Deep V continuous rocker proa. version 2.0
I have sailed my model. I loaded it down with 2,42 kg of rocks for a total weight of 4,83 kg. That equals 4,83 tons for the full sized deep v proa ( 64 feet).
I tested it without the added weight, and it was a little faster, but not as big difference as one might imagine.
There was very little wind, and the wind was changing all the time, so it is a quite boring video. I post it here anyway to document the steps I take in the development of this proa.
Cheers,
Johannes
Gourgoes shape to the vaka, there is something VERY right about fore and aft symmetry compared to cat or try hull
Tink
What happened to your 24’ er?
I must update my respons to that question a little bit. These last 2 months I have been learning how to weld and work with steel, instead of plywood and epoxy. I notice I often feel really bad after working with larger amounts of epoxy, even though I use a mask and work outdoors. I have been drawing steel versions of this deep-v proa. I believe it is the best shape possible for a light weight and easily built steel hull.
The Swedish company SSAB can deliver a high strength easily weldable steel quality called Domex 550W and 650MC in large sheets, which cuts down the amount of welds and the time to build it. Both are very strong and tough. I could use quite thin steel plates.
I want to build a model out of steel, but I find it hard to weld 1 mm sheets with a simple AC arc-welder and 7018 electrodes.
I have been thinking about just tacking it together and filling all the cracks with some caulking instead, but that does not give any real indication of strength and stiffness.
According to my calculations my 24 foot vaka would become a 27 foot steel-vaka and have a weight of about 240 kg (3 mm Domex 355W “Corten” steel). If I build a larger one I will consider the higher strength steels Domex 550W or 650MC to save weight and get a stronger and tougher hull.
This is just ideas at the moment, but I am trying to find a way around my problem with working with large amounts of epoxy. I love working with steel. I think it is a very exciting material.
Cheers,
Johannes
Gourgoes shape to the vaka, there is something VERY right about fore and aft symmetry compared to cat or try hull
Thank you Tink! I really like the long overhangs and the very sharp pointy ends of this kind of hull. They behave really nice in waves, and have a very soft low harmonic fluid motion.
Cheers,
Johannes
I could use quite thin steel plates.
The problem with using thin steel sheet is that if you use steel that’s thin enough to be just strong enough, it won’t be anywhere near stiff enough, and if you use steel sheet that’s thick enough to not oilcan you will end up with a very heavy boat. Steel just doesn’t scale down well, it’s great for large and/or heavy boats, corrosion issues aside, but for a 27’ proa I think you’ll be very disappointed.
I think your best bet would be to work on ways to limit your exposure to epoxy before you abandon it altogether.
I notice I often feel really bad after working with larger amounts of epoxy, even though I use a mask and work outdoors.
What kind of mask were you using?
If you were having your epoxy sensitivity problems while wearing shorts and a t-shirt with just a paper dust mask then there are a lot of things you can do to lessen the unpleasant effects.
Not all epoxies are same regarding toxicity and sensitivity.
For me a general rule is that the 2:1 type systems are much more benign than the 5:1 systems.
The only exception is the 2:1 high strength structural epoxies used in composite aircraft; that stuff is truly toxic.
Cheers,
Skip
I have been using the recommended gas-mask and long sleeve skirts and pants. I am extremely careful not to get any physical contact with the epoxy. I use plastic gloves which I change regularly.
The epoxy is Nils Malmgren NM275. NM275 PDF
It is known to be much kinder (less toxic) then West epoxy, but I have never used anything else, soo I can´t compare.
The problem I have is my CFS. I am allergic to a lot of stuff like gluten and nuts and seeds, and my body is prone to allergic reactions to a lot of stuff. Small amounts of epoxy is ok, and more soo when working outdooors with a mask. It is autumn here and getting too cold for epoxy outdoors, and that means waiting untill May next year for any outdoor work. I don`t have any barn or shed of any kind.
I can weld steel outdoors any time of the year. It is not sensitive to cold and snow, even though I would probably heat any steel slightly if it freezing cold.
3 mm steel plats are quite stiff. If I use some stringers and frames, I don`t think oil-canning will be much of a problem.
