Building a single screw steam tugboat

[Tugger]

This is my first posting so please excuse me if I waffle on a bit!

A few years ago I decided to build a steam powered Murray River Paddle Steamer similar to the Adelaide or the Emmy Lou.  First of all I built the Miniature Steam Gem twin cylinder horizontal engine from castings and started to build the reduction gear for the paddles so that I could decide on the scale to build the final model.  Then a mini disaster struck!  I had an "episode" with my ticker that required a triple heart bypass to fix it up.  I was not allowed to lift more than a kilogram for 4 months.  The 4-jaw chuck in my lathe weighed at least six times that so I had to suspend my boat building for a while.

The biggest mistake I made was to take up building model aircraft instead as they were so light and I could build and fly them during my recovery.  It took me a while and a substantial number of dollars to figure out I was a hopeless model aircraft pilot although the planes I built did fly extremely well in the hands of our 14 year old junior members!  Whatever!  My lack of piloting skills put a serious dent in my enthusiasm for model building.  Then I started to tinker with my boats again as the boating incidents were generally far less expensive and traumatic.

A turning point came when the company I work for gave me a nice little cash award for 45 years long service.  I decided to invest the money in something I would remember for years so I bought a fully certified three inch boiler from Miniature Steam, a nice Tug kit from Caldercraft, a steam engine kit from Graham Industries, a steam attenuator and still had a few dollars left over for a few odds and ends.

For anyone out there who is interested, I would like to outline the reasons I chose the various items I have used and how I have or plan to use them in my model.  I am sure not everyone will agree with my decisions or reasons but surely that is why a Forum exists?  Nobody has a monopoly on correctness.  I look forward to hearing your views.

After reviewing my original idea to build a complex paddle steamer, I decided I should test out a lot of my ideas on a much simpler craft.  That was why I decided on a single screw tugboat.  This would have plenty of room to experiment and try out some of my ideas.  Of course, the major deciding factor was that my wife had always had a love affair with tugboats so it was so much easier to go over budget with one of these!

I looked at several plans and kits and decided to go for the Caldercraft kit of the Marie Felling as I could support one of our local suppliers in Melbourne and it was just the right size.  The only problem with the Marie Felling kit is that the hull is not to scale as it is actually from another model of different length so you could never enter it in a scale competition, or at least should not enter it in a scale competition.  That, fortunately does not worry me in the slightest as my model building skills are nowhere near good enough to even consider scale competition.  The hull is quite well molded and looks good when painted.  I have made several fibreglass hulls myself from scratchbuilt hulls and molds but the ones produced for some of the kits these days add an extra touch of realism with the plates and rivets showing that would take many extra hours to replicate if building from scratch.

First attachment shows what you get in the Caldercraft kit.

The first thing I did was to measure the dimensions of the hull and work out roughly what the model would have to weigh to sit correctly on the waterline.  This was somewhere on the heavy side of 20kg.  Obviously weight was not going to be a problem.  In fact, the more weight the better as it is always better to have the model weighing a lot due to substantial build quality than to have a lightweight model full of ballast in my opinion.  So the first step was to double the thickness of the hull with another layer of fibreglass and plenty in the bow for extra strength.  Heaven help anyone who tries to ram this boat!

I then manufactured my own propeller shaft and housing instead of using the stock one supplied by Caldercraft.  I don't like most commercial shafts as they leak oil into the water.  One of the most common reasons we as a model boating fraternity lose the use of a stretch of water is because of oil films being left on the water surface so anything that can be done to minimise this should be done.  My prop shaft is a quarter inch stainless shaft turned down at the prop end to 5mm to accept the prop thread.  The shaft runs in two flanged sealed ball races, one at each end of a half inch aluminium bar turned down towards the stern to just fit through the keel.  There is also the added security of an oil seal in the housing because the shaft is running entirely below the waterline.

Fig 2 shows the prop shaft housing installed.  Fig 3 shows the prop end and the brass rudder skeg that I made to replace the useless bit of white metal in the kit.  I epoxied in some threaded brass posts to screw the skeg into so the rudder and prop can easily be serviced. (fig 4)

Four brass posts were fibreglassed into the hull to accept the machinery baseplate which was a quarter inch thick brass plate.  Having this very heavy plate right at the bottom of the hull gives the vessel enormous stability plus it makes it easy to make modifications as new ideas come to mind.  Fig 5 shows the engine test mounted on the baseplate during the alignment phase.  I use two flexible couplings and an intermediate shaft between the engine and prop shaft but near perfect alignment in the first place makes the system run much more smoothly and uses less steam.

The next stage is to construct the decking support frames so that the position of the funnel can be accurately determined.  That is one of the reasons I have such a huge machine plate in the bottom of the boat.  It allows me to easily position items such as the boiler to ensure a perfect match with the superstructure. (Figs 6 - 9)

The next step is to determine the various linkages for rudder, steam valve opening, reversing gear etc and ensure you have enough room to place all of these components without interfering with each other.

