Thread: MSD Rowboat built in Maine - Compass Project

We have been challenged with building the first MSD Rowing Skiff to completion. To date we have the bottom prepped for fiberglassing and need to install the tank tops and seats. The midship seat still needs to be constructed.

We are also prepping an Echo Bay Dory Skiff for painting. Governor Baldacci and Superintendant Shuttleworth have purchased this skiff to put in the high school to commerrate being the first class of the Compass Project-Jobs for Maine's Graduates Youth Apprenticeship Program at Morse High School.

HI and welcome!

Are you one of the builders?

Best wishes
Michael Storer

We've been following your progress via the web. Looks like it's coming along nicely. What has been the most challenging part so for? Most fun part?

Just to clarify, confirm MHS Compass is the classroom teacher's sign in that the students will be using to make posts. Should we move it into the ongoing thread? I can show them where it is Tuesday when we meet. If any of the students are reading this, you'll see a MSD skiff thread already started. It is pretty long. Go to the end of it to make a post.

Clint

The ply in the Goat does the same thing. It is supposedly impossible for a flat sheet of plywood to be forced into a compound curve but that is what is happening, or so it seems.

I remember checking the verticals at various places along the sides. There was convex curvature forward morphing into a flat amidships then a tiny amount of convexity creeping back in at bulkhead 4. I could be wrong but it seemed there was a wee wee bit of concavity between 3 and 4.

MAM,

I experienced the same thing: just a tiny bit, but the convex curvature was definitely noticeable in exactly the same positions you mention.

It is probably a trade off because of using the lightest of ply. I you don’t put a ruler next to it however, you won’t be able to see it. So, to cap things: no influence on looks and performance à not important enough to be bothered about (although I do admit that it did keep me awake at night for some hours )

Regards, Joost

That's part of the designer's job ...

I spend lots of sleepless nights worrying about building procedure. So I want to share them with you to.

As well as all the other benefits.

MIK

Howdy ... Good if it is in the thread .. then it has context of what has happened.

If the builders could give their name too would be good ... They dont have to give their real name if they don't want or could choose a nickname to use.

Michael

Originally Posted by Compass Project

Just to clarify, confirm MHS Compass is the classroom teacher's sign in that the students will be using to make posts. Should we move it into the ongoing thread? I can show them where it is Tuesday when we meet. If any of the students are reading this, you'll see a MSD skiff thread already started. It is pretty long. Go to the end of it to make a post.

Clint

I can move the post or posts to the Compass thread any time you want.

MIK

Originally Posted by MiddleAgesMan

The ply in the Goat does the same thing. It is supposedly impossible for a flat sheet of plywood to be forced into a compound curve but that is what is happening, or so it seems.

I remember checking the verticals at various places along the sides. There was convex curvature forward morphing into a flat amidships then a tiny amount of convexity creeping back in at bulkhead 4. I could be wrong but it seemed there was a wee wee bit of concavity between 3 and 4.

You are exactly right MAM,

But computers allow a lot more freedom.

Here is a 3D representation of half the Goat. The viewpoint is down below the chine so that you can't see the sheerline.



Looking at the half bottom panel, see that all the yellow lines are parallel ... these lines represent the lines along which the plywood is perfectly straight.

As we know the bottom is untwisted so that's why all those lines are perfectly parallel. They might look slightly out of parallel because of a vanishing point effect as this is a true perspective drawing.

Each yellow line is called a "ruling line" and if you lie a flat piece of plywood on any of the lines it will contact the side of the boat along each of these straight lines.

If there is compound curvature in two directions the ruling lines will start crossing over.

For the side panel the situation is much more complex.. the back two thirds of the boat has a slight twist meaning that there is a slight conical shape in the back part with the apex (or series of apexes) well below the boat out of sight.

Up in the bow .. see how the straight lines radiate out of the corner - this is much closer to a conical shape with the bow corner as the apex. it is not a true cone as you can see the spacing of the lines varies a little - this is something the computer can do that people cannot.

Note how the radiating lines cross the position of the first and second bulkheads. This means that they have to be curved and the computer calculates this curvature for the frame and gives me a correction. This happens with almost every boat ... the forefoot at the bottom of the stem, whether curved or straight will almost always create this radiating apex forcing the first frame to have some curvature.

With a Vee bottom boat ... this all happens in the bottom panels and the topside panels are usually more straightforward.

With the frames behind number 2 there is also some slight curvature ... but as soon as it is under a couple of millimetres I ignore it because it is not perceivable.

