pvb
Well-known member
Ah, I understand you! The big engine is needed to overcome the inherent inefficiencies in the diesel-electric drive train.
Bought a Never splashed Colvic Countess 33 on eBay, Looking for infos
- Thread starter GregOddity
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Ah, I understand you! The big engine is needed to overcome the inherent inefficiencies in the diesel-electric drive train.
anoccasionalyachtsman
Well-known member
Sorry Greg, but for one who claims to be a Mechanical Engineer you're not making any sense. You can put a 500hp engine in if you like, but you're only going to need 35-40 at most - yes? And if you're only using that much, guess what figure determines the prop size?
GregOddity
Well-known member
Funny you should say that. It seems that HIGH EFFIENCY is achieved with the principle being used on practically everything from boats to trains and buses and submarines and new airplanes.
Its only when faced with shelling out 10k for a LUMP of really old and antiquated and OBSOLETE 1920’s tech that you get told it’s inefficient.
Meanwhile the whole world moves that way …
You’re not going to tell me that the marine engines on sale are efficient I hope or I would have to ask to back that up with proper science.
The only efficacy about them is the way they market a lump of cast metal for over the price of a new car. Funny enough as well there is way more science on the efficiency of auto engines and they are a FRACTION of the price. There are even companies specialised in changing diesel drive trains in vehicles to diesel electric to make them more efficient. Its just the MARINE efficiency that somehow does not exist?
The efficiency in question can be resumed to the word MARINE. (then add 5k £ and Voila)
https://en.wikipedia.org/wiki/Diesel%E2%80%93electric_transmission
pvb
Well-known member
Diesel-electric is used on trains because it resolves complicated transmission issues, which don't apply to your boat. Diesel-electric is used on some ships as it simplifies the use of multiple power units, and can also allow the fitting of azimuth thruster pods - again, these don't apply to your boat.
You need around 30hp to drive the boat, but you're going to fit 75-85hp because you're going to use the engine as a generator too. With a spare 50hp, you could have about a 30kW generator, so you'll have plenty of electricity for the nav lights.
Fr J Hackett
Well-known member
Re: The Oddity PROPlem
1 agree Paul 35Hp is perfectly adequate for that boat and matched with a 3 blade folding prop would be ideal.
1 agree Paul 35Hp is perfectly adequate for that boat and matched with a 3 blade folding prop would be ideal.
Skylark
Well-known member
I’m afraid that I struggled to understand much of the above. Are you trying to correlate the price of an automobile engine with its efficiency, compared to a lump of old, antiquated and obsolete 1920s tech (whatever that is supposed to be)?
What do you mean by marine engine efficiency by proper science? Why not look at a manufacturers published BSFC (brake specific fuel consumption) curve and use the calorific value of the fuel burned to determine efficiency? That was the science I used when I spent 20 years involved with automotive engine combustion/gas exchange.
Price tends to be driven by whatever the market can bear and a smaller part to do with manufacturing costs. Nothing new about the black art of marine sector pricing and it has nothing to do with drivetrain efficiency.
As I understand it you’re claiming that an oversize engine coupled to a generator coupled to an electric motor is going to be more efficient than a correctly sized engine coupled to a simple mechanical gearbox. Really?
pvb has already explained why diesel electric has an advantage in train and ship applications.
GregOddity
Well-known member
Re: The Oddity PROPlem
I disagree with the 35 hp for a boat that is going to weight in somewhere around 10 metrics tons when finished and supplied and with with a few people on board. I’m not looking for optimal power to weight ratio without having a good bit in reserve for that through you have to climb out of. Ideally, I would always want a minimum of 50 bhp but that is my OWN personal opinion based on what I read and my understanding of it and what I was taught. Things break when you are working at the edge of tolerance. I rather overpower. It has no detriment on weight in this case so I fail to see any advantages except the Marine Pricing System for Diesel motors.
For the prop I understand that the 3 bladed props are better for manoeuvring and higher acceleration and the 2 bladed folding for speed. But that is as far as our knowledge combined goes at this stage. I must admit I got no idea whatsoever what were looking for as a prop.
Needs to be something with high thrust and good reverse capabilities as heavy boat needs to stop just before the pontoon and not trying to climb over it. Not really looking for speed but the drag is a consideration unless we use it for power.
I disagree with the 35 hp for a boat that is going to weight in somewhere around 10 metrics tons when finished and supplied and with with a few people on board. I’m not looking for optimal power to weight ratio without having a good bit in reserve for that through you have to climb out of. Ideally, I would always want a minimum of 50 bhp but that is my OWN personal opinion based on what I read and my understanding of it and what I was taught. Things break when you are working at the edge of tolerance. I rather overpower. It has no detriment on weight in this case so I fail to see any advantages except the Marine Pricing System for Diesel motors.
For the prop I understand that the 3 bladed props are better for manoeuvring and higher acceleration and the 2 bladed folding for speed. But that is as far as our knowledge combined goes at this stage. I must admit I got no idea whatsoever what were looking for as a prop.
Needs to be something with high thrust and good reverse capabilities as heavy boat needs to stop just before the pontoon and not trying to climb over it. Not really looking for speed but the drag is a consideration unless we use it for power.
