CS17 #315 continued

[cprinos]

Ok, so a big hint that I'm taking too long is that my build thread got archived 

 

Original one is here: http://messing-about.com/forums/topic/7392-cs17-315/ , and I'll pick up where I left off with this new thread.

 

Last thing I was doing was fitting seat tops and playing around with the carlin/side decking. I had trimmed some of the 1/4 ply for the forward seat tops, but not yet joined them. So I made a butt block for the underside, and epoxied the two halves together. Once the epoxy cured, I went ahead and did some precoating to the underside, as that would be a tough spot to try to get to once installed in the boat. Edges left dry where they will be joined to the seat stringers.

 

 

 

 

 

 

[cprinos]

Next up were the carlins, about which I fussed to no end. Two things I kept playing with: the width of the side decks, and the amount of curvature in the forward portion. I decided to opt for side decks with about an inch extra width, and a bit more curve forward than called in the plans. Also, from about midship back, the side decks on mine have a constant width. The plans call for a more narrow taper amidships.  It's possible this will cause me some problems w/ rowing clearance, but I figure the middle position is not going to get heavy use and I really wanted a bit of extra width.

 

I ripped up two carlins and clamped them in place with space blocks until I got the layout where I wanted. Those buggers kept on springing out on me as I was trying to fit them in, but I eventually wrestled them into place. Once happy with the positioning, I mixed some epoxy and glued & screwed the carlins + spacers. I had some extra epoxy and used that to make small fillets at the spacer/carlin and spacer/inwale joints

 

 

I did make a miscalculation here. At some point between measurement & fitting, I must have added som additional curvature to the carlin, and as a result it came up short at the aft end by about 1/2 inch. I don't think that should be an issue structurally -- there's going to be a corner brace there at some point, and I will plan to fill the gap with a small filler piece and some epoxy, and all will be hidden below the decking

 

[cprinos]

A couple of more items added to the deck framing:  the main mast and reefing mast reinforcement blocks.  I'm not 100% sure I will actually end up making the full reefing position as some folks have said they didn't think it was worth the trouble, but at this stage I figured I would keep my options open.

 

[cprinos]

In order to do some cleanup and be able to blow dust around somewhere other than my garage, I pulled the whole kit outside. My irritating driveway slope means once the boat is out the door it wants to head into the street, but it's not too heavy at this point and I had some locking casters on the building frames to keep it out of traffic. This was the first time I think I had it totally out of the garage, so it was nice to be able to step back and see it from some different angles that I can't really see from in the garage.

 

[cprinos]

I was going to start on the centerboard next, but didn't have the lumber to start, so I began looking at what was needed for the centerboard trunk instead. In the nesting diagram, it shows it being a tight fit between one of the side deck panels and the short part of the centerboard case. In my case I flipped the orientation of the side decking [middle center in the nesting pic below] which gave a little more margin for error (and as it turns out, gave me the proper finished side up).  To mark my progress in this project, I shade in the pieces on the nesting plan as I go along. I made a rough cut of the starboard side deck while getting out the trunk side, and I made sure it would cover the appropriate area over the side decking.

 

 

Now that I've got a couple of rough cut trunk sides, I'll work on building up the trunk and scribing to fit. A first look at what I was up against created an opportunity for an important milestone: I got to step into the boat for the first time instead of just walking around it.

 

That's all for now. I've got a little momentum now in my feast-or-famine style of building, hopefully will post more on the centerboard trunk & centerboard soon.

[Alex]

Looking good so far. I can't wait to start my Coresound 17 sometime in the near future. I am wanting to travel some serious distances as I am a little restricted in my Son's Spindrift 12 that we built last year. Love that boat but can't wait for a bigger and faster boat.

 

Alex.

[cprinos]

I could use some advice on the centerboard trunk..... Should it be built in place?  Built/assembled separately and then fit in?  Without much in the way of longitudinal support apart from top rails, how do you make sure the thin 1/4 ply maintains a constant width slot throughout it's length?

 

I find this part also a bit more difficult because parts of the trunk have to conform to the as-built hull, and parts have to be quite exact (centerboard fit).

