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Posts to this blog will happen infrequently, if at all. The blog will remain accessible for historical purposes.

Wednesday, January 31, 2007

Return of the Mechanical View

I finally got around to updating the mechanical plan. There is much more to do of course. But, I got the heads mostly sorted out. PDF is on the sidebar under links.

Sunday, January 28, 2007

Stay fillet, stay!

This weekend saw the beginnings of primary bulkhead installation on the Westsail. As the aft floors are in, bulkhead installation starts there. First is the bulkhead between the engine room and aft stateroom. Measurements were taken with a tick-stick and the bulkhead side pieces were cut out using CAD generated templates as described in earlier posts. The pieces were then glued to the hull using structural adhesive using special jigs to hold them in position and in the same plane as the corresponding floor joist/lower bulkhead (already permanently in). These were allowed to set overnight. The bulkheads will be tabbed in over 1 inch foam fillets. Trouble is, the foam fillets are straight. Here, the curve of the hull is gradual enough that the fillets can be kerfed such that they bend against the hull without snapping into pieces. Whats more, the fillets need to be tacked to the hull before tabbing or they will just spring back to their original shape. So the picture you see here are the fillets set with thickened resin and clamped into place. This is where those fancy one-handed bar clamps are handy. One can never have too many of those. Especially when you need one hand to keep you from sliding into the bilge. I have an idea for a type of jig that will make this easier for future bulkheads. Now, these side pieces for this bulkhead is it for now. The remainder center section will just get in the way as the rest of the stern is built out. Also, it may not be until the deck is attached that it will finally go in. If I keep the center section as one piece, it wont fit though the companionway or the cockpit floor. So I will have to save it till the deck is off. Not a big problem as there is really no cabinetry that joins with this bulkhead. Also this weekend the lower bulkhead sections were tabbed in the bow. But, I ran out of glass tabbing stock. I need to cut more this week. The Seattle Boat Show is going on now. My boat techie wife is working at the show a few days this week so she is a bit frazzled. I plan on attending next Saturday. It is time to start talking to the Aquadrive people about drivelines.

Saturday, January 27, 2007

9 inches Discovered!

It occurred to me that I never checked the dimensions of the deck against the original drawings. The outline in the CAD drawing was electronically traced from scans of the original paper drawings. Well, it turns out that the deck slope between the main and forward salon is actually 9 inches forward than described on the drawing. It turns out that a lot of dimensions on the original drawing have been inaccurate. For example, the original drawings show the beam a couple inches wider than it actually is. I guess some of this is to be expected as the drawings are 30 years old and were drawn by hand. But a 9 inch descrepancy seems a bit much. Anyway, so I updated the CAD drawing to account for the 9 inches. The result is the main salon has been stretched forward, and the forward salon has been shrunk. This works just fine as we would like spend more time in the main salon, and, the bunks in the forward salon were a bit long anyway. This also means that tankage and counter space increases. I also have changed the style of the CAD drawing. Before I was using actual line thickness to denote bulkhead and framing thicknesses. This was getting a bit messy and tedious and it made difficult identifying the joints where things meet. So I converted such lines to standard line widths and used double lines to denote thicknesses. Drawing measurements should be a bit more accurate now. I also added more artistic renderings to the interior plan. The CAD PDF file (to the right) has been updated.

Saturday, January 20, 2007

Electronic Cutout Templates

Click here for all posts about using a Tick-Stick
As mentioned in the previous post, once you have the curve of the hull in CAD, you can take that curve and make a cutout template for the bulkheads. Well, I did the first one last night. I was initially somewhat nervous as I didnt want ruin a good $500 piece of Coosa board, but things went pretty well.

I used a shareware CAD utility called ABViewer that easily prints out full scale drawings tiled over multiple sheets of paper. I took the curve for the starboard bulkhead between the aft stateroom and the hallway, trimmed it to where it meets the floor and deck, and fitted a rectangle around it to help identify the minimum sheet stock size needs to cut. I then printed it full scale over two sheets of paper using ABViewer. Trim off the edges and lay it against the material to cut. Trace the outline. And cut!

The fit was near perfect. A little hand trimming was still needed as, with the hand layup of the hull, there is the occasional "bump" usually where the edge of a layer of glass roving ends. These bumps were missed by the tick-stick measurement. Cutting a shallow "divet" where the bump is makes it fit nicely.

Monday, January 15, 2007

When it is too cold to build a boat...

...go diving! Weather has been in the 20's and 30's for the past week and the snow and ice is still hanging around. Too damn cold to do anything on the westsail. However, I did a bit in the shop and CAD. Took sunday off and went diving. Nice sunny calm day. 50 degree water is much warmer than the 25 degree air.

Sunday, January 14, 2007

Advanced Tick-Stick Techniques

Click here for all posts about using a Tick-Stick

Up until now I really havent had a need to accurately measure the curvature of the hull. The floor supports were small enough that I could just approximate the piece using doorskin and fit it by repeatedly fitting and trimming it. The pieces were small and the doorskin easy to cut right there in the boat. Once the doorskin fits snugly, use it as a template to cut the actual piece. Upper bulkheads, however, are much bigger, and using the same method would be a pain.

So, how to measure and cut the bulkheads accurately and efficiently? I had searched the web over the past few months for tools that may help. One would be to call someone in here to get a point cloud scan of the interior and take a cross section at the station line and plot a template from that. But, it costs at least two to three thousand dollars a day to get someone in the boat to do that. Plus there is the time in cutting through the resulting points which would require a lot of post-processing in CAD or Rhino. I did come across a device, used for mapping tunnels, that would rotate a mirror and take sights in a 2D plane. That would have been convenient, but that cost a few thousand dollars.

