Dave Culb has posted another thread around this possibe shape, his graphics are better and more understandable.

http://proafile.com/forums/viewthread/408/

Michel

luckystrike118 - 25 June 2014 06:07 PM

Hi Marco,

the 5.4 Ama should be long enough and it is absolutly not neccesary to hold the 20:1 Ratio. A 16:1 is more than enough for a very low resistance hull.

Foam and Glass is a possibility, but be aware that if you shape it from a full block of styrofoam (styrodur, jackodur) foam (30kg/m³) it will weigh a lot. Better to build it like a moth dinghy with 3cm thick walls and foam bulkheads. Glass over with around 500gr/m² glass and epoxy. Wheight will come out similar to strip planking.

A good possible wavepiercer design could be the “optimum hull” I found in a old book and posted some time ago. You just have to make ist equal fore and aft without the 90° rotation of the shape at the middle bulkhead.

Minimum surface, good volume, good hydrodramatics, low resistance.

http://proafile.com/forums/viewthread/197/

Best Regards, Michel

You’re the man Michel! 😉

The 10kgs of wasted displacement of an all foam ama were bothering me. I figured about as much where the 5.4m length of the ama was concerned, and I liked the max displacement values much better too with a lower L/B ratio just like you suggested. I did all that about a week ago.—Building it in foam on a mold in quarter sections is brilliant though, I love it! 😊 It should be really fast and comparatively easy to build.

What kind of foam would you recommend using? Seeing as we don’t live that far apart, is there any particular manufacturer / product you could recommend perhaps? Something like Airex costs >100€/m^2 at that thickness, so there’s no way I’m using that; some normal much cheaper foam would be just fine in my opinion; when the laminate gets soft and mushy, I can just build another one, especially if I have the mold on hand. 😉

I’m thinking an open male mold (just a ‘skeleton’ if you will) might be the easier mold type to work with; you can fill the gaps in the foam with foam wedges directly. If you don’t put foam in the cracks right away, because you have a female mold for instance, I’d be worried about the epoxy running into the cracks en masse.

I found this little 7 page handbook on building a carbon and foam moth. While I’m going to be using cheap foam and fiberglass, it’s making good reading so far so I thought I’d share: http://www.teknologika.com/mothblog/content/binary/HomeBuildingACarbonMothPart1.pdf

Setting up the frames and all is pretty much the same procedure as with strip planking. There’s a second part as well (9 pages), on building the foils. There’s probably some pretty useful stuff in there between the two documents. 😊

Cheers,
Marco

Hi Marco

I think you misunderstood me.

There are a few materials that work on a that quartermould. A cheap insulation foam as a sandwich material between two layers of glass will NOT work! Because the insulation foam has unsufficient sheer strength, important in sandwich construction. If you want a classic sandwich construction, there ist no other foam (I know of) than the Boatbuilding Foams like airex or símilar. For a hull like your Ama take 400gr/m² glass outside, 9-10mm foam (60 - 80kg/m³) and 220gr/m² glass inside, bulkheads as required.

The chaep solution
Is the insualtion foam with 30 - 40kg/m³. This one is shaped in form like you do it with a surfboard, then glassed over. To get it lighter build up the blank like a moth so that there is air in the middle and reasonable thick walls when the shaping is done. You can use foaming pu-glue for the bond between the foam sheets. Before glueing sand the foam surface, because the factory surface will not stick to the glue. The rest as discribed.

The quarter mould
No matter if male or female (i would prefer female) you can laminate two 3mm veneers (and glass outside and inside) onto / into the mould.
Or laminate two layers of 3mm plywood (good industrial quality with wbp glue) and glass or not.
Or you can strip plank it and glass over inside and outside.

These are the posssibilities building the Optimum Hull with a length of 5.4m

Do not try out a sandwich wich surely will give someday up just because of cost. If it breaks at the wrong time you can loose your life!!!!

When you decided for a material or buiding method call me and I will make you a glass layout for the choosen material.

Best Regards, Michel

The link you posted some hours ago is a high tech moth, meaning build with airex or so.  I mean something like a low tech moth….

