The purpose of the internal blocking is to support the fin system, leash and vent plugs, and any tiedowns or accessories you may decide to build into your board. Internal blocking can add significant weight to the board if materials aren’t chosen carefully. Some builders use paulownia or balsa for internal blocking and some use high density EPS foam. Watertight compartments for extended touring (if desired) should be finished prior to the internal blocking. Deck hatches should have appropriate support blocking attached to the underside of the deck.
The photo below shows the internal blocking for a five fin surf SUP with the vent and leash set blocking. Note the notched block on the lower right of the photo which is the air path for the brass vent.
Careful layout and planning will avoid time consuming and frustrating problems. Selecting the fin system, vent and leash sets you are going to use early in the process is critical to “getting it right”. I’ve found Robin Mair/Gearbox Surf to be an excellent source of information about fin placement for surf SUP’s https://www.gearbox.surf/gearbox/fin-setup-primer/ You can also check out https://www.gearbox.surf/gearbox/install-details/ and
Carrying grips for SUP’s care be as simple and attractive as a block of wood machined to for a hand pocket. The block is glued into position along with the other internal blocking. Off the centerline grip installations suit many builders and doesn’t disrupt the integrity of the spar. The fore and aft balance point should be determined after the fin and vent/leash blocking is installed.
There are many ways to learn to safely use the tools and execute the processes necessary to build your hollow board. But the bottom line is this: Tools and the dust they create are dangerous. If you are a novice woodworker, educate yourself about tool safety and proper shop practices. Power tools are very unforgiving and trouble can happen quickly if you are not prepared and diligent in your approach to how you use these tools. Regarding the health consequences of breathing wood dust, take this issue seriously. Use good respirators with fresh, clean filters when cutting or sanding wood. This is also true for applying and sanding epoxy and other finish products. Uncured epoxy is toxic. Most of the ultra violet inhibiting finishes that go over the epoxy for the final finish are also toxic. Use the tools and materials at your own risk. Educate yourself and work smart and safe!