Dumas 19ft Racing Runabout - Page 3 - RC Groups
Thread Tools
May 02, 2007, 11:35 PM
Grumpa Tom
Kmot's Avatar
mcfly: Graupner motors are outstanding. I have used a few of them. Specifically the Speed 700's and Speed 600. They are powerful, will take far more voltage than they are rated for, and last a good long time (forever) as long as you don't over volt them so high that they melt down. Water cooled brushes and can are a good idea when over volting, however. As an example of what they can take, the go fast guys get the 9.6V version of the Speed 700 and then run it on 14.4V and it lasts forever. I have a Speed 600 rated at 6V and I run it on 8.4V in a monster truck.
Sign up now
to remove ads between posts
May 02, 2007, 11:51 PM
I used the Dumas High Speed #2025 in mine. The speed is good, it planes out nicely. I drive with a heavy trigger finger and was a little disappointed with run times on 6 cell 3600 Nimh packs. I swapped the motor with another 2025 that I had purchased for my next Chris Craft and only got 5 min run times so I put the first one back in. I get about 15 minutes at speed which I guess is okay since the motor is ready for a cool down by then. The MACK 3600 is intriguing to me but I haven't bought one yet.
May 03, 2007, 12:25 AM
Kmot, My LHS has a nice selection of Graupner motors but all the variations confused me and when I asked questions I got shrugged shoulders from the kid behind the counter. I figured that I'd better wait until I was smart enough to know what I wanted.
May 03, 2007, 01:04 AM
Grumpa Tom
Kmot's Avatar
Originally Posted by D Anderson
when I asked questions I got shrugged shoulders from the kid behind the counter.
Unfortunately, that is a more typical response than not. I get the same thing here. Ask one kid if they have a certain part. He looks for five minutes and says no, not in stock. Ask the next kid and he turns around and immediately pulls it off the board.

What ya gonna do?
May 03, 2007, 06:09 PM
Registered User
I was thinking about the Speed 600BB; I figured it would be up to the task. I found it for 29.99 online, seemed like a good price when compared to similar motors in the price range.

Said to operate from 6 to 9.6 volts. I'll probably stick with the 6 cell configuration at 7.2 volts. I am presuming that the mAh will have an effect on run times? Is there a particular mAh rating that is ideal for such a set-up (decent run time and speed)?

I figure 6 cell will stick with the proper balance according to the instructions. Also, the weight of the Speed600 was listed less than the weight of the Dumas 2025.

I was looking at Propeller selections and it is hard for me to make heads or tails of whats out there. Obviously, if I replace the stock plastic one the replacement needs to be of roughly the same diameter (to avoid interference problems). I am wondering on two or three blades? Three bladed props seem to be less common in the 1" to 1.25" diameter. The parts list in the instructions list the propeller at 1.25" diameter, but upon measurement, it seems to be closer to 1". I was thinking about a standard Octura metal two-bladed unit--mainly to replicate the stock plastic one.

Just throwing around a few ideas--I could be way off, since this is all pretty new to me. Thanks again for the advice!
May 03, 2007, 06:35 PM
Registered User
I'd go with either an octura x430, or x432 prop
May 04, 2007, 11:28 PM
Registered User

While I wait for my running hardware...

I started to look closer at the metal fittings....they look less than ideal, to put it nicely. I removed castings marks on the "gas cap" with small files and then used some standard 320 grit paper to roughly smooth everything out. Next was some 2000 grit that I "polished" it all down with. I am going to get some metal polish from work; hoping that will remove all the swirls and really get things polished.

It took a little bit just to do the gas cap--still have window frames, exhaust tip, bow light case, vent caps, etc...quite a bit of tedious work. I think the end product--highly polished fittings--will be worth the effort.

Just waiting for my running hardware to arrive so I can get that installed, then finish up sanding the mahogany. Once the hardware arrives I'll be sure to get some pictures of it posted. Until then...
May 05, 2007, 12:27 AM
Grumpa Tom
Kmot's Avatar
You did a nice job on the gas cap. Just like wood, you can keep sanding metal with finer and finer grit to get the metal to shine up and have smaller and smaller swirl or scratch marks.

