Project Solar Boat

[drbobbob@aol.co]

Hello to all,
I am a newbie, not only to this website, but to the world of boating.
I am working with a great group kids from Santa Monica HS (called Team Marine) who are building a solar powered boat as part of the Solar Cup competition put on by the MWD (Metropolitan Water District) in So Cal.
We built a boat last year flying by the seat of our pants and this year we hope to put a lot more thoughtful engineering into our project.

Your input, experience and advice (which may include referrals to a good psychologist) are appreciated.

Here is what we are working with. All teams start with the same hull. (pictured below) I would describe it as a 15' flat bottom canoe. The electric motor (Agni Motors 95 series) powered by 2 12v Optima Yellow Cap batteries in series. From the performance graphs, at 24v, it puts out about 10HP at 800 RPM. Weight of the boat with skipper is about 300 to 350 lbs.

Project 1 is the Drive Train.

Given the HP / Weight / Hull type we are trying to determine the best propeller Diameter, and Pitch to use as well as what kind of gearing ratio we might be able to use. I have been to some sites with "select the right propeller" calculators, but our motor and hull type are never an option.

We can go with two propellers as there are two very different races.
One propeller would be to provide the most power for a 200meter sprint.
The other would be to provide the best efficiency as we try to see how far we can go in 90 minutes balancing the power drawn by the motor with the the solar panels ability to recharge the batteries.


I would think that the smaller the angle of the drive shaft, the more forward force produced. (The prop cannot extend beyond the stern, so the max shaft length would be about 6') I realize also that as shaft angle decreases, the diameter of the prop you can use will decrease.
Presently we have a 12° angle. (Would a flatter angle and the use of twin (smaller diameter propellers be an idea worth pursuing?) I am not sure if we have the means of dropping the shaft at 90° to the bottom of the boat and gearing another 90° shaft so the propeller angle is Hz (or // ) to the boat's bottom. Other thoughts include Duo propellers.


With respect to gearing.
Previously we ran a direct shaft to the prop. This year we are considering increasing to a 1.5 or even 2.0 to 1 drive. Would this be too much for the motor? ( I am guessing this would also depend on or change the parameters of the propeller)

I know this is an odd collection of parameters and applications to work with, (at least it feels that way to me) but we greatly appreciate and help you can give us.

Thanks
Bob

[Rick Willoughby]

Bob
There are a few basics that are worth considering.

For the high power run I expect the batteries will limit the performance you can get. It is unlikely to be anywhere near 10HP unless they are very large. What Ah rating are they?

The best prop configuration will be a large diameter propeller, turning slowly on a curved shaft.

A pushing propeller is self-aligning to the flow so does not need much support (really none) if it is aligned with flow. Without any support it dangles when at rest and wanders to the side when turning so it is best to have a shaft strut that provides some constraint. The strut can be made very small.

I use spring steel for curved shafts. They can be designed for infinite fatigue life.

Marine propellers have evolved the way they are for a variety of reasons and efficiency has not been a primary driver. Hence the typical marine propeller is not very efficient and really unsuited to what you are trying to achieve.

You are likely to find a large model plane propeller that will be most suited to what you want to do.

I can do design for you but it is a school project so it is a matter of how much learning you want to get from the exercise.

The first thing to determine is the maximum power that the batteries can deliver for the 20 to 30 seconds it will take to do 200m. You may be able to ditch the solar panels if that is permitted. The weight reduction will reduce drag. If the batteries have been sitting around then cycling them to about 50% capacity a few times will probably lift their power output.

The second step is to determine the drag curve for the hull. There are ways to do this that give reasonably accurate results in displacement mode and not quite so accurate at planing speed.

Third is to estimate the combined power you can get from the solar panels and batteries for 90 minutes.

Let me know what input you would like and we will see where it goes from there.

This is one of my boats fitted with a 59gram model aircraft motor geared to swing a model aircraft prop:
http://www.youtube.com/watch?v=GJedBprmSkk
It did 12kph in this configuration.

