SURPRISE CHAPTER AVAILABLE TO OUR BLOG READERS – Setting up and building the hull

All I ask is a Tall Ship  Available now on Amazon eBooks

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CHAPTER 8. Setting up and building the hull.

The first job is to build a cradle. This will not only be used to securely hold the structure as the steel on the floor is raised to the vertical, but also to launch the completed hull. Every extra cm height of cradle means 1cm less clearance beneath the roof. It will require that much extra tide to launch the boat and will also require that all parts, including myself, having to be lifted that much higher into the hull. This last may sound insignificant but I appreciate the point after my thousandth lift and after the ten thousandth time I have climbed up the ladder to the deck. I do the calculations and decide that 200mm (8”) deep channel section around the perimeter with 200mm girder crosspieces are the minimum that will give the required strength and rigidity.
Coincidently I have a quantity of these sections in my “It might come in useful one day” steel pile. My road trailer is pressed into service. After completion I measure across the diagonal and find that welding distortion has pulled the supposedly rectangular cradle 10mm (3/8”) out of square. A salutary lesson. I will have to be much more accurate when building the boat. Initial errors tend to grow during steel construction so I resolve to change my normal attitude of “near enough” to working to the nearest millimetre (1/25”).
I spend a whole day getting the cradle fixed into position. I first choose a spot some way down the slipway to give me extra headroom but still above high water. I measure to find the centre between the railway lines, drill into the concrete and fix two lugs ahead and astern of the build. These are immovable and will hold either end of my centre line. To define this I run 25m (80′) of MIG wire between these points and tension it with a bottle screw. The wire runs under the cradle but clear of the ground over its full length. During construction it is often broken by being tripped over, burnt with weld spatter or by having steel parts either being dragged over or dropped on to it. However the ends are immovable and the wire is easy to replace.
Using a plumb bob I centre the front and rear of the cradle over the wire. I use a water level to level it crossways and adjust it to give an incline from front to rear of exactly 96mm (4”) to match the slope of the yacht’s keel. I then weld the front of the cradle to the rails and while constantly checking all dimensions use heavy bottle screws, and baulks of timber tightened with wedges to hold it immovably in place.
My design calls for the after edge of the keel to be 2.85m (9′ 04”) below the load waterline. The after end of the keel rests on the rear of the cradle so this point is used to define a vertical datum. This is transferred with the water level to an accuracy of a mm to one of the shed’s structural steel pillars. A steel tape is set up on this pillar with the zero exactly 2850mm above this point. Readings relative to the Waterline can now be taken directly.
My chain hoist, Camlok and lifting chains already come with lifting certificates and my shackles are all marked with a safe working load. Because other people will be involved it is sensible to also obtain a test certificate for my gantry. I call in a surveyor, attach the lifting hook to a ring embedded in the concrete and apply a strain to the gantry of 125% of the Safe Working Load. In the absence of a collapse a certificate is issued. We test for 1000kgs (2200lbs) but as none of my parts exceed 500 kgs and being paranoid I paint a lower 750 kg (1650lbs) SWL on the beam. I am ready to receive the steel.
This arrives one Friday morning on a 12m (40ft) trailer. I arrange to keep the trailer over the weekend, so the truck disconnects leaving me with 20 tonnes (44,000lbs) of steel to shift. I employ a labourer and we lift many of the lighter parts off by hand. Heavier items such as the bilge plates are dropped onto tyres and then wheeled inside on a sack truck. The remaining shell plating and bulkheads are too heavy for this so I hire the yard crane to get them inside the shed. With hindsight it would have been possible to do this by backing the trailer under the gantry but this would have meant leaving the shed unlocked all weekend, which would not have be appreciated by my new neighbour. There is a 2m (7′) diameter steel worktable in the yard. This is massively constructed and weighs two tonnes (4,400lbs). It forms a really accurate flat base on which to weld and we manage to borrow it for the duration of the build. The crane sets it up ahead of the build area.
We finish unloading Saturday midday and I spend the rest of the weekend checking the parts and trying to arrange the hundreds of smaller pieces into a logical order. I also use the gantry to lift and then, a plumb bob to position the 25mm thick 350kg (780lb) keel exactly into place on the cradle.
On Monday morning we start construction. Peter tack welds the keel to the cradle. We then use the gantry to place the three parts of the main bulkhead on our worktable where they are welded together. The whole sheet now weighing 500 kgs (1100lbs) is lifted turned over and welded from the other side. Permanent stiffeners are welded to this bulkhead along with a temporary one from top to bottom, which is tack welded in place. Flat steel is very floppy and long section may not even support its own weight when lifted. Throughout the construction 4m (14′) lengths of 3” x 3” timbers are “G”cramped to fragile pieces to stiffen them when lifting.
The bulkhead is lifted from the table to the vertical and the gantry pushed aft, before it is lowered it into place on the keel plate. It will be held here with scaffold poles so temporary lugs have been welded on the top corners. These prove too temporary as I use right angle scaffold fitting cut in half, unfortunately they are made of a different grade of steel to the bulkhead. The result is that early in the build I notice that they are tearing loose, threatening to destroy all our work and to drop the 4.4m (15”) high bulkhead on top of our heads. Such happenings produce nightmares. I replace the lugs with mild steel plates with scaffold diameter holes, while holding my breath, in case everything suddenly collapses.
A scaffold pole runs across the top and scaffold poles are used to form “A” frames at either side. The poles are drilled for a pin then fitted into the bottom half of “Acrow” props to make them adjustable. A template positions the bulkhead in place on the keel and datum triangles pre-designed on the bulkhead allow it to be accurately levelled. A plumb bob checks that it is vertical and measurements to either side from the forward end of the centre line check that it is exactly at right angles to the fore and aft line. It is welded to the keel. In one stroke I have created a three dimensional object that if packed in a box would takes up a space of over 90 m3.(3000cuft)

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