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what shells are you making?

I’m making rowing shells, they are sometimes called racing shells. It’s the type of boat that someone would use for the sport of rowing.

I read boys in the boat. How big of a shell / how many seats? I’ve never tried rowing, but I live by a major river and on my summer morning bike rides I’ve seen rowers out on the water. Looks cool.

Nice, that’s a good book!

The shell that I’m building is a 1x or a single (sometimes referred to as a single scull or 1x scull also) which means that it has 1 seat for 1 rower. I rowed a TON throughout high school. I rowed varsity during freshman, sophomore, and junior year but I left the team this year. The my shell is 23.5ft in length.

Compared to other shells my shell is just a little shorter and the hull is a little wider. The wider hull will improve the stability of the shell. Maintaining stability/balance (sometimes referred to as “setting the boat” or “set”) is crucial in rowing. The only downside is that additional stability sacrifices a little bit of speed. However, in my case the hull isn’t crazy wide so it’s a happy medium. I’ll attach some photos

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You will have to share your progress here.

My high school son has caught the rowing bug big-time!

He keeps wanting to make a shell, and knows that we can use the maslow to do it, but we have been lacking in plans! I keep telling him, I need more than a napkin sketch, I need something like blueprints or even better digital files.

What design are you going with and where did you get the plans digitized to turn into gcode?

-M

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I’m using the plans for the Angus Rowboats “Cambridge Racer” A fast racing shell you can build - Cambridge Racer - Angus Rowboats

Those plans are pretty much perfect for what you’re looking for because they come with DXF files. (which is what I used) However, my shell is slightly modified from the original plan, I just gave it a more aggressive lines near the bow and stern, I changed the curvature of the bow, and I made the hull a little bit thinner.

As for going from SVG/DXF to Goode… I did it myself. I used adobe illustrator to fix/clean up the DXF file a little bit. The DXF files that they send are need to be cleaned up as some paths aren’t fully joined and there are lots of lines that can be simplified. (It’s not hard to do this)

If you buy these plans let me know as you need to flip the bottom bow panel, and theres lots of advice that I can give.

Once I had a clean, connected SVG it was time to make the Gcode. I had used makercam to do that but sadly makercam doesn’t work anymore because flash was discontinued. I’m hearing some people talk about Easel though, I’d give that a try.

Cutting the Parts:

This boat is a stitch & glue construction boat so you’ll have to cut long, 8ft panels. (18 of them to be exact)

While your son is absolutely right that you can use the Maslow to cut the panels… using the default frame Maslow won’t work, as it’s not big enough. I posted my setup that I used to cut the panels a few months ago: New Frame Design! Can cut long/wide (I’d be happy to send you additional info about the setup if that would help) There are also many other setups that others have posted as well… my setup has worked very well for cutting the panels.

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Here are some photos of the shell!
Currently I’m in the process of sanding which will get rid of any bumps, irregularities, or orange peel prior to varnishing. After that, I’ll be applying two coats of varnish, which will give the boat a nice, smooth, mirror finish.




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Your work is always mind blowing beautiful.

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What kind of plywood?
And where did you source it?
M

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Fantastic information! The build quality looks amazingly good. Thanks for sharing. Does your scull need to change size with your mass? If I’m 200 vs 150, would I use a different width/length for optimal stability/buoyancy? What oars will you use (make/buy) and will you use a sliding seat mechanism?

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I used okoume plywood (4mm) however many other types of plywood can be used. I got it from a lumber supplier near Sandusky, OH it’s called Homestead Hardwoods. Okoume can get pricey so it just comes down do what you want your boat to look like. (Whether you plan to paint or varnish)

Thank you very much for the positive feedback, I really appreciate that!

Yes, the rowing shell that one would use would DEFINITELY depend on their size/mass, the rowers weight to be specific. Variables like the rowers height, leg size, etc can all be accommodated for by manipulating or fine tuning the boat’s rigging.

In general rowing shells are divided into different weight classes:

FLYWEIGHT: 40-59 kg / 90-130 lbs.
LIGHTWEIGHT: 54-73 kg / 120-160 lbs.
MIDWEIGHT: 68-86 kg / 150-190 lbs.
HEAVYWEIGHT: 82-100 kg / 180-220 lbs.
HEAVYWEIGHT PLUS: 95-113 kg / 210-250 lbs.

The boat that one would purchase would likely go off of their weight class. It’s more important that someone who is a heavyweight doesn’t row in a light weight shell as they will sink the shell, putting a bigger hole in the water which will make it much harder to row because it creates lots of extra drag. It’s also important that lightweights don’t use a heavy weight boat, but I’d think that heavyweights using a lightweight boat would be worse.

Since being underweight or overweight in a boat will either raise or lower the height of the boat to the water respectively stability will be effected…

Since being overweight for the boat will sink the boat a little bit essentially, it will make the boat awkward and uncomfortable to row which will make it difficult to keep balanced/stable.

Being underweight for the boat will make it rise up more, making it less stable because there is less hull in contact with the water.

