Boat Construction (7)

   While I was working on the inside hull, half of my class were working for a deck. I did not join in them directly,but I helped them sometimes and saw the processing. It follows same way of composite in 'F.R.P' course.  

In brief, on the moudle we waxed five times and polished with cheese clothes as well. Then we coated 'PVA' slightly.  After it dried, we put ' boat coat' and 'double bias' with expoxy resin. Put form on the glasses with microballoon gap filler and pressed them with vaccum bags.The method is that by sucking the air in the bag so odjects are keeping stuck together. In invers order, put double bias and boat coat on that. Last, put 'Low density fairing filler' on the top, because it is able to do sanding and painting easily. Once finish this procedure, it could be demoulding and join to hull.

Boat Construction (6)

For finising I needed to do coving. It is commonly used for making strong and tidy joint. However, it was much harder than my expectation. To obtain nice clean cove-shape,I firstly vaccumed the area and  prepared  a plastic rounded filleting tool, box of Aceton, a putty knife and rags. Once I make a glue with

Half model3

 There were gaps between the plug and the backing board, soI filled the gaps using a putty. Then, I must ensure that the surface of plug is very clean.

After that I did waxing on the surface. It helps to come off from the matrix which I will finally make. Normally, we need to do waxing around four times to six times. (I did six times for my half model) Also, we need to wait awhile for drying before spreading next wax. Actually, there were two kinds of wax in our workshop. 'TR 108 Basic Mould Release Wax' is that I used for coating my plug. 'Honey wax' is another one http://www.specialtyproductsco.com/specialty/Paste-Wax/Honey-Wax%C2%AE/flypage.tpl.html.

Two of other students who used honey wax, did not use PVA film liquid. It has a silicon additive so it prevents PVA

We have to make one more layer with  PVA (Polyvinyl acetate). I put the PVA liquid thinly with an edge of sponge. It needs 30minutes to an hour to dry. 

   The next step was gel coating.  For progressing this job, we need M.E.K.P as a hardener. The ratio of M.E.K.P to resin is between 1.5 to 2%. I used 700g of gel coat and I put 11ml (approximately 1.5%) of MEKP.

   Once mix these two liquids, we should start working immediately. It does not take long time to be solid.

   With an air brush, spay on the surface gently. Put sufficient amount of gel coat (between 0.75 to 0.5mm) especially the edge part because it might be cracked during the demolding proceesing.

I waited around three more hours for letting then dry.

The final stage was making the matrix with 'fiber stitchted rovings' and 'chopped strand mats'. I prepared 500g of Polyester and 2% of M.E.K.P (10ml). My group and I had to work quickly because the resin also becomes hard in a little while. At the first, filled all of edge part with fiber stitched rovings to make a clean out line. Then tore the chopped strand mats and pasted them onto the plug. Once the chopped strand mat is wetted by Plyester, it becomes limp. With a brush, sticked them nicely and get rid of all air bump with a compression roller. 

Half model 2

 Unfortunately,  my timber has pine resin, knots.  In addition, the bow part has some flaws so I needed to fix it. Actual process is coating the epoxy resin on the plug, however my half model had some scars, so I used another processing. My tutor suggested me to use "Dura tec" instead of epoxy resin for coating my plug.  It can cover all of bump surface of my half model and it is easy to do sanding.

       For using 'Dura tec' , we need a catalyst as well. M.E.K.P (Methyl Ethyl Ketone Peroxide)  is common catalyst with polyester resin. Normally, put 2~3 precents of primer's weight, so I used 1370 g of 'Dura tec' and added 30ml of  M.E.K.P

Primer (Dura tech) + 3% of Catalyst (M.E.K.P)

1370  + 30(M.E.K.P)

I used an air brush for coating 'Dura tec'. One of important thing when we work in F.R.P is wearing safety equipments. The materials are flammable and poisonous. It would really harmful for human body. That's why we have to ware safety equipment and must know how to deal with when emergency happened.

To fill the gaps, I brushed thickly. After drying Dura tec,  my group and I sanded the surface of the plug until all of scratch disappearing. 

Half model

I had a 7.3m yocht half breadth plan for making a half model plug.  

Cutting list

?? x 120 x 20(mm) radiata pine tree 

I put the plan on the pine timber and punched along the line. After that I cut them off along the dots with a band saw.There are nine timbers that I overlapped and between timbers become 'water lines'. Therefore, there are eight water lines. I put a thin dark colour timber between 3rd and 4th timber and it is 'load water line'.  

I made two dowel holes to put togerther easily. 

After gluing them together I shaved the model with a block plane and a spoke shave.

My group members made keel and rudder as well. The front point of the keel is positioned at station 7. The rudder is positioned on the transom

Size

Keel (pine)

Top - 88.7 left - 105.3 bottom - 61.3 right side 88.6 thickness - 5.4

Rudder(pine)

170 x 50 x 5