Fr J Hackett
Well-known member
Re: The Oddity PROPlem
My point about a 35 Hp engine is that I sailed a long keel boat that had a cruising weight of somewhere close to 9 tonnes and a 35 Hp engine coped very well although I did not use it to drive a generator and then electric motor which to be honest I think is rather fanciful but each to his own. The other point is do you intend it to be a sail boat, motor sailor or motor boat at the moment it is looking like the latter. If you are thinking in terms of "ocean" sailing then motoring is one of the last considerations as you won't have enough fuel to make significant contributions to the passage.
On the subject of props a 3 bladed sari pitch is the way to go, if you have the cash burning a hole in your pocket.
My point about a 35 Hp engine is that I sailed a long keel boat that had a cruising weight of somewhere close to 9 tonnes and a 35 Hp engine coped very well although I did not use it to drive a generator and then electric motor which to be honest I think is rather fanciful but each to his own. The other point is do you intend it to be a sail boat, motor sailor or motor boat at the moment it is looking like the latter. If you are thinking in terms of "ocean" sailing then motoring is one of the last considerations as you won't have enough fuel to make significant contributions to the passage.
On the subject of props a 3 bladed sari pitch is the way to go, if you have the cash burning a hole in your pocket.
jordanbasset
Well-known member
Re: The Oddity PROPlem
Greg, I had a 55hp egine on a 40 foot boat, it was overpowered and anything above 1800rpm caused the stern to dig in ad we did not go any faster, just burned more fuel.
Have a serious think about this before you make any decisions
Greg, I had a 55hp egine on a 40 foot boat, it was overpowered and anything above 1800rpm caused the stern to dig in ad we did not go any faster, just burned more fuel.
Have a serious think about this before you make any decisions
GregOddity
Well-known member
I am Indeed. Let analyse the efficiency, shall we?
£800 for Golf Engine 75 Hp 110.000 KM
£362 (in my case) For fabrication of the cooling system
£1200 for Lithium Iron Batteries (we may extend capacity further)
£350 for 48v DC Motor (second hand)
I got the rest we need.
Solar not priced yet.
Battery power alone will allow for in and out of harbour with a range of 30m at 4 knots at our weight with a couple of hours of cruising at 2.5 knots Should we need further we start the engine.
We recharge batteries on the berth at local electricity prices
Only for long period cruising do we need to switch on the engine to charge batteries if we decide to motor for long periods.
This are the REAL economics of it on our case. As opposed to
£6k for a lump of iron and filling our diesel tanks at every harbour. 500 L of diesel at Asda prices at this very moment is £573 I rather spend that on batteries.
So if we want to go cruising extensively for a year If we only use half the fuel we can buy 1 battery more every time we tank.
GregOddity
Well-known member
Re: The Oddity PROPlem
Yeah, I know what you’re saying but the motor will only power the gen unit for the electric motor. The possibility of using it to drive the prop should we have an electrical problem is the thing that needs to be considered but not the primary means of propulsion.
Yeah, I know what you’re saying but the motor will only power the gen unit for the electric motor. The possibility of using it to drive the prop should we have an electrical problem is the thing that needs to be considered but not the primary means of propulsion.
pvb
Well-known member
This is fascinating; may I ask what Ah capacity of Li-Ion batteries you can buy for £1200? And what current does the motor take at 4kts?
GregOddity
Well-known member
Re: The Oddity PROPlem
Off course motoring is not our primary consideration therefore the electric as much as possible and really any engine will do if you manage to steady the optimal RPMS for electric generation.
On our case this one is cheap and does the job. We also don’t intend to use it much as its cheaper to recharge the batteries then use diesel. But it does solve range as we can power the electric motor directly and charge the batteries.
Sadly, it’s not burning a hole on our pockets. That being the reason we’re going Diesel Electric.
Off course motoring is not our primary consideration therefore the electric as much as possible and really any engine will do if you manage to steady the optimal RPMS for electric generation.
On our case this one is cheap and does the job. We also don’t intend to use it much as its cheaper to recharge the batteries then use diesel. But it does solve range as we can power the electric motor directly and charge the batteries.
Sadly, it’s not burning a hole on our pockets. That being the reason we’re going Diesel Electric.
GregOddity
Well-known member
I’m not a mechanical engineer, Systems is my thing. The point of the Diesel motor is only to generate direct ac current for long periods of motoring we may need or recharging the batteries. Not the primary means of propulsion.
GregOddity
Well-known member
Yes you may and I will gladly post it later but now I gotta go for dinner as everyone is waiting.
PaulRainbow
Well-known member
I'm sorely tempted to use my favourite word "nonsense" 
People who have actual, real, boats, and who use them are giving some real World figures, but on planet Greg that counts for nothing.
I'll add my figures. My boat is 35 feet and weighs around 10 tons. It is fitted with an old tech 42hp diesel engine, a Mercedes OM636. It will push the boat along happily at 1600-1800 RPM. If i run it anywhere near full speed the prop cavitiates and it starts to bury the stern, classic case of overpowering the boat and trying to exceed hull speed (as reported by others here).
