Sunday, March 13, 2011

Pram build - Step 3 - Assembling bulkheads

Once the bulkheads are framed the next step is to actually mount them on the building jig. I used 1x4 planking to mount the bulkheads but anything of reasonable size can be used. I cut my planking to 2' but that's actually longer than required. 18" is probably lots for these.

The height of the bulkheads above the building jig isn't on the plans directly but can be derived from them. This took me a little bit of time to figure out initially. To save you the same effort, here are the table of values for these heights. The last column has the values of interest, the others are for reference. All measurements are in inches (and fractions of inches):

Here are the steps:

  • Install the 1x4 vertical boards at each station. Make sure that they are square to the jig. I offset the boards by 1/4" so that the bulkheads would sit exactly at the station mark.
  •  Next I installed a temporary baseline from end to end of the jig. This was used to validate my measurements against the plan measurements (since they are mostly done in relation to the baseline.) I used a simple piece of string strung between both ends at the baseline height (2' 21/2"). I also used this as a guide for centering the bulkheads as I mounted them.

  • I then marked on each of the verticals the height for that bulkhead. (using the values above)

  • I then mounted each of the bulkheads at the measured heights. I hung a plumb line off of the baseline in order to line up the bulkheads. 

Since the bulkheads and temporary molds are different sizes it makes the whole thing looked a little wonky when you get them mounted. I checked the overall shape by using a long thin piece of wood and laying it from end to end at various positions on the bulkheads. Everything seems to check out well. I did adjust bulkhead #2 down 1/4" to make sure it was fair. 

I'll cut off the extra bits of the vertical pieces once I've got my stringers in place. 

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