Mast Compression Block

Getting some errands out of the way earlier in the day, I managed to grab a couple hours in the shop preparing the mast compression block.  This block will eventually find its home underneath a floor timber at the primary/ mast bulkheads, and is designed to take and transfer the mast's load directly to the keel through a mast compression post spanning the vertical space from the overhead to the floor timber.  The compression block will be a lamination of 1/2" fiberglass sheet, as well as teak and purpleheart woods.  The fiberglass will be used as the bottom layers of the lamination for its obvious density and ability to take load, but also to avoid deterioration of the block as a result of potential water contact - any water draining from the chain lockers will run along this upper part of the bilge on its way back to an aft bilge pump.

I began by roughing up the factory-finished surfaces of the 1/2" fiberglass sheet.  The pink-colored board you see in the picture below began as a fairly bright shade of red.  Abrading the smooth surface will promote a good bond in the laminating process.  Next, I divided the sheet into four 6" blocks.

Since fiberglass is so harsh on the blades, I put an aging, sacrificial blade in the table saw prior to cutting the 1/2" sheet.

I took the four 6" X 6" blocks up into the boat to take some preliminary measurements.  After stacking the four blocks on top of one another, I slide them underneath the floor timber, resting on the keel, and took a measurement aft of the floor timber...

...and on the forward side of the floor timber.

The measurements varied from roughly 2 3/4" forward to 2 3/8" on the aft side.  This variance was due to the port bulkhead "hanging" a bit lower than the floor timber that rested against it.  The void between the top of the fiberglass stack and the underside of the floor timber would be taken up by hardwoods capable of taking substantial compression force.  The species I have decided to use are teak and purpleheart.  I would of liked to have had a single block of teak to use in conjunction with the fiberglass lamination, but no such luck.  The 1/2" sheet of purpleheart will be placed on top of the teak and, having a modulus of rupture measure of 22,000 pounds force per square inch, would provide great strength in the overall mast compression block lamination.

The mast compression block as it will be laminated, and to be placed underneath the floor timber to span the space between the underside of the floor timber and the keel.

The compression block measures about 4.5" in thickness.  Epoxy, thickened with cabosil, will be used to set the mast compression block in place and to fill any small voids.  Next step will be to epoxy bond the lamination together to create one, solid block.  The block will also be completely sealed with epoxy as it is placed in its final resting position.

Total Time: 2.5 Hrs