Friday, March 25, 2011

Gearbox Mounting Bracket

The Involute gearbox needs to be securely mounted on the torque box. The gearbox has four threaded holes in the bottom and four threaded holes on the top. The holes are fairly close to the corners so as to maximize leverage. It is possible to drill and tap additional holes, but four should be enough if the mount is done properly.

In this boat the mount has to also be adjustable in position fore and aft so as to accommodate the different leg lengths of different pilots. It is also useful in the event that I incorrectly measure my own preferred leg extension while pedaling.

So, the plan is to mount two 1/8 inch thick by 2 inch wide by 14 inch long aluminum plates on either side of the top of the torque box parallel with the top panel of the torque box. This panel is parallel to the stuffing box, so the gearbox can move fore and aft without affecting the angle of the propeller shaft. Two bolts through the torque box (and through the foam block inside the torque box) will secure these plates.

The gearbox will rest on two 7 inch long by 1.25 inch wide by 3/4 inch high aluminum 90 degree angle brackets, sort of like a sled. As the gearbox is narrower than the top panel, the mounting holes will be drilled in the angle brackets to center and align the drive shaft with the stuffing box.

Two bolts through holes along the top of the aluminum plates and through the raised sides of the angle brackets will secure the brackets and gearbox in place.

In addition, the side plates are not just flat pieces of metal. They, too, are angle brackets, with all but 1/4 inch removed from one side. This leaves 1/8 inch on the inside of the angle protruding, which captures the top edge of the gearbox sled and keeps it from being able to move in the upward direction. So, one can remove both sled securing bolts without fear of the gearbox somehow flopping out. This also spreads any upward load from the sled along the length of the aluminum plates, strengthens the plates, etc.

You might ask where one gets such strange sized angle brackets. I happened to have a bunch of 2 inch by 2 inch by 1/8 inch square aluminum tubing laying about from a previous project. A bit of quality time with a bandsaw to cut the pieces roughly to size, followed by some time with the bench belt sander was needed to convert these pieces to the proper size and shape.

Ok...this is cheating a little, blog-wise, but today (Saturday) I finished drilling the brackets with the exception of the holes to secure the mounting brackets to the torque box. I also removed the spider from the cranks I intend to use, and polished the gearbox.

Sunday, March 20, 2011

Sanding, sanding

Saturday was spent sanding the bottom and other parts of the hull.

Most of the time was with the orbital sander. With care, one can sand the edges of the cloth to merge smoothly with the resin covered wood or cloth in the layer below the 6 oz tape that covers the edges of the hull. By smoothly, I mean so that by touch or by sight you can't tell where one surface ends and the other begins.

In some cases I ended up using the sanding belt scrap to remove the high and low points where the resin seemed to drip from the 6 oz. This was done in particular in the areas where the orbital sander couldn't reach in the cockpit area, and in areas where the orbital sander was likely to sand too deeply such as along the edges of the hull. I am continually amazed at how long this 2-1/2 inch by 3 inch piece of aluminum oxide coated stiff fabric continues to stay sharp and how much resin and glass it removes per stroke. It is far better than any normal sandpaper I've tried.

Now that the hull is pretty much as strong as it will ever be the next step will be to determine the precise positioning of the gear box and the seat back.

A fellow human powered boat enthusiast with a similar boat came up with an idea that does away with the dipping rudders and improves the steering. Here is a link to his post on BoatDesign.Net:

Saturday, March 12, 2011

Bottom Covered

I took the day off Friday to work on the boat. There is something about doing this sort of thing on a day where one does not take away time with the family that makes the process a bit more enjoyable.

Of course, having only a 4 day work week helped, too.

The second coat of resin was very glossy, but a little bumpy here and there from drips. The cloth from the patched areas was a little rough in places, too, but that was expected.

Two hours or so of sanding with the orbital sander and hand sanding smoothed everything quite nicely. By the end of the process it sounded like the filter on the shop vac was pretty clogged with the fine resin dust. It will need to be cleaned for the third time this project!

I flipped the boat upside down, resting on the front of the cockpit and on some foam blocks near the middle of the rear deck.

Additional 4 inch wide 45 degree bias cloth tape was cut from the 6 oz fabric. This was needed to tape the edges of the hull. Segments of cloth to cover the bottom were cut from the 4 oz roll, with the width more or less the width of the bottom panel.

A T-shaped slit was cut in the cloth that was destined to cover the hull where the stuffing box emerges.

