So my nephew, Mike, is opting to scratch build a boat from full sized plans (ambitious for a first model). But he is creative and talented so I think there is a chance at success. I will try to post progress as we move forward on this project. I can't wait to see this model steaming up the Russian River in the wine country.

The positioning does look a little after but that depends since there will be a full tank of fuel forward. Best way to test is a real float test. You can even do it before the hull is fiberglassed or sealed. Just wrap it in plastic sheeting and tape it to the inside gunnel. Put everything in it you intend to add. Nice design on that hull.

Originally Posted by esaley4527

The positioning does look a little after but that depends since there will be a full tank of fuel forward. Best way to test is a real float test. You can even do it before the hull is fiberglassed or sealed. Just wrap it in plastic sheeting and tape it to the inside gunnel. Put everything in it you intend to add. Nice design on that hull.

I don't think the balance will be an issue as I expect we will have to add a lot of ballast to drop the model to the waterline. I was planning on just using the camp stove gas cartridges to fuel the boiler and they don't weigh very much. Your idea of wrapping the hull in plastic is a good one. When I balanced the Borkum I didn't realize that I needed to take care about the lateral balance and had to retrofit some large lead sinkers to keep it from listing.

Hi Bill,
What size camping stove cartridges, are you using. The smallest I can find in my area are the 8oz ones, used to find the 4oz ones but they are not carried here now.
Gerald.

Originally Posted by steamboatmodel

Hi Bill,
What size camping stove cartridges, are you using. The smallest I can find in my area are the 8oz ones, used to find the 4oz ones but they are not carried here now.
Gerald.

Gerald,

I can get the 4 oz. ones here (3.5" diam.). our local Big 5 Sporting Goods carries them. I think REI carries them too. The store offers more than one variety, but I am not aware of any differences. My experience is that they provide more than enough heat for reasonable power. On my Borkum I added a servo to control the gas flow, but haven't run it enough to know what the optimum setting is. I haven't worried about fuel efficiency but know that it's not good as running the Borkum on the bench in the shed sets off the CO monitor.

Bill

I believe Mikes machine can mill material in 3D, and he has a 3D mathematical description of a full sized steam launch which he can control his machine with. I am suggesting that he mill two blocks: one for the bow and one for the stern. I made a drawing of my concept of how the hull would frame up.

Mike sent some more drawings. He moved the engine/boiler forward and down and has defined a bulkhead/rib structure.

Bill, its a small world. I too am building the Gemini as a steam model. I don't have the computer skills your nephew has, so I broke out the pencil and paper, and lofted the frames from the offsets at a scale of 1 1/2 inches to the foot. The frames were then cut out on the bandsaw and sanded. 1/8" balsa was used as planking. The fantail stern was a bit tricky, but I got it planked up okay. I am going to glass the hull and paint, so not worried about needing a little filler. I am currently waiting for the first coat of filler to harden so I can begin fairing.

Not to hijack this thread too much, as it looks like your nephew is off to a great start. But I am wondering about power for this boat. At the scale I am using, the boat is 27 inches long, and 8 inches wide. Now, this is my first steam build, and I really have no clue how to size the engine to the boat, nor the boiler to the engine, so bear with me please. The engine I was planning on building is the Elmer's #15 Fancy Wobbler. Its single acting, 3/8" bore, 1/2" stroke. Steam is going to be from a 3 inch diameter copper boiler, not sure of the height. The engine seems to be similar to the Midwest Heritage, which from the literature looks to be just big enough to power this boat. I would assume that building a boiler similar to the Midwest one would then be about in the ballpark.

If anyone has any insight they can share, comment on my current direction, or even some resources I could check out, with respect to sizing engines to boats, and boilers to engines, I would greatly appreciate it.


Thanks much
Chris

Originally Posted by cglynn

Bill, its a small world. I too am building the Gemini as a steam model. I don't have the computer skills your nephew has, so I broke out the pencil and paper, and lofted the frames from the offsets at a scale of 1 1/2 inches to the foot. The frames were then cut out on the bandsaw and sanded. 1/8" balsa was used as planking. The fantail stern was a bit tricky, but I got it planked up okay. I am going to glass the hull and paint, so not worried about needing a little filler. I am currently waiting for the first coat of filler to harden so I can begin fairing.

