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1/2A Size Dumas Boat Club

Old 02-25-2011, 05:40 AM
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Default RE: 1/2A Size Boat Club

Now I'm old but that video is older then me!! That poor guy in the center ,gotta get dizzy thanks MatejO
Old 02-25-2011, 07:04 AM
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Default RE: 1/2A Size Boat Club

You are welcome.
The video was found in the begining of this topic (1/2A Size Boat Club)
Old 02-25-2011, 11:05 AM
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Default RE: 1/2A Size Boat Club

To start 1/2A boat set-up just use a O-ring and small starter, or a lenght of rope under the flywheel (but then it take more than two hands!)
Old 02-25-2011, 12:51 PM
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Default RE: 1/2A Size Boat Club

I just use an old shoe string, wrap it around the flywheel a few turns and let it rip! Just be careful about doing it while the boat is on your lap or you might change religions
Old 02-25-2011, 01:32 PM
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Default RE: 1/2A Size Boat Club

So that is clear.
What about the lenght of the boat for 0.8cc engine?
Old 02-25-2011, 04:07 PM
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Default RE: 1/2A Size Boat Club

40 to 50cm would be optimum (16"<20") and it need to be very light, for props I have used 1" Dumas but want to try X427 Octura in my next build. I Europe it might be easier to find the small 29mm Graupner and trim if needed, for shaft I use .098" Octura cable with 1/8" stub shaft but a 2mm solid drive shaft could be used too with the Graupner prop or Zig-zag prop. There isn't much hardwares available for that size commercialy so almost everything has to be home build! I have a Tarno carb to use with Cox engines but I found and exhaust ring to be easier to use because of the sub-induction of most Cox engines which preclude the use of a muffler. Trottle control is actually not really necessary with .049 size boats, they run happily full trottle until the tank runs dry and not using trottle control save you the weight and space of an extra servo! Weight reduction is important with that size of boat and even the rudder doesn't needs much torque because of the low masse and speed,no need for more than a 9 grams servo and since the run is short you can get away with a small Rx battery. I now uses a small 2 cells Lipo in conjunction with an old esc (for its bec) but an UBEC could also be used.
Old 02-26-2011, 06:23 AM
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Default RE: 1/2A Size Boat Club

A better prop selection is what is really needed for these. Everything is so touchy because there's basically no horsepower to work with, and being able to vary the prop is the only link to get to what horsepower is there. Small changes have a big effect you can see on these.

My first boat I flip-started with my finger. Not impossible to do but be sure to bring a dry rag with you. Any water or oil on your finger or flywheel, it's going to get frustrating. Cracking the glow head open a little helps if you're not having any luck.

It is very important you have a good engine mount system, not just wood screws through the motor, or if you do...make sure theres lots of solid wood and use the longest ones you can find.

Most all of Dumas 1/2A boats are designed around 18" in length. Miss Thriftway, Atlas Van Lines, SkeVee-10, Short Stuff and SK-Daddle Jr. are all 18" long. I do not know if this is a good manufacturing length for them or if it just is a good size for the engine but I think it is about right.
Old 02-26-2011, 09:36 AM
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Default RE: 1/2A Size Boat Club

Jetpack thank you for your informations.
I saw your work in the front of the topic and all I can say is: respect!
18" long is the boat in my avatar.
It has got 700grams (1.543 pounds) but it is fast as hell (electric)...
I hardly belive that Cox can push the same boat to the reasonable speed.

I will use lighter materials on this vintage build!

I got all the needed information that I asked for.
When the project hits the working desk, you guys will be first to know
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Old 02-26-2011, 10:31 AM
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You won't be able to match the performances of electric with a Cox .049 because of prop restrictions and frictions in the drive train. On the other hand an air boat design as used for tethered speed might be very fast but tricky to implement as r/c. There is some good ideas in that site about small electric (a .049 Cox has about the same power as a Graupner Speed-400/6V)which can be converted to small IC power:
http://www.microhydros.com/
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Old 02-26-2011, 11:12 AM
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Default RE: 1/2A Size Boat Club

That's a really cool hull
Old 02-26-2011, 04:46 PM
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Default RE: 1/2A Size Boat Club

Here is a WenMac outboard in action!

http://www.youtube.com/watch?feature...&v=vS30hQZgNiQ
And the Allyn Sea Fury:
http://www.youtube.com/watch?feature...&v=iCZSik6GCTo
Old 02-26-2011, 05:16 PM
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Default RE: 1/2A Size Boat Club


Here is a good one = )
[youtube]http://www.youtube.com/watch?v=ohyQuig0E2g&amp;feature=related[/youtube]

http://www.youtube.com/watch?v=ohyQu...eature=related
Old 02-26-2011, 05:50 PM
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Default RE: 1/2A Size Boat Club

Not bad for a reedy(Cox black Widow),wonder what size of prop they uses as the engine doesn't sound too loaded. Wonder what the performance would be with that kind of .049 engine:
http://technohobby.com.ua/online-sho...ine-profi-08cc
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Old 02-26-2011, 07:41 PM
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Default RE: 1/2A Size Boat Club

LoL. now I know how the "S" word is pronounced in german... Very good videos tho. I always knew that if properly done a Cox. 049 can push a hydro at decent speeds.
Old 02-26-2011, 08:25 PM
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Default RE: 1/2A Size Boat Club

by
Old 02-28-2011, 12:16 AM
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Default RE: 1/2A Size Boat Club



