catzooks.com

Building strongback rails

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posted 2004 Mar 30

Starting with a 4'x8' sheet of 5/8" ACX plywood, I started cutting out all the pieces for the centre and side strongback rails.

The sides are easy - cut off 1" at the end, and then cut:

• four strips 1 15/16" wide
• four strips 1 11/16" wide

While you're at it, cut another two strips 1 15/16" wide (and the full 96" long) for the centre rail.

Next up is cutting everything for the centre rail. This is a little more complicated, because the pieces can't be flipped over to get the "A" side of the plywood to be on the outside of the finished piece (if you care). The best way I could think of to do it is to flip over the plywood between cutting each of the two "L" pieces required (pieces D & E).

Here is the picture I used to make all my first cuts (original Visio diagram).

Then, one of the "short L's" and one of the "long L's" need to be further cut down, to add a 12" divit on the end, like this:

Here is the cut list:

	item	qty	width, in	length, in
A	small rails, top & bottom	4	1 15/16	95
B	small rails, sides	4	1 11/16	95
C	middle rail, top & bottom	2	1 15/16	96
D	middle rail, long L, sides (needs additional cuts)	2	4 11/16, 2 11/16 for 36"	96
E	middle rail, short L, sides (needs additional cuts)	2	4 11/16, 2 11/16 for 36"	59
F	middle rail, bottom (completes 71" section & 12" section)	1	1 15/16	47
G	middle rail, bottom at front and back (divits go between sides)	2	1 15/16, 11/16 for 12"	48

All of this I cut with my trusty circular saw, using the rip fence to ensure the straight lines were really straight.

With all of the pieces cut, I did the work to modify the last 12" of what will be the stern of the strongback - cut it down to 1 11/16" for the last 12 inches. I then glued and screwed it all together.

The only thing I found when I was gluing it up was that it is important to ensure that everything stayed straight. The plywood has a tendency to bow, usually towards the flat A (finished) surfaces (not the edges). On the centre rail, when I screwed the top down into the edges, I found that the tops and/or sides "moved" slightly. The pieces for the centre rail are arranged like this . I screwed the top onto the sides at the ends like this , so the sides would stay vertical, and then screwed the top down over the red area. What happened was the black gap grew tighter, causing the rail to veer off to one side (the top in the image). I wound up cutting out a sliver of the edge in the black gap, so the rail wouldn't veer as much. Getting these things straight is critical.

[Update 2004 Oct 5: Greg mentioned in mail that plywood was the wrong thing to use for the rail, because it bows due to the stress of the layers on each other. I agree - using chipboard would have ensured the rail was straight, which would make alignment much easier.]

I also built sawhorses. The construction manual shows divits cut from plywood, and Kayak shows sawhorses, so I compromised. I screwed a divited piece of plywood into the end of sawhorses. The sawhorses stop the entire assembly from falling forward or back. On the website, Bram says that the short one should be 24" to the notch, and 30" on the tall one ("People over 6 feet tall may want to make them a bit higher"). Mine are 30" and 36" to the notch, respectively. I used plain ol sawhorse brackets to build the actual sawhorse, and made the legs 27 1/2" and 30". About 4 inches is added to the top of the leg when it's all assembled.

(13 images)

Building side rails, epoxying stations

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posted 2004 Mar 22

I glassed the bevel blocks. At first I was going to get the glass to stick to the 1/4" wide side of the bevel block, and I was using an elastic and some plastic to try and get this to happen. But there were a ton of air bubbles and I couldn't get everything to stay (even as the epoxy kicked) and so I finally gave up and just put the cloth along the top.

I also epoxied both sides of all the stations, so they would be less likely to expand and contract with the changes in temperature and humidity of the garage (Bram suggests this here). Once cured, I aligned all the centerlines and waterlines of the stations, and drilled a number of 3/8" holes through them. This way, when I have all the stations aligned on the strongback, I can use a laser level and ensure that the stations are all correctly aligned.

I then wrapped (clear) packing tape around the edges. Using something like fibre-reinforced tape might have been easier - it's no fun pushing down the overhang on all the edges.

Finally, I cut out all the holes for the strongback rails in the stations. I drilled holes to allow the jigsaw blade through, then cut everything. I went a bit overboard - station 6, where the side rails stop, I cut out the holes for the side rails anyway. I'll have to epoxy the pieces back in.

