Core Sound 20 Hull #102

[JeffM]

Ray, you commented above on the optional bulkhead hatch, which is what I have.  I wonder about people's experience in use.  I find it difficult to use a lot of the volume via the bulkhead, and wonder if its easier from above via the original hatch.  After many experiments, I put cooking gear and dishes, etc in one big plastic tray and snack food in another.  These can be slid around inside the lazarette to make room for one or two other bulky things.  Even so, I'm sure I've never used even 1/3 the available volume--especially the upper half.  Oops--another thread, maybe!

[wkisting]

Jeff, I was wondering about the usability of a bulkhead mounted hatch. What is the biggest downside in your opinion?

Anna and I considered putting a bulkhead hatch on our aft compartment, but we liked the looks of the aft hatch (kind of balances the look of the boat a bit if there's a hatch up front also), and in our previous experience, we've found side-mounted hatches more difficult to use than top-mounted... especially if the compartment is large, as with the CS20's aft compartment. One option is to cut a very large hatch, but then there can be difficulties getting a good seal. How large did you make your bulkhead hatch? Does it seal well?

Just curious...

[JeffM]

Since I don't have a deck hatch (except on foredeck), I can't compare that well.  But it seems to me that it would be easier to see and maybe reach the contents from above.  In addition, pretty much all the volume above the hatch edge is inaccessable unless you want to get down on your hands and knees and pile stuff up.  On the other hand, I have access underway.  And I don't ever have to lift anything--just slide it out.  I also perch on that aft deck sometimes so like to keep it clean.  A tiller lock also crosses deck (doubling as a nifty hold-down for my open chartbook.)  On Saturday in Buzzard's Bay the noon wind was so light I wished I had a book to read.  Instead I opened up the lazarette and made myself a hot lunch and coffee.  Would have been harder with tiller blocking access.  My hatch is a So-Pac series 3000 rectangular large.  (I have vented about these in several posts already--they only leak when exposed to water!  With the hatch vertical, I've only had this one leak when the water in the bilge was over the hatch edge).  Since it hinges at the bottom, I put the hatch edge only a few inches off the floor so the open hatch could rest supported by my aft floorboard.  The boxes I slide in and out of there are pretty heavy and I didn't want to break the hatch.

[wkisting]

Been working my butt off on the deck hatches for the past three days. Got the rims glued to the boat, then decided they were too high, so I cut them down to 1-1/4" tall. But the 3/8" Meranti ply I used chipped out badly from the saw, so I had to sand, then fill coat with thickened and color-matched epoxy and all is well again.

Then I got to work on the hatches, which were a BIG project, but they came out very nicely. I had to cut them down too. Then I rabbeted the mahogany frame for the ply top so that (contrary to the design shown in the plans) the edges of the plywood top would not be exposed. I think this looks neater, but it is a lot of work to get a nice, tight fit with no gaps. I spent hours taking very deliberate, careful swipes with the block plane. Then, to get fancy, I decided to have radiused corners instead of square, so I spent about 15 minutes slowly whittling down each corner to a good fit with a block of sandpaper. The patience paid off... these look very nice, and much better than my woodworking skill (or lack thereof) should allow. 

At the same time, I decided to try steam-bending the plywood for the cockpit coaming. I don't have a bandsaw, and I didn't want the extra seams to either side of each corner piece (I'm finishing it bright). So, I got to work experimenting with the old tea kettle and hot towel approach. It took awhile to refresh my memory how this works, but after breaking four pieces, I finally got the hang of it. I double-bent each piece so that one continuous section of plywood could wrap through two corners, which means I'll only have four seams total in the finished coaming. Not sure I would recommend this method to others unless you have a lot of patience and an extra sheet of plywood. It takes a lot of strength, yet a lot of gentleness to form these pieces.

Pics below...

[wkisting]

Yep, I think that's why I had four failed attempts before managing to get these coamings into shape. I didn't pre-soak. But also, it took me awhile to remember (from the last time I tried this) that you have to pour on the boiling water incrementally and let the heat gradually raise the temperature of the entire piece. If you just pour on the boiling water and attempt to bend, it will break. If you keep pouring on some more every 20-30 seconds and giving the wood a few minutes to really heat up, it is much easier, and much less likely to break. But if these hadn't worked, soaking overnight would've been the next plan.

I've also heard that wood bends really easy if soaked in a mild ammonia solution, but I tried to avoid that since the ammonia also significantly reduces the strength of the wood ever after (so I'm told). One guy on an internet forum told me he's seen 1/8" thick wood wrapped around a pencil multiple times using the (heatless) ammonia soaking method--though I find that hard to believe.

