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Need a bag? (...and some other questions)

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Need a bag? (...and some other questions)

Postby keyes1 » Sat Apr 02, 2011 7:39 pm

To make fiberglass laminated boards do you really need a vacuum bag? I've made longboards (the wheeled type - not surf) in the past by just laying it up by hand (onto a wood core) very successfully, but is there any advantages to a vac bag aside from being able to add more form/concave/rocker to the board? Does the pressure applied by vacuum bagging make it stronger through better adhesion?

Just asking since I'm in the process of making my first board (wood core). I don't have a bag, but I wasn't planning anything too elaborate, and I'm just wondering if there are any drawbacks or problems that I haven't considered.

I'm also wondering about some standard measurements for kiteboards. These are what I've found already, but maybe I'm missing some or have some mistakes:

Fins bolt centers - 1.5"
Footstrap baseplate centers - 6.5" (or 6" for cabrinha)
Grab handle centers - not sure yet?

Any other measurements I need to consider? Also, are footstraps placed along centerline or slightly towards toe side?

Sorry about the 20 questions, but thanks in advance for the help!

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Re: Need a bag? (...and some other questions)

Postby mattma » Sun Apr 03, 2011 12:43 am

Hi there

I'm not an expert in the area but have don a couple fo boards now and experimented a bit with vacuum bagging. I recently blog the whole process and thinking I wen through with my first board including making the vacuum pump and rocker table. I googled and worked through a lot of the questions that youve asked

Also a discussion has opened up on seabreeze about a guys first attempt at a ply board

Some quick answers based just on my googling and attempts
i) if your core is going to be made of dense wood ( ply ) then you can still produce a good board without vacuum bagging as the core provide so much of the flexural strenght that you may only need 1 layer of glass each side (ive even seen some folks just seal it with varnish) so there is almost no resin etc. If its lighter wood (balsa) or PVC foam ( Klegecell or Divinycell) then you board will suffer for not vacuuming bagging though again its not terminal. As far as I understand bagging does not imporve adhesion to the core material greatly. Epoxy ( recommended over polyesther) mechanically bonds to imperfections on the surface and if you are using plastics then many chemically bond with it ( especially if you rough them up and flame them to oxidize the surface so that the chemical bond is strong). What vac bagging will do it apply lots of evenly distributed pressure so that you get uniform coverage of the resin (no peaks and troughs which can introduce weakness a fault line) and it will squeeze out excess resin so that you get the right reinforcement/resin ratio. The weight saving when you are using multiple layers of glass can be very significant (up to 60%) .

ii) other measurements - the width and the rocker have a first order impace on performance. I've found that lenth is less important than may think and is trumped by the impact of width.
No standard measurements I'm aware of as it depends on your weight and you ridign conditions and the style you prefer. The most common baords I see are 39-41cm wide and 132cm long.
Rocker 2.5cm is considered 'flat' and is great for flat water, early planing and light wind boards. 5cm is about as much as you'd want in a kitebaord because as you add more rocker to it the board crerates more drag as it moves in the water which means less upwind ability and slower board but the pop will be great! Wakeboards have around 6cm of rocker. Concave can help stiff the board and help the rail grip as it increases the angle the rail digs into the water.
10mmm concave is a lot and 5mm is pretty common. Lots of concave does tend to increase how frequently you dig your toeside edge in buyt you can compensate for that with your stance.
However, for the the dury is out on whether you need it for really stiff core material.
Its important to remember that stiff cores that start out life flat and you bend them through wetting drying them will spring back and you can loose up to 20% of the rocker and concave you put in. So over estimate.

iii) The foot strap placement. The instep fasteners typically go on or just above the center line and the outside ones about 1" below. The typical spacing for the pads is 6" but this is not standard so might be worth getting the pads before you place the holes. For example
my crazy fly ones are 6.25". Boots are typically 8". The stance width (measured centre to center of the pad) is around 18"-24" range. Wider stance is better for solid landings and poping, narrower better for free ride. Ulitimately you just need to make sure its comfortable
so that it doesn't get you off the water sooner than you need to.

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