[Update 2004 Oct 5: Once the holes are cut in all the strongbacks, be sure to put the strongbacks back on the patterns to ensure the holes were correctly positioned. This ensures that you've cut the right spot. I didn't do this and should have, it would have made things easier during alignment.]

(15 images)

The spin block

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posted 2004 Mar 17

I shaped the bow piece and the spin block. The parts shipment also arrived - so I've been poking through the box and trying to ensure that all the bits and pieces are there.

For the bow piece, I sanded off some of the curved area, mostly to remove the rough edges, but largely left it alone. It will mostly be cut apart when it is installed on the hull anyway. I did sand the flat edge flat, however, to ensure a good fit.

The spin block started out as 7 sheets of glued-up strips, each 3" x 5". Once I had taken it out of the nails and sanded it down so there was no epoxy left on the edges, it was a block 2" wide by 2 1/2" tall, by 4 1/2" long. I took that piece and then worked it on the bench sander to give it a nice shape, with plenty of extra to handle the heavy loads of the spinnaker block that will be bolted to it. I rounded the edges, and then glassed it - the first attempt at glassing didn't go so well, so I pulled the glass off and will try again with a better cut piece of glass.

As an intermission from the spin block, I cut down part of the sheet of 4'x8' into the pieces that will be used as the strongback rails. I really need a cut sheet, so I only did the simple pieces for the side rails and top of the main rail. Having that (clean) sheet of 4x8 also let me spread out the pieces from the parts kit, so I could ensure everything was there.

I did the last step on the centre rail - I drilled the holes for the vang. I used a gadget I recently picked up. It's a flat piece of plastic which holds a metal insert exactly vertical. The metal inserts are sized for your drill bit. You hold the plastic flat to the surface, and you'll get a hole very close to vertical. It worked perfectly - the holes are dead on. I used a 7/32" bit - a 10-24 bolt will fit in 3/16", but it drops into 7/32", without touching the sides. I filled them with epoxy, drained, and pounded the tee-nuts into the bottom (I also found out that using a paperclip works better to grease the threads than a Q-tip. The paperclip leaves more grease behind.)

(24 images)

Spinnaker block, bow 'ball'

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posted 2004 Mar 14

I completed the spin pole ring saddle. I sanded both edges to a bevel of 23°, and the ends to 45°. I then glassed the top, bottom and sides. When that cured, sanded off the excess and glassed the ends.

With some of the excess epoxy/207 from the spin saddle, I put a sealer coat on the bevel blocks. I also put a second layer on the e-glass tape I wrapped around the bevel blocks. It flowed down to the bottom a bit, but I think I can safely call these parts "done" now.

I also sanded down the fairing compound on the vang pedestal and coated the entire centre rail/vang pedestal in three coats of epoxy/207/graphite. The second coat I didn't add enough graphite to make it opaque, so I had to sand it down and put on another coat.

While I was waiting for everything to cure, I started work on the spin block. For this piece, you need seven layers of wood, each layer with grain running in opposite directions. Between each layer is s-glass and epoxy/406 (and I added 403 as well). I glued up all the little boards, and then using the same system as the centre rail (nails in the tabletop) I layed up the block and weighted it down with some paint cans.

For the bow piece, you cut 6 pieces. 5.5" is the diameter of the top piece, and 1.5" the diameter of the bottom edge of the bottom piece. The top edge of that bottom piece (piece F) should have a diameter of 2.1" - the bottom edge will be worked down to 1.5". The grain should alternate directions between each piece, to reduce the chance of splitting.

piece	diameter, in	radius, in	grain
A	5.5	2.75 (2 3/4)	—
B	4.8	2.42 (2 7/16)	|
C	4.1	2.08 (2 1/16)	—
D	3.5	1.75 (1 3/4)	|
E	2.8	1.42 (1 7/16)	—
F	2.2	1.08 (1 1/16)	|
-	1.5	n/a	n/a

Once all the pieces are cut, I just bonded them all together with epoxy/406/403 and s-glass between the layers. The "tower" of blocks wants to slide apart as it gets tall, so watch out!

(22 images)

Centreboard trunk and spinnaker pole ring saddle

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posted 2004 Mar 07

More little stuff. I'm getting to the point where I do a bunch of construction work and batch up all the epoxy work, so I can epoxy a number of pieces at the same time. Saves on materials, I throw out less leftover epoxy.

