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| The Enterprise, Hull #99 |
I will be telling you how I built the masts and at times may suggest other ways, giving you the choice. You are the one who will be building your mast, therefore you are the one who makes the decisions about how it is to be done. I do not consider myself to be "the authority" on this and I recommend that you also find some books on the subject. I highly recommend Robert M. Stewart's "Boat Building Manual" and Howard I Chapelle's "Boat Building." In Stewart, look for "spars, wood" and in Chapelle for "masts/hollow" in their indexes. If you feel you can't make the masts and must hire out the job, it is a good idea to know as much as possible about the process to be comfortable about the work being done for you.
The two masts are built essentially the same. Four full length-plus staves are prepared, rabbets are made in the forward and after staves (top and bottom while in the building stage), solid blocking installed on the after stave, interior waterproofing applied, required wiring installed, and the whole is glued together. In a nutshell that's it. You realize, of course, that there are several details to which attention needs to be applied. The first is the staves.
THE STAVES are of vertical grain (quarter sawn) Sitka spruce, 1-1/8" thick. Other "authorities" (one is Reuel B. Parker in his "The New Cold-Molded Boatbuilding," chapter 30, Masts and Booms, page 218) recommend Douglas fir over spruce. the fore and aft staves are 5-1/2" wide, the side staves are 5-1/2" wide for the main and 3-1/2" wide for the mizzen. All staves are made a little longer (1 foot or more) than the finished mast, basically because you may need to juggle the pieces so as to keep scarfs away from each other, and the mast tenon will be cut after the mast is glued up.
Before you order mast materials chose the type of rabbet you want to use. The type chosen may change the needed width or thickness of the side staves. We used what I called "plywood rabbets." This allows for the spruce to be milled to the dimensions given above. The "rabbets" are made by gluing 1/4" plywood on the fore and aft staves to form the rabbets. Brads 3/4" long were used to mechanically hold the plywood until the glue dries. The plywood is cut to a width equal to the width of the stave minus two times the thickness of the side staves. In my work I found that if the plywood was a little narrower than called for by the formula it would leave a little overhang of the fore and aft (top and bottom as built) staves. This made for much less sanding than would be needed if the side staves were full of (that is, sticking above) the fore and aft staves. The plywood rabbets are made and glued to the spruce after the four staves are assembled (which is after all four staves are tapered and assembled full length). You do not have to use this plywood rabbet. The rabbet can be cut out of the fore and aft staves. The thickness of these two staves must be increased the same amount as the depth of the rabbets or the width of the side staves must be increased the same amount.
You now know what type of rabbet you will be using, so you can now find a source of wood for the staves. The main mast uses the same widths for all four staves: 5 1/2". This gives the designed 5-1/2" X 7-3/4" sectional size of the main. The mizzen mast is smaller and uses 3-1/2" side staves to make the 5-1/2" X 5-/3/4" designed size. For the two masts you need to make six staves 5-1/2" wide and two staves 3-1/2" wide.
NOTES ON GLUING THE SCARF JOINTS: It may be thought that you should line up the boards of the full length of the mast being scarfed together when gluing the joint. Not all the boards are truly straight even though they are milled to size, so don't even try using mechanical means to hold the boards straight to each other at this point. Just make sure each edge at the joint is lined up properly. Natural curves are straightened during the mast glue up. The mast press has two true surfaces with a 90 degree common corner. Pressing or clamping to the corner straightens things out. During glue up of the scarfs put in a couple of brads to prevent slipping. I put the brads along the length, not the width, of the joint thinking the further apart they are the better their holding power.
CAUTION--Because the upper eight feet of both masts are tapered, all of the upper pieces should be at least eight feet long plus the length of the scarf, but keep their lengths different enough to separate the joints properly. I tapered these four pieces of each mast before the scarf glue-up because I used a bench shaper with a 3/8" plywood pattern to do the tapering. Do the tapering before the pieces are scarfed. Bear in mind the side pieces traditionally have scarfs opposite each other so that the tops of the joints are inside the mast.
