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.

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.

Chines and Stringers

The second layer of chines and gunwales and the smaller stringers have been installed. All of these are attached with bronze screws and thickened epoxy.

The boat may look like this for awhile. Next I have to shape the frame so that the pieces of plywood planking will fit up nicely. But before the planking, I'm going to make the centercase (or centerplate trunk) and maybe install it. And I have to sand all the unwanted epoxy lumps off.

Garage Sealed and Heated

The garage has been getting too cold to epoxy. The temperature needs to be at least 55F for a few days at a time for my epoxy to set properly. So I either have to wait until spring or come up with a way to heat the garage. I was thinking about buying a heater and garage door insulation, but all of that costs a lot of money. I found a way to satisfactorily heat the garage without spending any money at all.

The most important thing was to stop all the cold air from coming in. Stopping all the drafts must be done before insulation is added. I temporarily decommissioned my garage door and covered it with a large plastic sheet and 2x4s that I had laying around, being careful to seal it as best as possible around the edges and bottom. I patched up some holes in the drywall and taped the cracks around the attic hatches. By leaving the door to the house open, the garage becomes part of the heated space of the house. I didn't need to install a duct feeding the garage, because the furnace naturally sucks warm air from the house into the garage when its running. It's not the most efficient or safe setup ... but it's definitely the most cost effective solution for one or two winter seasons. It's not efficient because the garage space isn't completely insulated and also the furnace is now sucking warm air out of the house and releasing it out the roof vent. Nonetheless, I now have a heated garage and only marginally more expensive heating bills.



The garage is at a cozy 62F when its in the 40's outside and 68F inside the house. It could be warmer if I added insulation but that costs money. The coldest surface inside the garage is probably the concrete floor ... and I'm never going to try to insulate that.

One problem is that my garage isn't long enough to plane long pieces of lumber with the garage door closed ... so I stick the ends of the lumber through the open living room door to feed them into the planer! (I have a very understanding wife ... as long as I have a curtain up to keep the sawdust out of the house).



The garage door probably won't be opened until the flipping.

Chines being installed

The first layer of the chines and gunwales has been installed. When I was installing them, none broke and only one sprung back and hit me in the head! Success. I started by cutting a bevel in the front to fit up to the stem. I attached each of them to the stem, then glued and screwed to the frames. A pretty simple process as long as the pieces of wood don't break.



I decided not to screw them into the foremost frame (frame #1), because I was worried that the screw hole could cause the piece to crack in this high stress area. This worked fine, except the force of the bent gunwale pushed this frame aft slightly. Some temporary wedges and clamps are used to hold everything in position until the glue sets.