Tuesday, January 30, 2007

Outer laminate A specification

After a great deal of huffing and puffing, thinking about e-glass, s-glass, carbon fiber and Kevlar materials. I have chosen to use the following for the A side specification.

The winner is two layers of a 7781 style 8.9 oz aerospace e-glass cloth from BGF. I think this will be a good match to my choice of the s-glass 6781 style for the inner B specification.

From the very beginning I have wanted to vacuum bag the laminations on the outer hull side, and I have seen how a very high quality laminate is achievable with two layers this style of cloth. It seems quite clear to me that the hand lay up of the inner hulls will seal the foam strips making the vacuum bagging of the outside hulls relatively straight forward.

More thoughts on vacuum bagging the panels

I made the decision at one point to first cut the foam panels out to the exact size of Ian Farriers full size templates and then laminate them. Over all, this has been successful approach. However, I have seen some evidence of the following issues where I might try to do better on future flat panel laminations.

  1. Peeling off the peel ply has resulted in lifting the laminate off slightly from an edge of the foam. It's been rare and I have tended to blame myself in getting carried away with the peel. After all, the ripping sound and required muscular effort in pulling the peel ply material off the laminate is quite therapeutic.
  2. The 90 degree corner of the foam probably weakens the laminate at the edge. Farriers build manual does warn about this issue.
So, next time I will laminate over sized foam panels by an inch or so and then cut them to the exact size with a jigsaw after lamination.

Saturday, January 27, 2007

Winter has arrived

I hope that my stored float half is OK.

Monday, January 22, 2007

Float bulkhead areas and calculation of resin to cloth weight ratios

I've finished a little experiment to estimate the resin to cloth weight ratio that I am achieving with the flat panel vacuum bagging technique. I understand that a good target is 40% resin content by weight to the fiberglass cloth.

I was wondering how best to estimate this ratio because you end up cutting off the extraneous cloth around the perimeter of the part. This makes the estimate of the amount of cloth on the final part difficult to calculate.

A better approach is to use Ian Farrier's dxf files which I purchased to CNC the main hull form frames. With the dxf files the areas of the floats can be computer calculated. These areas are shown in the picture above.

With these areas the specifications for the foam and cloth can be used to calculate weights.

For example consider the forward beam bulkhead

Calculation of the fiberglass cloth weight

  • 6781 style s-glass from BGF has a finished weight of 8.9 oz/yd^2
  • Both sides of the bulkhead are laminated with the top 18 in of each side getting extra reinforcement.
  • Full area of bulkhead = 265358 mm^2 = 411 in^2 = .317 yd^2 times two = .634yds^2
  • Extra reinforcement area = 192756 mm^2 = 298 in^2 = .23 yd^2 times two = .46 yds^2
  • Total cloth weight without resin is = (.46 + .634) yd^2 * 8.9 oz/yd^2 = 9.74 oz
Calculation of the foam weight
  • The Divinycell H80 foam has a weight of 5.0 lbs/ft3.
  • The bulkhead has an area of 2.85 ft^2
  • and has a volume of 2.85 ft^2 * .03125ft = .089 ft^3
  • and a weight of .44 lb * 16 oz/lb = 7.125 oz
  • This compares to an actual weight measurement of the foam at 6.5 oz taken before laminating.
  • I will take the average between the two at 6.81 oz +- 9%.
  • The final part after laminating was weighed at 25.3 oz.
  • Subtracting out the foam and the cloth gives 25.3 - 9.74 - 6.81 = 8.75 oz for the weight of the resin in the vacuum formed panel.
  • This gives a resin to glass ratio of 8.75 oz/ 9.53 oz = .92