OR, FORGET THE CAUTION: If you have the ability to do the tapering on the glued up staves (they will be at least 40 feet long) go ahead and glue up without figuring which piece will go where. The top and bottom (when on the mast press) pieces can be scarfed and glued and tapered before you even think about where they will go. If you have these two stacked and the glue lines of the joints are similarly inclined, all you have to do is turn one over. It's different with the side pieces because their taper is only on the top edge.
TAPERING: The fore and aft pieces (when vertical, being the top and bottom pieces in the press) taper both edges toward the center, and the side pieces taper only on the top (forward) edge toward the bottom (after, or back) edge. Make tapering patterns of 3/8th plywood, eight feet long. The top and bottom pieces of both masts are tapered the same, so one pattern will do. There is a two inch difference between the widths of the side straves of the main and mizzen, so the curves will be different, necessitating two patterns, one for each mast. Using a router with the proper bit and the patterns you now can easily cut the tapers. Place the pattern in position and scribe a line along its edge or edges. Remove the pattern and saw most of the excess wood off. Replace the pattern, and holding it with a few c-clamps (moving them as needed) or with some brads or small nails, trim the wood to the edge of the patterns.
You now have four staves almost ready to put together, but not quite: don't forget the rabbets. They have already been discussed, but a few notes should be mentioned. Keep all glue off the mating surfaces where glue will be applied on final assembly. To aid in this, set your combination square to 1-5/32" and scribe a line that distance from both edges. Keep all glue well inside the two pencil marks. After you glue up the plywood keep an eye on it for squeeze-out. Clean off the glue before it sets too much or you may find it harder to clean off when it sets up solidly.
Now, are you ready for assembly? No, not yet. Two more operations must be completed. SOLID BLOCKING must be prepared.
SOLID BLOCKING is placed in masts for specific reasons. The basic reason is strength. In a back-handed sort of way, the real reason is to give you a hollow mast (as hollow as it can be considering some places are solid). so, here's my ideas on placement of the blocks. The head and foot blocking closes the ends (which makes a hollow mast out of a box tube), provides a solid tenon to hold the weight and prevent mast twist (pivoting) at the lower end and strength for the head fitting and halyard sheave slot at the upper (head) end. The interior blocks give strength, basically compression resistance, to places of high stress. where are these high stress places? At the partners, shroud and stay tangs, and the spreaders.
Each mast has different needs. The head blocking is about the same in main and mizzen: a solid block with nothing fancy. The foot blocks are different. Both have a water drain that is common with all blocks except the head blocks. The mizzen foot block is just that, and has no other purpose. The next block in the mizzen is a combination block: it serves as the partner block (at the dog house top) and backing for the mizzen boom and possible (this is still being researched and may prove inaccurate) "mule" tang stresses (see the picture "Mule"). The lower block in the main mast serves as the foot block, partner block and backing for the main boom. As I remember it is about 12 feet long (not sure of its length). Other blocks are in both masts and serve as backing for the lower shroud tangs (both masts) and spreaders (main only), and the forestay tang (main only). I think there were four blocks in the mizzen and five in the main. ((We need verification on the number of blocks in the main mast, the length of each block and their heights up the mast, measured from the foot (top of the tenon) to the bottom of each block. Recent (October 2014) research has found that there are five blocks in the mizzen mast and we now have the lengths of the blocks and their position inside the mast, so we only need this information on the main mast.))