This is the link to the frizzz moth made from insulation foam. And a interesting forums thread about moth building (or better the beginnung of it but you will get some informations

http://imoth.mottenfieber.de/class/ifrizz/ifrizz.pdf

http://www.boote-forum.de/showthread.php?t=135471

Best Regards, Michel

Way to talk right past each other… :D Would have been way too easy. 😉

We’re essentially talking a moth-hull-shaped plywood box on the inside, with (cheap) foam all over it to give the ama the requried overall shape, where the foam bits that go over the plywood box are made as quarter-sections in a mold, correct?

4mm airex is apparently enough for a foiling moth (loads will be higher in a coastal cruiser though), and 4mm Airex still costs around 30€/m^2, so I’m still not really jumping at the possibility here, I like the above better…

Cheers,
Marco

For the shape you are looking at, strip planked foam might be an option. Use regular extruded insulation foam (2#/ cubic foot) Make two halves then glue together. A little more work but it will give you the lightest low tech solution. My old rule of thumb was once structure got more than 3” thick it was lighter to go with sandwich consruction rather than solid foam.
http://www.duckworksmagazine.com/09/projects/easyb/index.htm

Skip

I’ve been pretty frusterated by the lack of time I’ve had for my project lately (and the lack of progress), but today I reorganized the garage a bit to make some space (had to get a bit creative with the canoe :DD), and then started construction of a full scale mockup of the cabin (the middle 50% of the vaka). Materials are cheap 24x48mm timber (the cheapest I could find, at 0.32€/m) and a roll of painter’s felt to tack over the rough structure when it’s done. That comes in at somewhere around 35€ total, so definitely worth the investment.

The intent is just to be able to sit inside and get a real intuitive look and feeling for how much space would be available in the boat. I did design it to barely exceed what I thought were the minimum dimensions for a cabin, to keep the weight of the boat and the required labor as small as possible—now I’m eager to see if the solution is actually workable though, or if it’s simply too small. 😉

My first impression after seeing the first couple of parts, is that overall the boat is really small, it really isn’t much bigger than a somewhat lengthened canoe (who would have guessed? xD). I’ll post some pics when I have some frames up, which is hopefully sometime on Sunday. Stay tuned! 😊

Cheers,
Marco

Good for you for mocking the cabin up, Marco. We can picture space in our minds all we like but the experience of space is always something different.
I can see your building space is indeed compact!

Looking forward to your pics

Hey guys!

A buddy of mine and I really got cracking for a couple of hours today. We got another two frames built for the cabin mockup, which brings me up to a total of 3 out of 5 frames; the midsection, and two sections at 850mm from the middle. In total that’s the middle 25% of the boat, and the two remaining frames will add another 850mm each, to bring the cabin up to its full size of 50% LWL.

This mockup omits the bottom 250mm of the hull, whcih is essentailly the underwater part of the hull, since I intend to place floorboards at about the waterline height. Below the floorboards there will be space for a car battery in a watertight enclosure, and holding tanks for drinking water, plus a bit of stowage space.

And below come the promised pics:

(1) The three middle frames set up vertically
(2) All three frames up against the wall
(3) Some more boards and a bit of plywood propped inside
(4) Me sitting ‘inside’ the mockup (that’s one happy camper! 😉 )
(5) Relaxing and enjoying the view; to my surprise it seems you an actually lie directly on the floorboards; I’d thought the width at the WL wouldn’t be enough for the shoulders, but that seems to not be the case. I’d planned to span a net at the pod-height to create the second sleeping spot, but I think down on the floor is better; it’s much simpler and the cabin feels much roomier that way too (can’t even reach the ceiling with my arm when lying down there).

It’s a tight fit, but I’m eager to finish up the mockup and spend a couple of nights sleeping inside just to see if it’s really up to what I intend to do with the boat, or if it needs another few centimeters here or there. My first impression is that the width of the pod could use another five.

Cheers,
Marco

Hey guys,

Something just ran through my head: the cabin floor could be placed higher so that it’s above the normal WL of the boat. If I make the floor and its hatches waterproof, then that way the cabin could be self-bailing… Knowing me and my love for fresh air, I’d say the hatch is going to be open a crack no matter what the weather is (I’ll figure something out so it doesn’t rain inside), even if I have additional ventilation elsewhere in the cabin. That means if/when the boat does capsize at some point (it is a very light boat after all), the hatch will probably be open, meaning the cabin will be partially flooded (don’t worry, the underside of the lee pod will have an emergency entry/exit hatch).