Lol yes we all learned a new German word .. thereed enginewas running lil rich. I tend to run the first run rich a few laps till I know the engine is warm as she goes then tweak the needle if you can pressure tap your exhaust etc.. you could keep steady fuel pressure is what I do. I really recommend this for steady smooth running. The black widow is a good lil engine but the tee dee motors will really make a hydro such asin the last vid reallymove out and scream on the straights.[8D]</p>
Old 02-28-2011, 08:52 AM
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Default RE: 1/2A Size Boat Club

I contacted the German boater for information abouth the lengt and propeller:
This boat is 42cm long (with Rudder 51cm)
and 6cm/20,5cm wide.
The weight is 450g complete with full Tank and RC Components.
The Engine ist the 0,8ccm Cox and i use a GAUPNER 29 Prop.
For the Hull i use only ply wood, the cavities are filled with
polyurethane foam.
I also post him he link of this topic...
It&acute;s funny to see my Vid on this forum.
and they learned a new german word.
It looks like he is a great guy

Here are the pictures of the boat on the upper video:
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Old 02-28-2011, 09:59 AM
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Default RE: 1/2A Size Boat Club

Thank for the details about that boat, it confirm what I tought about using a larger prop than Dumas for .049 engines. Will start converting one of my old FE, seems to be lot of good boat builders in Slovenia!
Old 02-28-2011, 01:24 PM
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Default RE: 1/2A Size Boat Club

Did some work on an old FE electric outrigger to convert to wet power. Some pictures of what I use to connect .098" Octura collet to a 1/8"/5-40 Cox shaft,just a cut 5-40 screw to fit into the 1/8" bore of the collet holder(I file a flat were the set screw is so it doesn't pull out). For this one I will use a reedy fitted with TD .051 piston&sleeve (a good combo) and a balloon tank since the hull is narrow. Will start soon on a semi scale hydroplane and "Wild thing" style mono for the two other marine TD I have. That video from Pond Skipper really got my interest in 1/2A running again

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Old 02-28-2011, 01:42 PM
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Default RE: 1/2A Size Boat Club

You guys are killing me, I thought we were buddies?

now you have me digging thru my plans and got me thinking about building another 1/2A hydro. Thats is a really neat little outrigger Coriolan. The other rigger that was used in the video was wood over foam construction which would be very light and was running faster than I imagined a .049 would go. Augh! I sold my .09 Medallion! That would have made for a beast if used in a small boat...
My two dumas hydro's I built eariler were typhical dumas construction and may have been a bit "overbuilt". If I do another hydro I plan on using straight 3/32 balsa thruout its construction instead of using the supplied 1/16 ply.
The plans I have are of the Dumas 18 inch "Miss Thriftway", i didnt make copies of the parts from my U-71 Atlas... D'oh!


Nice thread you started JetPack..... 14 pages and still going strong...




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Old 02-28-2011, 02:02 PM
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Default RE: 1/2A Size Boat Club

Its still a bit cold here so its time to tinker, I too was more than impressed by that video first time I see an 1/2A boat produce a genuine rooster tail! Good thing that MatejO was able to talk to the builder and get some infos about props. I always had the feeling that the Dumas 1" prop just didn't had it and glad to see a Reedy swing a 29mm Graupner with authority. I am a fan of Octura props but never dared to use even an X427 with an .049 thinking it would be too much. Since MatejO from Slovenia is on line now I would like to know about those nice props in the picture he posted and the carb on his Cox engines.
Going back to Dumas boats they are indeed over engineered (wood must have been cheap back then!)and all the boats I build now less than 20" in lenght just uses 1/32" plywood for skin and only 1/8" for the transom to attach everything. The Outrigger skin is actually 1/64" plywood over a stick frame and the sponsoon are 1/16" balsa over pink foam with carbon fiber tubes
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Old 02-28-2011, 02:30 PM
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Default RE: 1/2A Size Boat Club

Graupner propeller K29 is not so special. In EU you can buy it in every hoby store for small bucks:http://mibomodeli.si/trgovina/index....roducts_id=503

The picture of cox motor and metal props is not mine( unfortunately ). I found it while I was surfing trought this topic...
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Old 02-28-2011, 03:08 PM
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Default RE: 1/2A Size Boat Club

Thank again for the infos, we can get the Graupner props here too from OSE(26mm and up)
http://www.offshoreelectrics.com/pro...for+4mm+shafts.
I was impressed by these small bronze props, the small 3 blades look more like for scale use than racing and the other might just be Octura! The two carb too are impressive,they kind of look like Tarno(except for the blue nut). Why don't you want to have the belt stay around the flywheel for running? Most IC boats from .21 to .90 run happily that way and you just need to tuck it away before lauching which is not a big deal
Old 03-01-2011, 02:21 PM
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Did some more work on the outrigger and discovered the purpose of that support for the front part with the German boat. With the reed engine the mount is so far away from the flywheel that the engine flex while starting, I'll have to make something similar for my "Hybrid" reedy. Not a problem with TD type which have a more solid arrangement for my next build! I made the radio box compartiment for the Rx ,rudder servo and bec( I'll use a small 2-Lipo in a bag up-front for radio power and just plug for on/off)the lid will just be a thin polycarbonate affair with tap since it won't need to be opened to access the battery. Kind of getting excited about that project and will start the building of more boats as soon as this one is complete, then just some warmer weather and a secluded pond with no irrate old lady around
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Old 03-01-2011, 07:31 PM
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Default RE: 1/2A Size Boat Club

I like the spring starter.......


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