6.3m (20ft8)Steel pathfinder

[turntide]

This boat will be built during the winter 2004. The steel will be clinker form and mostly frameless. The center board and rudder will be formed 3mm stainless sheet. external motor bracket. 2mm galv bottom round bilge, 1.6 or 2mm galv sheet formed sides and nominal 100mm formed planks. 9 each side. Higher than spec combing.
Floor == ply,on steel supports from hull, with flexible connection/seal to hull. possible block foam displacement underfloor flotation. possible rotational molded stowage.
Yawl rig.
Hooped canvas soft top
Any comment appreciated

[John Bell]

What do you reckon it will weigh?

[turntide]

Originally posted by turntide:
This boat will be built during the winter 2004. The steel will be clinker form and mostly frameless. The center board and rudder will be formed 3mm stainless sheet. external motor bracket. 2mm galv bottom round bilge, 1.6 or 2mm galv sheet formed sides and nominal 100mm formed planks. 9 each side. Higher than spec combing.
Floor == ply,on steel supports from hull, with flexible connection/seal to hull. possible block foam displacement underfloor flotation. possible rotational molded stowage.
Yawl rig.
Hooped canvas soft top
Any comment appreciated

[turntide]

If the hull has 20 square metres of metal total and half is 2mm and half is 1.6mm then the hull will weigh 300kgs.

[turntide]

http://www.home.xtra.co.nz/hosts/turntide/turntide%20website%20wheels%20on%20clinker.htm
These pics give an idea of the strength of a light clinker steel hull. The clinker panel here is from 1.6mm mild steel an is spanning 500mm and is 270mm wide. The clinker profile depth is 19mm which is large. the vehcile parked on the panel is a 4x4 toyota landcruiser (rear wheel)The clinker panel is fabricated not continuous rolled. the test panel has minimal shape. It has become obvious to me that plates as light as 1mm could be used for a boat up to 20 ft. the limiting factor is ease of welding with manual arc process which is my process of choise because of its reliable penertration and strength.

[MarkC]

Very interesting!

Im thinking about you bending the 'planks' into the shape - will they take the shape? How many planks (how wide must the metal be) ?

Isnt it a bit thin for arc? Invest in a Mig or tig?? or perhaps copious rivets??

Also, why dont you run your ideas through the designer? - Can't hurt - Test your ideas and get some advice regarding framing or bulkheads and weight - might save you a lot of time and money.

Yawl - I dunno , dont you need more power? Big main, I envisage a cutter.

Thoughts out loud.

Cheers
mark

[turntide]

The wheel thing is just a demo. The shape is achieved by cutting planks out to fit the plug created with frames and strakes. the upsidedowm plug has a chine for every plank.(planks are only nominal 90mm wide) once the plank is cut to shape (8mm over size all round , the 8mm extra is beaten over 90 degrees in opposite directions at each side of the plank to form the clinker profile. Its then layed on the plug and tacked to the previous plank. The arc welding is a proffesional choise. Im a very experienced welder in many processes and know that mig is inferior to stick in many ways. The fact that the plate is thin is just a welding skill/procedure issue.eg tests have shown me that a fast cold run on one side followed by a slower hotter run on the backside of the butt joint works on 1.6mm sheet. But the machine must be a DC welder running negative to hand-piece and positive to earth which is generally back to frount Arc will ensure that the welds are full penertration and can therefore be safely ground back flush The rods of choise for 1.6mm galv sheet are 1.6mm and 2.5mm Phillips 28's(6013)
The Designer approves the system, but I will mention the yawl rig power and see what he says. Somehow I think he'll have a good reason to stick with the designed rig

[ 04-15-2004, 07:15 AM: Message edited by: turntide ]

[MarkC]

Sounds good - Im no expert on welding, I only have read that the Mig and Tig can produce a colder weld/solder. I must admit I am a bit bewilderd by the welding choices - arc, mig, tig, gas shielded, acetelye etc. I guess each has its own benefits.

I have been interested in the steel hull-ply deck combination with its strength and longevity-ease of mainentaince - provided the painting is done correctly.

If its going to live on a trailer and taken back home howabout installing an electric drive with 4 heavy duty batteries as ballast? Charge it up during the week. There is a good article on this in one of last years 'Australian Amateur Boatbilder' magazine.

The web site www.boatdesign.net (http://www.boatdesign.net) have a metal boat building section where you might get more technically savy imput that I can provide.

[turntide]

Mig and tig are more suitable for lighter gauge metals. Tig is really only used to weld high quality components eg ,stainless, Ali, and pressure pipe. as far as hull constrution goes,it doesnt really apply. Mig uses very fine wire compared to stick so can produse a smaller weld pool. hence less heat in job. May sound complicated but is easy once you gt to know a bit about it.
The great thing about wood is that its available to everybody and can be worked with relatively inexpensive tools. One can afford to make mistakes etc. having said that I once saw a believe it or not TV show where an American bloke built a 100ft wooden boat in his back yard in the middle of a town, miles from the sea. When asked what his next project would be he promptly replied "a 250 ft steel boat" mind you he was obviously a bit different.