Not to hijack this thread too much, as it looks like your nephew is off to a great start. But I am wondering about power for this boat. At the scale I am using, the boat is 27 inches long, and 8 inches wide. Now, this is my first steam build, and I really have no clue how to size the engine to the boat, nor the boiler to the engine, so bear with me please. The engine I was planning on building is the Elmer's #15 Fancy Wobbler. Its single acting, 3/8" bore, 1/2" stroke. Steam is going to be from a 3 inch diameter copper boiler, not sure of the height. The engine seems to be similar to the Midwest Heritage, which from the literature looks to be just big enough to power this boat. I would assume that building a boiler similar to the Midwest one would then be about in the ballpark.

If anyone has any insight they can share, comment on my current direction, or even some resources I could check out, with respect to sizing engines to boats, and boilers to engines, I would greatly appreciate it.


Thanks much
Chris

Chris,

Congratulations on your ambitious project, and thank you for your comments. I thought about the power questions when I built the Borkum, wondering if the Mamod engine would be powerful enough to power it at a reasonable speed. As a fundamental guideline I simply consider how efficiently I can utilize the heat from the camp stove burner I am using. I knew that it would put out tons of heat so if I can use it to heat the water without loosing too much up the stack I can get a lot useful power. I am guessing that the steam engine might be about 30% efficient, but that should be a fairly constant number. The other important parameters are the pressure limit of the boiler and how rapidly the loaded engine will turn at that pressure limit. I am sure there are experts that can compute this last number, but I would just plan on being able to run at 60 psi. That should give you plenty of speed (as long as you aren't trying to keep up with the electric boats).

Bill

Originally Posted by cglynn

The engine seems to be similar to the Midwest Heritage, which from the literature looks to be just big enough to power this boat. I would assume that building a boiler similar to the Midwest one would then be about in the ballpark.

Chris,

Reconsidering your question: isn't the Midwest Heritage engine the one intended to power the Midwest Fantail II Launch? I built that and have enjoyed running it, but it is by no means overpowered. It put-puts along at a pretty modest pace, but then the power provided by the Sterno in the fuel cup is pretty limited. If you are going to the trouble of scratch building a planked hull you might want to consider a twin, double acting, reversing and self starting motor, like the new one from Mamod or the Twin V kit from PM Research. They are both reasonably priced and give you the advantage of a lot more control.

Bill

Thanks Bill. That is kind of what I was thinking. The good news is that engine choice is not really limited to anything, as in addition to building the hull, I am going to build the engine. My dad has a hobby machine shop in his basement, so I have access to a small lathe and mill, and he's got the tooling, taps, dies, etc, to build an engine. He has been tinkering with little hobby live steamers for as long as I can remember, and got me started on this project. He ordered the plans for Gemini to build in full scale, took a look at them and decided he wanted a less involved boat building project. I lofted the plans with the intention of putting an electric motor inside a dummy boiler. It was then suggested that we could spend a few nights in the basement shop and under his tutelage building a proper steam plant for the model, which would be more appropriate for the design, and way cooler than electric.

So short story long, I thought of two things. One, as it is a wobbler engine, I can slightly increase bore and stroke on the Fancy engine, add a couple of ports, and a lower cylinder head, and make that double acting, or go with a twin, which would look really cool.

The one thing that concerns me with engine size is that I am finding the Gemini, at the scale I chose (mostly for the convenience of lofting...inches to 8ths is easy enough with a good ruler) the model is kind of in between. It is almost too big for a simple single wobbler, but too small for something like the PM research twin. My dad does have a spare casting set for the PM research single double acting though...I just wonder if that is too big to go in the boat.

Decisions, decisions.

While I am thinking about it, are there any hard/fast rules, or even suggestions for that matter, of engine displacement vs boat size/displacement, assuming in this case a boiler that is 3 inches in diameter, with a roughly 27 cu in reservoir, fired by sterno?

