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Old Sep 26, 2004, 05:48 PM
7th Dimension Member
andre's Avatar
San Jose, California, United States
Joined Mar 1999
313 Posts
Plans-Built Ski Cruiser

All,

This is my first RC boat, a semi-scale electric ski boat. Hull built from Jerry Dunlap plans (Model Builder plans catalog, #US 3872). Hardware scratch built. Designed for 05 car motor, but used what I had on hand:

Speed 400 6V (currently air-cooled)
8 cell CP1300 NiCd
Speed Control: homebuilt with old servo, solid-state amp, resistor
Dumas props 25 and 30mm
Drive shaft: 1/8 inch steel, brass housing and bushings
Rudder assembly: 1/8 inch steel, brass housing / bushings, hard nylon blade

Balsa hulled fiberglassed and painted with acrylics. Pics/run report/questions to follow.

Regards,
Andre

First pic: Bare hull, stuffing box and motor mount installed
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Old Sep 26, 2004, 05:56 PM
7th Dimension Member
andre's Avatar
San Jose, California, United States
Joined Mar 1999
313 Posts
more pics

2) Close-up of stuffing box (lube port taped over temporarily) and motor mount (balsa / light FG sandwich reinforced with CF strips).

3) Other end of stuffing box, supported by ply plate wrapped with FG and CA.

4) Wood sealed with oil-based poly-u. After drying and sanding, 3/4 oz FG cloth applied with polycrylic and a foam brush. This is really easy to do (compared to epoxy).

more coming...
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Last edited by andre; Sep 26, 2004 at 06:21 PM.
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Old Sep 26, 2004, 06:05 PM
7th Dimension Member
andre's Avatar
San Jose, California, United States
Joined Mar 1999
313 Posts
almost there

After FG, sealed with couple coats of polycrylic mixed with baby powder. Sanding, primed with Krylon sandable primer, wet sanding. Airbrushed with Tamiya acrylics and lots of masking tape. Top coat is Future acrylic floor wax, airbrush w/o thinner.

Bathtub tested both props, the 25mm felt anemic, so went with the 30mm for sea (lake) trials....
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Old Sep 26, 2004, 06:19 PM
7th Dimension Member
andre's Avatar
San Jose, California, United States
Joined Mar 1999
313 Posts
action shots

With a fresh battery, boat gets on plane immediately, moves right along. After a couple minutes of mixed throttle use, motor is very warm (uncomfortable after 2sec of finger contact) and so is ESC.

This I expected, from what I've read here and other sites 30mm is a lot for submerged drive and a 400. Just didn't want to cut the prop down without really knowing how to do this and rebalance etc.

Anyway, it's been a fun project that achieved my goals of passing a few winter hrs really cheaply. Now that I know it runs very stably and doesn't leak, naturally I want more (sustainable) power Looking for suggestions:

Water cool this current motor / brushes?
Speed 600 (version/battery/prop?) (Lots of people using 12 cells/700. The cells will fit but maybe not the motor. Could the hull even handle the power...?)
Car motor?
Brushless Mega (22 versus 15/turns/battery/prop?)

Any ideas would be welcome.

Thanks in advance,
Andre
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Old Sep 26, 2004, 07:11 PM
Sea Dragon-Lover
Umi_Ryuzuki's Avatar
PDX, OR
Joined Dec 2002
10,461 Posts
Changing the motor, or water cooling it is a good next step.
It also looks like the bow of the boat rides high, or may bounce.
Add some trim tabs to the back of the transom and bend them down slightly.
This should help the boat plane better.

Nice build up. Now you need to add the Water Skier
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Old Sep 26, 2004, 08:13 PM
7th Dimension Member
andre's Avatar
San Jose, California, United States
Joined Mar 1999
313 Posts
Quote:
Originally Posted by Umi_Ryuzuki
Changing the motor, or water cooling it is a good next step.
It also looks like the bow of the boat rides high, or may bounce.
Add some trim tabs to the back of the transom and bend them down slightly.
This should help the boat plane better.

Nice build up. Now you need to add the Water Skier
Umi,

Thanks, I've learned some build techniques from you and others on this board.

The water skier would be neat, probably need a bit more speed first

The boat doesn't bounce, but does surge bow-high under full power. I'm guessing that's related to the angled shaft? I'll try the trim tab suggestion, thanks.

-Andre
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Old Sep 27, 2004, 03:06 AM
Useful Idiot
Asturias, Spain
Joined Mar 2001
3,550 Posts
For something like this I wouldn't recommend anything bigger than a 600 on 8 cells max. The 400 on 8 cells is pushing it a bit, especially with the 30 mm prop. I'd use that prop for the 600 on 8 cells but drop to a 27 mm for the poor overworked 400 with 6 or 7 cells unless you have an unlimited supply of 400's. 2,000+ mAh cells would ensure a better run time.
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Old Sep 27, 2004, 11:55 AM
7th Dimension Member
andre's Avatar
San Jose, California, United States
Joined Mar 1999
313 Posts
Thanks for the input, Martin.

The 27mm prop would be the easiest change at this point. Will probably also add the cooling, then try a motor swap to 600.

As with the car motors, there are an overwhelming variety of premade packs (is this mostly marketing? I can't tell). Any packs that you can recommend (I'm also comfortable with soldering cells into packs)?

Thanks,
Andre
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Old Sep 27, 2004, 01:57 PM
Useful Idiot
Asturias, Spain
Joined Mar 2001
3,550 Posts
If your comfortable soldering your own packs, it's cheaper and allows more flexibilty of installation. E.g., a 7 cell pack could be split 4+3, which would enable you to move the c/g around more easily. In that case try to put the 4 pack on the port side and the three on the starboard. This will help overcome prop torque. Suppliers, I can't say (I'm gussing from the decoration of the boat that you're in the US ) but the e-zone advertisers deserve our support
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Old Sep 27, 2004, 02:52 PM
7th Dimension Member
andre's Avatar
San Jose, California, United States
Joined Mar 1999
313 Posts
Martin,

Good guess on the location, yes in central California. (That's Millerton Lake for any locals reading this). Was hoping to have this be a 4th of July boat, but hey what's a few months here or there.

Thanks for the advice on the pack placement. And yes, for most electric stuff I avoid ordering from the big T if possible

-Andre
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