Now consider the centre bulkhead.
  • Full area of bulkhead = 230009 mm^2 = 356 in^2 = .27 yd^2 times two = .54 yds^2
  • Total cloth weight without resin is = .54 yd^2 * 8.9 oz/yd^2 = 4.8 oz
  • Volume of foam 2.4 ft^2 * .03125 ft = .075 Ft^3
  • foam weight = 5 lb/ft^3 * .075Ft^3 = .375 lbs = 6 oz.
  • The final part after laminating was weighed at 14.05 oz.
    Subtracting out the foam and the cloth gives 14.05 - 6 - 4.8 = 3.25oz for the weight of the resin in the vacuum formed panel.
  • This gives a resin to glass ratio of 3.25 oz/ 4.7 oz = .69
So with ratios in the range from 70-90%, it does not look like I have achieved the theoretical optimum. However, I do suspect that the ratios appear high due to epoxy resin filling the perforation holes that are required in the foam. I do not want to remove any more resin.

Sunday, January 14, 2007

Laminating the second float bulkheads

It became a little cold to start the float hull lamination outside in the garage, so I have moved the work to the basement where I have set up the small vacuum bagging table to laminate the float bulkheads.

Laminating indoors you say, well, the Aeropoxy epoxy resin has almost no smell. The hardener has a bit of an odour, but after the resin is mixed there is very little to offend. The family has not complained at all. I just make sure I have lots of disposable vinyl gloves on hand. Home Depot sells them in packs of 100. They seem to stand up to the epoxy very well.

Quoting from the product bulletin

These products can be considered low toxicity materials that have minimum hazard potential when used properly and in a clean and responsible manner. PR2032 does not contain any hazardous diluents or extenders. Hardeners PH3660, PH3665 and PH3630 do not contain methylene dianiline ( MDA), or other potentially harmful aniline derivatives.
Anyway, I have 'bagged' the bow, stern and central bulkheads this weekend. Here are some of my current thoughts.

Since I have used a very slow hardener (rated at 2 hours), I tend to be most concerned about forcing too much of the epoxy out of the laminates and into the breather material, leaving the laminates possibly in a dry state susceptible to delamination.
  1. I am very careful not to start the vacuum pump too soon. I wait 2 hours after mixing the resin before starting the vacuum pump.
  2. I now use a finishing nail to perforate the foam. I used a hand drill earlier and I think I opened up the holes too large.
  3. I never use more than 2 layers of the breather felt material. I used more layers earlier thinking that 'more is bettter'. Quit often it is not.

Monday, January 01, 2007

Planking with structual foam - take two

Happy new year!
Now back to work.
My goal was to get the port side outer half planked and ready for laminating over my Christmas break from work at the office. I shall certainly achieve this goal. Work has proceeded much faster and my workmanship has improved from the first float half construction.

In the picture above you can see some of the elements of my current best technique.

  1. First I cut enough panels to the correct width and keep them handy. I am cutting them to 7 inch widths and use a table saw and guides to get a decent edge quality. The form frames on the deck side provide a handy storage location.
  2. Then I fit the individual panels. I use a tape measure to get the coarse length and cut the panel square. With the panel held in the frames and butted up against the deck flange I mark with pencil the width angle required and cut. I then carefully carve the edge on the keel side to the angle required to meet flush with the keel strip. This sequence repeats until you have enough fitted strips that can be glued in a work session.

  1. In a glueing session the strip edges are coated with the adhesive and then clamped together by using screws through the form frame battens from below. The screws I use are number #8 1-1/4 inch length applied with a washer to grab the maximum amount of foam without poking through the top surface of the foam. I am using a waterproof polyurethane construction adhesive that is relatively easy to apply and work with. The excess glue that is squeezed out onto the top surface I immediately clean off using a Popsicle stick. The adhesive does foam a bit during the curing process leaving a small high point. This cuts off readily with the sharp utility knife when fully cured. I do not try to clean up underneath. I have found that the excess adhesive, with the aid of gravity, does not smear and is easily cut off when the float is removed from the form frames.
I am not tracking hours on this project but this float half took me two foam fitting sessions and two gluing sessions. A session for me could never extend over 4 or 5 hours with the required dog walks and shopping with the family.