Firstborne: 8m light cruiser
Hey guys,
Sorry for the long silence! There were a lot of things I didn’t like about the old design. It’s been a bit of a slog the last couple of days, but I’m making progress again. I figured the best way to get unstuck would be to go out an do some boating, so I spent one afternoon on the nearby river in the canoe I built last year, and another afternoon with a friend sailing on his inflatable catamaran on a nearby lake. Both definitely helped clear my head a little, and provided some some fresh inspiration. Now there’s two major topics which are floating through my head:
(1) I want a cabin. A buddy and I were out sailing on his inflatable cat on a nearby lake the other day. It rained a little, we had a modest amount of wind (3 bft or so), it was 15C, and I was out there without a neoprene suit. While I didn’t get cold, I can’t imagine that I would be keen on having to set up a tent in the rain, and then sleep in a cold wet tent, if I’d just been out all day instead of all afternoon, with twice as much wind, and with pissing rain and lots of spray, instead of just a light drizzle. Having a boat that you can comfortably take cruising even if the weather isn’t warm and sunny, would be a massive plus.
In terms of volume, the hull can easily take the extra weight, so that’s not something I’m worried about. At the moment I’m thinking of having a lee pod which sleeps 1, and having what are essentially trampolines which you can span inside the vaka at a moderate height where it’s wide enough, to sleep 2 more, end to end. I think having a comparatively large lee pod integrated into the cabin, while not strictly needed to sleep 2 in the boat, would probably be a good idea; without it I think the cabin would be very very cramped.
Sleeping two, end to end in the vaka, doesn’t kill the idea of having a disassemble-able 3-section vaka either; the bulkheads leading from one section to another just have to have large openings cut into them from about midway up to the top, so that when sleeping on one of the vaka beds, you can put your feet into the bow section, providing the required length (thank you Rael!). Due to the division into sections, you would have to have a large o-ring seal around that spot there, but given the sections will be bolted together, and that you can design the bulkheads to have a grove to fit a suitable o-ring and design that seal cleanly by the book, I think getting that watertight shouldn’t present too much of a problem.
All in all, the hull didn’t require a lot of modification, but things do kind of depends on one major factor: how much clearance does a lee pod need over the waterline for coastal cruising though? At present it’s only ~280mm (about 1’) above the waterline when the boat is heavily loaded (800kg total displacement), or 380mm when singlehanding without cargo (450kg). Do you guys think that’s enough clearance? Does anyone have the numbers for how high up the pods on Cheers, Madness or any of Russ’ proas are?
(2) I stumbled over the Dinghy on a stick v.2-thread a few days back. That has me thinking a bit; since bikes are a no go, having a flat bottom canoe for 2, along could be a nice alternative to bikes, and if it has watertight stowage compartments in the bows, then you could use it to get stuff ashore. Even cooler would be if the canoe also doubled as a small proa, with a simple rig, ama, and akas lashed to the floor inside the canoe for storage, so you always have them along. The question of whether the lee pod and canoe could be designed so they fit together, without having to badly compromise either one of them, is definitely still open, but having a super-shallow draft canoe along would definitely be a nice extra (something one can add later though, provided the pod is designed accordingly).
In terms of the design, there’s more to come! I’m also starting construction of a scale model of the vaka in the next few days.
Cheers,
Marco
And one more pic… 😉
One thing I really like, is that just about the entire hull can be built from plywood. The only spot where strip-planking is necessary with this geometry, is at the sharp bend on both ends of the lee pod. 😊
Edit: Concerning the waterline of the boat—it’s around about the point where the bow stem meets the boat bottom. When heavily loaded the waterline is about a little above that point, when loaded for cruising with 2 the waterline is slightly below that point, at least with present mass estimates.
I really like the looks of this design and the reasoning behind it, Manik.
Thanks James! I’m also quite fond of how the shape came out this time; I’m really going to try to keep the overall look of the vaka, but I’m still worried about the clearance issue. I don’t know how much clearance the pod needs, and if it needs more than 300mm, then I’ll likely be forced to make the boat taller since I can’t really flatten the pod a whole lot more if I want to be able to sleep on my side.
