January 19, 2003

 

Progress on the PH8 is proceeding well, although it is taking more time than budgeted.

    We are now concentrating on the aft portions of the hulls, from engine room to the aft transom and the territory comes with many technical problems to solve, like propeller shaft housing, rudder, engine mounts, to name the most challenging ones.

As a sort of "side job" the hull plating continues and more than 2/3 of the plating is in place. With a very baffling problem. The inside of the hulls are almost completely plated and we were speedily proceeding with the plating of the two tunnels, when our second welder (a lady) asked an innocent question: "Once the tunnels are plated, how are we going to weld inside the hulls?". I admit that for the first moment I was baffled, but suddenly it also dawned on me. Both welding machines (TIG and MIG) have about 8 m long cables that go from the welding machine to the welding grip, which is about the maximum recommended length by the equipment manufacturer, especially for the MIG welding machine, where the welding wire is supplied though the cable. We may just reach the bottom of a hull from the outside, draping the welding cable over the side, but this would mean that we have to constantly move a machine weighing about 300 kg and another weighing about 100 kg from side to side. Not a satisfactory solution. Or we could place the welding equipment on the wing deck when working inside the hulls, on plywood to distribute the weight. But I don't know if I want to subject at this point the structure to such a concentrated weight.  Besides the equipment would have to be moved up and down, so at this moment I postponed any decision by not plating one side of the tunnel. 

We also had our first inspection by RINA,  the Italian certification agency. It went well except that we have to make quite a bit longer welds.  We tried to get away with a healthy minimum of welding, in agreement with our Italian engineer. Not because of time, but because the more you weld, the more you distort aluminum and have to work hard bracing and clamping to keep distortions to a minimum. When I started to argue saying that in New Zealand the original design called for the frames on the sides not to even touch the hull skin he told me that he would never accept such a way of constructing a boat, then looked at me in the eyes and said:
" I understand you want an A (unlimited) CE classification"
"Yes"
"And you plan to go out on the ocean yourself with this boat?"
"Yes"
"Then follow my recommendations.  You will sleep better".

 

Welding distortion is a big problem when building a complex boat like a catamaran in alloy. (The aluminum used contains 4 to 5% of Magnesium).  When you weld a complex part, like the hull where the propeller shaft exits, the resulting forces will find a weak spot, sometimes with tragic results.

The propeller shaft housing is an alloy tube of 80 mm  OD, and a wall thickness of 5 mm. It cuts though the keel, and I was not worried about the wall thickness, because eventually the skin would take a lot of the load. Then we started to weld the skin on the bottom part and suddenly the perfectly round prop shaft tube, where the cutless bearing was going to be, had become oval. Not just a bit but an eccentricity of about 5-6 mm!  Welding had exposed a weak part.

 

    The remedy was to make a hole in a 400 mm long and 105 mm thick alloy bar and manufacture a stronger tube to go though the keel.

The picture shows the new tube only tack welded to the keel, with a provisional inserted steel tube and steel reinforcement to keep the alignment during welding

The RINA inspector told me that the boat will have to pass quite a few tests, a few of them, like the stability tests, with the cat in the water. Another test will be the hydrostatic test of the two fuel tanks.  They will have to be filled with water and then pressurized to 0,2 Bar.

So I have come to the decision that, regardless of the possible transport problems, I will launch the cat this Summer in the lake and do all the testing here, where we have all the facilities at hand, and not in some yard somewhere at the seaside. This will enable us to finish all the interiors and extras not in  a hurry, since I will then take the finished and certified boat to the sea in the Spring of 2004. The testing and running such a novel big boat on Lake Maggiore will be an interesting experience, to say the least.

 

2003-01-19
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