Quad versus twin compound

A special section just for steam engines and boilers, as without these you may as well fit a sail.
RGSP
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Quad versus twin compound

Post by RGSP » Sat Aug 31, 2019 8:56 am

A couple of days ago I had an hour out in "Falcon", an 1890s steamboat now giving short tours from Stalham in North Norfolk. Falcon was given a new compound twin engine last winter, built by Steamboat Jack of this forum, and I'm pleased to say it's running nicely, and quietly. The previous engine was a lovely thing, a Simpson Strickland 2-crank quad compound, but it was so rattly that you couldn't hear what someone sitting next to you was saying. Furthermore the valve gear on those 2-crank quads is a nightmare to get precisely adjusted, and the old engine was reluctant to reverse. According to the boat crew, the new engine also needs a bit less coal than the quad did, though the boiler is unchanged. Falcon has a keel condenser, and as is very often the case it's too big, so the hot-well temperature only got to perhaps 30C after an hour's steady running, rather than the 70C I would be aiming at.

The boiler is an example of the very common Steam Boat Association design VFT102, but is in my experience unusual if not unique, in having an engine-driven fan. The old engine needed the fan to keep pressure up in the boiler, but on my trip recently, with the new engine, it was up at 170 psi almost the whole time, with the safety valve just hissing gently: I doubt whether the fan is now needed at all, but it does give a quick response to firing.

Of course I still don't know how the Simpson Strickland Quad would perform if coupled to 250 psi or more, and its valve gear rebuilt to give accurate timings. It would undoubtedly be better, and perhaps very good indeed. However, even our slightly staid steamboat world isn't immune from Boy Racers with their love of go-faster-stripes, and other gizmos, and I do wonder whether in 1900 the small quad was a form of expensive snobbery rather than something of significant benefit. In larger sizes no doubt the benefits would have been clearer, but going to a steeple 2-crank quad rather than a 3-crank triple must always have been a marginal advantage, and I suspect a 4-crank quad would have been much easier to maintain, perhaps evidenced by these being fairly common in larger ships.
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Re: Quad versus twin compound

Post by TriangleTom » Sun Sep 01, 2019 6:43 am

I've been looking at the Simpson Strickland engines for a while, and I was lucky enough to come across this quote on the Elliott Bay Website

"At 175 lbs. boiler presure the company claimed 10 indicated HP, and at 250 lbs., 14 HP. At these high pressures the engines suffered wear and were noisy, but the company's goal was high speed, and in 1878 speed won sales in a competative market for small power boats."

Given that in the 1870s the fastest machine you could reasonably expect to own was a steam launch, I'd say you are correct in your assumption that these were the "boy racers" of the day.
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Re: Quad versus twin compound

Post by Joe » Thu Mar 12, 2020 8:06 pm

Hi , just spotted this, I feel that RGSP was doing a bit of a hatched job on the Simpson Strickland Quad. We run one, if it is too noisy to hear conversation then there is something wrong with it.It should sound like a busy sewing machine.And if it declines to go astern then the valve timing is probably out.There are experts out there, Mike Williams has now rebuilt several,including mine and the one in Mr Koc's museum in Turkey. And with a good condenser vacuum it is extraordinarily economical. For a typical day steaming at the Dartmouth regatta or Calstock we allow 2 off 10 Kilo scuttles of coal. and we often end up with spare. Cheers
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Re: Quad versus twin compound

Post by Mike Rometer » Thu Mar 12, 2020 9:33 pm

Joe wrote:
Thu Mar 12, 2020 8:06 pm
Hi , just spotted this, I feel that RGSP was doing a bit of a hatched job on the Simpson Strickland Quad. We run one, if it is too noisy to hear conversation then there is something wrong with it.It should sound like a busy sewing machine.And if it declines to go astern then the valve timing is probably out.There are experts out there, Mike Williams has now rebuilt several,including mine and the one in Mr Koc's museum in Turkey. And with a good condenser vacuum it is extraordinarily economical. For a typical day steaming at the Dartmouth regatta or Calstock we allow 2 off 10 Kilo scuttles of coal. and we often end up with spare. Cheers
I think it is well known that that particular engine was in serious need. I too had a run on it and could easily see areas that required a bit more than just 'attention'.
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Re: Quad versus twin compound

Post by Lopez Mike » Fri Mar 13, 2020 4:30 am

I would be most interested to know more about the engine driven fan. Is it in the stack or blowing into the firebox? And if into the firebox, how do you shut it off for adding fuel? And how is it arranged mechanically? I mean the drive train from the engine to the fan.
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Re: Quad versus twin compound

Post by steamboatjack » Fri Mar 13, 2020 8:48 am

Falcon's fan blows straight into the back of the ash pan, it is driven by a vee belt from the free end of the engine, I have no idea if there is any shut off arrangement when firing? I suspect not. I did suggest that the quad could be repaired/rebuilt even with a cracked casting, but they were not interested.
I completely rebuilt an early 'B' size quad a few years ago. The idea of a quadruple expansion engine sounds good if you have 250 PSI boiler pressure but the SS version is in fact not like a sea going large engine. The SS is arranged with very late cut off so although it expands through four stages the total difference is probably equal to a compound engine but with the addition of complicated slide valves and a lot of reciprocating weight. They look good but are rather flimsy rather like that other light weight the Lifu engine which has its power rating based on speeds & pressures which are not anything like what people often use these days.
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Re: Quad versus twin compound

Post by Lopez Mike » Sat Mar 14, 2020 3:14 am

Thanks Jack.

