Sunday, March 16, 2008

Vacuum bagging hull stiffeners

I decided to glass in some Taco hull stiffeners to add some stiffness to the hull. They are made of a stiff but flexible plastic and were very easy to install. When accidentally stepped on they would deform and spring right back into shape, a nice feature when installing them into confined spaces where the odd mis-step is inevitable. Two of us held them in place and drew the location on the hull, then they were removed to the cockpit for safe keeping and the area was sanded with a Dewalt zirconia flap disc. The area was vacuumed several times and the stiffeners were spot glued into place using a hot glue gun. A final sanding was done with 80 grit da disks and the area was vacuumed once more. Mastic was applied around the area to be bagged.
Note: In the picture below the mastic was applied around only one stiffener, we changed this to surround both stiffeners when we realized the bagging film was large enough to cover two at once.

I borrowed the propane tent heater from work and set it up under the boat and ducted it into the lazzerette hatch with 16 inch insulated flex duct. The heater was ran for an hour to warm the hull and turned off during the glassing layup. The temperature of the outside of the hull was taken using an infra red temp gun. The cockpit area was 131 degrees F., the temperature dropped as readings were taken moving towards the bow with the outside hull temperature in the area of the vacuum bagging being 75 degrees F.

The biaxial glass and vacuum bagging materials were cut to fit and placed in the cockpit.
West system epoxy was used and the resin dispensed into several mixing tubs ready for the hardener to be added as required. The first batch was mixed and placed into the wringer basin, a small amount was taken below and rolled onto the area to wet it out.
The cloth was fed into the resin bath and then through the rollers to remove excess resin. This is definitely a two person job! Be sure to tape the leading edge of the cloth to prevent stray strands from winding themselves around the rollers. The cloth is throughly wet out but can held on edge without resin dripping from it. The cloth was taken below, laid in place, and rolled with a 4" foam roller. Peel ply (release fabric), breather cloth, and the plastic bag film were then applied. A small cut was made in the film and the vacuum suction cup placed onto it. This was the first time I had used the vacuum bagging equipment and it was impossible to achieve a vacuum on the irregular hull surface using the mastic alone. After several failed attempts to achieve a vacuum, shrink wrapping tape was applied around the perimeter and a vacuum was created. For the next round of vacuum bagging the area where the mastic is applied will have a coat of west system epoxy thickened with some low density fairing compound applied to ensure a smooth and regular surface for the sealant.

Once the vacuum was achieved the heater was turned on and the tools cleaned with acetone.


eggersd said...

I need to add hull stiffeners to my 22 foot boat also. I've seen a lot about "hat shaped" square profile, but not much with a 1/2 tube profile. How does the strength compare? Where did you get the 1/2 tube mandrel?

Don said...

I got the plastic stiffeners from Taco metals (link below) They do a very good job at stiffening the hull, have not compared them to hat stiffeners but they seem very appropriate for small sailboats.

eggersd said...

Thanks Don, Hey what size stiffener did you use? I have Merit 22'
and need to stiffen up the aft quarter section. She'll never be a
blue water boat, mainly lake sailing, club racing, and light coastal
cruising. I want to keep the weight down.
Thanks for your advice.

Don said...

Derek, I used both sizes depending on the area and how much deflection pre-existed. If you send me a mailing address I'll snip a few inches off both sizes and send them to you so can decide which would be more suitable for the application.
I approve posts before they are published on the blog and will not publish you address.

Cheers, Don

Don said...

Derek, Parts are on the way :-)