Welding a steel hull

Yes the kit includes the material. I estimate that uncut material would be about half the price of the kit.
Would a supplier only charge a tad more to cut for such a small project? That is what I would like to know.

 

just a little clarification on CNC cut plates. Some mention is made elsewhere that one can negotiate and only pay for the actual cut plate. This is true and not true...

Usually the off cut pieces are paid for by client and the vendor keeps them period. Put it this way, you want to have a disc cut from plate lets say 400mm diameter, you are going to pay for the plate needed, iow, pay for 400mm square plate, and not for the disc area.
If the vendor only charge you for the disc, it will be at a premium price that covers the off cuts. It even gets worse, if the whole plate is not going to be used, and no off cut available to cut the disc from, another surcharge will be added because the plate is cut and can not be sold a a full plate anymore and the vendor is stuck with it until smaller jobs can eventually consume the plate.

 

Yes I use propane. One bottle of acetylene will burn one big bottle of oxygen. One 20 lb bottle of propane will burn 6 big bottles of oxygen , you own the bottle outright, no contracts, costs a fraction the cost of acetylene and if you run out on a sunday you can get it filled anytime . You still have to buy the propane bottle for your galley anyway. Welding equipment suppliers always use feeble arguements to try talk you out of propane because conning you into leasing acetylene bottles and buying fills from them is extremely lucrative. Using acetylene doesn't eliminate slag, not by any stretch of the imagination.
Using acetylene makes no sense whatever.
Brent

 

again Brent, you have the chicken by the tail again. As mentioned before, Im a qualified boilermaker for the last 32 years and a cutting torch
is a daily part of my life as little willy and can explore on your statement.

When using a 0 size nozzle on Harris torch - can cut to 12mm easily with it - the ratio between 11.5kg oxygen and 8kg acetylene cylinders used are about 3.5/4 to 1 meaning acetylene goes a long way. This with the small rental monthly makes it cheaper to use than propane. The simple nozzle much cheaper and easier to clean than a propane nozzle.
Fact of the matter is because acetylene is a much much more hot flame than propane, the cut is better and you can actually goes a bit faster than propane. Due to the extra heat, the oxidation process (cut) is better and it definitely leave a better cut.

Due to the small tip of an acetylene/oxy torch, the heat is more concentrated, plate get heated much faster and cutting faster, leaving less heat absorption into surrounding plate resulting in less distortion of plate, fact. We are now talking 2 - 6 mm plate commonly used on small boats. Not so with propane as mentioned - slow to heat plate, big nozzle etc.
BTW, propane cannot even brace when needed.

During all my years as a BM I had tried all types of gasses to save money - we even has a hybrid gas that is basically a mix of acetylene and propane that is a bit better than clean propane but at the end of the day my setup is an oxy-acetylene for very good economical and quality reasons

When reading your post, how did I knew you were using propane? - experience man and you described the symptoms so to speak....

 

Having said all the above, I actually uses a compact plasma cutter that can cut up to 10mm mild steel and 6mm stainless steel for most plate cutting.

It only uses a bit of electrical juice and plain clean compress air - do not come much cheaper than that.
Cut is fast, clean and cold - no distortion whatsoever of plating

 

Though an oxy-propane(2500deg.C) flame is cooler than oxy-acetylene(3500deg.C), hence longer preheat & slower travel speed, it makes a cleaner cut.

The supplied oxygen requirement for a neutral flame with acetylene is 1 to 1, with propane is 4.5 to 1.

You will find that large shipyards/drydocks use propane, natural, or Mapp, not acetylene, to save costs. Of course, we also use manifolds, with up to 16 torches being run off each manifold & several manifolds per ship.

 

Welder, we have to bear in mind that small ships uses much thinner plates than ships, and slow travel speed is the last thing one wants on a thin plate for example 3 or 4mm, as the heat absorption is more in the plate resulting in plate deformation/buckling etc.
As I mentioned, plasma cant be beaten for speed, efficiency, cost and quality of cut.

Perhaps propane is much cheaper abroad, but here in SA very expensive - we use acetylene on manifold system with liquid oxygen at large steel fabrication companies and found that the cheapest route.

 

Wynand,
I was merely pointing out that acetylene is not used in most large shipyards, due to the higher cost associated with doing so. You seem to be of the belief that all ships use thicker steel than boats, which is incorrect. Hull plate aside, most of our ferries are constructed of 1/4" bulkheads, decks, etc., which is not much greater than 3/16", the boat deck on one of our ferries - M.V. "Queen of Alberni" - had boat decks composed of 3/16" plate & 1/4" angle, installed during it's last refit. We have the same challenges when making long cuts on plate and, normally, cut reliefs on the "scrap" side of the cut, to alleviate deformation. Definitely, plasma beats the hell over most oxy-fuel cutting &, in the right hands, makes nice bevels at a much faster rate, as well.

During the early 1990's, I built two 83' fishing boats, in the southern Philippines, and have been involved in other smaller builds, both sail & power, since. During various ferry refits, I have also done a lot of sheet metal fabrication/fitting/welding.

