Somewhere between a Deep V hull and a Bolger Advanced Sharpie
Hi all!
I have been exchanging some mails with Dave Zeiger of Triloboats.
Triloboats blog
A barge in the making blogspot
He gave me the idea that I could build an advanced sharpie, but permanently tilted 45 degrees, and add freeboard on top of that 90 degree V hull.
This way the vaka will have a very clean and hydrodynamic efficient shape, but still be easy to build of any sheet material. I could even add a chinerunner to the keel-line of the V.
All this is based on the works of Phil Bolger which we share a deep respect for.
As usual I am building a scale model of steel sheets.
Cheers,
Johannes
By keeping the 90 degree angle in the bottom V part of the hull, it is very easy to design and build. Most sheets have 90 degree angles and edges. It will also be a bit wider at the waterline then a “normal” deep V hull, giving more available displacement for a given size.
It is going to be 197 cm long, 21 cm wide, 11,5 cm deep and have 10 cm high freebords. I could easily add more freeboard if I could weld thinner steel. I have calculated the weight to about 10,0 kg and the max total displacement (the chines between the V and the straight sides at waterline) to about 12,5 kg.
I was searching around for V-shaped hulls and found Jim Michalaks Weevee and Vireo rowboats. He argues that the clean V shape is faster/low drag because the water is free to flow as it likes around the hull, as there is no curvature except between the fore and aft. If the V has some curves except the rocker, the bulging sides will try to force the water to go the shortest route around the hull, which might not be the most straight and least drag.
Both Jim Michalak and some builders say that Weevee rows much faster the classical wave-theory dictates, and faster then other boats of the same length and width.
I think this is very interesting stuff, and I have found the same behavior in my deep V hulls - as long as I keep the rocker a clean circular arc shape and the hull sides flat (no forced extra curvature in the steel or plywood).
Cheers,
Johannes
I fired up Moby - In this World - on Spotify and put my welding helmet on.
Perfect calm music for welding.
I have just tacked the hull together. I will probably weld the rest tomorrow. This time there will be 4 long welds in thin sheet, as there are one chine on each side.
Cheers,
Johannes
This looks promising…
Thanks Michael!
I post two more pictures to show the hull-shape. This is just the underwater-body, and there will be vertical sides on this later. I must cut them from my steel sheet, but I hate the noise and the sharp steel sawdust blowing in my face (I wear goggles). I have to buy a plasma cutter soon.
Cheers,
Johannes
Today I cut out the pieces for the sides of the hull. I have not welded the bottom to the sides yet. It is all held together with with duct tape. I hope I can start welding tomorrow.
I do like the looks of it, and I hope to have the hull floating before the ice covers lake Mjörn.
Cheers,
Johannes
Today I have tacked the bottom and sides together.
I use about 45 amps current, which is quite low for 2 mm 6013 electrodes. I still burn some small holes here and there.
I use 2 pieces of flat bar as stems.
The hull is extremely stiff even though it is only tacked together. I tried to prey the sides apart a little bit, and even though I am quite big guy I had to put some muscle behind it.
Cheers,
Johannes
I want to show how easy it is to weld together the bottom part with the sides on my new steel scale model.
I love the fast progress and very forgiving method. Just duct tape the pieces together and then tack them with short welds. I can hold the pieces together and in the right position with one hand and weld with the other.
No drilling holes, no cable-ties, no waiting for the epoxy to cure. I can weld outside even though it is late autumn and -2 degrees outside. No mixing epoxy, no wiping the surfaces with acetone etc etc…..
The low amperage is the reason I sometimes have some problems starting the arc. I weld with about 40 - 45 amps, which is very low current on 2 mm 6013 electrodes. I prefer cold welds to burning holes through the steel.
Cheers,
Johannes
Holly cow, you’re using a stick welder?!?!
Wait until you try MIG. Its MUCH easier to get a beautiful weld. And it almost never sticks to your work piece the way a stick welder does. You’ll burn a lot fewer holes too.
If you want to do really nice work, with tons of control, TIG is the way to go. But if you want to stitch stuff up nice and quick, MIG is basically as easy to use as a hot glue gun.
I am welding outside and I am afraid the wind would blow away the shielding gas if I use a MIG or TIG.
I don´t know why, but I don´t like MIG welding. I have never tried so I can not really explain why.
I will learn TIG welding as soon as I can afford a TIG torch and a bottle of argon gas. I want to weld stainless and copper, and TIG seems to be the best way to weld those metals (low heat input, good penetration, good precision, very clean welds, etc).