[lbrewer]

The hatches look fantastic!

[Peter HK]

Wes said

At the same time, I decided to try steam-bending the plywood for the cockpit coaming. I don't have a bandsaw, and I didn't want the extra seams to either side of each corner piece (I'm finishing it bright). So, I got to work experimenting with the old tea kettle and hot towel approach. It took awhile to refresh my memory how this works, but after breaking four pieces, I finally got the hang of it.

There is an alternative for those not so fussy with grain orientation/joins- I suppose that especially applies if you want to paint it rather than bright finish. If you orientate the ply so that you are only bending 2 plies against the grain rather than 3 it's much easier. I have just been fitting the coaming corners on my CS17 and they bent around easily without any steaming at all. Might vary with the type of ply. I certainly didn't break any. The disadvantage is shorter (4ft) pieces.

Here's a picture of the dry clamped pieces.

[wkisting]

Nice job on your coaming, Peter. I did find that I could bend the pieces without heating them, but when I clamped them dry to the boat like that, one of them suddenly cracked after about an hour due to the strain. I had a concern that if I glued them on, they might crack in the future if I didn't "ease" the strain by steaming first. But perhaps not, since the glue will surely help hold them in shape. I just didn't want to risk it.

I spent all day yesterday gluing on a mahogany "doubler" of the coaming that runs around the outside of the Okoume I already applied. I did this because the gunwales will be mahogany and so are the hatch frames, so it looked better to have the outside perimeter of the coaming in mahogany also. But the mahogany was VERY tricky to bend, even with hot towels, so I ended up making a steam box of some PVC tube and steaming the pieces to a very hot temperature to get them into shape. The problem with the mahogany is that it feels "noodlely" and easy to bend, but very little pressure can suddenly crack the strip. I cracked about 8 pieces (using the hot towel technique) before I decided to do a genuine steam bend, and then I had no more trouble thanks to the steam.

I'll post pics when I get everything cleaned up. Right now, it's a mess of epoxied mahogany that needs to be sanded and planed to match the already-installed Okoume coaming.

[wkisting]

Coaming came out nicely. I LOVE Ray's suggestion to put a second 1/4" doubler around the outside of the coaming and run over both top edges (inside and out) with 1/4" roundover bit on the router. It makes a very nice, sturdy, impressive-looking coaming.

Had a chance to test fit the (unfinished) masts also. The alignment with the boat seems dead on. When viewed from the front or back, there is no angle variation between the masts, which is a relief. They're perfectly parallel. From the side, they both show a 3-degree angle, but don't look quite perpendicular to me. The picture exaggerates it a bit due to the wide-angle lens.

[lbrewer]

Wes,

That boat is turning out really really nice.

[paul_stewart]

Wes,

Congratulations on the birth of your beautiful shiny new CS20!  She needs her play clothes, eh.

--Paul

[wkisting]

Thanks for the compliments, guys. I am very pleased with how it's turning out. The flaws in the exterior hull paint and building smudges/scars still frustrate me, but I can touch all that up next season and it will be good as new. The deck is coming out beautifully, and will deserve to be varnished nicely.

All that remains is to add strategic reinforcement for the blocks, chocks, cleats (well, only one cleat, at the bow), etc. and then to seal all the fastener holes and bed the hardware. I also have to finish and paint the masts. I'm sure I'll be done in time to make Graham's meet in October, but probably if I can find enough free time in the next few weeks, I'll have it done (fingers crossed) by the middle of September.

[wkisting]

Yep, I agree Ray. Trouble is that in my case, I was having difficulty envisioning the exact placement of the hardware, so I had to wait for the deck to be installed to figure it out.

I know I asked this already, but how much reinforcement is necessary (or what parts need to handle particularly high loads)? For example, I'm going to raise the mizzen cam cleats on 3/4" tall riser blocks to help route the mizzen sheet over the 1" coaming as you suggested. Shouldn't that be plenty of added thickness (above deck - due to the riser block), or do I need to add additional reinforcement underneath for those as well?

Also, do you drill and then epoxy seal your hardware/fastener holes? Or is it better to overbore, fill with thickened epoxy, and re-drill to create a bushing around each hole?

[JeffM]

With holes that are not immersed, I've had pretty good luck drilling, putting in screw, removing screw, soaking epoxy into the hole, and then waxing and putting screw back.  'Course, I wanted to get in the water in the worst way...

[tom151]

For example, I'm going to raise the mizzen cam cleats on 3/4" tall riser blocks to help route the mizzen sheet over the 1" coaming as you suggested. Shouldn't that be plenty of added thickness (above deck - due to the riser block), or do I need to add additional reinforcement underneath for those as well?

