Blackrock 24 (Build)

A sequence of glassing one side of the board.


Fairing filler coat applied to "green" epoxy.



Sanded fair.



Building finish coats.

 

A change of pace.

Laying out a frame or two. A cut-off piece of straight grain fir was milled to about an 1/8" and used as a batten. To digress, widths and heights were laid out and 2 1/2" nails were driven into those locations. Then the batten was sprung around the nails,



I purpose made a couple more battens for use throughout the build. Here the deck camber is being laid.



The first of seven (eight counting the transom) frames to be laid out. I'll get the front two frames and the stem laminations out of this sheet of ply.



Somewhere at 40000' thinking about boats.

 

A nifty little trick.

Here is a little trick I came up with all by myself.

As you are cutting off a chunk of plywood that you would rather not have drop uncontrolled to the floor, clamp the ends where it's clampable and then insert screws along the cut to hold up the excess. As long as the gap stays close, your material will stay put.

 

What do you do with a sheet of plywood?

You make a giant cookie cutter and make funny shaped cookies. Yeah, I know. Pretty lame.








And then, you put then together like this.



This is where the main steps.


The triangular piece is the base of the mast step and will seal the area from the rest of the hull so that it can be drained overboard.

 

Just a couple of photos. The stem is glued up. I had reservations on the mast step causing a stress concentration at the forward edge of the mast due to the sharp corner and diminished cross-section. The cross-section itself was adequate, but seeing parts in 3D is different than looking at drawings. I extended the mast-step cheeks around the corner alleviate some of the stress there. I've added the lightening holes and have been building the epoxy coats. The inside edge of the stem is also the race for the mast heel as it is being stepped. A layer of glass tape was added here for abrasion resistance.



As an aside, in an earlier post I showed the installation of some bamboo "trunnels" in the centerboard. I downloaded a data sheet on bamboo to see how effective the use of bamboo trunnels might be. I was pleasantly surprised. In tension, bamboo can be anywhere from slightly less than the strength of steel to over two times as strong as steel. I would never bank on the high side of the equation, but I'm willing to go with the lower end with a safety factor of two. Half the strength of steel is still good and it come at the price of zero weight and being electrically inert. In places where extra tensile strength is required, I think that it is an acceptable alternative to metallic fasteners if properly applied. The key will be having enough material thickness to transfer the tensile stresses through the glue joint to the trunnel. I see the rudderhead as a good application and maybe even the deck to shelf connection. Bamboo is a cheaper than bronze and stainless steel.

 

just one more photo of the stem. I had to hog out some excess material. Ounces equals pounds and I'm trying to keep an eye on them. The second hanging frames has some blank areas in it down low. I was going to originally put lightening holes there. I've decided that I have some areas forward that might be a real pain to provide easy access to, so I'm thinking real hard on making then buoyancy chambers so, for now, I'll leave the panel intact. Instead, I routed out half of the material thickness on the other side leaving only a sheer web.



Otherwise, I'm producing drawings as I go. I'm working aft from the bow on the frames and will start with the longitudinals when the frames are done. The next frame is laid out and rough cut waiting for me to move on with it. Funny how a little surgical procedure slows things down. It's given me time to re-read engineering texts and relearn lost knowledge.

 

The second sheet of plywood wasn't as productive as the first. One bulkhead and a couple of pieces for the chain locker. I wasn't happy having to go horizontal with the grain, but that was preferable to having to a scarf a vertical joint. The horizontal joint is at deck edge and leaves me the option to change cabin profile. The upper portion won't be added until after roll over. This will allow the hull to be closer to the ground during the build...maybe.



Some of the visible lines are for additional cuts and cleat locations for furniture.

 

Cutting up the third sheet of plywood. Hole saw are your friends. I found them to be invaluable for defining lightening holes and a paddle bit was good for getting at inside corners that would be hard to get at otherwise.



The four pieces in the foreground are what I got out of sheet number three. They are getting their epoxy treatment. You can also see cleats that are being installed for furniture support. It is so easy to define the locations while laying out the pieces that is doesn't make sense to wait. I'm really hoping to have most pieces self-locating by the time coming to start putting components together. I was trying to use partially driven nails to locate and clamp these pieces. The locating aspect worked real, but partially driven nails don't give the required clamping force. Plan B was to use clamps. Thank goodness for all of my lightening holes. They gave easy access for clamp usage. Their were only two pieces that I couldn't get clamps to and a thickened epoxy paste was used there to insure proper bonding. Later, when the epoxy was cured, I came back in with a plane and router to chamfer the lower of the cleats.



