Sea State 12 foot SUP: deck plug forming

We polished the mold and trimmed the edge of the mold.  But before casting parts we decided to start making the mold for the deck of this SUP.

To do this, we are building up the shape we want in rigid foam and spray foam.  This gets disk sanded to shape.  After we get the shape roughed in, we will cover the foam with glass cloth and epoxy.  We will gradually work the shape into a moldable plug.  Then we will create the mold and will have all we need to begin producing parts.

Here is today's work:

The deck plug being formed inside of the hull mold.
The flange is clearly visible and will provide space to form the deck mold flange.

Tools of the trade.  The pioneers would not be impressed.

A radius edge piece provides a fair line.

SUP Plug: Step #8

Taking it up to a polish.
After a bout of other work, I have been able to spend some time on the plug this week.
Our goal is to make a mold of the plug before Sunday.

This will be the first of at least two molds.
To get there, we need to sand up through the grits to about 1500 grit.
Yesterday, after a little more spot filling and sanding, we achieved the uniform shape we needed.
So today we gave the plug a even sanding with 120 grit paper then 220 paper.
Tomorrow we will do 320 grit dry then 320 grit wet.
Each finer pass we will do first dry then wet.
After we get to 1500 wet, we will use buffing compound and a wool pad to bring it up to a mirror finish.

SUP Plug fairing: Step #3

The new Sea State board we are molding is in the first stages of fairing.  The substructure, built of wood is as close to fair as possible.  This is helpful.  It allows us to keep the fairing materials we will add thin and get to the finish sanding stages sooner.  If there are underlying rough spots in the plug's structure, you can spend a great deal of time fixing it.  It pays to go slow and not create problems that have to be dealt with later.

Today we are giving the entire plug a skim coat of fairing material.  Later today it will get a sanding and an additional fairing coat.  After that is sanded we will decide if additional passes are needed.  Once this process is completed, it will be time to move to spaying gel-coat.  Gel-coat bonds to the plug and provides a surface that can be sanded and buffed to a high gloss.

These two photos show the bow of the SUP before and
after a bit of fairing.

The dimensions of the board are:

12' length

32" max width

5" thick

The estimated volume will be about 230 liters.  This will be a stable board for novice riders up to 275 pounds.

Here is an overview of the bottom of the SUP's plug..

SUP Plug forming: Step #2

 After the bow is pulled together, the hull bottom naturally forms a nice gentle v shape.
So now after the shape is secured, we have the heights or thickness of the board established.  The next thing to do is to set the sheer line or top edge of the entire deck surface.
I do this by ripping some 1/4 inch strips of wood (poplar).  I then mark out from the hull bottom 1 inch around the edge of the hull.

I do taper in to "0" at the bow and stern.  Next I shoot in the poplar strips to these markings.  This edge gives us something to fair to and hopefully keep the shape of the sides fair.

Next I fill in the void with foam.  I've used bondo and wood before, but foam is fast and it is only a base for further fairing.

Here you can see the poplar strip at the bottom edge of the sanded foam.

A couple of passes with great stuff, let it firm up then sand it down.

These two photos show the foam before and after disk sanding to the chine and shear line.

 Next I mark the center line with a string to make sure we are straight.  On this board I wanted a detail at the centerline to provide a little thickness for strength.  It will not be a skeg, just a slight rounded v.  The internal deck supports made of carbon fiber tube will rest on this centerline.
To form this, first we start with a furring strip.

The bow will have a pronounced v section and we form this by adding a vertical piece of wood. 

After the epoxy holding it sets, we mark a nice fair transition  and plane it down.

Then we sand it below the eventual
final surface.

Here foam is shot in to conserve
fairing compound.

Next we will start adding many passes of
fairing compound.

Non-traditional plug fabrication

Having never learned surfboard shaping with a foam blank and a Skill 100 planer, I approached our paddle board plugs more like a small thin boat hull.
This means math and lofting.
On paper we decided on the overall characteristics for the board, next we decided on where the split would be in the form.  Then we start with the bottom half of the hull and build it up from a strong back.  Unlike a our past boats though, the strong back is a plywood plane.  (our second board has the rocker built in to the strong back (see below).
With thin ply, foam and fairing we shape the rails, rocker and concave.  This method allows us to easily keep the board symmetrical.  It also provides a great surface for the mold's flange.

After passes with gel coat, fairing and addition gel coat, the plug / form can get as smooth and fair as you like.