Onshape is FREE for non-commercial work. It does NOT require a complicated download or install. It is EASY to use in Free mode.
Onshape is entirely cloud based - which is a mixed blessing. You can't really export your native design details (that I'm aware of) - though it wouldn't really do you any good, as the format would almost certainly be proprietary.
The good news about Onshape being cloud based is that you can log into Onshape from any computer and access your projects. Since the interface is cloud based through a web browser - you can seemlessly move between Windows and Unix.
Onshape seems is richly featured. There is PLENTY of documentation, training, and help videos and information available on the internet. While I liked the thread and coil feature of Fusion 360 better, there does at least exist a thread feature in Onshape. I've tried it once, and wasn't tremendously impressed. I may typically use a body hole and then tap holes. Best case, maybe do the threads and plan on running a tap.
The BIGGEST NEGATIVE about Onshape is that for non-commercial accounts (hobby mode, free mode) - ALL content is public domain. ANYONE can access your work. This is a BIG consideration if you want to develop projects to be shared on Thingy-verse, etc. This may also be a consideration if you are developing objects that certain states might analyze and decide look too similar to known restricted shapes... (I have no idea how this will work out, and at the very least am extremely thankful that I do NOT live in one of the ridiculously restrictive states that wants to audit every shape I would send to my 3D printer!)
So far, all of the projects I have worked on with Onshape have been for my own personal use, and would not be likely to have any public interest from anyone else. I guess the cup holder I designed for the boat could possibly be used by someone else, but as long as someone doesn't start selling them and making a profit on my design, then I probably would be happy if someone else found it helpful. Though I also suspect it would be unlikely for anyone else to find that design...
For boat design work, it seems best to set up the views so that station frames and bulkheads are drawn on the X-Z plane (x dimension is width, z dimension is height). The Y dimension then provides the spacing between frames.
While it may seem intuitive to use the X-Y plane for drawing the frames, that is "top view" when adding the z-axis. If you draw your frames in the x-y view, and use the z-axis for frame spacing, then you will be looking down at the bow, with each successive frame below the bow.
There are two types of variable tables: "Variable Studio" and "Part Studio".
Generally, I will use the "Variable Studio" table for variables. These values are available for the scope of the entire drawing. Variable Studio entries can be copied from one drawing to another. Part Studio entries cannot be easily transferred to another part or drawing.
When possible, without over-doing it, put all major measurements in the Variable Studio table. This will allow you to quickly tweak one variable in the table, and have that propagate through the entire design.
Start by "hiding" everything possible (other sketches and planes) other than the plane you want the new plane to reference. If referencing off the "Front Plane", then select the Front Plane from the left view/sketch list.
Select the Plane tool
Enter the offset
Check the direction (diagonal up/down arrow) to switch the offset plane to be in front of or behind the existing plane.
Select the new plane (highlight), then click "Sketch" - this should show the new plane in details for the schedule.
3D splines can be drawn once multiple planes are enabled, using the spline tool.
Lofting is similar, but more advanced than simply filling in splines. Lofting can be used to create shapes from the selected points of the frames.
Once the 3D view of the model is created, waterline volume calculations can be made by "splitting" the model on a plane.
Start with the top view of the model. Create an offset plane at the desired waterline height. Once the model is split on that waterline, Onshape has an analysis tool that will calculate the volume of the enclosed shape.