High pitch trolling motor prop for solar boat

Me and a couple of buddies are trying to build a solar powered catamaran.

Its based on a 16 foot hobie cat hull with either twin 30 pound thrust trolling motors or a single 55 pound one. We are still trying to figure out the design.

While I like the Torqeedo motors we don't have the budget for one. I also like the idea of having twin motors mounted on the inside side of each pontoon to reduce cavitation.

So I can't seem to find any commercially available higher pitch props for trolling motors. (other then Kipawa) Has anyone tried to modify a composite prop for a 2.5-5hp outboard to fit a trolling motor?

And if we were to do this would it destroy the trolling motors motors over time?

Fully loaded our boat should weigh 1120 and we would like to travel around 8 knots with a combination of electric and oar power.

 

for how many minutes?

 

8-12 hours ideally.... I know that sounds crazy but we want to use it as an adventure set up. Maybe cruising at 4-5 kinots is more realistic.

We hope to have a 700 watt solar set up to recharge the battery as we go.

 

Just the speed part. 4-5 knots is much better.

If you mean the panel ratings add up to 700W, you still face an energy crisis. You will not beat a Torquedo on price, that's for sure. A homegrown system of the size you need will cost a lot more unless you are an electrical engineer. The biggest problem is always how to charge the batteries. Can you do it at the right rate for the right amount of time every day while cruising.

What I find works decent is to use a small generator such as a Honda 2000 to bulk charge lead acid batteries up to about 80% charge, then let the solar take over from there. The solar needs to provide only about AH/40 or AH/50 Amps this way, which is a bit more reasonable for onboard use. You're still looking at a pretty hefty setup and a catamaran is the wrong platform. You should go with a monohull like a sharpie or even a big jonboat or whopping great canoe. I'd design it around the cheapest Walmart deepcycle batteries for the first go round. West Marine used to sell a cheap 60 Amp solar controller. If you put about 500W rated of panels and ran it to this $60 unit, you'd be about as cost effective as a 12V system could be. If you are considering more than 8 series 24 or 27 batts, I'd seriously look at jumping up to 24 volts.

 

So trying to do something like this wouldn't be a good idea?

http://youtu.be/tq-JHzVRM4o

I appreciate your well thought out response, the reason we're looking into using a 16 foot hobie is that we have one really cheap. Of the three of us building it we have a bio-medical engineer, a gun smith, and I work in disaster restoration.

I do have access to a electrical engineer, who I think would be willing to help with questions. We are trying to enter a challenge that only allows solar and human power so the generator would be out.

If the catamaran is wildly impractical then we will have to start looking for another hull. For some reason, I really like the idea of a cat but I have no experience in boat design.

How do you think this motor

http://www.amazon.com/Minn-Kota-Freshwater-Transom-Trolling/dp/B0042TIIRW

with 6 of these panels

http://www.amazon.com/Renogy®-Monocrystalline-Bendable-Solar-Panel/dp/B00IK19VF6/ref=pd_ybh_15

would work. The panels only weigh 4 pounds.

 

Also considering this boat with a solar canopy.

http://www.boatstogo.com/kayaks_sk487.asp

We thought about up grading the oar locks and using it with the 55 pound thrust trolling motor and one battery. When the battery starts to die down we could row for a while.

I'm new to all of this and have very thick skin. So again if this is crazy let me know.

 

If by fully loaded you mean a Hobie Cat with three people and a small cooler, you may keep it at 1120lb. High speed always comes at a cost. If you are on a budget, the speed is the first thing to give up. The amount of power increases exponentially. Basically, twice the speed needs four times the power. That means the batteries last about 1/5 of the time. If you put more batteries the weight goes up and you need more power; a downwards spiral. You can machine a propeller, but it will cost a lot if you don't do it yourself. An outboard prop could be modified too.