The blocking is first glued to the bottom (after) stave. These can be built up from Sitka spruce or Douglas fir lumber or from a single piece of timber. We used solid fir back in the last of the old days. The thing to consider is the advisability of making the blocking while you cut the plywood for the rabbets. Start on the blocking first, jointing the bottom and an adjacent side (to square the one surface to the other) of all your solid blocking. Now set your fence to the width of the plywood strips for the rabbets and saw out all you need (you'll need 80 feet for the mizzen and 100 feet for the main). The width of the plywood strips and the blocking is one and the same. So, crank the blade up to its height (you made sure the blade was square to the saw table surface before you sawed the plywood, didn't you?) and cut out the blocks. The height is to be the distance between the two plywood rabbet pieces in the assembled mast. We put a 10° to 15° bevel on the upper end of the blocks (except the ones for the heads) and half inch wide by three quarters inch deep groove centered on the forward face of the blocks to drain any condensation or intruding water. (PS: The drain could be on the after face of the blocking but remember the slope of the top of the block must be toward the drain and the drain slot must be waterproofed [including that part of the plywood rabbet that makes the slot a tube] before fastening the block to the strake.) This drain tube goes all the way to the bottom of the masts and the water goes into the bilge (and it (the drain tube) should be well waterproofed along with the tops of the blocks). It is instructive to see how Robert Stewart's book pictures and describes the blocking. It requires longer blocking but there is much to be said for it.
Those are the details, most of them anyway. Now, for the plan of construction, the how of how to do it.
1. Choose your rabbet type: The rabbet sets the outside width dimensions by maintaining the spread of the side staves during glueup. That will set the size of the spruce you'll need.
Note in the drawing that if you do not use the "plywood" rabbet you will need to purchase enough 1-3/8" thick spruce for the top and bottom staves. It would be simpler to have just the one size to build the masts. There are two things on which to base your decision: the handiness of one size and the comparative cost of a quarter inch of spruce 5-1/2" x 80' (for the mizzen, plus 100' for the main) and the same length of plywood at 3-3/8" wide. My guess is that the plywood is cheaper--but I've been proved wrong before.
2. PURCHASE YOUR LUMBER, remembering that the main is four lengths of 5-1/2" wide material and the mizzen is two of 5-1/2" and two of 3-1/2" widths. Also order what you want for the solid blocking. Decide first about using Stewart's recommended type of blocking (with what we called "squid cuts" on the ends, which uses more material. The drawing below, from Stewart, shows many interesting things concerning mast and spar building, including the squid cut. Note in the mast building jig at the bottom of the drawing the squid cut seems to be recommended only for the bottom block; but note other details for blocking. Read the book, it is worth its cost and the time to read it!
3. STAVES:
In the "details" section above we mentioned putting the staves together with scarf joints. The picture below gives my details of constructing the jig in which to plane the scarf in the ends of the spruce pieces.
Use a reasonably large diameter pipe for wedging against and a low angle wedge with the long grain toward the pipe (the grain parallels the face against the pipe). It would be best to cut the point off the wedge so you can place a block against it and hammer the wedge back to release the stave. Note that the bottom piece (A in the diagram) extends out beyond the end of the stave so that it supports the stave as it is being cut. We used a large, heavy electric plane (we called it the Terrible Termite) that was 6 or 8 inches wide and had square sectioned bars about 1/2" or 5/8" square on each end of the plane that rode on the side pieces of the jig. The scarves can be hand planned with a plane that has a body long enough to span the sides while at a decent planning angle. You can start with the stave sticking out the end of the jig as shown on the drawing or start with the stave held back so as to have just a small bit to plan off, then keep moving the stave further ahead to plane off more (but this sounds like it requires a lot more work).
4. GLUING THE SCARPHED PIECES TOGETHER, FORMING THE STAVES: Even with all the preparations this is the point at which mast building begins. This step will produce the four staves of each mast that are the four sides of the box, long and skinny though it be. Let's look at it:
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This drawing is without scale so only gives an indication of what is done. We used steel plates to make the clamps, which were about 3/4" thick. Ten 1/2" bolts were use. The length of the plates is at least 2" longer than the scarf so as to overlap the ends of the joint.
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5. MAKING THE STAVES: It is unlikely you can get lumber 40 to 52 or so feet long, but get the longest you can. Longer pieces make for fewer scarf joints needed to make the length you need. We used a 1:12 scarf angle, When scarfing, make sure the stave is tight against the bottom of the scarfing jig in which the scarfs are made. I sometimes needed to lift (wedge up) the loose end of the stave to make sure the end being cut was tight down on the jig. Scarf the ends on opposite sides of each piece so that all the scarf angles run the same way. Though there is no law that makes it illegal, tradition calls for the top end of the scarf joint (on the mast when vertical) to be on the inside of the mast. Keep this in mind when making the stave full length, and bear in mind how the scarf joints run when making the rabbets and when assembling the left and right side pieces.
