Converting a yacht to electric propulsion - maximise hydro generation

[Scotopia]

Hi,

I'm currently in the process of converting a sailing vessel to electric propulsion and need some assistance/ideas on generating maximum power for battery charging.

Details of the system

Motor - 48v 20kw motor
Battery - 32 x 400ah 3.2v LiFeP04 cells - Connected in series/parallel for 51.2v 800ah
Solar - 4 x 340w 38.1Vmp - Victron MPPT max output 35a
Wind - 1 x 350w 48v


Based on maintaining a depth of discharge <50% for motoring (capable of 80%), during normal operation I will have maximum of 2hrs under motor.
The motor draws 400A at max but expected draw is 200A to motor at 6kn which is sufficient. In most cases this is adequate to motor in/out of a safe harbour and rely on sailing for all other momentum.

However, as I'm going offshore I must consider all possible situations and build in redundancy where possible. I'm would like to avoid a diesel genset if possible but that is my fall back. Which leads me to my question, what is the maximum power I can produce through hydrogeneration sailing at 5-6knts.

I can purchase a 48v 200a DC brushless alternator that requires 1500rpm but can I produce enough torque/rpm from to power it via hydro?

Any help or ideas would be great, thank you.

 

[alec_t]

Welcome to ETO.
If I understand correctly, you want to use the boat's motion to spin a turbine to drive the alternator to generate electricity to power the motor to drive the boat? That sounds like an over-unity attempt . Or did you intend using the turbine only when under sail?
Extracting energy from the turbine will have a braking effect on the boat's motion.

 

[tcmtech]

Which leads me to my question, what is the maximum power I can produce through hydrogeneration sailing at 5-6knts.

I can purchase a 48v 200a DC brushless alternator that requires 1500rpm but can I produce enough torque/rpm from to power it via hydro?

Really rough guess I would say no not even close unless you can set up 1000+ square feet of sail and have 15+ knot winds at your back for days on end and a 5+ foot diameter hydro prop under your yacht to make everything go.

An alternator that size would take ~20 HP to spin whereas you maybe have 1 - 2 HP to work with in ideal situations and half that or less in realistic ones.

As is the rough numbers on recharging your system with your 4 x 340w solar and 350w wind system in combined ideal conditions of high sun and wind for 12 hours a day is near a weeks worth of run time.

 

[Scotopia]

That sounds like an over-unity attempt . Or did you intend using the turbine only when under sail?

Thanks for the welcome Alec.

it's definitely an over unity attempt but only meant for a situation where I can't wait for my other units to restore power and need to move a reasonable distance to safe anchorage. Under sail I will already be regenerating through the motor with an expectation of producing 1kw at 7kn, however we won't know for sure until testing.

What I need to solve ( and I know I'm challenging Newton on this) is to generate ample power when using the motor for an extended journey. Guaranteed solutions are increased battery bank or diesel genset.

Extracting energy from the turbine will have a braking effect on the boat's motion.

It certainly does. Existing setups produce a maximum of 600w (48a 12v). This is achieved with a 240mm propeller with imperceptible drag. At most, some tests showed a reduction in speed of 0.2kn. I'm willing to accept greater drag for increased power. No doubt it has diminishing returns but I expect there is a compromise point that will suit my needs. How do I calculate it though?

 

[tcmtech]

it's definitely an over unity attempt but only meant for a situation where I can't wait for my other units to restore power and need to move a reasonable distance to safe anchorage.

Unfortunately the laws of physics don't care what situation you are in. You get less out than you put in, period.

If you need reliable and sufficient back up power then the diesel genset is your only option.

 

[Scotopia]

An alternator that size would take ~20 HP to spin whereas you maybe have 1 - 2 HP to work with in ideal situations and half that or less in realistic ones.
.

My calculations worked out that 15hp will be sufficient. If current units can produce 1hp with barely noticeable drag, surely I can get to 8-10hp?

To be clear, I want to produce the power while using the motor. If I can sail (conditions favorable) I don't need more than my existing power reserve and I intend to sail as much as possible, that's what I love and look forward too. Most offshore sailors recommend that you should be able to steam/motor for 1,000nm, best case scenario.

 

[Scotopia]

Unfortunately the laws of physics don't care what situation you are in. You get less out than you put in, period.

I completely get that. I would like to understand what the actual calculations are for producing power vs. drag. Surely if I can accept greater drag and a slower vessel speed, I can generate increased power. 600w is pointless...

I don't expect to replenish 100% of the power I'm using, that is impossible. But, surely I can extend my time under motor.

 

[tcmtech]

The balancing act of how you want to take the power out of the wind is the issue.

If you use the prop in the water to generate power you slow the boat down s you add more load until the prop stalls.

Or you add a bigger wind generator and catch more wind which as the load on the generator is increased the forces pushing the boat increase and thusly move it faster.

Or you find yourself in the calm before the storm under cloud cover with no wind and the movement no matter what.

Cost Vs performance Vs practicality to work in all reasonable weather conditions dictates that the diesel genset is the only workable option that will do what you need when you need it every time.

 

[Scotopia]

Thanks tcmtech.

Hoping for the impossible and checking all options before going that route.

 

[alec_t]

I want to produce the power while using the motor.

Doing so with a hydro-electric generator is a non-starter. Assuming you can get N Watts from the generator, you will need more than N extra Watts to power the motor to compensate for the drag, so you finish up with a nett energy loss from the battery.

 

[tcmtech]

One of the bigger issues I would be looking at is the overall cost plus other investments vs real world gains (if there are actually any) that having a hybrid system will get you and to what realistic timeframe of ownership and operation they require to theoretically pay for themselves Vs having used a conventional internal combustion engine based propulsion systems would have.

