2 Generators

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Capt.Bill11 said:
Sharing is tricky, spitting is not. :D
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Wifey B: I'm not an electrical expert, but apparently you're saying there is a simply way that if you spit the generators do magic things? Do you spit just saliva or tobacco or gum or? How far must you be able to spit? :rofl::hide:
 
BandB said:
Wifey B: I'm not an electrical expert, but apparently you're saying there is a simply way that if you spit the generators do magic things? Do you spit just saliva or tobacco or gum or? How far must you be able to spit? :rofl::hide:
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Spitting combined with large hammer can work miracles when it comes to some things mechanical. :D

But in this case I should have typed splitting.
 
Britannia said:
I don't think I have room for a wing engine - at least not without getting rid of the 20kW generator. I am thinking that electric would be the most compact and simplest to install. Motors are still quite expensive but the price and performance is really improving as they are gaining popularity for transportation in general. Maybe in another 5 years or so it will be a no brainer.
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Ok, we must have a different layout. On the Krogen 42, the genset is midline aft of the main engine. The battery bank to port and the wing engine to starboard. Hard to believe the Krogen 54 has less room.
 
Bay Pelican said:
Ok, we must have a different layout. On the Krogen 42, the genset is midline aft of the main engine. The battery bank to port and the wing engine to starboard. Hard to believe the Krogen 54 has less room.
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Ok - I take that back. There probably would be room - on the port side in my case. I could move a couple of things around and fit one in. I wouldn't want to though - it would be hard to work on and make other systems harder to service. I'm sure it could have been put in easily when the boat was built. Much more work now.

Richard
 
Richard-your idea using an electric motor may not be such a bad one, and may not be as expensive as you might think. Some years ago we looked a doing a one off build designed as a diesel-electric hybrid for 57' trawler. The drawback is that you may need a larger generator. Your 20kw generator will produce about 27 HP. That is not going to move you very fast. A good naval architect or engineer can give you an idea of how it would do. In our design, the Siemens engineers we worked with figured we needed between 275 and 300 HP or 205-224KW. That would drive two shafts, i.e. two electric motors, and move a boat designed at ab0ut 85,000 lbs a comfortable 8-9 knots. The actual parts of the system are not cost prohibitive. The Siemens motors we examined, about 140 HP each, were around $4,000. The control unit for two motors was about $3,000. Motors that size are not very large and the ones we looked at were around 150lbs.

If the power from your 20KW is sufficient, you should be able to mount an electric motor parallel to the shaft and use a chain drive, assuming your transmission will allow the shaft to freewheel. You could gear it 1:1 or maybe gain some efficiency by playing with different drive gears.
 
With a hydraulic drive it is easy to install a pressure modulating setup so that the prop can spin at various speeds. Varying the speed of an AC or DC motor in the 20 + KW range can certainly be achieved but becomes costly and requires a fair amount of moisture proof space.
 
THD said:
Richard-your idea using an electric motor may not be such a bad one, and may not be as expensive as you might think. Some years ago we looked a doing a one off build designed as a diesel-electric hybrid for 57' trawler. The drawback is that you may need a larger generator. Your 20kw generator will produce about 27 HP. That is not going to move you very fast. A good naval architect or engineer can give you an idea of how it would do. In our design, the Siemens engineers we worked with figured we needed between 275 and 300 HP or 205-224KW. That would drive two shafts, i.e. two electric motors, and move a boat designed at ab0ut 85,000 lbs a comfortable 8-9 knots. The actual parts of the system are not cost prohibitive. The Siemens motors we examined, about 140 HP each, were around $4,000. The control unit for two motors was about $3,000. Motors that size are not very large and the ones we looked at were around 150lbs.

If the power from your 20KW is sufficient, you should be able to mount an electric motor parallel to the shaft and use a chain drive, assuming your transmission will allow the shaft to freewheel. You could gear it 1:1 or maybe gain some efficiency by playing with different drive gears.
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I agree that 20kW is a bit low for a get home. David Gerr's formula shows that I could make 3.5 kt with 20kW. And that's power at the prop. With the various losses in the system I'd be lucky to make 3kt. That's marginal even for a get home system. Boats my size typically have something like a 45HP wing engine. That would achieve up to 5kt.

Richard
 
sunchaser said:
With a hydraulic drive it is easy to install a pressure modulating setup so that the prop can spin at various speeds. Varying the speed of an AC or DC motor in the 20 + KW range can certainly be achieved but becomes costly and requires a fair amount of moisture proof space.
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At only 3 kt (see my previous post) I wouldn't need a throttle. Forward and reverse would be sufficient.
 
Britannia said:
At only 3 kt (see my previous post) I wouldn't need a throttle. Forward and reverse would be sufficient.
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I was on a Northern Marine 57 and its 20KW smooth water hydraulic drive speed was 4.5 kts. Then how to do it from a prop and shaft standpoint. Lots to think about as you well know. No argument from me though that 20KW is pretty small. What is your RPM to achieve 3, 4 and 5 kts currently? That will give a pretty good replication of power needed for a get home.


