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CS17 mk3 and CS20 mk3


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There is about 50# more plywood, the tabernacle weighs 5# and there is 15# of lead on the tip of the centerboard. The solid stock weight will only increase slightly because some of it is eliminated and some is added. There are the usual options, like whether to glass sheathe or not. The water ballast is 360#

 

I have widened the chines slightly to carry the extra weight. The rocker is as close to the mk1 as I could make it. I have increased the sail area to compensate for the higher sailing weight. It will be interesting to see how they compare, I suspect that they will average about the same with one or the other being slightly superior in certain conditions.

 

The bulkheads at either end of the bunks are 6'5" apart which should fit most people. The 17 mk3 was mostly drawn with the interior laid out before the 20 mk3. When Doug wanted to use the 20 mk3 in the EC I pushed on the 20.

 

The Thetford Porta Potti will fit in the 17. I can't recall the model name that I used but it is their smallest. On the mk2 I put it under the berths forward but on the mk3 the berths are too low and I put it on top of the ballast tank below the bridge deck. This means that it must be moved to be used. We have the under berth potti on our OB20 and I move it out to the cockpit before sleeping every night so that you do not have to wake the other person to use it. On the mk3's it can be used down below during the day for privacy. I know that this is not ideal but the boat is only 17' long and if you want your ladies to participate, it is a viable solution.  One character I met recently said that one of his tests for a prospective mate was to ask her if she would crap in a bucket, if she said yes, it could go to the next level.

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Yes, make a battery box and mount it in front of the water ballast tank and the lid will be the step into the cabin.

 

There has been a lot of discussion here about the canvas hatch cover. After thinking about it for a few months and having come up with some absurdly complicated methods I am going back to the most basic. There will be a 3/8 (9mm) ply coaming around the hatch shown in magenta. The red shape is a L shaped piece of wood that doubles as a grab rail. The blue is Sunbrella with fiberglass battens sewn at 12 "  centers. The battens are 1 1/14" by 1/8" and are sprung over the coamings and are held down by the L shapes/ hand rails if one has to go forward over the cabin. There is a toe rail around the deck edge for security.

 

There is a channel between the coaming and the grab rail to drain the water that will run off the cambered canvas. there will be a flap that snaps onto the top washboard.

 

In light blue I have drawn a section of luff tape. I will sew that down both sides if the canvas. If there is any tendency for the battens to come out from the L shape grab rails I will put a track under the L to keep it corralled. The toe rail will be drilled with a series of holes so that I can tie stuff down, attach a snatch block or tie fenders in place when at a dock or rafting to another boat.

 

I have been concerned about leaking through the stitching. One idea is to make a two ply hatch with sail cloth on the under side with the batten pockets sewn just into the sail cloth and a top layer of Sunbrella which is only sewn around the perimeter. Alternatively there might be a good stitch seal out there.post-127-0-60623400-1395620404_thumb.jpg

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What about stretching an uncut/unstitched piece of heavy canvas over the entire hatch opening with rib supports, with little (elastic? bungee shock corded?) side tabs sewn on either side (about every 6 - 8") that run down to little "cars" mounted on a piece of sailtrack on either side of the hatch. There would be no seams over the hatch to leak, and the cars should run smoothly to push the canvas forward to open the hatch, like sliding open a shower curtain.

 

Haven't thought it through... there might be a design problem I'm not considering, but it seems like that kind of idea could be made to work without seams.

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Graham, your solution seems brilliant in its simplicity. My SA20 uses coated Sunbrella for the hatch cover, and has never leaked a drop. My bimini is regular Sunbrella, with seams, and those leak a bit despite repeated efforts to seal the seams. Do you envision a flap on the forward end with a few snaps? Bungee around the tabernacle? The forward end needs to be well secured when trailering (hurricane force headwind!).