I hope to show you a few different approaches in my next post.

Keep Tugging!

[steamboatmodel]

Welcome to Paddleducks.
That looks like it is going to be a nice build.
Regards,
Gerald.

[kiwimodeller]

Great start to your project, look forward to keeping up with progress but it would be good to see you ressurect the paddler one day also. I am sure you will be happy with your engine choice. I started off with one steam paddler built up for myself. I now have five steam powered boats. Every time I go to the lake somebody asks where to get steam engines and equipment so in the last couple of years I have imported and sold 17 of Mr Grahams engines and a lot of items such as lubricators and throttles. I have not had one complaint about the engines, every custom has complimented the way they go together and the performance and several have moved on to a second, usually larger, build. Keep up the good work, just be careful with the heavy lifting! Cheers, Ian.

[Tugger]

Hi Ian,

Thanks for the kind words and support.  I hope to be able to get cracking on several different types of boats in the not too distant future.  I am just hoping I haven't left my run a bit late as I sneak past 70 this month and I am still working full time so don't have a lot of spare time to spend on the models yet.  I have always had a fascination with paddle steamers which is why I built the horizontal twin engine to see how it went and try to guess what would be the best scale to use it in.  The tug is really a test bed for all the steam plant.  I have built five steam engines over the years from a simple oscillator years ago to three different twin cylinder slide valve engines.

I was very interested in your comments about the Graham engine as that is the only part I have been having problems with.  Apart from the fact there were quite a few screws missing from the original kit and the difficulty of getting any replies from Mr Graham, the engine went together very easily over a couple of evenings after dinner.  It ran beautifully after a few minutes bedding in.  As it has run, the T-slide has worn very badly so the eccentric strap moves a lot from side to side on the cam as the engine goes from the up to down stroke and vice versa.  This reduces the movement of the slide valve so I have had to constantly move the reversing lever to a more extreme position.  Finally, if I stop the engine to change direction, I find that it will not start because the steam goes straight through to the exhaust.  I originally thought this was due to the slide valves lifting off as they can sometimes do on vertical engines.  I relapped the valves and made sure they were not too tight on the actuating rod but that made no difference.  I decided to strip the engine down completely to see what else I could find before a full rebuild.  I was surprised to find that the O-rings in the cylinder seem to have shrunk down so that they require a huge amount of very thick steam oil to get any sort of seal in the cylinder at all.  I am sure that when I built the engine the pistons sealed quite nicely.

Mr Graham does not say what material the O-rings are made of.  I am going to try replacing them with fresh EPD O-rings and see if that fixes the steam leak through.

Nice to see so many people out there still enjoying the wonders of steam!  Please keep in  touch.

Kind Regards, Peter

[derekwarner_decoy]

Hi PD's........Peter you may have a few issues here

1. EPDM [ethyene propolylene dienne rubber] seal elastomer is only rated to 150 degrees C....our model boilers @ 3 Bar approach or exceed this temperature
2. EPDM is rated as 85 Shore A hardness which is relatively soft & of low abrasion resistance ....it is sometimes dyed BLUE
3. Viton elastomer also is 85 Shore A hardness, but also rated to 200 degrees C which exceeds our model boiler temperature ranges
4. Viton elastomer is also totally compatible with fluids  such as steam & fatty based steam oil lubricant's ....yes ...Viton elastomer is often green or brown  
5. Silicone [methyl vinyl silicone rubber] is suitable for the same applications & up to 220 degrees C...you will see these as the RED O-rings in certain builds
6. NBR [Nitrile] elastomers have an upper limit of say 100 degrees C & will mechanically & physically degrade  & reduce in size or volume if exposed to over temperature

My best recommendation would be Viton or Silicone replacement o-rings for your engine rebuild...........Derek 

[Tugger]

Hi Derek,

Thanks for your interest.  I think there has probably been more written on the pros and cons of O-rings than almost any other subject.  This is mainly because there is no ideal material for the job.  I just happen to have a few EPDM rings of about the right size from work.  I quickly knocked up a test piston with a groove depth to suit the rings and tried them today and that does seem to be the problem.

I think EPDM is a better material if the steam is still fairly wet and less than 2 bar when it should not exceed 120 degrees C.  The trouble usually arises when superheat is used as the steam temperature can then really shoot up.  I have always used Viton when building engines from scratch.  It would be nice if I could just stick to cast iron rings!

Silicone rubber suffers from a high coefficient of friction and is structurally unstable which tends to negate its temperature properties.

My problem was that Mr Graham does not mention what material the original O-rings are made from and it is difficult to analyse them without damaging the ring itself.  I could try running a couple of IR spectra at work this week and see if I can get enough information to identify the material.

Cheers,
Peter