So, final solution, use the tried and true tick-stick method, but with a high-tech twist. This requires the following:

  • a large sketch board with paper clamps

  • a 2x4

  • long thin stick about 7 feet long with a point on the end

  • a yard stick

  • large sheet plotter

  • CAD program

Mount the sketch board to the wide side of the 2x4. Tightly clamp the wide side against the lower part of the bulkhead already installed on the centerline. In the CAD program, plot a 1-inch grid to fill the largest sheet of paper you can print (24x36 in my case). Put the paper on the sketch board. Attach the yard stick to the long stick, such that you can read a measurement at the grid at the widest and narrowest measurement. Put the pointy end of the stick against the hull at the point you want measured while laying the side of the stick against the grid. Rotate the stick up or down until you can match an inch tick on the yardstick with any interesection on the grid square (this is best done with two people, one person holding the pointy end against the hull). Once you have matched, take a fine tip pen and scribe a line on the grid paper, using the tickstick as a ruler, from the intersection towards the hull. Read the distance off the yardstick and write it on the line (dont forget to add the offset from the end of the yardstick to the pointy end of the stick). Move the stick along the hull 5 or 6 inches and repeat until you have traversed the area to be measured. You now have a sheet of "vectors", the ends of which mark the inside of the hull.

Next, place the grid sheet on the dining room table, take a protractor to each of the vectors and measure the angle. Write the angle on the vector.

In the CAD program, call up the original document that generated the grid sheet. Plot the vectors in the CAD document, just as they are on the sheet. Best done by entering the points as polar coordinates in degrees (if your CAD program cant do this, get another CAD program!). You now have transfered the measured vectors to the CAD program. Now connect the ends of the vectors to get the curvature of the hull (multi-point spline curves seem to work the best).

You now have a pretty accurate measure of the hull curve in CAD. At this point, you can print it out full scale to make a cut-out template. You can also export it to your 3-D software to help in 3-D modelling.

For incorporating this into other drawings there are somethings you can do to make things easier and accurate: level the grid paper before taking points (assuming the boat is level, which the westsail is). Mark the centerline on the grid paper.

Monday, January 08, 2007

Aft Floors are IN!

Well, roughed in at least. The new year is off to a good start with the aft floor joists and pads permanently installed.

Referring to the first picture, looking aft, the aftmost is a small 3/4 inch piece of laminated coosa tabbed with two layers of glass. It will mostly be used to support a part of the double berth. Next one forward is the mizzen mast step, more on that later (see below). The next one forward is a floor support and the thrust bearing plate for the Aquadrive. It is two 3/4 pieces of Coosa laminated with three layers of glass. It is tabbed with 4 layers of glass on either side feathering out to 6 inches against the hull. Finally, the last support is in fact the lower portion of the bulkhead separating the engine room from the aft cabin. It is one 1 1/2" piece of coosa laminated in glass.

All floor supports were first tacked in with structural adhesive. All supports were tabbed in using 17oz biaxial glass knitted with chopped strand mat over a 1 inch foam fillet (on the straightmost bits at least, the fillets dont bend very well, even if you saw kerf them).

The pads are 3 layers of glass over shaped closed-cell high-density Airex PVC foam that has been bedded with Corebond.

This last picture is just the temporary work floors laid atop the supports.

What next? Well, in the aft section at least, work can begin on installing upper bulkheads and main cabinetry framing.

A note on the mizzen step

The mizzen step was not glassed in for the following reason: steering. The brand/type of steering system has not been finalized. The current favored system is the Lewmar Mamba Steering System which uses drive tubes, bevel gears and u-joints to connect the wheel to the rudder. This by far is the most flexible installation whilst maintaining strength, wheel feedback and low maintenance. In this installation, such a system would see the drive tubes go underneath the floorboards and through the supports. Cutting holes in place on the smaller supports would be no problem, but the mizzen mast step is 5 inches thick. Cutting holes in place would be quite difficult. So it will remain unglassed until the steering is designed and ready to be installed.

While we are talking steering systems

I will not install a cable/idler steering system of the type that originally came with the Westsail. Too many wires and pulleys. Anyway, I want to keep a nicely designed engine room and the last thing I need is steering cables criss-crossing the space. The Lewmar Mamba system is nice in that the small bevel gears allow a complete 90 degree turn which would otherwise need to be done with large 4 inch idler pulleys (two of them). It would follow the same path, down the centerline aft to the rudder post, as did the original system (sans large idler pulleys). Another thing I like about the Mamba system is that the autopilot drive unit can be attached to any point of the system where there is a bevel gear. So, for the center-cockpit westsail, it could be installed in the engine room, underneath the cockpit floor.

Another possibility is a cable wire system in conduit. Edson and Lewmar have such systems. They allow the wire-in-conduit to make gradual turns without pulleys. On the westsail, such system would see the conduit make a hard turn to port from underneath the pedestal towards the edge of the hull, another hard turn pointing aft, then gradually follow the hull to the rudder post. Such systems are higher maintenance than the Mamba system (conduits must be lubed frequently). Both systems would be easier to install than the original type.

Sunday, January 07, 2007

Latest Design Layout on Blog

Since I redid the blog style some months ago, the PDF for the latest plan for the westsail has been absent. And, before that, it had been out of date for some time. Well, its back. See the "links" section on the side bar. Of course it is being continually updated. And, now that floors are being permanently installed, the drawing has been updated to reflect the minor tweaks that inevitably happen during construction.