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.