Steel deep V proa, now on Youtube
Since my deep V thread has gone in a unexpected direction (steel) I start a new thread about my steel proa experiments here.
I am building a scale model as usual, but this time I build it out of steel.
Today I bought a 1000X2000X1,5 mm steel sheet. I hope I can weld 1,5 mm steel without burning holes and excessive distortion. We will have to see I suppose.
I will use 2,0 mm 6013 electrodes with my AC welder. I want a TIG welder, but can not afford a suitable TIG at the moment, so the AC MMA will have to do. (At least I will have something to blame my failures on!!!)
I will try to share my plans and post pictures of my build for anyone wanting to know how I build my steel deep V vaka.
Cheers,
Johannes
Since the steel sheet is 2000 mm long that will be the length of the sides of my steel deep V vaka. I like to keep it simple, and I need all the displacement I can get. It is 1,5 mm steel. It seems like most people consider 1,5 mm steel plate to be excessive weight for 16 - 24 foot proas, and this is going to be a 6 1/2 foot vaka with a total displacement of about 6 kg.
I choose 1,5 mm thickness based on me hoping to be able to weld it. I would much prefer 0,5 mm steel but than I would have to rivet or copper/bronze braze it with the TIG I do not own…
200 cm long sides gives a 199,4 cm long hull, so that is going to be the LOA of my vaka.
199,4 X 18,3 X 15,6cm (L X W X H).
By some simple aproximations/measurments I get the total amount of steel sheet in the hullsides to 0,47 squaremeters. 0,47 X 1,5 X 7,9 (amount X thickness X density) = 5,5695 kg.
By the same simple measurments and aproximations I get the expected displacement for the designed waterline to about 6,3 kg. I will not need any frames, since it will be so extremly overbuilt anyway.
If I were to scale this design to a fullsized 65 foot steel vaka I would not use 15 mm (5/8 inch) steel plates, even if I use 1,5 mm now.
Based on my two previous deep V scale models I have choosen 130 mm keel rocker and 50 mm deck rocker - the two points my penciles show in the picture below.
I will draw the lines with two pieces of plywood, and then I will cut out the pieces with a jigsaw and a metal blade.
Cheers,
Johannes
A great youtube chanel for learning how to weld.
I have learned 99% of everything welding I know soo far.
I can really recomend his videos to anyone who wants to learn how to weld.
Cheers,
Johannes
This is all probably obvious for everybody here on this forum, but this is my very simple way of drawing the keel radius and the shape of the gunwale/deck radius.
Now I will cut out two pieces in this shape with my jigsaw.
It is raining outside, soo I will probably wait for some better weather.
Cheers,
Johannes
One more picture.
I have 5 cm deck-rocker and 13 cm keel rocker.
Cheers,
Johannes
The rain stopped for 45 minutes.
I cut one side with my jigsaw, and that was very interesting. 1,5 mm steel is much harder to cut then 24 mm plywood. I get a lot of confidence in steel when working with it.
One side has a weight of 2875 grams so the hull should weight 5750 grams plus 30 - 60 grams more from the welding rods. With some paint and about 150 grams from the crossbeams I make that 6,0 kg.
I have designed this hull to have an intended displacement of 6,3 kg, so that leaves 300 grams for rudders, rig etc…
Not too far of.
If we scale these figures 1000 times we get a 65 foot steel hull with a weight of 6,3 tonnes. I would not use 15 mm steel plates in a 65 foot multihull, since that would be a stupid way to design a structure like this. With one third of the plate-thickness we get 5 mm, and we have 4000 kg left for frames, interior, deck, cargo and all the other stuff needed.
I know this is controversial, since “everybody knows” steel is heavy. I tend to think that a 6 kg steel vaka is almost as light as a 6 kg carbonfiber/epoxy vaka, even though the CF will cost a lot more then the steel.
I know one can build a much lighter structure in foamcore-CF, but for cruising I prefer the extreme toughness and low cost of steel.
I am scared shitless of the welding I have to do. I have only 2 hours of welding experience, and I have to weld 1,5 mm steel sheets with an AC buzzbox….
Cheers,
Johannes
I am scared shitless of the welding I have to do. I have only 2 hours of welding experience, and I have to weld 1,5 mm steel sheets with an AC buzzbox….
If it proves too difficult, you could probably get away with just making a few tacks and then running a fillet of JB Weld (or the European equivalent) along the inside. But, ironically, it’s an epoxy. 😉
But, ironically, it’s an epoxy. 😉
Lol!!!!
