Wakesurf board rocker mold partline

You may remember back a post or two ago where we were removing all the sludge and imperfections from James’ 2011 wakesurf board in preparation for molding. The wakesurf board is a plug and will have several layers of gelcoat and fiberglass laid over it. However, the mold will be a three piece mold, basically a two piece top and a bottom. The top pieces and the bottom will mate along what is referred to as a flange that will mirror the wakesurf board rocker. The flange keeps the mold from “over compressing” and thereby retaining the correct shape of the final board. We’ll also use the flange to create alignment bumps so that when the top and bottom parts are aligned we can be assured that the inside cavity is also aligned.  We’ll attached some reinforcement along the middle of the mold to prevent the interior from flexing too much and the wakesurf board rocker will be retained by virtue of the flange areas and this extra reinforcement.

In order to create that partline for the flange, we need to have an foundation, so that we can apply succeeding layers of gelcoat or fiberglass over the mold being made, and prevent that from moving while the polyester resin is curing. We’ll start with a rather stout piece of pressed board, the one in the picture is about 3/4″ thick. It doesn’t readily flex and has significant mass so that it can be easily moved. The wakesurf board we are molding is about 4’5″ length overall and the foundation board is about 4 inches wider and longer to allow the flange to extend 2 inches around the outline of the board, in all directions. 

Once we have the foundation board we are going to create a rocker that mimics that of the wakesurf board, as closely as we can bend the board to match. In the picture below you can see scrap wood being aligned and tested that matched the wakesurf board rocker of the existing wakesurf board/plug.

Once the main crossmembers have been located a surface sheet is attached and affixed to the crossmembes such that the curve of the surface sheet is almost a perrfect recreation of the plug’s/wakesurf board rocker. We use a sheet of door skin luan for this surface sheet and we try and attach the surface sheet to the crossmembers as far to the outside of the sheet as possible. The reason being that as we lay down the gelcoat and fiberglass, we don’t want that to stick into a screw hole and cause a problem with the mold releasing.

Once the surface skin has been attached to the underlying framework, we go back and check for gaps or the skin tilting and shim the surface skin as needed to eliminate tilting and gaps.

Once the surface skin is aligned and affixed, we glue the plug to the surface skin using silicone. We want to be able to remove the mold and plug from the framework when we go to do the bottom half of the mold, so the silicone in a large thick bead will be easy to remove and will adequately hold the plug to the framework as we are applying gelcoat and fiberglass. One trick, we run a solid bead all along the perimeter of the board, just inboard enough that it won’t squish out and get in the way of the tucked rail, but close enough that any flowing gelcoat won’t get underneath the plug and stick it to the framework. We have also waxed the bottom of the board, so that just in case anything gets underneath it won’t stick!

This method works quite well when the wakesurf board design has been tested and finalized.  It’s also possible to create a plug from wood, or foam or anything else and the flange could actually be built into the plug itself.

Ok, so that’s all until the mold wax arrives and that should be here today. Thanks so much for following along and watching us build this mold.

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