Chine Stringers for Our Sportfisherman 26

Continuing with the 26ft sportfisherman project, the next step is to fit the chine stringers. This boat has a chine step that will be planked with Douglas fir strip. On the inboard edge of the step there is a stringer to support the outboard edge of the plywood bottom skin. These stringers fit into slots in the bulkheads and are housed at their ends into the transom and the stem.

That sounds like a simple process and for most of the hull length it is simple. Toward the bow it becomes more difficult because each stringer has to twist to follow the bottom panel and bend to follow the chine. It takes considerable power to pull that twist into the stringer as it goes into place.

The stringers also have to pass through the forward ends of the girders, with slots fashioned to fit the stinger path. The shapes of the slots through the girders are not easy to establish, so there is considerable work with saw, chisel and rasp to form the slots and filled epoxy is needed to fill in the inevitable gaps.

The end result is good. The photos and captions show the process.

The slots through which the stringer must pass on its way to the stem. The slot shape only applies on one surface of the bulkhead or girder, which must be used as a guide for shaping the bevel angles for the stringer through each member. In these photos the light coloured bulkheads are temporary formers, the darker ones are permanent and the horizontal members are the girders.

The slots through the temporary former and the girder have been shaped and the stringer is a reasonable fit. The upper edge of the girder will be bevelled to match the bottom skin, which will bring it into the same plane as the outer face of the stringer.

This photo shows how to establish the bevel shape of the stem to match the hull skin, also giving the front edge of the stringer when housed into the stem in the correct position. The stringer is now in the bulkhead slots but is short of the aft face of the stem, so it is lying at the correct angle relative to the stem. The saw is used to cut into the stem, down to the point that the saw teeth are touching the outer face of the stringer. The resulting saw cut is an extension of the line of the stringer.

The socket to receive the end of the stinger is easily made with a saw and a chisel. Housing it in like this is a stronger option than simply gluing and screwing to the side of the stem.

The socket for the aft end of the stringer in the transom is done in similar manner to the one in the stem. 

The stringer glued into its slots, passing through bulkheads and girders. The blue painters tape is there as a bond breaker to prevent adhesion where it is not wanted.

Here you can see how we pulled the twist into the stringers. We fitted the two in parallel, gluing both in the difficult twisted bow sections first before moving aft on one, then the other. The clamps are holding the twist in the forward ends, with the clamps lashed together with ropes pulled tight to provide the torque needed.

Stringers showing fair curves and securely lashed until the epoxy has fully cured.

The next stage of building will be to prepare the bottom framing to receive the bottom skin, by planing bevel angles on bulkheads, girders, keel and stem.

This design is not yet complete, so is not on our pricelist or website. See our full range of designs on our main website or our mobile website.

The Sportfisherman Grows a Transom

In my last post about this new powerboat project we installed the keel and the graceful S-curved laminated stem. This post mostly deals with the other end of the hull, installing the transom and the plywood gussets that will support the outboard engine bracket.

In the interim, Kevin has been busy fitting Douglas fir cleats in the corners of the internal structure of the hull. These cleats are triangular and are easier to do than epoxy fillets on these straight joints.

Douglas fir cleats fitted into the corners of the structure with temporary screws. The cleats across the top of the photo are on the edge of the girder and will be planed down to match the angle of the plywood bottom panel to increase the gluing area.

The transom was laminated previously over a curved former, from four layers of plywood, shown in a previous post. It is a strong and substantial piece of timber, so needs careful planning before starting the installation. You don't want to lift it and wriggle it into position more then absolutely necessary because it is pretty heavy and you need to show it who is boss.

This transom doesn't have the outboard motors clamped onto it, it has slots through it for a series of gussets that will be bonded onto the girders and keel inside the hull. The gussets are the internal structure of the bracket that will carry the outboard motors, cantilevered aft of the transom. The gussets must be installed in tandem with the transom, so there is time pressure to get it all done and properly secured before the epoxy goes off.

Before doing a dry-fit, test fit the various parts. The end of the keel must fit into a socket in the front of the transom. Check this with an off-cut of the transom rather than offering up the heavy transom to the keel. Check that the gussets all slide easily through their slots. There must be enough slop to leave a narrow gap (about 1mm) to fill with epoxy, to do its bonding work.

You will also need to trim the keel to its final length, which means pushing the transom in as far as it can go then measuring how far it still has to go to be in the correct position. Measure this distance onto the keel and mark the position to cut the excess off the aft end. This needs the transom to be removed then replaced again after the keel has been trimmed.