I’m wondering about another topic as well; cold-water cruising. I don’t have a clue what that’s like, I imagine that sailing with the temperature near freezing could get pretty miserable, but given my home is northern Germany and southern Finland, and I’m quite fond of cold weather in general, equipping this boat so it can handle freezing temperatures seems like an idea worth considering. Basically I’m thinking something on the order of 50mm polyurethane foam insulation, and a small closed-loop kerosene heater should get the job done.
I did the math, if you factor in heat losses through the cabin walls and energy needed to heat up of all the air needed for ventilation for two people, you come in at around about 1 liter of kerosene per day to keep the cabin 20C warmer than it is outside, with a little to spare. It’s a small cabin and 50mm of good polyurethane insulation is pretty good, hence the low figure. All that insulation would also help keep the boat a bit cooler in the summer, but the foam would take away a bit of cabin space and require 100mm more freeboard, for the same amount of sitting headroom & pod clearance.
Have any of you been sailing in freezing temperatures, if so, what was it like? Is that something that you can do, and enjoy, with the appropriate gear and a warm cabin, or is that generally such a miserable experience that I can just rule out ever trying it, without missing anything worthwhile?
FWIW P52’s ‘weather’ pod had about 350mm static clearance and never slammed (was memorably brushed by a dolphin pair (adult and juvenile) once). This included some time in fairly rough small craft warning conditions.
Absolutely no idea about cold weather conditions.
I agree with James, design is looking very very nice.
cheers,
Skip
I’ve sailed a bit in near-freezing weather (winter, Vancouver, Canada). I think you absolutely need survival clothing - something that is designed to contain body heat when you’re wet or fall into frigid water, yet allows you to move comfortably. I have an old Mustang “floater coat” and pants set that keep me warm enough for a day’s sailing even after wading in to launch my boat. You also need thermal footwear and gloves, since cold hands are surprisingly weak. Neoprene gloves are smelly, but effective at keeping hands warm.
The next thing for cruising IMO is to have an area that is always warm and dry for sleeping. Also, you need a separate area to get in/out of your wet clothes. If you’re in a rainy region (like Vancouver), this presents a problem for extended winter cruising on a small boat, since there may not be enough covered space for both areas.
I’ve also heard that ice/snow buildup can be a great hazard, since it adds great weight to the top of your boat, making it unstable. On a proa, this is much less of an issue, but maybe should still be considered.
I’m in no rush to go winter sailing, but having the right cold weather gear can greatly extend your cruising season.
I’m wondering about another topic as well; cold-water cruising. I don’t have a clue what that’s like, I imagine that sailing with the temperature near freezing could get pretty miserable, but given my home is northern Germany and southern Finland, and I’m quite fond of cold weather in general, equipping this boat so it can handle freezing temperatures seems like an idea worth considering. Basically I’m thinking something on the order of 50mm polyurethane foam insulation, and a small closed-loop kerosene heater should get the job done.
I agree that it’s worth considering, if only because it could really increase the length of your sailing season. Try looking at blogs/websites about high latitude cruising for more ideas. A lot of the information won’t be applicable, but those are the most knowledgeable folks around when it comes to staying safe and comfortable on a sailboat in cold weather.
I have no personal experience either, but I think even more important than an insulated cabin would be making sure that you stay dry and out of the weather while at the helm. Even with proper gear I can’t imagine it would be very fun to sit out in the spray and the wind in ~5˚C weather. A removable dodger out on the akas (sort of like the shelter on a tepuke) would be a really good thing to have in the spring and fall, and you could take it off in the summer if you wanted to. Spray rails on the windward side of the vaka would probably be a huge help as well. The ultimate solution would be a helm station set up inside the cabin (ala Cheers or Bieker’s Jester class proa) with a perspex dome on the companionway hatch.
On the insulation, consider using rigid polyisocyanurate or extruded polystyrene boards instead of sprayed in Polyurethane. The simple large radius curves of the hull should be pretty easy to match with 4 layers 12mm foam sheathing laminated together. And it seems to me that on such a small scale project, it would probably be a lot cheaper than hiring someone to spray the urethane.
Thanks for the clearance value from P52 Skip! I’m just looking at the study plans for Madness; if I’m interpreting the scaling right, then Madness only has ~255mm clearance for the pod and cockpit floor at its cruising waterline. To me that seems like a very small height, but if you google around for some pictures, then it really doesn’t seem to have a lot of clearance there… That said, if you did fine with 350mm, then I think I’ll just bump the pod up to that height as well, and call it at that. 😉 It’s only missing another 50-70mm for that anyway.
