The Steamboating Forum

Impressive...

Thanks Ranier.

The Doty Compound is slowly coming back together...

My father cut the packing gland portion off of a large gate valve that was junk and we're using it as the gland for the condensate pump. Stem with valve handle is in there at the moment "just because". Obviously the piston and valve rods aren't in there yet as I've still got some things to do with the valves and LP piston.

Sorry for the poor quality cell phone pictures.

An interesting engine, nice to see “proper” double bar marine links and I particularly like the cast eccentric rod ends. The distance between the eccentric rod ends on the link looks a little short, I would be interested to know the distance (relative to full valve travel) Loco people use about 2 x but all my old marine books state 3 x. Could you also comment on the crosshead pin bearing arrangement? Cannot see from the photos, always interested in different ideas.

Regards
Jack

Wes,

Great progress! It's going to be great to see that engine running on steam again.

-Ron

Whats the dimensions of this engine? I presume you will be removing the flywheel when it goes in the boat? With a sufficiently large propeller the flywheel shouldn't be necessary, especially as the engine appears to be balanced. Are the counterweights larger on the LP than the HP? On Kapanui's Simpson Strickland they are wider on the LP. Definitely an interesting looking engine. good to see more positive progress.
Daniel

Jack,

It truly is a "proper" marine engine, what with cast back columns and slanted turned front columns. The aesthetics are probably the #1 reason my father decided to run it in the boat rather than the French "Calparede" compound.

I will have to measure the valve travel and rod end distances on the Doty and the Claparede for you.

The connecting rod and wrist pin arrangement is much like a locomotive's. Here is a picture of one of the crossheads:





You can see that the tapered pin bore has been repaired at one time. This is the LP, which also had the pumps working off of it via walking beam (it either has a new pin or the extensions have been cut off), so that may have something to do with why it was repaired.

Here is a much larger Doty compound with similarly close eccentric rod ends. This is about the size of the engines in the R.M.S. Segwun. Notice the wheelchair in the lower right-hand corner for scale:




Thanks Ron!

We're getting excited. It's hard not to be tempted into just throwing it together. I am taking a couple cast iron plates and bar stock to get blanchard ground tomorrow for new crosshead guides. Some parts are going to have to wait for future refurbishment though.

Daniel,

The engine is 5"&10"x6". The flywheel is original to it so it will be staying with it. Seems that all of Doty's engines came with them and all have holes in them for baring over the engine.

The counterweights are all the same size. I am in the process of finishing up a hollow aluminium LP piston to even out the weights of the reciprocating parts. The original was 30lbs heavier than the HP, at the moment the new one is only 5 lbs heavier. I weighed all of the original LP reciprocating parts (crosshead, rod, piston) and it came out to something like 70lbs! For the HP it was "only" 40lbs.

Funny, Doty seems to have put counterweights on all of their engines, even on the large Doty pictured above. A bit unusual for engines of that size.

dhic001 wrote:With a sufficiently large propeller the flywheel shouldn't be necessary, especially as the engine appears to be balanced.

I used to believe this as well. After running without a flywheel and with the flywheel, I have concluded that a balanced multi-cylinder engine definitely runs smoother with a flywheel even though one is not needed for rotational inertia. The propshafts we typically run are long and smaller than ship-sized diameter in scale which can twist under torque loading. This flexing prevents the engine from befitting from the dampening effects of the mass of the propeller. Smooth engine output results in smooth power transmission to the propeller eliminating this twisting cyclic action thereby reducing vibrations.

-Ron

I agree with the flywheel needing to have a rigid torsional connection to the engine. On the Margaret S. the paddlewheels, are the only flywheels in the system. I had to find a flex coupling with NO free-play, and very stiff torsional connection between the engine and the rotational inertia. A long relatively small diameter drive shaft to the propeller is so flexable in torsion that single cylinder engines will experience significant wind-up and wind-down when running under load. A multi-cylinder engine is better, but you need at least three cylinders (six if single acting) to eliminate an engine connected flywheel and still avoid the variations that come without one.