I'd like to see some of Gregs figures for this 75-85hp engine/generator for charging the batteries. How does one get all of the power that you could generate from such a large engine into the batteries ? Magic ? Mirrors ?
A small, 3 cylinder, 25hp engine, running at just 1500 RPM will run a 13kw 240v AC gernerator. That's enough electricity for a small house.
How much does the 75HP engine, gearbox, generator and attendant batteries weigh ?
People who have actual, real, boats, and who use them are giving some real World figures, but on planet Greg that counts for nothing.
I'll add my figures. My boat is 35 feet and weighs around 10 tons. It is fitted with an old tech 42hp diesel engine, a Mercedes OM636. It will push the boat along happily at 1600-1800 RPM. If i run it anywhere near full speed the prop cavitiates and it starts to bury the stern, classic case of overpowering the boat and trying to exceed hull speed (as reported by others here).
I'd like to see some of Gregs figures for this 75-85hp engine/generator for charging the batteries. How does one get all of the power that you could generate from such a large engine into the batteries ? Magic ? Mirrors ?
A small, 3 cylinder, 25hp engine, running at just 1500 RPM will run a 13kw 240v AC gernerator. That's enough electricity for a small house.
How much does the 75HP engine, gearbox, generator and attendant batteries weigh ?
Spyro
Well-known member
I'm sorely tempted to use my favourite word "nonsense"
How much does the 75HP engine, gearbox, generator and attendant batteries weigh ?
Don't forget the electric motor as well.
Concerto
Well-known member
Greg
I have a Westerly Fulmar, which is 32ft and weighs 5½ tons in normal loaded trim. The original engine was 24Hp and has been re-engined with 28Hp. I very rarely use full revs and cruise at about 2,200 rpm compared to full revs of 3,400 rpm. The later Westerly Storm was 33ft and was fitted with only a 18Hp engine.
If you are intending to sail mainly, rather than motor, then do fit a folding propellor. Your boat speed will increase by about ½ to ¾ of a knot. Over long distances that makes a significant increase in performance and shorten you sailing days or enable longer distances to be attempted. If you sail across the pond, then you will cut days off your arrival time.
Your boat will probably weigh between 9 and 10 tons. The idea of a 75Hp engine sounds too large even if used solely for power generation. I would suggest not looking at car engines, but small industrial units made by Kubuto or Misubushi. They will be lighter, which is why they are used by many marine engine companies as a base unit. Parts are also widely available around the world, but some older car engine parts probably will not.
I have a Westerly Fulmar, which is 32ft and weighs 5½ tons in normal loaded trim. The original engine was 24Hp and has been re-engined with 28Hp. I very rarely use full revs and cruise at about 2,200 rpm compared to full revs of 3,400 rpm. The later Westerly Storm was 33ft and was fitted with only a 18Hp engine.
If you are intending to sail mainly, rather than motor, then do fit a folding propellor. Your boat speed will increase by about ½ to ¾ of a knot. Over long distances that makes a significant increase in performance and shorten you sailing days or enable longer distances to be attempted. If you sail across the pond, then you will cut days off your arrival time.
Your boat will probably weigh between 9 and 10 tons. The idea of a 75Hp engine sounds too large even if used solely for power generation. I would suggest not looking at car engines, but small industrial units made by Kubuto or Misubushi. They will be lighter, which is why they are used by many marine engine companies as a base unit. Parts are also widely available around the world, but some older car engine parts probably will not.
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NormanB
Well-known member
There can be no economic benefit or logical argument for a diesel electric hybrid drive in a small yacht. UNLESS you inherited all the equipment necessary for no cost. I think there is a case for electric drive alone if it meets your needs (see Sailing UMA on YT).
There can be no doubt it is an interesting technical exercise but to then translate that into reality at your cost is indulgent and foolhardy.
Regenerating electrical power on a small (slow) monohull via the trailing prop is minimal and insignificant to needs.
There can be no doubt it is an interesting technical exercise but to then translate that into reality at your cost is indulgent and foolhardy.
Regenerating electrical power on a small (slow) monohull via the trailing prop is minimal and insignificant to needs.
anoccasionalyachtsman
Well-known member
I think what he's doing is planning to use a cheap secondhand car engine. Not a bad plan and very doable.
There must be some pretty small and fairly light units from contemporary cars which will certainly be a bit more fuel efficient than most contemporary small marine diesels. They're not going to be particularly happy running at low rpms day in day out, but as long as people keep crashing cars there will always be cheap spares around. Whether the associated electronics are quite what you want on a boat will be food for another few dozen posts...
ps. This is from someone who's putting a Ford EcoBoost 1 litre engine into a Land Rover, so I do feel some sympathy.
There must be some pretty small and fairly light units from contemporary cars which will certainly be a bit more fuel efficient than most contemporary small marine diesels. They're not going to be particularly happy running at low rpms day in day out, but as long as people keep crashing cars there will always be cheap spares around. Whether the associated electronics are quite what you want on a boat will be food for another few dozen posts...
ps. This is from someone who's putting a Ford EcoBoost 1 litre engine into a Land Rover, so I do feel some sympathy.
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