Getting rid of alternator?

[mcarthur]

Well the verdict is certainly in, and I think unanimous. We’ll keep the alternators and think when and how to jettison the generator. Thank you!

I’ll have to think more about the size of the alternator - a move to a larger one . I don’t understand the reasoning yet! Anyone feel like explaining in smaller words? The idea of a larger alternator seems to be the basis of the Integrel system (cf. Calder ).

In keeping the alternator, we’d already thought about a DC genset for when we hybridise and want the long range at lower speed (diesels would be for medium range and mid speed, and diesels for stonking along). I hadn’t thought of modifying an engine alternator for DC instead of AC. I’d love to find out more if anyone can point me in the right direction?

I won’t explain the hybridisation choice as if you can’t understand, nothing I say will change your mind. I certainly don’t feel the need to justify (and )...

[valhalla360]

With our old Gemini, if we ran at 6kts, we got about 6MPG. I played with it a few times and if we dropped back to 5.5kts, we went up to around 10MPG.

To get 1-2% improvement in fuel efficiency would likely be around speed of around 5.999kts (drag is not linear so significantly less than 1% drop in speed will give you 1% less fuel consumption). Of course, adjusting the throttle to get even a 0.1 kt difference in speed would be difficult.

[Q Xopa]

Originally Posted by valhalla360

With our old Gemini, if we ran at 6kts, we got about 6MPG. I played with it a few times and if we dropped back to 5.5kts, we went up to around 10MPG.

To get 1-2% improvement in fuel efficiency would likely be around speed of around 5.999kts (drag is not linear so significantly less than 1% drop in speed will give you 1% less fuel consumption). Of course, adjusting the throttle to get even a 0.1 kt difference in speed would be difficult.

I agree with what you have written. But I'm not sure I understand who you are responding to. What is the reference to 1-2% efficiency about?

[valhalla360]

Originally Posted by Q Xopa

I agree with what you have written. But I'm not sure I understand who you are responding to. What is the reference to 1-2% efficiency about?

The original post was suggesting an improvement so small as not to be measurable in normal conditions.

I was just providing a real world example of how you likely couldn't reliably adjust the throttle to get such a small difference in fuel consumption.

[Q Xopa]

Originally Posted by valhalla360

The original post was suggesting an improvement so small as not to be measurable in normal conditions.

I was just providing a real world example of how you likely couldn't reliably adjust the throttle to get such a small difference in fuel consumption.

Ah ok, yes you are correct. Sorry wasnt thinking back that far.

[seabreez]

[QUOTE=mcarthur;2960877]Question - any reason not to get rid of the propulsion engine alternators, and
Question - would I expect any fuel consumption benefit?

If you can afford a 50' power cat, you will at one point need the alternators. I have never seen anyone be comfortable and confident to a point of doing away with alternators even if you have alternate power sources. Furthermore, if and engine was designed with certain parts... do not change or modify a design. I am not an engineer... but the thought going in to designs is not worth changing by an amateur trying to save a few cents on fuel, especially at sea...

[lordgeoff]

Originally Posted by Dockhead

My numbers are WAGs, so you'll need to do your own research. But they should be in the ballpark, and I think you'd need an order of magnitude difference to those to even want to THINK about this.


Looking at the bigger picture, with a massive solar installation and no air con, I would keep this simple.



I would put school bus alternators on both main engines, with a Balmar Centerfielder regulator, sell on the generator, install a large bank of industrial LEAD batteries (although I'm a big fan of lithium), sized at 4x average daily consumption (which will give you usable 2 days consumption), a couple of ganged Victron Multipluses, and call it good. For all of the massive benefits of lithium, you don't really need those benefits with a massive solar installation, and industrial 2v cells in such an installation are extremely durable -- will last at least 10 years and probably more. Hybrid drive will bring you nothing worthwhile, and those Perkins beasts will outlive you. Go cruising instead of tinkering, and spend the $50 000 or $80 000 you save on women and booze.



My advice, maybe worth about what you paid for it , but there it is.

Totally correct. When I read people wanting to reinvent the wheel and spend big bucks to do it I just figure they dont understand cruising......