[Keith Wilson]

Very interesting! As I understand it (and I certainly know a lot less about welding technique than you do) it's relatively difficult not to end up with some waviness in thin plates. This boat is smaller than most steel hulls, and has a lot of curvature in the plates - John always designs very shapely hulls - which should help, and I've read that one can minimize this by welding in the proper sequence so that shrinkage tends to pull it tight rather than loose and wrinkly. Can you enlighten us?

One further thought - How are you going to make the rudder and centerboard? Just a 3mm steel plate would seem to be awfully flexible, since both of these can sometimes get substantial side force.

[turntide]

Unfortunately the pics are off line for a while but they show 1.6 mm sheet metal welded with no distortion. The key to this is the clinker shape. Distortion will not travel past a 90 degree fold from one plane to another. There are of course limits to this but the method described is within these. Its important to grasp the concept clearly. each clinker board of sheet metal represents the outside 1.6mm thickness of a wooden plank clinker pattern. the weld join in each board is along the length of the part of the clinker board that represents the board thickness and is a butt weld. so if a 16mm board representation is required then 8mm of the edges of the board are folded 90 degress in oposite directions and butt welded to the previous board. any distortion that showed, as in any sheet metal work can be completely removed by hammering the weld against a backing dolly to relieve the stresses or stretch the metal. The skills are the same used to repair a bent car panel.

[turntide]

I for got to describe the rudder and center board detail. Ive said 3mm stainless but may use 2.5mm.
Its important to relise the strenght of a steel hollow section. A good example is a car or truck chassis.
The method I will use wil be to form the stainless sheet to form pretty much the design cross-section, in two halfs. If the X section thickness at the widest part of the foil is 38mm then a length of 38x10 mm s/s flat bar will be placed in the hollow section at this point and the two halves welded together along the leading and trailing edges. a cap or end is welded to the bottom and top and a pivot bush is welded in also lead may be poured in ( must check periodic table) and the rest of the hollow section can be filled with another dense resin type material, eg concrete or inert material, to maintain shape under load if required.
A good example of a hollow section foil is an aircraft wing.

[Keith Wilson]

Ah, hollow-section CB and rudder - OK, that's what I didn't understand. WAY stiffer, no problem. I'd bet that the thinner wall would be fine, and that with a couple of ribs filler material might very well be unnecessary. There were a lot of boats built in the US in the '20s and '30s that had galvanized steel plate centerboards, usually 1/4" (6.3mm), and the board was vulnerable to being bent, but thicker hollow ones are another matter entirely.

That's a very interesting method of building a hull in steel; bending flanges on the top and bottom of each "plank" and butt-welding them together, producing a thin shell with steps that duplicate the original lapstrake shape. I can see how it would just about eliminate any waviness in the plank. The welds are almost invisible, so you don't have to be so careful cleaning them up - can you get by without grinding them at all? Very clever. Do you form the flanges by rolling? I suppose you have to - it's a complex curve in both directions. How do you keep the bottom (inside) flange from crinkling? 8mm isn't very big, so maybe it's not a problem.

I know this is the wooden boat forum, but I mostly work with steel and aluminum structures, although rarely sheet metal, so this is interesting to learn about.

[Ken Leap]

Your project is very interesting. I am currently building a plywood clinker yawl (Oughtred's Caledonia Yawl), but have always wondered how a clinker-type hull could be fabricated in steel.

In my new career as an artist (I was an engineer), I am doing quite a bit of welding. I don't call myself a welder yet because I haven't 'paid my dues,' as my welding mentor tells me. I have skinned a couple of sculptures with 1.6mm stainless steel. In both cases, I started with a mild steel frame and covered the frame with sheet metal. My first such sculpture was a 3-foot-diameter ring (for a sundial). To my amazement, the cylindrical sheet metal surfaces actually straightened out the frame (which had minor irregularities)! In this case the frame ended up conforming to the sheet metal, rather than the sheet metal following the form of the frame. As you suggest, curved sections of sheet metal are very stout. This has me interested in frameless steel fabrication. But I know it's not that simple. Controlling heat distortion is a real art and science.

I too plan on a fabricated stainless-steel centerplate (or do you say 'centreplate'?). My current strategy is to create a step-wise linear approximation of a foil by stacking steel plates and then covering the works with 1.6mm stainless steel to create a smooth surface. The leading edge will be a stainless-steel round bar. All joints will be blended to give the look of a solid piece of steel. If it doesn't work out, I'll just plant it in my sculpture garden.

Please keep us posted on your progress and your thoughts.

Ken

P.S. Doesn't welding galvanized steel produce some noxious fumes? How do you handle that?

