Thursday, March 8, 2007

Second float half planked

I finished planking the second float half tonight. This was my chance to try out some of the tips other builders have given me, so I was pretty motivated to move through the work.

There were three things I changed while doing this float half:

  • I had previously figured out that one big reason I was having trouble with the first float half was that I was using 1" panhead screws (panhead so they don't sink into the batten) but this was giving marginal results since I was only getting (roughly) about 1/8" penetration into the foam. That meant excessive thermoforming was needed to ensure the foam didn't pull away from the screw (if you go look at pictures of my first float half, you can see lots and lots of scorch marks - sometimes made myself sick with the smell of toasted corecell.) To fix this I changed over to 1 1/4" panhead screws, with a couple of washers underneath the head. Penetration is much better, you can sometimes see the pointy end of the screw through the foam. I didn't replace every single screw in the battens though, just on the three-four battens nearest the keel foam where the hull curve is greatest. This helped so much that I was only thermo-forming about a minute or so per plank, on the curved parts. However it is time-consuming to mess around with two washers for every screw, and I may look for a different solution when I get to the main hull. In retrospect, I really, really, should have experimented a bit more with different screws before getting started on my first float half (but Home Depot was cheap and local, and I was eager to get started).
  • Planked without the keel foam in place, then did a scribe cut to get the right miter angle on the vertical planks. This change was a total success, and I'm grateful to those who suggested it (and feeling stupid because I didn't think of it myself). Without having to worry about an exact keel foam fit on each plank, you can really move quickly. When done, I was able to slide the keel foam into place pretty easily -- the plank-to-keel meeting line looks nicely uniform the entire length of the float (unlike on my first float half ).
  • Planked without the deck flange mold plate in place. It definitely aided progress to not have to worry about the overall length of each plank. When I got around to trimming the excess foam at the deck join line, I made a mistake and trimmed it flush against the last batten. Unfortunately I did not realize that the last batten was not screwed in flush against the deck mold plate - so now I have a gap between the deck mold plate and the edge of the planks. The gap varies between 1/8" to 1/4" - not good, I'll have to fill it with putty which will make the boat slightly heavier (but I don't feel bad enough about it to make me want to unplank the entire float half). This was my fault -- I should have used the deck mold plate, or a piece of plywood the same thickness, to draw a line and cut against that. Despite its advantages though, I am having second thoughts about this change -- with my first float half, I was able to completely cover the plank-to-deck-flange angle with masking tape so there was no sticky issues there during unmolding. It's hard or impossible to do that here, when you slide the deck flange mold into place after the foam is planked. Guess we'll see when it comes time to remove it from the mold.

I hope my notes above help other F22 builders to not make the same mistakes I did.

Still though, I have to say that planking this float half was a success -- in about 8 hours I planked the entire float half from start to finish, completely by myself, and I feel confident that the planks are set nice and fair against the battens. Also note that this was all done with 8" wide planks (less than that in a couple spots), mainly so that I could re-use all of the same batten screw holes -- the process might go faster had I tried to use wider planks where possible.

This is the rough-fit of the foam against the keel batten (no keel foam in place):

(Notice there are very few scorch marks this time. The float half is completely planked except for the last foot or so down by the transom).

At first I used a piece of foam for my keel miter cutting guide, but it kept getting cut up by the jigsaw blade. I switched over to a piece of plywood, not perfect but good enough to finish the job. Here's a shot of how I did that:

(this was a self-posed shot -- so no, I don't actually make cuts with the jigsaw coming toward me :) )

Here's the view of the final cut:

This cutting of the keel plank angle actually worked so well, that in some places it left the fit a bit too tight to get the keel foam back into place. Had to go back and loosen those up a bit. I now have the keel foam back in place but I am now wondering if it will be difficult getting putty in between the planks and the keel foam. Guess I can always use a putty knife to open up a tiny gap temporarily, or even loosen the screws on the batten closest to the keel.

Finally, here is my planked float half with deck flange mold back in place:

Weather forecast calls for chilly weather and a zillion days of consecutive rain, but hopefully I can make more progress on the float half this weekend.


Tom McCaw said...

The easy way to ad washers to screws is to get a cardboard box and tape a sheet of wax paper to it. Take your screws and washer and dab some epoxy on the screw….a gun dispenser from the local building store that mixes as you pull the trigger will speed this up. Now screw the pieces into the cardboard box and let dry.


Tom McCaw said...

At first I used a piece of foam for my keel miter cutting guide, but it kept getting cut up by the jigsaw blade. I switched over to a piece of plywood, not perfect but good enough to finish the job. Here's a shot of how I did that:

If I am following what you are trying to do here….a trim router with a ½”bit with a bottom mount baring will follow the exact shape of that top batten and allow the keel foam to slide right in.


Jay said...

Tom, the router tip is a great idea! (Why didn't I think of it...). I will try that on the next float half. It sounds like it will be much, much easier.

Weird how these projects go...I have all of the tools, but just haven't fully grasped all the neat ways in which they can be used. :)

Jay said...

Update: I did attempt to use the router trim bit idea. Unfortunately, it didn't work so well - the keel batten is generally not that wide (3/4 to 1" or so), and the position of the planks is often below or nearly the bottom edge of the keel batten. So there just wasn't enough batten there for the bearing on the trim bit to ride against. I ended up doing the rest of my float halfs with the jigsaw, but it seems to have worked out.