We eased this whole process by hanging the transom on the centre gusset, which was clamped very securely into its slot in the keel. This allowed us to have the keel take most of the transom weight while we fine-tuned the fit.

The centre gusset is 3 layers of 12mm plywood, fitted into a slot in the keel. Here is it clamped in place to assist by carrying the transom weight when fitting the transom.

The transom is in position and supported on adjustable stands. The centre gusset assisted by carrying the transom weight while getting it into place. The two outer gussets each side are dry-fitted to be sure that all will go together without problems.

 Next, the two legs that tie the transom to the building stocks were fitted. Each had a bevel angle cut onto one face to match the angle created by the curved shape of the transom. With the legs screwed to the stocks but not to the transom, we added a short wooden block to the side of each leg, tight up against the transom edge and projecting aft beyond the transom. They gave us additional temporary support points for the transom.

With everything fitting properly, we kept the transom in against the legs and supported on the blocks but pulled the top aft away from the girders and keel. That allowed us to spread epoxy into all contact areas. We excluded the centre gusset from this gluing process because it was dry-fitted and would need to come out again. before gluing. 

Transom supported by blocks on the support legs, with a clamp on the centre gusset preventing it from falling off the boat. Now all gluing areas can be reached to spread glue. Be sure to first brush on liberal amounts of unfilled epoxy onto all end-grain surfaces and allow it to soak into the grain before applying glue and closing the joints.

After this first phase of gluing, the second phase is gluing in the four outer gussets and setting them to the correct angles and heights. Temporary screws will hold the transom and gussets.

The third phase of gluing was for the centre gusset. Once unclamped, this came right out to give access to the bonding surfaces. Once epoxied it went back in, clamped back into the groove in the keel.

The transom has now been glued to the girders and the four outer gussets have been glued. Note the 2x4 on top of the framing, clamped to apply pressure to hold the transom against the other structure. The centre gusset has been removed

View of the inside of the transom, showing the gussets bonded to the girders, fastened with temporary screws and fender washers. The centre gusset has not yet been fitted.

All glued and waiting for the epoxy to cure.

During this process, care must be taken to get epoxy all the way through the various joints. That means working it into the joints by squeezing with a spatula or with a syringe. Clean up all superfluous epoxy while it is still wet, it will be a pain to clean once hardened.

The next phase of the project will be fitting chine stringers and planking the chine flat.

This design is not yet complete, so is not on our pricelist or website. See our full range of designs on our main website or our mobile website.

Installing the Sportfisherman Backbone

In my previous post Kevin laminated the keel and stem, the two components that make up the backbone of the new boat. Now we must shape the scarph joint that will combine them into one piece and then install them.

That introduces a tricky problem that may confound some builders who may not have done this before. The problem is that the keel and the stem have to both occupy the same space before the joint that bonds them together is shaped. This joint must be very carefully shaped to create an effective scarph joint with the two parts correctly aligned. Trying to do this by measurement has a pretty big chance of an error causing a mismatch, with a bad joint the result and possibly having to make a new stem or splice in an extension on the keel.

This photo shows the keel being laminated in position, extending to Frame 1. The frame that is in front of it is Frame 0, at the forward end of the design waterline (DWL). The stem has been made to extend from the tip of the bow, over Frames 0 and 1, ending at Frame 2. The overlap between the two allows us to blend them at the joint.

A template is needed to get the cut angle correct, with the template used first on the keel, then on the stem. But if we do that off the boat the chances are that we will get it slightly out of position or at slightly the wrong angle, yielding a bad scarph. A small difference in thickness between the keel and stem will throw out the angle substantially. To remove this considerably risk, the template needs to be on the hull framing and it must be done in a way that it can be used to mark the angle on the two components individually.

To accomplish this we needed three battens. These we set up with the keel in position and the ends of the desired scarph marked onto the top and bottom of the keel. Two of the battens are clamped against the frames, one on the aft face of Frame 1 and the other on the front face of Frame 2. Both are vertical and away from the side of the keel by the thickness of a batten. The third batten is clamped to these first two against the side of the keel, in a position that the lower edge crosses the top and bottom faces of the keel at the previously marked lines showing the ends of the scarph. Clamp them all tight so that they cannot move but the keel must be free to move. The template is now complete. Draw a line onto the side of the keel along the lower edge of the third batten, then slide the keel aft out of the way.

