Clipper's Vera Cruise Build

Clipper's Vera Cruise Build

Sunday, March 29, 2015

Bottom Skin Installation Continued

After fitting the first bottom skin, I knew that I wanted to apply a pre-bend to the second forward bottom skin (port side) before gluing the starboard skin in place. By pre-bending the second skin first, I could take advantage of the still open framework for clamping.

I decided to try a slightly different approach to fitting the chine edges of the skin. On the starboard side I basically laid the flat edge of the plywood on the flattest area of the side skin edge and then trimmed the ends after bending and determining how much overlap there was. On the port side I overlapped the entire chine edge by a small amount. My thinking was that I could use measurements on the side skin to determine a line on the bottom skin and then connect the measured points for a more accurate edge.

So I made measurements about every six inches along the side skin edge. I measured down three inches and made a cross mark and repeated this along the length of the skin. Then I temporarily installed the full plywood sheet with the slight overlap mentioned previously. It was held in place by three screws, one at each end and one in the middle. The panel was bent around to the stem as well.

At each of the measurement points I measured back up the full three inches which gave me a reference mark for the side skin edge. Unfortunately, I only took one picture of this process.

After making these reference marks every six inches on the plywood, I connected the reference points together with lines using a yardstick. This represented the side skin edge transferred to the bottom skin. I wasn't totally confident with this approach so I decided I would cut short of the mark and sand it. Then test fit and sand more off if necessary.

While the plywood was in place, I roughly marked the excess area that I would remove by the stem and keel. This was a very rough line and drawn well enough away from the final dimension. I was primarily interested in getting rid of excess material so that the panel was lighter and easier to bend on the next fit up.

My garage is quite cramped and finding a place to cut large pieces of plywood is difficult. Usually, I have to pull out several pieces of yard equipment and then set up a temporary workbench so that I can make the cuts. This time I decided to improvise and use the boat to make the rough cut.

 I cut off the excess and trimmed the edge where I had made the measurement marks. The flat area of the boat bottom served well for this purpose although it was a bit high to work from. The skin was reinstalled to check the fit of the edge. It still overlapped some but it was close enough now that I felt I could pre-bend the panel. The panel fit about the same as the starboard skin panel and would require "persuasion" from the hot water  as well.

This time I avoided burning my foot when putting the boiling water on the panel. After a day of drying, I marked the stem/keel excess a little closer to the final line and placed a perpendicular line at the aft edge where I wanted to butt the next skin up to. The skin was then removed and I began preparations for installing the starboard skin.

It had been nearly a week since I had removed the starboard bottom skin and I was a bit afraid that it was going to flatten out and negate the pre-bend I had performed on it. So I was anxious to get it installed, but had to wait several more days until I had enough time to perform the task.

In the meantime, I started doing clean up on the inner side skin surfaces. There was plenty of this work to do and I have not touched any of it in over a month, mostly because it is a pain in the rear to get inside the boat, but also because I am not a big fan of sanding.

Anyway, yesterday morning I started the starboard skin installation. I used the same approach for glue up that I have used throughout the build, namely pre-wet the bonding surfaces with un-thickened epoxy, then re-coat with thickened epoxy, install the panel and screw down with steel screws and plywood washers using wax paper between the plywood washers and the skin. I installed the screws into the panel in the same order I had done when fitting so that I insured that it fit correctly.

It took about two hours from start to finish which surprised me as I expected it to take three hours.

One thing I did which I hadn't originally planned on doing was to use three shorter bronze screws to hold the kerfed batten together in the area aft of the panel. Readers may remember that I cut slits in the battens (kerfed them) back to about 1/2 inch from the frame. However, the panel ends about 8 inches from the frame. I had to put epoxy in the kerf slits during the glue up. But there was no pressure on the exposed 8 inch section of the batten so the screws were added to pull the two kerfed pieces together. Since I will eventually be placing other screws in this area of the batten when I install the next set of skins, I made sure to stagger these "pull down" screws off to the sides.

A few hours later, I removed the plywood washers and replaced the steel screws with silicon bronze screws. The panel was now in position. I also took the opportunity to fill in the screw holes and the seams between the skins with more thickened epoxy.

All of this was sanded down this morning.

The only remaining task for this skin was to sand back the excess material where the skin overlapped the stem and keel. Like the side skin installation, the port skin will eventually overlap the edge of the starboard skin. However, as you move aft on the stem, the angle between the two bottom skins flattens out to a point where it is not practical to overlap one over the other. Instead they will need to butt up against each other. This required a transition joint. I am planning on using a similar technique on the next set of skins where they change from overlapping the side skins to butting up against the side skins. But I only realized I needed a transition on the bottom this morning.

This transition is somewhat hard to visualize but the following pictures should clarify what I am doing. First, here is the way the skin is sanded back on the front of the stem. This is where the port skin will overlap the starboard skin.

You can see more of this overlap in the next photo, but them you will also see the transition to where the skins will butt up against each other.

Here is a closer shot of the joint.

At the bottom of the picture is where the skins overlap. Then the skins changed to where they butt in the middle over the keel center line. The reason the skins need to butt rather than overlap is because the shallower angle between the skins means that the overlapped skin edge would have too much material removed and the overlapping skin would have too much edge material exposed.

I will show more of this when I get the second skin installed and post on that next time. I am on vacation this week, so I am hoping to make some good headway on finishing the skinning.

At this point, I am ready to reinstall the port forward skin and do the final fitting before installation. I should have it installed within the next day or two. Then I will be moving on to the next set of skins aft . These will require but joint backing plates like the side skins did, however, the plates will be shorter in length because they will be installed between the battens. I will cover this in a future posting as well.

Until next time, take care.

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