[Dockhead]

Originally Posted by mcarthur

Well the verdict is certainly in, and I think unanimous. We’ll keep the alternators and think when and how to jettison the generator. Thank you!

I’ll have to think more about the size of the alternator - a move to a larger one . I don’t understand the reasoning yet! Anyone feel like explaining in smaller words? The idea of a larger alternator seems to be the basis of the Integrel system (cf. Calder ).

In keeping the alternator, we’d already thought about a DC genset for when we hybridise and want the long range at lower speed (diesels would be for medium range and mid speed, and diesels for stonking along). I hadn’t thought of modifying an engine alternator for DC instead of AC. I’d love to find out more if anyone can point me in the right direction?

I won’t explain the hybridisation choice as if you can’t understand, nothing I say will change your mind. I certainly don’t feel the need to justify (and )...

So the point of larger alternators is two or maybe three-fold:


1. Large-frame alternators are designed to produce power in bulk. Car-type alternators are not, and will burn up if you try to pump maximum rated power out of them for sustained periods of time, or their output will be dialed right down by thermal protection. Large-frame alternators have the cooling and the mass in the rotor and stator to produce their maximum rated power 24/7. For any service where you need bulk power, as opposed to just running light systems and topping off a start batt, you want a large frame alternator if you can practically mount one (not all boats can). This is especially important with lithium batteries since the acceptance rate doesn't taper off and they will push the alternator to the max whenever they are being charged.



2. Large alternator puts a better load on the engine in case you're producing power without doing propulsion at the same time.


3. Large alternator lets you produce the amount of energy you need to store in a shorter period of time -- less running of the motors.


4. Producing power from a main engine driving a large alternator while not doing propulsion will be more efficient, because you will load the engine better and run it for fewer hours for a given amount of power produced, saving hourly maintenance and amortization (usually more expensive than fuel), and saving a noticeable amount of fuel.



OK?


Now the topic of hybridization is NOT indeed off topic, because if you are really going to do that, then it changes everything in your electrical system design. If you're going to get rid of the propulsion engines then obviously you can't get rid of the generator, and if you have a big generator, then that changes the job of the alternators.


If you don't want to discuss the hybridization job, that's fine, but before taking the plunge, I would urge you to throw emotion and sales propaganda, fuel map magic, etc. out the window, and do the NUMBERS. The NUMBERS don't lie. Before spending that kind of cash, you should consult an actual engineer, and not one employed by a company selling hybridization gear, and convince yourself that I'm wrong about this:


* Unless you can regularly, like every day or two, store a large quantity of cheap mains power, OR if you move very rarely and can do your propulsion with stored up solar power, hybrid propulsion is less efficient than direct drive and will result in an increase, not decrease in fuel burned.


* Some hybrid companies claim that you can make up for conversion losses of hybrid power by operating the diesel engine in a better part of the fuel map. But a generator running wide open is not in the best part of the fuel map, either. And in any case, these gains can be quantified and can and should be compared objectively -- don't just believe the sales pitch.



* Do the numbers on how much practical propulsion you can do with stored solar or regen power. Don't use theoretical numbers based on ideal conditions but number from realistic everyday conditions.





OK, probably more than you asked for, but I'm hoping it will be helpful. Cheers.

[CatNewBee]

135hp engines do not care about a small alternator, there will be no difference. Usually the belt is driving not only the alternator, but also a water pump for cooling, so you will need the belt anyway.

Regarding hybrid conversion.

You have a 50ft power cat with 270hp in total for the fun, and no sails or other propulsion. After conversion and using the generator as range extender you will have a boring slow powerless cat 6.5kW generator is about 9hp, that divided for two electric engines ends up to 4hp per hull. This is 1/15th of what 50ft sailing cats have to maneuver into a berth or motorsail. The alternators are your least concern. The windage and water resistance alone would forbid to take this boat out to sea if there is a tidal current, swell or a breeze.

We took a passage through the Messina strait some time ago and arrived late, so had the current on the nose, we needed both engines 40hp each and the sails to get through the strait entrance in 2kn SOG, in an almost 2h fight. Would be Impossible with a hybrid setup and small engines.

