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Author: Elmer
Progress in 3D
Some work-in-progress renders of what I’ve come up with this weekend. I feel I have the design pretty much done. Of course a lot of the fines details need to be sorted, but I’ll get to that once I start building.
I’m not entirely sure about the rigging. I like the simplicity of a sprit sail, but I might change my mind. I’ve added chine runners for course stability. For sailing lee-boards might be required, but I can easily add them when needed.
View of outside
Roof and decks removed
Bulkheads and interior framing
Interior view. Grey circles in the front compartment will be inspection hatches
Open
Open with cabin sides
Interior without floor
All enclosed
Bottom, from the front
Floor framing and bulkheads
Clean view of the interior
Added a person for scale. 2 adults can sleet either side , with their feet sticking in the rear compartment. Bunks are about 70cm wide. Walking space in the middle is 30cm.
My previous project, a little scow
The tiny house boat or weekender, or whatever is ends up becoming, wasn’t my first project. A few years back a made this little scow-like vessel. Thought I’d show some pictures for whoever is interested.
I build this pretty much free hand, no designs and way too little planning. It’s not stable, neither practical. But, it was the most fun I’ve ever had building it. She does about 4 knots with my 50 lbs trolling motor. I had planned to put a mast on her, but never got around to actually doing that.
If anyone is interested, I need the space in the garage so any offers are accepted 🙂
Complete change of plans
As much as I like my designs so far, after speaking to people who know more about boats than me (which is just about anyone really) I’ve decided to completely change my plans. The enclosed pod-like will have to go, as does the catamaran hull. An enclosed vessel would be extremely difficult to moor. Even more so because the high structure would catch the wind all too easy. And the catamaran hull looks good, but the tunnel through the middle is just too inefficient.
So, this is what I’ve come up with as an alternative:
I’ve changed to a scow or barge type hull, giving optimal stability and interior space. I’ve lowered the upper structure, minimizing wind susceptibility. I’ve added deck space for easy access during mooring (and sailing). I’ve narrowed the beam for better course stability. And I’ve added a mast as the main means of propulsion. Not sure if I’ll be adding an electric of traditional fuel outboard, but with the sailing capability it becomes less pf an issue either way.
Dimensions are now:
- Beam: 1.70 m (5.5 ft)
- LOA: 3.5 m (11.5 ft), excluding rudder
- LOW: 3.35 m (11 ft)
- Height: 1.2 m (4 ft)
- Draft: 15 cm (6″)
I’m not sure about the interior layout and the steering position needs work. Also, the rudder is probably pointing forward too much at the moment. And I want to add chine runners along the bottom to help when sailing.
That’s it so far.
Essential hull changes and other small stuff
After recalculating the estimated weight of the vessel, I decided to enlarge the hulls by a few centimeters in both width and height. The added buoyancy will give additional safety margin when the vessel is at full weight. Unfortunately, this also means some inside space is lost, but so be it.
The calculated draft is between 13 and 17 cm, depending on the number of people and cargo on board. The hulls are heightened from 20 to 24 cm and 5 cm wider compared to previous designs. A 1:10 model will have to proof my calculations.
Inside
Inside the vessel I’ve moved some stuff around. The kitchenette moved forward a bit to make room for the door. The steering position is smaller and also moved forward. And the benches/bed are now U-shaped around back. This means it’s no longer possible to sit with more than 2 people. But I recon the vessel is too small for that anyway.
Outside
I’ve added proper doors both sides and added some detail to them. I’ve added 2 hatches in the roof, allowing a grown person to stand up and look outside. And I’ve added a large hatch in the bow. This will probably be a 2-part hatch, split horizontally. The upper part will swing up, just like a hatchback-car. The lower part will fold down as sort of a ramp, allowing easy access to the vessel when beaching.
Outboard engine sketch
Here’s what the vessel could look like with a traditional outboard engine attached. I’m thinking about a 6-10 HP, water cooled model. I still prefer electric propulsion, mainly because it’s quiet. But it’s also expensive and has limited range.
I’ve also added running boards and hand rails. Even though the running board is very slim, only 6 cm, it should be just enough to make mooring a bit easier.
Interior
Here are some sketches of what the interior might look like. The table drops down to form a 2-person bed in the back. I might add a door in the front, between the steering seat and kitchen block, not sure yet.
And back to catamaran
After some careful consideration (and a few glasses of wine) I decided to go back to my original catamaran design. The main reason for considering the box keel was improved living space and standing-height inside the vessel. My initial catamaran design had quite high floaters, roughly 50 cm. This meant I also had a 50 cm tunnel traversing the vessel. I decided to lower the height of the floaters to only 20 cm, making the tunnel less pronounced and thus increasing inside space. The designed draft is about 10 cm, so 20 cm floaters still provides ample safety margin.
Pictures below show the two catamaran designs side-by-side. The second design clearly shows the less pronounced tunnel in the middle. The pointy bows help increase length over water (LOA), which helps course stability and efficiency.
Other arguments for a catamaran design:
- Good stability, especially in calm, inland waters
- Good course stability: the smaller contact area with the water means a better width to length ratio. The box keel, or flat bottom, would have a ratio of around L=3.5 / W=2 = 1.75. The catamaran, having 60 cm floaters, would result to L=3.5 / W=(.60 × 2) = 2.9
- More storage in the floaters for batteries etc
- Smaller surface contact area means more efficiency; more speed from the same energy
- Looks cooler imho
3D sketches
My initial catamaran design. There will be doors in the bow and starboard side. I might also add a door on the port side too, not sure yet. The interior shows a table and benches, which can be converted into a 2-person bed.
Updated design with box keel and some more details on the upper structure.
Change of plans, from catamaran to box keel
My initial plan of a catamaran hull has advantages, like being super stable and having lots of storage space down low. Parts of the hulls can also be sealed into flotation chambers to keep the vessel afloat in case of an emergency.
There are definitely also some disadvantages, the biggest being the lack of interior space. The tunnel in the middle means standing-height in the middle isn’t really an option.
So I’ve been thinking about changing the design to a box keel hull. I would sacrifice some stability for a more practical interior. The keel would have to be wide enough to provide some walking space, but small enough to not push the boat up and make it want to tip over. For now I’ve made it about 70 cm wide and 20 cm deep. This gives is about 400 kg upward pressure, which should match the weight of the empty vessel.
Time for another prototype…
As the last picture shows, the box keel is not as stable as a catamaran. By far. I will not be able to carry the 10 or 12 people the catamaran could. But all in all it does seem to hold up, even in pretty extreme situations. Good results. I think box keel is here to stay.
Until next time…
Tiny house boat 