If the cabin is self-bailing, then it’s easier to get the water out after a capsize. The downside of course is that requires more height, and with the current fit, I need to add a centimeter to freeboard for every centimeter I move the floorboards up… More height means more weight and more windage, though it does increase stowage space under the floor as well, and stowage space does carry quite a premium on a boat this small. On the other hand, maybe the floor can stay where it is; if after rerighting, the two people wander over to the ama, the vaka should float high enough to self-bail even with the current positioning of the floor. One could argue that, if the weather is such that you capsized the boat, you woundl’t want to have to do that wandering over to the ama, but compared to rerighting the boat, which the crew has already done at that point, going over to the ama to let the vaka self-bail doesn’t seem like that much of an extra hassle.

I’ll try to get a rough guestimate of how much weight it would cost me at some point today. It’s a tricky tradeoff… What do you guys think? Good idea, or is a self-bailing cabin, when the crew is on the ama, good enough in your opinion?

Cheers,
Marco

Hi Marco,
I’m enjoying watching your build and getting some ideas from it.  Nice to have a mock up… and it looks plenty roomy and spacious for that size of boat.
Looking forward to seeing your future installments.
Cheers
Claudio

Thanks for your kind words Claudio! 😊

I was just playing around in Inventor a bit to get an idea of how much heavier the boat would be if I enlarged the pod by a few cm and added a bit to freeboard. I’m going to estimate around 4kg/m^2 for the skin and stringers all together (6mm plywood would be about 3kg/m^2, and then add the epoxy, glass, and stringers).

- My reference vaka design has 24.4m^2 of outside surface area
- Making the pod 70mm wider, bringing it up to just under 600mm width, makes the surface area rise to 24.7m^2, which is hardly an increase (1.2kg of extra weight)
- If I stick with the enlarged pod, and then increase freeboard by 100mm at the midplane and 50mm at the bows, increases the surface area up to 26.0m^2, so 5.2kg heavier than the enlarged pod variant, and 6.4kg heavier than the reference design

So overall we’ve just learned that making the pod a little wider basically costs nothing from a displacement standpoint, while increasing freeboard is rather expensive, though I’ll admit that 100mm is quite a big increase. Overall that’s a very intuitive finding, the pod doesn’t have the full length of the vaka after all, and at constant flare angle, increasing freeboard means the boat is wider at deck height as well, which accounts for the rather rapid increase in displacement.

I think having a clear idea of how much stowage space I’m going to need, would be quite helpful with the freeboard decision. Maybe I should make a list of gear I need, and then try and gather up as much as possible of it on the floor, and see how much space you really need… I haven’t been cruising yet (my experience thus far is with dinghies or daysailing on yachts only)—anyone have a good lightweight cruising supply list on hand? (Link please! 😊 )

Cheers,
Marco

Uhh that was not so clever of me… Before everyone posts their lists of favorite cruising gear here, let’s take that part of the discussion to another thread, so that this thread doesn’t wander off of it’s own topic. That’s better for future reference for everyone anyway! 😊

I got a good 6.5 hours of boatbuilding in today in the afternoon and evening, which was enough to get the remaining two frames finished, so I’ve got all five on hand now. Saturday is the next day when I’ve got plenty of time for boatbuilding, so everything looks good for completion of the cabin mockup then! 😊 I also had a good chat with a buddy about the rig, and some of the peculiarities/details of the design, and that provided some fresh insights as well, so it’s been a great afternoon!

I’ll try to get my (pretty outdated) CAD model back up to the newest state sometime soon, so I can post some pics! The mock-up comes first though, and I need to build a stand for the storage of plywood sometime soon as well, since I’m getting my first two sheets of plywood (one in 4mm and one in 6mm, for material samples) sometime in the next few days.

It feels great to finally be making some hands-on progress, and the mock-up is already proving to be a big help in resolving open design issues, even with only the frames on hand thus far.

Cheers,
Marco