Midwest 47' MLB Question

[Rudderman98]

Hey all!
I usually post on the "E" flight discussion forums but I recently discovered this forum so I thought I'd chime in.

Being an e-pilot is fun! But now and then, I need to take it slow. I got into scale ship building about four years ago and have enjoyed this hobby just as much as I do the airplanes. I have also ran fast electrics but the race schedules conflicted with my family time so I had to bow out. Although it wasn't a total loss for I made alot of very good friends along the way that I still keep in touch with.

Well here's my question,
I have a Midwest 47' MLB that I completed in October of 1999. Since then I have probably run the boat 4 times. Why 4 times? Because the motors get too hot and the Esc shuts down. I tried to prop it down like you would an airplane motor when it gets too hot and it worked but still has a short run time.

Has anyone else had this problem with this ship and if so, what was the remedy and what system are you using.

Specs on my MLB:
Twin 05 Direct Drive motors
6 or twelve cell sub "C" operation.
Props: 32mm Graupner propped down from 35mm
Esc: MCD SC-330

Thanks!:D
Perry

http://albums.photopoint.com/j/AlbumIndex?u=1653371&a=13918601

[Paul]

I don't know a whole lot about electric boats, but I'll give it a shot.

Have you checked the current draw with a Whattmeter?

To solve the overheating problem I have two suggestions:

1. Cut some cooling air inlet and exit holes some where on your boat. Even a little airflow will help a lot.

2. Put water cooling on your motors. I have seen setups on electric boats that take in cool water with a brass tube, sent it through a brass tube wrapped tightly around the motor, and expell the heated water overboard. I think most of the time the cooling water is forced through the tube by placing the inlet bedind the prop wash, but it might work in other places as well.

The first thing I would do is make sure your motors and batteries are drawing a reasonable current and have some air flowing over them. These are basic items to consider, just like in e-flight.

I am interested in this problem becaused I am looking for a slow, scale type of model (much like yours) for my son to drive around a local pond.

[Rudderman98]

Paul,
I have thought about watercooling the boat but it's speed wouldn't pick up enough water to do any good. I have a pair of new Speed 600 motors with internal cooling fans that I am going to use in lieu of the ones that came with the boat that do not have any cooling fans. I have seen where some modellers have actually used a make shift water pump systen to cool the motors. I wouldn't mind doing that but I also do not want to add more weight.

I unfortunately don't have any way for the heat to escape the motor compartment and I am looking for a place on the deck where I can add cooling holes without ruining the scale appearance of the model.

I had another MLB which was the Dumas kit and it never gave me any problems whatsoever. But the boat had larger props and used a 12 volt gel cell battery instead of the nicads.

Oh well, something to play with this winter.;)

[eddp]

I suspect the props could be the problem. Are you using the "racing" style props, or the "scale" style props?

The scale props have a much finer pitch and will provide a slower top speed but a longer (and cooler) motor run. Remember, a 47' MLB can only make about 25-30 knots, it's not a deep vee offshore racer!

In my scale boat experiences, I cannot recall ever having a problem with motors overheating, especially to the point of blowing an ESC. On the other hand, racing boats generally need cooling coils, and a 5 minute run time is par for the course.

To provide easy water cooling, place a pickup just behind the prop. The pickup is a piece of, say, 1/8" brass tubing epoxied into a hole in the bottom of the hull. Bend a right angle into the tube and cut one end off to make the scoop (imagine a piece of pipe with a 90 degree elbow on the bottom.) Alternately, the tube can be cut on a 45 degree angle, with the open, angled side facing the prop. Put the pickup scoop about 1/4~1/2" behind the prop disk, but avoid putting it directly behind the shaft centerline (less flow.)

Take some plastic fuel line, attach it to the pickup, wrap it around the motor a several times and then attach it to another piece of tube exiting the side or the transom above the waterline. When you are running, you should see a stream of water exiting the outlet.

God Luck!

-Edd

[Rudderman98]

Edd,
I have been using the scale props since day one. They are three bladers. The ones that came with the kit I think were 35mm. I dropped it down to 32mm and it seemed to keep things a bit cooler but still the motors would get pretty warm to the touch. There is NO ventilation as of yet. I'll look for an area that would make a good candidite to drill some cooling holes without taking the scale appearance away.

About the watercooling. I really do not want to drill anymore holes in the hull if I don't need to. I have watercooled some of my other boats with great success but I can't come to drilling any holes in this boat yet. I'm trying all other options first. This boat was an early version and I'm sure engineering changes have been made to the newer kits. In fact, I read that Midwest nows suggests a new Esc for the boat over the one they originally issued in the early kits.

[Sabrejock]

Perry: I recently installed running gear on a (approx 40") CG cutter owned by a pal. It's a twin screw single motor settup with 1:1 gearing to transfer power from motor to the two shafts. I had convinced him not to go the Mabuchi can route and he got a big Graupner marine motor (about US$70). This thing has power to spare and runs at a max of 4A on a 6 cell 4400 pack. He and grandkids run it for over an hour at a time. At this low current it doesn't get hot. It runs enclosed with an electronic control. I suspect that your motors are pulling way more amps. Tex.

[Sabrejock]

I confess, I lied in the above post. The motor I installed is a Dumas 2004. It's a 6v. It has a brother 2005 which is 12v. I've just confirmed with the owner and he says that after an hour of hotrodding it is barely warm. Price is lower than I said also, about US$50.

I guess the old adage buy cheap, buy twice applies to boats as well as planes. Tex

[Rudderman98]

Tex,
Well I did some bath tub testing today. Last night I added the new motors I bought off ebay which I was told are 12 volt Johnson Control motors. They look exactly like Speed 600 motor but they have an internal cooling fan. You'll love the price on these! How's 6 bucks a piece sound to you! I can get them ALL day long. I still have the guy's email address if I want more. Dumass wants waaaayyyy to much for the motors they sell. They can charge those inflated prices because most guy's who build scale boats have never played with "E" planes enough to know any better. Not that they don't know about electric motors, it's just "E" flyers do more with these type of motors.

Anyway, the motors were barely warm to the touch after running them on a six cell 2000 Sanyo pack for 10 minutes. The boat can accept 12 cells. The batteries are run in parallel. Amp draw on the twins was 18 amps max as was checked on an Astro Watt Meter using the original 35mm props that came with the boat. I thought I'd go back to the original props just to see what wuold happen. The esc was getting pretty darn hot considering it was a 35 amper. Hmmmm................. I really didn't like that esc to begin with.

I tested the boat with another esc rated for 35 amps BUT can handle 6 to 14 cells. Guess what.......no more overheating. Problem solved! I hope:rolleyes: