# Model boat engine requirements



## CanuckMike (Feb 3, 2015)

Hello, I am currently building a 36" steam launch, hull has been planked and all mechanical bits have been fitted (rudder, stuffing tube, etc). I'm wondering if anyone has any suggestions for an engine for a model this size. I have made several small steam engines previously, but this is my first boat build.

Thanks, Mike


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## Corrado (Feb 4, 2015)

Hi Mike,
You will need a small twin cylinder engine,   either oscillator or slide valve so that it will self start.
Oscillators are easier to reverse but slide valve engines leak less steam & are more efficient.  From my personal experience, I can personally recommend the PM Research V Twin or the Graham Industries TVR1bb.  I assume you have a reputable boiler.
Cheers ...Corrado.


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## Blogwitch (Feb 4, 2015)

A litle small for some of the commercial units about, but if it is your first foray into steam powered boats (I did it for many years) then a small twin oscillator of about 1/4" or 5/16" bore should be more than ample.
If you go too conplicated with your first efforts, and I have seen some right efforts in my time, you just might spend more time on the bank fiddling with it rather than sailing.
So just keep the C of G low, so maybe a horizontal boiler to begin with, and as I said, one of the smaller engines, that should give you good sailing with no surprises.
A sure case for KISS.
I have found that if making one yourself, with a little bit of good machining, the one at the bottom left on here could be made half size and would be perfect for your sized model.

http://jpduval.free.fr/Plans_moteurs_vapeur_p1.htm

Go to this page and you can go searching the site and there are all sorts of free and paid for plans available for download and have a look at.

http://jpduval.free.fr/

This is my version of the engine I mentioned above, made slightly easier to produce, and next to the blue engine which is the one in the picture below.







This is one of my steam boats from way back, sailed for ten years almost every weekend without a glitch. 4Ft long and powered by a commercial unit, which I still have in my collection.






I hope this helps a little

John


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## Blogwitch (Feb 4, 2015)

Just a little update to the above post.

This is the above mentioned engine made into two different versions, the upright for going into a launch and the horizontal for a paddle boat.






This engine will easily power a model of between 5 & 6ft long.

John


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## /// (Feb 4, 2015)

Lovely launch John, one of these is on my 'Round Tuit list.


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## gus (Feb 4, 2015)

Blogwitch said:


> A litle small for some of the commercial units about, but if it is your first foray into steam powered boats (I did it for many years) then a small twin oscillator of about 1/4" or 5/16" bore should be more than ample.
> If you go too conplicated with your first efforts, and I have seen some right efforts in my time, you just might spend more time on the bank fiddling with it rather than sailing.
> So just keep the C of G low, so maybe a horizontal boiler to begin with, and as I said, one of the smaller engines, that should give you good sailing with no surprises.
> A sure case for KISS.
> ...



Hi John,

Great steam boat!!!

Still trying very hard to fit in to build a steam powered boat. Looks like will be done in 2107.


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## Blogwitch (Feb 4, 2015)

I don't want to hijack Mike's thread, but just to put you in the picture.
That boat started life as a commercial kit, 'Krick Victoria' which I started to build in the early 80's while still in hospital, I bought it to pass the time. The engine that came with it was absolutely rubbish, a Willesco 'toy' engine and boiler, so I did the first ever conversion to a Cheddar Puffin plant, which later Krick took up as well as the standard plant for it.
Later on it had a major refit, and I planked and epoxied it all over, inside and out, and basically it was bomb proof. I sailed it for well over 10 years, without having to do anything major to it. I gave the hull away to a friend about 7 years ago, when I couldn't manage to launch my own boats any more and so gave up model boating forever after about 40 years. But I still make and repair engines on commision for other people.

John


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## CanuckMike (Feb 4, 2015)

Thanks to all for the great feedback! I had pretty much decided already on a wobbler of some sort (I love their simplicity) I was more uncertain about having enough "oomph" to push this thing through the water. None of the little engines I've made have been used to power much of anything. A horizontal boiler will be used as I have some extras leftover from previous projects. Any suggestions as to what PSI you would run for a small twin wobbler in this application? I usually run 15 PSI for static or stationary stuff.

Thanks again, Mike


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## Blogwitch (Feb 4, 2015)

Mike,
I always used to run mine at a max of 20PSI, any more is wasteful. 
If you over pressurise a wobbler, all it will do is lift the port faces off the standard, there should be no steam escaping around the port faces, if there is you have too much pressure going to the engine.
When in the water, the engine should only be doing a couple of hundred revs when it is fitted with a good 45 degree steam prop.
Where steam scores over i/c or electric power, it has got a lot of low down power, especially if you use a long stroke engine, like the one I directed you to so you don't need to over steam it to get enough power to your prop.

