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June 1, 2002.  Well, here I have made two hull halfs by joining the top quarter sections together with epoxy mixed with cut fibers. I also did that with  the two rear (stern) sections.  I did this while the pieces were on their sides to make it easier to epoxy.  I will wait to join the halfs until I have the lift duct in place as I do not want to  have to flip over the entire hull unless I have to.  I also need to add a 1' section to the rear which I will do this week (I hope).  Others have used foam in the can or two-part foam to join foam sections together.  That may be a better approach as the epoxy is over kill but it was easier than trying to figure out how to keep the foam "glue" from pushing the foam blocks apart when it expands.  The epoxy does not expand so the foam blocks stay in alignment.   Mike is holding up the foam....
Another view of the foam halfs after being cut and epoxied.
The piece of square foam in the front has not been cut to shape yet with the Hotwire cutter.  The block is needed as the middle of the big blocks was cut out to make the side risers with the hotwire cutter. Now I have to fill in the space in the front.
June 5, 2002. Front piece of foam is cut to shape.  The wood guides are 1/2 x 2 wood screwed into the foam to provide a guide for the hot wire bow.  It worked well.  I will leave them on to cut the lift duct later. 

 
The end foam block is also now cut to the correct size of 8" thick.  It will make up the stern of the HC. I will attach it this weekend.
These are 1 x 8 pine that I am coating with epoxy.  They will be attached to the bottom of the stern section  with epoxy to help distribute the weight of the engine like in a UH-15T.
June 8, 2002.  When cutting the hole for the lift duct I found that there was a large void between the foam quarters.  It looks like the epoxy got too hot and melted the foam some.  Not a big deal as I will fill it with foam but kind of a pain.  I will drill holes in the rear half along the center joint and fill in any voids in that section also.  Since the foam will be laminated with a wood and fiberglass deck and the bottom will be fiberglassed, the strength of the joint will be a minor factor in the overall strength of the hull.  But I will use foam to join the bow and stern halfs now that I know.  However, I could not break the two pieces of foam apart using considerable force even with the void.
June 10, 2002. To test how well the foam in the can would fill the void I made a test with the foam I had cut out for the lift duct.  I sprayed in the foam and let it cure over night.  Then I cut out a section to see what it looked like.  It did well and the can foam is denser than the Styrofoam.
Then I filled the gaps in the bow section by drilling holes along the joint line and sprayed in the foam.  Took almost a full can.  I would start the fill at an end hole and wait for the foam to start coming out a hole down the line.  Then I would repeat the process by injecting the foam in a further hole.  Kind of a mess but it works.
Did the same for the stern but there did not seem to be any major voids.  I guess the heat was not as great.  Maybe we used less epoxy but I really do not know.  The long drill bit is what I used to make the holes into the center of the foam.
Here are the groves cut in the bottom of the hull for the engine mount reinforcement wood.  The wood will be foamed into place later.  The groves are 24" center-to-center, 9" wide and 1.5" deep.
June 12, 2002.  The front of a 12T4 has a shallow curve to it.  Here we are cutting the curve on the front of the hull with a gravity hotwire cutter.  It worked pretty well but we cut proud of the line to prevent a mistake.  We will now sand it to the line we drew on the hull.  Mark is a future aeronautical engineer and does a great job.
June 14, 2002.  Well today Mark and I filled in the duct area with a combination of foam-in-can and 2-part foam.  Then I used a router to route out a groove for the aluminum skirt attach strip to fit into.  The plans call for a wood strip but I figure aluminum with fiberglass over it would be better.  I used a long piece of wood as a router guide and clamped it to the side hotwire guides I had left on the bow.  BTW, a router makes quite the mess.
Used 2-part foam to glue in the aluminum attach strip.  I will fiberglass over it when I fiberglass the bow which may be tomorrow. 