[a64pilot]

From my drag racing days I seem to remember that a spinning tight belt on an idler pulley robs 3 HP. An alternator not making power is essentially an idler pulley. But that was also probably at real high RPM too, the power required due to friction goes up with RPM.

If it were me, I’d only remove one engine when I did the hybrid thing, and I’d leave the generator and the other Diesel engine and only run the single electric one as a proof of concept.
I’m going to go out on a limb and state that’s it’s my belief that if you want to go to electric propulsion, your going to need to harvest every possible source of electric power, that includes a School bus alternator or two on your remaining engine as well as the generator and as much Solar as is possible.

There have been a few pure Solar power Cats built, maybe find as much info on them as you can, how much Solar did they have, what is their gross weight and what is their average sustained cruise speed.
That will give you an idea of what your going to end up with.

My prediction is that on electric drive only your going to have a 3 or 4 kt boat and will have to be very selective about when you travel to ensure it’s not into too much headwind etc., and that keeping that second Diesel in place will end up being your savior.
Your limiting factors will be electric production and storage, you won’t need twin electric motors to use all the power you will have.


The best use case for an electric boat in my opinion is one that does short day trips and is plugged into shore power every night, if that’s not you, for goodness sakes keep one of those Diesels.

[AndyEss]

As I understand the OP, he wants to be as fuel efficient as possible, and was exploring options. I agree with the consensus that getting rid of the genset, at 2% of total boat weight, makes far, far more sense than removing propulsion engine alternators.
But why stop there? Parasitic weight increasing draft greatly increases hull
wetted surface area, which is a great source of drag.
Dump as much of your stores and interior as possible. If your SO is old and weight challenged, trade her in for a newer, sleeker model. Silicone probably weighs less than adipose tissue anyways. Don’t cruise with friends and only carry freeze dried foods onboard to further keep weights down.
As the old joke goes, to live forever, you have to give up sex, good food and drink. But if you did that, why would you even want to live forever?

[a64pilot]

The key to fuel efficiency is speed, water is extremely dense, takes a lot of power to push it out of the way, if you have any kind of wake at all, your going too fast for efficiency.
Over the years as have graphed fuel consumption over distance for three different power boats, without exception idle was the most fuel efficient, from there the MPG decreased.

You may want to install flow scan meters, or one will tell you, you don’t need one on both engines.
If the motors are newer common rail, it’s likely the computer can tell you fuel consumption, but it’s dead easy to compute MPG yourself or most fuel flow meters if connected to a GPS will tell you MPG.

[mcarthur]

Thanks everyone.

We have definitely heard the consensus here - the question was asked here because we didn't know the answers, not because we had already decided and were seeking confirmation.

A pair of flow meters (Maretron) are already on the buy list for one side of the boat. The old Perkins NA aren't common rail and the closest a computer has come to them may have been in their design (although I doubt it, and if it did then it would have been the old size-of-a-room type ).

Going hybrid, we would replace the genset with a much larger DC which removes some of inefficiencies of the AC when feeding batteries and certainly the size limit of the poor old 6.5kW Onan AC.

We have pretty good estimates (note!) of 6-6.5kn under electric using the DC genset until the diesel runs out.

[AndyEss]

Originally Posted by mcarthur

Well the verdict is certainly in, and I think unanimous. We’ll keep the alternators and think when and how to jettison the generator. Thank you!

I’ll have to think more about the size of the alternator - a move to a larger one . I don’t understand the reasoning yet! Anyone feel like explaining in smaller words? The idea of a larger alternator seems to be the basis of the Integrel system (cf. Calder ).

In keeping the alternator, we’d already thought about a DC genset for when we hybridise and want the long range at lower speed (diesels would be for medium range and mid speed, and diesels for stonking along). I hadn’t thought of modifying an engine alternator for DC instead of AC. I’d love to find out more if anyone can point me in the right direction?

I won’t explain the hybridisation choice as if you can’t understand, nothing I say will change your mind. I certainly don’t feel the need to justify (and )...

