CS17 #226

[Apteryx]

Hello, all,

This coming week I plan to begin a Core Sound 17.  I think I'm hull 226 - that's what it has on the license sheet, but the invoice references 227.  Not sure what the '227' is on the invoice...

Anyway, I'll be building from the CNC kit, and although I have no timeline for completion I would be ecstatic if I could build her in time for next year's Texas 200.  My skills are minimal, though, so I will complete the boat as I learn what it takes.  When she's ready to float, I'll go sailing.  ;D

I've specifically requested a slow shipping date from Graham, both to make it easy on him and to give me the time I need to do some shop-cleaning.

Before the kit arrives I'm going to build the centerboard, and I hope to begin that task Monday night.

What wood is best?  The plans just suggest a hardwood.  I will glass over the centerboard, and since it won't be seen (what, me capsize?) I don't really have any cosmetic preference for wood.  I think all I need is something tough that takes epoxy well and I imagine I'll paint the centerboard white.

I'm sure I'll have plank-sawn wood, so I'll be flipping end-for-end and turning every other strip 90 degrees.  I'm curious about a strength issue, though.  Is the best laminate just flush surfaces?  Tongue and groove sounds good, but the tongues would take sheer stress from side loads on the centerboard along a weak grain axis.

Would setting dowel pins, perhaps staggered, between the laminations enhance the strength?  Or, is that sort of thing just pointless?

I have a powered self-feeding planer that I think will work well to take the centerboard down to the dimension at it's thickest.  Just thinking it through, I think I'll use a router to put a rounded cut down the center of the leading and bottom edges.  Then before glassing over the centerboard I'll lay a piece of braided line saturated with expoxy to armor the vulnerable edges.

Any comments appreciated.  Particularly with regard to better over-engineer the simple stuff.  That's one of my favorite hobbies!  ;D

[Maria CS20 104]

Welcome. I to am new at this experiment and we are having a ball having cut out all hull items including beams and rudder parts along with cutting wood for centerboard.  On the rudder we used instructions directly and hand sanded close to specifications.  Really looks cool with the shape finished out and sanded to smooth, using the ply on the rudder I found as I sanded through the plys I could get a good simetrical board by measuring the distance on the exposed wood in each play, on each side.  On the centerboard, a friend gave us hickory and black walnut which we cut in strips and alternated the strips by grain orientation.  Looks cool even though the only it will be seen is when removed completely for transporting the boat on a trailer.  Don't want it supported by a line and catch when driving, bouncing and rattling around I am concerned it could drop.  We are going to buiscuit it between each strip.  I think right now about three between each strip.  Plan to place at about 8" in from top to bottom off set by about 4 inches and one down center of each strip off-set by 3 inches between each strip.  I am sure it will be more difficult to build, set buiscuits and epoxy up and clamp together, but I THINK IT WILL BE COOL and WORTH it.  Best of luck and have fun learning and building

Jim Atkinson

CS 20  104

[Ken_Potts]

   I haven't heard of a single failure of a built-up CS centerboard.  I'm not sure if tongue and groove would be stronger than the regular breadboard style once it's been fiberglassed but I don't know if the extra strength is necessary.

   I would be careful about mixing species though since I'm currently trying to figure out how to deal with cracks in my thwart seat that happened (I think) because I paired walnut and ash for looks.  The different woods expand at different rates when things get humid around here.  Jim, you may not end up with the same problem once you've glassed the board.  My thwart isn't glassed, it's just coated in epoxy then polyurethane.

   The good news about experimenting with centerboards, though is they are relatively easily replaceable...

[paul_stewart]

... centerboard [will be] removed completely for transporting the boat on a trailer.  Don't want it supported by a line and catch when driving, bouncing and rattling around I am concerned it could drop. ....

Jim,

When our CS20 #103 is on the trailer, the forward end of the fully-retracted centerboard (CB) is held firmly in the boat by the pivot pin and the aft end rests on the trailer's middle roller.  The trailer has 3 rubber rollers: one under the stern, one under the bow, and one mid-ship.  I had not given any thought to whether or not the middle roller would support the CB  --it just turned out that way.  Works fine.  Have not needed to remove the CB for trailering. 