Cheers,
Johannes
I have welded every seam, and grinded every weld almost smooth. There are some holes I will weld over and then I will grind and sand everything smooth.
I hope I can throw it into the water soon. Tonight it was snowing, and I am afraid the lake will freeze very soon. I am racing the winter to try my new proa.
Very nice!
I just saw your welding video on youtube, and was surprised to say the least!
I’ve been working on a complete redesign of Firstborne in camper cruiser size for the last few months, and our hull designs are really similar: deep-v below the waterline, and vertical sides above WL. Easy to build, and you get the comparatively high draft and (hopefully) smooth motion of a deep-v hull, but without the performance penalty of flared sides when going through a chop. Makes it a lot easier to build too.
I really like how easy your geometry is to build compared to mine, because you can actually take flat panels for the section below the WL as well; I can’t, as I have vertical sides, but an ogive deep-v. I’ve started building a 1:5 model of the vaka to see if plywood can be convinced to take on that shape, but if not, you’ve presented a great alternative here. 😉
Personally I think there a couple other nice things about this particular hull geometry; in terms of weight, freeboard comes a lot cheaper when you’re going up vertically instead of having a hull with flare (it really makes a big difference if you want a moderate amount of height; I was quite surprised when I saw the numbers), so you end up with a fairly light hull for X amount of freeboard.
Another thing I noticed while mucking about with a CAD program is that increasing freeboard at the bows, while leaving it as it is at the middle, hardly increases the weight. I’ve got 55cm at the bows and a bit over 30cm in the middle, over a length of 7.2m. That helps shave off a good deal of weight as well, and you get the extra freeboard and buoyancy in the bows where it’s needed most. The resulting sloped deck is problematic (geometrically) for a bermuda rig, but for a crab claw it should be fine.
Chances are your model is going to hit the water sooner than mine, so I’m really curious to see how it performs! Keep it up! 😊
Cheers,
Marco
P.S.—And no, there’s nothing on Firstborne 2.0 on proafile just yet, but I intend to post soon, I just have tons of other work on my hands at the moment. :(
Thanks Marco!
I agree with your findings about freeboard and weight. I think this is a very good hullshape, and not much more complicated then a barge or deep V. I don´t want to say much about it before I test it, but I do hope it will be a nice balance between the deep V and the ASP.
It is very easy to build in steel, with lots of potential displacement for using a build method slightly similar to “Strongall”, with thicker plates and fewer stringers and frames. The chine really adds lots of stiffness to the hull compared to the simple deep V shape.
I got the idea from Dave Zeiger, and I hope I can “review” it once I can get it into the water.
I hope we can see and read about your revised Firstborn 2.0 soon.
Cheers,
Johannes
Dashew Offshore Heavy Weather Issues
Good reading. Partly explaining my keen interest in steel hulls.
We have the structural capability to drive hard into big head seas. We like knowing that we can push just as hard as we can personally stand, without worrying about bending the hull!
A quote from above link that pretty much sums it up.
Beowulf Sailboat 27 knots - Autopilot
A comparably heavy ballasted aluminum monohull maintaining 25 knots in heavy seas.
Imagine redistributing that weight to a much more slender hull with longer water-line length, much higher righting moment and a more powerful rig. I can not imagine why it could not be fast even though the hull would be made of steel?!?!
Cheers,
Johannes
I tested my new 90 degree V steel vaka today. Since my crab claw sail and mast blew away and sank last time i tried to sail a scale model - I could not sail my new scale model today.
It is by far the most heavy proa to date (10,8 kg). This was very noticeable when I tried to pull it through the water. There was much more resistance then my much lighter plywood deep V hulls and my red barge hull.It is 20 cm wide at the waterline, and that is more then twice the width of my green Deep V hull.
I do like the calm smooth movement when it is riding softly in the small waves.
It will keep on moving through the water a long time after I pulled on the cord. It does not slow down much when moving through a wave. I don´t belive it is as fast as my deep V proas, but it will probably be able to keep a good speed even in very steep and confused waves, just slicing through anything that comes in its way (powerboats, nasty chop, semi submerged shipping containers, logs etc…)
Cheers,
Johannes
I like the clean wake and the slight bow up tendency.
There is some pitching in the video, but I am happy it is not worse then that.
Since the weight is evenly dispersed along the whole hull, the ends are way to heavy. On a large proa this would not be a problem, since the the cargo, food, water etc is stored in the middle of the boat, and a much less percentage of the weight is in the hull-“skin”.
Cheers,
Johannes