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1/2A Size Dumas Boat Club

Old 12-11-2009, 09:48 PM
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Default RE: 1/2A Size Boat Club

I'm still anxious to hear robot's report seems he's the closest ready to go. I was looking at his radio box and what it would take to make a hatch.

I've been sanding parts from my SK-Daddle, Jr. kit. I think that will be the first one to hit the building board. I'll be trying my hand at making my own veneer plywood for that. The thick solid mahogany bulkheads are in rough shape being twisted and lots of raised grain. Not to worried about it though because these will just be used to trace.

I read somewhere how to relax wood like this with a spray of 50/505 mix of laundry soap/fabric softener and water using weights and paper and might try it before I trace them. I'll need plate glass shelf units for that, or stone.

I had a plate glass shelf I used to build airplane wings on and two of those for press plates would work good laminating the veneers with epoxy. I am going to try an idea of pre-finishing parts in epoxy after they are cut out using plastic sheeting over the parts in the press.

A small pegboard topped sanding box would sure be nice to knock together to sand over. I want to build one of these.
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Old 12-11-2009, 10:19 PM
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Default RE: 1/2A Size Boat Club

I have a Short Stuff still in the box. The radio compartment has a 1/6 ply top that sits on a lip around the radio box, and its held down by 8 small screws.

Theres a trick I used before with great success to make curves in plywood, such as sponsons sides. I grab my wifes ironing board, and spray a lite mist of water over the ply and iron over it, gently pulling it up making a curve that would match the curve of the sponsons sides....I used this method on all my boats....works great...
Old 12-12-2009, 09:11 AM
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Default RE: 1/2A Size Boat Club

Here's the parts for the SK-Daddle, Jr. kit that I am sanding to give an idea how many parts are involved.

The boat is built upside down flat on a board, gluing the bulkheads down onto the edge formers and then adding the strip wood chines and keel parts to the notched bulkheads.

After that, the bottom is sheeted and then it is pulled from the board and the second half of the bulkheads are added to their tops to form the curves of the deck.

The sides will have to be softened and clamped due to the large change in curves. The are made from 1/64th ply and have to go from a tube shape at the transom to a twisted curve towards the keel. After drying from the pre-bend they'll be glued in place. The deck goes on last as well as building up the radio box and lid.

RJ's trick with the iron will probably be tried along with that veneer softener recipe for the sides so they dont split and aslo clamp easier.

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Old 12-12-2009, 09:26 AM
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Default RE: 1/2A Size Boat Club

ORIGINAL: Pond Skipper

Found this kinda neat, notice there is no flat surface for the sponsons. I'm sure this helped some in steering when free running. On tether the edged sponsons should provide less off set of the prop and rudder to minimize excesses that rob speed. Notice with no gear this lil guy could go into the 30's. Last thought the chance of less flipping with edged sponsons. The fronts really like a wide deep vee in the nose with an air trap.
Thanks for the Atwood hydro plans! I've been someday wanting to own one of the old outboard motors and have been collecting ideas for a hull for it.

Here's a few that I've got. The small Hedlund hydro drawing comes from Scott Smith who also built a copy of his stock outboard runabout that is pictured. When I contacted him he was in the process of drawing up this second model.

I've been playing around in Paintbrush with what he provided a start for and finishing up some of my own drawings of it for patterns.
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Old 12-12-2009, 10:42 AM
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Default RE: 1/2A Size Boat Club

robot,

It looks like you have a cool little boat once you get her back together and running. Just a note about the Davis Diesel head. The Davis Diesel head uses funky little floracarbon head compression seals. These things are a complete pain in the butt. If you try to run the engine with any real rpm it blows these seal out and the engine stops of course. When I first tried running a Cox diesel conversion engine I too started with the DDD head. Once I figured out how to start the engine the first 3 runs resulted in three blown seals!!!! I had to either run the engine slow or ran a larger prop to keep engine rpm down to keep from blowing out those pesky seals. The much much better diesel conversion head is the Mecoa/RJL head. It is a real diesel head with an o-ring on the contra piston in the head. Anyone I have talked to that tried a COx diesel engine and tried the DDD head all had the same problem and ended going to the Mecoa/RJL head.

