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Core Sound 20 Mk 3 -- #4 "Chessie" . .


Pete McCrary

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I have never used rollers, probably because I was taught to use a squeegee (plastic spatula) and brush. I built an entire airplane that way. It is important when glassing to get the balance right between too much and too little epoxy. You know its right when the weave is visible but not dry or white. Too much epoxy and you risk floating the glass cloth off the substrate. When I fill the weave I put some micro balloons in the epoxy, it does a great job of filling and is easy to sand. Then a final coat of epoxy to seal the lot - no water is getting in there! After that, of course, is several coats of primer and finish coat.

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Fabricating rub rails for "Chessie."

With the sheer strakes tac welded in place, I removed the 20 foot (plus) 1 x 2 (.75" x 1.5") yellow pine fairing battens that were back-screwed to the outside of the side panel with the top edge about 1/8" proud of the sheer. That really smoothed out the entire sheer line.

Now I have two long battens that I plan to use as rub rails. However, after being attached to the hull for a over a week, these very flexable battens have a "set" that makes them hard to manage on a table saw. Trying to save space on the shop floor, I clamped them together (concave sides facing each other). That made a very straight and solid piece with a square 1.5" x 1.5" xsection. Fairly stiff and (with a helper) easy to push thru a table-saw setup.

post-4915-0-12320200-1462539014_thumb.jpeg Rub Rail xsection based on Graham's design for "Carlita."

The drawing shows a pair of rub rails. On the right is one of the fairing battens yet to be shaped -- and on the left is the other batten with the desired shape. These battens will be clamped together for three of the four cuts require (for each side). The cuts c1, c2, and c3 (all with blade angle at 30 degrees) are made in mirror-image pairs -- port and starboard. After the first cut (of each pair) the clamped-together piece is turned end-to-end for the second (the mirror-image) cut. The c4 cuts are made (saw blade straight up) after the clamps are removed and the battens separated.

The rub rails will be attached to the hull with their tops just at the sheer/side-panel seam with 1.25" SS FHWS thru the hull and into a .5" x 1.25" inwale. I probably have enough left-over mahogany for the inwales. The three sharp corners will be rounded over with block plane after attachment. My plan is to have the rub rails attached with bedding compound so that they may be removed for repair or replacement.

I haven't started their shaping yet -- so COMMENTS & SUGGESTIONS are welcome.

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That's a very nice way to do rails with a hollow back. Done this way, the hollow backs will act more like a solid back, which is good. I don't know if I'd use mahogany for the inwales, but if it's what you have, they'll be fine inwales, that's for sure. If you 'glass the deck, extend the fabric over the rail enough so the hollow back can cover the edge. It'll make replacement a little more difficult, but will help keep moisture from getting behind the rail. Of course, if the rails are bright, just wrap the fabric around the topside planks and mount the rail over bedding afterward.

 

Yes, the inwale/rub rail assembly really stiffens up the topsides quite a bit, offering an idea of the structural significance in this element of the design.

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I like it. PAR has way more experience than me, but I would put that on top of the glass. I'd pre-finish the rails and bed with butty tape.  I think with yellow pine you will be replacing this sooner than later. 

 

One suggestion....I'd use good featherboards on my table saw with a zero clearance blade insert. The floppiness of the rails wouldn't matter if you had them holding this molding captive with both side and down pressure. This would add a level of safety and have more accuracy.

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Little-by-Little -- and progress is made. Graham recommend that a 5/8" x 1" batten be inserted inside the top edge of the sheer strake at its intersection with the cabin roof. Notches had to be cut in Blks 1, 2, & 3 and the cabin knees. Now the sheer strake is beautifully fair from stem to Blk 3. The battens are a little proud of the roof beams so that they may be bevelled for a neat fit under the roof panels. Tomorrow I'll install another pair of battens from Blk 3 to the stern.

post-4915-0-93155300-1462827004_thumb.jpeg

I think a boatbuilder's term for this part is a "clamp." Like a "sheer clamp" providing a means of attaching the deck to the hull along its sheer. I could be wrong. Here, would it be a "cabin roof clamp" ??