Steel is much heavier than plywood, but I don´t thing 240 kg is very heavy for a 26 - 28 feet vaka.
Cheers,
Johannes
Have you considered doing radius steel? Curving the panels will add a lot of stiffness and you get a more efficient hull. Also have you considered aluminium?
-Thomas
I have been considering aluminum since it is a light weight and strong metal, but I do not like its shortcomings. Steel is much tougher and will resist abuse that would shred an aluminum hull to pieces. When we go cruising we are not very careful and cautious with our boat. We like to moor our boat alongside cliffs and old worn down jetty, and have spent many nights banging the boat into a jetty with every wave. That is not a very nice way to spend a night, but sometimes we have not found anything else before dark. We don´t like marinas or other crowded places, and we try to avoid them as much as possible. There is lot of places in the world where a tough and impact resistant hull can be the difference between nice cruising or death.
Aluminum is also very expensive compared to steel. I like to test stuff to get a “feeling” or reality on it. I have tested to break apart a piece of aluminum, banged on it with a hammer and twisted it with pliers and compared to steel it will break apart very fast. Usually it looses the strength after very few bends or blows with a hammer, while the steel will resist this kind of abuse a lot longer before it shows any cracks. Even if I use twice the thickness of aluminum it will not resist abuse as long as the steel.
I know I seem to be some “weight insensitive loony” who should be building heavy tug-boats instead of flying proas, but my experience is that some weight only makes the boat behave better in heavy weather. A Colin Archer rescue boat is my idea of a very safe boat for blue water cruising in the north Atlantic. I believe one can use the same principles of design for a proa as a Colin Archer boat. A deep hull with a lot of lateral area, low freeboards with very low windage to enable good control even when sailing in very large breaking confused seas, a low aspect, low CoG and strong rig that is reliable regardless of windstrength. An easily driven hull and big rudders that will control the boat regardless of weather. All these things should make a proa the best hard weather boat possible.
A very light boat in an hurricane will probably go airborne which is quite undesirable.
I really like the simplicity and efficiency of using a multi-chine hull-shape with steel, and I have been reading a lot about multi-chine, radius chine and origami steel boat design. I have made some simple paper models of origami hulls, and I believe that is a viable way to build a strong and good shape from simple steel plates with few welds and cuts.
It seems to be especially good for proas with two symmetrical ends, as it is a simple shape and it is easy to get a fair and smooth shape with minimum welding distortion from quite thin sheets. An origami vaka could be built from aluminum, plywood, flat sheets of fiberglass and epoxy, Duplex stainless steel, Monel, Hastelloy C276 or titanium too, depending on the budget.
I do like the extreme simplicity of the straight sided deep-V hull, and they seems to be stiff enough with very little internal framing or structure, and will gain much stiffness from added internal structure. There seems to be some nice properties with the straight sided deep-V shape that might not be soo obvious at a first glance. I recommend anyone who is curious about it to build a simple model a test it. I really can not describe it very well in written form here on the forum, but I am very impressed by this simple shape.
Cheers,
Johannes
I have been considering aluminum since it is a light weight and strong metal, but I do not like its shortcomings. Steel is much tougher and will resist abuse that would shred an aluminum hull to pieces…
I like to test stuff to get a “feeling” or reality on it. I have tested to break apart a piece of aluminum, banged on it with a hammer and twisted it with pliers and compared to steel it will break apart very fast. Usually it looses the strength after very few bends or blows with a hammer, while the steel will resist this kind of abuse a lot longer before it shows any cracks. Even if I use twice the thickness of aluminum it will not resist abuse as long as the steel.
Your tests are giving you inaccurate results because they use inaccurate load cases. Bending aluminum back and forth is an extremely fatigue inducing scenario that would never occur in a boat hull.
Aluminum hulls are actually very tough, as evidenced by the abundance of aluminum workboats and skinny water aluminum jetboats (hard groundings at speed are a common occurrence for those guys). Here is an article you might want to read, and this is a quote that gives a pretty good synopsis:
The result in practical terms is that a boat built in aluminum will be far less easy to dent by running into stuff (roughly 29% higher regional yield strength), and will have a slightly higher resistance to ultimate failure (around 12.5%).
