Starting the second hull half

I know, been here, done that ...  But wait, before you tune out, read on for all of the wonderful new techniques we are trying out on this half.

Here is the start of planking the second hull half.  Upon first glance it may look remarkably similar to the start of planking the first half (I promise I didn't just repost the old photo).  But if you look closer, you might notice the screws are silver instead of black!  Amazing, I know.  Well, with the (black) drywall screws we were using, the wood clamps tended to form a divot in the foam when the screw head pushed through the wood.  To reduce the amount of filling we have to do, I am using lathe screws that have a broad pan head.  Since the lathe screws don't sink into the wood, there shouldn't be any damage to the foam aside from the screw hole.

The other change to our technique is that we are using a heat gun instead of the toaster oven for thermo-forming the foam planks.  The scalloping of the planks occurs when the planks are heated and bent into the tight bend.  The heat gun allows us to better control the amount of heat applied, as well as limiting it to local areas.  Most of the plank will bend to the form without heat.  Just the tight bend where the hull transitions from the side to the deck of the hull requires heating to prevent breaking.  After trying this on a few planks, I found the use of the heat gun results in a better final form in less time.  The unheated sections are very fair, so the final product should be superior.  There is still some scalloping where heat is applied, but I can reduce the distortion by minimizing the amount of heat applied.  The seams also stay very straight, so I shouldn't have to do too much trimming when I glue the planks together.  At the bow and stern ends where we get into compound curves, the seams need to be trimmed at top and bottom, but the middle then comes together nicely.  With the toaster oven, the edges tended to distort along the entire length of the seam, so we had to do more trimming.  So far, I prefer the heat gun for this thin (9.5 mm) foam core.  I can imagine the toaster oven would be better for thicker core material, or when more complex forming is required.

Hopefully we will finish the planking tomorrow and plan to laminate the inner surface next weekend.  Check back soon for updates.

Hull removed from form

Before we left for our world travels, Dawna and I popped the finished float hull half out of the forms.  It took a little motivating to get all of the seams to release from the tape, but with some patience working around the hull we were able to free it without any damage.  The tape worked well at preventing the glue from adhering to the form.

Here you can see the hull sitting on a couple of saw horses next to the form frame.  There was a lot of expanded urethane glue on the outer surface of the hull.  If you recall, we sanded the excess glue on the inside, but had problems with accidently gouging the foam.  We wanted to clean up the outer surface before moving on to the next half, but didn't want to remove any core material.  I tried a cheese grater type of plane and it worked like a charm.  You can see the hand plane sitting on the hull.  Dawna finished off the clean up with the hand planer in a couple of hours and it looks great.  The outer surface seems pretty nice, but after we looked closer, we noticed waves in the surface due to the scalloping of the planks.  The ends seem to be the worst.  So we will have to put some effort into fairing the surface once we put the hull halves together.  We will try some different techniques on the next half to improve the initial fairness.

Since we won't be working on this hull again until we complete the third half, we needed to get this half out of the way.  I didn't want to store it outside since I haven't sealed the outer surface yet.  So I decided to build a shelf to support the hull overhead.  Here you can see how it turned out.  Only took a couple hours to build the supports.  The hull is very light, so the 2x4s are more than adequate.  Of course, lifting a 24' long hull half over my head, walking it outside, rotating, walking back in, and placing it on top of the supports at 7 feet above the floor made it seem somewhat heavier.  Dawna was at her friends house, and I wanted to get going with the next half, so I was impatient and did it myself.  It would have been very easy with Dawna helping.  In any case, this worked out well and you can see the hull is out of the way.  I am debating whether to make another set of supports on the other side of the boat house to store the second half, or add a second layer to these supports.  Stay tuned to see the exciting conclusion of this conundrum.

Bulkheads installed

The vacuum bagged bulkheads turned out very nice.  The laminate table top actually pulled up a little in between the bulkheads while under vacuum.  Just another examples of the power of nothing!  Should be fine, I just had to roll it down tight again so the contact cement could adhere.

Today we spent about four hours installing the bulkheads in the hull.  Dawna made expert batches of epoxy while I cursed at the glass tape bits that wouldn't give in to my will.  Nonetheless, as you can see, they all went in as planned.  The join between the bulkheads and the hull is filleted with an epoxy + microballoon + cabosil putty (or "bog"  as they say down under!)  The microballoons add bulk and keep it light.  The cabosil adds viscosity and makes it more putty like.  I probably needed to add more cabosil and microballoons to my putty since it tended to sag before I could get the taping done.  The fillet is the white stuff at the joins.

My talents at filleting are certainly suspect, but good enough to serve the purpose.  The fillets are covered by double bias 4" wide tape that actually does the work of holding the bulkheads in place.  The fillet is just intended to give a more gradual transition from bulkhead to hull.  In the next hull, I may try using foam core fillets as Ian suggests for the larger boats.  I am definitely better at cutting foam on the table saw than I am at making perfect coved fillets.

