Forward removable bulkhead

[GreenLake]

In all projects to reduce weight, you might profit from figuring percentages. Say you can save 5 lbs. That's less than 1% of the weight of the hull, not even counting rigging and crew weight. Anywhere near the center of gravity for the boat I'd contend that kind of weight savings is in the noise.

If this weight was at the transom, or at the top of the mast, then, yes, it would make a much bigger difference.

[JACK FLASH]

I hear what you are saying about weight. Truth be told I could diet and lose five pounds and be better off for it regardless of my sailing. The other two reasons I was planning on using carbon were stiffness, and I wanted to play with vacuum bagging carbon (a project I have yet to undertake in my amatuer boat repair endeavors). The weight thing is pretty minor as I don't even know how often the boat will be raced. Most of my racing time is on my F18 catamaran.

[GreenLake]

I do know the feeling of simply wanting to try some technology for its own sake. That's a goal in itself and answers to different cost/benefit rules.

I'm currently splicing amsteel into a halyard "just because".

But what kind of stiffeners in what configuration do you want to put there? A central post? A central post connecting to a rib underneath the deck? A simple rib all along the opening?

I'm sure we're all curious.

[JACK FLASH]

I want to add a horizontal stringer (for lack of a better name), that will cross the opening of the cuddy and attach to the sides of the cuddy just in front of the DaySailor badges and aft of the mast. The plank will serve two purposes. First it will help to stiffen the boat and reduce twist and the tendancy for the sides to want to squish in under load. Secondly it will be a foundation for the cleats to all of the lines from the mast ie halyards, topping lifts, and probably the vang as well. In addition I am planning on the jib sheets routing back into there as well so their cleats will be on the plank. And finally since I have the deck off during this project I am strongly considering running the spin sheets under the deck. If I do, there is a good change they will be in the area as well.
As I did on my DSII all of the lines on the mast will be internal. I very much enjoy the look of a clean boat and the lack of spagetti all over the place. I know from previous experience with my DSII that the cudy was never used for anything except for the laundry basket with the spin. The little cooler went in the back under the tiller. I had a really nice Harken midboom traveler on the DSII that I am deleting on the boat to make it a little more family oriented. The mid boom traveller really effects the cockpit in terms of kid and even adult freindlyness. I am not however a big fan of the rop triangle style travelers seen on most DS's so I am considering a Harken track at the transom, but I am still figuring out how I will do that with out interfereing with the tiller.

[GreenLake]

I wonder if this would simply have been called a deck beam in wooden boat construction. I probably knew the right name at one time, but can't come up with it. Stringer seems more appropriate for fore-and-aft members.

Anyway, if you are thinking of making this solid, or at least from some incompressible material, so you can back blocks and cleats in it, then, the gains from carbon would seem to become even more remote. (I had based my previous discussion on the idea of hollow stiffeners).

If you just support the cuddy opening it might make sense to continue these down to where they meed the hull, if possible. to be really effective against widening at the level of the rubrail. If you make them slightly diagonal at the transition between horizontal and vertical (and perhaps increase effective thickness there as well) you could possibly give the whole construction some stiffness against shear as well (think how the "drawer" stabilizes the "shell" of a matchbox)

The existing bulkhead is highly effective for that purpose, except it may be too far forward.

However, I'm thinking, you will also need some sort of support forward of the mast, or your deck will give when it's being stepped on.

For your rigging, why don't you make a new thread under rigging - I'm sure it's interesting to both DS1 and DSII sailors.

[JACK FLASH]

The stiffining purpose of the crossmember is to help keep the sides of the hull from "squeezing in" under the load of the shrouds. This "plank is just in front of the shroud anchors. It is not intended to stiffen the deck in the sense of stepping on the deck support. I was planning on leaving the forward bulkhead in place anyhow.
As for construction I was going to use carbon on a foam core. The load from the cleats will be in shear so I am not worried about the core offering crush resistance.