Does it make sense to spend 20-25 minutes to remove two pounds of material from a panel. The panel below is 3/4" ply and is my bridgedeck panel. It started at 12.4 pounds and weighed 10.4 pounds after 20-25 minutes of router work and belt sanding. The middle portion is now a little over 1/2" thick while the perimeter remains at 3/4". I suppose, structurally that the perimeter should be thinner and the middle should be thicker. Hmmm.



The results of yesterdays exertions. Four panels were thinned. Two non-structural panels were thinned to 1/4" in the middle.

 

I am my own CNC machine.

No major progress. The previously mention panels have gotten epoxy coatings and the cockpit soles and chain locker panels have been laminated with some 7 oz. cloth for abrasion resistance.

I've laid out and cut out the next frame. It's the aft cabin bulkhead and is essentially my midships section. It is my most complex frame and took a bit of time to lay out and cut out. In retrospect, I should have laid it out before any of the other frames as it was the first time I was looking at this section of the boat in full scale. A cardboard mock-up might also have been worth while as when I saw certain elements in real life, I knew that changes had to be made. The quarter berth openings were a bit short in height and had to be enlarged some how. The short of it was I had to add two inches to my sheer height midships forward. To the aft, I let it taper to original height at the transom. The sheer increase and a more exact lay-out gave me an additional 3" in height for the quarter berth openings. This also raises my cockpit a couple of inches and the extra freeboard isn't a bad thing. My freeboard at midships is 32" so I think I'm not pushing any limits here.

I've also gone back and modified the forward frames so it's time for progress again.

A frame freshly cut.



The frame cleaned up and ready to be entombed.

 

I've been framed!

I've finally worked through all of the frames. Note the scabs on the forward frames. This is where I've added 2" to the forward sections. They are glued and doweled for now and will get additional layers of glass when the decks are filleted and taped. I'm laminating mahogany to the transom frame and have cut out the longitudinals that run most of the length of the boat. The mahogany on the transom is from a massive stereo cabinet that I built in my 20's. Ten years ago the glue joints started failing so I knocked it apart and have be dragging the lumber around the continent not knowing what I was going to use it for. A nice little legacy moment for the build.



I took advantage of some nice weather and did a preassembly check of components and ended up setting up all of the frames in the yard for a mock up inspection of the boat.

A quick tour of the boat, so far. Starting with the stem, forward mast step and V-berth area.



Going down the right side, we have the V-berth entry...



galley to port and settee to starboard...



...settees port and stbd leading to quarter berths.



Stbd quarter berth leading to deep internal storage. Note the centerboard slot and central access storage. A recent mod added a bridge deck so that there would be adequate room below for an ice chest if desired.



Cockpit view with internal transom for the kicker motor. Also of note is the aft end of the centerboard trunk that is part of the mid cockpit frame.



Cockpit storage is to port.



Port quarterberth...



..and back to the galley and the V-berth partition.



The time to take it 3D permanently is approaching quickly. I have the vertical longitudinals to assemble, the central horizontal panels and the clamps to scarf. Very exciting! I could be planking before years end. That would set me up for a spring roll over. I'm planning on two roll-overs. I want to do a right side up assembly of all of the skeletal components because I want to be able to roll it out into the drive before I do the final locating of the clamp. I want to be able to step away from the boat and get a good look at the sweep of the sheer before locking it in. I've built in some room to play with the forward sheer so I'm hoping this will help me "tune" it for a pleasing appearance.

 

Looking nice. All that work is starting to become a boat.

 

I have to assume, you'll have a mast boot around the lamp post, where it comes through the deck to prevent leaks?

 

Thanks L.G.

Paul, I was thinking I could put red and green lenses in it and use it for my nav lights.

 

Assembling the longitudinals. I can't think of a boat term that applies the these components. They form the sides of a box beam that forms the backbone of the boat along with a double layer of plywood that forms a central broadstrake and cabin sole assembly. The double layer is 1 1/2" thick and allows me to not have any floors penetrating cabin proper. So, the longitudinals may provide some keel type function, but I can't call it a box keel because I see a box keel extending below the hull proper.

First two photos show my alignment method. These are the first pieces of the build that require joining of more than one piece of ply, plus they are central to the hull's form so correct alignment is of utmost importance. There are three main pieces being joined for a total length of 22 1/2'. Each piece was given an alignment reference based off of dominate edges on the panels. A line was from stretched from the end points of these references and the rest of the panel reference was aligned to the line.

