Opinions on cradles

[Aaron_G]

I've read in past posts that when stitching the hull together, having good support in the center is essential in order to get the right amount of rocker.

What do you guys think: is it better to wire the boat in a cradle, or on the ground, transfering to a cradle when the stitches are good and secure? I thought I've read (but now can't find) posts saying that stitching on the ground works fine. If the dimensions of all of my pieces are close to the plans (for example, no error greater than 1/16"), does it matter where the wiring is done--i.e. will the bulkheads/sides/bottom all pull themselves into the proper position?

I'm getting pretty psyched: my CS 17 #125 is nearing the point of stitching together.

[JeffM]

Ray,

I also hope to be stitching my CS20 in a week. My cradle has angles taken from the plan (supporting at the two bulkheads and the temp frame). Would it do to simply put blocks at the ends of each support so that only the chines are supported, and the rest of the bottom and keel hang?

Jeff

[mustangermatt]

Building a cradle is way less work than trying to get things right without one. There have been some of the core sounds built with a pronounced sag even in cradles if the center isn't supported. We wired the two halves together at the keel on the floor, lifted them onto the cradle and unfolded. We then did the rest of the wiring on the cradle.

Another advantage I didn't foresee was that the solid midship bunk kept the bottom sheet all lined up after I cut the centerboard slot so I could glue in the trunk without worrying if the bottom had deformed. It is also nice to be able to level the cradle and boat, so I can use a bubble level to set up mast rake, seat framing etc.

Finally, the castors on my cradle have made it possible to compfortably build the cs 17 in a workspace 17 x 10.

[Aaron_G]

thanks for the feedback. I just got back from Home Depot with some casters and 2x4s for the cradle.

Looking at the position of the waterline in the plans, it looks like if I build one support at the aft bulkhead, one support at the front bulkhead, and a support exactly between them, that the middle support will need to be 2" lower than the fore and aft supports. Does this number sound reasonable for a CS 17?

[Scott Dufour]

Aaron,

I just finished 3D-ing a CS17 last week and I built a cradle on casters like you are going to. I simply took the angles from the forward and aft bulkheads, and the temporary center support to build the three supports. I took a WAG (Wild- Azz Guess) as to the heights from the plans and came up with something like you did.

The bow ended up a little too high (or the stern too low), so after it was stitched, but before hitting it with any epoxy or even seriously de-twisting, I just re-adjusted everything so the bow was 10 inches higher than the transom at the side. Then I tweaked the center support to simply "support".

Incidentally, I found the three supports to be a great help in making sure the angles of the bottom were correct. The aft bottom was way too flat according to the support. When I put in the aft bulkhead, the combination of it and the support made forcing it's shape much easier.

By the way, for those of you who know, is "Rocker" the curve of the bottom from fore to aft, or side to side? It's the side to side stuff the supports helped with. The fore to aft was determined by what the wood wanted to do anyway.

[Ken_Potts]

I have a nasty dip or two in my boat too, Ray. I set up supports cut the same as the bulkheads and the temp frame but I just guessed at the amount of weight to let the center support carry. I think the suggestion of using the supports to carry the load at the chines is a good one.

I'm going to be okay with the ugly dips because they are on the bottom of the boat where I won't be looking at them

Scott,

Rocker is the fore and aft (the curve of the bottom when the boat is viewed from the side).

[Aaron_G]

Finished the cradle.

I just rechecked my 2" inch number that I mentioned above and discovered that 1 1/2" would have been better. Looks like I'll be shimming the center.

Per Ray's suggesting, the supports go out to the chines, which means that the cradle is 60" wide. I was a little worried about torsional and longitudinal stiffness, but I put most of my weight on it and it seems to hold fine.

All thats missing now is a boat to go on it.

[Joe Nelson CS#35]

Hey neighbor,

I think that stitch and glue boatbuilding is great, but in the quest to make it seem simple enough for first time builders the designers tend to over-simplify the process. Using 3 stations fore/mid/aft assures you that your boat will be true.

One other way to make sure you have the proper amount of rocker to the hull is to make sure that your stringers that are pre-glued to the inside of the hull prior to stitching are straight (after stitiching). If they have a sag, your hull has that corresponding sag...jack up the middle until the stringers are flat between the fore and aft bulkheads.

If you need any help or would like to do a cultural exchange tour, let me know. My number is 503-...on second thought, contact me with a private message and I will give you my number.

Joe

[Scott Dufour]

All this talk made me go back and modify my center support. Now it is really two seperate supports. One that matches the angle of the bottom, and a seperate that only supports the bottom at the chines. I've snugged them up , but the chine supports are carrying most of the weight. I'll monitor closely for any dip, and raise the chine-only support with wedges if needed.

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[mustangermatt]

My hull had a slight dip just aft of the forward bulkhead while stitching. I found that it was caused by the bevel on the mating bottom pieces was not quite true. Once this was corrected there was no tendancy to dip with my suports that only go about two thirds of the way out.

I think the difference may be the doug fir ply. It is not as stiff as the okoume across the grain (so decks and seats have required a little extra framing) but boy is it rigid along the grain!