I scarfed enough stave material for one mast at a time and stacked the pieces four deep for gluing. The clamps we used were steel plates about 3/4 inch thick, wide enough for the bolts to be clear of the wood using five bolts to each side. The glue will squeeze out, so put enough wax paper under each layer to prevent gluing the pieces together. Use the glue of your choice, but use its directions, too. We used urea formaldehyde (Weldwood) glue, but that was the best available at the time.
The joints should be staggered in the finished mast. If your pieces are all twenty two or more feet long you can build the mizzen with only one stack of joints. If you need more than two try to keep the pieces between the two end pieces the same length. That will allow you to glue up all four staves at once, saving considerable time. In clamping the joints (tightening the bolts) apply the right amount of pressure according to the glue manufacturer's instruction. The glue we used needed flat surfaces and a lot of pressure. Some modern glues do not work well with that kind of pressure. So if you are not experienced with the glue you are using try gluing up a few samples to "get the feel of it" before you start with the pieces you'll be using to make the masts. Numbering the ten bolts from 1 to 5 (far side) and 6 to 10 (near side) I finger tightened all ten bolts, starting in the middle (3 and 8), then worked both ways to the ends, 4-7, 2-9, 1-10 and 5-6. Next I re-tighten with finger power and then using the by now familiar pattern I tighten with open end wrench on the bottom and a box wrench on top, taking up on each one a little at a time until it's "just right." Keep the squeeze out glue cleaned out as you go and after you're done. After the glue sets up (I always waited till the next day) and you take the bolts out and separate the layers, you can dress down the last of the glue on the sides of the joints keeping the side surfaces straight and square, making them ready to become a mast.
6. PLYWOOD RABBET and the SOLID BLOCKING: Now we are really getting into mast building. If you have decided to build out of 1-3/8" thick stuff the top and bottom (fore and aft) staves you must cut in the rabbets cut them out to 1/4" deep and 1-1/8" wide (the thickness of the side staves). If you have decided for the easy route and are going to install the "plywood" rabbets, that will be next.
7. THE "PLYWOOD RABBET": This is nothing but a layer of 1/4" plywood on the inner surface on the forward and after strakes of the standing mast (top and bottom strakes when under construction). Eight foot long strips of the plywood, 3-3/16" wide, are sawed out, cutting enough to equal twice the length of each mast being built. The top eight feet of the masts are tapered and the plywood must match that change in width. A pencil line scribed 1-5/32" from each edge of the strake which is a guide for applying glue and setting the plywood on center of the strakes. The information here is echoed in the ninth paragraph from the top of this article.
I used to put the plywood rabbet on the full length of the staves. Recently it has been mentioned that the plywood is a good water catcher and therefore a good source of rot (not ever considered "back then"), so it might be a good idea to not have the plywood in the areas of the solid blocking. That would remove the plywood from the the head and foot of the masts, protecting the plywood from possible water intrusion at the ends of the masts. This would require the solid blocking to need a half inch more depth in the top to bottom (while building the masts) measurement to replace the plywood. Remember the need to set up your table saw once (and do not change that setting) and saw out the widths of the plywood rabbets and the solid blocking. That will keep the entire mast consistent in width.
more info may be coming--today's date: 8/31/16
The drawing above is a 'folded over' to get it on this page large enough to read. The original of this has been cut in half at about the 18' mark (the numbers across the top). The key colors are tan, for the spruce; red, for the wire way and drain tube; dark brown, for the solid blocking (the white numbers within are the length of that block); and yellow, the quarter inch plywood "rabbet."
This drawing, above, shows the basic construction of the masts. The differences between the two are the width of the side staves, the number and positions of the solid blocking, and the wiring that must be added in the early stages of building.
The masts are built up on the after stave.
