Tuesday, January 16, 2018

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.

Monday, January 15, 2018

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.


Wednesday, January 10, 2018

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.