Clipper's Vera Cruise Build

Clipper's Vera Cruise Build

Sunday, January 31, 2016

Spray Rails - Part 2

A stretch of very nice weather with temps in the mid 70's (even low 80's) this last week and weekend has allowed me to  make some more progress on the spray rails. The first order of business was to get the port rail extended and fitted up against that side of the boat. I wanted to insure that I could install both rails and have them line up at the front, and still look correct as they travel aft.

During the early part of the week, I kept trying to visualize on paper, how the tapers would look on the forward section. I wasn't having much luck with this. But with the starboard side temporarily mounted and the side taper drawn and taped off, I realized that the the thickness taper needed to be performed first regardless. I also decided that for now, I would not taper the top edge in the aft and middle sections because the transition to the tapered front would look strange.

For the thickness taper, I needed to determine how far aft I wanted it to start. This worked out to seven feet and was mostly due to the curve of the hull. The plan was to thickness taper the two laminations at the same time in order to get the angle to blend in nicely. This required alignment marks at the back end of the rail.

It also required that I insure that I had enough length on the second lamination in order to have the start of that lamination's taper have material to cut. I laid the second lamination on top of the first one and worked out the amount of taper increase from the front end. Using this amount of increase, I worked out how much length the second lamination needed in order to have material to cut.

This probably sounds confusing, it was to me. But basically the thickness tapers from 3/8" to 1 " over 7 feet. Somewhere along that seven feet the taper crosses the 1/2" thick portion of the rail. The second lamination needed to be at least that long in order to have the taper transition properly.

I pondered several different ways to cut the thickness taper, but in the end I decided on a modification of the scarfing approach I used elsewhere on the boat. With previous scarfing efforts I had precisely measured and cut two angles as determined by the ratio required of the scarf joint. Depending upon the thickness of the material this varies. Then I placed the material to scarf between the two angles and cut the scarf joint with a router.

However, a taper over seven feel from 3/8" to 1" requires a very shallow angle and I realized I could never make two of these accurately enough.

Instead, what I did was cut an 8 foot long 2 by 4  board in half lengthwise to form two router rails. These were hinged on one end and mounted to a wider flat board.

The opposite end could then be raised as desired to get the appropriate angle needed.

Then when the wood to taper is placed between these two rails, the router can cut the taper. Fairly simple concept, however, execution was a bit more difficult.

To start, with the hinged end mounted directly to the flat board, the angle came to a thin end, but I needed my rail no thinner than 3/8". That mean I had to move the rail back sufficiently in order to get to a wider part of the angle.

Because the jig is only 8 foot long and I needed to cut a 7 foot taper, this movement placed a significant portion of the tapering area outside the jig rails. The solution was to mount the hinges on 3/8" spacers.

A few additional problems cropped up. The jig was so long that it drooped when mounted to my table saw / portable work bench. I had to put supports (using cinder blocks and wood) under each end. The thickness of the router guide rails was decided upon to try and prevent bowing in the center. However, this thickness was too thick forcing me to slide the router bit nearly the entire way out of the router's chuck. This meant I had to go real slow while cutting the taper to prevent chattering and periodically check to insure that the router bit was still firmly held by the chuck.

Cutting the jig rails to a thinner thickness, would have left them with more tendency to bow under weight. Nonetheless, if anyone copies this approach, I recommend using thinner jig rails. But support them at various points along the length.

During routing, I had difficulty seeing the wood remaining that needed to be cut. I tried darkening the wood with a sharpie prior to cutting but it was still difficult to see what remained to cut and that experiment was considered not worth the effort.

Once the various challenges were overcome, the jig looks like this. This photo doesn't yet have the support under the near end of the jig. I also added more clamps to better hold the parts in place.

It took about an hour after setup to taper the part. One problem I had, was caused by attempting to taper from the thin end. When I got to the point where the second lamination was nearly done (near he end of its taper), the wood started chipping out. I tried going from the thick end of the taper and this worked better.

Today, I performed remaining fitting tasks, sanded, cleaned the parts, and installed the starboard rail (first lamination only). This was fairly straightforward, the parts was epoxied and screwed into place. I made sure to make he new screw holes in locations that did not conflict with the screws in the bottom and side skins (the blue tap has these locations marked). I also marked the locations of the screws holding this first lamination as i will need to avoid them when I install the second lamination (unless I can get them out after the epoxy cures).

In this last photo, you can make out the side taper which is the look I was after.

Because the spray rails, are rectangular in cross section, and because the plywood skins are rounded at the transition from bottom to side skin, there is a significant gap between the rail and the skin after mounting. This was expected. This gap will be filled in with thickened epoxy later.

What may also not be apparent is the angle at which the rail is in relation to the hull bottom skin. It turns down somewhat from the skin. This next photo illustrates this. When the second lamination is added to this rail, this will be more pronounced. This downturn is intended to deflect the water away from the hull when the boat is in motion.

So that's it for now. I'd like to glue the second lamination into position, but at the moment, there is no one here to aid in the installation. For the most part I can do this myself, but it helps to have someone to support the other end after the epoxy is applied to avoid getting it all over the boat. Perhaps this evening. Take care.

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