Monday, January 6, 2014

Mast Compression Block Install

After final preparations were made to the mast compression block (laminating, wrapping in cloth, fairing minor imperfections), I got around to installing it Sunday, the 5th of January.  The mast compression block would be the final leg of a vertical structure taking the mast load to the keel.  The block measures 6" x 6" x 4.5", a cube, and is laminated in construction; it consists of 4 1/2" thick solid fiberglass sheets, an 8/4" thick teak block, and a 1/2" thick block of purpleheart.  With some last minute trimming of the port mast bulkhead to bring in line with the underside of the floor timber, I vacuumed all surfaces and wiped down with solvent to prepare for the installation.

Placing the solid block into position, I took some measurements for length of cloth (1708 biaxial) and generally preparing for the installation - rehearsing the install mentally so as to avoid unnecessary complications.

The dry-fit from overhead shows good position for the block to accept a distributed load from the floor timber.  A final section of the floor timber will go in after this installation of the mast compression block.  For the picture below, the final 3/4" thick meranti board will be attached to the existing floor timber on the forward side (the upper portion of the picture).  This final section of the floor timber will serve to accept the forward sole substrate.

The dry-fit of the mast compression block standing forward of the floor timber, looking aft from the starboard side...

...and a final picture of the dry-fit from the port side.

Satisfied with the mast compression block's dry-fit, I went ahead and measured for the cloth needed for the installation.  Only one length of 1708 biaxial would be used for this initial bonding in of the compression block, the balance of the pieces would be used to clean up the uneven glass in the forward portion of the salon's bilge.  There were voids that I wanted to fill and clean up in this area.  The glass cut list, shown below, is sitting in the referenced area. 

With final preparations made, I moved the epoxy dispensing system to the boat and set-up a work area for mixing and saturating the cloth.  First step was to mix a small amount of the epoxy to wet-out the work area.

Another shot of the work area prepped for further work.

With the temperature in the mid-70s, I work feverishly through the bonding process to ensure maximum working time before batches of epoxy began to cure - time is money when it comes to working with epoxy!  So, as a result of my frantic pace, I took no pictures of the bonding process.  The remaining pictures show the completed installation of the mast compression block.  Wet cloth can be seen standing  proud of the top of the floor timber, and this will be ground off after it fully cures.  The picture below provides a good overview of the work area.  With thickened epoxy (colloidal silica), I applied a liberal amount directly on the keel / bilge underneath the floor timber.  The uneven surfaces would be filled by this thick mixture and provide an excellent foundation for the block.  I spread a good amount on the top of the block as well, and then placed the 14" length of cloth (saturated with epoxy) on top of the block.  I then slid the block into place, resting underneath the floor timber.  I wrapped the lengths of glass up both the forward and aft side the floor timber, and rolled out air bubbles in the cloth.  With the balance of the thickened epoxy and with a squeegee, I presses the mixture into the voids, top and bottom.

As mentioned above, while I was working in the area, I took the opportunity to address some sloppy glass work from the boat's initial lay-up.  The water tanks will eventually be installed in this portion of the bilge - the main salon, stretching nearly 11 feet - and wanted to prepare as reasonably smooth surface for the bilge.  I began by applying thickened epoxy (colloidal silica) to the voids and valleys.  I then came back with 4 pieces of 1708 biaxial to improve the surface in this forward section.

The mast compression block after the installation, top view.

Finally, the mast compression block installed - standing forward of the floor timber and looking aft.  There will be further tabbing work on the floor timber as well as dressing up the fillets around the base of the mast compression block, but this served as the initial install of the block.

Total Time: 5 Hrs.


  1. Did you source the 1/2" fiberglass sheets or make them yourself? I'd be interested if you had a source.

    1. Tate, I purchased from McMaster Carr. Incredible inventory + super speedy delivery = you're new favorite store.