Well, Mike, Mark and I sanded and shaped today.  Does not look like all that much got done but the sanding took a long time.  We added the grove for the upper skirt attach strip but I ran out of two part foam so could not finish today.  We were also patching the front some but while we fixed the indent we had, we created two indents to either side of the patch as the foam sands easier (a lot easier) than the epoxy with micro bubbles.  I will add a piece of fiberglass to the front to protect it then we will go through the drill again to get a smooth front.
June 22, 2002.  Not much activity this week but I did foam in the top attach strip and sanded it down.  This I filled in the holes remaining with an epoxy/glass bubbles mix.  The glass bubbles are really really fine glass.  I use a face mask and mix them outside and stay up wind of them....
Then I added a 8.8 oz layer of fiberglass down over the section.  The 8 oz glass is pretty stiff and hard to work with.  It actually came out ok.  In the picture it what looks like air bubbles are just different color fill material underneath the glass (mostly).  However, I think I will go to the vacuum bag technique to help prevent air bubbles.  Ken Jansen wired up the pump so it should be good to go with the vacuum system.  We will soon see.
June 29, 2002.  Joined the hull half together today.  I used a router to add groves about 3/4" x 3/4" x 6.5' in the ends of the two halfs to allow the 2-part foam a place to expand and lock the two pieces together well.  Chris Keirs helped level the two halfs and then we used duct tape to seal the sides and bottom (well almost seal) to constrain the foam from flowing out as we poured it in.  We each poured in foam from different sides as the foam starts expanding faster than one person can really deal with it.  We ended up using about16 oz of the 2-part foam to glue the halfs together
Although the halfs were joined, the foam did not expand enough into the corners so we did a mini-pour to fill in the gaps.  Chis being the chemist was elected to do the mixing and pour.  I supervised (someone had to!).  The other picture is the foam expanding.  It expands a lot!!!  The 2-part foam is from Raka.  I liked the stuff so much that I went through the first set of cans before I started building the hovercraft - it is pretty cool stuff.
June 30, 2002.  Added upper side skirt attach strips.  Used a router to make the grove and then foamed in the aluminum strips.  My partner, Tim Trop, helped today with the strips and rear of the HC.  Don't know if he will come back again....
Mark and I used the hot wire bow to cut the rear 2' section into the proper shape while Tim operated the transformer.  I still have to cut the last 1' foot of the section flat as that is what the 12T4 plans show.  Tim and Mark are taking off the hot wire templates.
Tim and I foamed the rear section on to the rest of the HC hull.  We used 2-part foam but ran out.  So I used the foam-in-the-can to fill in the gaps.  The hull is full size now.  It is big looking.  I need a longer garage.
July 4, 2002. Here Mark and I cut the rear section flat as per the 12T4 plans with the 7' hotwire bow.  Then Mark cut the slots in the rear section with the hotwire slot cutter.  (see the hotwire section for shots of "Hotwire Mark" in action)
Cut the rest of the skirt attach strip slots with the slot hotwire cutter.  It is much better than the router.  Also used epoxy with microbubbles to glue in the side top attach strips (I ran out of 2-part foam).  Microbubbles are very fine glass balls that are so small they look like powder in the bag.
July 20, 2002. Action shots of Mark and I.  We started to fiberglass the bottom edges of the lift duct.  We rounded the edges so the FG would lay over the edge better.  Using 8 oz glass for this.  We also added a layer of FG tape over the upper attach strips.  Getting there....
July 24, 2002.  I am using the tube sander to sand the inside fillet foam.  The fillet was added to help the fiberglass transition from the flat floor up the side.  Heavy weight FG does not like sharp bends.  Next time I build a HC I will make a smooth transition in the base foam and save considerable time.  The 12T4 has a 90 deg bend but it is made out of wood and  FG is not used at the junction.
Mark made the tube sander from a paper towel cardboard tube that he fiberglassed.  The tube gives about the correct curve to the fillet.  We wrapped a piece of sand paper around the tube and sanded.  You still get tired sanding 30 linear feet of foam but it worked pretty well.
July 25, 2002. We are foaming in the right and left side attach strips.  Using 2-part foam again.  We put spacers behind the aluminum strips to allow the foam to get behind them and keep them flush with the side.  We also used tape to seal, for the most part, the bottom of the strip to the side to keep the foam in place when it was poured.