 I am reasonably satisfied with the installation.  I am sure I used more epoxy than I should have, especially at the forward bulkhead.  But there are also many elements coming together at the forward bulkhead, with layer upon layer of additional reinforcement.  I am sure the next hull will show improvement based on this experience (though the boat might heel a bit to starboard).

Here you can see a closer view of the forward bulkhead (but hopefully not so close as to expose my sloppy technique).  Note the reinforcing gusset that is also filleted and taped in place.  There is a matching gusset on the other side.  There will also be another pair on the other side (top in this view) of the bulkhead when the other hull is joined.

Well, that is just about it for the inner half of the starboard float hull.  Next we will be removing this half and starting the outer half of the port float.  Hopefully I will remember to flip the bulkheads over, otherwise we will have two starboard hulls.  Progress should be faster on the next half since we have the basic techniques and tools in place.  Unfortunately, it will be a while before we get started since we will be traveling for much of July.  So keep watching for updates in late July.

Vacuum and the power of nothing

Vacuum sucks!  Okay, just had to say it.  We are finally starting to use the vacuum bagging table for what it was primarily intended.  You will notice in the photo that I switched from the original plan to use a pond liner to a sheet of hard laminate for the table surface.  I tested the pond liner (not cheap) but it tended to pull up around the bottom of the parts being pressed.  I am not sure if this was distorting the parts, didn't seem to, but I didn't want to take any chances.  So off came the pond liner and on went a 4' x 8' sheet of laminate.  It was easy to apply and turned out very nice.  The laminate is also more durable than the pond liner, so less worry about gouging or stabbing the it when doing other work on the table.  And to top it all off, it cost more money, which seems to be the underlying goal in this endeavor!

Based on my experience so far, I can say that this 4' x 8' table is definitely the minimum size I would use.  All parts I need to make for the F-82 will fit on it comfortably, but I definitely would not want it any smaller.  It also works great for rolling out the fabric to cut, but since the rolls are generally either 50" or 60" wide, the table is only barely adequate for fabric prep.

In the photos you can see our auto-cycling, super-sucking, hyper-cyclonic vacuum system on the corner of the table.  I used the kit and plans from Veneer Supplies, aka Joe Woodworker (see link in column to the right).  Works great.  I made the vacuum reservoirs (pvc pipe bombs on back) about the size specified in Joe Woodworkers plans, and it seems to be about perfect.  The system cycles on and off about every 15-20 minutes when the vacuum layup is nicely sealed.  The pump cycles on when pressure rises about 4 inHg and it takes a few minutes to get back to the set point.  I am using the Gast twin piston pump available from Veneer Supplies, and it is very quiet.  Outside the boat house I can hardly hear it when running, inside it is definitely tolerable.

I also have a resin trap installed between the vacuum system and the vacuum bag, just in case I get carried away with resin application and it manages to get sucked through the vacuum hose.  I figure you only suck resin into your pump once before it needs to be replace.  Although not expensive given the performance, the pump is also not cheap (again meeting the fundamental requirement of boat construction - to spend money).  The trap would be easy enough to make, but I chose to buy this one from Fiberglass Supply.  Works well and didn't suck up yet another day of effort to fabricate.  You will notice the vacuum gauge is reading about -20 inHg, which is perfect.  This is also the best the pump could do, so good thing this was the target pressure.  Note that we are at 6500 ft elevation here in the mountains of New Mexico, so atmospheric pressure is about 12 psi, as compared to 14.7 psi at sea level.  The result is less atmosphere available above us to press down on the parts we are making.  So the pump has to work harder to get to the desired vacuum.  I am sure that at sea level, where most (slightly less crazy) boat builders probably live, the pump would do several inHg better.

At last, parts being made in vacuum.  Once everything was precut, the lay up went remarkably smooth.  It only took about 25 minutes to lay out the layer, adding resin where appropriate along the way.  From bottom to top, the lay up consists of:
1) Release wax on table top (very important assuming we don't want to permanently install the bulkheads on our table top),
2) Peel ply for a nice finished surface on bottom,
3) Bottom layer of glass fabric, in this case 12 oz bi-directional glass,
4) Foam core with custom perforations,
5) Top layer of 12 oz BD glass,
6) Top layer of peel ply,
7) Perforated release film to allow excess resin to migrate out of parts to upper layers and also allow parts to release from upper layers,
8) Bleeder fabric, which is kinda like a light fluffy blanket, used to absorb the excess resin and provide a vacuum path to the vacuum hose,
9) Vacuum film to make the upper vacuum tight surface.