Concerning the cold-water sailing: extending the length of the cruising season is a very strong argument. Up in Helsinki the night-time temperatures don’t go into the double digits until June, and while 10C is easily in the region of what you can do with a good sleeping bag, having the ability to easily maintain cozy temperatures in the cabin would definitely be a nice extra. If that 5-10C band was cruisable in this boat, then cruising could be possible in Finland as early as May (provided the sea-ice has melted completely), and down here in Germany you could conceivably start as early as March or April and go all the way into October or even early-mid November, which would be great.
I’ll definitely look into the insulation materials in more detail as well. I hadn’t considered the possibility of just laminating several layers together to get more curvature out of prefabricated panels. That would indeed be much easier, and a lot cheaper(!) than having someone spray polyurethane. Thanks for the tip!
The ultimate solution would be a helm station set up inside the cabin (ala Cheers or Bieker’s Jester class proa) with a perspex dome on the companionway hatch.
😊
Manik,
I seem to remember Russell Brown saying that because the pod is on the lee side it didn’t seem to need as much clearance as something on the weather side might require to avoid slamming.
You could (with a little extra work!) regain your 100mm lost to the interior height/clearance by foam insulation and gain an extra 50mm clearance (and overall freeboard) by placing structural (corecell or similar pvc) foam on the outside of the keel and deck and skinning it with either f/glass or another skin of plywood. You could go lighter with the ply which would now be on the interior side of the resulting sandwich to gain back some of the increased weight (which would take a little of the increased freeboard away). Structurally, your proa will be many times stronger/stiffer using a sandwich with structural foam than sticking or spraying on foam (with no second skin) on the interior side of the plywood
If you put a non-skid surface over the fibreglass skin over the foam on the deck, it would save a lot of fairing work. You might need to vacuum it down anyway and this would leave a pretty fair surface, in any case. Same goes for the keel (good place to use some kevlar, too, but cover it with f/glass).
I’d stay away from spray-on foam as it does absorb water over time and is very toxic to apply. Although operators use positive pressure breathing equipment, you might find it hard to get someone to apply it inside such a small volume, anyway. Plus it is not attractive and adds litlle to strength. With foam on the outer surface of the ply, you would have greatly increased strength and your attractive timber interior surface back 😊
Insulation, Ventilation, Heat Source
On a boat this small, your own body heat can be the heat source, or a large part of the heat source. Insulation can be foam added inside the plywood between the bulkheads. You will need some ventilation to remove the moisture from your breath, but not so much ventilation that you lose the heat that you have captured in your hull. So ventilation needs to be adjustable. Condensation is dealt with by avoiding large uninsulated areas (especially metal or glass), allowing enough ventilation to evaporate (hopefully) and a heat source to assist/encourage evaporation. Condensation and moisture are a bigger problem than actual temperature, because it is not difficult to insulate your body with appropriate clothing or sleeping gear, as long as you can stay dry.
On this small of a boat I would recommend a simple heating system such as a pressure cooker half filled with water heated on a cooking burner, heated up to pressure, and then secured in a position where the heat will radiate or rise to the pilot.
A kayak skirt equipped hatchway combined with a Grundens anorak would allow handing of lines and steering from an outside position while still providing very good weather protection. It also keeps all of the breath condensation out of the cabin.
On Whaleback, I have 2” of construction foam under the deck and 1” in the hull sides. I have an inside steering position, and the halyard and sheet for the sail can be led inside the cabin. There is good visibility out of the windshield, although at this point I don’t know how bad condensation will get and how it will affect visibility. The boat can be sailed with the hatch closed. I am very concerned about capsizing while piloting the boat from inside the cabin. The boat is currently being tested so I can’t claim any success at this point, however, the boat was designed for cold weather operation.
You seemed to have moved your cruising grounds…!!!!
If you need insulation, James’ suggestion to use it as the core of a ply / insulation / glass sandwich is absolutely the way to go. I would use end grain balsa especially for the bottom and kevlar under glass sheathing as well on the bottom.
