Category: Boatbuilding methods

After stripping the bottom planking off (see Remove the Bottom), it’s a good time to take another look at the soundness of the bottom framing.  Now you can see it from it’s most vulnerable angle–the joint between the frame and the bottom planking.  This is where water is most likely to collect (the bottom of the bilge) and be absorbed into any unsealed wood.  Remember, any wood with over 20% moisture content is a great place for rot spore to grow.   The factory may or may not have sealed this joint with paint, but that was 60 years ago.

After taking another look at the bottom framing, it’s in pretty good shape for being 60 years old, but still, it is 60 year old wood.  It leaks around the transom joint, and is oil-soaked under the engine.  We’re going to be putting a newly rebuilt engine in this boat and it is, after  all a speedboat.  You wouldn’t put a new engine in a 60 year old car without addressing the chassis.  It would soon shake apart.

Aside from all that,  the original bottom frames are made of  Philippine Mahogany–a wood with little to no rot resistance.  We’ll replace them with white oak which is a traditional boatbuilding wood because of it’s good fastener-holding and rot resistance properties.

We’ll use the old frames as patterns to cut out new ones.  Then we’ll  install each new frame, using the old keel and chines to get the lines right, along with battens, and bevel the new frame in place.

Finally, disassemble the whole thing, seal the new frames properly, and permanently install them.  This gets the new frames sealed at the joint surfaces–a very important step that keeps them from soaking up moisture where you can’t see it.

So we’ve got the bottom off (see Remove the Bottom), what now? Well let’s take a moment to look at the chines (the longitudinal piece of lumber that creates the “corner” between the topsides and the bottom).  While we’re at it, we’ll take a look at the keel as well.  These pieces are made of white oak, so that’s good material.  But they’re also 60 years old, and very perforated.  The keel is oil-soaked under the engine, which weakens wood considerably.  It also has a bad dip in it forward, with no good way to smooth that out.  Once you’ve come this far, you’d be crazy not to replace these pieces.  So off they come.

In order to get the chines off, you have to remove the first topsides strake (plank) next to the chines.

The first step in removing the topsides strake is to strip the varnish off it to make removal of the bungs easier.

We haven’t made a decision yet on whether to replace this plank, so to avoid splintering around the bung holes when removing bungs, we strip the finish which acts as a glue and can pull splinters of this delicate old wood.

Once the finish is stripped, the bungs can be removed by splitting them with an ice pick, and pulling the pieces out carefully.  This exposes the screw heads which you can carefully back out, trying not to catch on the side of the bung holes and splintering the wood.  You will inevitably break some screws and find some already broken.  Mark them for later drilling and extraction.

After you’ve got the planks removed on both sides of the chine, it’s a pretty simple matter to unfasten the chine and remove it.  Broken fasteners holding the chine in shouldn’t present too much of a problem since we’re replacing the chines and the bottom frames.

A poultice is a moist, soft mass used to treat inflammation of a body part.  It is often applied with heat.  It can also be used to draw out stains and other contaminants from a porous material.

In our case, it is a way to draw out oil from oil-soaked wood.  The stringers in this boat have, over time, absorbed engine oil that has been spilled in the bilge.  They’re not damaged enough to warrant replacement, but I want to get the oil out of them to facilitate sealing of them, and paint adhesion.  A good way to do that is by making a poultice of ground up non-scented kitty litter (dried clay) and lacquer thinner.  The lacquer thinner is a solvent that soaks into the wood, dissolves the oil, and keeps it in solution long enough to leach out through osmosis to the kitty litter where the oil concentration is less.  This may sound like snake-oil.  But it really works.  Try it.

Removing the bottom is a pretty straightforward procedure.  With the proper tools, it doesn’t take much time at all.  It can be done in a day.

The basic procedure is to abrade away the wood at each screw head, and back out the screws in the  main frames, auxiliary frames, keel and chines.  The other screws, in the intermediate frames, and those holding the inner planking to the outer planking, can remain.

The trick is to get all of the screws you need.  Invariably you will miss a few that will show up when you get the pry bar out to take the bottom off.  Be patient and don’t tear anything up.  Just keep taking them out til you get them all.  Then the half bottom lifts off, easy as pie!

Each half of the bottom can be lifted off as a unit and saved for later review.  The planks on one side can be taken off individually to be used as patterns for the new bottom.

The tool of choice for abrading the wood at each screw head is a 4-1/2 inch grinder with a wire rope wheel.  As you might imagine, this destroys the old bottom planks.  So you can only do this if you’re not preserving the old bottom planks.  But why would you be replacing the bottom if you weren’t going to use new wood?  Some would argue that you should preserve as much of the original planking as possible, but I can’t see the logic behind putting back 60 year old, tired wood.  We’re replacing all the planking and bottom frames with new wood.