This shows the drive set up:
http://www.boatdesign.net/gallery/data/500/V11JE_Drive.wmv
The motor is a small black outrunner that you can just see turning over driving the two stage belt reduction. I used 12:1 reduction to get the required prop speed using this high revving motor. The prop shown will get efficiency around 85% in applications like this.

Rick W

[gonzo]

Weight is the most important parameter that you can control. If you have all that equipment that is the same for all, your skipper should be as light as possible. That alone can make you win.

[marshmat]

Within a tightly controlled fleet like this, resistance is pretty closely linked to weight.

In solar car races, weight is so critical that they had to set a minimum weight limit for the driver- 80 kg fully dressed, and if you weigh less, you have to add ballast. If your class doesn't have a similar restriction, training your lightest jockeys to drive is a wise idea.

Rick makes some good points- he's done quite a few ultra-high-efficiency, low-speed designs and you'd be well advised to consider the suggestions he made above.

[drbobbob@aol.co]

Great feedback! Thanks! You are correct Matt, the weight of the skipper is set at a minimum, with ballast added to make up the difference. Weight is one of the big issues and a tricky one when it comes to batteries. They are a set to a maximum of ~55lbs.
Rick, your offer to run some numbers is really appreciated. The set up in your video is simple, but so innovative. I have to check the rules to see what, if any limits there are on propeller location. I am surprised to hear that airplane style propeller would be more efficient than boat propeller.
I will get back to you with more info. In the meanwhile here is the power curve for our motor.
Thanks
Bob
/Users/drbob/Desktop/Agni Motors :95.png

[Rick Willoughby]

Bob
Are you permitted to use lithium batteries or is the type set? Can you afford lithium if permitted?

What is the time scale for this project?

Unless you are permitted to use lithium batteries the batteries will be the limit rather than the motor on top speed. You need to do power test on the batteries.

If you provide the dimensions of the boat and the loaded weight for the races then I can produce a drag v speed curve for it.

Rick W

[drbobbob@aol.co]

The short answer is no. We are presently using Optima Yellow top batteries.
12v Cold Cranking Amps @ 0 F: 750 Cranking Amps @ 32 F: 870
Reserve Capacity: 120 Capacity (C/20 Rate): 55 We use two in series.

The long answer as written in DA RULES is:
"Only secondary (electrically rechargeable) batteries are permitted. Fuel cells, primary batteries, or mechanically rechargeable batteries will not be approved. Each team is responsible for supplying their own batteries. The batteries must be commercially available, lead-acid, unmodified with their weight consistent with the Rules. Craft are allowed to carry a total battery
weight of not more than 25 kg (55 lb). Batteries must be absolutely stock (as manufactured) in every sense. The battery modules may not be modified in any manner, including the addition of electrolyte additives, case modification; or plate addition, removal, or modification."

IMO the highest CCA batteries that weigh in under 25kg would be the ideal for the 200m Sprint.
I am also researching if there are batteries that have a higher reserve capacity for the endurance competition.

[drbobbob@aol.co]

Rick, The boat is 4.6 meters (15 ft, 1 in) and .81 meters 32 inches wide. pictured above. It is also referred to as the 6 hour canoe. The bottom is flat, the engine/drive train and batteries must reside behind the bulk head which divides the boat into 6 1/2ft and 8 1/2 ft sections. We work to keep the batteries and motor (the bulk of the weight) as close to the bulk head as possible. The skipper must be a min of 40" ~1 meter from the bow.

Hope this gives you what you need.

Once again, Da Rules state:
7.2 Technical Specifications
7.2.0 If a boat does not meet any of the technical specifications penalties will be assessed by the event officials.

These are the two rules that might dictate what type of prop design we can use.
7.2.1 Length - The length of the craft will be approximately 4.6 meters (15 ft, 1 in). Nothing may extend forward beyond the bow of the boat. Only the rudder may extend beyond the stern of the craft.
7.2.2 Width - Nothing may extend more than 36 cm (14.2 in) to the boat center line beyond the deck edge of the craft at any point.
7.2.3 Height - The maximum allowable height above the waterline is 1.5 meters (4 ft, 11 in). This height can never be exceeded during the events.
7.2.4 Depth - No restriction. An excessive depth may make the craft awkward to handle near shore and may increase the likelihood of encountering underwater obstacles.

