Project Solar Boat

Military surplus flooded nicad batteries formerly used for starting passenger jets and helicopters have higher CCA if you can still find them with a google search. Their prices are reasonable and would also have a higher reserve capacity. Lithiums are the best, but what is your personal budget and is price also a limit in the contest?

Porta

 

Not how sure you figured that , but here is the approx breakdown.

Batteries 55 lb
Motor 20 lb
Panels 80 lb
Skipper min 130 lb
Hull etc ~100 lb maybe less

(if we could wire our own cells together on foam core that would reduce the weight a lot. Maybe a project for next year)
total ~385 lb / 173 Kilo The max permissible weight of the boat is 450 lbs / 205 kilo

 

Oops, just saw you have to use lead batteries. But if you are using 2 of the smallest 26# to get under the 55# limit, seems like you overstated the CCA at 750 from Ricks yellow top post? Do you have a site for the motor, 800rpm seems low if it has not been geared down. A geared down outrunner model plane motor may be more efficient, as has been suggested.

Porta

 

Bob

What is your time frame?

Are you able to get spring steel round bar say two length 3m long and 8 or 10mm dia?

What batteries are you actually using? The one you nominated will exceed the weight allowance as far as I can determine.

Are you able to do a load test on the battery? The peak power that the batteries can deliver in a 10 to 20 second burst needs to be determined.

What controller have you got? Do you know the current limit?

The prop is a 16 X 16 and price is about USD13.

The APC prop will be suitable for the sustained run but may not be suitable for the sprint. That is why it is important to know the power that can be produced from the batteries. It is likely unrelated to the motor rating when you have small batteries.

Rick W

 

If you have a chance to make a few practice runs with your vessel, try shifting the skipper forward and back within the allowable cockpit to optimize trim. My guess is that you'll get your best speed with the stem just barely submerged.

 

bob

Noted, and best way!

In designing prop's, i take the same position with anything i deisgn...i run the numbers and check all the what if scenarios and let the final answers dictate and converge on the final solution. If i start with an assumption that one solution is better than the other i may miss something, regardless how many times i've done the calc's before. Due process still needs to be done, to prove it!

Hence in some situations an airplane prop may be worth while, owing to the low thrust on the prop, in others not, such as probable cavitation. I prefer not to to put the cart before the horse.

 

I stand, kneel and grovel corrected. The Opitma Batteries we are using are the D51s. Their specs are as follow:
12v
38 Amp Hours
450 CCA
and weigh 26 lbs.
I am not sure how changing our available CCA 1500 to 900 Amps will change our prop, but I sure it must.

We have two 160 watt Solar Panels. Connected in series the should provide 34 volts. We use a Morning Star to control the charging rate. (The Solar Panel are used only during the 90 minute endurance competition.)
Thanks
Bob

we have 2 160 watt solar panels connected in series with a max of about 34 volts

 

My understanding is that you intend to use the two batteries in series. The relevant cranking current is 450A not 900A. However even 450A is unlikely to have any relevance to what you can pull for 10 to 20 seconds from a 38Ah battery.

What controller have you got or are you intending to use? What is the setting for its low voltage cur-out? What is its rated current? These are more relevant parameters than the battery CCA.

Rick W

 

