Pictures: Dudes discussing about calculation methods.
08/25/2010
Lofting blog 4: Angled transom
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)
08/23/2010
08/22/2010
Modelling dinghy in Rhino
This is the dinghy modeled in Rhino. Well, I had some problem with maxsurf, so I turned to Rhino based on AutoCAD lines plan. This model is not perfect, it still needs some improvement. But this is only a try out
modelling the dinghy in Maxsurf - I need help
I am trying to model our dinghy in Maxsurf. As I thought with the table of offsets and the AutoCAD plan, it is possible to 're-construct' the dinghy in Maxsurf.
The first step is to add a surface and resize it according to the table of offsets.
The second step is to set the frame of reference and the zero point. select Fwd extend for the Longitudinal and DWL for the Vertical Datum.
The third step is to construct the design grid.Add sections, buttocks and waterlines, and change their labels and coordinates according to the table of offsets.
The fourth step is to shape the surface following the table of offsets:
4.1 add control points at each station
4.2 move control points in the half breadth to shape the deck line
4.3 move control points in the profile to shape the sheer and canoe body
4.4 According to my original plan, it is time to use buttocks and waterlines to shape the surface. As I have input value for waterlines and buttocks, the Maxsurf already generated them in the model:
Here comes the problem, I do not know how to shape these waterlines and buttocks. I tried to construct several new columns and rows of control points to shape waterlines and buttocks, but this does not work.
How can I use these waterlines and buttocks to shape the hull? Or there are other ways to shape the hull in maxsurf?
08/19/2010
Lofting Blog 3: Stem
Stem face
Stem face is a crucial part of the lofting. If you just using existing intersects, it will be hard to get the right curve. Because the stem face needs more details. The solution is to go back to the CAD lab, using CAD to drawing several ghost lines to construct a new grid (with higher density of grid lines) for the stem face, and measure those intersects of the stem face and ghost lines, then you get your stem details. Once you figure out how to do this, stem face is an easy task.
Stem section (Wednesday, 25/08/2010)
After finish the body plan, I started to draw the stem section after lunch yesterday (Tuesday). Thanks Chris for his detailed explanation for how to draw the stem section. Once you figured out how to do this, it is not a hard task. Especially with a sticker (which has markings for moulding, 1/2 siding, PT), you can draw stem sections quickly. Following are steps:
-Go to the stem face and pick a point on the curve (point X), draw a perpendicular line (line A) to point X (you can make a guess by imaging the tangent line to the curve at point X).
- Start from the intersect of line A and the butt 50, draw a ghost line (line B) which is perpendicular to line A, with length of 50. Use the point X and the endpoint of ghost line (line B) to draw line C.
- As the PT (planking thickness is 4 mm, we need to offset line C (offset distance: 4mm) to get line D
- From the start point of line D, draw the moulding (32 mm), and get the faying surface.Then from the endpoint of molding, draw the 1/2 siding (15 mm). From the endpoint of siding, draw a perpendicular line to line D. Notice the round corner at the intersect of the mold and the siding.
- Add some shading.
Picture below: finished stem sections and the sticker with markings for moulding, 1/2 siding and pt (the sticker is made by Chris)
08/18/2010
Lofting Blog 2: Lines
Grid:
Before we start to draw curves, we need to construct grid. The grid consists of several straight lines, including FP, AP, Stations, Waterlines in the profile and Buttocks in the half breadth. LWL is the first line to be drawn, then the CL, the the FP. When it comes to stations, trammel arms are used to draw these perpendicular lines. We first drew one station of every three, then we can use these stations as reference to construct the rest and to check whether our measurements and drawings are correct.
After finish the grid, it is time to draw those curves. The standard process is:
1. Measure the intersects of the curve and stations in profile according to the table of offsets, and mark them out.
2. Find a good batten, and use nails to bend it to the right curve (in this case, it will be the sheer). Then use nails to fix the batten
3. Draw the curve.
4. Pull nails out, and put away the batten.
Sheer in profile:
Sheer comes after the grid according to the lofting schedule. So it will be the first curve to be drawn on the cut board. Sheer is not a tricky curve, so just follow the standard process.