Here is the template set up against the keel. A line is then drawn onto the keel along the bottom edge of the sloping batten, then the keel is slid aft out of the way.

The template still in position with the keel out of the way.

Now place the stem into its correct position. To do this the bow end of the stem must be trimmed to the correct deck angle and height above the building stocks, which comes from the drawings or the stem template. The stem must also be set on a block to get it to the correct height. Also, draw the waterline onto the side of the stem from the pattern, to assist in ensuring that the stem is correctly set up relative to the frames, by using the laser level. With the stem in place, draw the cutting line onto the side of it along the template exactly as was done for the keel.

The template is till in place and the stem has been slid in to replace the keel. The cut line is drawn onto the side of the stem in the same way as was done for the keel.

The keel and stem can now be removed from the framing for the scarph to be cut. Before doing this, draw the ends of the scarph line across top and bottom of both the keel and stem, then draw the scarph onto the opposite face as well. Cut the scarph with a skillsaw or hand saw. Don't cut right on the line, cut about 3mm (1/8") away from it. This will allow you to finish it more accurately with a sharp hand plane to a smooth and straight surface.

Scarph cut onto front end of the keel, then finished with a hand plane.

Now the keel and stem can be dry-fitted in place on the hull framing to check for accuracy, before being permanently glued into the structure.

Keel and stem dry-fitted and clamped to show a near-perfect fit and a nice fair curve.

At this stage the girders haven't yet been glued in, so we elected to glue the girders to the frames, to get the structure solid before gluing in the backbone. After that we glued in the keel, followed by the stem. The scarph was glued while gluing in the stem.

The new scarph joint glued, clamped and excess glue removed. A nice clean joint.

The next step in the assembly will be setting up the transom. I will blog about that next week.

This design is not yet complete, so is not on our pricelist or website. See our full range of designs on our main website or our mobile website.

Backbone of the Sportfisherman

The backbone of a boat is its keel and stem. For our new 26ft sportfisherman those members are made from Douglas fir, aka Oregon pine, which is laminated to the shapes needed. Laminating is the process of cutting the timber into strips, then gluing them back together again while bending them to the required shape. The thickness of strip needed depends on how tight the curve is, the tighter the curve the thinner the strips needed.

Newcomers to woodworking are sometimes petrified, or at least anxious, about tackling a laminating job. But this process of taking straight timber and changing it to a convoluted shape is strangely satisfying. The first time that you do it, you look at the result and think to yourself "did I really do that?".

It is really a fairly simple procedure and, with careful planning and common sense, has small chance of going wrong.

The hull frames form a handy and accurate mould over which to laminate the keel. The strips have the glue applied then are laid into the sockets in the frames and clamped in place until the glue has cured. It should not be glued to the frames, so the sockets are protected by tape, waxed paper or other bond breaking material. This allows the member to be removed after the glue has cured, for easy cleaning with a belt sander. The sharp corners that will be inside the hull should also be rounded off with a router while it is out of the boat.

The keel has little curvature, so can be laminated from a small number of relatively thick strips. Kevin used 4 layers of 20mm (3/4").

The stem has tighter curvature and the double curve of an S-shape, so it is laminated from thinner strips. The curve also needs more definition than the hull frames can provide, so it is laminated on a table or workbench with a former that defines the shape. In this case, the former is made from a series of timber clamping blocks that are screwed to the table. The shape that Kevin Agee followed was shown on a full-size pattern that we provided.

Shaped blocks screwed to the workbench over the template. Blue painters' tape on the blocks is to prevent the product from bonding to the blocks.

The stem glued and clamped to the blocks. This glue-up is being done in two stages because there are too many joints to safely glue in one step.

There should always be a dry run of clamping the strips onto the formers before doing the actual glue-up. This will allow you to find out before-hand whether or not there will be any problems or any tricks that will be needed to get it done with the glue starting to go off. Don't be over-optimistic and try to glue too many strips in one go. The more strips that there are the longer it will take and the more that they will slide around when you are trying to clamp them accurately. Play safe and do it in two stages to minimise the chance of failure.

Leave laminations plenty of time to cure before releasing them because releasing the clamps before epoxy has fully cured can result in some straightening of the piece. If that happens, you will not be able to pull it back into shape, possibly even by trying to clamp it back onto the former. A simple laminate like the keel with little curve is not likely to give this problem but the tight curves of the stem can do that if released too soon. In winter this could mean leaving the piece clamped to the form for a week.