Also, do you drill and then epoxy seal your hardware/fastener holes? Or is it better to overbore, fill with thickened epoxy, and re-drill to create a bushing around each hole?

Your riser blocks might actually add leverage against you and therefore need a bigger backing block than otherwise.

For me, plywood is too soft (in  crush) to be used for backing blocks.

For bolting down hardware - I only use epoxy-filled holes and bolts (never screws) if penetrating the hull/deck skin.  There are many situations where the loads are close to 100% shear (like cam cleats, clutches, bullseyes) where I add a riser or wedge to get a fair lead and will often screw the hardware to the riser first, then simply epoxy glue/fillet/tape the riser to the deck resulting in no penetration of the deck/hull skin at all.

The more tension loads or bending loads on the fastener the more backing block area is needed, even requiring gussets in high-load situations.

The bigger the loads the more oversize the epoxy bushing needs to be.

It is very important (IMNSHO) to align hardware to minimize bending loads.  You will often see U-bolt type hardware installed with loads not parallel to the plane of the fasteners for instance.

For filling holes (repeating myself from other posts?) there is no substitute for a syringe with a tip long enough to reach the bottom of the holes - so you can fill them from the bottom up and avoid air bubbles (remember to do this stuff when temps are falling.)

My 2 cents...

[wkisting]

Well, I'm going to get at the hardware today, I think. I have to go buy some SS fasteners yet, but should be able to find what I need at the local West Marine store.

I've decided to use 3/8" Meranti as a backing material. I agree with Tom that (Okoume) plywood is too soft in crush, but the Meranti I have on hand is significantly denser and more crush-resistant, and it also seems to have superior stiffness, so I think it will serve nicely. I'll through-bolt most of the hardware, but probably drive in the mizzen blocks with screws into the transom stringer, about 3" long, which should yield plenty of bite. I'm reluctant to through-bolt there because I left the bottom edge of my transom stringer square, so I would need at least a 4" bolt, and it would be difficult to drill perfectly straight through without wandering into the transom ply or out the front face of the stringer--I don't want to risk it since I'm drilling blind.

How do folks attach the eyestraps to the centerboard? The taper in the lifting arm (per the plans) doesn't seem to permit through-bolting the two eyestraps together using the same bolts, so I'm guessing screws inserted from each side, no? And perhaps slightly offset so they don't bottom out on each other?

I can't tell from the plans: Where should the downhaul for the mizzen be placed? It seems to me I saw a picture of a CS20 (maybe Graham's CS17 Green Heron?) that had the downhaul running right down to the thwart, but I can't recall how exactly it was set up.

Also, my plan sheet doesn't show the setup for all three lines to be run from the main back to the cockpit (only two are shown, and not labeled). If anyone has pictures of any of this stuff, that would be great. I've seen very few pics of a CS20 that are sufficiently close-up to clarify the rigging layout/hardware choices.

Thanks!

[Charlie Jones]

I tape the two eyestraps in place, then drill in from both sides to meet in the middle. Works every time. Just drill in about half way as accurately as you can, then come in the other way.

Not difficult.

[wkisting]

Well, I tried your bevel gauge trick for drilling the CB eyestraps, Ray, and it worked great. The bolt heads on one side don't seat perfectly flush because of the mild taper in the lifting arm, but they're close and seems very secure with both eyestraps are through-bolted together.

We've had so much rain lately that I'm not making much progress on the boat. It's in the garage, but I need to finish the masts outside because they're too long to fit in the garage conveniently. I'm reluctant to fit some of the blocks to the boat until I have the masts in place and can actually run the rigging on deck. But all the hardware for the mizzen sheet, main sheet, and CB uphaul/downhaul is in place. Just have to go back and seal all the holes.

[wkisting]

About the hiking blocks that some folks mount on the CS20's rail for more comfortable sitting on the rails... Should they be glued on permanently? Or attached with a removable bedding compound? Mine are solid mahogany, so I'm wondering if it would be wise to attach them with some kind of removable bedding compound in case they ever deform/warp or need replacement. Of course, I was planning to mount the oarlock through the front edge of mine, so maybe they must be glued?

Also, do most folks attach the (removable version) gunwales with screws, or is there a bedding compound that will do the trick for that without screws?

[wkisting]

Arrrgh... no progress to report. It's been doing nothing except raining in GA all week. Must be weather left over from the tropical storm. But it's driving me nuts. I probably could've been varnishing by labor day, but now, I won't even be able to finish the masts and lay out the rest of the deck rigging before then, let alone seal all the holes before varnishing.

Anyway, thought I would vent. Hope others are having nicer boat-building weather.