 

I'm thinking about modifying something like this.

http://www.amazon.com/Solas-Science-Engineering-Tohatsu-3-3Hp/dp/B003C7YFFY

If it could do 4 knots with a 55 pound motor at 50-75% throttle that would be ideal. This weekend we are going to load the hulls down with sand bags and borrow a trolling motor to get a basic idea of how it might work.

 

Also would tandem 30# thrust trolling motors be more efficient than one 55#? I watched a youtube video where a guy seemed to think show, and his boat was moving rather quickly. However it dosn't make sense. One prop seems like it would be more efficient. Maybe because of the high torque nature of trolling motors 2 are more efficient then one?

 

Um, you better keep it at UNDER 1120. 1120 in an H-16 makes it a submarine, or at least a SWATH.

Tell us more about the solar/HPV contest. I think you want a war canoe, 21 foot minimum, but longer would be better. You want a Displacement-to-length ratio near 60 for excellent propulsive efficiency at displacement speeds. (D/L = D in tons divided by cube of L/100, L is waterline length in feet.) So this gives you a design target as far as weight, speed, endurance, and boat length is concerned. If you get those four to match the event requirements, you will do pretty well. If you find that you can get to 6 or more knots for the whole race, you need to look a boats with a tiny bit of submerged transom, like a 26 foot canoe with two feet lopped off the stern. Those speeds just over "hull speed" are tricky to design for because the optimum shape is only good for a very narrow speed range.

For more info on solar, check with SUN Electronics of Miami. In the past, they have had great prices and been very helpful with tech and recommendations. I like those panels, but kinda pricey.

Please get the hobie 16 idea out of you head unless you can get the total payload down to 500 pounds or so (and it will still be slow). The video showed one guy running lithium batteries. Light, but very pricey.

 

Just to put things in perspective. Suppose you have a 21' canoe with 1000 pounds of gear powered by a 2hp motor. I have a few thousand miles of this sort of experience. For three days, you carry a six gallon tank of gas. That weighs about 40 pounds give or take. The equivalant weight of lead acid batteries would be 100 x or 4000 pounds. Lets say you are willing to carry 300 pounds worth (about 4 batteries). You need to cycle them 13 times in three days. That won't work very well. So basically, all you have is a four hour buffer and you really just have to run directly off of solar and plan to stop and get the batts up to 85 or 90 percent every day at some point to avoid deterioration. With a little genset, life can be much easier because you can run the genset for maybe two hours each day, which isn't too annoying, and carry on just fine with only half the solar equipment. But you need a $1000 genset and about a $900 charger to do that, Plus the same 6 gallons of gas. So now you have 300 pounds of batteries and about 80 pounds of other stuff and you have less peak power than the original setup. But you have maybe ten hours of epower per day. I could be very happy doing this solo, but tandam, there simply isn't the room. I'd need a 23-24 foot boat. And now I'm looking at 24 volt systems and six 24 series batteiries.

 

The way I came up with that weight number was the weight of a hobie 16 hull plus its max payload. Us plus our gear would be 800 pounds. I'm including solar panels, motor and one battery (80 pounds) in that number. We are planning to row with oars as well, the bio-medical engineer in our group is busy coming up with the most efficient oar system for our boat. He is also working on a human powered propeller system.

We are trying to complete the 300 mile water tribe everglades challenge with a boat using solar auxiliary power. We would like to be under epower during the hottest part of the day for 8 hours or so and sleep in shifts. We would be under human power at night, with the battery in case of emergency.

We have a lot of boating and survival experience between the three of us, this is just our first shot at design. I'll start looking at longer boats, I still really like the idea of being on a platform up out of the water though lol.

 

Would it be possible to have a very small battery and only run the motor when the solar panels are at full output? I think we could get 8-9 hours a day doing this in Florida.

And we are planning on putting in a substantial amount of human effort, we all three go to the gym at least an hour a day. We're doing this instead of our annual fitness competition with each other.

 

Does the Water Tribe allow motors????

 

In expedition class, there is a provision that allows solar power.