Well, the thread started with the OP asking about the effect of removing the alternators from his two 135 hp diesel engines on his power cat. He mentions repeatedly a plan to hydridize his propulsion system by some sort of electric drive from a diesel genset.

Let's look at some of the numbers thrown around - removing the alternators and their parasitic load might save 1-5 hp each, from a 270hp dual engine propulsion system. Very small efficiency improvement, with multiple downsides.

As for the eventually desired hybrid system, the boat currently is propelled by 200kW of diesel power.(note - this is roughly 3000% of the current 6.5kW genset.

Electrical generation (AC or DC) has efficiencies of converting mechanical energy to electrical of around 80-95%. After getting this electric power, you need to re- convert it back into mechanical power to rotate your prop shaft(s). DC motors have efficiencies of 70-90%, so the total efficiency of the hybrid drive train would be in the range of about 55% to 85% of the original dino juice engine's fuel efficiency. I.E that 200kW genset would only get 110 to 170 kW to the prop shaft(s) to propel the boat.

That assumes low rpm electric motors, not requiring substantial gear reduction. Mechanical transmissions for diesels run 98-99% efficient as they don't typically reduce rpm much, and are mostly for being able to get both forward and reverse propulsion. High speed electric motors require deep reduction which is less and less efficient as gearing becomes more complex.

Changing kW back to HP, the hybrid system (at the full 270hp currently on the power cat) would lose about 45hp to 120hp when using electric drive as compared to a direct dino juice propulsion system.

You are totally right in my not getting your rationale in your attempts to improve propulsion efficiency. You worry about 2-10 hp going to alternators, but are unconcerned (apparently) by losing 45-120 hp in electrical energy conversions.

I still say your best changes for better fuel economy are to get rid of the old bat for a new sleek, young model, don't cruise with overweight friends, dump everything on board that isn't absolutely essential - and most importantly keep a clean bottom.

[Dockhead]

Originally Posted by AndyEss

Well, the thread started with the OP asking about the effect of removing the alternators from his two 135 hp diesel engines on his power cat. He mentions repeatedly a plan to hydridize his propulsion system by some sort of electric drive from a diesel genset.

Let's look at some of the numbers thrown around - removing the alternators and their parasitic load might save 1-5 hp each, from a 270hp dual engine propulsion system. Very small efficiency improvement, with multiple downsides.

As for the eventually desired hybrid system, the boat currently is propelled by 200kW of diesel power.(note - this is roughly 3000% of the current 6.5kW genset.

Electrical generation (AC or DC) has efficiencies of converting mechanical energy to electrical of around 80-95%. After getting this electric power, you need to re- convert it back into mechanical power to rotate your prop shaft(s). DC motors have efficiencies of 70-90%, so the total efficiency of the hybrid drive train would be in the range of about 55% to 85% of the original dino juice engine's fuel efficiency. I.E that 200kW genset would only get 110 to 170 kW to the prop shaft(s) to propel the boat.

That assumes low rpm electric motors, not requiring substantial gear reduction. Mechanical transmissions for diesels run 98-99% efficient as they don't typically reduce rpm much, and are mostly for being able to get both forward and reverse propulsion. High speed electric motors require deep reduction which is less and less efficient as gearing becomes more complex.

Changing kW back to HP, the hybrid system (at the full 270hp currently on the power cat) would lose about 45hp to 120hp when using electric drive as compared to a direct dino juice propulsion system.

You are totally right in my not getting your rationale in your attempts to improve propulsion efficiency. You worry about 2-10 hp going to alternators, but are unconcerned (apparently) by losing 45-120 hp in electrical energy conversions.

I still say your best changes for better fuel economy are to get rid of the old bat for a new sleek, young model, don't cruise with overweight friends, dump everything on board that isn't absolutely essential - and most importantly keep a clean bottom.

If you didn't notice, his hybrid system will be "good for 6 to 6.5 knots", so he is definitely not replicating the power of the original propulsion system.


I guess you only need 20hp or so to drive an average 50' power cat at 6.5 knots, but you'd better stay away from lee shores in bad weather.