Any flat panel of any material that is able to bend this far will duplicate the same curves fairly closely because it will attempt to minimise the energy involved in the curve.

So that is the assumption my designs I use. I use a minimum of frames to use the tendency of the plywood and chine and sheer clamps to run in a fair curve. And the matching of the centreline of the bottom to the centreline of the bulkheads ensures the boat is symmetrical.

With more controlled boat building over a mould .. we normally try for a high level of accuracy, but usually find about 6mm in a goat sized boat is acceptable. Most important is fairness. A friend once had a Heron family racing dinghy that wouldn't perform. I redid the rig and it started going OK, but never really well. He decided to repaint it and found that the hull was 1 1/2 inches wider on one side. But it was a lovely fair curve on both sides so you just could not tell. So my designs focus on fairness and the building method is focussed around that - I think my methodology (yes, largely stolen from others) results in an amateur built boat that is much more fair than one built over a frame, purely because there are less frames to prevent the timber doing what it naturally wants (ie run fair)

This computer method is not super accurate when used for very twisted panels and accuracy rapidly diminishes. For example my Eureka Canoe was built full size and we found the disparity between the computer shape and the ply shape was considerable. If you imagine the bilge panel of the eureka ...



There is a lot of twist in the end of the bilge panel. The result is that the stress in the material forces it to compound or bend in two directions at once, which is what the plywood will do to minimise stress. So this means the computer and plywood don't match any more. The computer's panels have no stress at all and can bend infinitely following the ruling line restriction.

There was a 15mm disagreement between them for panel shape - which the Biting Midge and I found with a trial build of a quarter boat.

The original 13ft Eureka .. a different design was about 25mm out.

Probably if you stitched the panels up without checking the shape, they would stitch OK, but the shape would be somewhat different from what was drawn by the computer and was intended in the design. No problem with the slight curvature in most of my boats..

Best wishes
Michael

Thanks for sharing this all Michael. The software is very useful. Wish I had it and the know how...I am continually procrastinating on learning to use computers for my own design work. In my rowboat recently completed, the garboard had so much twist in it that a compound curve developed and the result was some unfairness where the panel flatened out to release the tension. I was able to hide the flat spot with the next couple planks. How did you fix that compound curve or what was the adjustment. Did you recut the first plank so it wasn't as high at the stem? I need to figure something out on my rowboat ao I can draw it better. Would love a clue if you have any ideas.
Do the ruling lines always meet at the bottom of the stem or is that an assumption?
Is there a way to create ruling lines in a hand drawing?

Whole bunch of questions there Clint!

The pic of the Eureka above is before it is stitched. - that design is really well resolved now and works easily each time.

With a trad boat, the only real way to do this is to divide the area up into more planks ... so each one takes less twist. Also to make sure that the plank is not being pushed sideways as it goes down which will cause a bulge on one side and a flat on the other .. Both hard to get rid of. I imagine you are quite careful about how much you push planks sideways!

With a ply boat ... you get rid of an unfair join like with the original eureka by measuring the gap and cutting the planks next time a bit wider to fill the gap up.

Ruling lines will almost always meet like the goats when the corner is a definite angle. When it is a curve they tend to be spread out.

You can't do ruling lines manually .. it is 3d geometry and relies on having them quite close together so the errors are small. This means a lot of lines and the computer is the only way to do it efficiently.

The old drafting methods of conical and cylindrical projection are just a simple case of ruling lines.

MIK

MIK

Hi this is: Carl, Hannah, Zack, Ben, Zac, Alden, Cody, Brandon, and Maria from Morse High School JMG Compass Project Youth Apprenticeship Program (MHSJMGCPYAP)!

We are enjoying ourselves building this boat, however the plans had a flaw with the bow tank top measurements. With the measurements from the plans the bow was not leveling up correctly. We are currently working on installing the tank tops and we fiberglassed the bottom. After April vacation we will finsh installing the tops and start sanding. We plan to launch the boat on June 1st.

Other then that the boat is coming out nicely. We are also working on painting the Echo Bay Dory Skiff that the Governor and RSU 1 Superintendent purchased for us to display at school to recognize us as the first students at Morse in this program. It will be painted with a blue interior and white exterior. We will be signing our names in blue on the dory. Blue and white are our school colors.

We are also making oars. The oar blades will be made from carbon fiber. The oar handles are eight sided right now and are prepped for 16 sided.

See you later! Bye!

Mik Sure lets move this and the post they put into the Welcome category and move them into the main thread on the rowboat. I am sorry this is a pain; we'll work out the details next week.