Thanks again

Bob

[Rick Willoughby]

Bob
The motor controller will likely have a low voltage cut out around 18V. Aiming for a battery voltage around 19V at full power should give the best overall result for the sprint.

Are you able to do a load test on the battery or find data on voltage droop with current?

Do you know if the motor controller has a low voltage cut out?

Can you advise your project time scale? Is there time for testing?

Marine propellers are defined by draft constraints and cavitation. They have evolved to be quite inefficient in small craft because power is abundant and fuel was cheap. In lightly loaded application like you have, with no serious draft restriction, an aircraft style propeller will be more efficient.

This is an example of a model plane type prop in operation with a boat doing around 15kts with less than 1HP:
http://www.youtube.com/watch?v=jh_RhkejWLw
The prop used is identical to the black one shown in my video linked above.

The people who have made curved shaft systems have had difficulty getting suitable shaft material. Spring steel is tremendously strong and tough. It is possible to use other materials but spring steel is the best without going to really expensive alloys. You are likely to need about 3m long that is say 10mm diameter for a shaft and I suggest you get enough for at least two shafts. I do not know size for certain until the prop is determined. If you can locate a suitable spring steel supplier that will supply small quantity it could save time.

Rick W

[gonzo]

Is the flat bottom a requirement?

[Ad Hoc]

drbobbob

If you wnat to understand more about the prop, i would suggest you contact baeckmo or daiquiri. As can be seen here:
http://www.boatdesign.net/forums/props/prop-doing-bad-29864-3.html
rick doesn't know how to design a prop nor what cavitation is...he only has a program with numbers, and doesn't design for real. As such doesn't understand what happens on real boats. It is your call, but i would go with beackmo...Rick is just a PlayStation designer.

You have said:
"..We can go with two propellers as there are two very different races.
One propeller would be to provide the most power for a 200meter sprint.
The other would be to provide the best efficiency as we try to see how far we can go in 90 minutes balancing the power drawn by the motor with the the solar panels ability to recharge the batteries..."

In either condition, as already noted by Matt, weight and weight and weight. Weight shall be the key to your success. this reduces the length displacement ratio. Reducing this parameter reduces the residuary resistance and trim effects considerably. It also smooths out any humps in the total resistance curve.

As for prop's:
Only 3 things to note, the speed of water in way of the prop, the power given, at the prop, and the rpm of the shaft. These will drive the design of the prop. The hardest, shall be the speed of the water, ie what wake factor to use which is related to your hull shape and location of the prop and any appendages. The rest, are details...but are driven by the basics above.

From the small pic, it looks like your prop is pretty much "open" water, the only other issue is to try and keep the angle of the shaft less than around 7~8degrees. Above this losses are incurred with increasing angle.

[Rick Willoughby]

Bob
I have modelled the hull for purposes of determining the drag. The curve attached is based on total displacement of 150kg. The dark line is a best second order fit of the calculated drag shown by the thin pink line.

There is an inconsistency in information you provided as the battery you nominated has a weight of 20kg alone while you are only allowed a total of 25kg. I have attached some information on the batteries.

Working on the smaller 38Ah batteries I figure you will operate at around 20A for the 90 minute distance run depending on the level of sunlight. Under these conditions you could expect around 7kts using the APC prop pictured. If you are able to use the larger batteries then you can get a bit more. The APC will still work well.

The figures in the battery table for internal resistance are very low in my experience. These indicate you can pull a lot of power from the batteries without losing much voltage. You may get up around 4kW. This is much higher than I have been able to get from similar size batteries. You need to determine what they can produce.

At the high power the APC prop is not the best choice. However before going into this I would like the battery details to be verified.

You have still not given the time frame that you have for the project.

Rick W

[gonzo]

What crew weight are you calculating the speeds with?

[drbobbob@aol.co]

Gonzo
The total weight of the boat with skipper is about 350 lbs or 160 kilos.