Here's this weekend's work:

• I bonded a cap to the centre rail/vang pedestal with an epoxy/405 mixture.
• Glassed the bottom of the bevel blocks. I put disposable zinc bolts into the tee-nuts to stop epoxy dripping through, covered the bottoms in grease, and then faired them with epoxy/405 left over from bonding the cap to the centre rail. Put s-glass on - I should have then pressed the glass in by putting it glass side down on the workbench, to make the bottom flat (pity I forgot). Covered it in epoxy/207.
• Glassed the gudgeon block already on the transom bar with the leftover 207. Doing this after bonding them together worked out well, it makes it a bit easier than the glass for the standalone block, because the draping glass sticks to the transom bar.
• Cut 1/2" wide strips of solid cedar for the centreboard trunk ends. Wrapped them in a piece of scrap hybrid, painted on epoxy, wrapped in plastic, clamped, let cure, and then painted again with a second coat of epoxy (when the first became tack-free).
• Bevelled the back edge of the centre rail to match up to the vang pedestal. This turned out perfectly, I'm happy with the results.
• Cut and bevelled a number of pieces for the centreboard trunk.
• Glassed the unglassed parts of the centre rail. Getting the glass to settle was tricky and I wound up using an elastic to keep the glass pressed to the edge - and I should have used plastic to keep them apart. Epoxy bonds to rubber nicely. With a triangle file and a round file, however, I managed to rectify my mistake.
• Faired the vang pedestal.
• Cut the spinnaker pole ring saddle from a piece of 1" thick solid cedar. It started out as 4" by 6", and I bevelled the bottom to match the top edge of station 1. I then used the power sander to remove some stock for the circular divit on the top - it should wind up to be a divit of 3 1/2" diameter, about the diameter of a WEST System fairing container. Bevel the sides in 23° and ends in 45°.

[Update 2004 Jul 28: it would have been worth it to assemble the entire centreboard trunk at this point, rather than when it had to be inserted in the hull. (instructions) This way you work in a shop that has room rather than on a cramped edge of your workbench.]

[Update 2004 Jul 29: also note that Bram has a new insert mechanism (local) which is easiest to install when you are building the centreboard trunk.]

(44 images)

The centre rail

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posted 2004 Mar 05

I cut the new vang pedestal in half, and then glassed both the outer edge of the pedestal as well as the entire centre rail with s-glass.

I also used 2" e-glass tape to glass the edges of the bevel blocks. This required a bit of effort to ensure the glass stuck - I painted the edges with epoxy/207, waited a while for it to get nice and tacky. While I waited, I cut strips of e-glass tape to the right length to wrap around the outer edges. Once tacky, I wrapped the outside with the tape. The short edge doesn't need the tape form fit along the vertical edge (which would cause the tape along the long bottom side to not align), but the tape must form fit along the tall vertical edge, which means that there are "tabs" along the bottom - look here for what I mean. With the remaining epoxy/207, I glassed one of the gudgeon blocks - I'll go back and do the other one as well.

Once the epoxy had gelled up on the bevel blocks, I cut away the overlap. The West System instructions talk about using a sharp utility knife to cut the edges and remove the overlap, but on such a small cut I found it a lot easier to pull off the wet tape (once it was gelled) and cut with scissors, and then cut the other side to match. Once you're used to how to cut, it's easy to make the two edges match.

Once everything cured, I sanded away the excess and smoothed out the edges. Next will be a second coat of epoxy, and glassing the bottom surface.

I also cut the cap for the vang pedestal. I used the 3 1/2" circle saw to get the starter shape, then mounted that on the drill to get it down to the right size. I had problems with it turning oblong (I botched one and had to do it again). What I wound up doing was cutting a circle of the desired (bottom) radius, taking off a bunch of material via the drill, and then getting the final size and shape by holding the piece with the paper on top of it up against the disc sander. This worked pretty well, you still have to be careful about removing material too quickly.

Last up: I started cutting the parts for the centreboard trunk. I aligned all the strips vertically in the trunk body, but the smaller pieces I will align them horizontally. They seem to be providing strength longitudinally, so horizontal strips seems to make more sense.

(16 images)