Or you could thick strip plank (using wide boards) with Paulownia (Kiri), which has an abnormally good insulation value. It is a light colour (looks like balsa) for good light reflectance in a narrow confined proa hull, and it has almost the equivalent strength of cedar….. It is also inherently fire retardant in case you decide to fit a wood heater as well…...(joking)
You could (with a little extra work!) regain your 100mm lost to the interior height/clearance by foam insulation and gain an extra 50mm clearance (and overall freeboard) by placing structural (corecell or similar pvc) foam on the outside of the keel and deck and skinning it with either f/glass or another skin of plywood. You could go lighter with the ply which would now be on the interior side of the resulting sandwich to gain back some of the increased weight (which would take a little of the increased freeboard away). Structurally, your proa will be many times stronger/stiffer using a sandwich with structural foam than sticking or spraying on foam (with no second skin) on the interior side of the plywood
That’s actually an all-around worse way to go about it.
A foam core will better insulate the boat than plywood will, absolutely true. And a thick foam core will make the vaka skin extraordinarily stiff, also true, though the strength of the sandwich will end up limited by the strength of the glass/epoxy skins, and there is definitely a point of diminishing returns in regards to the value of the stiffness of the hull skin of the vaka. The problem is that corecell a500, for example, has a thermal conductivity of 0.04 W/mK and a density of ~100 kg/m^3 whereas polyisocyanurate foam board has a thermal conductivity of 0.023 W/mK and a density of ~40 kg/m^3 and XPS has a thermal conductivity of 0.029 W/mK and densities as low as ~20 kg/m^3.
To get the same level of insulation as 50mm of XPS board (about the same thermal conductivity as the sprayed in PU that Manik did his calculations on), the structural foam core would need to be ~70mm thick. Compared against a 9mm okoume plywood core with equally thick grp skins and 50mm of XPS, the all-foam core option would be 10mm thicker, 1.3 kg/m^2 heavier, and a lot more expensive. The ideal combination would be perhaps ~12mm corecell core and ~37mm of rigid insulation boards which would be ~10mm thinner and ~4 kg/m^2 lighter than the plywood/xps hull with roughly the same insulation value for not a lot more money (but I’d still want plywood for the bottom, personally).
Besides stiffness, you also need impact->penetration resistance. Thin skins on either side of foam do not give you very good penetration resistance. A single, appropriate thickness plywood with a layer of glass/epoxy does much better with impact penetration resistance. Although with expensive carbon and kevlar cloth this might not be true.
Although with expensive carbon and kevlar cloth this might not be true.
Nope, still true. Carbon just lets the skins be even thinner/lighter with the same tensile strength, and Kevlar is more abrasion resistant and a bit tougher, but neither will stop a rock from turning a foam core into mush. Which is why I said that I would want a plywood bottom in any case, as IMO foam has no business being on the bottom of a beachable flat bottom boat.
I definitely agree with greg and skyl4rk on this one. Foam on the outside will turn to mush sooner or later, even if it weren’t for the beaching. Today I spent a couple hours getting the skin weight estimate and the thermal calculations all down into a spreadsheet so it’s easy play around with the numbers, even for multi-layer setups. My thinking was, and still is, to have 6mm Okoume with a single layer of 200 or 250g/m^2 glass over it on the outside. Inside the cabin I would then have approximately 50mm insulation laminated onto the panel, with a bit of framing, and a 1.5mm plywood panel over the interior insulation foam, to get that nice wooden look again, and more importantly to prevent the interior foam from being turned to mush through abrasion, standing on it, etc.
With my present estimate I’m getting around 9.4kg/m^2 for cabin panels, and 6.7kg/m^2 for non-cabin panels (which don’t have the insulation or extra 1.5mm plywood). I’m hoping a total of 3mm epoxy is enough to get the wood coated on both sides, glass laminated on, and the insulation layers and covering plywood bonded together. Maybe that’s being way too optimistic though?
Do I have to glass both the inside and outside, or would glassing on the outside be enough?
Cheers,
Marco
P.S. - I’ve opened up another thread where I explained what I have in mind for heating and ventilation, so things don’t get all mixed up here. 😉
P.P.S.:
You seemed to have moved your cruising grounds…!!!!
Well… I wouldn’t say moved my cruising grounds, more like extending them a little. 😊 The Wadden Sea is my #1 destination, but if I can take the boat further north / have a longer season, then that would definitely be a nice extra.