Anyway, about your motor. That is an excellent choice. I am sure you will be happy with it. You will be surprised how much power it has on a 6-cell pack. As for MAH, the larger the amps the longer the runtimes. But this can be a double edged sword. Electric motors will get hot, it's the nature of the beast. You can easily overheat them and damage them if you run them too long without a cool down period. You should experiment for awhile with your new boat. It may be able to take 15 minutes of run time before it needs a cool down period. It may run an hour or more and never overheat. But you won't know that for sure until you test it first. What you should do when you first run the boat is take it out for a minute or two at high power levels and then bring it in and mesure the motors temperature. Either with your hand or an infrared thermometer. The standard rule for testing with your fingers is 5 seconds. If you cannot hold the motor for at least 5 seconds without feeling like your burning, it is too hot. If you find your motor is just warm, or even cold, run it again for a few minutes and then bring it back in and test the temp again.

If the motor is getting hot, in a short period of time, you need to go to a smaller diameter, or less pitch, prop to take the load off the motor. If the motor only gets hot after a very extended run time, then you can use that as a judgement call to figure how long you should run it until you bring it in for a cool down period. If your motor never seems to get too hot, then run it to your hearts and battery capacity's content!

You can buy battery packs now with 4600 mAh storeage. That is 4.6 Amp Hours in a stick pack. Amazing! You could get extremely long run times potentially.

If all you want to do is blitz around at WOT the whole time, you may find your run times reduced and your motor temp's elevated. There is no standard answer to your question. It will take some trial and error to figure it out.
May 05, 2007, 12:41 AM
Registered User
Kmot--very well said. I will definitely do some experimenting once all is ready for the maiden voyage. I would like to be able to feed some speed to her when I feel the need; but I will not be buzzing at WOT all the time...although it sounds like fun!

I thought about building another mahogany boat (such as the Thunderbolt, or a barrel back) and just go all out on the drive train to get some serious speed...might not be scale, but one of these mahogany cruisers jetting across the water would be way cool...

Quick question--does the mAh rating change the battery weight?
May 05, 2007, 01:17 AM
Grumpa Tom
Kmot's Avatar
Slightly. But only because the larger mAh batteries are physically larger in size. Although the cells are all referred to as sub-c cells, they are thicker. I found that out a while back when I bought one of the newer high capacity batteries and I had a hard time stuffing it into the molded battery compartment on an r/c car.
May 06, 2007, 11:53 PM
Grumpa Tom
Kmot's Avatar
what's he got in that thing??!!
Probably a small block Chevy with an intercooled ATI supercharger.
May 07, 2007, 02:01 AM
This one has a Chris Craft MBL. 158 hp flathead six. A 350 is a common choice for repower, but Chris Craft never put a V8 in these. "Stoli" is a very nice example. I got to judge this boat at the Lake Minnetonka boat show last Sept. It won Best classic Runabout 19 feet or less.
The lever in the center of the steering wheel is the throttle. I've never seen manual spark advance in a postwar boat.
May 07, 2007, 10:58 AM
Grumpa Tom
Kmot's Avatar
Wow, the stock flathead six pops this boat out of the water like that?? Cool....
May 07, 2007, 11:04 AM
The MBL moves this boat along nicely, but Mitch is landing after a wake jump in this photo.

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Dumas 19' Racing Runabout P. Tritle Scale Boats 61 Jun 13, 2017 10:23 AM
Build Log A beginners build of the Dumas 19' Racing Runabout -=Odie=- Scale Boats 32 Nov 20, 2006 04:36 PM
Dumas 19' Racing Runabout, bow section dmb Scale Boats 5 May 22, 2005 11:40 AM
Fair price for Dumas Racing runabout ? K Lipskie Scale Boats 0 May 18, 2005 06:26 PM
My Dumas Racing Runabout arrives downunder! jb4845 Scale Boats 1 Feb 04, 2005 06:26 AM