 

Joel

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They make waterproof thread especially for use on awnings, tents and marine applications.  It does however lose it's waterproof characteristic usually before the fabric.  Then go to a seam seal as ricknriver suggests.  I would not do this until you had to as it is not overly permanent and recoating builds up and makes a mess.  Unlike varnish, it isn't so simple to strip so you can start over fresh.  My Sunbrella dodger on Hirilonde is 5 years old, is left up for the entire 6 month season and still waterproof.

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Wes, yours was close to my original idea. Alan and I got into it one day and ended up with a round roller furling extrusion with a roller and track etc. It kept getting more clever but more complicated. I decided that I had to get back into the spirit of the home builder with limited resources and keep it simple.

 

I like the idea of parts doing double duty like the outside coaming/ grabrail.

 

Joel, it is not clear but the coaming has a front and the canvas cover will be snapped around the front and tensioned back when the rear flap is attached to the wash boards.

 

Dave, I have had my share of dripping seams and if I can eliminate them completely I will be happier. 

 

This design may change many times by the time I am happy with it but I will start from here.

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I have been thinking about the big step down into the cabin.  I have been using a plastic two step stool from Costco during construction.  The battery box Graham mentioned would be a good idea, but it would take up some of the precious foot room for taller people (shorter folks can sit farther toward the bow).  Ann went online and searched for "folding step stools," finding some good ideas.  I'll post pictures of stools in the companionway and updated pictures tomorrow.  Just about ready to flip her and do the bottom.

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Looks real good Doug! Hard to tell from the pics whether the slot goes all the way forward to (nearly) the forward end of the cabin-top, or if it stops a couple feet short. Is the length of the slot, relative to the length of the cabin sole, what you were referring to when discussing battery box concerns? Or the height from the bridge deck to the sole (appears to be about 2'). Or foot room when sitting on the berth in the cabin. (Or all the above?). Good luck with the turn-over!

Joel

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Joel, the slot goes the whole length of the cabin sole, but the top continues a couple of feet to the forward bulkhead (look at the top picture - the combing is the front of the slot. The step was already on my mind , then there was the discussion of where to put a battery. ( above).

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Doug, is there any structural or other reason why the slot could not be carried forward all the way to the forward bulkhead (which is how my SA20 is set up)? Seems like that would permit easier access to the tabernacle bolt and the anchor/bow lines. Sorry to pester you with questions, but I (and I'm sure others) am building this in my mind along with you, your photos have been great and pretty well lay the process out. But its always hard to visualize from photos, without actual dimensions or people in place, what the ergonomics (can't think of a better term) are that affect sitting, standing, reaching, crawling etc on a small boat. Anyway, looks great so far!

Joel

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Joel,

 

I stopped the trench on the 17 mk3 18" from the mast because I wanted some real estate for the lines from the mast back to the cockpit and room for the canvas depending which method of hatch is used. For the mast raising, I have tested kneeling on the berth holding the mast with my right hand and spinning the wing nut onto the lower bolt with my left hand.

 

We have turned the lower mast bolt around. It is to fixed to the mast with the head forward and the thread aft. When the mast is raised, the bolt goes through the forward bulkhead and the wing nut goes on the aft side. Mc Master Carr sells  a stainless steel threaded nut like lathe handles with a small knob on the end. It gives good leverage and cannot unwind because of gravity. Paul has one on Dawn Patrol. I usually make them but I would rather give them $15.00 and have a better one. I think that an O ring on the bolt will stop any water from seeping into the cabin. I think that driving into rain could leak into the cabin so we will have to figure a way to put a cork in the hole.

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Graham, thanks for the explanation, makes perfect sense to bring the bolt in thru the bulkhead. I looked at the main tabernacle design on my Princess plans, and noticed the nut was on the aft side, so I kinda figured you might do that. My reach, with pelvis pressed against a bulkhead, is nearly 40", so I should be able to reach bow cleats, anchor launcher, etc, from forward end of slot. Chest against bulkhead I can grasp horizontally at nearly 26", so that 18" works in that position as well. I was wondering about line leads with a full-length slot, sounds like you have that covered. Everything seems pretty well dialed in on these boats. Now, about those oar storage coamings, that could get interesting.......

Joel

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