page has been excerpted from what has already been written down. Our initial topic involves getting out planking, specifically lining off and spiling. The information comes from the pages of Lapstrake Boatbuilding, Building Sunshine, and Building Lapstrake Canoes(direct quotes from the books are italicized).

In the future we may well cite magazine articles written for Wooden Boat, National Fisherman, and the old Small Boat Journal. Where this page differs from its printed counterpart is in its interactive capability. If something still baffles you, highlight it, and use the email link to forward it to us along with your question.

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Planking Overview

As in many learning situations, the task is easier if the person attempting the job has some insight into its attendant idiosyncrasies. Planking just isn't all that difficult, but it is demanding, and in some instances it can be tedious. What this all boils down to is that everyone contemplating construction of a traditionally planked boat must decide for himself whether or not he is truly willing to work to that end. To read and study is fine, and it has its place, but you must actually work at planking if you are to learn the process fully.

To plank a hull successfully, the planking procedure must be constantly in mind from the time the moulds are completed. Everything you touch from that time on will affect the planking job and its final appearance. Simply put, the whole operation can be reduced to: (1) cutting the rabbet, (2) setting up and fairing off the mould's, (3) lining off the hull, and, finally, (4) installing the planks themselves.

Planking can only begin after all fairing and lining off has been completed. Even before starting, you'll need clamps–at least enough to hold the plank to each mould and to bow and stern, and, ideally, enough lap clamps to place one wherever a frame will eventually cross that plank. For a 16 foot double ender with five moulds, that would call for seven planking clamps and fourteen lap clamps. Marks denoting frame positions are laid off on the keel or keelson–one at each mould or station and others divided up individually between, as the plan dictates. Planking is accomplished most readily if you fit and fasten one plank, spile to that plank to get the shape of the next, and then fit and fasten the mate to the one previously fastened. There are exceptions to this sequence (particularly when steaming is called for), but the rationale is that in this manner only one set of clamps is required (as noted above). The reason I suggest spiling as soon as the first plank is fastened is that the spiling batten also requires a full set of clamps to hold it in position.

One of the boats I normally build is a seven plank double ender (counting in pairs) whose first and second planks require steaming. Reducing the entire planking process to list form, the sequence is:

1. Spile and get out garboards/steam port
2. Fit and fasten port/spile for #2/steam starboard garboard
3. Fit and fasten starboard garboard/steam #2 port/spile for #3
4. Fit and fasten #2 port/steam #2 starboard/get out #3
5. Fit and fasten #2 starboard/fit and fasten #3 port/spile and get out #4
6. Fit and fasten #3 starboard/fit and fasten #4 port/spile and get out #5
7. Fit and fasten #4 starboard/fit and fasten #5 port/spile and get out #6
8. Fit and fasten #5 starboard/fit and fasten #6 port/spile and get out #7
9. Fit and fasten #6 starboard/fit and fasten #7 port
10.Fit and fasten #7 starboard





This is what expanded planks look like for a Matinicus Double Ender. The sheer strake is at the top and the garboard is at the bottom.





In general terms, each step on the above list corresponds to a day's work throughout the planking sequence. It really makes little difference whether you can complete each step in a day, but such is a typical schedule for a professional builder. Unfortunately, even with professionals, the planking stock does not always cooperate. Just when you find yourself approaching the traditional "one streak a day, clear 'round," you find that what looked so good in the rough has a three foot check right where the hood end was supposed to be. Such problems cannot be helped. A schedule makes little total sense, as speed is not of prime importance and should not even be strived for until you have the art of planking well in hand. My sole reason for introducing such a list here is to acquaint the reader with the common sequence of events when everything is going as it should.

Once the plank is clamped into position on the moulds and secured to the preceding plank (or keel) with lap clamps, start at the midship mould and fasten toward each end of the hull. If there is a discrepancy in the new plank, fastening in this way from the midship mould will halve the amount of hogging (edge setting) necessary to get the plank into position. To put that another way, if you start fastening forward and proceed all the way aft, any problems of plank shape will necessarily transfer (and possibly multiply) themselves throughout the entire length of the plank. In that sense, beginning fastening at one end is much like trying to lay rolled roofing–or any other rolled material–flat by starting at one end and proceeding to the other. It can be done, but the whole process would have been easier if the starting point had been in the middle.

