Help with Autonomous Boat Propulsion

I wouldnt normally post about things like this... giving advice on something to travel the world and be reliable I dont need hanging over my head if it all goes to pot (which its bound to)

but heres some top advice ....

1 if your going to do it.. and want it reliable .. ''cheap & tight budget'' arnt words you use in your project ever...

2 one of the golden rules when building things KISS... keep it simple stupid! > this relates to your propulsion methods hmmm... none are reliable, all are pron to getting bogged up in one way or the other.

flat out the water jet is out.. that will suck up anything and if its something bigger than the gap the blades can push through then you have motor burn out and possibly worse.. Fire... then projects a dead stick... ofc u could add a guard over the intake.. but that wont take long to get blocked up either and then your back to dead stick.

skid steering > long term exposure to sea water is corrosive.. it won't be a few weeks to travel this thing world wide... long term (months and months) motor bearings and bushes will be ground down in no time running in salt water. i put my money on bushing and bearing wear out within 3 days 10 days if u use a teflon bearing.. not to mention those pods also tend to house the motor underwater.. which is fine for fresh water short term but not for salt and long... i'ld give em 36 hours till totally dead.

My advice life boat style incased props on a stainless steel shaft with titanium bushings (yes u can get them) the ''life boat style'' means the props are surrounded by most of the hull. this will reduce damage to the props and keep them running with out seaweed and other things tangling up too much ... its still going to happen but this might be the best solution to reduce damage.

Prop shaft should be packed with marine grease. > no bearings EVER!




now the advantage of this tunnled prop is it will incress thrust to an extent... but realistically you'll be running about 3V with solar recharging your RPM is going to be SLOW.. so this will give it at least some torque since its going to have next to no speed... you'll have to do the math here on your motor(s) draw, and recharge rates of the batterys > lipos, LA, NHMI? voltages? and those depends on the size of the boat to start with.....

also life boats tend to roll back over by design so its not going to die any time soon.. providing you can keep it water tight or at least boyant even if its full of water. (which it propably will in 1 rough sea)


Not to be a downer to your project... but this isnt something i would advice anyone to too.. i've sailed very sea worthy boats down a 7 mile river and some have almost sunk in the past (charity events) and ive had a couple of decades of sailing & building at this point! >>> just an fyi those were run on 12V motors and not tiny things big 950's and T12/T24 motors. >> this is where hte math on power and motors come into play mentioned above..

By all means go for it.. i've love to see it run but like most challenges such as this it will prob wash up somewhere only a few miles away or never to be seen again ... the most sucsessful ones have been sail boats.. and that a whole other kettle of fish...

but i'll give u the best bit of advice you ever gonna get about this project... build A boat and sail it, LEARN from that first... no ammount of info given can beat experiance IMO.

Wow, thanks for the full and detailed response!

Ha ha, yes I'm sure it'll probably sink or run aground in a few days, but it'll be a fun and educational project while it lasts.  As I said, I'm at the information gathering stage and even that has been fun. 

I'm starting to realise how difficult is is going to be - it's a harsh environment out there for a start.  From what I've read, and you have said below, reliability of the moving parts is going to be the hardest bit in salt water.  I guess that's why a lot of people have opted to go for tracking a floating buoy rather than a powered boat.   I shall definitely look into the encased props design. 

This is all before I've even started to look at the navigation issues and comms!  

Thanks again for your thoughts.

Dochas.

7 miles down the Tamar from Wilcove to Mount Edgecombe... most of these boats were/are in the 3-4 foot in size too... totaly time to do 7 miles 5 hours.. ( battery swaps every 45 mins while they sail... big 12v 7ah lead acids) and thats with boats turning 16,000 rpm Avg. > after this two boats were retired simply due to the water damage!

good luck!

Cool photos!

Thanks, I think I'll need it!!  

Well Dochas , I am not sure what motivates this desire , but if RR will allow me to add my five penath , as a qualified [ retired ] ex dive instructor I would respectfully point out to you that the oceans are far from being free from debris that will almost certainly foul your propulsion system up ! 
 with ingested trash 
I can only agree with everything he says , and I would recommend that you contact the RN about your proposed venture as there is also the legal aspect of sending any Remotely controlled vessel into any countries  territorial waters even assuming you are heavily backed financially to enable such a venture .

This type of Device would certainly attract their attention and this type of venture is a very touchy area of expertise which would be frowned on by the M.O.D. and the Admiralty , especially since the very type of device you describe was washed up on our coasts recently and caused an international incident .