Those things said, in theory, the heavyweights in the lightweight boat would experience better stability than the lightweights in the heavyweight boat, but the rowing stroke would be so awkward for the heavyweight folks that it wouldn’t matter. (Good form is essential to keeping the boat balance, if form is bad, balance will be bad)

Heavyweights will need a longer, wider boat to keep them from sinking. (Imagine if someone who was very heavy sat on a tiny boat made for a child)
Lightweights will need a boat that is shorter and thinner.

For the oars: I plan on borrowing some from the boathouse
For the sliding seat: Yes, I will use a sliding seat. The sliding seat is essential to rowing as it allows the rower to use his/her legs to move the boat which will make it easier to row and much much faster. Rowing is 60% legs, 20% arms, 20% abs/core.

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I have been watching this thread for a while because it’s just very interesting…

But now I have a pickle of a problem that maybe my maslow and this forum can help me solve.

I have a 35-foot sailboat with a rotten rudder.

One option is to pay someone for a whole new rudder: several thousand $$$. :frowning:

One option is to simply replicate my existing rudder with various molds and such: but the current rudder is not a spectacular performer and is very lumpy so I would have to spend gobs of time making my crappy rudder fair enough to make a mold.

Or somehow use the power of Maslow, this forum, Fusion360 (insert boos and hisses about F360 here) to design and build a new one.

I have very few pre-conceived notions about the best way to go about this.

Here are some options that i’ve thought of, but am very interested in whatever alternatives my follow maslow-ites have on this:

#1: Use maslow to cut “stations” for the top and bottom of the rudder profile and use hot-wire-foam cutting techniques to get the bulk shape

#2: Use maslow to create a left and right half mold box, similar in concept to the pram molds mentioned above. make port and starboard skins and fill with expanding foam around the rudder stock.

#3: Convert it to a metal-maslow-2 style gantry, and true-3d-cut the entire profile and shape from foam

4: Use Maslow to cut very thin sheets of foam into a varying profile and glue them up afterwards (like cutting a topographic map by mapping each isocline to one layer of ply, cutting each layer separately and then gluing them all up when done)

The only real hard spots is that I would like to do some sort of glass-over-foam constructions, because solid wood (or 100% ply) for this application would make it prohibitively heavy.

As far as dimensions go, the rudder is mostly rectangular (actually trapezoidal, but only a little). it’s about 40-inches top-to-bottom and about 30-inches front-to-back.

Thanks!
M

(picture of theboat with crappy rudder at the stern)

#

Perhaps you could cut one out of wood (or something else), sand & plane it to get your desired shape then and use epoxy & fiberglass to get the curves towards the ends of the rudder to your liking.

This approach gets my vote…although I’ve never built a rudder. My main concern would be that it might be weak in the direction that the rudder most needs to be strong in. Maybe each layer could have some holes cut in it and carbon fiber or fiberglass rods could be run vertically to help the layers stay attached?

You can also epoxy a layer of glass cloth betwwen each of the layers of foam, so they will act as a section frame.
But I guess you will still need some higher density parts in the rudder where you attach the rudder stock or shaft to. Those higher density parts could be plywood.
Is weight really that important? A full ply and epoxy rudder will still float.
I once made a rudder for a 31ft sailingyacht, of 4 layers of 18mm marineply glued around the stainless steel rudderstock. Afterwards shaped into a nice aerofoil shape and covered in glasscloth. This makes a very strong rudder.
And you could still use the Maslow to shape the aerofoil shape, even without a gantry.
The way to do that, I tkink, is to machine 3D adaptive pockets of about 10x10cm, leaving a centimeter between the pockets that will form a kind of grid for the sled to slide upon (the bottoms of the pockets are the desired aerofoil shape). Once one side is shaped, turn the rudder and do the same with the other side. That grid will eventually have to be removed ofcourse, but that is a lot less work than shaping the whole rudder by hand. And you’ll get a more accurate shape.
Good luck,
Arjen

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Just spitballing here but another option might be to create the shape in Fusion360 then use the Slicer function to create interlocking slices of plywood (like ‘parametric’ furniture) that could then be filled with expanding foam and wrapped with fiberglass. I’ve never used F360 but I’ve done this pretty successfully using Sketchup. You could just use 1/4 ply to get the shape or up to 1/2 or 3/4 for a pretty strong part. Gap size can be adjusted to in order to minimize wood content or weight.

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Initial Shape
Screen Shot 2021-03-17 at 7.23.46 AM

Sliced

!

Parts cleaned up a bit, cut, slotted together

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This is an intriguing idea.
Since most of the strength in compression and tension comes from the skins, the “skeleton” in the middle wouldn’t make much difference.

-m

That last idea about milling pockets and leaving a grid is also intriguing.
I’ve built a rudder as you describe with plywood before. it was for a much smaller boat, and it was super heavy. Given my need to manhandle this into position in the boat, if it’s too heavy it will be impossible.

-m