It is not wise to remove all clamps as soon as the fastening is completed, particularly in the lower planks, where there is a great deal of shape at the hood ends. It should go without saying that, even following steaming, there is considerable strain at these places. The longer the plank remains clamped in position, the less the strain at the hood ends. The old builders I knew would say that the planks become "accustomed" to their new shape, and, as a matter of fact, they do. For whatever the precise reason, the internal strains decrease with time in position, until the point is reached when they cannot be removed and straightened fully without breaking. Because the strains do decrease with time, it is a good idea to give the planks a little extra time before allowing them to bear fully on their hood end fastenings. To do so, I leave a 4" "C" clamp in position so that its pad covers all the hood end fastenings of the new plank. It must be removed, of course, before the next plank can be installed on that side of the boat, but in the meantime it will serve as cheap insurance.

The other time to use a clamp as insurance against plank damage is when the hood ends are being fine fitted–fine fitting meaning those minor adjustments in dory lap bevel that must be made to make the planks fit together as they should. This fitting is not done until the midship sections are already fastened (otherwise, the plank could "creep," necessitating refitting). The "insurance" clamp, then, would be the last clamp left in position between the fastenings already finished and the hood end. It protects both the new and the previous planks at the already fastened lap, and also prevents unnecessary strains from being exerted on the lap fastenings.

Lining Off

Simply defined, lining off is the process with which you project the final plank layout onto the hull. Personally, I don't know of any two builders who use the same method; but as long as the planking job is good looking, it makes little difference.

Some builders employ one batten to denote the top of each plank and fasten them all to the moulds from bow to stern. The advantage of this method, obviously enough, is that before planking starts, you will have an idea of what the hull will look like when completed. The one striking disadvantage is that you are locked into a scheme of plank dimensions from the onset–if not physically, at least psychologically. I can't speak for other builders, but my own spiling and getting out of planks doesn't always give me the exact dimensions everywhere that I had initially intended.

I do the best I can to keep such situations from arising at all, but if it does happen, what then? Do I make it all up on the subsequent plank, or do I allow a little here and there until it is eventually made up and I am back to the original lining marks? Professional builders have been in such situations often enough that it doesn't present any particular problem, but for the novice, it can be quite another situation. My point is that it is not necessary to encumber yourself with such potential problems.

Before what I am saying is taken in the wrong light, I should say that I'm not advocating that anyone building a boat put forth less than his best effort. You would be foolish to do otherwise, as you are the one who ultimately will pay the penalty. The garboard that I am considering at the moment is a plank with considerable fore and aft twist, and it requires more work to fit properly than any other plank on the boat. To make it fit to the rabbet as well as to fixed lining marks can stir up ulcers.


Here is a properly lined off Lincolnville Salmon Wherry. Curious, isn't it, that even without understanding a thing about lining off, an onlooker instantly recognizes when the job has been done right. They don't know that plank widths match everywhere–and they don't care–what matters to them (and what should matter to the builder) is that she looks the way she should. When it comes to lining off, "if it looks right, it is right."


This general information is fine, I suppose, if all you are doing is reading because you are interested in traditional boats, but if you are about to start building and don't quite know how to handle the lining off, what you need most is specific information. You must have some point from which to start, so what I do is determine just where, ideally, I would like to have the top of the garboard land. At the same time, bear in mind that the whole planking job will go easier and look better if you allow the hood ends of the garboard to rise as high as possible. A narrow garboard is easier to fit, but one that is wider fore and aft will result in straighter subsequent planks and will thus make the remainder of the planking job easier. You can estimate plank widths at each station by dividing the distance from rabbet to sheer by the number of planks. Then use a lining batten to connect the heights determined for the top of the garboard to the stem and stern rabbets. In lapstrake, as opposed to carvel construction, planks are seldom equal in width at a station. In both construction methods, garboards are usually the widest planks on the hull, and a tuck has to be taken into consideration (it is better to run a narrow plank into a tuck because wider planks can crack upon application of fastening pressure).

Once the plank heights have been estimated, get on with the spiling and get out the garboards. Clamp them to the moulds and keel amidships, steam the hood ends (soaking process discussed under steaming), fit and fasten. If the upper edge of the garboard was fair on the bench, it will still be when fastened to the hull. This, finally, is the point at which I do the remaining lining off measuring from the top of the garboard.

And now for some words of caution with regard to the garboard. When in the process of checking and tuning the rabbet, the lining batten should not be fully trusted at the forefoot–it often indicates that more should be removed from that point than is necessary. Garboards that must be steamed are not flat, in cross section, once they are installed. The combination of bend and twist required in order for them to fit into the rabbet results in a cross section that is convex to the outboard surface. Because the lining batten is narrow and therefore requires little or no twist to land in the rabbet, it cannot fully determine or anticipate the characteristics of the garboard that is to follow. A little extra wood left at the bearding line can be trimmed off after the garboard is steamed, but in the meantime, it acts as insurance against removing stock unnecessarily and makes the difference between a garboard that will fit solidly in the rabbet and one that will not.

