Wednesday, September 5, 2007

Hull planking begins

Had some errands to run in the middle of the day, and when I got back home I was short on time and feeling a bit desperate to make some progress on the planking. So I resorted back to the old-fashioned method; here she is folks, the first hull plank of my F22:

May she spawn many more overnight, while I'm asleep!

You can see in the above picture that I've changed over to running the masking tape along the join lines, rather than along the full length of every batten. For the most part I'm using 10" planks, with three screws through each batten. And I never did try to track down a better screw, so I'm still using the panhead screw + two washers combination that worked well for me on my floats. I'm getting a really tight "suck down" with the screws, and the foam is following the battens very nicely IMO.

As soon as I got the above plank in place, I realized that I'd forgotten to make provisions for the high-density strip that runs along the keel. It's only two inches wide (4" in the finished hull), and I'm going to use marine plywood for that part. I didn't want to make the join hanging in open space between battens, so I mounted an extra batten right beneath the keel batten and ran some tape the length of the battens:

I'm not attaching screws to the top batten in the area where the keel strip goes, and leaving plenty of room in the batten below:

The fourth plank was almost 16" wide (decided to not rip it in half), and I started to feel the need for some extra "hands":

For this extra wide plank, I used four screws per batten. The plank straddled a form frame, which made things fun.

At the "bottom" of each plank, I do a quick-and-dirty scribe so that the planks follow the rising edge transition:

Nothing precise here, I just use the jigsaw to cut to the line as best I can. Any gaps in the join will get filled in with putty\bog. Note that I'm running some masking tape along the batten that helps form that edge, since I expect a lot of putty squeeze-out in that area.

I finished five planks today, doing almost five feet of hull:

Not too bad of a start.

I'm somewhat conflicted regarding the heatbox versus the heat gun techniques. Frankly, as long as your screws have good holding power it doesn't seem necessary to have each plank perfectly thermo-formed to the battens (at least for the F22, other boats might be different). For example, here is my second plank ready to be screwed down, after a tiny bit of thermo-forming; obviously I didn't spend much time with the heat gun here:

I would agree that a perfectly thermo-formed plank will lay more nicely and makes the screw holding power less important. It also might put less stress on the final composite (and the half-laminated composite, before the hull halves are joined and the exterior laminated) -- but I don't know how important the latter point is, or if it matters at all. Anyone know?


Tom McCaw said...

Jay many moons ago I worked at a display house that did a ton of vacuum forming. The machine they used at the time was hand built probably before I was born. So that said it was not state of the art. Did I mention they did a ton of forming? The oven was heated with kell rods, similar to what you find in house hold oven, only straight. Unlike today’s modern thermoform ovens with ceramic dishes that can be controlled individually so that you can reduce hot spots and get a sheet to heat up evenly …here it comes… my point that is… and once I tell ya…well you know….in this oven there where wires stung across under the rods about 10” down. On these wires where laid metal screen like you have in a screen door. if the sheet was heating up to fast in one spot Stan the Man would place a piece of screen in, still to hot he would put another piece on top of it. The heat would be reduced and spread out it worked like a charm. It would appear by your photos that hot spots are being created where the bulbs are. That the foam is not heating up evenly.
Boy have you ever progressed. The bent panels on the form look great. Take a bow.


Jay said...

Tom, thanks for the tip about the screen heat-spreaders. That might come in handy.

Thanks for the compliment, but I'll defer taking a bow for now...long way to go and I don't want to jinx myself. :-)


Menno said...

Hello Jay,

Just like you I've been wondering if it's necessary to heat-bend the foam a lot. I decided to only heat-bend it a bit in the lowest curve. Even without that not much force is needed to keep the foam in the right shape. Hope some more experienced builders can tell us the pro's and con's of heat-bending.

Menno (

wjquigs said...

It's not necessary to heat the foam unless the screws won't hold it cold. Forcing the foam to conform to the molds has zero impact on the final strength or on the shape once you remove it from the molds. Once that inside laminate cures you will see that there's no way the foam can try to bend back to its original shape.