Sportfisherman 26 - Let the Skin Begin

Since my last post on Kevin Agee's project the 2nd and 3rd layers of the sheer clamps have been laminated onto the first one, to take it up to its full size. These layers were easier to do because the first layer was already in place, defining the twist and giving a convenient surface for clamping. There was no need for a Spanish windlass to pull them in.

Second layer of sheer clamp glued and clamped.

The 2nd layer of the bottom skin has also been glued on. It is secured and pulled in tight with temporary screws and fender washers, working outward from the centre of each sheet toward the edges, forcing air and excess glue out at the edges. A boat like this will sometimes take some hard hits on the bottom when running into rough conditions, so bad lamination in the bottom must be avoided. The screws will be removed and the holes filled with epoxy, inserted with a syringe.

2nd Layer of the bottom glued and fastened with temporary screws and fender washers.

Time was approaching for the side skin to be started. This is being done in bead and cove cedar that was bought in 4" plank widths, then cut down to the desired widths on a table saw. After scarphing to the lengths needed to cover the hull in single lengths, they were run through the router on a router table to form the cove and bead. This was done with a crown molding #3 router bit, using the convex part of it for the cove and the concave part of it for the bead. The two fit together nicely for the bead and cove joint.

Crown molding #3 router bit sourced from Lee Valley.

Fit of the bead and cove strips cut with the router bit shown above.

With a large stock of newly-machined strips scarphed into long lengths and waiting on top of the hull, the pressure was on me to finish shaping the bevels on the stem to to the correct angles to receive the ends of the strips. This is done by holding (clamping if there aren't helping hands available) a strip against the sides of the bulkheads and frames, with the forward end in correct position to run fair into the stem and with the tip just short of the stem. Then a saw cut is made into the stem with the saw running against the upper face of the strip until the teeth are flush and parallel with the inner edge of the strip. This is repeated in a series of positions until representative cuts have been made the full length of the stem where it will be crossed by strips.

The stem is still rectangular in section but has saw cuts to show the bevel angle needed by the skin.

Next, the bulk of the timber is taken out with a chisel to give the rough surface , finished off to the final surface with a plane and/or a Shinto saw rasp.

Using a chisel to remove the bulk of the excess wood. This side of the stem proved tough to break out due to the grain direction, the other side came out much more cleanly. This side needed the Shinto saw rasp to finish it, whereas the other side came in nicely with a plane.

The completed stem bevels, ready for the bead and cove strips.

A decision has to be made by each boat builder where to place that first strip. Some like to start at the chine, then work toward the sheer. Others prefer to start at the sheer and work toward the chine. Still others will start somewhere between the two and work in both directions. This third option was our choice, mostly because the boat has a broken sheer that gives a convenient start line.

We started by clamping the strip with the lower edge flush with the lower edge of the straight aft sheer clamp. Forward of that aft sheer clamp, we slid the forward part of the strip up and down against the framing until we found the line that placed the least stress on the strip. In that position there is minimal force needed to pull the strip against the framing, so fitting is easy and the same should also be true for the rest of the skin.

The first strip glued flush along the lower edge of the aft sheer clamp and the forward part aligned for least stress in the timber.

Starting to look good, with six strips fitted. The strips are run past the ends of the hull, then trimmed back after the epoxy has set.

The strips are nailed to each other with plastic brads that are shot in with a pneumatic gun. Temporary screws and fender washers are holding them to the framing. Due to the low-stress alignment chosen for the strips, hand pressure was all that was needed to hold each strip against the previous one for fastening, no clamps were needed.

With much of the hull skinned both sides, time to stop. The chine flat must be built first from Douglas fir, then the side strips will be finished against the chine.

Scarph joints in the strips to make hull-length strips. The strips are positioned to spread the scarph joints out so that they are not all in the same place on the boat.

Building the chine step will be next, on the program for tomorrow.

This design is not yet complete, so is not on our pricelist or website. See previous posts on this blog about the 26ft Sportfisherman for more info. See our full range of designs on our main website or our mobile website.

Aluminium Expedition Cruiser Cockpit Takes Shape

When I last wrote about the aluminium expedition cruiser build in British Columbia the cabin was being built and the side decks had been fitted.

There is a lot of detailed construction in the cockpit that takes time to build. It includes the casing of the swing keel, the drainage trough that runs full-length of the long cockpit, the seating for rowers and helming, and the outboard engine well. All of the seating houses storage lockers for equipment and personal gear, with watertight lids that require careful construction. That cockpit work is now nearing the end.

View along the cockpit, nearing completion. The channel down the centreline is a drainage trench to dump water fast through the keel slot and engine well if she were to find herself in rough seas and take a big one aboard. It will be covered by a flush perforated plate. There are 8 rowing positions, with watertight crew stowage under them. Between the seats are food and ice lockers with watertight hatches through the cockpit sole. The horseshoe seat aft is for helming and has outboard engine stowage under it. In the U of this seating is the well for a small outboard engine for in-harbour use. The swing keel is ballasted and raised with a heavy duty trailer brake winch.