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Modern materials, design and construction make terms awkward some times as I said in another thread.  Your correlation to the shear clamp is accurate, but dunno if there is a proper equivalent for this application.  Your term Pete would seem appropriate.

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A sheer clamp is left over from stick built boats, where a set of frames would be bridged on their inboard faces with a clamp. This clamp often was tied to a shelf, which was a piece fitted between frame bays, forming an "L" shape, against the planking. Graham correctly notes it's an inwale, which is the opposite of an outwale and lives on the flat, inside the sheer strake or planking. The outwale is another term for a rub rail, though can have other meanings as well. The same guy that came up with ceiling as the wall coverings also dreamed up these terms.

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One more thing done. The "inwales" aft of the cabin are now set in epoxy. This setup was much more difficult than the ones for the cabin roof. Probably the compound curve that required the batten to be split [for about 36") in order to make the "ski-jump" curve up to the cabin roof. Wow !! Looking more like the boat I want to build. This is fun.

post-4915-0-61962900-1462925192_thumb.jpeg Does one ever have enough clamps?

post-4915-0-12673200-1462925285_thumb.jpeg Keeping the sheer-line profile "fair" at the cabin / cockpit transition.

post-4915-0-13623900-1462925464_thumb.jpeg A port-side outboard view.

Tomorrow I'll start making the companionway frame and roof beams match the design cone or (perhaps) a cylindrical shaped roof.

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Now I'm ready to fillet and glass the corners all around the inside from stem to stern. This is how I got there:

1. Graham's posting that he "back-screwed" a .75" x 1.5" fairing batten (stem to stern) on "Carlita" made (in my opinion) all the difference in preparing for installation of the sheer strakes. And those battens can be effectively used [later] for rub rails.

2. With the cabin knees wired in place and with the design beam dimensions at the cabin knees (that Alan provided), I was able to come pretty close to those dimensions by jamming spacers at the sheer line.

3. With the beams braced close to the design at the sheer line and at the tops of the sheer strakes AND (aft of the cabin) the strakes braced at the 75.2 degrees (provided by Graham) -- I then tightly wired the knees and Blks 3, 4, & 5 to the side panels and sheer strakes.

4. Then notches were cut where needed and the cabin /roof inwales were dry-fitted making quite fair the top of the sheer strake all the way from the stem to Blk 3.

5. Then I did the tac welding everywhere (except for the inwales). After releasing the bracing, there was very little "spring-back."

6. The next two days I removed the inwales (for minor adjustment and trimming) and upon replacement, glued them in place forward of Blk 3 and then [next day] the inwales aft of Blk3. At this point the whole structure is very stiff.

7. Previously I had built the frame for the companionway-hatch module (OD of 24.5") to fit between Blks 1 & 3. It was made an exact rectangle with cross beams aligned exactly with the forward edges of Blk 2, fwd knee, and aft knee. The beams were oversized in height so that the arc of the cabin roof could later be marked and cut on each beam.

8. The notches in Blk 1 were each cut 1/8" wider so that Blk 1 and Blk 3 would form a perfect rectangle with an outside dimension of 24.5".

9. Using a very straight 1 x 2 batten laid fore and aft with ends fixed at their appropriate notches, I marked the ends of the knees (Blk 2, fwd & aft knees) to be "in line." Two were already "just right", and four needed slight (< 1/4") trimming. After trimming (with saber saw), all lined up very nicely.