What are you goals and relative likelihoods of said goals being achieved let alone having any legitimate real world justified value over anything else of well known conventional design?

As is you have an admitted at best 2 hour (~ 10 - 15 nautical miles travel distance) run time before your dead in the water and given your present self contained recharge system you could be looking at only being able to squeeze another 2 hours of propulsion per week out of the system in a emergency assuming you lost your sails or the weather simply did not cooperate with you for that long.

Whereas with a engine drive propulsion system you could conceivably carry 50 - 100+ hours of flat out run time (hundreds of nautical miles travel distance) with minimal investment plus the ability to be refueled at ease at any time.

 

[crutschow]

Since generating energy while using the motor gives you a net loss in energy, I think the most economical would be to use the prop as a generator when you are under sail, and take when that can give you.
Perhaps using a bigger prop would allow more power generation from that.
So that, along with the solar panels, would provide battery charging.
Any additional hydro generator would see to be quite expensive for any gain in energy.

Otherwise you go to the engine backup as tcmtech suggested.

 

[audioguru]

It will work if you can find an ocean that has a steep hill to sail down.

 

[flatfootskier]

I remember as a teenager I grabbed the prop from an outboard and plunged it into a dustbin. I was staggered at the torque produced.
50V x 800Ah = 40,000Wh storage
Wind turbine = 40,000/350 = 114h = 5 days at max rated to fill battery
Solar = about the same as wind, but only during sunshine & when facing the sun & perpendicular to it +/- 20 deg.
Motor = 10kW @ cruising = 4hrs cruising till empty or 2hrs if retaining half charge.
Water turbine = 240mm = 10 inches = comparative area of 5^2 = 25 (multiplied by pi, but we can drop that). 600W = 2 months to fill
25 sq.in <> 600W
so assume a 3ft diameter = 18" squared = 324 sq in.
324/25 = 13x power
13 x 600 = 7.5kW
so 3 days to replenish 50%
The maximum power output depends on the cross section area and the cube of the velocity. So there's a sweet spot somewhere I guess...
A 3ft turbine out the back of any sailing boat would be a challenge though if it's going to survive open oceans. Are you thinking of replacing the keel with a monster turbine?
I can't imagine you'll get more than low hundreds of rpm, so you'll probably need to custom wind the generator and salt-waterproof it. Or have the weight & noise of a gearbox.

Just a few thoughts, and best of luck with it. If you sail past south west england call in & show me!

 

[camerart]

Hi,
This is off topic, I know, but I once saw an experiment with a yacht with a windmill instead of a sail. It could sail directly into the wind.
I suppose that as it didn't 'take off', then it was a waist of time, but interesting nevertheless.
Camerart.

 

[tcmtech]

Hi,
This is off topic, I know, but I once saw an experiment with a yacht with a windmill instead of a sail. It could sail directly into the wind.
I suppose that as it didn't 'take off', then it was a waist of time, but interesting nevertheless.
Camerart.

I don't find it all that off topic. As someone who has played with wind power for nearing three decades now I have always found it fun to ponder on the practicality (or utter lack thereof) of it suse in different applications.

I think that for low energy non critical applications (supplemental power) its wellworth the pursuit of its use if the numbers remotely add up to being favorable. The problem I always find is the practicality limits that show up in the less than ideal situations along with the the realities of what those limits come from (cost, complexity, stability and service life footprints) and how often they do inevitably come up in normal real world applications.

For example. Since my place got switched over to a smart meter system a decade or better ago and my local utility company set up their website to allow us customers to view our power usage numbers I have tracked my average power consumption over the years and have seen a solid downward trend in my overall average day to day usage rates. In fact I am now at my lowest daily averages ever which are now down to about 25 - 30 KWh per day, a good 10+ KWH per day reduction from my peaks 5 - 10 years ago, even with the addition of an electric water heater a few years ago!

By those average daily usage numbers I should be able to run my whole place off a small 2 KW AE power system with room to spare. Unfortunately the reality is my actual hour to hour usage rates are nowhere close to ~ 1 - 1.2 KWH that those numbers suggest.
What they are now is a lot of .3 - .5 KWH spans with a few 5 - 10+ KWH peak hours from week to week. And even the recorded peak numbers not totally accurate either given that during those there are many times, where I know from personal monitoring, my short duration loads (a few minutes or more) are up in the several 10's of KW!

Total off grid RE power for me is totally impractical despite the outward appearance that my average power consumption looks to be well within the practical working range of such sources at this point simply due to the need to have the capacity for such high short duration (30:1 overhead) load handling.

 

[camerart]

Hi T,
I have a motorhome, with two switch over leisure batteries, and indicators for when they are low. At first when they were both low, I would drive till they charged up. After fitting two 50W solar panels plus two charging controllers, the difference in needing to drive, changed dramatically, so in this instance, they are essential.

I noticed however, that the angle to and brightness of the sun made the output 5 to 10% of best conditions. This means for for my practical use I should have 'say' 3 or 4 times that for practical use.

Regarding your yacht windmill, have you thought of changeable blades to match the conditions?

Definitely off topic, my motorhome alternator has just packed in!
C.

 

[large_ghostman]

Does it have to be Hydro? I do have an idea might not be super cheap but does work and isnt over unity. What I dont know is how much energy i can get you per $, I will need to calculate it out. the other bad news is it will need replacing now and then.

 

[camerart]

Does it have to be Hydro? I do have an idea might not be super cheap but does work and isnt over unity. What I dont know is how much energy i can get you per $, I will need to calculate it out. the other bad news is it will need replacing now and then.

Hi G,
What does 'isn't over unity' mean?
C

 

[large_ghostman]

means it works