I opted to use simple butt blocks to join the panel as they are self-aligning when clamped or screwed. I toyed with using half-Payson joints, but chose the simpler approach though by the time I cut out the splices, et.al. I might have been time and money ahead with the Payson joints. The butt-blocks are all hidden inside furniture so you'll have to go looking for them to find them. The sole and broadstrake panels will get half-Payson joints. These two components back each other up and their joints will be staggered so I think I could skip the joints all together. The cabin sole panel is critical to shaping the longitudinal laterally so I want to build the cabin sole as a single unit to get proper shaping for all of the components the joint to it down the road.



Poor man's peel ply. More like a cheap man's peel ply. With the first longintudinal glued up, I was able to use it as the guide for the second one. The plastic keeps the panels from getting glued together and lets me match the second assembly to the first for a uniform construction.



The second longitutinal assembled and glued to on top of the first. Note the difference in the mid panels in the assemblies. You can see, on the starboard (lower) panel, the additional material for the centerboard box. The biggest portion of the board is hidden in furniture.



Transom is now planked.

 

Bit by bit.

Progress slows...or at least feels that way. Funny how work tends to get in the way of life (boatbuilding) sometimes. Mostly, I think that I'm at a point where real visual changed are going to take place with this build and it takes all of my will power to keep on track to complete those tasks that are more easily completed on a work bench than inside of a boat. Coating panels is one of these tasks. I could very easily start assembling the bare ply panels to make the boat look farther along than it is, but to what end? Working patiently, methodically and strategically may take more time in the beginning, but I anticipate returns in the early time investment by way of short overall time to build and easier completion of internal finish items.

On the other side of the coin, you also have to be careful to avoid doing thing that will cause more work down the road. Going router crazy is one of these. i.e. putting that nice radius only where it is needed and not getting carried away and routing everything in sight only to be filled back in with thickened epoxy at a later date. Another might be when cleaning up the transom to leave a little excess in those places where mentally the completed assembly might still be a little fuzzy. And, of course, to really confuse things, removing excess material at this stage because it will be a real bugger down the road.

The transom is coming along nicely. I spent a couple hours with it removing excess epoxy and hand sanding to get the desired level of finish. I bounced back and forth between 36 grit and 80 grit on a sanding block to work down the high spots and then give it a decent finish for epoxy application. Truth be told, I hit the transom with my belt sander and 80 grit to remove the excess epoxy. Bent sanding is always risky on something like this and even with judicious use, most of my hand sanding afterwards was to remove the inevitable gouging left by the belt sander. I took some artistic license with the tiller opening. I had an inverted triangular opening for the rudder head and tiller opening and added a couple bumps to make the shape it is now. I think the result is pleasing and it lends an appeal for the fairer gender that is always good in a project like this.



The longitudinals are progressing. This one has one side of the centerboard box combined with it. I am glassing the "wet" side with 7 oz cloth. The middle photo has the glass wetted out and a board doubler being installed. The longitudinals are not straight, but follow a contour that I have designed into the boat. This means that the outboard section of the C/B box is also contoured and has a variable width. It took some coaxing, but I was able to keep the width variation to a minimum. This doubler serves multiple functions. It narrows that portion of the C/B box. the longitudinal joint was placed at this location and the double works in concert with the splice plate on the opposite side of the longitudinal and lastly, this is the location where half or more of the C/B torsion forces are absorbed into the hull. This give a full 1 1/2" of material thickness at this location. The inboard portion of the C/B box will be made of 3/4" ply and the companionway ladder will have a support bonded to the box there that will provide additional support for loadings on the opposite tack. The third photo has me filling the 7 oz. weave with epoxy thickened with wood flour. I like the wood flour here as I feel it makes a hardened surface and if applied carefully, does not require much sanding to prep it for over coating. I also try to do this while the wet-out coat on the glass is still green. Once the wet-out coat is cured, I'm not sure how to get a good mechanical bond without sanding into the weave of the glass so I try to plan for build coats and filling weave before a full cure. I suppose in most cases when weave filling is required, there is no structural bonding taking place over it.



A close up of the doubler (Sorry, bad photo). I used some 18 oz. glass here since it will be subject to board loading and also constant abrasion from the board being raised and lowered. Note the nice radiused transitions at the edges to allow the heavy cloth to drape nicely. This area will get the same wood flour and epoxy treatment to provide a smooth surface for the board to bear against. I'm at a bit of a quandary about finishing the edges of the 18 oz. material. I have smoothed the edges some and a couple of coats of epoxy will seal it up, but am I being lax by not fairing the edges completely or am I going "over the top" by thinking about doing a good blending/fairing job? There is no function being served by blending this juncture as it is completely hidden, does not have any flow over it and only needs to be waterproof.