Lastly, pieces of 12 oz biaxial knit cloth were cut to reinforce the lower bow and stern.

With the garage door open and the wimpy ventilation fan running, I put on my resin jacket and latex gloves, adjusted my organic vapor filtering respirator mask and started mixing the first cup of resin.

One cup doesn't go very far on virgin wood. It was barely enough to wet the wood, the fabric on the bottom panel and the tape on the seams. Some of it was applied to the 12 oz fabric for the bow - yes, that stuff sops up resin like a sponge. Anyway, it is far better to apply the resin to that cloth while it is sitting flat on shrink wrap plastic than to try to apply it to dry cloth on the sides of the hull. Picking up the saturated cloth and molding it to the hull was trivially easy. I didn't even need to clamp it in place once the air bubbles were worked out.

The rest of the boat took about one cup of resin per bottom panel of cloth, working towards the stern. Along the way resin was applied to the the sanded or still bare wood sides of the hull, turning it to a warm, rich color. Resin applied to the previously sanded resin areas went on very thinly. Resin applied to the wood was a little thicker. At first, one could easily see the old resin as darker blotches, but after a while it all merged into the same color.

3-1/2 hours later, the last bit of the stern was completed.

As I had some resin remaining I applied it to the outside rear joint of the seat back and the top, placing some tape over the joint and some scrap pieces over the top rear side joints. Given the strength of the wood and the interior fillets and taping, this should be adequate. The front of the seat will get 6 oz cloth and possibly 12 oz along the side seams, though 6 oz is probably enough for there, too.

Now that almost all the wood has been sealed I can turn off the dehumidifier!

Monday, March 07, 2011

Seams Sanded - Again

I spent Friday evening and Saturday sanding the areas where the resin had been applied to the top and sides of the boat. Areas where the resin left a sort of dripped appearance on the resin covered sides were pretty much sanded flat, and the transitions from the glass covered seams to the resin covered wood were smoothed.

The rough surfaces of the resin impregnated cloth were sanded mostly smooth, too, with care taken to not sand through the weave.

Several areas ended up with voids below the cloth. In particular, the gaps between the wood fillets and the panels were not always filled with resin, and sometimes the cloth managed to get pulled away slightly, leaving voids below.

All of these voids were sanded open, with the glass removed until the wood was reached.

All this sanding was done with the random orbital sander, with 100 grit discs. I ended up going through 3 discs, but the results were quite nice.

Both the bow and stern ended up with a good, solid covering of glass. The glass at the bow actually extends beyond it by half an inch or so, tapering to the thickness of a credit card. We'll have to see how well this works in practice, or if other boaters will complain.

I used both the block sander and the remaining fragment of the aluminum oxide sanding belt held in my hand to round the bottom edges of the hull in preparation for taping. The hand-held sanding belt fragment did a great job in sanding the hard to reach areas around the cockpit as well as small areas that were just better done with the pressure of one's fingertips.

On Sunday I cut the vanes for the dipping rudders. These were made from a 4 inch wide piece from the old top of the torque box and from a piece of scrap plywood. I then took the long, skinny pieces that had been cut from the upper sides of the torque box and decided they would work as the lever arms and reinforcement backing for the vanes.

I spent some time salvaging some of the 6 oz cloth that had inadvertently had some resin dripped on it. Some of the pieces would serve to patch over the void areas.

Everything was ready for the step: filling and fixing the voids, and sealing the sanded areas.

I mixed up a couple of spoonfuls of fillet material in a cup, and applied it to the wooden fillet voids. A spoon worked pretty well to force the fillet material into the void and to smooth the surface. A paper towel cleaned up the surrounding areas.

There were some other minor voids in the hull seams that were also filled, but a major fillet area was where the stuffing box exited the bottom of the hull. Here the tube was filleted towards the stern so as to provide additional support if or when the boat rests on it.

A cup of resin was mixed and applied to the rudder vanes and lever arms. It took a bit longer than expected, so by the time I got to apply the remaining fillet material it had already started to set. I ended up applying a rather lumpy and stringy bunch of fillet material anyway, figuring they will sand pretty well on the belt sander when I try to turn them into a bit more of a foil shape.

I applied resin to the port foredeck and the port side of the cockpit, patching bits and pieces of cloth over the bare wooden areas. This seemed to go fairly well.

The sanded and now newly resin covered areas look very nice and smooth. Hopefully they won't require much in the way of additional sanding before the job is done.