Category Archives: Boatbuilding & Design

Tepukei-Style: An Accomodation Pod?

I’ve been looking at another approach to try and reduce costs. The idea is to have a long hull, but with comparatively low freeboard, and sealed off, like a beachcat. Overall, a lot like the Tepukei.

The intricate connecting structure and the sealed deck are characteristic of the Tepukei.
The intricate connecting structure and the sealed deck are characteristic of the Tepukei.

I’d build an accomodation pod ontop of that, out of relatively cheap polyerathane foam and fiberglass, and mount that between the hulls. It has a well-protected opening to the leeward side.

The hull is 9 meters long with 60cm freeboard most of the way. The pod itself is 2.8m by 1.2m and 70cm high. It has a 65cm overhang to leeward, to provide a very sheltered seating position outside. One thing it definitely does need however, is the ability to walk to the ama, fore-and-aft of the accommodation pod, so that definitely needs to be changed. I also don’t quite know yet where/how to step the mast on such a design.

While the accommodations are much more minimalist, I think it does have clear advantages where insulation and moisture is concerned. With a cabin in the hull, water will always tend to seep down through the hatch, and condensation on the walls is a major issue. A well-insulated accommodation pod doesn’t suffer from these problems, and the boat as a whole is way easier to build and a fair bit cheaper. Going around the Baltic in that, seems pretty daunting, but maybe with a bit of work, this can actually be made into a viable concept! 🙂

Cheers,
— Marco

Lightweight 8m Design

I grew a bit concerned with the lack of seaworthiness of a possible 6m design and aimed for something smaller with removable bow sections so it would be build-able in a garage. The interior of this boat would be extremely cramped, but even so, reducing the length to something on the order of 7.5 meters is still on my mind. I think it’ll be time to build another cabin mockup soon! 😉

Going Even Smaller?

I made a few changes to the parametric model of the hull, and then had the computer spend a couple of hours doing an optimization over a very board range of parameters. My goal was to find an even shorter hull capable of carrying the required load. The length-to-width ratio of the hull started coming down, the draft was increased slightly, and I ended up with a 6 meter hull capable of supporting 700 kilograms, which would be adequate for single-handed coastal hopping.

I also went through the mass and cost numbers for the boat. My best estimate is about 5000€ to get this boat ready to go (since I already have the ama built and quite a lot of epoxy in storage). Ontop of the cost of the boat, there is the potential cost of a workshop, which provided I can actually find one sufficiently close to me for regular work, would cost on the order of 100-150€ a month. Over say 18 months that adds up to another 2000-3000€. Looking at the ~9000€ needed to complete a 9.2m boat, that would make for a cost of 12000€. That is a sum of money which I absolutely do not have, and couldn’t even come close to racking up with a student job on the side.. The 6m boat on the other hand could be built in my garage, by building the middle 5.5 meters of it and gluing or bolting on two 25cm end-pieces, right at the end.

Figuring out how to support the rig on such a tiny hull proved tricky, but of the 4 available options, a supporting strut on the windward side, is the easiest to build and to operate. KISS. An even simpler and cheaper solution would a traditional Polynesian crab claw rig, but reefing is a bit of an issue, and with a lofty Hobie 16 mast I can get a heck of a lot more sail area on the boat than with a single crab claw sail. I’m going to need a bowsprit for that gennaker though… 🙂

Giving up loads of interior space and comfort doesn’t bother me so much, but with the reduction in length you take a massive loss in seaworthiness. While the maximum speeds of either design probably would not be that far apart, the average speed of the boat will also suffer significantly, even more so because the average number of hours where the boat is moving forward will also be less, on account of more in-port days (heavy weather) and I figure getting such a small boat to sail by itself under autopilot would likely be quite a challenge, at this size it’s more of a beach-catamaran than anything else. All that said, there’d be little sense in trying to build a boat I can’t afford, and if anything, the smaller boat would promise a real adventure!

Cheers,
–Marco

A Cute Little Proa

I spent about 4 hours today drafting a fresh design from scratch, to look into the possibilities of a much smaller design. I love how enormous the rig looks on that little boat, and I think she came out really cute! 😉


As it stands, my 9.2m design would cost around 9000€ and 600-800 hours of construction time to complete (with the ama already nearly done). I don’t have anywhere near to that amount of money. This much smaller design would take way less than that, and would be much cheaper in its upkeep as well. If I could keep condensation and moisture in the tiny cabin under control, then even this boat might be enough for a solo run around the Baltic. Here are the specs of this design:

specs

The underwater design is machine-optimized using the Galapagos evolutionary solver, which comes as part of the Grasshopper plugin for parametric modelling in Rhino. I spent quite a lot of time building a parametric model for proa hulls, and incorporating a couple of nice tricks, but now that I have it set up it’s amazing how good the numbers on these machine-optimized hulls turn out. I’d probably need another couple of hours to update the loading list and do the mass estimates for this design, but that’s for another time. 🙂

Cheers!
–Marco

 

Something is Cooking…

I’ve been busy the last few days, with preparations and shopping. Oriented strand board (OSB) is not a boatbuilding material, but can anyone guess what I might be up to? 🙂