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1/2A Size Dumas Boat Club

Old 12-03-2009, 09:20 PM
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Default RE: 1/2A Size Boat Club

Dumas does have a hardware kit for .09 engines as well. On the Thriftway's box, it does say that its designed for 1/2A or A engines...I'm not familar with the small airplane engine sizes. What displacement is "A"?
The dumas .09 prop has aslightly larger dia. than the black 27mm props, and about the same as the MRP red props. Im guessing without measuring, thats its about 30mm, but the dumas prop does have less blade area....I was just going to hand launch the boat at full throttle and see if the larger props bog it down, if so I'l trim it a little.

The cox mini servos weigh nothing, .21 ounce or 6 grams.

I built the Thriftway my way, slightly more robust. I used epoxy in its construction, added a fillet of epoxy along the inside joint of the sponsons running area, added a 1/8 ply doubler on the right sponson inside for a brass turn fin. There are three 1/8 ply's to form the transom. and a 1/8 ply double for the strut that will be mounted on the bottom near the transom...
In addition, I added 1/8 square balsa along areas that I felt needed more area for glue along the deck. I did replace the deck with 1/32 ply because I did feel that the mahagony would soak too much sealer. I think next time, I may just skin the whole thing with 1/32 ply....The dumas mahogany looks good, but it too dry and thirsty..
I'm going over to the dollar store tomorrow and see if I can find a 4" spiderman figure for a driver....
Old 12-04-2009, 06:15 AM
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Default RE: 1/2A Size Boat Club

well it looks like you boats go faster then mine

i had been soo bizzy that i hadnt had any time to work on it.

i do have som spektrum micro servo's

but not i micro spectrem recever (why spektrum cus it has 2.4 ghz and i love that)

Old 12-04-2009, 01:01 PM
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Default RE: 1/2A Size Boat Club

Heres where I'm at today,

I made a framework for the 1/64 ply cone to attach onto. Now i have a choice to make as how to mount the fuel tank, it is a perfect 3/4 oz. wedge tank....The best way I came up with was to cut a wedge shaped hole thru the deck behind the engine bulkhead so the tank will be mounted under the deck as in the pic....
What do you guys think?
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Old 12-04-2009, 04:24 PM
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Default RE: 1/2A Size Boat Club

That's not actually a bad spot. I built my Atlas with a rectangular tank in the same location, only it pointed left to right.

I like the idea of seeing the tank sit right next to the motor in the engine bay but not sure how much room you have to play with there and how well the tubing layout would work.

Either way I think you will have decent fuel draw and not much change in balance as it empties.

Having a hidden fuel tank would really keep it clean though, and really let the motor show off all by itself.
Old 12-04-2009, 05:29 PM
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Default RE: 1/2A Size Boat Club

It has some room to play with in the engine area. but i do like a clean & functional look.....Also, Since I'm using the 3/4 oz tank, installing it this way makes it the most logical and cleanest way of accessing the tank for maintaince without modifing the deck in that area...

Check out with how I mounted the cowl...

The thriftways cowl is very thin and flimsy & I wanted it to be able to slide on & off under the deck. So I had to beef it up somewhat.
I trimmed a 1/8 piece of scrap wood from the kit and fitted it in the front of the cowl with a bit of a lip hanging down. then 1/32 ply for the bottom, the original wood for the fin was warped from age so I traced a new one from 1/16 ply.
The cowl is much stronger and sturdier as seen in the pic...It actually fits pretty well. I willmost likely use 3M tape along the seam for water sealing the radio area.
In thecockpit area the bottom of the plastic is tissue thin, and in the directions,it says to cut that little square part out, probably to access the universal or wire to adjust the rudder for free running. I did cut it out cause it wasso thin and to also allowme to lay a bead of thin ca on the inside. I'm going to fill in whatever gaps there are with plastic wood filler...
I ordered someklass-kote from an ebaystore which is an 2 part epoxy paint for thisone and my other boats....

Now I know what I have been doing adds weight, but it also adds years to its longevity and structurial integrity which to me at least, is important to models that I care about.
I only wish there was a racing club or interest out there for sanctioned racing in these little Cox boats...

This is going to be a cool looking boat when its done...

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Old 12-05-2009, 03:34 PM
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Default RE: 1/2A Size Boat Club

R.J.,

Just understand that if you mount that old wedge Perfect tank on it's side like that you are going to lose about half of it's capacity without removing and reconfiguring the vent tubes.

LAter,
Tim
Old 12-05-2009, 06:35 PM
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Default RE: 1/2A Size Boat Club



I have about 5 Perfect wedge tanks, 4 are 3/4 oz. & 1 1/4 oz...The tubes on the 1/4 oz is positioned right but 1/4oz. isnt going to get me far, as hot as it gets down where I'm at I'l probably run for about 30 seconds and the rest lost to evaporation...I tried to sell them on ebay so I can purchase a retangular tank, but no luck selling them, so if anyoneneeds a 3/4 or 1/4 wedgie send me a pm with an offer...

