The Core Project

[K.C. Walker]

GreenLake,

Okay, I've got to draw the line somewhere on stiffness. After all, I would like somewhere to sit while sailing!

Thanks for pointing out the primary vs. secondary bond thing. The reason I was thinking of doing it in two steps was to plug my guide holes with the first layer of glass. It really does make more sense to plug the holes first and then do the glass and foam all in one go.

The "give" of the corecell was a concern before I had the material in hand. After standing on it and observing no "give", with my thumbnail, I pushed as hard as I could and did make a thumbnail mark, but not very deep.

On your comment about centerboard trunk/boat stiffness, unless I dreamed it, I think I saw somewhere on this forum where someone had built a pair of "bulkheads" underneath the thwarts and said that it stiffened up the boat considerably. As I recall they also put a mid-boom traveler in for the same reason.

KC

[Phill]

Greenlake,....CB trunk bulging.

The side walls of the trunk are very thin. When sailing I can feel the sides of the trunk move with the water pressure aft of the CB head area.
The pivot areas are built up, but they have no support to prevent the top of the CB from leveraging the sides of the box and a allowing the CB to cant ( the CB head does not go all the way to the top of the trunk ). If you think about 2 people standing on the end of the CB, necessary to recover from capsize, you can see there needs to be some spreading of the load where the top of the CB, in the trunk, is pressing against the sides of the trunk about 4-5" below the top of the trunk. When sailing, i believe the CB side loads are even greater. The twisting load is prevented at the hull/trunk opening if the CB head is properly fitted. Being a minimulist, I think only the one 'tube' stiffener is needed to prevent the canting. I have seen others with 3 or 4 spaced along the entire trunk. Having them futher back than the width of the CB top seems to be unnecessary.

Extra helpful info: On the O'Day built DS's, the CB trunk is not square. Nor is the hull opening. I was told this was done to get the trunk off of the mold easier. So when fitting a CB, take into account that the trunk is tapered top to bottom, wider as it gets lower. And the hull opening is tapered at both ends, thinner at the ends and wider in the middle. This makes getting a really good CB head to trunk fit a bit of bother. I choose to belt sand, custom fit the head for best fit when the board is all the way down. That is when the best preformance is needed for upwind, IMHO. Shimming the opening would work....for awhile. But I felt that the shims would eventually fail, fall out, get damaged....so I did the fitting the harder way, but have never had to fix it since 1991. There is also a class rule about how narrow you may shim the sides, and the ends can not be custom fit to the CB leading edge, or any other shape that alters the factory stock opening.

Hope this helps.

KC, your foam must be much stronger than the Divinycel I used. If I kneeled on mine before glassing, it would leave a good dent. Also sanding, with homemade 2x4 block for belt sander belt, did a nice job getting the foam to fit all the rounded edges and other joints.

[GreenLake]

Thanks Phill, I'll keep my eyes open for signs of bulging when I go out next.

[Phill]

I feel the movement when my feet are against the trunk. Never have seen a visable bulge.

[GreenLake]

Ah, good.

Re: the number of stiffeners - I tend to agree with you. If needed, one set should be enough.

[K.C. Walker]

Okay, maybe I'll draw the line after I stiffen up the centerboard trunk.

[Phill]

KC, if you really want the stiffest DS...

Dont forget: (tongue firmly planted in cheek.... ummm mostly)

Rod rigging instead of wire
mast inserts (jammed in 2x4s) and diamond spreaders/shrouds
boom inserts to spread vang loads
rudder head, saw a homemade one fold (not mine)
tiller, bent mine once when foot slipped
spinaker pole, maybe 8"dia. carbon fiber from an America's Cup boat
UHMW 3"x 1/8" hiking straps
Hard wing sails like some of the land and ice sailors use.
There must be a way to also stiffen the sheets and control lines.
(maybe thats where we could use the kerfing... yeah! thats the ticket! )

[K.C. Walker]

Phill,

I love the extra helpful info. You already knew I was thinking about making a centerboard, didn't you! My plan for this spring was to make a centerboard and rudder, but then I got sidetracked into fixing my stringers BIG-time. I may have to put off the centerboard and rudder, even though that would be the fun part.

KC

[K.C. Walker]

I posted this one originally in the totally wrong thread. So,I'm posting it again here.

Okay, it's a little OT but you guys brought it up first (Phill & GreenLake). My centerboard trunk was showing some problems anyway. However, I had not noticed the thin walls of the centerboard trunk flexing, that is until I went out there and pushed on them and grabbed the handle and flexed it and watched the centerboard walls flex.

