Stuart versus Semple

[wsmcycle]

I have an 18 foot boat with a 7 foot beam. It was powered by a Semple 34dw single. The max boat speed was 7.5 mph. I wanted a compound engine just like my wife wants a new dinning room suite.
I repaired and completed the work of a "partialy built" Stuart6a kit I purchased on Ebay to replace the Semple engine. I swapped the engines thinking I would have ample HP and the Stuart would waste less steam (power). What I found was that the Stuart 6 would only move the boat at 5mph. I sought a method of prop measurement and I know now that my prop has a 16 inch pitch. I was thinking about changing it to a smaller pitch and let the Stuart 6 run at a higher rpm. However, this may result in using the same amount of steam as the Semple engine did. The Semple was certainly less finnicky.

In order to build the Stuart engine, I received all but one of the prints and no building method. I tried to obtain from Stuart the missing print and any build information they might have. I was told by them twice (several months apart) that their blueprint machine is not working. I had to make a few "best guess" decisions in order to get it running (it is running). If some of you run a Stuart6, pehaps you might kindly help me with a few problems I am having.

First I would like to know what type and size packing to use. I used 3/16 round and it kind of works. I tighten it and it seals but ten minutes latter, it is leaking again. I tighten again. I have not run out of packing nut thread but i have run out of hope that my packing is going to work.

The engine has "D" valves. If I tighten the slide plate to its shaft during timing, the steam pressure cannot seal the valve plate against the face. I had to use jamb nuts above and below it to position it verticaly w/o constraining it horizontaly. This allowed the valve plate to be blown tightly against the valve face. Was this Stuarts intended method?

My next question requires some "story". I am running along, ginning just fine at 80 psi. The engine begins to slow and 30 seconds latter, it has stalled. I turned off the throttle and took a lever to the flywheel bolts in order to turn the motor. I can turn it backwards with some difficulty. I don't think it is seized up mechanicaly. I can turn it forward with a little more difficulty. So, I rock it backwards a few turns and it seems to loosen up. I open the throttle, roll it forward and off she goes. Running just as well as it did before the problem. This scenario has repeated itself 4 or five times, different days, different trips. The water level was at about 3/4 in the sight glass or i would have thought it had flooded and hydraulically locked. I am puzzled. What might be the problem?

[gondolier88]

Hi Wsmcycle,

I believe your first symptom of leaking gland packing and your lock-up problem are directly related;

I would say that your the gland/s you are having problems with are off centre from the crosshead guides- as you tighten you temporarily close the gap, but within a few revs it is back to the shape it was before and is leaking past- in constantly tightening up you are pushing the piston rod off centre, this in turn is making the big end very tight at BDC and TDC when hot, stopping for a little while is allowing it to settle back to running fits and carry on.

I would remove the gland nuts and make sure the bore is concentric to the thread.

Greg

[wsmcycle]

Gondolier88
That is an interesting conjecture and I will give it some thought.
I see now that things which i thought unimportant to include in my opening statements are in fact important.
I am sorry you have to eek out the info from me. Regarding the over heating of the bearings
due to non-concentric problem, let me interject. The engine was only stalled for a minute (not enough time to cool)
and after it restarted, it ran twice as long as the time previous to the stall. In fact, it did not stall at all
afterward that day which was this past Saturday.
Regarding the non concentric gland leak, I hope you are wrong but i think your conjecture fits the facts
quite well. I can't think of a fix for that one short of removing and tearing into the engine. I dont think
the concentricity of the gland nut bores to their threads would cause the problem. But, the
piston rod not moving concentrically as it moves up and down would cause the problem you described.

[Lopez Mike]

As to your question about the valve being held against the cylinder face by steam pressure; Yes, that is how it works. The valve needs to be free to slide horizontally relative to the valve rod. Just the minimum of end float on the rod.

I hope I understood your question!

[preaton]

Do you have cylinder drains? Are you sure the engine is not stopping due to water in the cylinders? If you have drains try running with them just open to see if this solves the problem.

Cheers

Paul

[wsmcycle]

Mike
double nuts top and bottom is the only way i could think to do it. Have you seen valve boxes with some better method of constraint?

Paul Auckland

I was in Auckland a couple of years ago and saw a steam boat slip into the wharf area near downtown. That was the first steam launch I had ever seen. it was so cool.
I did ride on that beautiful boat on the lake at Queentown. It was fantastic!!!
Regarding hydraulic lock, I didn't have to open the drains to restart the engine but next time it happens, i will check your theory.


Thanks

[Mike Rometer]

Mike

I did ride on that beautiful boat on the lake at Queentown. It was fantastic!!!

Yeah, yeah, yeah. Been there, done that! S.S. Earnslaw, lovely trip out up the lake.

[87gn@tahoe]

An indicator of water in the cylinders would be a pinging noise corresponding with one of the pistons reaching TDC or BDC.

Are you using a follower with your packing? (metal piece that goes in after the packing, under the "cap", that presses the packing down)

How large is the hole in the cylinder cover underneath the packing in relation to the piston rod diameter?

[Lopez Mike]

If you have room for the double nuts, that's a fine solution. I have used all stainless lock nuts. The sort that lock because they are, essentially, distorted. I've even had very good results using these sorts of nuts to hold a piston on to the piston rod, a very difficult application with very strong reversing loads.

The small Stuart engines simply have the valve rod threaded though a small insert that floats between ears on the back of the valve. This works but only because the loads are small, the hours of operation seldom accumulate enough to wear things out, and the engines are never subject to testing with an indicator or examined carefully.

[artemis]

Locate a commercial/industrial supplier for pipe and steam fitting supplies (most major cities have at least one). You need "square" (meaning NOT round) packing material. Round is for rotary motion, like a water valve; square is for reciprocal motion. The packing should be graphite impregnated for "slickness".

Valve-valve rod - when double nutting make sure that there is enough "slackness" when making the adjustment that when the engine is "up to temperature" the valve can still "float" on the valve rod.

Keep to mind that Stuart models are not designed to "work hard " like real engines. Consequently bearings, etc. should be somewhat stronger than what is specified. Modifying Stuart engines to really "work" is why people like the late Alex Ritchie were able to build "improved" Stuart engines that functioned quite well. I personally know of a compound he built that developed 7HP at 500 rpm and 150psi and propelled an Elliott Bay hull weighing 2000 lbs at 7+ knots. Ritchie built this engine and a local propeller shop in Portland, OR, USA provided the owner with a proper 18"D x 22"P Michigan "Equipoise" propeller with 53% blade area that produced the desired speed at about 520rpm. Mr. Ritchie's recommendation for the "best" engine speed was 480 to 525 rpm.

A given boat requires a given amount of steam to move it at a given speed. Yes, there are some advantages to compounding over single cylinder "simple high pressure" engines; condensing over non-condensing; preheating feedwater with an econmizer; etc. but in our "little" boats the savings are not great enough to warrant the extra complications. It was only done in large vessels to improve efficiency and extend cruising area. But when a 10% increase in efficiency affects an hourly fuel consumption that is only about 2.5 gph of liquid fuel or 5 to 6 sticks of wood... Fun per mile, not miles per hour.