However this particular wedge thats shown in the pic, you cant see it in the photo but the tube on the left side is angled down into the bottom corner...

Has anyone else out there started to work on their Dumas Boats? I would like to see more out there.....</p>
Old 12-05-2009, 07:07 PM
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Default RE: 1/2A Size Boat Club

I dont own any dumas boats just 1/2A boat gear n engines. Does anyone know where there are some dumas hydro plans to download?
Old 12-09-2009, 08:29 PM
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Default RE: 1/2A Size Boat Club

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 tetherthe edgedsponsonsshould 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 frontsreally like a wide deep vee in the nose with an air trap.
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Old 12-09-2009, 09:16 PM
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Default RE: 1/2A Size Boat Club

Hi Pond Skipper, welcome aboard,

Thanks for sharing with us. The boat looks pretty cool, I havent seen a sponson design like that, perhaps being from that era, maybe sponson design was still developing?

Those .049 Atwood outboards you can still find sometimes on ebay...

Do you have a boat, or any projects?
Old 12-10-2009, 12:37 AM
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Default RE: 1/2A Size Boat Club







some more pictures of my boat with controlles


and here is a vid of the controlles


[youtube]http://www.youtube.com/watch?v=wJ8KRMHguA4[/youtube]
Old 12-10-2009, 01:06 AM
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Default RE: 1/2A Size Boat Club

hey thats pretty cool, how about a video of it running in the water?
Old 12-10-2009, 03:43 AM
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Default RE: 1/2A Size Boat Club

well i have to do 2 or 3 things to do that

1 make a cover for the battery compartment
2 test if it leaks on a inflateble pool (and test the run time)
3 wait til it stops raining and go to a lake.
4 find a boat to retreve it when it stalls..
Old 12-10-2009, 06:09 AM
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Default RE: 1/2A Size Boat Club

sorry for the double postlook what i ordered (i convinced my parrents i need a glow plug for my hovercraft)so I placed 1 order (glow plug adapter)and a cox 049 diesel enginehttp://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=390116835008so i can bypass my parrents if i have to
Old 12-10-2009, 06:28 AM
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Default RE: 1/2A Size Boat Club

I looked at the motor that is one nice conversion. I read the running instructions and they still say that it takes Cox 1/2A Glow Fuel, it didn't go into any detail about how to mix or run it on model diesel fuel.

That might be a better fuel for you to come up with if buying nitro fuel is a problem. I think it is equal parts of ether (starting fluid out of a spray can), parrifin oil (lamp oil) and castor. I would have to check on that.

Glow plugs were always hard to get my parents to buy for me and the hobby shop was miles away, and if I had any idea there was diesels I probably would have tried one. I still might try because I've always been curious.

Your boat I bet you can't wait to try. Looks like its all ready to go. If you stay with a small pond you could use a fishing pole with a tennis ball to cast out to it to bring it back in, but its always better to have a boat to use.

Just get everything all set to go at anytime and keep talking to people about your boat maybe someone will help out getting a fishing boat to the lake.

You should check out the 1/8A and 1/2A Airplane Forum on RCU here theres lots of great engine talk there if you haven't found it yet. Lots of great tips on running Cox engines.

I have been looking at ball thrust bearings to maybe put in somewhere by the engine to take the thrust load off of it and get a slicker driveline. Also looking at dental bearings that are small and very high speed to maybe work into my own strut and propshaft.

I might try and work in a ball thrust bearing behind the prop driver by machining some of the nose off the case. The intake collar of a TeeDee or Medallion can be used to adjust the final clearance and a set screw put into it to lock it down??? I don't know if it would be worth the effort or not.
Old 12-10-2009, 05:13 PM
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Default RE: 1/2A Size Boat Club

Hey Jetpack, I remember those thrust bearings by MRP. If you are lucky enough to find a set I think they would work out great in these boats...Or if its possible to fabricate something similar....What it consists of is a plastic ring with ball bearings evenly spaced inside the ring, sandwiched between two steel washers, all bored out for 1/8 shaft...

Thats why I went for a replacement Cox crankcase with a brass driveplate...The prop turns left, so that would apply pressure going into the engine, so I thought that with a brass driveplate it may act as a thrust bearing...Those crankcases were intended for a pusher prop engine, thats why they're made with brass....
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Old 12-10-2009, 07:58 PM
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Default RE: 1/2A Size Boat Club

The brass fronts are great because the brass is harder than aluminum. Aluminum to aluminum is not the best bearing surface because it continually eats itself, oil or no oil. Oil just seems to form a slurry for it to act faster. Brass on aluminum is an acceptable bearing surface if theres plenty of oil which there is.

I'm not sure if they used thrust washers in those assemblies or not, but plan on using stainless washers. The phenolic type do not hold up but can be used with a stainless washer putting it up to the engine, not the prop driver. You always want the stainless against the prop driver if using both.