I do accept that there are places in the world where acetylene may be more easily accessed than the alternatives, yet, I haven't been to a place where one could not get one of the 3 alternatives I have mentioned for less than acetylene.

 

Wynard, Im curious as to why you do not use CNC?

 

No problem Welder

Since we are on cutting thinner plates another good tip that some may know already and others not. When cutting 3mm or thinner plate with oxy-fuel cutting equipment and the plate wrap or in bad cases sort of "fuses" together again, it help to lift the torch to about 20 - 30 degrees angle at the handle, iow, nozzle pointing toward you and the problem cured.
Reason very simple. By angling the torch cutting, one actually "thickened" the plate so to speak by cutting through at an angle instead of perpendicular to the plate and better heat disputation as a result and cut cooler/cleaner.

 

I had built my last steel boat and retired from that finally.
Now it is small GRP stinkpots, bassboats, canoes, dinghy's, other glassfibre products and custom build kitchens.

I never liked CNC because if the programmer erred, you are stuck with it. This usually come to the fore when you are well away with construction and nothing seems to come together. Since steel expand/shrink a lot with heat, the room for error and misfits greater. I had measured a v/d Stadt 34ft hull built outside early in the morning and at midday on a summers day and it stretched by 20mm!!

But it boils down to ability and in my personal case pride as well. Im still of the old school, like to loft the boat, see if it fair and if not, adjust the loft. Then start the frames etc from the loft and at the end of the day everything is super duper with no nasty surprised hidden along the way.
I rather measure and cut my own plate - allow for shaping if needed and have a perfect fit every time as I go along. When the boat is all done and dusted, you have that great feeling of satisfaction knowing that I have done it all - nothing beats that, better high than LSD, ask any boatbuilder doing it from scrap all by himself....

I am getting a nuisance now with all my recent postings and gonna lay low a bit giving other chaps a chance to chime in again

 

Excellent point. As it is one of those things one does that becomes habit, one forgets to mention little tricks such as this. We do this most of the time on ships, when cutting, because it keeps the heat directed in the direction of travel, which allows one to travel at a better speed & keep the heat from being concentrated in any certain spot.

Sorry to read that you have retired from building steel sailboats. I was looking forward to having a look, first hand, on my next visit to S.A.
Best of luck with that itchy glasswork!

 

Wynand
"..I never liked CNC because if the programmer erred, you are stuck with it...But it boils down to ability and in my personal case pride as well..."

This i often over looked and is actually a two fold function. Which depends upon how the 'design' is derived.

The hull must be fair. So the lines plan, has this been done by someone who understands lines, rather than how to press buttons? The two are chalk and cheese! So having a decent fair lines is half the battle. If this is wrong to start with, if wont get any better...

Second. The person drawing up the structure. Have they allowed for any 'green' and have they also drawn the structure correctly in autocad, or another? Selecting the wrong line types when in the CAD package can also affect the way the cnc m/c cuts. In addition, if the person drawing up the structure has missed something on one frame, it may well be carried across to all the frames.

These are the same 'teething' problems we had in the early 90s when we first started using plasma cut parts. Took a while to sort out. But once all involved become more aware of the pit-falls and where errors can creep in it got better.

This whole process, which many people do not fully appreciate is ..well, has...replaced the old mould loft system, totally. It has also replaced the time-served structural draughtsman too....everything has now been replaced by one machine and often one program!

To fit all this 'knowledge' of shipbuilding from many different disciplines into one program has taken the best part of the last 15 years.

Today the computer programs are so much better than those days in the 90s. BUT, it is still prone to operator error! So, do you trust the source of the data being supplied?

The way you want to construct the boat and whether the metal being used is steel or ally not to mention the size, also plays a part in how you do this whole procedure.

 

ive heard it said sense all manufacturers use the same programs , airplanes all look alike

wonder if that can be said of boats

 

Here in Canada a bottle of propane costs around $20. The last time I priced a bottle of acetylene it was $40 plus $40 a year for the contract. That was decades ago and I doubt if the price has dropped since then. That is why almost all fabricators here have switched to propane. They keep very careful records of costs.With the acetylene bottle filled with acetone and filler to stop it from exploding, there is not much room in one for acetylene. As mentioned, I go thru 6 bottles of oxygen per bottle of propane enough to almost build a 36 footer with one bottle of propane.
True, acetylene is hotter on the preheat and thus better for heavy or rusty plate, but how much of that is there in a small boat?
We once hired a Texan to cut out the plates on a 36. He used to work on cutting out huge oil tanks. He tilted the torch up to 60 degrees in the direction of travel. That also helps pre heat, and lets you cut much faster, because you are heating the very thin edge of a wedge. He tilted the torch slightly away from the keeper piece, and there was almost zero slag on it. He used propane.
He said that those who tried to cut while crouching , only lasted a couple of days before their backs were screwed. He lay face down on the plate on a piece of cardboard and was like a human plasma . His cutting speed and accuracy were amazing.
There is only 119 feet of seams on my 36 foot hull to cut, anyway.
Brent