This weekend we started the process of forming a plug to make a mold to make out next line of SUPs.
The plan was to make some improvements that would allow us to make a hull that is more rigid, lighter and a little more graceful.
The new hull form is that of a flat water touring hull. This is a displacement hull. This means a long form, low rocker and a water cutting bow. SUPs that are used in surf become planning hulls and benefit from rocker and being as short as practical. All SUPs that are not being used this way (95 + %) are displacement hulls whether they are designed this way or not.
Our new board started out with these concepts in mind and this sketch:
From this start we began to loft the shape onto ply.
We have worked out a process to get to the plug.
Here it is...
We first get a ply material. Of course, the plug never gets anywhere near water, so almost any ply will work. In the past we have used masonite, this time we are using OSB.
We use battens to draw on a half profile. This is one side of the board up to the centerline.
We use the machine edge of the ply for the center because it is reliably straight.
Once this is cut we use a hand planer to smooth the outer profile. Then we use this shape to cut out it's other half. These two halves are then affixed to the molding surface.
Because the length of the board is longer than standard sheet goods, we have to sister together the parts. We do this by adding a ply piece on the underside with glue and screws. This makes a stiff spot in the bendable ply but if it is in near the middle of the board this is not a problem and will be sanded and faired away.
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| This is the lap joint. |
The next thing we do is to make a surface which mimics the shape of the eventual deck of the SUP.
We do this by bending an oversized piece of ply on saw horses. The extra width provides a place for the flange of the mold. The plug is formed right up to this plane and when the parts come out of the mold they have this same curved shape that will accept the deck. Here some photos:
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This is the sistered together half board profile. It is 11 feet 9 inches.
Once the fairing is complete, the board will grow to an even 12 feet. |
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Here is the deck molding surface. We introduced some rocker into this plane for fun and beauty. The half shape is being affixed with specific heights and with a taper.
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| The thickness of the board is determined by this height. We have set the maximum thickness of this SUP at 5 inches. |
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This shows the two halves set on the centerline.
A bit of material was removed on both sides in the rear.
They are screwed down flush at the tail and nowhere else yet. |
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When the bow is pulled together, this introduces a
little pucker which gives the hull a 'v' profile.
A sistered board underneath holds it together.
Then shims and screws are used to support this
shape.
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