BTW, an FPB 64 with a JD 4045 get home will make 7.5 knots comfortably.
 
sunchaser said:
I was on a Northern Marine 57 and its 20KW smooth water hydraulic drive speed was 4.5 kts. Then how to do it from a prop and shaft standpoint. Lots to think about as you well know. No argument from me though that 20KW is pretty small. What is your RPM to achieve 3, 4 and 5 kts currently? That will give a pretty good replication of power needed for a get home.


BTW, an FPB 64 with a JD 4045 get home will make 7.5 knots comfortably.
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The only number I have in that range is at 1000 RPM I'm making 4.8kt. The engine is a JD 6068T - the power curves only begin at 1000 RPM and aren't easy to read. Propeller power may be 15-20HP at those revs?

It may be hard to predict. I'd definitely have a propulsion expert do the calcs.

Richard
 
sunchaser said:
I was on a Northern Marine 57 and its 20KW smooth water hydraulic drive speed was 4.5 kts...
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That's a 120,000 lb boat - I just looked it up. This is surprising and encouraging. I don't know how well Gerr's forumula works down at the low end. I suspect it's really designed to figure out how much power is require to push a boat speeds in the 1.0 - 1.3 range of S/L.

Thanks

Richard
 
Britannia said:
The only number I have in that range is at 1000 RPM I'm making 4.8kt. The engine is a JD 6068T - the power curves only begin at 1000 RPM and aren't easy to read. Propeller power may be 15-20HP at those revs?

It may be hard to predict. I'd definitely have a propulsion expert do the calcs.

Richard
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Easier to calculate required HP in those situations by measuring fuel consumption. Take the fuel consumption and multiple by 15 HP per gallon. 15 is a better reflection of HP per gallon as the engine is running very inefficiently at that RPM.

Ted
 
O C Diver said:
Easier to calculate required HP in those situations by measuring fuel consumption. Take the fuel consumption and multiple by 15 HP per gallon. 15 is a better reflection of HP per gallon as the engine is running very inefficiently at that RPM.

Ted
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Not just easier but far more accurate.
 
O C Diver said:
Easier to calculate required HP in those situations by measuring fuel consumption. Take the fuel consumption and multiple by 15 HP per gallon. 15 is a better reflection of HP per gallon as the engine is running very inefficiently at that RPM.

Ted
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My Floscan indicates that it's burning 1.2 gph at 1000 rpm and 4.8 kt. That equates to 18HP by your formula. If that's true then it's evidence to suggest a 20kW generator may be enough. The accuracy of the Floscan is always a question. But these numbers line up with others I've seen on similar boats.

Thanks for the suggestion

Richard
 
Britannia said:
At only 3 kt (see my previous post) I wouldn't need a throttle. Forward and reverse would be sufficient.
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And at 3 knots, depending on the prevailing wind/current, you may be going in reverse without being in reverse.

I hope this isn't a derail that breaches etiquette, but once I was salmon trolling at about 2.5 knots against a 3+ knot current, so I was actually going backward. So, our lookout was in the cockpit with everyone else as we literally watched the scenery pass us by backward.

Another vessel was traveling at about 25 knots on a crossing heading. Because the current was dragging him backwards too, he was on a near collision course. Fortunately, I happened to be at the helm at the time. To avoid a collision, I put the boat hard into reverse, so he missed us by a few feet.

Lesson learned, but if he had hit us (my bow could not have hit his, it would have necessarily been the port side of his boat hitting my bow), under the ColRegs, whose fault would it have been?
 
MYTraveler said:
And at 3 knots, depending on the prevailing wind/current, you may be going in reverse without being in reverse.

I hope this isn't a derail that breaches etiquette, but once I was salmon trolling at about 2.5 knots against a 3+ knot current, so I was actually going backward. So, our lookout was in the cockpit with everyone else as we literally watched the scenery pass us by backward.

Another vessel was traveling at about 25 knots on a crossing heading. Because the current was dragging him backwards too, he was on a near collision course. Fortunately, I happened to be at the helm at the time. To avoid a collision, I put the boat hard into reverse, so he missed us by a few feet.

Lesson learned, but if he had hit us (my bow could not have hit his, it would have necessarily been the port side of his boat hitting my bow), under the ColRegs, whose fault would it have been?
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Yes - 3 knots may be too slow even for a get home. Although further anaylsis is suggesting I may be able to do better than that. Even so, you don't fight currents and sea state in a get home situation. If I'm half way to Hawaii I'm going to pick whichever direction gets me somewhere. Plenty of small sailboats spend days averaging 3 knots on the way to or from Hawaii. I watched a youtube video of one that took about 45 days to do Hawaii to Washington State. That's an average of not much over 2 knots!

On your bizarre colregs question I'm guessing that if it was his port side hitting your bow then it was crossing from your starboard. If so, then it was the stand on vessel and you were at fault. It really doesn't matter that there was current - you were both in the water and moving relative to one another. I don't quite see how the current was pushing him towards you if you were in the same current. Surely the current makes no difference.