LAter,
Tim
Old 12-12-2009, 11:04 AM
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Default RE: 1/2A Size Boat Club

can the diesel cox be used in a boat

it seems that that would be awsome
Old 12-12-2009, 12:07 PM
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Default RE: 1/2A Size Boat Club

Sure a diesel converted Cox engine would be great in a boat. With the added torque of the diesel you could turn a prop with higher pitch. It's just the DD head has issues the RJL head does not .

Later,
Tim
Old 12-13-2009, 08:50 PM
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Default RE: 1/2A Size Boat Club


ORIGINAL: Tim Wiltse-RCU

robot,

It looks like you have a cool little boat once you get her back together and running. Just a note about the Davis Diesel head. The Davis Diesel head uses funky little floracarbon head compression seals. These things are a complete pain in the butt. If you try to run the engine with any real rpm it blows these seal out and the engine stops of course. When I first tried running a Cox diesel conversion engine I too started with the DDD head. Once I figured out how to start the engine the first 3 runs resulted in three blown seals!!!! I had to either run the engine slow or ran a larger prop to keep engine rpm down to keep from blowing out those pesky seals. The much much better diesel conversion head is the Mecoa/RJL head. It is a real diesel head with an o-ring on the contra piston in the head. Anyone I have talked to that tried a COx diesel engine and tried the DDD head all had the same problem and ended going to the Mecoa/RJL head.

LAter,
Tim
Had the same problem with that teflon disk in DD head, made myself a punch and die to punch as many disk I need out of any thin metal. First tried aluminium from pop can but then switched to copper of similar thickness(it has more flex to allow many increase or decrease of compression)
Old 12-15-2009, 04:23 PM
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Default RE: 1/2A Size Boat Club

cool so you make seal disks?

may i buy some

my engine came in.

anyone know what the manual means with a closed compresion screw
Old 12-16-2009, 10:55 PM
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Default RE: 1/2A Size Boat Club

My Cox diesel conversion has been only with planes, but with the DD head I could swing a 7X3 MAS prop with a converted TD .049 and Tarno carb. 1/2A Dumas boat ran Ok back then with just a reed valve cox and the 1" low pitch Dumas prop. My first Nitro boat was a Dumas deep-vee 10 (wood) with a Cox TD-049 on Nitro and it was a bit underproped with that Dumas 1/2A prop. Now there is real nice small props available (thank fast electric!) from Octura; X427, 1427, sure a diesel conversion would swing even a X430 in surface drive
Old 12-16-2009, 11:39 PM
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Default RE: 1/2A Size Boat Club

Thats the point I was trying to make in my Atlas build. Move that prop out the back instead of under the hull as designed and take advantage of modern prop design. at the time these 1/2A boats first came out I dont believe there were any prop choices out there that we have now. So they were designed with the thinking and technology alvaiable back then. with modern radio gear and the rise of eletric micro hydro gear out there, I think, at least thats the theory, that we should get some speed out of these things...
Old 12-17-2009, 12:40 AM
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Default RE: 1/2A Size Boat Club

well here are some more pics
img35.imageshack.us/g/img244m.jpg/
Old 12-17-2009, 12:44 AM
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Default RE: 1/2A Size Boat Club

That Deepvee-10 wasn't super fast (Was build as designed) mostly because of being too heavy, Dumas kits of that period where very over-engineered! I was using regular standart servo and Rx (25 years ago!). With what is available now and build lighter it could be much better. These new engines from control line combat (Fora,etc) would be impressive
Old 12-17-2009, 11:21 AM
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Default RE: 1/2A Size Boat Club


ORIGINAL: robot797

well here are some more pics
img35.imageshack.us/g/img244m.jpg/
See its a reed valve Cox, they brake crank easily when converted diesel except if you use the re-enforced crankshaft made by DD. The cool clamp might not be necessary since diesel run colder than nitro engines and 1/2A engines are already over cooled by convection due to the relative high surface in relation to displacement. Thats why smaller engines require high Nitro content to run at proper temperature
Old 12-17-2009, 12:11 PM
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Default RE: 1/2A Size Boat Club

it has a stronger crankshaft

it is a full diesel engine.
Old 12-18-2009, 10:26 AM
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Default RE: 1/2A Size Boat Club

sorry double post


my boat is as strong as a beats

i started her
i put it in a small container
and the water splassses evry were.
and it is the normal setting.

video soon
my other 1.2 cc boat is not as strong as that

but i has a problem.

the water isnt goeing into the cooling line.....