Thanks old greg!
I guess I will start with just tacking it together, but then I will try to weld half inch long beads, backstepped and spread out all over the keel. I will try to weld with as little current as possible. I really don’t care much if the welds are a little cold with less penetration, since it is ridiculously overbuild anyway.
Today I cut out one more piece. I have both sides and once the rain stoppes I hope I can start tacking it together.
I placed the pieces side by side so it is easier to see the distribution of rocker between the gunwale and the keel.
I want the ends low to keep windage and CoG down, but still high enough to ride above the surface even in big steep waves. It is always a matter of balance and tradeoffs.
Cheers,
Johannes
I want the ends low to keep windage and CoG down, but still high enough to ride above the surface even in big steep waves. It is always a matter of balance and tradeoffs.
Johannes,
Out of curiosity, how much freeboard are you expecting on your 20 metre yacht at your target load displacement of 6300kg??
Cheers,
Rob
If I were to build a 20 meter long steel deep V proa today, based on this scale-model, it would have about 60 cm (24 inch) high free-board with a lot of flare. From this gunwale there would be about 15 cm high “side” with a lot of tumble-home (?) and then the deck.
I test welded on some scrap pieces from the same steel-sheet. (see first picture below).
I was very surprised by the simple and easy welding. I had to weld a little faster then I am used to, but it was not very sensitive. I did burn a few small holes in the hull but nothing that is not easy to patch with small weld.
I have done about two thirds of the weld along the keel. The hull is extremely stiff and feels very strong. I could probably sink a modern yacht with this hull. Even if I press my hand very hard into the side of the hull, the steel-sheet does not bend much (1 - 2 mm at most). This is without a deck, frames, bulkheads or stringers.
I am very impressed by this very simple shape, and the extreme simplicity of welding it together.
The last picture is of the ugliest weld (long-arc-blob-splatter-feast) I could find on the hull. I don’t want sugar-coat the appearance of my welding skills.
Cheers,
Johannes
Two more pictures of the hull.
Cheers,
Johannes
Picture 1: I can weld about two inch at a time without any visible distortion.
Picture 2: This is no x-ray quality/code quality welds, but with some tacks and some blobs i could fill the small holes and pores I could find.
Picture 3: I am pretty happy considering my 3,5 hours of welding experience. I don’t aim for perfection. It is a scale-model and the first thing I have welded in thin sheet steel.
Best of all is that I don’t feel sick from working with epoxy.
Now I will paint the hull. (It is a one part non-epoxy paint!!!)
Cheers,
Johannes
If I were to build a 20 meter long steel deep V proa today, based on this scale-model, it would have about 60 cm (24 inch) high free-board with a lot of flare. From this gunwale there would be about 15 cm high “side” with a lot of tumble-home (?) and then the deck.
Johannes,
Are you sure about your freeboard calculation? Is it not nearer 42cm than 60cm? Plus 150 tumble home of course, which makes 57cm freeboard.
In any case, freeboard at 75cm for a 20 metre boat is very low. That is table height?? With the top 15cm tumblehome deflecting green water up over the deck. It will be a submarine??
Rob.
Are you sure about your freeboard calculation?
No.
In my past two deep V scale models my calculations where reasonable correct, and I have not changed much except the over all size and intended displacement. I hope I have not made any mistakes in my design and calculations. I hope to have this model in the water sometime next week, and that should answer this much better then my calculator and measuring tape.
In any case, freeboard at 75cm for a 20 metre boat is very low
It is low compared with modern monohulls and bridgedeck catamarans, but not compared with kayaks and Hobie-cats. The height of the freeboard is based on the intended displacement, not length, and with lots of flare in the freeboard you can make them lower (within reason of course). It is actually more a question about reserve displacement, and I like to have about 3 times the displacement as a reserve in the freeboards.
This is all based on my experiences with my scale models. I have loaded them down with rocks and tested them in waves. I can load my green deep V proa down to a total displacement of 6 kg before I see water coming up on deck when sailing in 25 - 35 cm high waves.
This will also be tested once I get my model into the water. I hope I can load it down to a total displacement of about 9 kg without excessive amounts of green water coming up on deck.
Cheers,
Johannes
What is your Bmax (or the included angle between the sides)???
Thank you for doing this experiment. If you were building a hull of a length of about 10m, how thick should the steel be?
Do you think that the weld is strong enough to stand up to grounding?
What kind of paint are you using?