Another reason for laminating from a large number of thin strips is to minimise spring-back. This is the tendency of the laminated piece to straighten out slightly from forces in the wood, even if the glue has fully cured. The more dense the wood that you are working with, the greater the chance of spring-back, so the thinner the strips that will  be required. Reducing the strip thickness and increasing the number of strips, in inverse proportion, will give better results.

The completed stem lamination, being cleaned up with a belt sander prior to trial fitting.

The completed keel lamination. The groove routed into the aft end of the upper surface is for housing the central gusset of the stern bracket that carries the outboard motors.

To speed up the lamination process and give yourself more time to work with the timber and get it right, you need an efficient way to apply the glue. Kevin used rollers to apply it quickly.

A roller applying glue to multiple strips at the same time.

The next post will cover installing the keel and stem on the frames, including how to cut the scarph to join the two together accurately.

This design is not yet complete, so is not on our pricelist or website. See our full range of designs on our main website or our mobile website.

Framing the 26ft Sportfisherman

The 26ft sportfisherman project now has its building stocks and is ready for framing to begin. The frames have been built, most of them permanent and a few temporary. A boat in construction often needs framing to be more closely spaced than it needs in use on the water. Temporary frames fill in the gaps where needed to add rigidity or to help shape parts of the hull where wood won't naturally take on the form needed.

Before setting up that first frame we needed to know how level the rails were that are going to support the frames until the hull is ready to be turned over. There is no point setting up the first frame sitting hard against the rails then finding as you progress that it is the lowest point on the rails. Using a laser level and a long batten we compared heights all over both rails to find the high points. Plywood spacers were added to the rails at the first frame position to get it above the highest point on the rails. All other frames are lifted as needed on plywood spacers and/or wedges to get them to the correct level.

Spacers under frames to get them level. The legs are screwed to rails and frames are screwed to the legs.

For this design I aligned Station 1, a temporary frame, with the forward transverse frame of the building stocks. For simplicity this frame is set up accurately in that position, then all others are referenced from that same location. It is good to measure all from that one position to reduce the chances of longitudinal errors. If you set up each frame measured from the previous one, the incremental errors can easily add up to 1/2" or more of cumulative error over the length of the boat. If you make one big error, that error would carry through the rest of the boat. You would discover it eventually when you attempt o lower the girders into place and find that they don't fit. At that stage you would have to reset all frames to their correct positions, wasted time and energy that is saved by doing it correctly from the start.

Station 1 (temporary) is on the left, set up first, secured and braced. The one on the right is a permanent bulkhead, supported by a temporary base and with light battens holding it stable. The deep slots in the upper edge are for permanent plywood girders that will be dropped in later to stiffen both hull and deck. The girders have matching slots and will accurately space and align the tops of the frames. Legs secure the frames to the rails. 

The frames are set up vertical and level by using a plumb line hanging from a line above the centreline of the boat and a laser level. The laser should be self-levelling for accuracy and should be set up so that it can shine onto all frames at the same time. Now is the time that you will discover whether or not your accurately-drawn waterline and centreline are really at 90 degrees to each other, as they need to be. The waterlines on one side are set up level for all frames while setting up the frames, then checked on the other side. There will likely be some minor errors on the second side to correct. Lift or lower that side of each frame where needed, bearing in mind that the frame will rotate around the contact point on the other rail, so the centreline of the frame will also move a small amount. So, correct the waterline to suit the laser and the centreline to suit the plumb line simultaneously. After all frames have been adjusted, move the laser back to the first side and check that, then adjust if needed.

All of the frames have been set up, accurately positioned fore/aft by measurement along the stocks and set up vertically with the aid of the plumb line that hangs from the centreline above the boat and level with the aid of a laser level. The light-coloured plywood is temporary, the darker pieces are permanent.

In this photo the frames have all been set up, checked and checked again. The laser level is at left, clamped to a post on the router table. The light is shining on all frames onto the waterlines that were drawn accurately from the drawings.

The forward two frames don't extend to waterline, so the laser won't shine onto them. To set the levels for these two you can attach a batten to the plywood with the waterline marked on it, or you can set the spacers to the correct level before setting up the frames.

Here one of the girders has been lowered into its slots in the frames to check accuracy. Other girders are lying against the frames. They are scarphed into long lengths from plywood. 

The next post in this series will cover laminating the keel and stem.

This design is not yet complete, so is not on our pricelist. See our full range of designs on our main website or our mobile website.

Deck Progress on the Expedition Cruiser.

