By David N. Goodchild
I was until recently, a crew member of the oldest and largest, wooden, squarerigged vessel still sailing on a regular basis in the world today. This is the Gazela of Philadelphia, previously known as the Gazela Primiero. She is a Barkentine of 177' overall, carrying a course, lower topsail, upper topsail and t'gallent on her foremast.
I was already thinking about TOAD in 1988 when we were down-rigging the vessel for the winter, and, while bringing down the yards, (some of which weighed over a ton), and carrying them with many willing hands to their storage yard, it occurred to me that a much lighter and even stronger spar could be built by cold-moulding veneers over an X-frame. Needless to say, the Philadelphia Ship Preservation Guild was not interested in replacing Gazela's spars with cold-moulded versions, and this idea would lay dormant until it came time to think carefully about the rig for TOAD.
I started out with the original idea. I laminated up a 24' long X-member from 1/4" plywood, with the idea of tapering it to the original boat's pole mast dimensions. I first ripped enough yellow pine to make a 24' long 1" square center core. This I dadoed to take the ply. I inserted the 1/4" ply pieces into this dado, cutting the mating ends at an angle to spread the stresses. I let it set up for a couple of days, and then was ready to taper it prior to laminating the veneers.
Here's where I started to become disenchanted with this method. Understand, I am not disenchanted with the method in general, and for another boat it should prove very useful, but I had subsequently decided that I wanted to be able to reef the topmast to reduce the overall mast height to just below 20' in order to pass under most bridges. In addition, it was clear that tapering the X-member was going to prove troublesome.
Something else was needed!
We had recently re-zoned the house to both improve the heating output and reduce oil consumption. In the process, we had re-routed some waste lines and there was some PVC left over and lying around.
Ah Hah!
If I used the PVC, I could reef the topmast by telescoping it down into the main mast! This I certainly couldn't do with the X-member n place, since it would be in the way. The mast wouldn't be tapered, but I could live with that, especially since I would be able to devise a simple tackle to lower the topmast down into the main mast easily and quickly. Besides, for gaff rig, a non-tapered mast would provide better bearing aloft for the gaff saddle.
I knew that Schedule 40 PVC was strong, since I had used it for the rudder tube, and in testing, it was very clear that the material was tough indeed. It was strong, but in long lengths it was as limp and whippy as a tired Casanova! How to fix that?
Referring back to the rudder tube construction in Part 5, (Building Toad Hall: A 12-Part Series in Messing About in Boats) it will be remembered that I steamed Maple veneer and glued it to the tube with contact cement, since this is the only glue which will adhere to PVC. I planned to use the same method to stiffen up the mast and spars. I knew that after I had laminated several layers of veneer over this first contact-cemented layer, and epoxied it all together I would have a very stiff and strong spar. And this is what developed.
I went to my plumbing supply store and bought a 10 foot length of 1 1/4" Schedule 40 PVC. When I got it home I set up the steam-box. The steam-box is needed, because the 1/16" veneer needs to be steamed first to achieve a close approximation to the diameter of the pipe in the small diameters used for the bowsprit, boom, etc. After it achieves this curve, it is then easy to coat with the cement or epoxy and roll it on to the PVC.
I had previously ordered 500 square feet (their minimum order) of 1/16" Douglas Fir veneers from the Dean Company in Gresham, Oregon. I could have used 1/16" Sitka Spruce, but they only offer short lengths of this and the 1/8" Spruce was a little too thick for easy bending to tight radii. The Fir veneers were beautiful! Absolutely clear with a fine grain and a Douglas Fir mast is certainly traditional!
Building the spars was easy.
It is first necessary to steam the veneers and for this I built a simple steam box out of plywood and 2 X 4's, some 3" smoke pipe and a turkey roaster set over our kitchen gas stove. It is necessary to clamp the steamed veneer around a "mandrel" to allow it to dry to a tight radius and for this I used ABS pipe of the same dimension as the PVC core I planned to use. (Don't use PVC for this; the steam will turn it into a noodle!). After about 20 minutes in the steam box I slid out the veneer a foot or so at a time and clamped it around the mandrel with hose clamps. This I let dry over night. After steaming, clamping and drying a bunch of veneers I was ready for spar building!
I started with the Mizzen Mast. After contact-cementing the first layer, I laminated up the additional layers with epoxy. I used 4 laminations of 1/16" veneer for a total thickness to the mast wall of 7/16". This is consistent with established scantlings for "built" masts of approximately 1/5 of the mast diameter as given in such diverse references as Kinney's Skene's Elements of Yacht Design, Nicholson's Boat Data Book and Buehler's Backyard Boatbuilding. One quarter inch of this mast wall is the veneer and the other 3/16" is the Schedule 40 PVC. This resulted in a mast diameter of 2 1/4". (The dimension of the PVC pipe is I.D., so a 1 1/4" pipe measures 1 5/8" OD, plus an additional 1/4" wall thickness of veneer for a total of 21/4 inches OD.). When I had finished the laminations of the mast, it was stiffer than my dinghy mast which was of equivalent dimension but built up in the conventional manner.