[GreenLake]

I'm curious how it'll turn out.

Crushing the core: what I had in mind was accidental crushing from tightening the through bolts for your cleats too hard. Agree, the loads may not be an issue, because of the way the cleats are loaded,

If I ever wanted to replace that bulkhead with a simple post, I might use a section of 3" bamboo. That material has some nice properties in terms of price, weight and strength. (It does need to be epoxy sealed, or it will crack).

[JACK FLASH]

To be clear, this is not a replacement for the forward bulkhead. It is more like a shelf aft of the mast just in front of the cuddy opening spanning from side to side.
Bamboo is pretty strong stuff but I don't believe it to be very stiff, but I have little knowledge, if any on the that subject.

[GreenLake]

Jack, for your shelf you get the stiffness from having the two layers of laminate separated by a spacer (some form of core material, or the side walls if you do a hollow stringer). With the typical U-channel stiffener, one layer would be the deck, the other the bottom of the U.

Looking at the geometry, if you squeeze the boat at the deck level, the deck would normally flex upward. Any beam you add below deck would then be loaded on compression. (The reverse is true if you stand on deck, but that's not what you are aiming for).

The advantage of carbon is its tensile strength. That wouldn't come into play here because it would be the original deck that's under tension when you squeeze the boat.

Other than weight, I'd expect that you wouldn't see much difference whether you use carbon or glass, when the loads are like that. You could even use bamboo, it's pretty strong under compression - after all they do use it in Asia to build scaffolding around buildings. Split lengthwise, epoxy sealed and held in place with glass tabs along the edges, I would think it should be just about as strong and bit lighter than a beam laminated from glass.

However, you are right, my suggestion had not been for that purpose, but for a deck support post (not beam) if one were to replace the bulkhead.

I've actually experimented with bamboo a bit for a spinnaker pole. I did add one layer of glass tape and the pole is lighter and to all appearances as strong as a similar sized aluminum one which I own, which was reinforced by inserting one aluminum tube inside another. (Both poles have an effective 1" ID to accept the usual fittings). Now that bamboo pole would not be class legal, but not my concern, as our races here are, well, more free-form.

I did get a good bit of good-natured ribbing when I first showed up with it, but I like it, and it works (and it's a steal compared to aluminum).

Here are some pictures (no, that's not my pole )

[jdoorly]

Just wanted to remind ya'll that carbon fiber cloth is not necessarily lighter than fiberglass (e-glass or s-glass). If your pulling a vacuum or autoclaving molds you can get pretty light but if your just doing a hand lay-up expect for the CF to weigh more than fiberglass. Same goes for kevlar and dynel. These exotics suck up a lot of resin, which can't be squee-geed out! For home projects I suggest s-glass- you can get the same level of strength as e-glass and yet save 2 ounces per square.

GL your bamboo pic reminded me of Italy where they build on steep slopes and use similar looking scaffolding UNDER buildings to prevent earthquake damage...

[JACK FLASH]

I agree completely that fiberglass would be more than suffecient strength for the job. The reinforcement is more the second reason for the install. The shelf for all of the cleats to mount on top of is the primary goal. The idea is not actually mine. The previous owner had come up with it using a 2x6. I had considered replacing it using something lighter. My first thought was aluminum, and then I turned toward a composite layup. Compared to the 2X6 either glass or carbon will be considerably less weight. Which way I go between the two materials is more about wanting to play with carbon on a peice that would not result in a catastrophic situation in the event of a failure.
To jdoorly, I do not have an autoclave but was planning on vacuum bagging my peice. I could use a shop heater if I wanted to autoclave it while under the vacuum. I had always thought special equipment would be needed to autoclave until I watched the video of the VOR Puma construction. They vacuum bagged the hull by attaching the bagging material to the walls, essintially vacuum bagging the whole loft, and then used one of those torpedo style shop heaters for the heat. I guess when your peice is 70 feet long you have to improvise or spend some big time money.