In any traditional model, the garboard calls for a very special piece of planking. It should be especially good quality, as it must take more twist than any other piece on the entire hull. It should be clear, at the ends at least, with no pin knots anywhere–pin knots will shear under a twisting strain. Cedar will take steam well, but if really good stock cannot be found, it is better to opt for oak. Oak will certainly give you one tough garboard, and it has the further advantage of taking steam better than any wood with which I work. I have never had to employ oak garboards, but I would do it without hesitation should the need arise.

As previously mentioned, divide the distance to the sheer by the number of remaining planks to be fitted. If still uncertain of your lining expertise, then by all means fit lining battens for the top of each plank. The distance from the top of the garboard has been divided equally without regard to lap width, so this will result in a sheer strake wider than the others by the width of the lap–and there are times when I even make adjustments to exceed that. On any hull with a pretty sheer, a widened and contrasting sheer strake will enhance the lines of the entire hull. Even if it is not to be finished in a contrasting color, there will be a guard installed along its upper edge, and that alone will serve to decrease the apparent width of the sheer strake.

In all lapstrake hulls, the final appearance is determined by both the run of the planks and their apparent equality in width; but if they are actually made equal, they will not appear so. The two places where this is particularly true are at the stem and stern rabbets. If you measure very carefully along the rabbet from the top of the garboard to the sheer, and divide that measurement equally, you will have narrow planks adjacent to the garboard with increasingly wider planks all the way to the sheer. The only time that this is not so is in plumb stemmed models–with these, the distance can be divided equally from garboard to sheer.

If you are good at it, you can lay off plank widths by eye; if you are not, do it mathematically. Probably the simplest method is to draw a line on the side of the stem from garboard to sheer. With a level, draw a second line from the peak of the garboard in the rabbet so that it intersects the first line and do the same thing at the sheer. Then measure the distance along the vertical line between the garboard and sheer marks, and divide that by the number of planks. Again, using a level, transfer your division marks from the line to the rabbet to yield plank heights. Since the "vertical" line is straight and therefore of equal slope from end to end, you will be making equal divisions from garboard to sheer; if you measure along the slope of a curved rabbet, you will not.

As is the case with every other boatbuilding operation I can think of, the process of lining off is, in large measure, intuitive. I know of only two concrete rules: (1) you can only understand the process fully by actually doing it, and (2) the ultimate appearance of the hull will reflect your accuracy. It can be a disturbing process for some, as there really is no visual progress being made, but the critics who point that out to you will be the same ones who will notice if she isn't lined off as well as she could be. For anyone with any pride in his workmanship, "good enough" isn't. Don't let yourself be rushed.

Spiling (spy' ling)

Spiling is the means by which a builder determines and measures the shape of any curved piece that must be fitted to a curved surface. It is accomplished by establishing a line of reference and by measuring from this line at regular intervals to where the new piece will fit.

Here's the crux of the spiling operation, positioning the spiling batten...

Spiling, like so many other things, is an operation that takes less time to accomplish than to explain. The keys to spiling planking lie with the spiling batten (a line of reference of sorts) and knowing precisely where to place it on the moulds. The batten itself must be a piece of clear stock (pine, spruce, mahogany) sufficiently flexible to be bent around the moulds, and sufficiently stiff not to hog, that is, to be susceptible to bending above or below the intended reference line. For traditional small craft of 12' to 18', I use a spruce spiling batten that is 7/16" x 3"–it will bend and twist as necessary, but only in one plane (toward or away from the moulds). If the batten is crowded up or down while being clamped in position, the spiling derived will result in a plank of the wrong shape either too crooked or too straight.

I clamp the batten to the midship moulds and work my way alternately fore and aft. Being certain that it lands fair (in this case, flat) to each mould, I push it up to each mould. Pressure of the batten on your hand should tell you if it is being crowded. To make certain that it hasn't been crowded (and this problem is usually encountered where there is a great deal of shape–curvature–to the hull), once it is fully clamped, loosen the clamp on the mould adjacent to the hood end. If it has been crowded, it will move. Clamp into the new position, release, and reclamp at the stem, and then try it once more to make certain. On the lower strakes where the planks will have to take a twist to be fastened, your batten will have to do the same. The same caution applies to spiling in a tuck. For purposes of instruction, I wish it were otherwise, but no amount of reading will tell you precisely what is meant by a batten "landing fair," or being "twisted slightly." You'll just have to keep these considerations in mind, and go to it.

