Clipper's Vera Cruise Build

Clipper's Vera Cruise Build

Sunday, June 29, 2014

Hull Fairing - A Small Illustration

I continue to perform the fairing process on the hull. It's a long business and requires a bit of getting your mind wrapped around areas. The overall process is simple in theory, but much more complicated in practice. It can be quite overwhelming if you think of it in its entirety. More than once, I've slipped into a funk thinking of the amount of work and wondering how I was going to accomplish this task.

One of the first things I realized was that like any complicated endeavor, it's best handled in small doses while keeping a portion of your thinking on the big picture. For me, what works best is to pick a small task and then focus on that to the exclusion of the remainder of the process.

What I mean is that I am going to focus on fairing a frame, not the entire side of the boat. Or I am going to fair the angle of the frame on the bottom at the sheer. Or perhaps sand a portion of the sheer back, but don't complete the fairing process in this area.

There are three benefits to this and one drawback. The drawback is that the overall process takes longer because I am not continually working on the boat. But the benefits are, first I don't get burned out and thus am more willing to tackle another piece later in the day or the evening. Secondly, these small tasks add up over time and the job gets done. Thirdly, and this is important; as I complete a section, the remaining amount of work become easier to visualize.

However, I also realize that all of this may be hard for viewers to visualize, so this posting will be about illustrating a small piece of the fairing process.

First, understand that fairing is about removing all the excess wood from the construction that will get in the way of laying the planking (skin) flat on the structure. The boat hull is made from rectangular pieces of lumber, but is a curved structure. This means that invariably, there will be places where an edge or a corner is sticking out somewhere. The next two photos illustrate this.

In this first photo,, you are looking down on frame 4. The chine is on the left and has been partially faired on its upper surface to match the frame angle (not seen in this photo). The chine is transitioning through this frame at an angle as it travels towards the bow of the boat. To the right of the chine, a portion of the frame is sticking out (circled). This piece sticking out would prevent the skin from lying flat in this area.


In this next photo, the same area after fairing. The top edge of the chine has still not been faired, but the frame portion that was sticking out, has been sanded back to match the angle of the chine, forming a nice flat surface to which the skin can be attached to.


Here is another shot of the same area from a bit further back. It is quite easy to see how the chine and frame area is now faired as it should be. You can also see the upper portion of the chine that still needs to be faired to match the frame angle at the top left of the photo.


At the sheer edge of the boat, the process is somewhat different. Remember that the sheer is actually the top edge of the boat, but since the hull is currently upside down, it is closest to the floor. Like the chines, the sheer is connected to the frames and transitions though each frame at various angles. Nearer the bow end, the sheer takes on a dramatic curve and passes through the frames at a sharp angle. 

In the next photo, you can see this angle of the sheer in relation to the frame. The frame is represented by the small portion at the top of the photo. The sheer is the long piece going from the upper left to the lower right in the photo. You can clearly see the sharp angle of the transition. also notice the line drawn on the sheer. More on this in a moment.


Because the frames meet the sheer at such a sharp angle at the bow, a considerable amount of sheer material must be removed from the outer sheer edge. This is why I had to add additional sheer reinforcement to the inside surface of the sheers in the bow area earlier this month. The sheer will be cut at an angle to match the frame angles coming down. This is one of those areas that is difficult to visualize and is best handled in small doses.

I started by drawing a line along the top surface of the sheer to indicate how far the outer edge needs to be faired back to. There is no actual measurement for this in the plans. It is simply a fair curve that runs from the point on the frame where it must be faired to to the point on the next frame where it must be faired to. 

I used a  three foot long, 3/8" square piece of wood, formed into a curve and temporarily clamped into position to develop this curve. I was looking for a curve that was similar to the existing sheer curve because only the top outer sheer edge is going to be faired back. The bottom outer sheer edge will remain intact. More on this in a moment.


The sheer's outer surface should end up at an angle that approximates the angles of the frames coming down. I determined where the lower outer edge is by fairing away a small section of the sheer at the area of the frame. The next photo illustrates this on the chine and frame junction. The process is similar for the sheer.


The next photo illustrates the two extents of the removal area on the sheer. The arrows in the picture show the two edges. The two lines drawn thought the sheer are trying to show the angle that will be achieved after fairing.

After these extents are established, you begin by roughly removing material until you get close to the line and the outer bottom edge. Then you go slower and finish removing material until you end up with a nice angle that follows the curve of the sheer between the two frames.

In the two following photos, you see a portion of the sheer before and after fairing. Notice in the first photo how the line on the unfaired sheer (on the left) is back from the corner of the frame.The frame will have to be faired back at an angle to match this line on the sheer. It will then be at the same angle as the sheer in this area. What is significant here is that this difficult area to understand is now easier to visualize. This is especially apparent in the second photo. 




One final shot of the same before and after area. Again, you can see that it is easier to visualize the next area to fair away.

Another complicated area that I have not gotten to yet is the stem and the fairing required on its forward edge. This curved piece must have a constantly changing angle as you travel around the curve. When I get to that piece I will illustrate its fairing in another posting.

So I hope this helps the reader better understand what is involved in fairing. I will be continuing this process, one section at a time. Until next time, take care.


Click Here To Comment:

  1. Hi Carl!

    Your progress is looking GREAT! I just wanted to forewarn you about a problem I encountered along the faired transition at the forward frame, where all the planking takes a sharper turn toward the bow:

    Be careful to not leave any sharp transitions that the plywood can "fold" on. I did. It was minor, but it was located on one of the floor battens, along the line on the aft edge of the forward frame (perpendicular to the floor batten). Although minor, this edge scored the inner surface of my planking and created a minor crack on the outer surface. Thankfully, the crack was VERY minor... not even all the way through 1 of the 5 layers of the plywood. Still, it was there. The whole thing could've been avoided if I'd rounded that edge off a little bit.

    Keep up the good work!

    -Michael

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  2. Thanks for the heads up Michael and thanks for the compliments. I'm just starting to get into the forward area of the boat and already running into challenges. I will continue to go slow and try not to miss anything. One of my things to do is evaluate each section after I get the initial fairing completed. I'll be looking for things like you mentioned. Probably create a check list before I start to try and mitigate any "old man brain" problems.

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