Hope this helps

John


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## CanuckMike (Feb 5, 2015)

Hello John, Thanks for the great input. I'm just trying to get up to speed with posting pictures. I'm not really tech savvy. The picture is of a twin cylinder wobbler I made with 1/4 bore and 5/8 stroke. I am thinking of going to 5/16 bore and setting this up in a vee configuration. You had mentioned 200 rpm as a good running speed, I'm not sure of the free running rpm of this twin. Under load I would imagine it would'nt be far off from the rpm you mentioned. I am a machinist by trade and love this little stuff. It really challenges me as I normally work on large equipment. 

Thanks, Mike


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## Blogwitch (Feb 6, 2015)

Mike,
When you see one of these engines on the water at normal cruising speed they should just be gently 'nodding' away, with no steam showing other than from the normal exhaust route. If they are going any faster than that, then you are under propped.
On my steam launch, with the small blue engine (3/8" bore and stroke), it was fitted with a 2.5" diameter 45 degree steam prop. So a 1/4" bore engine should be able to turn a 2" steam prop quite easily.
People usually make the great mistake of putting too large an engine in their boats, which then needs a larger boiler, you soon reach a catch 22 situation.
This is a 5ft long boat which used to have a large engine in it, and he swapped the engine for one of my 3/8" bore x 3/4" stroke engines. It doubled his time on the water and the launch went much faster with the same sized prop.






You can see just how small my engine was, his was almost double the size. Not needed.






Hope this helps

John


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## Piston_Broke (Feb 6, 2015)

The only way to go!


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## Jasonb (Feb 6, 2015)

John, just out of interest what ran out first, the gas or the available water?

I can't see a feed pump on that last photo so is it a case of filling the gas tank so you run out of gas before there is a chance of running the boiler dry. I'm assuming they are gas fired.

J


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## Blogwitch (Feb 6, 2015)

Jason,
It is always the gas that should run out first. I had about 40 minutes water in my boilers but a max of 20 to 25 minutes worth of gas.
After about 20 mins you are ready to come in anyway, and the engine is ready for an external lube. The displacement lubricator could easily last two sailings before needing a refill.

John


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## CanuckMike (Feb 7, 2015)

This is a question for John. I'm assuming you use butane as a fuel. Have you used any other fuels in your boats? With any of the static/stationary engines I've used hexamine tabs(Esbit), ethanol gel and coal. What would you recommend as a fuel in a marine application? The ethanol gel has worked fantastic, especially indoors. Also for a double acting twin as you've described, what would be the minimum boiler size requirements? I really like the idea of keeping this small and simple. I'm not out to break any speed records and am shooting for about 10 mins or steaming time on the water.

Thanks, Mike


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## Dave Sohlstrom (Feb 7, 2015)

Mike

This is way more than what you need, but I thought you might like to see this.

Dave


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## Blogwitch (Feb 8, 2015)

Mike,
It is a totally different thing between running engines on a bench under controlled conditions, and having a model free running or under R/C control outside in the elements. The fuel reacts in different ways, and the wind does play an important factor. I have seen small solid fuelled model boats out on the water, and they really are unpredictable, most having run out of fuel or had the flame blown out, and if you were sailing by yourself, you could actually be walking away from the water without your model, stuck out in a weed bed in the middle of the lake.
Only in my early days did I use something other than gas. All the 'solid' fuels were deemed not contollable enough, and only used for 'toy' steam engines.
I used to use self pressurising methylated spirits burners, but they were a little difficult to design and make, but once perfected they did a rather good job, but very dependent on outside temperature, really cold days, no sailing, as the burners relied on heating up pure methylated spirits in a tank, and on cold days, you couldn't get the heat to transfer from the burner head to the tank to sustain the vapourisation process. But once you got used to them they could easily be timed so that you came in before the fuel ran out.
Then came along the butane/propane mix burners running from a rechargeable tank, and they have now revolutionised steaming in a big way. Very controllable and consistent burning using a ceramic burner head.
Once I had bought one, and found out the necessary safety rules and pressure test figures, it was an easy step to making my own rechargeable tanks and burner heads, it kept the price for them very low, the only things that needed to be purchased were the jets, which if still doing it now, I could make myself, as I now have the equipment to drill super tiny holes with ease, and the gas control valves for turning it on or off. I suppose again, I could now make those myself as I got a lot of experience making miniature valves of that type when I went into having a precision workshop, and the ceramic material for the actual heads. I could make approx 6 burner heads out of one piece of material costing a little less than £10, 15 bucks. 
I do still use gas burners and rechargeable tanks, but not for steam generation, but for running my engines.
Please excuse the narration, I had a very bad chest infection at the time. You can just see the old rechargeable tank on the LHS.

[ame]https://www.youtube.com/watch?v=Mi_T60n52jg[/ame]

John


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## gus (Feb 8, 2015)

Hi John,

Take care. Get well.


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## Charles Lamont (Feb 8, 2015)

I would think this might be a suitable engine:

http://www.stuartmodels.com/item/89/stuart-twin-oscillator


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