However, I had noticed that my centerboard trunk was a bit canted. I did some measuring and found that the thwarts were different in length by 1 inch. I also noticed that the front of the centerboard trunk did not line up with the keelson and in the same direction. I got poking in there with a chisel and found that the original glassing work between the keelson and centerboard trunk was not adhered very well. So, I decided to go at it. Apparently, they had not sanded the gelcoat before glassing those parts together. Also, I think it must've been Friday and already beer time.

Once I cut the fiberglassed tabbing out the centerboard trunk lined up with ease. I cut the long thwart and taped the piece to the short one as a shim. Everything lined up so I started to glass it all back together. I figured while I was there I would go ahead and reinforce the centerboard trunk walls around the pivot point. I had some extra corecell so I decided to use that. I put a little carbon fiber cloth down and then glued the corecell to that. I'll do carbon fiber cloth on the outside and then cover that with glass.

Because I have not worked with this material before I thought it might be a good small project for a shakedown. Here are some pictures from today http://www.walkerguitars.com/photos/daysailer/CB/

KC

[K.C. Walker]

Okay, now I'm responding to GreenLake who responded to this post in the other thread.

His post:
K.C.,
some thoughts/comments: First, as always, thanks for sharing this. Next, I note that your trunk has this cute 'cap'. Something mine doesn't have - it's all laminated in one piece.

I think your corecell is going to be effective in distributing the load over a wider area - but I doubt that you will get any benefits of having used carbon fiber other than perhaps a bit of weight. The reason is that the carbon sits on what will be the inside of the skin for your sandwhich. Because of geometry, it would seem that most of the tensile load will simply go to the existing laminate. I also wonder whether that layer was even necessary at all (except if you had evidence that the laminate of the CB trunk walls had already failed).

What could make a bigger difference might be whether and how well you round the corners and fair the edges of your reinforcement. Right now, it looks like you are going for all right angles and abrupt transitions in strength. I'm afraid that sets you up for stress cracking if you're not lucky.

For the outside laminate, I think you are into overkill territory, but I know I won't be able to talk you out of your carbon fiber

I bet that a single layer of glass, even ordinary fabric, not biaxial, would probably be sufficient for the expected tensile loads, and as your corecell sounds like it supports out-of-plane loads really well, there's less need for providing impact protection via a thick skin.
_________________
~ greeen ~ lake ~ ~

Yes, the cap on the centerboard trunk is "cute". I have not seen that in pictures of other boats so wonder if it's unique to Can-Am boats. It seems to be a high density quarter-inch layup a lot like the forward bulkhead thickness. It may have been a way to try to use a lighter centerboard box because the walls on mine are easily flexed by finger pressure.

I tapered the edges of my reinforcement after gluing it on. I was having a bit of trouble cutting the core foam at an angle without losing some of the little contours squares. I thought I'd try gluing it down 1st and then taking a utility knife and slicing off the edges. I worked okay but not great. Apparently a fairly common way to deal with the square edges of the foam is to use lightweight filler as a fillet.

I'm sure you're right that carbon fibers is over the top here! I wanted to try it out on a small project to see how it handled before I tried using it elsewhere. It's a pain in the butt, by the way. The edges fray easily. It does, however, wet out quite easily and worked fine for a bedding for the foam. The other 2 cloths that I was using to join the keelson to the centerboard trunk was 18 ounce biaxial and 12 ounce biaxial with a mat. The 18oz is easy to wet out and conforms very easily and does not take much resin. The 12oz with Matt takes a fair amount more resin and it's harder to wet out but stays put with the resin where as the other biaxial squirms around a little bit.

I am going to add a little more foam to the top of that reinforcement to tie it into the cap also.

KC

[K.C. Walker]

Phill,

Did you consider putting some kind of bulkheads underneath the thwarts to tie the centerboard trunk and the seats together? I'm guessing that after you put the core in that it was strong enough. But I was just wondering if you have thoughts on that.

KC

[GreenLake]

K.C.,

I know your question was addressed to Phill, but I wonder what you are planning. To me it sounds ilke you are trying to turn your poor DS into something that's reinforced like an ice-breaker - only the armored bow is missing.

As designed, the thwarts appear more than sufficient to prevent the CB trunk from twisting sideways relative to the rest of the boat. They translate that twisting moment to the hull in its entirety.

The question to answer is whether this twisting moment is ever sufficient to deform the hull to a degree that matters. A way to picture this might be to visualize your boat resting on its side on one gunwhale. Now someone steps on the CB, while others hold the mast down. (At least I think that's the worst case scenario).

