Lofting angled transom includes two parts: the first is to draw the angled transom in profile and half breadth, the second is to loft the transom on a separate card board.
In order to draw the angled transom in profile, we need a trammel arm. As in the case of this dinghy, the transom is angled 10 degree. So, just use the trammel arm to draw an arc (use the intersect of AP and sheer as the center for the arc). Pick the point on the arc which is 100 mm from the intersect of AP and the arc. Draw a line through the arc center (intersect of AP and Sheer) and this point. Then you get the angled transom in profile.
To draw the angled transom in half breadth, you need to use a sticker to measure the distance between all the lines (sheer, waterlines, buttocks, chine and canoe body) and the AP. Then, you use the sticker to transfer these data to the half breadth. With all these points, you can get the transom in half breadth.
After finish the angled transom in profile and half breadth. We can start to loft the transom on a separate piece of card board. This is the real tricky part. The center line on this card board should be paralleled to the transom in profile, which means that the center line should have an angle of 10 degree. Then draw buttocks and water lines. Then you get the grid. Use the sticker to measure width of lines (sheer, waterlines, chine) in half breadth and transfer the data to the lofting of angled transom.
Notice that transom thickness (TT) is 27mm. So we need to offset the angled transom in profile with distance of 27 mm. Use this new line to develop angled transom in half breadth and the lofting of transom.
Have to say that this angled transom is really a challenge. Drawing the transom in profile is easy, drawing it in the half breadth is ok (just be careful with the sticker and measurements), but lofting it is not easy. I had some errors on lofting the transom, but I can not figure out what was going wrong. Thanks Sebastien and Tian for his help. Sebastien helped me to find out that my horizontal lines are not perpendicular to the center line. And help me to mark the measurements and doubled checked the lofting for me. Tian helped to rubber out wrong lines and checked marks and measurements. (see pictures below)
How is it? Tick sticks make transfering intersect easy. No need to remember numbers, but you really need to know what the ticks mean. Tain is very quite but he seem to know how to help. Thanks for asking him to help you. We all get stuck at times. I know I ask people for help when I do.I like the way that you have renamed the photos. This renaming describes what's in them, or what I expect to see in them. Chris and James have made a very good video on drawing a section through the angled transom. Have you seen this yet?I hope that you have got a lot more understanding of what lofting is all about?Keep up the good work Wei.
Posted by: clovegro | 08/27/2010 at 08:23 AM