By the way, to lower the CB while the boat is on the trailer (e.g., in order to examine/repair/remove the CB) requires sliding the boat backward on the trailer several feet so that the boat almost falls off the back end of the trailer.  Of course the tongue of the trailer must be anchored down or hitched to a vehicle for this maneuver and it is best/essential to have a separate 4th roller mounted on a stand to support the stern as the boat slides backward.

Trailer:    http://www.messing-about.com/forums/index.php?topic=5825.msg51577#msg51577

--Paul

[Apteryx]

Well, finally I am getting started with our hull.  The side stringers are noted to be tapered from the forward bulkhead down to 1/8".

Which axis is tapered?  My guess is that the stringer is tapered so it stands 1/8" proud of the hull surface at the forward end.

I'm not sure about placing the forward bulkhead, too.  The plans show the bulkhead 14 5/8" forward of the station at 144" from the stern on the topsides, but 12 7/8" forward of the same station on the bottoms.  I bet it makes more sense once the hull is 3D - maybe that will answer my questions.

Those dimensions come from the Hull Cutout Sheet in the plans.

Man, am I excited - finally getting a start.  ;D

[Maria CS20 104]

I would find, it hard to mark once putting the hull together and recommend marking before folding up.  I marked every line and point of connection provided in the plans and checked three times to ensure I was right on target or best I could get them.  You are working a flat surface and as you back measure points they will come together as you make them with greater clarity.  I too was confused for some time and I reviewed the plans for three months before I marked a stick or sheet of ply.  Just another engineer, but I did find it worth the effort to best understand all points identified, I even marked them in different colors depending on the purpose specifed by Graham.  I have pencil lead, red, blue and green lines and I coded the plans for future reference to avoid my own confusion.  It is cool thte way it comes together, plug through and keep posting all the questions and progress.  These folks are GREAT at keeping me straight and providing sound easy to understand advice.  Sometimes it sparks lots of really interesting conversation, go with the flow and read it all twice, they really want us all successful and it is a great comfort to have this resource.  Thanks to all you folks out there behind our dugouts in the stands.

Jim Atkinson

CS20-104

[John Burritt]

You're right about the tapering on the stringers.  The vertical height remains constant, the horizontal thickness gets smaller.  Makes it easier to go 3D with the hull and minimizes the chance of a hard spot.

John

[Charlie Jones]

And if the CB should happen to miss landing on a trailer part, you can easily do what MacGregor does on their trailers, In the correct location to catch the CB, drill holes in the trailer side beams for eyebolts, Then run a heavy stainless wire across between them, The wire would carry the weight of the CB easily.

[Apteryx]

Thanks for the centerboard advice.  Wood planed to a precision surface bonds very well with epoxy, it seems.  Mine has a couple of places that need some filling, but basically my centerboard is complete.

I'm curious about what kind of wood to use for the dimensional lumber pieces.  All my life I've thought yellow pine was basically junk wood but I've heard it spoken well of in forums.  Yellow pine is commonly available around here.  It seems heavy, but would yellow pine be appropriate for the keel batten?

What should I use for the stringers?  Douglas Fir can be found at the local lumberyard - is it flexible enough to use for the stringers, or would pine work well there, too?

As might be gleaned from my posts, I'm just getting up to speed on this stuff.  I'd hate to say I'm an idiot, but, heck, every village needs one... I've got your back, man....  ;D  ;D  ;D

[John Burritt]

Both fir and pine will work.  It just needs to be knot-free and relatively straight grained.

[Charlie Jones]

I prefer Fir for stringers, etc. Yellow pine is ok, but remember TRUE yellow pine is becoming a rarity- it's a really hard wood, but few trees are allowed to grow large enough for being useful anymore. Other pines are being substituted.

I like working with clear fir myself.

Now when I built the Princess 22, I found a piece of used wood for the keel. It was a piece of hard yellow pine that had 162 growth rings in a 4 inch section. The wood came from a torn down 105 year old house. So we figured that tree was growing when the Revolution was going on, if not before. THAT chunk of pine will last as long as the lead keel does ;D ;D

On the Core Sound 17 and 20 I built, I used a strip of fir for the keel strip. A piece of fir I had gotten when a school was rebuilding bleachers- it had been a bleacher seat for 30 years and I had had it around for 17years. VERY straight grained stuff.