AH,
With respect to the parameters you talked about, "As for prop's:
Only 3 things to note, the speed of water in way of the prop, (we're in a reservoir so it's flat) power given at the prop , and the rpm of the shaft. " (per the motor chart posted about 10Hp or 80 newton meters at 1600 rpm)
What is your opinion with respect to use of a more airplane style propeller?

Like on the 190SL forums, another project of mine, there are some strongly differing opinions. Now I'm just the guy that walks in a bar to ask for directions. So please, if I am getting differing information, nobody be offended if I don't take sides.http://www.boatdesign.net/forums/images/smilies/smile.gif

Rick
My bad, I originally listed this HP at 800 rpm. I am not sure if this changes your calculations. Also, from the pict of the APC prop, I could not tell what model, size, pitch etc you were suggesting.

Sure I may sound like a broken records, but we really appreciate this help The kids are getting more and more pumped with the prospect of coming in with some designs and application never used before.

[gonzo]

That would be a 10 kilo skipper

[portacruise]

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

The short answer is no. We are presently using Optima Yellow top batteries.
12v Cold Cranking Amps @ 0 F: 750 Cranking Amps @ 32 F: 870
Reserve Capacity: 120 Capacity (C/20 Rate): 55 We use two in series.

The long answer as written in DA RULES is:
"Only secondary (electrically rechargeable) batteries are permitted. Fuel cells, primary batteries, or mechanically rechargeable batteries will not be approved. Each team is responsible for supplying their own batteries. The batteries must be commercially available, lead-acid, unmodified with their weight consistent with the Rules. Craft are allowed to carry a total battery
weight of not more than 25 kg (55 lb). Batteries must be absolutely stock (as manufactured) in every sense. The battery modules may not be modified in any manner, including the addition of electrolyte additives, case modification; or plate addition, removal, or modification."

IMO the highest CCA batteries that weigh in under 25kg would be the ideal for the 200m Sprint.
I am also researching if there are batteries that have a higher reserve capacity for the endurance competition.

[drbobbob@aol.co]

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

[portacruise]

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

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

[Rick Willoughby]

Rick
My bad, I originally listed this HP at 800 rpm. I am not sure if this changes your calculations. Also, from the pict of the APC prop, I could not tell what model, size, pitch etc you were suggesting.


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

[narwhal]

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.

[Ad Hoc]

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.

[drbobbob@aol.co]

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

[Rick Willoughby]

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.



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

[drbobbob@aol.co]

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

[Rick Willoughby]

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

[drbobbob@aol.co]

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?

[Rick Willoughby]

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

[Submarine Tom]

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...

[portacruise]

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

[portacruise]

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

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.

[gonzo]

What do you need a controller for? If you are looking for efficiency and top speed run it at its maximum. An on/off switch should be enough.

[portacruise]

Notice the specks are quite different at 24V than at 12V, so it is necessary to know which voltage will be used:

http://agnimotors.com/95_Series_Performance_Graphs.pdf

Porta

Ps. Gonzo, the website indicates direct switching or through a resistor is possible. Would get you off the line faster from a standing start of zero. I ran troll motors overvolted with series-parallel switches for years without damage or need for a controller.

[Rick Willoughby]

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.

Vic
The boat prop that Bolly make is 15 X 25. With the high pitch it does not need to spin fast to get a decent speed. It is very strong and incredibly stiff for its size.

The amount of power in the sprint is getting beyond what the Bolly will deliver efficiently so there might be something else more suitable.

Rick

[Rick Willoughby]

Notice the specks are quite different at 24V than at 12V, so it is necessary to know which voltage will be used:

http://agnimotors.com/95_Series_Performance_Graphs.pdf

Porta

Ps. Gonzo, the website indicates direct switching or through a resistor is possible. Would get you off the line faster from a standing start of zero. I ran troll motors overvolted with series-parallel switches for years without damage or need for a controller.

Vic
This is a very powerful motor with low winding resistance. You would never make a light weight drive train that could handle the DOL torque.

There is also the fact the the 90 minute efficiency run gets a lot more points so that it what needs to be the focus. The controller will drop 1 to 2% and keeps everything under control. It avoids snapping the neck of the pilot as well!

