Tuesday, January 13, 2015

Joining the mast sections

Last weekend we put in a good day on the aft rig. The big accomplishment was joining the two sections of pipe for the mast. We used a backing strip and full penetration weld. The trickiest part of this operation was getting the two sections lined up perfectly and keeping them that way throughout the welding process. We used three heavy flat bars for this, along with a lot of checking for true as we went along. The end result looks great and is totally true and straight. Next was welding up the "cross trees" which (along with 1/2" plate gussets) form the foundation for the crows nest, and the attachment points for the fwd diagonal bracing pipes that transfer most of the load from the paravanes down to the anchor points on the wheelhouse roof. Again, lots of measuring and eyeballing here to make sure we get everything straight and true. At the last minute, I decided to have the outboard 4 feet of the cross trees flanged so they can be bolted in place. The overall length of the cross trees has to be almost 6 1/2 ft on each side in order to provide a cradle for the down rigger poles. If welded to the mast in all one piece, this would have made the mast really cumbersome to move around and work on, so I think it was the right call. In the last couple of pics the crows nest is rough fitted on to the mast. Next workday, we"ll be squaring it up to the mast and welding it in place.

I am starting to put together a parts list for the exhaust extension, which will take the main engine exhaust up the mast and have it exit clear of the sail and other rigging. Here's some of my "cocktail napkin engineering" on that concept:

The next round of work on the rig will also include finishing up the down riggers and support pole connections. We got a little head start on laying these out and the geometry and clearances all look good so far. In the orientation shown below, the fore and aft hinge plates would be welded to the side-shell of the hull- the main down rigger pole hinge just aft of the wheelhouse and the fwd support strut hinge just ahead of the wheelhouse. According to the measurement below, it looks like we'll be able to board through the side gate and the stbd wheelhouse door with plenty of head room when the poles are stowed in the up position.

Also, I've been looking for a source for nice pre-made heavy duty bolt on pipe collars/brackets(?) in stainless for standard sch 40/80 pipe. These would be handy for attaching some of the cross bracing structure on the rig, the exact location of which can't really be finalized until the mast and down riggers are actaully installed on the boat. I've seen them on Nordhaven rigs and other fancy trawlers spars. We could fabricate these if necessary, but its quite a bit of work to get them right for a structural application. If anyone has any leads on these, please let me know.

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