Thanks

Originally Posted by cglynn

Thanks Bill. That is kind of what I was thinking. The good news is that engine choice is not really limited to anything, as in addition to building the hull, I am going to build the engine. My dad has a hobby machine shop in his basement, so I have access to a small lathe and mill, and he's got the tooling, taps, dies, etc, to build an engine. He has been tinkering with little hobby live steamers for as long as I can remember, and got me started on this project. He ordered the plans for Gemini to build in full scale, took a look at them and decided he wanted a less involved boat building project. I lofted the plans with the intention of putting an electric motor inside a dummy boiler. It was then suggested that we could spend a few nights in the basement shop and under his tutelage building a proper steam plant for the model, which would be more appropriate for the design, and way cooler than electric.

So short story long, I thought of two things. One, as it is a wobbler engine, I can slightly increase bore and stroke on the Fancy engine, add a couple of ports, and a lower cylinder head, and make that double acting, or go with a twin, which would look really cool.

The one thing that concerns me with engine size is that I am finding the Gemini, at the scale I chose (mostly for the convenience of lofting...inches to 8ths is easy enough with a good ruler) the model is kind of in between. It is almost too big for a simple single wobbler, but too small for something like the PM research twin. My dad does have a spare casting set for the PM research single double acting though...I just wonder if that is too big to go in the boat.

Decisions, decisions.

While I am thinking about it, are there any hard/fast rules, or even suggestions for that matter, of engine displacement vs boat size/displacement, assuming in this case a boiler that is 3 inches in diameter, with a roughly 27 cu in reservoir, fired by sterno?

Thanks

I encourage you to build the engine. That would be the most challenging and satisfying. If you are building it from scratch the single cylinder wobbler would be a good engine to start with, but I think that would be too small for the boat you are building. I don't think the PM Research engine would be too big for your boat.

Ultimately the boiler and engine parameters are governed by basic physics. I am sure there are engineering equations that have been derived governing the parameters you are interested in, but if you are familiar with basic physics you can derive them yourself. I would find that very satisfying.

Bill

Thanks for the advice Bill. I will ultimately look into putting together some equations that would work for boiler size vs engine size.

In the mean time, as honestly, I like building more than crunching numbers, I sort of brute force reverse engineered the problem. I searched for steam launch kits that were about the same size as mine, and then looked at the specs for the recommended engine.

I am going to use the PM Research double acting single as the basis for my engine, modify the base/post to be a bit smaller to fit in the boat and a bit fancier (actually going to scale up the Elmer's Fancy base/post) and use a smaller flywheel so it can be mounted lower in the boat.

So the engine is sorted. Now I've got to figure out the interior fit out. I like the look of the Elliot Bay Launch interior, so going to emulate that. The tricky part is figuring out how to gain access to the radio gear in the back of the boat. I was thinking about making the aft seating unit removable, so that whole section will simply lift out of the cockpit, and allow access to the battery pack, rudder servo, rudder post, and RX.

Fortunately, cereal boxes are plentiful around my house, so I can try some different mock ups until I find one I like.

CG

I have seen shots of the "Elliot Bay Launch" both full size and model that have a flush mounted hatch on the stern deck.
Gerald.

Originally Posted by cglynn

Thanks for the advice Bill. I will ultimately look into putting together some equations that would work for boiler size vs engine size.

In the mean time, as honestly, I like building more than crunching numbers, I sort of brute force reverse engineered the problem. I searched for steam launch kits that were about the same size as mine, and then looked at the specs for the recommended engine.

I am going to use the PM Research double acting single as the basis for my engine, modify the base/post to be a bit smaller to fit in the boat and a bit fancier (actually going to scale up the Elmer's Fancy base/post) and use a smaller flywheel so it can be mounted lower in the boat.

So the engine is sorted. Now I've got to figure out the interior fit out. I like the look of the Elliot Bay Launch interior, so going to emulate that. The tricky part is figuring out how to gain access to the radio gear in the back of the boat. I was thinking about making the aft seating unit removable, so that whole section will simply lift out of the cockpit, and allow access to the battery pack, rudder servo, rudder post, and RX.

Fortunately, cereal boxes are plentiful around my house, so I can try some different mock ups until I find one I like.
CG

Chris,

Good luck with your project. Mike just sent some new drawings.

Bill