Tuesday, December 29, 2009

Planking started

I'm starting to put the plywood planking on the frame. First I have to scarf pieces of plywood together to make longer pieces. I'm not sure how you are supposed to do this, but this is how I am doing it. I clamp the plywood sheet over the boat, mark the outline where I want to cutout, then cut it out.

To make the scarf joint, I clamp four plywood pieces on top of each other on a table, with the edges stepped 3 inches apart. I use a hand plane and belt sander to make the 3 inch steps into a smooth ramp (with a 12:1 slope). Here is what it looks like finished. Not bad for my first plywood scarf.

I then test fit the pieces onto the boat and mark a straight line across the scarf joint, so that I can line them up about right when I glue them. I cut the pieces slightly wider than necessary, in case I don't scarf the pieces perfectly straight. Then I trim them more accurately with a hand plane after they are scarfed together.

Here is a pic of one plank already on the boat and another set being glued together. I just wrap the glue joint in plastic and put textbooks and an old axle on top to press it all together. I like textbooks, because I have them laying around and they are flexible, so they create even pressure on the glue joint. Sandbags or something would also probably work.

After the scarf joint is glued and the plank is trimmed to fit, it's glued and nailed to the frame. The nails went into the wood frame without splitting it, but I had quite a hard time sinking the nail heads below the surface of the hard plywood when installing the first plank. (Imagine me quickly hammering on a nail punch trying to finish before the glue cures, cursing while I keep smashing my hand with the hammer). So I modified a cheap wood drill bit to make a counterbore. The bit makes a nice flat counterbore with a shallow dimple to help start the nail (but not an entire pilot hole). This makes nailing the planks much easier. I make the counterbores very shallow, since this is very thin 1/4 inch plywood.

So I clamp the plywood to the boat (again), countersink all the nail locations, remove the plywood, apply the glue, and quickly nail it all back together before the glue cures. I punch the nail heads slightly beneath the surface of the plywood and cover them with thickened epoxy.

And here is a picture outside my garage workspace ... cold and snowy, but I'm still building in comfort.

Hmmm let's see, do I have any good animal pics ... here's a good one.

Sunday, December 20, 2009

Centercase installation

Building a boat takes a toll on your relationships with your loved ones. Here is Chloe barking at me telling me to stop working and pay attention to her. I listened and took a break.

This week, the sides of the centercase were glued together. I also added vertical strips of lumber on the side of the case for attaching the bulkhead. I attached those at this stage, since I wanted to nail it from the inside before putting it together. I also drilled the hole in the case logs for the centerplate pivot bolt, since this would be almost impossible to do after it's in the boat.

The centercase was then installed in the boat. The case was wiggled into position and pilot holes were drilled for the 3" bronze nails. The oak is really hard to screw into, so I had to put it all together (to make sure the screws went in without a problem), take it apart, then put it back together again with glue. Quite time consuming with 20 large screws, but the epoxy cures too fast to try to do it all at once.

Here is a pic after its installed with thickened epoxy. After it was screwed in, I poured unthickened epoxy in all the cracks on the top to fill in all the joints. The unthickened epoxy would normally leak out of a joint, but the thickened epoxy underneath kept it from leaking out. Temporary wedges were jammed into the slot to close the vertical glue joints nice and tight. It went together without a problem, except its sitting SLIGHTLY crooked, but I don't think anyone will notice except for me. The top of the case is about 3/16" off vertical. Not a problem.

The next day when the glue is dry, the wedges are removed and the sides are trimmed flush with a saw.

This is a top view of the front of the centercase. If you look close, you can see a thin white layer of fiberglass on the inside of the case. You can also see that the inside of the case has some epoxy fillets that I made when I was gluing the case together.

The keelson (large backbone member) is then shaped (with a hand plane) into a wide v-shape, so that the curved plywood bottom can fit up to it. So I guess that's it ... here's a skeleton of a boat! Next week I'll start the plywood planking.

Sunday, December 13, 2009

Transom Installed

The inside of the centercase is being fiberglassed. The process involves multiple coats of epoxy and one layer of fiberglass fabric. The fiberglass is transparent after it soaks up the epoxy. (Thanks to my heated garage I can epoxy all winter long).

Also, the transom has been cut out and installed. The transom was glued and nailed with bronze ring shank nails. At first I was more comfortable using screws, beacuse I was worried that the nails would split the frames or something. However, so far the nails have worked great with Douglas Fir, but I have to predrill little holes when nailing into the white oak. I've been punching them a little below the surface of the plywood, which hides the head and also helps close any gaps on the other side and gets good glue squeeze out.

Here are pics of the plywood being marked for cutting and then the transom after its glued and nailed. The plywood was roughly cut and the edges will be cleaned up after the glue dries. It's 3/8" plywood, thicker than the 1/4" used for most of the hull.

Wednesday, December 9, 2009

Modified centercase slot details

Here is a section view showing how I modified the centercase connection to the keelson, in case I lost you on one of those previous posts. As I said in a previous post, I widened the slot from 3/4" to 1-1/4" and extended the 1/4" plys through the keelson. This makes the connection much more rigid and makes nice continuous plywood sides on the inside of the case, instead of having the keelson exposed for rot to start. I'm going to epoxy the centercase in place instead of using mastic.