Rick,
With respect to the batteries, wouldn't 2 - 12v 450CCA batteries in series yield 24v and ¿900CCA? or would the amperage remain 450. Been work on humans for the past 25 years and I am rusty at this.
With respect to the Motor Cnntroller
So most of this went sailing (pardon the pun) over my head so I just did a copy and paste.
The Controller is an
Alltrax AXE 4844
400 Amps
24-48 Voltage Range
Programmable via RS232 comm port using PC or Laptop
Integrated anodized heat-sink with multi bolt pattern for flexibility
Fully encapsulated epoxy fill - environmentally rugged design
Advanced MOSFET power transistor design for excellent efficiency
and power transfer
1/2 Speed reverse option and "Plug Brake" options available
Type: DC "SERIES WOUND" motor controller
Under-voltage cutback: adjustable
16-30 VDC, preset to 12 volts under your battery pack voltage
Over-voltage shutdown: adjustable
30-60 VDC (48V models) (60VDC MAX)
Operating Frequency: 18kHz
Control voltage range; Key, Throttle and Reverse inputs:
Reverse Horn Output: 50mA sink max
Standby Current (Powered Up): < 35mA
Throttle Input:
ITS (inductive)
Resistive 0-5K ohm (+/-10%)
5K-0 ohm (+/-10%)
0-5Volt
6-10Volt
Operating Temperature: -25C to 75C, 95C shutdown
Adjustable via Controller Pro software:
Throttle acceleration / deceleration rate and map profile
Armature current limit
Brake current limit
Under / Over-voltage shutdown

There is a 650 amp model, the Alltrax 4865. I am not sure if we should upgrade to that. Am I correct more amps would = more torque?
Thanks
Bob

 

Bob
In series you will get 24V and CCA of 450A. This is preferred to parallel which will give 12V and CCA of 900A.

The 400A controller will be adequate. I doubt that you will even want to go this high. Pulling the CCA current from a battery will drop the voltage. So you get more current but power does not go up proportionally. To carry the higher current efficiently, you need to use heavier leads so the boat gets heavier; requiring more power and there is a point where you go backwards.

You should do some testing on the batteries just to confirm voltage droop. I am taking a guesstimate that you can get 300A at 20V from the batteries for the sprint. This is 6kW. It will be enough to get to 20kts with an efficient prop. This should be competitive but you need to check previous results.

This power is well beyond what the APC prop can deliver efficiently. There is a Bolly boat prop that has adequate strength but it will start to cavitate above 13kts and efficiency will drop off.

The APC prop is OK for trials and would suit the 90 minute run.

I have attached a photo of the Bolly boat prop that is not ideal for the sprint but will get you to a decent speed. Off hand I do know of a better commercially available prop but I will look around. There may be a 2-bladed sailboat prop that would suit.

Rick W

 

Thank you so much.
Let me see how I might be able to work that into Da Rules governing design.
I know that we cannot have anything extending beyond 14" from the mid point of the boat and nothing, other than the rudder past the stern. That would not limit how deep the prop could be beneath the boat. But I would imagine that the efficiency would drop off and that this would place more stress on the propeller strut.

Wild idea, but would two smaller props, one on each side of the at the boat just short of the stern could be as much as 8" to 10" in diameter. Does that make any sense?

 

You will be able to direct drive the Bolly prop from the motor. With two props you need to set up a more complex transmission and that involves losses.

No idea what you mean by work that into Da Rules. The Bolly prop is 390mm diameter so it will extend less than 8" beyond the centreline.

Rick W

 

Wild idea, but would two smaller props, one on each side of the at the boat just short of the stern could be as much as 8" to 10" in diameter. Does that make any sense?

No...

 

Prop for sprint

Dr. B, the type of prop you use for the sprint depends on how the 200 meter sprint is run. Is this a STANDING START sprint from zero or a SPEED trap TOP SPEED type to measure the highest speed achievable over 200 meters?

Also on your controller, you list a "series" specification. It is not clear if the controller is meant for a series field wound motor or if the controller is meant to be placed in series with a brushed motor. It might make a difference. If your motor is a brush type, and really runs at 93% efficiency, it is surpassing what most of the super efficient brushless outrunner types can do. That makes is an excellent choice, but will be quite a surprise to me and others on this list.

Porta

 

Rick, I picked up a bolly yesterday approximately 11X8 inches from a discontinued bin for $2 from a hobby shop. They had some other small ones and some 16"X14 bollys as well. The enclosed printing indicates they are hand made of carbon fiber. Quite a bargain, and essentially rigid while being lightweight! I can see why you like them, absolutely no flexing, even driven above full power.