| The strong-back as its name suggests needs to | | | | length. With one end of the timber resting against |
| carry the finished weight of the hull and remain fairly | | | | the strong-back I used the timber a leverage to put |
| rigid during the building of the hull. If it warps or | | | | tension on the piano wire, and then blocked the lever |
| twists, then the hull will take up a shape that could | | | | at that position to maintain the tension. I used a line |
| be noticeable and very disappointing to say the least. | | | | level which is a small bubble level with hooks that |
| I build the strong back from 200mm x 50mm rough | | | | allow you to hook it over the piano wire. I adjusted |
| sawn timber, as a long rectangle about 1M longer | | | | the piano wire level by tapping the bracket that was |
| than the yacht, and screwed some diagonal bracing | | | | clamped into position with a hammer until the wire |
| underneath it to prevent it moving. I built this frame | | | | was level, and then screwed the bracket to the |
| on top of stumps that I concreted into the ground, | | | | strong-back. now it was time to set the mould |
| but could have been simply bolted to a concrete | | | | frames into position onto the strong-back. |
| floor if I had one. Then using the Grainger Yacht | | | | Each hull mould frame had to be set upright with a |
| design plans I marked out accurately the distances | | | | accurate long builders level 90 degrees to the piano |
| for each station, (mould frame position), as these | | | | wire, and the (DWL) datum water line fro each |
| markings were to be for the bearers that the mould | | | | frame had to be the same height up from the piano |
| frames would be screwed to. A tight piano wire was | | | | wire, and while that was being done a builders large |
| set up along and 25mm above the centre line of the | | | | plate square was used to make sure that each mould |
| strong-back. This was the reference point from | | | | frame was square at 90 degrees horizontally to the |
| which to set each temporary mould frame centre line | | | | centre line or piano wire. You can see that there are |
| and datum water line height from. Fixing the piano | | | | several planes that need to be considered, checked |
| wire was easy, but explaining it below seems a bit | | | | and set up level and squared, and rechecked and |
| long winded, sorry about that. | | | | checked again. I cannot stress anymore just how |
| I cut a couple of pieces of 50mm (2") angle iron by | | | | important it is too do this accurately, as the fairness |
| about 150mm (6") long and drilled a couple of holes | | | | of the hull depends on the work and care put into |
| near one end for wood screws to attach the angle | | | | this stage of the project before the first plank is |
| iron to the strong-back. At the top end I drilled a | | | | attached to the mould. A rough job of the strong |
| small hole for the piano wire to pass through. Once I | | | | back and mould frames setup will definitely end up |
| had one of the brackets attached on the centre line | | | | just a compromised finish later, consisting of humps |
| at each end of the strong back with the piano wire | | | | and hollows in the hull sides that will require a lot of |
| hole about 50m above the strong-back timbers I | | | | patching etc and may never look good. To prevent |
| then clamped the 2nd bracket to the opposite end. | | | | the hull becoming bonded with West system epoxy |
| the piano wire was passed through the hole and one | | | | resin to the mould frames the edges of the mould |
| end and tied off, and passed through the 2nd | | | | frames were covered with insulation tape to prevent |
| bracket and then tied around a piece of (4" x 2") | | | | the DuraKore from bonding to the mould. |
| 100mm x 45mm x 1.5M timber about 1/4 along its | | | | |