24’ EZ Build, sad model
I built a model of my design ideas so far for an easy to build 7.2m (24’) proa. My lack of model building skills and patience are quite evident, but it does illustrate the concept fairly well.
The concept:
- 7.2m main hull, approx 14:1 L/B ratio, flat bottom, some rocker near ends. Slab sides with flared bilge panels.
- hull is built in 3 sections, foldable for storage
- room for 2 to sleep and sit up comfortably in cabin. Would be nice to be able to sail from inside. It’s often rainy around Vancouver.
- ‘sandbox’ cockpit for nice day sailing and socializing
- 30cm (1ft) PVC pipe outrigger
- Solid timber akas with metal plate hinges for folding
- buildable in a 16’x10’ space
- schooner rig using 2 Laser rigs with sheeting for both shunting and tacking, but optimized for shunting
- construction is mostly 5mm ply over ply/timber frames with timber stringers.
- needs to be beach launchable using a cart and yard winch
- haven’t decided on rudders yet. Kick up quarter rudders on the windward side for easy beach launching.
- no lee pod. Instead, lash a kayak to lee side of cabin
The model:
(hopefully the attachments display)
I love it. might need some kind of adjustable lee/dagger depending on your rudder design, but great concept.
Tom
I love the folding of the ends, but I’m confused about the purpose. Is that so you can store it in a small space?
My wa’apa is designed to come apart for storage, but I haven’t needed the storage space enough to go through the unbolting process yet…
The kayak (or dinghy-ish thing) as a lee pod is definitely an interesting idea. Take a look at Sven’s excellent detailed discussion of how the pod works on Pacific Bee. Can you get that kind of overall displacement out of a kayak? How would you orient it?
I’m concerned with the weight and windage of all that skin.
If you’ve never read Tom Jones’ Multihull Voyaging, he talks about how much weight and windage building a big house can cause—using a Wharram design to demonstrate his point. Definitely worth reading.
I’d be concerned about a 12’ long cabin house. My Palindrox, which has a lot in common greenhouse wise, to your design, only has 8’ of cabin house, and it definitely scares me, weight and windage wise.
If you figure out a smart way to get the sheets inside, without inviting water in, I’d love to see it. I have a couple of strategies for steering. But getting the sheets inside, preferably on the leeward side, and having them accessible from the windward side when driving outside in nice weather, is a bit of a trick.
Love the your funky model. Its the right resolution for the idea!
Best,
Chris
Hi Tim, Chris, thanks for your kind and thoughtful feedback.
Rudders - I’m guessing I need about 3 square feet per rudder, which is about 4% area of a 76 sq.ft. Laser sail. So either a beefy, high aspect kick-up quarter rudder, or a low aspect swing keel (which will swing up if hit from either direction). That could possibly incorporate a spade rudder. I’ve grounded enough to know I don’t like dagger boards, especially when they’re out of reach.
Storage - I pay per square foot at the boat yard, so if the boat folds down, I save $$. Also, it’s much easier to maneuver in the yard with reduced beam.
Kayak lee pod - a 4m play boat would displace maybe 150kg before being submersed. I would just lash the handles at the kayak’s bow and stern to beefy deck cleats at the ends of the cabin. The kayak would hang on its side, but it would be upright if the proa capsized. The kayak would need a tight fitting cockpit cover to avoid getting swamped. Or, I’d inflate air bags inside it.
Windage - I definitely hear you. I’ll look at shortening the center peak of the house, But I feel constrained by an overall height minimum of 140cm for sitting headroom (berth at the chine at 40cm). Also, the Laser masts have 50cm clearance between deck and boom, so the cabin ends need to be at 100cm height. I’ve thought about using a pop top instead of a fixed house. More complex, but could allow the whole cabin to be lowered. But then no comfortable sailing from inside.
Weight - Yes, a concern. I’m hoping to keep the main hull under 200kg. But I haven’t estimated lately. I currently launch and retrieve over 500kg using the yard’s winch. Hullform tells me that at 400kg displacement, the draft would be less than 10cm, so that’s not an issue.
Sheeting - haven’t thought much about it yet. The sheeting blocks will want to be on the cabin roof and to windward of the end decks (or on the quarter rudder mounts. Maybe it would be adequate to install cleats in the cockpit next to the hatch, and have a small opening port to reach through for adjustments. I’ll have to think about steering too…
Thanks for the Firth Jones book suggestion. I’ll check it out.
Curtis
The interior head room thing is what I fight when drawing up 24’ boats. They all look way too tall and boxy on that length when I get the vertical clearance I want inside. I’m in Portland on the Columbia river, so i share your desire for a protected steering station. The other thing is a wide enough bunk flat far enough over the waterline with a bit of headroom over it to roll over comfortably.
This is probably why Skip and so many others have come up with so many schemes to use a small tent at anchor.
Guess I should just build a 32 footer, the proportions look great at that length 😉 If only moorage was free….
Tom
OK, I’ve figured out how to chop 20cm off the cabin and deck height, and still have sitting headroom. The tradeoffs are sitting like in a bucket seat instead of an easy chair, and I’ll have to move the portapottie somewhere else when both seats are in use. And you can’t sit up fully in the berths.
How to people compare windage on different boats? Sail area over beam windage area?
I’ll post another pic after I chop down my model.
curtis
chopped and lowered. Looks like I should reduce the windage from the beams and cockpit too.