Monday, February 16, 2015

Aka Brackets

The plans call for four hat-shaped brackets on the back of the main bulkheads to carry the akas. These are simple e-glass structures.  Further structural steps on the akas will keep them from laying flat, so these need to be moulded now.

The green tape shows the designed width of the brackets.  The blue tape is a target area for me to layup.  I made them oversize so that alignment issues and rough edges can be removed.

This shows nine layers of wet glass. I used some 4 oz. plain weave left over from another boat.  There was a small amount of colloidal silica in the epoxy to help fill the weave.  The dark area on the right is where epoxy seeped through the packing tape covering the beam below the layup.

This is a rough trimmed part.  This will be properly trimmed when it goes into the boat.  It would be easier to glue them to the bulkhead on a flat table before going into the hull.   The bracket would block access for filleting the bulkhead to the hull, so it will have to wait.

Task time: 8 hours
Total project time: 490 hours

Saturday, February 14, 2015

Big Bag

I have been working on the last layups for the main structural element of the beams.  The akas required a lot of fairing due to the stair-step shape of the pultrusion laid on the tops and bottoms. Unfortunately this added a bit of weight and lost some of the advantage of pultrusion over regular uni.  The layers did not quite span the width of the beam.  Some of this may have been caused by rounding over the edges of the wood frame prematurely.  We had not decided to use the pultrusion until after this step was done.  I have not done all the math, but I might have been able to get layers of six rods across if I had had the full flat width of the beam.  But, that might have required rounding of the edges of pultrusion causing a loss of strength.  Future builders should definitely look carefully at the options to cut weight and fairing effort 

I ended up laying battens on the sides to dam up fairing compound.  I then sanded the tops and sides to square corners.  The corners were then true enough to run a roundover router bit down the edges getting an even, eased corner and removing some of the excess weight.

This is 6 inch diameter 14.2 oz sleeve (481 gm/sq m) rather than 11.7 oz called for in the plans.  I had my choice of 7 oz or 14.2 oz cloth, so I went with the heavier.  This again is extra weight, but it will add strength and stiffness.  The sleeve came from Soller Composites. ACP Composites is another source.  They seem to have pretty much the same product line.

The python in action.

The 6 inch sleeve was able to conform well to the variance in circumference on the beam, from 13 to 22 inches.

A shot of the 18 foot vacuum bag.  It took two of us about two hours to wet out the sleeve and bag up the aka.  I bought some extra slow hardener to give us some more time.  The shop was about 65 degrees.  Once the vacuum was on, I raised it to 78 degrees and left it overnight.  The wet beam was quite unwieldy.  It had to be flipped several times.  As with the mainsheet beams, I felt I could not get pre-wetted carbon over the beam.  I got a little paranoid with the epoxy and used plenty to ensure it was wet all the way through.  I figured the vacuum bag would remove the excess.

Overall, I am fairly pleased with the result.  The sleeve is well adhered and the weave is well filled.

I had some annoying surface wrinkles.  I think this is excess epoxy that pooled in some places.  I am able to flatten these with just a few strokes of sharp 220 paper on a flat board.  The dust is white rather than black, so I'm not sanding carbon.  Wrinkles in cloth this heavy would have been much larger. Getting peel ply and perforated release plastic on the compound curves was a pain, especially having to shift the aka multiple times.  I wish I knew more about these processes, so I could get nicer results.

Foam cowlings now have to go on one side before the last layer.  I will probably use carbon or fiberglass sleeves over the foam.  It is smoother and maybe stronger that patches of regular cloth.  The shape with the foam will be even more challenging.  Perhaps it should be infused?

With all the fairing, these steps on the two akas are taking about 80 hours.

Task time: 80 hours
Total project time: 482 hours

Saturday, February 7, 2015

More of the Same

There has been slow steady progress.  Most of the work has been on the akas and mainsheet beams and I have posted about those before.

This is the 16th and final pultrusion glue up on the beams.  Nice to have that done.

Here is a quick vid of the outer sleeve going on the second mainsheet beam.

The wet-out went on for a while to force epoxy through the sleeve.

Task time: 40 hours
Total project time: 402 hours 

Friday, February 6, 2015

First Double Bias Layup on Second Aka

Here are a few shots of my evolving technique for laying heavy 12 ounce double bias carbon on an aka over wood and pultrusion.

Cut the cloth.  I was using about 4 foot sections.  On the first aka I used longer ones, but they were difficult to handle.  They also did not want to conform to the curve of the beam well.  They would trail off over the side make for uneven overlap points.

Prime the raw plywood on the beam.

Start wetting out the cloth.  This stuff soaks up crazy amounts of epoxy.  You need to use plenty and be very patient about getting it thoroughly wet and even.

I spread a wave of epoxy back and forth making sure to get all edges.  I have been using a very liberal amount.  Excess epoxy rolls off the cloth, but can be scavenged back to the middle.  After one side is wet I flip the cloth and start over.  Usually the other side of the cloth is only about 10% wet when turned.

Once both sides are quite wet, I fold the plastic over the cloth to create an envelope.

The envelope is squeegeed with heavy pressure.

The squeegee creates a wave of air and epoxy.  It is very difficult to see how wet the cloth is prior to this.  I pull the epoxy in about six directions (+-90 and +-45).  I flip the envelope and do it again on the other side. At this point, I'm pretty sure that it is wet all the way through.  I carefully peel back the envelope and the peel off the cloth.  This needs to be done with even pull as one does when removing tape.  Uneven peeling will distort the cloth and fray the edges.

The cloth is transported gingerly to the aka.  I have been overlapping about a half inch.  The wet cloth is firmly milked  across the beam with the gloved hand  I Want it tight and smooth.  

Later, the rise in the overlap will need to be carefully ground back smooth. I only want disturb the second layer and feather it in.

Peel ply is stretched across the surface.  It gets wetter than this picture as it is worked to get the air out smoothly.  The peel ply is a lot less compliant on the curves than the carbon and usually needs a few darts along the sides.

Task time: 4 hours
Total project time: 362 hours