Loadout for Custom Boat with Raspberry Pi Controller

[pgc_frc]

Hi,

I'm new to the community but I have been building a type of custom boat I want to eventually build from carbon or glass, but right now I'm prototyping based on milled foam. It's 43" loa and about 2'beam I have 2 leopard 3660 2050kv motors paired to jet drives and an 10Ah 8s battery bank. However I believe the batteries have an overcurrent protection at 20A. I'm looking for the boat to be able to travel up to 15kts for 1hr+ run time, do you think this is possible? Right now it weighs in at heavy 30lbs based on the prototype construction.

I have been trying to control the motors from a raspberry pi, with little luck getting them up to enough power output to even get on plane. From what I can tell, I'm drawing a max of 10a split between 2 motors and maxing at 240W, I know the motors are rated much higher than this and I think the batteries are the limiting factor.

Does anyone have experience with running ESC's with input from a raspberry pi, Arduino, or any other microcontroller? To test it I might stop trying to be cute and just get a standard radio and esc setup just to test the limits of the equipment and get accurate info on the hull form.

Also looking for feedback on what may be the necessary upgrades to run the motors and controller up to their specified limits.

Thanks,
Peter

[Panther6834]

I don't have any experience with Raspberry Pi, or Arduino...but, I do have some (limited) experience with a TFL Jet Boat. Granted, it uses a single motor, and single jet drive...but, I'm assuming the "operating characteristics" are probably still the same. The thing is, my jet boat NEVER gets 'on plane', and or never will. The jet drive, essentially, "sucks" the boat into the water...so-much-so that I've even tried to flip it, and have been (thankfully) completely unsuccessful at doing so.

I've tried higher kV motors, and, to while slightly faster, it's still not excessively fast. The stock impeller is a 2-blade, with a high pitch...and, while I haven't had the time to test it yet, I've also acquired TFL's optional 4-blade impeller (with a lower pitch). I think part of the 'problem' (not really a "problem", as it's part of the boat's design) is the flat section of the hull. A 1:1 jet boat, as well as jet skis, have true V-hulls, in that almost none have a flat area - they're either a 'V' the entire length of the hull, or there's a concave section at the rear. Of the few designs I've seen work any flat section, the 'flat' is very small, to taking up a very tiny portion of the hull. On the case of the FTL Jet Boat (and other jet boats, I'd assume), the 'flat' area is quite large (in proportion to the entire hull), thus there's really nothing for it to "get on plane".

Now, with a cat, I see a better possibility...and, it's actually something I'm interested in testing out. Whatever happens with your boat, I wish you the best of luck. Please, post photos, as I'm sure I'm not the only one interested in seeing what you're working on.


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[Jesse J]

1 hour run time? I don't see how FE set up would be reasonable for this "performance" requirement.
15 knots would barely be on plane, and be drawing the max load.
maybe I'm missing something..

[NativePaul]

Assuming this is a monohull 2' beam is VERY fat for a 43" hull and it will be pretty inefficient, 30lb is also pretty heavy which pushes up the planing speed. Water jet drives are also the least efficient form of propulsion.

I think getting 15knots from your hull and weight will take a lot more power than you have available to you and if you were able to supply that power your run time would be well short of your goal.

Are you married to that hull form and propulsion system? A narrow semi displacement hull would take a LOT less power to get going fast, and a prop drive will give you more thrust per watt.

[pgc_frc]

Thanks for the quick feedback, I'm not married to the hull form, and I plan on actually testing a trimaran model as well as a more traditional hull shape--a 'sport fisher' hull form.

The idea of the flat wide section area aft with a few degrees of bow up pitch was supposed to help it plane efficiently, with the hull speed of between 2.5-3kts, it should be planing pretty quickly.

Is there guidelines for when jet drives are preferable over a prop? An empirical approach? I was having trouble trying to determine the relative thrust per watt when making the prop vs jet decision. I have these 4-bladed impellers with the lower pitch, it looks like its the same part in the TFL.

I have to imagine that if I could drive the motors up to their full power of 1700W each I would be able to get the boat in a more efficient planing mode, thats almost 5hp for 30 lbs, right? Maybe Crouch equations don't scale down very well, but for a moderately efficient hull-form, 180 Crouch constant would plane with 90W, and I can push a big bow wave up to 240W and about the hull speed.

I would actually be ok if the impellers were causing a bit of bow up pitch, I think the weight will prevent it from flipping, but would be nice to get a little help to nose up over the bow wave.

Im using GPS and a tie in to chart plotter systems to help this navigate alongside a bigger boat all powered by a pair of raspberry pis, hopefully the final product will be pretty cool. Id like to have max speed of 15kts, but regularly operating at 10 kts.