You can also see the vacuum seam tape (yellow lines around the perimeter of the vacuum film) which seals the vacuum film to the table surface.  It's kinda like slightly chewed yellow bubble gum - very sticky.  To get the vacuum hose through the vacuum film you can either wrap the hose with seam tape and wrap the film around it or use a vacuum feedthrough like I did.  The feedthrough goes through a hole in the film and seals to both sides with neoprene rubber washers.  Then the hose just connects to the exposed side of the feedthrough and voila, vacuum!  I got the vacuum feedthroughs at Veneer Supply for about 8 bucks each, which was about a quarter the price of other variations I found.  They were very effective and easy to use, and are reusable until I get resin into them, but they are cheap enough that such a mishap won't break the bank.  Also the feedthroughs made the process of sealing the vacuum film very easy since I didn't have to worry about wrapping the film around the hose, which was a key location for leaks in my early tests.

If you look closely, you can see the three bulkheads being vacuum pressed under the lay up.  Works like a charm.  I'll post pictures of the finished product soon.

Foam core torture device

Vacuum bagging the bulkheads starts with a little torturing.  Here you can see the evil miniature bed of nails that I used to perforate the foam core (and occasionally my fingers!).  Dawna is thinking of a few other uses for this tool as well, ouch!  In order to pull vacuum on both sides of the core without trapping air, the core has to be perforated.  I made this bed of nails with nails in a 1 inch by 1 inch pattern.  I pre-drilled the holes for the nails on the drill press so the nails would stay in the nice neat pattern I wanted when they were hammered through the board.    If one was so inclined, you could epoxy the nails into the wood, or add a backing plate to keep the nails from coming loose over time, but I was not so inclined so I occasionally had to hammer a stray nail head back into the wood.  It really wasn't much of a problem, but on a bigger job or with thicker foam core, it may be beneficial to better secure the nails.  I kept the board large enough to cover the area in reasonable time, but small enough that I could pry it off after stabbing the core.

To pry it off, I simply used a piece of scrap wood that fit between the rows of nails.  I also avoided pushing the nails through more than necessary, stopping when the nails just poked through the other side.  I had to be careful not to be too aggressive with the pry bar so I wouldn't crack the bulkhead.  Just let the pry bar do the work.  It is impressive just how much friction forms with 30 small nails piercing 3/8" thick foam.

Here is a closer view of the aft bulkhead after the torture session.  You can see it makes a very nice pattern of holes about 1/16" diameter each, just as specified in the plans.  You can buy the foam pre-perforated, but this way seems to work well with patience.  If I was doing a lot of vacuum bagging on the table, I might think more about the pre-perf foam.

Fitting the bulkheads

The next  significant step is installation of the bulkheads.  This is also the last step before we start construction of the next float half.  Here you can see the foam core for the three bulkheads, in order from left to right, the forward, shroud, and aft bulkhead.  The cutout in the forward and aft bulkheads is for installation of the beams, which connect the floats to the main hull.  Of course, installation of the beams is far in the future, so for now they are just very precise holes.  The foam bridging the top of the bulkheads will be cut out once the hull halves are joined to make room for the beam ends.  The placement of this cutout is a critical measurement, so I made up some jigs to hold the bulkheads in place while installing.  The slot in the shroud bulkhead is for installation of the carbon fiber chainplates, again some time in the future after the hull halves are joined.

Here you can see the jig holding the forward bulkhead foam core in position.  I had to slowly file the edges of the bulkhead core until it fit the actual contour of the hull with the various layers of reinforcing installed.  Patience was definitely a virtue in this process.  The result was a good fit with minimal gap.  I traced the final profile on to the poster board templates I made so I can use them as a starting point when fitting for the other half of the hull.  Since the bulkheads will be permanently installed in this half, fitting the second half could be more difficult.  Assuming the other half will have a similar profile with reinforcements, the traced profile should save some headaches, maybe.

You can also see the reinforcing gusset on the stringer.  These will be installed on both sides of the bulkhead, both inboard and outboard.  Only the forward bulkhead gets this extra reinforcement.

If you are particularly observant, you might also notice that we finally know which side of the boat we are building.  Up until now, this half could have been part of either float.  But we now have determined that this hull half will be the inner side of the starboard float (that's the float on the right side of the boat for you landlubbers).  This was determined once we decided on an orientation for the bulkheads.  Notice the bulkheads are asymmetric due to the cutouts for the beams and the angle of the slot for the shrouds.  You may ask "Why did you decide to make this the inner starboard float half?"  And I would give the terribly enlightened response "I dunno, just the way I started fitting the bulkheads ..."  To which you would become further convinced that there "ain't no way" this boat is ever going to float.  Luckily, Ian assures me that even I can build one of his designs, so on to the next step - glassing the bulkheads on the vacuum table for a high quality, low weight, strong set of bulkheads, or so I'm told ...