I'm always watching for stuff like that- I just rack it up- someday it'll go into a boat ;D

[Apteryx]

I haven't set any speed records getting started on my CS17, but I'm plugging away.

I've got the bottom pieces laid out ready to glue, but I'm not sure about a construction detail.

The plans call for pinning the parts in position with brads, which I take it are the little 18 guage or so miniature finishing nails.

The brads holding the bottom layer of the glue stack in place will have to be driven in fully flush so the other layer can lay flat, or so that's how I envision it.

Seems like those brads will be difficult to pull without damagine the plywood after the glue has cured.

Any ideas on a method for keeping the pieces aligned?

[Charlie Jones]

Just use the brads- once it's cured, a small set of diagonal pliers will nip in and get the brads out with little damage to the surface. Or you can just push them back from the other side.

[Charlie Jones]

an addendum- put the brads way out towards the edges- those edges will mostly be covered by fillets and glass tape during construction, plus you'll be drilling a BUNCH of wire tie holes out there.

Don't worry about the brads.

[Apteryx]

Thanks, Charlie!  Now that I think about it, the brads won't hold very well to the backing 1x8, not in tension, anyway.  I should be able to pull the parts up, taking the brads with them, and push them out.  Particularly if I think ahead and use brads that don't penetrate very far into the 1x8.

[Apteryx]

Still stumbling along here, making haste at a very moderate pace, but making a little progress - but I have to say the step scarfs are engineering marvels.

I got set up to glue the aft scrafs on the bottoms, and was just all thumbs.  I forgot to mask the scarfs until after I mixed the epoxy, then after wetting down with unthick epoxy I realized I'd only masked the top sides.

First joint jitters, I guess, but then the brads disappeared for a quick tour through an alternate universe.  First they were 'right there', then they weren't, then after a few hectic minutes, well, heck, there they were.  Had to be an alternate universe, tools in a shop don't just disappear...

So there I was, 20 minutes into my pot time and still looking to glue tab 'a' to tab 'b', and worried about the epoxy kicking.

Not coming up with any better ideas, I very carefully pushed the scarfs together, adjusted the lateral alignment as best I could and clamped the joint without matching it to the other side.

Definitely not the way to do that.  No doubt a reliable formula for failure - except after gluing up the second piece there isn't so much as a hundreth of an inch difference between the two halves, maybe not a thousandth.  Running my finger along the edges of the two halves stacked feels like one thick piece of plywood.  Precision alignment, despite very flawed methods on my part.

Kinda like my boat is already starting to take care of me. 

[Apteryx]

The Core Sound 17 plans call for thinner plywood for the forward bottom pieces, so there is a step-down in thickness.  I don't have the plans in front of me, so I'm not sure if I'm using metric thicknesses or not - getting the kit relieves one of so many decisions! 

Anyway, I found if I laid the bottom pieces for gluing so the gap was in the middle it was very close to the thickness of the thinner plywood, 1/4 inch or whatever metric equivalent.

The glue sandwich was plastic, starboard bottom (outside surface down), plastic, 1/4 inch plywood spacer, plasic, portside bottom (outside surface up), plastic, clamping 1x8.  It turned out great, and the two halves are precisely the same outside shape with only a little fairing required at the scarf joints.

The adventure continues...  ;D

[John Burritt]

You are discovering the marvels of step scarfs.  While its best to work with matched pairs, things still line up when you don't.  One of the real advantages of working from a kit.

[Apteryx]

Ray, I hadn't thought about letting the un-fair side of that step be the outside side.  Do you eliminate the eight stringers on the bottom that way?  They would be easier to fit with that little stair step to the outside of the hull.

I overlook the most obvious things.  Over the last week I've been trying to puzzle out how to keep from drooling epoxy all over the place while warping the seat stringers into place.  Then it occurred to me I could use plastic sheeting to mask off everything except where the seat stringer goes.  Masking, what a concept! 

The step scarfs are really nice, quite an invention.  My bottom and topside halves are precisely the same outside shape.  I'm hoping that will translate into a fairly exact, true hull.

[John Burritt]

Regarding the seat stringers - they should be glued in place on the sides and longitudinal bulkheads before the boat goes 3D.  Then there's no worry about getting them in the right place.  I'm presuming Graham marked the locations on the sides.