The rules require the boat to have controllable speed and you do not want to achieve that by manual switching.

Rick W

Rick

[portacruise]

Rick, I agree it wouldn't be practical to use series-parallel switching for this racing situation. I meant to imply it worked well for me in SOME lower power situations.

Looking at the motor curves and the 55# battery limit, what do you think of using 3 -17 or 18 lb. , smaller AGMs in series? http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/80161?&cid=chanintel&ci_src=14110944&ci_sku=80161

At least for the drag racing part, the batteries only need to hold maybe 30 volts for probably under 30 seconds, or whatever the record is. If the rules allow, the batteries could be switched out for others with better reserve capacity (if needed) for the 90 minute run.

Porta



Vic
This is a very powerful motor with low winding resistance. You would never make a light weight drive train that could handle the DOL torque.

There is also the fact the the 90 minute efficiency run gets a lot more points so that it what needs to be the focus. The controller will drop 1 to 2% and keeps everything under control. It avoids snapping the neck of the pilot as well!

The rules require the boat to have controllable speed and you do not want to achieve that by manual switching.

Rick W

Rick

[Rick Willoughby]

Vic
The motor and controller look well suited to 24V and this gives a good motor shaft speed for direct connection to the Bolly prop. This saves the losses of more complex transmission or less efficient prop.

For the sprint the current is starting to get high for cables that are not going to be significant in the total weight. Proximity of battery, controller and motor are a consideration in this regard.

They are permitted to use two different battery packs but they must be charged from solar power through the day. No external power. They are limited to 320W of solar.

I would be inclined to give the Bolly prop a go and see how it behaves at high power. If I was racing I would make my own prop. The most suitable marine prop I can find so far weighs 15lb. It is ridiculous for this application.

I have not looked at what a smallish outboard prop might do but it is worthwhile considering. One of these might need to be spun faster and it would make sense to use direct drive rather than gear up - this is where 36V would make sense. It opens up another option.

Rick W

[drbobbob@aol.co]

Sorry Rick, when I refer to the Da Rules, I am referring to the rules of the Solar Cup Competition that dictate and control all aspects of design. As I read your posts I think you may have even found the website and read them yourself.

We can use no more than 24 volts, I just read there is a mandatory 350A fuse inline btwn the batteries and the motor. That being said, I am redirecting my search for batteries along the lines Porta mentioned for the sprint competition to batteries that can put out 350A to 400A for 30 seconds, but are very light. I would then switch to a higher Amp/hour rated deep cycle battery for the 90 minute endurance race.
(also, the Solar Panels are used only during the endurance competition)

Now I get to illustrate how little I know (again), a propeller 15x25 denotes what by what?
Last of all, is Bolly Prop no longer in business? The website said something about closing their doors.

[Rick Willoughby]

Bob
You should treat the nominated CCA skeptically until you verify it. You also need to consider the power available; not just the current. 350A at 22V is much better than 350A at 16V. You need to test the actual batteries under heavy load conditions. A weight saving with them in a sprint is unlikely to be beneficial.

I scanned the rules briefly. I cannot recall the 24V limit.

I was mainly interested to find out the time frame. You do not have much time to engineer and build a good system. The design needs to be presented and reasons for selection understood. You and students will be working up a steep learning curve and you need to make sure whatever is done is within the rules.

Attached indicates how a curved shaft could be set up for a 10mm spring steel round bar. The prop shown is a little larger than the Bolly boat prop as it is one I had a drawing of.

The shaft support skeg needs sealed ball bearings to work well. The shaft tube needs a sealed ball bearing and lip seal. The shaft connections should be tapr-lok type wedging couplers and sleeves.

One of the issues that might be raised will be the critical speed of the shaft. My response to that is - Have you ever tried to play a stringed instrument underwater! However there is a limitation and that is that you should not take the motor to full rpm when the boat is out of the water. The shaft will flutter madly and may break the strut or shaft tube.

As a final note these competitions aim to encourage leadership and teamwork as well as the technical aspects. Good project management that considers every aspect of the scoring system gets the best results.