This modification isn't a novel idea. I read in forums that some Hartley builders have done this and its actually listed as an alternative on the TS16 plans. They say they are happy with it and it makes a nice watertight connection. I'll let you know in a few years if I still think it is a good idea.

A brief lesson on centerplates

For those of you not familiar with trailer sailboats, let me explain what the centerplate is and how it works.

As shown in the diagram below, the centerplate rotates on a bolt or pin. It's completely lowered during sailing and raised for trailering and beaching the boat. It's raised and lowered using a pulley system (also shown in the diagram) or winch. The centercase has an open slot through the bottom of the boat. Since this slot is basically a large hole in the bottom of the boat, the centercase will fill partially with water. It has to be well sealed and the sides have to be high above the waterline so the boat doesn't take on water. (Or on some boats, the top of the case is sealed somehow).

So why does my boat even have a centerplate? Well, I won't get too into all the physics, but it's because sailboats need a large underwater area to provide lateral resistance. This lateral resistance allows the sailboat to sail upwind. When sailing upwind, the force created by the airfoil of the sail on the boat is diagonal, trying to pull the boat forward, but also trying to push it sideways. The centerplate keeps the boat from slipping sideways across the water.

Smaller sailboats use daggerboards, which are the same as centerplates, except they are simply pulled out of the top when not in use, instead of rotating into a centercase. If the boat runs aground in shallow water, the centerplate rotates up and the boat is usually undamaged. The more rigid daggerboard can cause more damage to the hull when running aground.

Small sailing dingies without a centerplate or daggerboard cannot sail upwind! Well, actually, it's difficult to sail in any direction other than that of the wind. Most larger sailboats don't need a centerplate to sail upwind, because they have large fixed keels that provide the necessary lateral resistance. The Hartley plans actually show two large fixed keels on either side of the bottom of the hull as an alternative to the centerplate, but this would make trailering difficult. I've never seen a Hartley TS14 or TS16 with fixed keels.

The centerplate on my boat is made of heavy steel, thus serving another purpose: ballast to keep the boat from heeling too much and make it more stable. So if the centerplate is not lowered before raising sails, the boat is unstable, difficult to control and may capsize.

But here is safety issue to think about ... what if the boat does somehow tip over on its side during sailing? Then gravity may cause the centerplate to flip into the centercase, thus raising the center of gravity of the boat, making it more likely that the boat will flip completely upside down (or "turtle") and making it very difficult to right. To solve this problem, a lot of sailboat owners have a locking mechanism to keep the centerplate down at all times, except when in shallow water. This locking mechanism makes the boat much more "self-righting". If a small boat gets on its side and does not self-right, the wet sailors simply stand on the side of the protruding centerplate and pull the boat back upright. And if the boat turtles even with the centerplate extended, the centerplate can still be used as a lever arm to try to right it.

Tuesday, December 8, 2009

Cutting slot in the keelson

Before I take the centercase apart, I'm cutting the slot in the keelson (the main backbone) and checking to make sure the centercase fits into it. A lot of sailboats have the problem of water leaking in around the centercase, including Hartley sailboats. I decided to modify the centercase design, like a few other Hartley builders have done. The standard centercase sits on top of the keelson (with a 3/4" wide slot through the keelson). I widened the slot to 1-1/4" and extended the centercase sides through the keelson. (Well, actually only one layer of 1/4" plywood extends through the keelson on each side, so the slot in the keelson doesn't have to be 1-3/4", which would leave too little of the 3-1/4" wide keelson.) And I'm going to permanently epoxy and screw the centercase into the keelson, instead of just using mastic and screws. This should keep the centercase from wiggling back and forth and leaking, however I won't be able to remove the centercase. (The original centercase design seems very difficult to remove also ... and why would I ever want to do that anyway?)

Here are some pics after I cut the slot. I used a circular saw and then a file to get it just right. The centercase is dry fit in place just to see how it looks. If you notice, I also had to cut one of the frames in half to make room for the centercase. The plans don't say anything about that. Luckily, I figured this out a long time ago and didn't screw the keelson to that frame.

Constructing the centercase

The centercase is going to be the new home for my centerplate. The sides are made out of 1/2" marine plywood. (I laminated two layers of 1/4" plywood with epoxy.) The lumber is white oak, glued and screwed from the inside to the plywood. The slot in the centercase is 3/4" wide, plenty of room for the 5/16" thick centerplate.

The pic shows the centerplate and centercase side-by-side. In this pic, the centercase sides are glued up, but the sides are just temporarily screwed together. I'm going to take it apart and fiberglass the inside of it for more abrasion resistance, then put it back together with glue and install it in the boat.

Shaping the frame

I'm in the process of shaping the chines, keelson, and stem so that the plywood planking will fit up nicely. I'm using a hand plane and belt sander. Also, I'm grinding off a lot of unwanted glue blobs with a dremel.

I'm also getting ready to put on the transom ply.