Mark's C21

[mmachonis]

Jacques,

I am constructing my jig. I have all the stations setup except for the transom and station A. FYI - keep in mind I am building the full transom C21 kit. At what position across Station F2 do I place the Supports that determine the transom angle? I assume they should be flush with the bottom of the transom, but where along that plane? In addition, the angle on the supports appears different from the angle on the stringers. I don't understand why this would be, what am I missing?

Also, any suggestions for keeping the stations from moving as I align them plumb with the notches in the stringers. I feel like the whole structure moves as I try to adjust the bottom of the station frame to align to the stringer notch. So as I move the bottom, the top moves and I feel like I'm not getting anywhere.

On the same subject of plumbing the stations, I am measuring the distance between stations at the keel, the chine and the sheer to make sure they are the same at each, correct?

Thanks.

Mark

[jacquesmm]

Jacques,

I am constructing my jig. I have all the stations setup except for the transom and station A. FYI - keep in mind I am building the full transom C21 kit. At what position across Station F2 do I place the Supports that determine the transom angle? I assume they should be flush with the bottom of the transom, but where along that plane? In addition, the angle on the supports appears different from the angle on the stringers. I don't understand why this would be, what am I missing?

The angle is the same.
For the location up and down: yes, flush with the bottom, with frame F2.
Lateral (distance from center), see the very first drawing in the kit building notes: flush with the stringers, on the inside face of the stringers. Clamp it or use screws.

Also, any suggestions for keeping the stations from moving as I align them plumb with the notches in the stringers. I feel like the whole structure moves as I try to adjust the bottom of the station frame to align to the stringer notch. So as I move the bottom, the top moves and I feel like I'm not getting anywhere.

Page 3 of the building notes shows drawings of 2x4's. Look at the gallery and do a search with the word "jig", you will see many pictures of the jig set up, same as my drawing. Do not worry about stability until all the parts are in place.
The stringer notches set the distance between molds, page one of the notes:
"Mark the strongbacks for the molds spacing. No need for extreme precision, the stringers will locate
the molds."
Once the bow mold and transom braces are in place, you will have some triangulation, it should not move anymore.

On the same subject of plumbing the stations, I am measuring the distance between stations at the keel, the chine and the sheer to make sure they are the same at each, correct?

Thanks.

Mark

Start with a level or if your strong backs are perfectly flat, a large square. The square can be a piece of plywood, a corner of a leftover sheet. Screw those corners to the strongbacks and mold uprights if you want.
Distances should be the same all along the molds but do not worry about 1/8". Give priority to the stringers nothces, not your measurements.
I give distances to help start the set up of the molds but you can build the whole jig without measuring anything: the stringer notches set the distances between molds.

[mmachonis]

Jacques,

I have completed my jig except for positioning the Transom. I have the transom set on the supports at the proper angle. My question now is where does the transom and the bottom of the hull intersect. The Transom is at an angle so it is not flush with the stringers or the supports at the very top of the transom as it sits on the jig upside down. Should the stingers intersect the Transom at the lower/near side edge of the transom or should the transom height be level with the stringers at the higher/far side edge of the transom?

Here are some pictures of the Jig so far:

http://gallery.bateau2.com/displayimage.php?pid=57415
http://gallery.bateau2.com/displayimage.php?pid=57413
http://gallery.bateau2.com/displayimage.php?pid=57416
http://gallery.bateau2.com/displayimage.php?pid=57417

As a final check before I start planking and stitching, I measured the distance between each station on each side of the boat at the chine and the sheer and tried to keep any difference within 1/2 inch ( you mentioned on the phone that the expert builders can keep the difference within 3/8 inch at best). Most were within 3/8. I think I had one station that was off by 1/2. In keeping this tolerance, the plumbness of the stations is slightly off. Is it common for this to occur? I know you mentioned measuring the diagonals between each station, but with the stingers in place, I can't run a straight tape from chine to chine. In addition, my strongbacks are in the way of measuring the diagonal from sheer to sheer. Can simply pick two opposite points on each station and measure those diagonals and achieve the same result as measuring the diagonals from sheer to sheer and from chine to chine? I also ran a string down the keel of the boat to see that all the centers of all the station frames lined up. I may have had one or two that were off by an 1/8 or less. Any other recommendations for verifying the positioning of the frames on the jig?

Thanks.

Mark

[jacquesmm]

The transom, stringer and transom brace bottom must be flush.




Viewed from above, the transom brace butts against the stringer inside face.
That drawing shows your kit.

I'll reply to the distance question later but there is no need to measure, the spacing between molds is set by the notches.

Do not compare with the plans: the kit has extra molds and you have an extra bulkhead for the closed transom.

The pictures look good but I can't see the height of the transom.
It has all to be flush. Think of how the bottom panel will lay on it. The brace and the transom must touch the bottom panel.

[mmachonis]

Jacques,

I wish my picture of the side view of the transom was a better picture. I took the picture before I had the question.

So if I understand you correctly, the highest point of the transom (meaning the lowest point of the transom, because the jig has the boat upside down) should be level with the highest point of the F2 Frame? This does not make them flush with the stringers on top, because the stringers sit in the groove cutouts and sit below the level of the highest point of the frame, in some cases. Is that correct?

Mark

[jacquesmm]

Everything has to be in the same plane: the bottom surface.
Frames and stringers have to be set so that when you add the bottom, their edges just touch the bottom panel.
Same for the transom.
If necessary move things around a little bit. Check that your baseline is where it should be: there are marks drilled on the molds.

The notches have a tolerance of a little more than 1/8" to make assembly easier but I would not worry about 1/8".
That alignment would also result in a straight line along the keel.
Straight does not mean horizontal.

[topwater]

This pic mite help.

Thats a 8' aluminum straight edge across the last bulkhead and transom . The outside
higher edge of transom is flush with everything.

Hope this helped.

[jacquesmm]

Thank you. That pictures shows how it should line up.

[mmachonis]

Thank you. That is exactly what I wanted to see.

[jacquesmm]

That is what I tried to explain but a good picture is far better than a long discussion.
Thanks again Topwater.