You need to give thought to project management. My suggestions are:
1. Appoint a project manager - someone with leadership skills, respected by the team members, able to delegate and include, ability to get others enthused about the project etc.
2. A quality manager - someone assigned to know the rules inside out and exactly how the scoring works.
3. A project planner - making sure the times can be met and people are prepared.
4. Technical area specialists such as boat, motor, batteries, solar panels, tansmission/propulsion.
5. A PR specialist - someone with the "gift of the gab" but also good at organising presentation material, organising presentations and getting others experienced presenting to diverse audiences. Being a good photographer or appoint a specialist photographer as project recorder.
6. Other roles as issues emerge that need a lot of attention.

It is primarily a learning exercise with a carrot and tangible result. It is certainly good to have the fastest and most efficient boat but also nice to win overall.

Rick W

[ExileMoon]

I think you had better make a catamaran.
So you can get more Solar board and keep small drag.
http://www.solarnavigator.net/images/catamaran_model_into_wind.jpg

[drbobbob@aol.co]

Rick, your outlook on this project and the importance you place on organization and division of the duties is something I am stressing with the kids. Some were a bit skeptical about being involved, as working with tools was not a strength or interest. However, when I explained positions were needed from project manager to media production and art work for the boat more kids found a talent they could bring to the team. We build the hull this saturday and getting to work on the rest right away. I inherited this project last year as a hull with a coat of epoxy that never set and we completed it in just over 2 months.
NOT fun and NOT to be repeated.
So back to Das Boot
How far below the boat is the tip of the propeller in this design? Is the prop you are suggesting 15" in diameter?
You recommend sealed shaft bearings. The shaft bearings I have seen and used with our aluminum shaft from last year are made of heavy plastic or teflon that are cooled and lubricated by the water.
As far as the batteries, we will be getting new batteries this year so They should be putting out pretty much peak volts and amps. With that considered, IMO saving 20 lbs takes us back to back to the basics of power and weight/drag.
With respect to design from motor to propeller, you would run the spring steel from the motor shaft through the stuffing box and shaft log to the strut? It would be able to handle this 12° bend from shaft log to HZ strut for the propeller? When you say shaft support skeg is this what I am calling the propeller strut?
How much more would the spring steel weigh v an aluminum shaft?
Here is a basic motor to shaft log design like the one we used and a strut / prop / rudder design so you can see what we are working with.
Thanks Again
Bob

[portacruise]

Sorry Rick, when I refer to the Da Rules, I am referring to the rules of the Solar Cup Competition that dictate and control all aspects of design. As I read your posts I think you may have even found the website and read them yourself.

We can use no more than 24 volts, I just read there is a mandatory 350A fuse inline btwn the batteries and the motor. That being said, I am redirecting my search for batteries along the lines Porta mentioned for the sprint competition to batteries that can put out 350A to 400A for 30 seconds, but are very light. I would then switch to a higher Amp/hour rated deep cycle battery for the 90 minute endurance race.
(also, the Solar Panels are used only during the endurance competition)

Now I get to illustrate how little I know (again), a propeller 15x25 denotes what by what?


THE FIRST NUMBER IS THE DIAMETER OF THE PROP (INCHES- if USA) AND THE SECOND NUMBER IS THE PITCH (DISTANCE FORWARD WITHOUT SLIP? PER TURN-INCHES if USA) THIS PITCH (25) IS VERY AGRESSIVE AND REQUIRES HIGH TORQUE, AND HAS BEEN USED FOR RACING IN PEDAL BOAT AS I RECALL.


Last of all, is Bolly Prop no longer in business?

GOOD QUESTION. THEY WERE NOT TAKING SMALL ORDERS ON THIS BOAT PROP LAST I HEARD. AN ALTERNATIVE IS THE APC 16X16 IF YOU CAN FINE TUNE THE VOLTAGE (RPM) AND CURRENT TO OPTIMUM, BUT THERE WILL BE LOSSES DUE TO FLEXING AND POSSIBLE FAILURE WITHOUT CONTROLLED ACCELERATION IN THE DRAG PORTION. IF YOU CAN FIND A METAL CRAFTSMAN WITH WELDING SKILL, RICK HAS A DETAILED PROCEDURE FOR MAKING THE BEST PROPS.

