Ignorance Exposed

[cyberbadger]

As far as practical experience with shaft horsepower...

I've gone through 3 different drive ratios. The first ratio the engine was operating very slowly (60rpm) and could never manage to pick up enough inertia. (The seaweed in the area really did not help matters... With the second ratio I learned that L series are really only good for 2-3hp and then they snap.

I would recommend 30mm wide HTD belts for a 6HP situation, but I would suggest bigger pulleys with more surface area then I have.

I'd actually like to try a fourth ratio, but the larger HTD pulleys are fairly expensive, and my current setup seems to work well enough.

At 150-200psi, I cannot give the 120yr old engine full throttle or she slips the toothed belt. The belt itself is almost indestructible. It probably wouldn't slip if I had the larger pulleys I want. With a seasoned hand I don't let the belt slip. I later drilled out a water escape hole in each groove of the pulley that is underwater, it may have helped a little, but it did not fix slipping at high torque.

I think though, it's only 6HP and a fairly heavy boat so it's unlikely that the top speed could be improved by very much.

-CB

[TahoeSteam]

I was just making the point that loading the engine down rather than let it freewheel and throw steam away appears to be better. We get into this discussion occasionally when it's mentioned that steam cars don't need a transmission. They do. The piston cylinder arrangement remain constant in regard to torque, mechanical resistance as well as port flow resistance is the cause of diminishing torque at high RPM. White and Brooks (and I think Doble) ran a two speed transmission for this reason.

Steam engines can be compared to stepper motors, both have all their torque at very low RPM. Both lose torque with increasing RPM, the stepper motor, it's resistance in the windings.

Ron

Funny you mention that Ron..

I made a balanced HP slide valve for the Doty compound in the big boat. A big success in that it reduced die block noise, made moving the links with the throttle open easier, and the engine seemed to run smoother... The engine also mad the same RPM at half throttle as did at full throttle previously... The problem is if you open to full throttle with the new valve, it just sucked the steam right out of the boiler which was completely capable of supporting the engine with the original unbalanced d-valve. Can't win for losing...

[Lopez Mike]

Speaking of "Ignorance Exposed" . . .(on my part!).

I guess I don't understand why it should use more steam. Something I'm not getting here.

Maybe too much percentage of balance thus not getting a good seal between the slide valve and the cylinder block?

Mike

[DetroiTug]

"I guess I don't understand why it should use more steam. Something I'm not getting here.''

Same here. Did the RPM increase that much with the new balanced valve?

[TahoeSteam]

More bites per minute vs the old valve.

Significant increase in RPM at wide open throttle (30-50+) vs with conventional valve. Boiler was almost at the limit before with current burners.

As long as Holman's throttle man can be disciplined with the throttle, not much of an issue...

[DetroiTug]

Significant increase in RPM at wide open throttle (30-50+) vs with conventional valve.

That's where I was at. Going up to a hungrier prop made better balance for the steam production, RPM and hull speed. Even now though I can only run full throttle over long distance on perfect wood, wrist sized and fully seasoned and staying right on top of it.

Going a little heavier on your prop might eek out another knot. Of course that's easier said than done.

When I went to the bigger prop I had to beef and brace up the crossmember engine mount made from 1/2 x 2 steel. The cylinders were shaking. Making her work for it.

Ron

[barts]

More bites per minute vs the old valve.

Significant increase in RPM at wide open throttle (30-50+) vs with conventional valve. Boiler was almost at the limit before with current burners.

As long as Holman's throttle man can be disciplined with the throttle, not much of an issue...

Yup... a steam engine at wide open throttle and 0 rpm will use only a tiny bit of steam... steam locomotives were actually more efficient than diesels below 6 mph.

If a steam engine has ample ports and no notable restrictions in the feed or exhaust, the steam consumption will be linear with RPM.

- Bart

[TahoeSteam]

Shame 3-1/2' to 4' diameter props weren't a bit cheaper...

The one on there is a 42"x42" or somewhere near that. Came with the boat, and my pops insisted on spending big bucks to bring it back from the dead (logging boom tug props don't lead an easy life) rather than drop the money on something more promising...

In a perfect world:
big prop, big bite, short straight smooth ports...

[barts]

A ex-cannery tender up here has a big Washington Ironworks diesel - 100 hp at 350 rpm. The prop is 5'x5'. When docking, a turn or so (using the planetary gear) at idle forward and backward will walk her towards the dock. For slow speed and heavy work, a big prop is exactly what is needed.

- Bart