As you might imagine, going after all the screw heads with a grinder will stir up quite a bit of dust.  So the first step was to rig up a tent around the boat to contain that dust.  I didn’t want it going all over the shop.  I was able to set up my tent so that it enclosed one of my air filtration devices, so I could filter out a great deal of the dust that I generated.

I also wore a tyvek suit and a respirator during this operation.

Now that the boat is upside down (a major accomplishment–check out how we did it in the post labelled “Roll Her Over“), the next step is to get it plumb and level.  Now let me just pause here and say, that plumb and level means absolutely plumb and level.  Any inaccuracy here will compound itself over the course of the project because there will be countless times when you need to determine if something is level or not.  If you can just plop a spirit level on it, that simplifies the measurement considerably.  If you have to resort to stringing up string lines every time you have to take a measurement, it takes a lot longer.  So get it dead level now.

So what does plumb and level mean?  Well remember in Plans, I said I had gotten a copy of the lines drawing for this boat?  The load water line on those plans tells you where the boat should theoretically float when loaded.  So that line is the one you need to draw on the boat and then get it level.  It doesn’t matter that the boat is upside down.  Level is level.  Then level the two corners of the transom.  When you have done that, the stem should be plumb (i.e. at an angle of 90 degrees) to the ground.

Now a laser level greatly simplifies this task.  Before these nifty instruments were affordable for the average boat shop, one resorted to a water level to get the boat level and plumb.  Builders used it to level buildings as well.  It’s a fine tool.  Look it up on Wikipedia!  Anyway, projecting a level laser line on the hull is a lot easier, so that’s what I used.

Once that’s done, you can determine how close your boat is to the original design.  This boat was very close.  The worst the keel was off was 1-1/16″ low at about station 4.  That was a combination of the chine and the keel being a little low–each about 1/2″.  The width was within 3/4″ over the whole length of the boat.  And there was about a 1/2″ concavity in the planing surface of the bottom, called a hook because it slows the boat down.  That’s not bad for a 60 year-old!  It took a good deal of time to determine this, but it was worth it.

Then of course there are alot of other things to measure and document–like where all the holes in the boat are.  A tape measure and digital camera are invaluable here.

Some of the key design lines are easily marked on the boat with a pencil.  Look closely in the picture here to see where I’ve marked the load water line.

Finally, I needed to add a walkway to either side of my rack so I would have someplace to stand while I work on the hull.  I was hoping to be able to work from the shop floor, but I need to be able to reach the center of the hull while putting substantial leverage and/or weight on a tool.  Hence the scaffolding addition.

Armed with a good platform to work from and a good knowledge of where the boat is out of true, it’s time to take the bottom off.  That’s a story for another day…

Once the boat is stripped of as much weight as possible (seats, ceiling, floorboards, engine, instruments, dashboard, rudder, fuel tank, other miscellaneous hardware), it’s time to roll it over.  Much of the work will be done with the boat upside down.  So you’ve got to figure out a way to get this thing upside down without damaging it.

Of course there’s always the “15 Friends and a Mattress” technique.  But I don’t have 15 friends that will agree to show up at the same time to roll a boat over.  And boats are made to be slick and smooth so they can mover through the water.  This makes them difficult to hold on to, particularly when you’re trying not to drop it!  I decided to employ the much safer method of using 2 gantry cranes and an iron pipe.

The first step was to make a rack to put the flipped boat on.  It’s a good idea to put casters on the rack, so you can easily move it around your shop.

Next, I suspended the boat by 2 four-inch load straps that were tied over a 2 inch black iron pipe suspended in a couple of bearing assemblies that my friends at a local machine shop fabricated for me.  The idea is that the pipe with the load straps will rotate in place, allowing you to roll the boat over while it’s hanging from the straps.

Next, I had to lower the boat and re-tie my load straps so I could raise the boat high enough to roll my rack up under it.

Then lower the boat onto the rack.  The cross-spalls on the rack were set at the right height so that when the top of the stringers were set down on them, the boat was level and plumb.  This is the kind of thing you can only pre-plan if you have a copy of the lines drawings.  See the previous post entitled “Plans”.

Then it was a simple matter to roll the rack into place on the shop floor.  Then the rack was blocked up to make it level and plumb.

Special thanks to Morgan Houtz who helped with the roll over, and Sadie the Wonderdog, who helps with everything.