Once in place, the batten itself becomes the line of reference. There is no actual line on it, but I designate it as such because it is the spiling batten on which both the intervals and the measurements are recorded. Each situation requires a somewhat different approach, but generally I use intervals equivalent to each station plus bow and stern, plus one fore and aft for the hood ends. I know from experience that changes occur between the end moulds and the ends of the planks, so add these additional reference points to compensate for those changes or, more specifically, to verify their presence.

The actual process of spiling comes with the laying off of measurements at the moulds. The traditional method employs dividers set to a constant width so that with the point on the lap mark (of the preceding plank), the pencil will scribe an arc on the batten. Once the spiling batten is removed from the hull and placed on the planking stock, you simply reverse the process: with the point of the dividers on the scribed arc, scribe an arc on the proposed plank. Repeat the procedure at each point along the batten, connect the points with a lining batten, and you will have the shape of the bottom edge of the next plank: you have the lower edge and the transferred station marks. From the lining marks on the moulds, transfer the heights to each station, and the bevels from the hood ends, and you have the outline of the new plank.

I use several methods to derive plank shape, and one that is worth remembering came from my work on large craft. There we used a spiling batten set at intervals with sections of 6" slotted mast track. Bolts passed through the batten and the track and were secured with wing nuts, so that they could be moved until they touched the plank edge to be joined, and then they were locked into position. When taken away from the hull and brought to the bench, the batten gave an instant view of the shape of the new plank. To lay off the new plank, the batten was tacked down and a lining batten was tacked against the points of the mast track so that the line could be drawn.

The small craft I build have plenty of shape fore and aft, so such a batten would not work–it would be too seriously weakened by the through fastenings to take the required bends. Happily, with modification, the method does work well. I use my usual 7/16 "x 3" batten, but instead of a mast track, I use additional smaller battens: these are about 1/4" x 3/4" and pointed at one end. To use this modification, place the spiling batten as previously described, and tack the smaller battens across it with 5/8" 18 gauge wire nails, so that these battens extend to the lap mark on the previous plank. The wire nails aren't large enough to weaken the batten seriously, but they are sufficient to secure the smaller battens in position. This arrangement has particular merit wherever you must spile for any plank with considerable shape, because when taken to the planking stock, it will show you instantly whether or not a plank is of sufficient size.

The photo at the right is of a Matinicus Double Ender with my spiling batten clamped in position with cross battens tacked on. The cross battens can be placed anywhere on the spiling batten. The sole requisite is that they be placed to identify and locate the lower edge of the new plank. Since the garboard is being measured here, the cross battens extend to the rabbet and to the leading edge of the stem (stem/cutwater construction). When there is a stem babbet, the cross battens extend to the rabbet.





Here's a drawing of the same part of the spiling operation.




It's the expanded plank shape that's wanted, ultimately, and to derive that, the spiling batten must be unclamped from the moulds and layed out on the planking stock. Here's the very same batten atop her mahogany planking. The ends of the cross battens clearly depict the shape of the hood end of the garboard plank–the broken line indicates the curvature of the stem.


And here's the next step. The spiling batten has been tacked to the planking stock and the long lining batten is placed against it so that the lower edge of the garboard can be faired in. The "1" on the cross batten indicated that that one was aligned with the first station–a vital piece of information, because the widths of the planks are measured fore and aft and at every station.


The third method used to derive the shape of a plank cannot properly be called spiling at all; but because it works, and works rapidly, it is worthy of consideration. You don't use a spiling batten at all. Pick out a plank that you feel will be large enough, and clamp it to the moulds. Then, trace along the top edge of the preceding plank and transfer height marks and hood end bevels directly–adding enough for the lap at the lower edge once it is removed from the boat. To help a bit more, mark along the midship mould while you are tracing, and the plank can be repositioned accurately fore and aft. It is a simple and direct method, but, obviously, it can be used only where it is possible to wrap a rough plank around the moulds. You will still have to know how to spile in order to fit the other planks.

A few final thoughts on spiling may help lend continuity to the whole process and possibly help avert a few problems. First, the spiling batten itself need not be straight. Very often one with an overall crown of six inches or so will lay to the moulds better than a straight one. Second, on small craft with plenty of shape, don't try overlapping two shorter spiling battens on the boat. It might sound like it would simplify the whole operation, but it will result in a distorted representation of the new plank. And third, don't try to second guess your own spiling batten. The batten will pick up subtleties of plank shape that you can't even see. The batten is the key to the whole process: trust it.

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