Overhead view of the cockpit.

Owner Tom McPherson has an Instagram site that has more photos, construction videos at various stages, as well as videos of the beautiful wilderness areas where his boat will be working, offering adventure cruises for teenagers. View them at Seaforth Expeditions.

I am still detailing the last drawings of this design, so it is not yet on our website. To see our other designs, go to our main website or our mobile website.

Sportfisherman 26 Sheer Clamps

Since my last post about Kevin Agee's project he has been working on the second 9mm layer of  the bottom skin. With this layer there is no chance of using clamps along the keel to assist by holding that edge tight against the structure while you work elsewhere on the panel. For that reason this second layer is most easily done in narrower pieces than what worked for the first layer.

Kevin is dry-fitting this layer from the bow, toward the stern. In the bow the pieces are approx. 300mm (12") wide, which has worked well. Further aft the twist reduces rapidly so wider pieces can be fitted without problem.

Second layer of 9mm bottom skin being dry-fitted.

The sheer clamp is the next major piece of longitudinal framing that must be added to the skeleton. This is a fairly complicated component and must be laminated in place. The sheer clamp defines and strengthens the top edge of the hull and joins the hull to the deck. The complication comes from the fact that it curves on plan and in profile, at the same time twisting to conform to the changing angles of the upper edge of the hull side. At the transom the hull has tumblehome, so the side leans inward at the top. At the bow it has a lot of flare, so the side leans outward at a large angle.

To further complicate it, this boat has a broken sheer, meaning that there is a hard break in the side profile instead of having smooth curves that flow from one end of the boat to the other. That means that the sheer must be done in two sections. The aft flat part of the sheer clamp is done first, then the forward curved part is built off the aft section.

Kevin laminated the aft section of the sheer clamp during the week, ahead of me arriving to help with the more complicated forward section.

This photo shows the twist that is formed in the aft part of the sheer clamp as it changes from tumblehome at the transom to the beginnings of flare at the break in the sheer.

The aft part of the sheer clamp is run through to the next permanent frame forward of the break and will be trimmed off flush with the front face. The first layer of the forward part of the sheer clamp is also in position, dry-fitted so that we can check fairness of the curve and also mark the bevels on the frames and the stem.

Preparing the framing to receive the sheer clamp needs to be done carefully, so should not be rushed. The frames are not difficult, the angles can be established with a shallow cut with a back saw to show angle and depth, followed up with a rasp to take the frame edge down to the saw cut.

The Stem is more complicated. The angle of the bevel for the skin must be marked and cut first in the area where the sheer clamp will fit. This angle can be established by running a batten across the forward 3 or 4 frames to check that it contacts all of them correctly and lies flat against the bevel on the stem. Once that stem bevel angle is correct the rebate to receive the sheer clamp can be formed.

In this photo the first layer of the sheer clamp has been glued in place. The narrow piece of stem bevel that shows above the sheer clamp is the bevel for the inside face of the hull side and is flush with the edge of the sheer clamp.  The broad piece of bevel that shows below the sheer clamp extends from centreline on the front face to the aft edge of the stem to form the bonding surface for the sheer clamp.

A slightly different perspective of the intersection.

The sheer clamp must also be prepared with its ends trimmed to properly meet the aft sheer clamp and the stem. The aft end is relatively simple, with an angle in only one direction that is easy to mark, rough-cut with a saw, then fine-tune with a sharp plane.

The junction of the two sheer clamps at the sheer break. The cut angle for a good fit is quite easy to work out.

The forward end is more complicated so it is best to first work out the cut angles (which run in two directions so that the bevel is not parallel to any of the surfaces of the timber) on a length of off-cut of identical size to the sheer clamp. Cut this off-cut and fine-tune to a perfect fit, then transfer the angles to the sheer clamp on the workbench, where they can be accurately drawn, cut and planed. Test fit on the boat.

Now comes the part that demands ingenuity, to deal with the enormous amount of twist in the bow sections. We were working with very nice clear Douglas fir, which is stiff and not keen to twist as we needed. It didn't work to rely on clamps alone to do this work, the timber came in most of the way but still needed about 20 degrees of twist. We set up a Spanish windlass to do all of the work of pulling the timber in against the stem so that the clamps would only have to work on the twist. 

This was our setup for the dry-fitting phase of the first layer of the sheer clamp.

We were not confident of being able to pull it in totally with slippery glue complicating the work, so we decided to leave it clamped for two days to set in some of the bend. When we returned to it the pre-set of the timber made it easier to pull it back in. Again, we used a Spanish windlass to apply the bending forces. We used a different clamp setup to do the twisting, with the handles of the clamps lashed together to apply the twisting force.

Our setup for the gluing phase. The Spanish windlass is visible just above the sheer clamp, pulling the two sides against the stem. The two black clamps with their handles tied together are twisting the wood to align the outer surface with the front face of the stem.

We were working with timber thickness to laminate the sheer clamps in three pieces. Doing it in four thinner strips will make it easier to pull to shape.

The next step will be to laminate the other two layers onto the sheer clamp, which should be completed in the next few days.