I scarfed enough stave material for one mast at a time and stacked the pieces four deep for gluing. The clamps we used were steel plates about 3/4 inch thick, wide enough for the bolts to be clear of the wood using five bolts to each side. The glue will squeeze out, so put enough wax paper under each layer to prevent gluing the pieces together. Use the glue of your choice, but use its directions, too. We used urea formaldehyde (Weldwood) glue, but that was the best available at the time.
The joints should be staggered in the finished mast. If your pieces are all twenty two or more feet long you can build the mizzen with only one stack of joints. If you need more than two try to keep the pieces between the two end pieces the same length. That will allow you to glue up all four staves at once, saving considerable time. In clamping the joints (tightening the bolts) apply the right amount of pressure according to the glue manufacturer's instruction. The glue we used needed flat surfaces and a lot of pressure. Some modern glues do not work well with that kind of pressure. So if you are not experienced with the glue you are using try gluing up a few samples to "get the feel of it" before you start with the pieces you'll be using to make the masts. Numbering the ten bolts from 1 to 5 (far side) and 6 to 10 (near side) I finger tightened all ten bolts, starting in the middle (3 and 8), then worked both ways to the ends, 4-7, 2-9, 1-10 and 5-6. Next I re-tighten with finger power and then using the by now familiar pattern I tighten with open end wrench on the bottom and a box wrench on top, taking up on each one a little at a time until it's "just right." Keep the squeeze out glue cleaned out as you go and after you're done. After the glue sets up (I always waited till the next day) and you take the bolts out and separate the layers, you can dress down the last of the glue on the sides of the joints keeping the side surfaces straight and square, making them ready to become a mast.
6. PLYWOOD RABBET and the SOLID BLOCKING: Now we are really getting into mast building. If you have decided to build out of 1-3/8" thick stuff the top and bottom (fore and aft) staves you must cut in the rabbets cut them out to 1/4" deep and 1-1/8" wide (the thickness of the side staves). If you have decided for the easy route and are going to install the "plywood" rabbets, that will be next.
7. THE "PLYWOOD RABBET": This is nothing but a layer of 1/4" plywood on the inner surface on the forward and after strakes of the standing mast (top and bottom strakes when under construction). Eight foot long strips of the plywood, 3-3/16" wide, are sawed out, cutting enough to equal twice the length of each mast being built. The top eight feet of the masts are tapered and the plywood must match that change in width. A pencil line scribed 1-5/32" from each edge of the strake which is a guide for applying glue and setting the plywood on center of the strakes. The information here is echoed in the ninth paragraph from the top of this article.
I used to put the plywood rabbet on the full length of the staves. Recently it has been mentioned that the plywood is a good water catcher and therefore a good source of rot (not ever considered "back then"), so it might be a good idea to not have the plywood in the areas of the solid blocking. That would remove the plywood from the the head and foot of the masts, protecting the plywood from possible water intrusion at the ends of the masts. This would require the solid blocking to need a half inch more depth in the top to bottom (while building the masts) measurement to replace the plywood. Remember the need to set up your table saw once (and do not change that setting) and saw out the widths of the plywood rabbets and the solid blocking. That will keep the entire mast consistent in width.
more info may be coming--today's date: 8/31/16
The drawing below is of the mizzen mast, based on the blue prints.
I still desperately need blocking measurements for the main mast!
If you are repairing a main mast and need to open it up to the point of exposing the bottom of any of the blocks, please get the distance from the bottom of the block to the bottom of the tendon, as shown in this drawing. If you are replacing the main mast and scraping the old one, please disassemble it to the point exposing all the blocks while maintaining the integrity of the back/bottom stave and take the measurements. You can skip the end blocking; they obviously are at the ends of the mast and easily placed.
The drawing above is a 'folded over' to get it on this page large enough to read. The original of this has been cut in half at about the 18' mark (the numbers across the top). The key colors are tan, for the spruce; red, for the wire way and drain tube; dark brown, for the solid blocking (the white numbers within are the length of that block); and yellow, the quarter inch plywood "rabbet."
The masts are built up on the after stave.