[turntide]

To answer keith's Question about the crinkle on the iternal bend,yes in theory there is a crinkle but it doesnt seem to matter with only 8mm of fold. The method Ive used to fold the edges is a scribe line and a dolly that has two hooks on it to keep the dolly face level with the scribline. The trailling hook is set 8mm back from the leading hook and fitts over the folded section. so first you manually fold a little bit up to start then use the dolly and beat the edge up and move along the edge taking care not to pound the fold to much and stretch the metal causing the edge to arc. This is labour intensive.
on a larger boat like the pathfinder the plank shape needs to be lifted of the plug/strake pattern usind either a suitably wide length of sheet metal or some other material that will hold true shape. Of course the planks can be made in shorter legnths and tacked together on the boat then welded and dollied to relieve stresses while off the boat then fitted to plug. a good point to metion here about sheet metal is that with any butt weld fit up particually stainless steel, the weld will pull the joint together to close any gap in the joint which can cause a lot of distortion. The secret is to have very tidy fit ups with absolute minimiun gaps in the butt. this is important when tring to create an invisible join. This dosent apply to the steel clinker system as the weld zone is well hidden from the eye and is a very narrow plane.

The stacked and covered keel system sound like it would work as long as you could keep the layers true to the axis. I can see the axis moving which may require a lot of grinding to true the shape.
A lot of carbon steel machines in the pulp and paper industry are clad in s/s which is a sound idea.
Welding a thin skin to a solid round bar can be a challenge. It may be easier to use a mild steel round bar and clad that with a section of s/s tube or pipe then attach the sheath to that

[Ken Leap]

Turntide,

Thanks for the warning about welding sheet metal to a solid bar. I was worried about that and had considered the option that you mentioned, using ss tubing. Now I think I'll start with the latter approach.

Ken

[turntide]

Ken
Just a few more words of caution. Dont use too lighter cladding, also be carfull when welding the cladding on as the heat can build up in the weld pool because of the close proximity of the core. this causes the weld pool in the stainless to spread out. I suggest a fusion weld. Also when working s/s sheet metal we use a system called close tacking where the whole job is tacked together with small tacks every half inch before the main welding starts this ensures the sheets dont move or cross over on you. s/s will change shape considerably when being welded.

[Ken Leap]

Turntide,

What is the 'core' that you refer to? Is this the filler rod or electrode?

So far, I have only used the TIG process for stainless steel. I have a new welder which supports two processes: TIG and Arc. I'm anxious to try Arc welding on stainless steel. Are these both considered fusion processes?

As you can see, I don't speak the language of welders.

I am aware of the need for tacking all around to minimize distortion, but this 'close tacking' that you mention sounds serious--tacks every half inch!

Very interesting.

Ken

[turntide]

The core is the metal plug. Because the cladding is hard against the metal plug the heat cannot escape but is reflected back at the weld pool which causes the weld pool to expand sideways making it difficult to weld. often the cladding will blow through. The remedy is to use a thicker cladding and fusion weld it which just means "weld with out filler wire" this method enables you to turn the amps up a bit and move along the seam more quickly. It allways pays to have a bit of fille-wire in your free hand for when you come to a gap which will need a bit of wire in to fill. You can weld the whole thing with filler wire if you want but it will become apparent thatyou cant weld to slowly and make a full penertation weld because of the reflected head build up that I metioned. The thicker the cladding the less relavant all this is. I think that 2mm would be a nice easy cladding thickness. Its important to remember that eventually you will want to grind the weld off flush. So you will need enough penertration to allow for this. Its when you use thin cladding and try for full penertration that the reflected heat thing happens.
Close tacking is definitly a must with s/s. If your tacks were 2 inches apart the butt join surfaces move up and down as youweld along. so at the end of a run you will find that there is what is called misalignment in the surfaces which is a major concern when you come to grind flush as you will need to remove more of one side of the weld than the other. possibly going beyond the penertation depth. If the plug on the inside is smooth and uniform, tack and hammer the tack back on to the plug as if it were a dolly then do the same every half inch You will find that s/s move twice what carbon steel does so you need to control it as much as possible. All this is done with the tig with a 2.4 or 1.6 tungsten

[Ken Leap]

Turntide,

Thank you for clearing those things up.

Fusion welding on a butt joint sounds tricky. Don't you need a little extra material, one edge turned up or something, to get a good fill?

Using thicker cladding sounds like the way to go.

Ken

[turntide]

No, just a good flush butt. If the joint is hard closed (go gap) then the weld will fuse well with the tig. remember that you will grind off most of the metal you put on with wire filler rod. The secret is to get a good close fit up. This all comes under preperation which is 80% of the job.S/S is not like mild steel in that the quality of the finish begins way back at the start of the job. A grinder will not tidy a rough job up.

[ 04-19-2004, 03:49 AM: Message edited by: turntide ]