The washer will grab the engine before the prop driver because the prop driver is always cut with a very slight bevel in the back of it, allowing a very small contact area at first and it grows outward as it wears in. I've seen many TD type prop hubs and they are always cut like that and its how I remember the wear when I ran my boat. After a few tanks, the dark gray sludge stopped forming around the nose of the engine and became more and more clear as it got run time on it.

After everything stopped wearing in somewhat and I got my first fun out of it, I took everything apart to learn where the wear was, inside the motor or elsewhere before any parts got hurt. The washer stays stopped against the crankcase and the prop driver is what starts to ride all the time against the washer. The case seems to have more grab on the washer than the prop driver does. I also remember bringing toothpaste with me to dab in with a wet finger just the slightest amount in the washer to help bed the washer. Just a short tank of fuel and a good rinse helps get the rings started for the oil.

This is when I also substitued the size of the roll pin in the Dumas Universal Joint to the next size up by driving out the original pin and drilling out the hole for the new pin size. It fits perfectly in the slot, no play. It gets its own clearance as you break it in. I remember mine going really slow with it at first and then sped up but after the run it was piping hot at the universal, but after a drop of oil on it before the next run after letting it cool it was great and stayed there.

Below are those thrust bearings we're talking about. I have to grab a TD and do some measuring now but I'm sure theres something that I can do. It looks like the ultimate hot rodding trick, but I have to tell you the washers do a fine job. I want to get away from the wear particles that take place there. They will eventually wear out your crankshaft bore too soon.

The other is a flanged dental tool bearing with an 1/8" ID but nothing smaller around than a 1/4" OD. That's too big already for me to want as a strut diameter.

They are however available with smaller ID's than 1/8" and a stepped propshaft might be a solution there, going from a 1/8" dia. for the prop and threads down to a smaller size but still have good wall thickness for the .098 cable bore. This will bring the OD down some, maybe to match the hub diameter of the props.
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Old 12-10-2009, 09:07 PM
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Default RE: 1/2A Size Boat Club

The first one with the ball bearing and two washers looks good. That would be my first choice if the right size is found. where did you find that one at?
Old 12-10-2009, 10:11 PM
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Default RE: 1/2A Size Boat Club


http://www.vxb.com/Merchant2/merchan...ry_Code=Thrust

http://www.vxb.com/page/bearings/PRO...arings/Kit7199
Old 12-10-2009, 10:49 PM
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Default RE: 1/2A Size Boat Club

That dental bearing can handle up to 450,000 RPM.....

I'm really diggin' those thrust bearings now...Thanks for the info! What size would you be looking at?
Old 12-10-2009, 11:58 PM
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Default RE: 1/2A Size Boat Club

Well I measured up the front end of a TD and here's what I found.

The bearing thickness has to be thin, the land area in the nose of the crank is only .125" and from there it is undercut so the case and ring can only be cut 1/8" or so...

A small amount could be taken off the back of the drive plate also to make room.

I would hate to loose any land area the crankshaft has in the case.

This is where I wonder if it would be worth the effort.

Sometimes if a bearing isnt installed right on the money it robs all kinds of power.
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Old 12-11-2009, 12:22 AM
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Default RE: 1/2A Size Boat Club

Why not just take back the carb retaining collar and go with a larger ID hole on the thrust bearing set so it slips over the crank case threads. All the pressure will be on the collar and bearings. = ) Now you have tons of room as that collar can be taken back plenty. There is another way. Take a look at the sketch you simply remove some of the prop plate from its back side.
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Old 12-11-2009, 01:27 AM
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Default RE: 1/2A Size Boat Club

Making an arbor for the prop plate would be the way to go and leave a wall for the splined portion, and also to leave a boss to locate the bearing.

That way I'm not touching the case at all, less parts to cut and not harming anything but a prop plate.

Sometimes its great to have another pair of eyes.

Thanks Skipper
Old 12-11-2009, 01:32 AM
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Default RE: 1/2A Size Boat Club

Your welcome laddy... lol its AM with a new water related name. Do to me skippin me hydro's on ponds. = ) Yes I think pic 1 will work fine long as theres enough meat around the spleen to avoid a crack once heated up fast.Another trick is setting it allup so thecrank shaftsfly wheel for the piston justfloats off the crank case a hair this will allow oil to flow better up to the front without rubbing the piston rod pin on the back plate.
Old 12-11-2009, 10:54 AM
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Default RE: 1/2A Size Boat Club

Hey Jetpack, looks like your thread you started here is really paying off!!!.......[img]file:///C:/Users/Ron/Pictures/rock1.gif[/img][img]file:///C:/Users/Ron/Pictures/rock1.gif[/img][img]file:///C:/Users/Ron/Pictures/rock1.gif[/img]


Keep it up guys!

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