I was in a sailboat race with a friend in SF Bay and we anchored because we were being pushed backwards by the current (this is allowed as long as the engine is not started). A boat was pushed back into us by the current. In that case it was the other boat's fault - you are the stand on vessel if you're anchored!

Richard
 
While 3K is slow for cruising as an emergency get home its still about 70 miles per day.

About what most rag boats cross oceans at.

And at just above idle the fuel burn will give the longest endurance , should the fuel supply be low.
 
Britannia said:
You're joking, right?
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Only a little.

You wouldn't need a very big outboard to move you along at get home speeds. 15 - 20hp? You may already carry one for your dink.

And this solution would be a lot cheaper than adding a wing engine. Especially if you only have a real need for the wing engine for this one long trip.

I've seen it done on other boats. And while they didn't have nor need the fuel capacity you might, it did work.
 
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Capt.Bill11 said:
Only a little.

You wouldn't need a very big outboard to move you along at get home speeds. 15 - 20hp? You may already carry one for your dink.

And this solution would be a lot cheaper than adding a wing engine. Especially if you only have a real need for the wing engine for this one long trip.

I've seen it done on other boats. And while they didn't have nor need the fuel capacity you might, it did work.
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Sorry my response was a little curt. I agree that in principle it could work. I do have a 20HP motor for my dink. The problem is that I'd need to carry about 500 gal of gasoline for it to give me the 1000 mile range that I'd need. And I might well want a bladder for extra diesel for the longer crossings.

My plan is to keep going after I reach Hawaii - so I anticipate many long passages.

Richard
 
Britannia said:
Thanks - the question for me is based around whether I want to add a hydraulic PTO to my existing 20kW generator for this kind of get home system. Alternatively I could use the 240V it's already generating to power an electric get home motor. It would seem to be a simpler solution - though I'm not sure if it would be cheaper yet.

Richard
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The limiting factor for the Eagle hydraulic bow thruster get home is the Perkins 35 hp. If the gen has to be replace a 50+ hp gen set would be installed. I would not size by kw but hp. To me a gen set is two separate items, a engine and a generator. The cruise gen is powered by the main 671 engine. Hydraulic you talking horse power.
 
Phil Fill said:
The limiting factor for the Eagle hydraulic bow thruster get home is the Perkins 35 hp. If the gen has to be replace a 50+ hp gen set would be installed. I would not size by kw but hp. To me a gen set is two separate items, a engine and a generator. The cruise gen is powered by the main 671 engine. Hydraulic you talking horse power.
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If I'm adding a hydraulic PTO to the engine that drives the generator then yes - HP would be the unit of power to look at. I think it's around 27HP for the Lugger that drives my NL. But if I add an electric motor and use the electric power output of the generator then kW is what matters. So it's all a question of what power transfer mechanism you are using. In my case I'm leaning towards electric.
 
Britannia said:
Sorry my response was a little curt. I agree that in principle it could work. I do have a 20HP motor for my dink. The problem is that I'd need to carry about 500 gal of gasoline for it to give me the 1000 mile range that I'd need. And I might well want a bladder for extra diesel for the longer crossings.

My plan is to keep going after I reach Hawaii - so I anticipate many long passages.

Richard
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No problem. I was just thinking out loud and wasn't sure just how often you'd be making long distance runs.
 
Britannia said:
If I'm adding a hydraulic PTO to the engine that drives the generator then yes - HP would be the unit of power to look at. I think it's around 27HP for the Lugger that drives my NL. But if I add an electric motor and use the electric power output of the generator then kW is what matters. So it's all a question of what power transfer mechanism you are using. In my case I'm leaning towards electric.
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Would be interesting to see what you come up with as far as electric motors. Above 10 HP, most electric 220 volt motors are 3 phase. Maybe a company like Siemens has some special purpose motors in the 15 to 20 HP range. The second probably tougher issue is starting surge load. Unless the motor is a slow starting variable speed, the electrical surge to start that motor in gear, very likely may trip the main breaker. If money is no object, maybe a variable speed prop for soft starting that could also be feathered to reduce drag and keep the shaft from spinning when not in use,

Lots of fun spending other people's money. Now I understand politicians. :rolleyes:

Ted
 
O C Diver said:
Would be interesting to see what you come up with as far as electric motors. Above 10 HP, most electric 220 volt motors are 3 phase. Maybe a company like Siemens has some special purpose motors in the 15 to 20 HP range. The second probably tougher issue is starting surge load. Unless the motor is a slow starting variable speed, the electrical surge to start that motor in gear, very likely may trip the main breaker. If money is no object, maybe a variable speed prop for soft starting that could also be feathered to reduce drag and keep the shaft from spinning when not in use,

Lots of fun spending other people's money. Now I understand politicians. :rolleyes:

Ted
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Yes - most of the motors I've seen for boats are DC with big battery banks. That's not really what I want - though it does solve the soft start problem. I've got quite a few years before I'll really need this so there's plenty of time for technology to catch up.

Richard
 
Variable frequency drive (VFD) will solve any "hard start" issues. Proven, off the shelf, common technology.
 

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