Copper vs Steel boiler components

[steamboatjack]

The real issue with using copper in boilers is its reduction in strength at high temperatures, this is the reason it is not recommended by the Steam Boat Association of UK.
An alternative for water tubes is Cunifer, 90/10 an alloy of copper, nickel & iron hence the name. This does not have this huge drop in strength around 200C and does not have the corrosion issues of steel. As for relative heat transfer properties, this is not a subject worth the mountains of text above in my opinion.

Regards
Jack

[DetroiTug]

Quote: "Even using propane as a heat source would be a variable, as the pressure from a new bottle will be different from a part used."

Not to spark a new debate, but just to offer clarification to that statement. A propane tank and a steam boiler both having liquid present have a pressure level directly relating to their temperature level. The only time the pressure will drop to zero in a propane tank above -44 degrees F is when there is no more liquid. The only times there are more or less pressure is when there is more or less heat. Similar to a steam boiler with different temperatures of course.

High demand can cause a pressure drop because there is not enough heat (exceeding vaporization rate), and then the idea comes to add heat to the propane tank which has caused some very serious accidents.

-Ron

[Ethelred]

The relative heat transfers are not an issue, however tube length is. The experiments done by loco boiler engineers showed, very approximately, that 80 percent of the heat transfer took place in the first 20 percent of the tube. So the modern tradition of tall VFT boilers is not as good as a shorter one with a wider diameter. This is a Simpson and Strickland from the good ol' days.
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[DetroiTug]

Quote: "80 percent of the heat transfer took place in the first 20 percent of the tube. So the modern tradition of tall VFT boilers is not as good as a shorter one with a wider diameter."

Depending on how it is fired that is not necessarily the case. My tug is a puffer with tall VFT, meaning the exhaust is ran up the stack, I can state with certainty, the fire is being drawn up the tubes and at times to the upper tube sheet. When the flues are cleaned which isn't very often there is only white ash - no creosote. A natural draft on certain boiler arrangements the "80% in the first 20%" figure can be pointed to with some accuracy, but like everything else steam related, it's not always cut and dried. With natural or induced draft, Flue diameter, number of flues, stack height, outside wind speed, fuel type, draft aperture all have an effect on the velocity of the flue gases.

And no I have no intention of running any sort of test to prove this . That would be a very involved setup to even arrive at some approximation of what is happening.

-Ron

[Ethelred]

You're perfectly correct Ron, there are certainly no absolutes with steamboats.
As you say if you can get the flames all the way up the tubes through forced draft or a tall stack then the figures will be different.
When you start looking into the history though, you find there's a whole lot of different ways of doing things and that 'experts', both then and now, are sometimes mistaken. Take the ratio of waterline length to beam for example; the British tradition is for a minimum of 5:1 and there's plenty of folk who quote it as the 11th commandment, however in the Americas a ratio of 3:1 is quite common and their boats go just fine. The fact is that the important figure is the wetted area and smoothness of lines and surface. Hence why sailing-boat hulls make good steamers. Length is obviously relevant for overall attainable speed, but that's all.
It's not just that I enjoy being a contrary old so and so, but with the kind of knowledge and technology we have available to us today it's always worth revisiting some of the received wisdom.

[steamboatjack]

I agree with Rob above regarding tube length etc. Incidentally the picture is “Falcon” taken in the 1980s when run by Rupert Latham. It has now been re boilered with a plain VFT boiler, pity.
I am thinking of having made a copy of the Simpson Strickland small boiler made for my boat and would be interested if anyone else wanted one? (UK) 21 sq ft no wet leg, very light for the capacity.
Regards
Jack

[RGSP]

I agree with Rob above regarding tube length etc. Incidentally the picture is “Falcon” taken in the 1980s when run by Rupert Latham. It has now been re boilered with a plain VFT boiler, pity.
I am thinking of having made a copy of the Simpson Strickland small boiler made for my boat and would be interested if anyone else wanted one? (UK) 21 sq ft no wet leg, very light for the capacity.
Regards
Jack

Falcon was using an engine-driven forced draught fan last season, and the clanking from the engine was so loud that you had to shout for anyone else in the boat to hear you.

I'm in the early stages of building a slightly modified 21'6" Indian Runner, and if you think 21sq ft would be enough, I might be interested in the said boiler.

[Ethelred]

I might well be interested in one of your boilers Jack. Could you furnish a few more details and a photo or two.
What pressure does it run at and what engine are you running on it and what are the steaming characteristics?