I had previously tested out the stiffness of the smaller diameter PVC/veneer combination with excellent results. Even the 1 1/4" PVC could support my weight with just two veneers applied. It bent certainly, but the comparison with the unstiffened PVC was dramatic. Also, the spars were very light, much lighter (and, I think much stronger) than their original solid counterparts.
The photograph above shows the construction, with the four veneers wrapped around the PVC core. I had originally thought that I would have to insert a piece of metal pipe into the PVC in order to stiffen up the flexible pipe so that it would be straight enough to apply the veneers. I found however, that the act of clamping and gluing a cylinder of a single 1/16" veneer around the pipe straightened it up immediately. When finished, the mast was absolutely straight.
The Mizzen Mast is not tapered since the Main Mast is not tapered.
I found another real advantage to this method of spar building; the elimination of the need for so many clamps. In fact, I built the Mizzen mast with one hose clamp (not counting the steam mandrel operation) and a roll of fiberglass-reinforced shipping tape. Here's how:
After the first layer of veneer has been contact cemented to the PVC, the second layer can be epoxied on. Spread your epoxy on either the mast or the curved veneer. (I use a slightly thickened mixture to eliminate too much soaking in to the veneer). Put on a hose clamp at one end about 6" in. Not too tight, just enough to snug the veneer to the underlying layer. (Remember, epoxy loves a gap, hates to be too tight). Wrap a piece of tape around the mast at the end. Move the clamp down further. Put on more tape (about every 6" along the spar). Keep moving the clamp and putting on tape until you get to the other end. Don't worry about the tape sticking to the veneer with the epoxy. It's a polethylene tape and the epoxy will not adhere it. There is a minor bond but it pulls right off. Sand down the epoxy squeeze out (if any) and you are ready for the next layer.
I am very enthusiastic about this method of mast construction. The naked PVC can be bent to 90 degrees without damage, the pipe walls can be compressed in a vise until they touch without damage, and the walls can be repeatedly hammered with a heavy sledge without damage. I know this because I have conducted all of these tests. I very much like the idea of this very tough flexible core living inside a stiff, strong and beautiful outer shell. While I am not an engineer, I feel very strongly that this combination creates a very effective spar. Should the worst happen, it is reassuring to know that there is a mast which, even if the outer veneers are fractured, has a second line of defense in the PVC. It might be whippy, but it will be there!
I had also been concerned about just how I was going to be able to get a good seam upon wrapping the veneers. This also proved simple. By wrapping the veneers around the mast, squeezing it together and marking it, one can run a small block plane down the edge until the edges just meet upon being squeezed around the spar.
TAPERING A MAST
While I chose not to taper this mast because I wanted to telescope the topmast and step the mainmast inside the stub mast tube, it is easy to do and I will do this with the course yard. In fact there are three ways that these cold-moulded masts can be tapered.
One simple means of tapering a spar would be to apply the veneers in ever-shortening lengths. The first layer of veneer, is applied from the heel to the truck. The second layer is applied from the heel to a distance below the truck. Additional layers are applied from the heel to an equal distance below the previous layers. This is simple, but probably not acceptable. A modification of this is to simply sand the ridges where the veneers end. This softens the transitions and this is the procedure I used to make the bolster for the Hounds Band on the Mizzen Mast. I applied three layers of veneer and sanded them to a soft transition as shown in the photograph.
The third method is the one I will use for the Course Yard. Once these first layers are on, (and there would be enough to build up the bunt and the yardarm to their respective design dimensions for the taper), then an additional covering layer is epoxied from the bunt to the yardarm using a thickened epoxy glue for the adhesive. This will result in a nicely tapered yard with a very smooth outer skin. This is shown in the exagerrated drawing.
IRON WORK
I now set to making the hardware. At my favorite scrap-steel yard, I had previously located some steel pipe with a 4 inch internal diameter. I got three feet of this for five bucks! With the help of a friend's chop saw, I cut a foot of this up to make the 2" top-mast band, and a 3" wide saddle. The 3" piece I reserved to use as a saddle or parrel for the course yard. With this saddle, which goes above the highest hoist of the gaff jaws, the entire course yard can be easily lowered to the deck in extreme weather. Toad also carries a raffee above the course.
The mast band for the Mizzen Mast is made up from a coupling for 2" black-iron plumbing pipe, and the tangs are made up from 5/16" plate, cut to the required shapes. The coupling is cut into two pieces and tabs welded to the sides in order to cramp the bands to the mast. These are not cramped very tightly, but instead are cramped snugly and rest on the bolster.
COSTS
Another appealing aspect of this method of mast and spar construction is the low cost involved. The final cost for the 9' 6" Mizzen Mast (including the hounds band) was $22.81. This was made up of the following:
9' of 11/4" Schedule 40 PVC Pipe @ .416 per foot $3.74
20 sq. ft. of Veneer @ .41 per sq. ft. $8.20
1/4 Gallon of Epoxy Glue at $35.00 per Gallon $8.75
2" Black-Iron Pipe Coupling $1.87
1 lb. 5/16" Steel Stock @ .25 per pound .25
TOTAL COST $22.81