Would you expect your hull to deform significantly in that scenario?
How about after adding your corecell?

My conclusion would be that whatever you'd observe would be below the level of significance for DS sailing performance. Here's why: as I understand it, of all the DS models, the DS1 has the most open cuddy entrance, in other words, it should have the least amount of transverse strengthening of the kind your below thwart bulkheads would provide.

If that mattered for sailing performance, you wouldn't see any DS1 boats among the winners. Therefore, my conclusion is that even if it has an effect, that effect is swamped by other contributions.

I know that playing with epoxy is fun
But don't you want to be on the water?

PS: I bet that the corecell addition itself helps not a little to reduce the amount of twist the hull will take on for a given twisting moment. According to my thinking, that's because the seats should very effectively prevent any change in curvature of the hull sides, so only the floor and the top of the sheers are free to twist in the rear part of the hull. And the floor is what you are making stiffer. Adding the strip of foam in front of the seats as Phill did, should have the effect of extending the twist-resisting bulkhead effect of the seat fronts a bit forward, by making that part of the hull stiffer as well.

PPS: There's another place that you could reinforce , and that would be to make a set of little ribs that go from underneath the deck to the side of the hull around the place where the rear end of the cuddy shelves are. They could be as deep as the shelves without seriously getting in the way. Those could be very effective at further preventing twist. Just a thought.

[K.C. Walker]

GreenLake,

Okay, I've been trying to come up with a name for my boat. Maybe it could be B.S. Galactica! So, here is my rationale for my pondering and inquiry.

While I was reinforcing the centerboard trunk and reattaching it to the keelson I was noticing that the hull flexes considerably more at the aft end of the trunk than it does at the forward end. In effect, it is a very substantial stringer that ends squarely in the middle of a very large unsupported panel. Though the thwarts take care of twisting and compression they do nothing for up-and-down motion of the centerboard trunk.

So the idea that was rattling around in my head was that a bulkhead of sorts underneath the thwarts attached to the centerboard trunk and the seats would tighten everything up lengthwise in the hull. It would not be the same as having a full keel but it would have somewhat the same effect.

It seems like being able to support the centerboard trunk and keelson with the seats as a bulkhead would help limit the movement of the rig tension pushing the mast down on the keelson.

You're right, I'd rather be sailing!

KC

PS yes, putting knees at the shelf end near the chain plate should add resistance to twisting. I'll put it on my list! No, wait a minute, I was going to draw the line somewhere here.

[Phill]

KC. I love boat name discussions. Spent long hours at campfires, sipping wine/beer, and 'helping' others name thier boat. Great fun as the beverages take full effect.

Boat name = "Foamy" ????

Thwart bulkhead violated my ''as stock as possible' sensabilities. (its a zen thingy)..
Besides, as GreenLake concluded, no appreciable preformance additions would be anticipated. (my best effort at 'tech talk')
In English, I didnt think it would help.....and i'm basically very lazy.
And, as Lollipop is now, I can feel no twisting while sailing. I could before the coring was done. I can not even get the hull to twist by lifting a corner of the transom. Before coring, I could lift the corner of the transom about 2" before any movment of the hull at the cuddy. Think plastic washtub. KC, I think you may have seen this when you were looking at the CB trunk and trying to avoid locking in a twisted shape.

Greenlake, Keep those very well reasoned and thoughful threads coming. I like the way you can describe what I kinda hoped where good ideas. Thanks.

phill

[K.C. Walker]

Well, the first installation of foam was successful but not quite as planned. I had planned on using my vacuum pump to vacuum bag the foam in place. It's not really desirable to pull a heavy vacuum while gluing the down foam because you don't want to squeeze too much epoxy out. So I was planning 5”or 6” Hg.

My vacuum pump only has 3.5 CFM which should be adequate if one can stop most of the leaks. Unfortunately, that was not the case this time. Shop vac to the rescue! Aside from the shop vac screaming away for hours it worked perfectly. The foam is down nice and tight. http://www.walkerguitars.com/photos/day ... 142641.htm

The other hitch was that I was using slow set epoxy to give myself plenty of time but I didn't get started gluing until late in the day. I ended up having to use a radiant heater on the outside of the hull to get the epoxy to set up because it was getting cold out. I first tried tenting the boat and putting a little space heater inside. Doh! Right, I had just insulated that part of the hull and the glue joint was on the outside. I could feel that the hull was warmer where the foam was not.

The further adventures of "Foamy the Little Red Boat".

KC