 

So any thoughts/advice on the sequence of work here would be appreciated, I think I'm getting a little intimidated by this part of the build as I have been staring at it for a few days now

[Peter HK]

I built mine off the boat and fitted it in when the seats were in and the thwart could be dry fitted to hold it in place. I made my case a bit deeper and cut a hole in the bottom wide enough for the case to poke through, then marked a pencil line so I could cut the excess off accurately.

 

When glassing the case in I duct taped a few wooden spacers cut to the right size to the inside of the lower edge of the case to keep the lower ply edges straight while the epoxy set.

 

Cheers

Peter HK

[Chick Ludwig]

I pre-built mine for my CS-20 Mk 2 and installed it on top of the bottom planking. I had a piece of wood inserted in the bottom of the trunk to hold the correct gap. I used one piece of wood as long as the inside of the trunk rather than several short pieces to be sure that the bottom of the trunk was held straight. (A little wax or clear wrapping tape on the spacer just to be sure it doesn't accidentally get bonded in when you glass the trunk in may be a good idea.) I used a router with a straight bit with a ball bearing follower to cut the slot through the bottom after I turned the boat over to glass the outside of the hull. Be sure to round over the edge and glass over the joint! This not only strengthens the joint, but also waterproofs it. Water getting in here will ruin your day!

 

By the way, did you (or will you) put a layer of glass on the INSIDE surfaces of your trunk? That extra protection with the board scuffing up and down is a good idea.  (Maybe I'm too fussy, but it's hard to come back later to fix trunk problems. A bit of extra care here will save worry later.)

 

Good looking job. Keep up the good work. Someday soon you'll be sailing!!!

[cprinos]

Peter & Chick,

Thanks for those replies, they were very helpful. Not sure why I didn't think of the spacers to hold the gap, that sounds like it will work very well.

Peter - The method you describe of making the trunk long and fitting all the way through the hull matches the descriptions of some other trunk installations (other kinds of boats) that I was researching, it certainly seems like it simplifies the matter of matching the bottom profile while keeping the right alignment for the top rails.

Chick - I just started dimensioning some of the timber parts, haven't yet committed any epoxy to the trunk. I do intend to glass the interior of the trunk -- totally agree that I don't want any issues creeping up with this part of the boat down the road.

Chris

[Gordy Hill]

If you add graphite to the epoxy on your rudder blade, center board, and inside of your trunk the board will operate a bit smoother and if you sand down to 600 grit the parts look like hi-tec carbon fiber.

How much is your guess. I just added "some" and liked the way it turned out.

[cprinos]

Courtesy of you helpful folk, I have a plan. Also Wes' awesome CS 20 build site  seems to always have a picture and an answer for my questions.

 

There's not a flat spot in my garage that doesn't currently have a boat or a bike occupying it and I wanted to make sure the trunk sides were nice and flat during construction. Happily the sides are the perfect size for working on my workbench in the basement shop. Unhappily, this means trucking all sorts of tools and materials from garage, through kitchen, to basement. 

 

I started out with laying out the rough cuts with the smaller side panel on top. I'm using a crummy 'shop' camera here, so don't mind the distortion. 

 

A batten laid free hand was used to help form the curve of the longer trunk side. As far as I can this curve is purely aesthetic, so I just played around a bit till it looked about right.

 

My 10 year old wanted to know what I was doing so I created this exquisitely detailed model to illustrate.  Please note that no original plan sheets were harmed for this photo.

 

Ok, back to it.   Because I enjoy a challenge, I'm making a port-side trunk. The plans show a starboard-side trunk. There's no functional difference, but I'm doing this because of the way I made the forward seat tops (the seam is to starboard). What it means is that every time I look at the plans I have to mentally flip the orientation, and then triple check it as I'm always sure I've got it wrong. If I don't launch the boat next year, I'm claiming this is the reason for the delay.

 

So I cut to the layout lines for the two trunk sides and then positioned the top rails in preparation for epoxy work

 

 

Then mixing up a batch of epoxy at a time (it's 90 today and the stuff is kicking off quickly) and tromping from garage to kitchen to basement,  wet & buttered the rails and then clamped the whole thing in place.

 

Of course then I noticed I forgot to place plastic underneath. I cleaned up the small amount of squeeze-out though, and for now am fairly confident that my workbench will not be a permanent fixture in my boat, but only time will tell.