Scott (rear), Mark (middle) and Kitty (front) were enlisted to help attach the attach strips.  Kitty "Grandma" Poulder was brought in to get the project back on schedule.  Thanks all for the help!!
Added the reinforcements for the landing feet.  FG will be added over the aluminum reinforcements and then Kevlar felt will be used on top of the FG as the landing feet.  This should be pretty robust.  There are six (6) reinforced areas and six Kevlar feet will be used.  The slots for the aluminum were made with the router and the aluminum was foamed in with 2-part foam.
Aug 9, 2002. Back is glassed now and the front has two layer of 8.8 oz tight weave and an additional layer of 9oz over the front edge.
Here is a picture of the bottom of the lift duct area.  I used carbon fiber under a layer of 8.8 oz tight weave FG.  Quite strong.
Pictures of the right and left sides.
Had trouble getting the vac bag to work.  It had lots of leaks that were hard to find.  Mark suggested we reverse the air flow and make the bag a balloon to find the leaks.  IT WORKED!  Joe "The Bag Man" Arrambide does vacuum bag house calls so he came over to help.  We ended up finding the larger leaks and were able to pull about 90 lbs on the bathroom scale in the bag.
I built a H shaped vacuum distributor out of 3/4" PVC pipe which helped greatly.  The bathroom scale measures 215 lbs once the smaller leaks were plugged.  That is about 288 lbs/sq. ft.  Not bad for a shop Vac.  Never was able to get the Gast to pull down the vacuum enough.
Aug 12, 2002.  Well the results are in.  I added two layers of 8.8oz tight weave FG to the side with the vacuum bag system.  The results are great!  The release ply is very reluctant to release but it comes off with some persuasion.
Aug 13, 2002. Chris Keirs came over to help with the engine mount support boards.  We drilled the appropriate holes and foamed them into place.  Again, Chris being the chemist was nominated to "work" the chemestry.
The chemist gives ... the chemist takes away....
Aug 18, 2002.  Chris, Mark and I installed the bolts and used a mixture of cut FG fibers and fumed silica to goo them in.  The nuts were welded onto the threaded bolts so they will not come loose (that would be a bad thing).  I used eight 3/8" bolts and the wood is 66" long.  The white covering over the boards is a mixture of epoxy, glass balloons and fumed silica.
Mark and I cut out what will be the landing skids from Kevlar felt.  We will use three strips stacked to make up each skid.  Bad news, school starts tomorrow and I will lose my able helper.
Aug 25, 2002. I vacuumed bagged two layers on the bottom.  The first layer is 10 oz carbon fiber and the top layer is 8.8 oz fiberglass.  I have sanded the top layer and it is ready for the next and final layer that will be Kevlar.  I will do the Kevlar layer this weekend.  All that will remain then is to add the landing skids (Kevlar felt) and flip the HC over and start on the top.
Aug 29, 2002. Joe and his brother Paul came over to help put on the new vacuum bag.  The last bag developed too many holes to keep up with.  Paul and I are putting in the duct plug to keep the plastic from stretching too much when a vacuum is pulled.
Aug 31, 2002.  Vacuum bagged the last layer on the bottom.  It is Kevlar and was added to give the HC some impact and abrasion resistance.  Now all that is remaining is to water proof the bottom with an epoxy slurry and to add the Kevlar feet.  Since I vacuumed bagged most of the bottom, there should not be many pin holes but you never know.
Jan 4-5, 2003.  Added the three skim coats to the bottom of the hull for water proofing.  I also added the landing feet.  The feet are made of three layers of Kevlar felt soaked with epoxy.  I also added a single layer of Kevlar felt between the feet to protect the hull from damage. 
The Kevlar strips at the front by the lift duct were added for protection when landing on rocks etc.  I have also decided to use the Kevlar for the attach strips as I do not want to put holes in the FG hull and risk water getting into the foam.  Kevlar is a pain to cut.