Duckworks - Seaclipper 20

Seaclipper 20

By David Kagan - Stillwater, MN - USA

Making Tapered and Beveled Stems for the Seaclipper 20

To date, all my boat projects have been monohulls. But, I’ve dreamed of building a trimaran for a long time. In the spring of 2010, Jim Brown and John Marples introduced their plans for the new trimaran design called the Seaclipper 20. As soon as I read about the boat and reviewed the study plans, my eyes lit up. Finally, here was a trimaran project that matched my skill set, could be built within a reasonable time budget, and matched the kind of day sailing I wanted to do. I ordered the plans and started to build in June.

The amas and main hull of the Seaclipper 20 use stems that are tapered and beveled. Many other boat designs also use tapered and beveled stems. So, even if you are not building a Seaclipper 20, this article still may be of interest to you.

Making parts that are only beveled or only tapered is relatively easy. But, I found that making stems that are both tapered and beveled was nontrivial for me given the tools I have in my shop. I tried four approaches. The first two didn’t work. The third worked, but was complicated and time consuming using mirror image patterns on a taper jig for the table saw. The parts that emerged from the third effort were fine, but unfortunately made from red oak. John Marples advised that red oak moves and is often not a good friend of epoxy. So, I used a fourth method, described here, to make stems from more suitable wood. The method is easy and fast, even for me. More importantly, I felt comfortable with the method and did not ever feel that I was testing the envelope of reasonable safety.

Fig. 1. It's still early in the building process, but already the parts are piling up. These are the bulkheads, transoms, stems, and butt blocks, for all three hulls. The big main hull bulkheads and transom are buried at the bottom of the pile. Also shown are the daggerboard blank, and rudder blank. Not shown are the stringers, ribs, and daggerboard box.

Fig. 2. The steps in this article show how to make tapered stems like this set of two ama stems and the main hull stems.

I used a Festool saw and guide to make the stems. The Festool guide and similar saw guides positively restrict the saw to move along a linear path only. These guides do not allow the saw to drift from the intended line unless something really awry happens. Before you lose interest on grounds that you don't have a Festool saw, the method described here will work for any circular saw guided by a straight edge that positively holds the saw to a straight line. I don't think that I would recommend this method with a mere straight edge that allows the saw to drift without positive control. The drift doesn't affect the workpiece since the drift away from the guide is into waste. However, saw drift while ripping or even crosscutting is not safe, particularly with thick wood blanks used to make stems.

Here is the method step by step.

Step 1: Make your blank(s) from suitable stock and layout your stem pattern(s) full size on the blanks.

Step 2. Drill two counterbores in the stem for mounting screws. See Fig. 4. I drilled counterbores that were 3/4 inch in diameter to fit the self-tapping Kreg screws I used for mounting the stem blank to the work table. Later these bores and the screw holes will be filled with epoxy.

Step 3. Grab some scraps and make the work table shown in Fig. 3. If you screw your head blocks to the table, position the screws well to the outside and make sure that your saw path will never hit them. In Fig. 3, my head block at the top of the table is way too short. I had to use a supplemental block to help support and clamp my saw guide to the table.

Step 4: Mount the blank to the table using self-tapping screws. I like Kreg screws for this. Position the blank so the cutting path runs up the table center and not through any screws on the outboard ends of the support blocks. The wide face of the stem faces up. You can position the stem blank anywhere you want so long as the saw blade path misses the screws. The main stem is 36 inches long, so this table is long to accommodate that stem as well as the shorter ama stem shown in the Figures.

Fig. 3. The simple work table takes only a few minutes to build. Blocks of wood are screwed to a ¾ inch scrap 2' x 4' MDF sheet or other board. The screws are well to the ends of the blocks so that the saw path never goes near them. The blocks support the saw guide and are the same thickness as the stem blank. The stem blank also is screwed to the table.

Fig. 4. The stem blank for an ama is screwed to the table. Precision is not needed for this at all, because the saw guide will be aligned to the cut line and not vice versa. The stem pattern is laid out full size on the blank. Two screws do the job of holding the blank to the table. The screws are recessed in counterbores so they don't interfere with the saw guide.

Step 5: Clamp the saw guide to the table, aligned with the desired cut line. Both ends should be secured as we will need to make multiple passes. This Festool saw has a lot of power and can crosscut a 2 x 4 easily, but the saw has to work way too hard to rip this tapered bevel in one pass. So, I used four passes, cutting deeper by about 12 mm (about ½ inch) with each pass. Because the saw guide keeps the saw on line, each pass goes successively deeper on the same cut line as long as the saw guide is not moved between passes.

Step 6: Set the saw depth for the first pass, about 12 mm. Place the saw onto the guide in position and make the first pass. Then increase the depth of cut about 10 mm to 12 mm with each successive pass until the cut is complete.

Fig. 5. Secure the saw guide in position to make the bevel cut. The guide is clamped at both ends to avoid movement of the guide during the cut. Note how the guide is aimed down the workpiece to cut the taper down the workpiece length.

Fig. 6 . The saw is placed into position on the guide. The saw is set to the bevel as specified in the plans.

Fig. 7. The first pass is complete. The saw’s cutting depth is successively increased adjusted to make 2d, 3d, and 4thpasses.

Fig. 8. After the 4thpass, the first beveled taper is complete.

Step 7: We want to make a stem with a cross section that is a trapezoid, not a parallelogram (I almost made some parallelograms). So, we need to remove the stem blank and remount it to make the proper cut. Remove the screws to free the blank. Turn the blank around so that the end that was at the head of the table is now at the bottom. The wide face of the stem is still facing up. If you do this right, the first bevel is now on the left and new bevel to be made is on the right.

Step 8: Secure the saw guide in position. Remember to clamp the guide at both ends so there is no movement of the guide during the multiple passes used to make the cut. Make sure you are cutting on the desired line and not the center line (I almost did this, too, on one stem). Double check to make sure the saw will not hit any screws at the foot or head of the table. If there is a screw in the way, you will need to move and remount the stem blank to avoid this.

Step 9: Again using four passes, cut the second beveled taper. Your stem is now done and can be removed from the table. The holes made in the stem for the counterbore and screws can be filled with epoxy to protect the stem from rot.

Fig. 9. To make the other beveled taper, the workpiece is removed from the table, flipped around, and remounted so the first beveled taper we made is on the left and the new beveled taper to be made is on the right.

Fig. 10. Here’s a close up view showing the stem blank remounted correctly. Note the wide face of the stem is still facing up. We flipped the stem around. We did not flip it over.