10. Finally, the previously constructed frame dropped nicely into place.

post-4915-0-65618800-1462996980_thumb.jpeg

Notice the oversized beams. The beam (cleat) on aft side of Blk 1 has already been trimmed.

post-4915-0-22960200-1462997293_thumb.jpeg

This is Blk 2 showing it's about 3/16" high. That carries off to the side as well (on both sides). It's definitely higher than the other knees. It seems to be properly placed with its angle right at the sheer -- so maybe the upper dimension [as cut] may be off a bit.

post-4915-0-21540400-1462997222_thumb.jpeg

This is the fwd knee. It's a little shy of where it should be. Probably because I couldn't make (force) the beams just wide enough. Probably that's also why some of the knee ends needed to be trimmed. My plan is to cut thin shims and glue them to the top of the [shy] knees -- then trim them to be fair with the other knees and Blks 1 and 3. For those that are high -- I'll trim them with a saber saw or maybe spoke shave.

Notice my "Construction Spacer." After I mark the beams with the profile of the cabin roof, I'll place the Construction Spacer next to the beam to be trimmed before its removal.

post-4915-0-77250700-1462997344_thumb.jpeg

Looking forward. The lower edge of the beam (cleat) at Blk 1 is cut at 1.25". This brings its lower (roundovered) edge just at the upper edge of the 1/4" roundover on the lower edges of the 1.5" longitudinal beams. It's my plan to make all the beams that width.

My measurements show that both top edges of Blk 2 are 9/64" high, stbd fwd knee is 1/32" low, and stbd aft knee is "right on"; and on the port side the fwd knee is 5/32" low, and the aft knee is 1/8" low.

I'm very pleased and impressed with the accuracy of this kit -- especially this far into the construction. I noticed that the side gaps are a little more on one side than the other. When installing the module it slipped into place with such a solid "thunk" that I didn't think to carefully inspect if it was perfectly centered. It probably could have been jiggled just a little -- then that small error could'v been multiplied later on in the construction.

All-in-all, I think this kits accuracy is absolutely amazing.

Pete McCrary, a happy builder.

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AMAZING ACCURACY -- From the keel to the top of the roof, the port and starboard cabin knees meet the companionway frame just 1/8" from the same elevation. And their spacing, port to starboard, was < 1/4" error from meeting right at the side of the frame. The cabin "hanging" knees rest on the longitudinal stringers glued to each side panel between two parallel "computer-drawn" lines. If either line (or the placement of either stringer) is off just a little -- then that error will be evident (even multiplied) by the time the builder is installing the companionway frame.

I'm getting close to roofing the cabin. I think that I'll roll "Chessie" over when the roof is secured in place -- leaving hatch fabrication and cockpit decking for later. However, I will have the cockpit sole and deck "dry fitted" and secured temporilarily with drywall screws to add some stiffness for the roll. In addition to completely finishing all that's required on the bottom, I will paint the cabin interior "overhead" areas while they are "up-side-down." Hopefully, when rolled upright, "Chessie" will never again show her "bottom up" !!

post-4915-0-83804400-1463184302_thumb.jpeg Frw knee about 1/8" shy of companionway frame.

post-4915-0-17504500-1463184440_thumb.jpeg Aft knee only about 1/16" shy.

Shimes cut and glued to make the knee tops fair. The knees of Blk 2 were about 3/16" proud of the frame and will be trimmed with a spokes shave.

COMMEMTS & SUGGESTIONS welcome regarding my plans for the rollerover.

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BATTERY Mount . .

Earlier I installed a battery box just above the keel inside the forward locker (between Blks 1 & 2). But now I've decided to follow Gramh's suggestion that a good place for the battery is on the keel just forward of Blk 3 under the first step from the cabin sole to the bridge deck. The Group 24 battery box is removed and on a shelf in my shop. I suppose it could still be used for a 2nd battery (but not likely).

The battery is a Group 27 "deep cycle" and rated at 92 amp-hrs. It's equivalent to about 58 lbs of ballast on the keel at mid-ship. The installation required modification of the removable cabin sole. It will fit nicely under the first step of the removable 2-step "ladder" leading up to the bridge deck. That ladder has not yet been designed. I'd like it to serve another purpose -- table, stool, game board ??? Suggestions please.

post-4915-0-14027800-1463406361_thumb.jpeg The battery base not yet epoxied to the keel.

post-4915-0-66943200-1463406590_thumb.jpeg Modified cabin sole in place.

post-4915-0-91798700-1463406680_thumb.jpeg Battery clamped down.

post-4915-0-39604700-1463406803_thumb.jpeg Showing battery top just below shelf for the Port-a-Poti.