Last month I introduced the aluminium expedition cruiser that is being built by John Dearden in British Columbia. At that stage the hull had just been turned upright. Now the cabin is taking shape and the cockpit has been started. I will let the photos and captions explain the boat.

How she will when look heeled over under sail. The very sleek bow will present little resistance to water flow. A colleague has said that her bow will peel veneers off the logs that she encounters. John Dearden has done a nice job of building fair lines with our experimental chine detail.

John Dearden working on the small trunk cabin. Ahead of this is a sunken foredeck with hinged hatch to an anchor locker. The sheer is trimmed all around with a pipe to soften the edges and to form a catchment area for rainwater.

View along the cockpit, with the side decks installed. On centreline there is a trench full length of the cockpit, with a perforated plate over it. This trench is open to the top of the swing keel casing and aft into the outboard engine well, providing copious drainage in the event of taking a large amount of water into the cockpit.

The aft end of the cabin is sloped for comfortable lounging under the partial protection of the dodger when under sail or anchored. It also gives room for the forward oarsmen to pull a full stroke without colliding with the cabin. The forward rowing thwart (there are 4 each side) is starting to take shape aft of the cabin.

General Arrangement drawing, showing cockpit layout, interior and the swing keel.

Watch this blog for more about this project. To see more of our other designs, go to our main website or our mobile website.

26ft Sportfisherman Build Begins

The new 26ft sportfisherman of Kevin Agee is starting to take shape. This series of posts will follow the project one step at a time, starting with the building site. This is somewhat of a manual on how to build this boat, showing the way that Kevin has chosen to do it, sometimes under my guidance.

First step was to find a suitable build location. Those who live in a temperate climate can build out in the open or under a lean-to carport. I built all of my big boats in Cape Town in my garden, without protection from a roof. Here in Virginia the climate is not as kind, so frigid winter conditions make building outside very uncomfortable and cause big delays when work must stop.

The site chosen is a small industrial unit, large enough to contain the boat, the power tools and materials, with large enough spaces left over where full sheets of plywood can be laid out for cutting panels etc. There should also be enough space around the boat to allow standing back to view the hull as it develops, to judge fairness of curves of planking etc.

The foundation for a good build is to construct a solid bed (building stocks) on which the skeleton of the boat can be assembled. This bed has to be strong and stable so that the skeleton that is built off it remains accurate and true to the intended shape. There will be large loads applied to it through the weight of the materials that are added step-by-step and also the bending loads that result from forcing straight timbers into curved and/or twisted shapes. Clamping those timbers against the framing bends those timbers and sets up forces in the framing and beds, so they have to be strong enough to hold shape.

Basic shape of the building stocks, constructed but not yet anchored in the final position.

 If the build is over a concrete slab then the beds can be anchored directly to the concrete, with steel angles and anchor bolts. If the build is over natural ground then the beds must be elevated above ground to a height that the rails can be properly levelled, with the rails bolted to legs that are concreted into the ground for stability.

Most concrete slabs are not totally level, so the beds need to be levelled as much as practical when doing the anchoring. I say "as much as practical" because the rails may be straight when you buy them and not quite so straight when you make the beds a day or two later. Get them as level as you can, anchor them down, then add wedges or spacers where needed to level the individual frames when setting them up.

Steel angle and anchor bolts tie the rails to the slab.

Wedges under the rails shim them where needed to improve levels

A very important part of the building stocks is a wire strung above the centreline. This allows every frame to be set up using a plumb line hanging from the wire for reference. I will explain the use of this plumb line in the post about setting up the frames.

Plumb line hanging from an overhead wire that is accurately aligned with the centreline on the beds. 

Ahead of making the building stocks, Kevin had already assembled the frames so that their erection could be started as soon as the beds were ready. Some of the frames are temporary, cut from cheap plywood or MDF. Others are permanent, so cut from high quality marine plywood, with temporary bases and legs attached for fastening to the stocks.

One of the temporary frames being assembled on top of Mylar templates.

Frames and bulkheads ready to be set up on the stocks.

The transom on this boat is upright but it is radiused on plan. That means that it has to be laminated from plywood layers over a curved form to give it an accurate and stable shape. This one is two layers of transom and two layers of internal doubler.

The inner transom doubler layers are laminated first.

Then the outer transom layers are laminated onto the doublers

The next post will start with setting up the frames on the stocks.

This design is not yet complete, so is not on our pricelist. See our full range of designs on our main website or our mobile website.