 

While I'm waiting for that, I'll probably start ripping up some fir for the centerboard.

[cprinos]

What type of fiberglass cloth is recommended for the centerboard? I've got enough 12oz biax for the inside of the trunk, but have to order new cloth for the centerboard.... I couldn't find a spec for it in the plans or materials sheet.

[hokeyhydro]

Not sure what the "spec" is, but I use 6 oz on centerboards, rudders, and their associated parts such as trunks. I lap the 6 oz over the leading edges to double up - seems to be enough. Oh yeah, mix graphite powder with the resin fill coats. Supposed to make everything slicker and it looks really cool!

[cprinos]

Thanks hokeyhydro... 6oz sounds like a good default and I was expecting to use that for the hull a some point as well.

[cprinos]

Didn't make it to the Mystic this weekend, but did get some time to work on the boat instead.

 

Ripped up some Douglas Fir 2x6's for the centerboard.  Flipped and turned as shown in the plans to try to get quartersawn equivalent and to relieve stress of the ripped boards. I let them sit for a day before glue up to make sure none wanted to twist or bend too much. 

[cprinos]

I unclamped the trunk rails & sides.   I'll wait to add the king posts until I have a final dimension on the centerboard.

[cprinos]

I laid out the centerboard  in the orientation I wanted and the clamps I was going to use.

 

I then laid out plastic on the bench and clamps and prepped the boards for epoxy. Here, all but the last strip has been turned to it's glue side.

[cprinos]

Next day, a finished blank popped out of the clamps

 

The blank was cupped slightly at the ends -- around 1/16", but the blank is slightly thicker than the finished thickness to accomodate flattening, so this wont be a problem.

 

I flattened the blank pretty quickly with a jack plane

 

When that was done, the blank was as flat as my bench, and did not want to rock or show gaps regardless of how I had it oriented (or which side) was on the bench.

 

Next up I need to cut out the board profile from the blank, then get to shaping the foil.  The plans show a generic foil shape (could be a 00 series perhaps), but I think I might try using a scaled leading/trailing edge template that I have from a set of Michael Storer boat plans. 

[cprinos]

One of the nice things about building your own boat is you can spend time on ridiculous things. In my most recent case I'm talking about foil sections for the centerboard. I'm pretty sure I'm going to eke out an extra .05 knots at least. 

 

As mentioned above, the plans show a small, generic sectional profile for the centerboard. It's not a NACA shape because it's got flats in the center, but the leading and trailing edges look like they could be NACA derived. Honestly it's hard to tell exactly from the plans because of the small size of the section.

 

A while back when I was trying to figure out what boat to build I went sailing with a Goat Island Skiff builder and he told me about the template that Michael Storer provides in the plans to create foils. They are Neil Pollack - derived sections that differ from NACA shapes in that they have parallel sides (flats), similar to what's called for in the CS17 plans. The leading and trailing edges optimized for boards where the thickness is 8% or less of the chord -- I think the CS centerboard ranges from 7.5 - 9 or so as it's tapered. In theory these should be as good or better then NACA until the thickness is up past 8%. Here's a page showing some XFOIL software analysis of some NACA and Pollack sections and a discussion of their applications to centerboard and rudders.

 

So instead of eyeballing the foil shape, I decided to go with the template approach to guide my work. I bought a set of Storer's OZ Racer plans ($20) -- they use the same template, then scaled the templates in photoshop to match the centerboard thickness of the CS17. Overlaying with a scan of the section shown in the CS17 plans, the Storer template is slightly fuller in the leading edge--more blunt, and very slightly more rounded through the trailing edge, but they are pretty close. After printing the templates, I glued them to some pieces of ply to make patterns:

 

Then did a rough cut w/ a jig saw

 

followed by a final trim to the line with a rasp, file, and cabinet scraper (this shows the trailing edge pattern being finished)

 

In the end, I've got a pattern that can be placed agains the bench (that's where the part labled 'baseline' goes) to guide the foil shaping. It took about 30 minutes of careful work to get a nice smooth template. To check for fairness, I use it to trace a pencil line and then did an eyeball test on the drawn line.  The trailing edge is the less critical of the two, so I did that one first, I'll do the leading edge next.