what to do
Old 12-18-2009, 11:15 AM
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Default RE: 1/2A Size Boat Club



the water will go thru the pickup line when the boat is at speed, it wont go thru the line if your holding the boat...you can check by running the boat, you should see water squirting out the hull where the exit line is.....</p>
Old 12-18-2009, 11:35 AM
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Default RE: 1/2A Size Boat Club

well i cant run it at great strait lengts of water now (all frozen up)

an when it is at rest it doesnt push it into the tube (engine runes)

i think i am adjusting it...

i also an cutting the video now so it should be up tonight
Old 12-19-2009, 01:54 AM
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Default RE: 1/2A Size Boat Club

When I built my first cox boat it was still winter with the lake in front of the house still frozen.

When the ice started to pull from the shore I would walk down and flip start mine, put it in the water just to test it and feel how strong it would be and check for any problems, fingers instantly frozen cold with fuel and stayed that way until I went in. Having flown these engines before, having one in a boat with a tiny 1" plastic prop struggling to free itself was awesome. You'll want both hands to hold it even. I kicked my single pick up tube over by taking out one of the screws and turning the bracket so the tube was behind the prop so the clamp was getting water.

I could tell as soon as the prop got rid of all its air and started to really grab that this boat wasn't going to be a putt-putt. It had plenty of torque for sure but found out on its first full free run it just didnt have enough pitch, or maybe even the wrong thrust angle. Either way it was slowed down by the prop setup.

The answer might be with the carbon props for electrics but those are very fragile to a glow engine. I'll be trying my hand at hammering a couple of the copper Dumas JG-1's.
Old 12-19-2009, 05:39 AM
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Default RE: 1/2A Size Boat Club

[youtube]http://www.youtube.com/watch?v=DcAcCGWQK0Q[/youtube]


my boat

and a small container
Old 12-19-2009, 01:43 PM
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Default RE: 1/2A Size Boat Club

Hey looks like Robots got a runner!
sounds like it wants to fly...I'm still putting the final touches on my Atlas hydro, but she'l be ready after the holidays. i'm looking forward in seeing your Deep V when spring comes around. I guess thats the cool thing about being in south Texas. winter average temperature here is 70 degrees. Today is 66...
I have three boats, the Atlas is almost ready, I'm painting my Thriftway now. And my Short stuff DV-10 is still in the box....I'm thinking about using a .09 in the DV 10 also...
The Thriftway may be my fastest 1/2A boat yet....
Old 12-19-2009, 06:03 PM
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Default RE: 1/2A Size Boat Club

well

good luck

spring isnt here until 2 to 4 months

and it freezes -8.4 degrees celcius.

and i like it.....

also we have snow
Old 12-24-2009, 03:30 AM
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Default RE: 1/2A Size Boat Club

Robot you need to build yourself a Lil' Swamp Buggy for the snow.

I wonder how well one would do on the snow??? Maybe not enough power, I wouldn't be sure...

I remember they pushed that Shrike prop power car pretty fast.

RJWest sent me tracings and a direction sheet of his Miss Thriftway parts that I was missing in my box. In the meantime I scanned the box art and the drawings, and even made a re-touched copy of the decal sheet for when I go to print mine.

Since there is very little around about this kit I will post some pictures.

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Old 12-24-2009, 05:12 AM
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Default RE: 1/2A Size Boat Club

it looks nice

i cant build more my parrents want me to get rid of most of my stuff (they say junk)

so i cant build much more

but i can make my hovercraft better
Old 12-26-2009, 08:21 AM
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Default RE: 1/2A Size Boat Club

Hey Jetpack! I recognize my boat! I just joined the forums and was poking around for outboard info and saw my Broccoli and Hedlund! I was actually considering building my Hedlund plan and taking closer measurements and photos of the 1:1 hull today. I ordered an Aquacraft EP1 and I think that hull in 1:5 or 1:4 might work well with that motor. 1:5 scale would put the boat at almost 23inches, which is small for the EP1 an 1:4 scale would put it at 28.5inces. I'll have to figure that out once I get the motor in my hand to see how it looks. I may also try to track down one of the Graupner 500-600 size motors.

My original design was (as you noted) for 1/2A power and was about 16-inches at 1:7 scale. Those drawings were "rough" shape drawings and not really perfect as I didn't have the full measurements on hand. I will send you a "fresh" set that are closer to the real boat. Drop me a PM with your e-mail address if interested...
- Scott

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