I’m not saying it’s the right material for your project, I just don’t think you should dismiss it based on a mistaken impression of weakness.
I knew a chap in BC, Canada who built a V-bottom (Wharram-like) catamaran out of aluminum, and was very pleased with it. I think it was about 30’ LOA and not for sailing, more a live aboard affair, but the hulls were V bottom and went together quickly and he loved how tough, durable, and impervious to rot they were, compared to wood. I don’t have any more details, such as plate thickness, welded or riveted, or weight, but I can try to find his contact info desired.
I agree with Old Greg…....and also the linked article is a good one. Dave Gerr also says the same in his various books on scantlings and boat construction.
Consider also that there are many more yacht builders (mostly French) who do standard designs in aluminium, rather than steel, most aeroplanes (with highly flexing wingtips) are aluminium. Those that aren’t are either carbon fibre composite or wood and fabric. All of the worlds high speed wave piercing catamaran ferries (see incat website) are aluminium. Even cars, the more high performance, the less steel and the more aluminium and FRG composite.
I would probably use aluminum if cost was no issue. With 2 X plate thickness and a good close spaced internal structure aluminum is very strong and tough. It does not take abrasion as well as steel though.
Aluminum is more expensive, even when the weight difference is considered. At roughly 6 times the price and 1/3 the weight and 70% of the strength, it is at least twice as expensive. I have never welded aluminum, but I suppose I could learn if I wanted to. I have grown up with a steel boat, so I am used to and value the toughness and ease of repair of steel.
Aluminum has a quite low fatigue limit/resistance (which was the point with the tests I made), and in an environment of cyclic repetitive stress (waves, the rig and mooring etc….) being the main load, that seems like a bad combination.
I have seen a lot of aluminum canoes and small boats with cracked plates, but I have never seen a steel boat with cracks in the hull plating (except for accidents).
Steel is much more forgiving of bad welds and simplified construction, and is much easier to repair in third world countries.
Yesterday I uploaded a video of some deep-V proa scale-model sailing.
Some sailing
I point my arm into the wind several times to give a reference for the upwind performance of my little scale model.
It is about 45 minutes of sailing condensed into 8 minutes of video. I try to sail it in every point of sail, but the wind is very uneven.
Cheers,
Johannes
I designed this boat to weight 3,2 kg. Yesterday when I was sailing it it weighted 3,3 kg. It sits at the designed waterline.
A 59 feet (18 m) steel vaka will have about 35 m2 steel plating. If I use 6 mm thick steel plates (1/4 inch) the plating alone would weight 1660 kg. That is half of the designed weight of the vaka. This might seem like excessive thickness, but it will simplify the hull. I don´t need any stringers as long as I have enough frames and bulkheads. I will probably use 2 stringers on each side down around the design water line anyway, and a heavy duty square tube along the outer side of the gunwale.
This is just my ideas at the moment. I will run a lot of calculations before I commit to any real build. I write this just to give an idea of what I have in mind. Probably 4 mm thickness is enough, especially if I use high strength steel like Domex 550W.
Thinner plates requires more framing and stringers, which I try to avoid. There is always a balance between light weight and simplicity. There is always a trade of at some point regardless of what kind of material is used.
Cheers,
Johannes
This video above shows the rational I have for a strongly built steel proa. I don´t think any sane person would like to sail an ultralight all carbon fiber/foam core racing proa in those conditions with their family aboard. I really hope I never encounter nasty conditions like that, but since I am living this far north and dreaming about sailing to Greenland, Jan Mayen, Iceland, Faeroe islands and the Outer Hebrides, I have to plan for surviving stuff like that. I believe a proa is the ultimate hard weather sailboat, if properly designed for it.
When looking at catamarans and trimarans at 55 - 65 foot length I came to realize that 3,5 tons is not very heavy. Most non racing multihulls in that size is much heavier. My deep-V vaka is extremely minimal considering the length, and that probably explains why I can keep the weight down despite using steel.
Cheers,
Johannes