Clipper's Vera Cruise Build

Clipper's Vera Cruise Build

Sunday, April 26, 2015

Bottom Skinning - Continued

Since the last posting, events in my life have keep me occupied and the boat build has slowed once again. I have come to the conclusion that this is the normal mode for me and that the only thing I can do about it is try to work on the boat every chance I get, even if for only 30 minutes at a time.

Of course, certain tasks take longer, gluing down a skin for example. Often during the week, I do not have 2 or 3 hours in the evening that I can devote to these longer tasks, so they must by necessity, wait for the weekend.

This last week was such a week, primarily because I was having to catch up on chores that I could not do the previous week because I was out of town for 8 days. So, it is what it is, and I continue to try and get tasks accomplished so that someday, I will be able to enjoy this boat.

Prior to my trip out of town, I had completed installing the two front bottom skins. This work was covered in my previous posting. I had also begun work on fitting the next two skins. I anticipated that these installs would be much easier because the skins are mostly flat (except near the bow where they join the front skins).

This curve at the front and the need to add a transition joint were the two primary wrinkles with the install. There is also the need to install backing plates for the butt joints. Because I was anxious to see the boat with more skin on it, I started by fitting the skins first.

As mentioned, there is a transition joint needed. This occurs on the joint between the side and bottom skins at the chine. This transition is needed because the skins gradually get a tighter and tighter angle in relation to each other. At the front, where the angle is wide, the panels more or less butt up to one another, But in the aft section, the bottom skins overlap the edge of the side skin. This means that end grain on the bottom skin is exposed at the seam.

This is not necessarily a problem since the seams will eventually be covered in fiberglass. But as the angle between the skins increase moving forward, there comes a point where the panel must be sanded on the outer edge in order to give the proper shape to the edge. This means that more and more end grain is exposed on the bottom skin, thus reducing the strength of the edge where it is glued to the chine. This is why the skins must butt together at the bow.

The transition from overlap to butt join is the transition joint and looks like the following photo. The location along the length is determined by where the the end grain exposure begins to get excessive. I felt that this was at frame 4.

These skin panels are the biggest pieces that will be installed, essentially consisting of nearly the entire 4 by 8 sheet of plywood. So there are a bit awkward to handle while fitting. The good news is that I had gravity on my side here since the skins are resting on top of the structure.

Of course, the final panel shape is not rectangular and the edges of the panel will overlap at all the seams. And there is the curve at the front end to contend with. This is not anywhere near as severe as the two front skins, but the curvature occurs over a relatively short length so it is still somewhat of a challenge to accomplish.

After the initial fit, where all the overlaps were marked, I removed the skin and trimmed it to the markings. The next challenge was getting it back into the same position and providing a means to insure I could do this each time I re-installed the skin. By necessity, the first re-install was by trial and error but after it was in place, I added small blocks to the structure so I could get it in the correct position on subsequent fits.

Once the panel was in position well enough, I marked the frame and batten structures on the inside of the skin panels. These markings would be used to layout out the screw holes. The panel had to be removed again and the holes marked out and drilled. Then the panel had to go on again to transfer the holes to the hull structure. At this point I was ready to do the final fitting.

Because there is some curvature to the panel in both directions (side to side & fore and aft), it is necessary to utilize screws and plywood washers to hold the skin down. These screws needed to be installed in a specific order to get the panel to properly lie flat on the structure. I installed them working from the aft end and side edge to "walk" the panel down over the curves.

There were some areas where the panel needed additional trimming to fit against other panels, especially at the transition joint. I tried to accomplish all of this without having to remove the panel each time. This is where a multi-function tool came in quite handy. Also quite useful was a 90 degree air powered die grinder with a 3 inch sanding disk.

The panel required a considerable number of plywood washers, to the point where I had to make more after having exhausted my previous large supply of these. The table saw is ideal for this sort of thing as strips of plywood can be quickly ripped and then cut into shorter squares. However, my table saw decided to die at this particular point, so I was forced to use my jig saw. Fortunately, I had already cut the strips of plywood and only needed the jig saw to cut them into squares.

After several hours the port panel was fitted. It lays in quite nicely and really adds to that look of a boat. The second photo shows the transition joint. Note the portion that overhangs and which will need trimming. This is where the end grain exposure I mentioned occurs. To the left of the joint, the bottom panel overlaps the side skin. To the right of the joint, it butts up against the side skin edge.

I had also started on initial fitting of the starboard panel, but still have more work to do on it. That was put aside temporarily while I took my trip out of town. When I returned, because of all the catch up work I needed to do, I decided to make and install the butt joint backing plates.

I initially made these rectangular in shape taking a few measurements from the the structure where they would be mounted. However, I had forgotten a lesson I learned when doing the side panel butt joint. Namely, that the backing plates are not square  because the areas they fit into are not square. Something to remember when building a boat is that there are no square joints anywhere on the hull.

So I took some poster board and used it to get the shapes I wanted. Then I transferred those shapes to plywood and remade them. Another thing I did for these which I had neglected to do on the side backing plates was to round the corners. Not strictly necessary, but it does look nicer.

One lesson from the side plates I did remember was the difficultly I had in getting these short flat plates to conform to the subtle, but still present curves in the skin These didn't require pre-bending like the side plates did, but they still didn't lie completely flat. I decided this time to use a few machine screws and nuts in strategic positions to pull the panel into place.

As with the side plates, I used silicon bronze wood screws over the entire plate. By using the machine screws in a few places, I got the plate to lie flat against the skin and I didn't have to use the wood screws to pull the plates down to the skin. They, along with the epoxy, would simply be there for holding everything together. Of course, using machine screws with nuts left some holes in the skin, but these can be filled with epoxy later. I limited the use of machine screws to just a few key places to pull the plate down so I could minimize the number of holes in the skin. On the inner surface, I installed all the wood screws, including some next to the machine screws. After gluing in the plates and waiting a few hours, I removed the machine screws, but left the wood screws in place.

One nice thing about these backing plates is that they must fit in between the battens, so they do not have to curve over a large surface like the side plates did. I completed both port and starboard backing plates by yesterday.

At this point, I am ready to install the port skin. It has been quite warm here the last several days so I may wait to do this until it cools down. With panels this large, it is going to be challenging to get epoxy applied and the panel installed in the shorter pot life caused by the warmer temperatures.

So, until I get that done, I have run out of material to write about. But one of the previous photos posted on this page gives some indication what the skins are going to look like when fully installed. I am looking forward to that point in the construction. Until next time, take care.

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