Clipper's Vera Cruise Build

Clipper's Vera Cruise Build

Friday, July 11, 2014

Fairing The Sides, Continues

As the title states, I am continuing with fairing of the hull structure. It's a lot of work, a lot of dust, and doing it in the summer heat means I can only work on it for an hour or so before I have to take a break and cool off. But I am making progress. The fairing process is actually four separate processes. There are the port and starboard sides and the port and starboard bottoms.The aft sides were initially easier and gave me time to develop skills and confidence to handle the more complicated portions up front. The bottoms will be handled after I complete the sides and install the bottom battens. I also plan on doing some clean up of encapsulation and glue joints on the sides before starting on the bottoms.

At the front of the boat, the sheer and chine curve in and meet at the stem. The rectangular cross section of these pieces will end up being more triangular for the sheer and more trapezoidal for the chine. I was initially stumped about how I was going to determine these angles when fairing. When you look at the unfaired hull, it seems an impossible task to fair it correctly.

As mentioned in my previous posting, I've used a few techniques to get through what I have accomplished so far. Each step completed makes the next step easier to understand. As long as I don't get in a hurry, I can get each section done without too much problem. I am handling this one section at a time, with a section being the area between and including two frames. But each section is further broken down into it's component piece.

I start with the sheer at the frame and remove material until the sheer is at the same angle as the frame at that immediate point. On these bow areas, I use the aft edge of the frame where it meets the sheer as the point I am trying to fair to. This point is on the bottom side of the sheer (the topside right now because the hull is upside down). This point represents the furthest inboard that I want to sand at this point. The angle of the sheer should be determined by this point and the outer edge on the top of the sheer (bottom of the sheer at this point).

I know this is confusing so I drew up this crude drawing to try and represent what I am talking about. This shows a sample frame when looking at the boat from the front. The frame is represented in cross section as is the sheer. The labels on the drawing help to understand what is being done.

Now if you imagine the chine curving around towards the bow when looking straight down, the furthest inboard cut has to follow that curve. However, it isn't quite that simple. The curve needs to blend into the next furthest inboard cut at the next frame forward. So you cannot simply draw a curved line that matches the curve of the sheer. You must draw a curve that blends into the next point.

I used a flexible wooden batten to accomplish this. It naturally forms a fair curve when bent. I clamped it into position at the two inboard cut points and then try to get the curve to be smooth and follow the curve of the sheer. The next photo illustrates this.

You draw a line along this batten and this represents the furthest inboard cut along the curve of the sheer.  The outboard cut is determined by the outer edge closest to the floor. I purposely mounted my sheers in the frames so that this edge would line up with the angle of the frame. So I can use this outer edge as the furthest outboard cut point. Then it is simply a matter of sanding the wood away at an angle until I get to the drawn line, making sure that I don't go past the outer edge in the process.

 Now I would like to add a word of caution here. This technique is what I am using. I combine this along with a lot of checking using a scrap piece of plywood to make sure the angle is correct before I do any sanding. I clamp the plywood on the chine and sheer and across the frame edge, constantly checking to make sure it is laying flat across all points.

This is really a trial and error process, requiring me to clamp and un-clamp the test plywood numerous times, tweaking as I go. I've heard of other methods of doing this and I even tried one of them, but I couldn't make it work. So far this has worked out fine and the plywood is conforming as I expect it to.

In addition to the sheer and the chine, it is also necessary to fair the forward edge of the frames. The frame itself is a curve so I use a similar technique to determine how much to sand off. Again, I only do this after a lot of checking. I trusted this too much initially and had to add a shim on one of the frame edges because I ended up with too big of a gap when I tested the plywood on that area.

Now on this boat, It is not necessary to get the plywood to lay flat on the frame edge as it curves down towards the sheer. In fact, you want a slight gap. The reason for this is because as the plywood curves around towards the front, it will try to bend over these frame edges if they contact it. This bend will form a hard point which may be visible on the outside of the hull. More importantly, this hard point is a potential failure point on the plywood skin. It is okay to add glue in this area when gluing the skin on, but no fasteners will be used on the frame edge. Fasteners will only be used on the chine and sheer edges of the plywood. This will be a little clearer when I get to that point in the build.

At the front of the boat, the fairing of the stem must be done in order for the forward most edge of the skin to lie flat on the stem when installed. This is another tricky area and I used the same curved line technique. However, I also used a tool I have to insure that the angle is correct. It is very important that the angle on the stem ends at the center of the stem forward edge so that when both skins are added later, they will meet at the center. I drew a line on the entire forward edge of the stem at the center as a reference. The following photo shows this tool in use on the chine. The inside corner of the cut out should lie on the stem center line if the chine is at the correct offset back from the stem forward edge (and thus also at the correct angle)

I initially sanded the stem in the immediate area of the chine to get that angle. The sanding went from the stem center line and matched the angle of the chine. At the sheer, I did something similar, but the aft edge of the angle had to blend into the curved cut line I had previously drawn using the flexible batten. The idea here is that as the plywood lays across the sheer and chine and meets up with the stem, it will continue to lie flat on the stem.. Once I established the two ends of the curved angle, I used the flexible batten technique to draw a line to sand to on the stem. Once again, I did a bunch of cross checking before finishing the sanding. Here is the end result.

At this point, I have finished the starboard side fairing (except for any additional tweaking needed when I start fitting the skins) and have nearly completed the port side fairing. However, on the port side I have an additional problem to deal with.

When I installed the port chine, it ended up being too low at the bow. Because I was too far into the glue up process, I could not correct this at the time. So I knew that eventually I would have to deal with this low spot. If you remember the tool in the previous photo that is used to check the angle on the stem, it would not work with the chine being so low. So it is necessary for me to add a shim to the chine in this area in order to get the mating surface up high enough. I used that tool to get an approximate idea how thick of a shim was needed and then glued that to the chine. It goes back far enough that I can blend it into the chine. I'm not a fan of using shims, but in this case, (and the other previously mentioned), it is better than not fixing the problem and having the skin distorted in these areas.

In this second photo, you can see how the shim has brought the outer chine surface out to the same distance as the chine on the other side of the stem. Once the epoxy cured on this, I blended this in in preparation for fairing the remaining section on the port side.

I did do one other small bit of fairing on the bottom. Where the keel meets the stem, the keel sticks up and needs to be blended into the stem. Here are before and after shots of this area.

Eventually, more fairing will be required on the keel to blend it into the angle of the frames on the bottom of the boat. I will be doing that later this month.

So that is it for now. I will be continuing this fairing process for some time. This is okay because I need to purchase eleven sheets of 3/8" plywood for the skin. At approximately $90.00 per sheet, plus tax and shipping, that gets pretty expensive. All this fairing work is giving me time to save the money needed for the skin.

Until next time, take care .

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    1. Yep, coming along. Sides are nearly done. I'll be doing some cleanup and adding the bottom battens and then start fairing the bottom. Hoping to buy the plywood for planking in September.


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