A V-belt is quiet and easily slacked with an idler wheel. Or I could arrange some sort of mechanism whereby opening the fire door closes a damper in the duct from the fan to the ash pan. Or both.

I've lost a couple of races (Race? Surely not us!) at gatherings. And by rather narrow margins. My stack blower uses quite a bit of water and some more sustainable way to get a few more r.p.m. would be most welcome.

On the other branch of this thread, I suspect that a deal more attention to insulation of piping, cylinders and receivers would gain as much or more than more expansions. Our club has several boats with no lagging and owners who complain of fuel consumption issues.
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Re: Quad versus twin compound

Post by TahoeSteam » Sun Mar 15, 2020 5:34 pm

I took the stock turbochager off my '87 Buick Grand National in the pursuit of more speed and more frequent tire replacements... We put it on my father's launch "George H. Sandin" initially as forced draught. It worked so incredibly well. You have to have very good sealing around the door, lagging, and ashpit. If you don't, toxic gasses will escape into the boat harming your passengers and crew. The Sandin has a pilot house so those gasses would collect in there. We have since made it an induced draught system and it still works quite well. No worries about opening the door, or need for special sealing. On suggestion if anyone decides to go a similar route is to either find a compressor side that is know to be less noisy, or have an intake "box" that is baffled so you get less noise from the compressor side of things. This turbo was quite large for the application, so it wasn't screaming and making 20lbs of boost, but it still made itself known.
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Re: Quad versus twin compound

Post by barts » Sun Mar 15, 2020 9:36 pm

Lopez Mike wrote:
Sat Mar 14, 2020 3:14 am
...
A V-belt is quiet and easily slacked with an idler wheel. Or I could arrange some sort of mechanism whereby opening the fire door closes a damper in the duct from the fan to the ash pan. Or both.
...
My stack blower uses quite a bit of water and some more sustainable way to get a few more r.p.m. would be most welcome.

On the other branch of this thread, I suspect that a deal more attention to insulation of piping, cylinders and receivers would gain as much or more than more expansions. Our club has several boats with no lagging and owners who complain of fuel consumption issues.
Certainly lagging the boiler appurtenances, steam lines and engine cylinder will help quite a bit, particularly if there's a bit of wind blowing, and is probably the simplest approach to more steam/speed. Getting more expansions will actually reduce power on a given engine, of course, but if the boiler is too small. more expansions is better than throttling the input steam. Forcing the fire is a time-honored way of going faster, but if one is short on boiler surface area a mechanical engine driven fan will be better than using boiler steam to force the draft. For experimental purposes (to see if it's worth doing properly) a battery driven fan would work nicely. If you have DeWalt rechargeable tools, they make a blower that's quite powerful and worth playing with.... also, using that air blast up the stack will be much more pleasant that forcing the fire directly.... make sure you have enough air intake, too!

When designing/reskinning a boiler, arranging for the boiler intake air to cool the casing or firebox refractory will help raise combustion temps, which increases both overall efficiency and boiler output. Arranging for some of the combustion air to come in over the top of the fire (secondary air) will help make solid fuel burn cleaner and leave less soot on/in the tubes than having it all come through the grate/ash pan; this is what all non-catalytic wood stoves do in the US now.


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Re: Quad versus twin compound

Post by TriangleTom » Mon Mar 16, 2020 12:30 am

TahoeSteam wrote:
Sun Mar 15, 2020 5:34 pm
I took the stock turbochager off my '87 Buick Grand National in the pursuit of more speed and more frequent tire replacements... We put it on my father's launch "George H. Sandin" initially as forced draught. It worked so incredibly well. You have to have very good sealing around the door, lagging, and ashpit. If you don't, toxic gasses will escape into the boat harming your passengers and crew. The Sandin has a pilot house so those gasses would collect in there. We have since made it an induced draught system and it still works quite well. No worries about opening the door, or need for special sealing. On suggestion if anyone decides to go a similar route is to either find a compressor side that is know to be less noisy, or have an intake "box" that is baffled so you get less noise from the compressor side of things. This turbo was quite large for the application, so it wasn't screaming and making 20lbs of boost, but it still made itself known.
This is incredibly fascinating to me. How did that work? Run liquid fuel with the stack hooked up to the exhaust side of the turbo?
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