Deck line in half breadth:
Deck line in half breadth is the same line called sheer in profile. Just follow the standard process. But I had a problem when I was drawing this line: the segment between FP and station 0 is not fair. It should not be. I checked my measurements, saw other guys got a beautiful curve for the their deck line using the same measurements and methods. That was really annoying. I tried several times, but failed to fix the error. The batten just tells me that this is wrong. I even started to doubt that may be my grid is wrong, that will be a disaster. Finally I got it. The deck line starts from the CL, but I made a mistake and my deck line starts from butt 50. This explains why I can not get it fair. When you are marking intersects, make sure you measure them from the right line (LWL in profile and CL in half breadth).
Chine in profile and Canoe body in profile:
Just follow the standard process, and with all the experience and skills I got from first two curves, these two curves seemed much easier.
Chine in half breadth:
Buttocks in profile:
I started to draw butt 400 in profile after finished the Chine in half breadth. Use the same technique and follow the standard process. One thing needs to be put special attention is the start of the butt 400. It is the intersect of butt 400 and the cheer. The coordination of this intersect can not be found in the table of offsets, but in the half breadth, you can find it. All you need to do is to draw a perpendicular line from the intersect of butt 400 and deck line in half breadth. The intersect of this perpendicular line and the cheer in profile, is the start of the butt 400. (see picture below)
The second crucial part of butt 400 is that this curve has a kink between station 6 and station 5. It starts at the intersect where the but 400 came across Chine. But I did not notice this (actually, I have no idea about this), so I just used the batten to draw a curve. Chris saw that and made a laugh at me (well, I am not the only one who had been laughed by Chris for this mistake, almost everyone made this mistake). Ben explained this to us by showing us a real dinghy in the workshop. So what should I do? Erase the segment of the kink, measure the kink in AutoCAD, and draw it again.
There is a kink at the front part of the butt 400 (it is located at the intersect of butt 400 and chine) as well. From the kink to the intersect of the butt 400 and the Cheer, it is not a curve, but a segment which consists of three straight lines.
Body plan (Monday, 23/08/2010)
This is the second week of our lofting training. I continued to draw waterlines in half breadth and buttocks in profile. I would say it went quite smooth despite some minor problems. The profile and half breadth were finished before lunch time.
I started the body plan after lunch.Thanks for Eran and Vaughn showed me the technique for body plan. There is no need for measurement of those intersects as we can get all the information from the profile and the half breadth which are already done. The technique is not complicated, or once you understand it, you would say it is quite easy. But it may take you days to figure out how to do this without introductions or explanations from an expert. Boatbuilding knowledge, experience and skills that handed down from generation to generation are high valued assets.
The first to do is to construct the grid for the body plan. With center line in the middle, butt 50, butt 200 and butt 400 on both sides of the center line. Waterlines are the same as those in profile.
The method to draw the body plan is to use a paper tape. At every station, you mark the height of every intersect in profile on one side of the paper tape and the width of every intersect in half breadth on the other side of the paper tape. Then you can just use these marks to locate these intersects in the body plan. After you draw these intersects, use batten to draw lines in body plan.
I finished several lines in body plan today, and still have four lines to go. I will finish them tomorrow.
Some guys have already finished body plan. James was the first (see picture below: James and his finished work). Good job!
Lines are finished on 25/08/2010. :) Picture below: finished body plan
08/17/2010
Lofting Blog 1: Lofting Schedule
Today is the second day of our lofting training. In the morning, Chris discussed about the lofting schedule with us. A lofting schedule shows the process or the code of the lofting. The following is the lofting schedule for the dinghy (actually, this schedule can be applied to lofting of any boats, as a good lofting schedule changes little)
Table of offsets
Grid
Sheer - P
Deck Line - HB
Chine - P
Canoe Body - P
Stem Face - P
Chine - HB
Butt 200 -P
...
As I finished the grid yesterday, I started to draw curves this morning. Following the steps of the lofting schedule, I can easily find out what should I do now and what to do next.
Picture below: Lofting Schedule
Blog for Lofting
In order to construct our e-portfolio for the lofting, we need to write 5 blogs which will represent five major stages the lofting training. Heading topics for these 5 blogs are:
Lofting Schedule
Lines
Stem
Angled Transom
Caculation
Picture below: Chris explaining blogs for lofting:
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