Just yesterday I completed all filleting and FG taping all interior corners and the sheer strakes to the side panels. Today I'll be measuring, cutting, and trimming the remainder to the cabin [roof] beams. After that I think I'll be ready to install the cabin roof.

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I'm not planning for a battery like that, so I can't comment. But I had a step like this in a Catalina Capri 18 I owned years ago. It was very sturdy and a nice piece of hardware.

 

26015.jpg

Manufacturer is here: http://www.garelick.com/Oak-Footrest

 

I've added a vertical piece on the starboard side of the module to attach it to. It's not wide enough so I'll have to make a new step and while I'm at it I'll make it a bit deeper. I was sort of surprised at the distance to the sole and I think at leas one step is necessary. This step was so sturdy on my C18 I used to stand on it when others drove and it was a good place to keep an eye out for other boats. Since you have the battery there permanently, maybe you might think of a box right over it as a step.

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Getting closer to the "rollover" event. The roof-support structure is all-but complete. Next will be glueing in-place the companionway & hatch frame, which is presently curing on the bench. The outboard beams are also glued in-place.

After all the roof-support structure is glued in-place, I will "fine-tune" the bevels and beams to achieve an "fair" match to the roof panels. Those panels are my next step: I'll epoxy (two coats w/o FG) and then "butt" them together the entire length of the centerline (leaving spaces for the xbeams). The butt-plates will be on the underside. On the topside I'll epoxy on a 3" FG tape along the centerline.

post-4915-0-35342900-1463672767_thumb.jpeg Outboard beams attached to Blks 1, 2, & 3 and fwd & aft knees.

post-4915-0-59666400-1463672792_thumb.jpeg The companionway & hatch framing curing on the bench. Also, the battery base.

Once the roof panels are joined, they will be the largest one-piece of plywood that I have ever attempted to do anything with. I'm thinking that I'll move it in-place for a dry-fit with 1" dry-wall screws -- carefully "indexing" its position in multiple places. Then mark the underside with the profile of the support beams and inwales. When the panels are removed [from the dry-fit}, the gluing surfaces will be sanded. Finally, the gluing surfaces will we wetted with neat epoxy and then thickened epoxy applies to the support beams and inwales. Then the hard part -- getting that huge roof panel in place and secured without scraping off all the glue. I'd APPRECIATE any helpful tips or suggestion on how to get this done.

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Pete, once again you have inspired me. I am back at boatbuilding and just at the planning stage for cabin construction, so I appreciate your ideas and pics. Bunk supports in and most of the internal glassing completed. I will upload some pics when I can remember to grab a camera, but so far my progress (and therefore pictures) is basically the same as yours, just a little behind. Today I dry fitted the rubbing strake to the hull and just stood there admiring the lovely fair lines that Graham designed into the boat.

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Thanks Drew,...

Yesterday Graham recommend that the roof support should have an additional pair of longitudinals running from Blk 3 fwd to Blk 2. xSection is .75" x 1" and half-notched where they cross the knees and meet over Blk 2. I'm cutting the notches and longitudinals this am. But if you haven't installed and trimmed the tops of the Blks and knees you shouldn't half-notch the them until they are trimmed and in place. Here is Alan's drawing showing their placement.

post-4915-0-72929100-1463750315_thumb.jpeg

I'm assuming that you are TEMPORARILY backs-screwing the "rubbing strake" to the outside of the hull as suggested by Graham as a means to make fair the top edge of the side panels. Remember to have its top edge about 1/8" proud of the sheer line. But before you attach the sheer strakes, cut the notches (for the inwales) into Blks 1 & 2 and both knees at the roof line and top of the sheer strakes. I didn't do it until after the sheer strakes were in place. It was a bear of a job.

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