The website said something about closing their doors.

SEE ABOVE.

Porta

[portacruise]

Almost forgot, Jake Free is your man on props in the USA:

http://www.freeenterprises.net/HPBoats.specs.html

I think he still does custom builds.

Porta


SEE ABOVE.

Porta

[Rick Willoughby]

Bob
That prop may actually be better than a Bolly for the high speed but the Bolly will definitely be more efficient for the efficiency run.

If you give me the pitch and diameter of the prop you have I will do some performance comparisons with the Bolly boat prop. It will give you an idea if further development is worth the trouble.

The efficiency of a propeller is related to the diameter and the aspect of the blades. The larger the area the blades sweep the less slip. The higher the aspect of the blades, the less induced drag.

The reason prop driven planes have long slender blades is to achieve high efficiency. In water, cavitation comes into play and it is the fundamental reason that drives the shape of water propeller blades. It shows its ugly presence as speed increases.

In your low speed case cavitation is not going to be a problem with a Bolly prop. However in the high power case it will be operating with cavitation. Given that you get more points for the efficiency part of it this is probably the best area to focus on.

Going for efficiency with a high aspect blades requires the prop to be aligned with flow to avoid high shaft loads and vibration. It is not so critical with a prop having wide, low aspect blades as your marine prop has.

The Bolly prop is 390mm in diameter and only needs to have about 20mm clearance to the hull. If it is too close to the surface it will ventillate when you accelerate. I have shown it deeper than necessary. The shaft strut does not need to be very heavy.

A spring steel curved shaft only needs to be 10mm in diameter to handle the torque. Having a very thin shaft like this and a thin strut reduces drag.

This video shows a boat I designed using one of my props running on a 1/4" spring steel shaft:
http://www.youtube.com/user/adventuresofgreg#p/u/12/OTITPVv_Rac
The prop is completely unsupported at the outboard end. It just hangs down unless rotating as you can guage from this photo:
http://www.boatdesign.net/forums/attachments/inboards/33194d1247576346-prop-shaft-systems-picture-14.png

Rick W

[Rick Willoughby]

Vic/Bob
I just had a look at the Bolly site and they are in administration - bummer.

I do have a Bolly boat prop but I am not inclined to part with it.

There may be a distributor in the USA still holding them.

The APC prop will be OK for the efficiency run. Will just cavitate and eventually break if you try to push 6kW into it.

I can do a design for fabricating but you need someone with good welding skills. Attached shows one of my better efforts.

Rick

[portacruise]

Here's some other ideas from a fast HPB:

http://www.openwatercycling.com/images2/20040219/INDEX.HTM

V

Vic/Bob
I just had a look at the Bolly site and they are in administration - bummer.

I do have a Bolly boat prop but I am not inclined to part with it.

There may be a distributor in the USA still holding them.

The APC prop will be OK for the efficiency run. Will just cavitate and eventually break if you try to push 6kW into it.

I can do a design for fabricating but you need someone with good welding skills. Attached shows one of my better efforts.

Rick

[portacruise]

More ideas in the thread "efficient electric boats" on this forum, pg 12 and beyond.
Torquedo has some 2 and 3 blade props which can be purchased as replacement parts. These should be very strong and possibly adaptable to your project as well.

Here's some other ideas from a fast HPB:

http://www.openwatercycling.com/images2/20040219/INDEX.HTM

V

[drbobbob@aol.co]

And alas there were no 15x25s to be found.
Here is a list of the Bolly props I could find,
16x13w, -2 blade
16x14 -2 blade
16x13 -3 blade
14x14 1/2 - 2 blade
There is also an APC 16x16
any thoughts?

Oye I also noticed that I was misreading the power chart on the motor.
It produces about 5 HP at 800rpm at 24V and 300A
I was reading the Efficiency of the motor not the NewtonMeters of torque.

[Rick Willoughby]

Bob
What size is the marine prop you currently have?

Rick W