sailorman
Well-Known Member
The over propping of my engine is intentional & irretrievable to this question
Turbos
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pvb
Well-Known Member
OK, so you've decided to overload your engine?
Skylark
Well-Known Member
It's pretty hard to design a turbo to deliver the required air to mix with fuel to develop, say, only 20 to 30 bhp. It would be very small and would rotate at something like 200,000 rpm at full speed. Scaling down brings a number of challenges.
The quantity of engines built in this power size is fairly small so, inevitably, costs would be disproportionately high compared to, for example, a 1.6 litre, 130 bhp road vehicle engine.
Turbocharging eloquently overcomes one of the biggest issues with a diesel engine. It struggles to get enough air to burn the fuel.
A naturally aspirated diesel can generate, typically, up to 9 bar BMEP. A modern turbo, intercooled engine will generate almost double that. Twice the power for the same displacement.
Turbos are inherently very reliable. There is no metal to metal contact and the rotors sit on semi-floating bearings. Unless neglected, they should be considered a "life of the engine" component.
The quantity of engines built in this power size is fairly small so, inevitably, costs would be disproportionately high compared to, for example, a 1.6 litre, 130 bhp road vehicle engine.
Turbocharging eloquently overcomes one of the biggest issues with a diesel engine. It struggles to get enough air to burn the fuel.
A naturally aspirated diesel can generate, typically, up to 9 bar BMEP. A modern turbo, intercooled engine will generate almost double that. Twice the power for the same displacement.
Turbos are inherently very reliable. There is no metal to metal contact and the rotors sit on semi-floating bearings. Unless neglected, they should be considered a "life of the engine" component.
pagoda
Well-Known Member
I wouldn't say no to a turbo. since we have 2 cars which are turbodiesels. They both pull well from 2000PRM, and with the appropriate top gear deliver most required performance at under 2500 RPM on out of town journeys.
The downside of turbos is the additional electronics/sensors to monitor / regulate fuel/ air mixtures. While car engines operate in a fairly nasty environment, it is much less evil than a marine environment with limited running time. Normally aspirated diesels are a dying breed, limited by the amount of air which can burn X amount of fuel, though their simplicity lends them lots of support. Almost any diesels in commercial boats have turbo charged engines today, so we should not be too afraid of the concept, but be wary of how well the transition is engineered.
scottie
Well-Known Member
TIMD 96A 1958 so nearly 60 years
Tranona
Well-Known Member
Pretty sure that you will find his 2850 is well within permitted limits with a max potential of 3000. You will find your Volvo has to achieve a minimum of 3000 out of its 3200 to get sign off from Volvo. We had to pay particular attention to this when mine was commissioned as a non standard prop was fitted, which allowed 3100 on trials.
Skylark
Well-Known Member
Not necessarily. Most sensors are there to control emissions. Turbos are a "gift" to the engine designer because they provide air. Our atmosphere doesn't provide enough air to burn with fuel to provide decent power without having huge displacement (per USA).
The only "problem" with a turbo is that it has an inherent mismatch to an engine. It's a high speed rotating device and it can never match the characteristics of a reciprocating engine, hence compromise is needed.
The problem is engine speed range. Most simplistically, on a medium speed engine (truck), a very basic, non-controlled, turbo will just about provide enough boost at low speed without over-speeding when delivering air for full speed/power.
It can't do that on a high speed engine (like a car engine). If it provides enough boost at low speed, it would be approaching burst speed at the other end unless it is controlled. That's where "waste gates" came in around 1980s. PWM valves were later added to improve control of boost charactersitcs. Later still, the some what crude wastegate was replaced by variable nozzle technology in the turbine housing, plus electrickery to control it.
All these developments simply provided greater control / software to meet (beat in VW case
) legislation.
pvb
Well-Known Member
So what does it mean when Nanni state "No wide-open throttle below rated engine speed"?
[70521]
Well-Known Member
My motor car's turbo has just gone, I really don't fancy dealing with that at sea.
macd
Well-Known Member
In effect it means open the throttle progressively until the point where opening it more produces no increase in revs.
sailorman
Well-Known Member
It rarely runs wot,, better a tad over than under. The chap who fitted the engine said it would be ok :encouragement:
RichardS
N/A
I've never wanted, needed or had a turbo on a car and have to go to exceptional lengths these days to avoid them on petrol cars. I'm hoping for a resurgence in normally-aspirated petrol engines before I replace my current car but the big Fords are now all turbos and I only managed to get the final non-turbo version by arranging a "special" deal with Ford.
Of course, in 50 years of car-ownership I've never owned an oil-burning car either, and never will, so my opinion of turbos is probably best ignored! :encouragement:
Richard
Of course, in 50 years of car-ownership I've never owned an oil-burning car either, and never will, so my opinion of turbos is probably best ignored! :encouragement:
Richard
pmagowan
Well-Known Member
I still don't know what the downsides are other than a vague notion of complication. I presume almost everyone has reasonably complicated engines and are not all running single cylinder things 'for simplicity' so why is the Turbo a step too far? Am I right that the turbo essentially boosts the engine but if it failed you would simply have a non-turbo engine, so the risk from failure is low or would the engine stop working if the turbo failed.
macd
Well-Known Member
It would depend entirely on the mode of failure. At worst, the turbo could 'grenade' and throw bits of itself into the intercooler (if one is fitted). It's also possible for failure to cause the turbo's lubricant to bleed into the engine, causing runaway combustion. Both are very rare: turbos are highly reliable and usually give audible warning of impending failure (bearing whine, exhaust smoke, etc). But I still don't want one
pmagowan
Well-Known Member
It would depend entirely on the mode of failure. At worst, the turbo could 'grenade' and throw bits of itself into the intercooler (if one is fitted). It's also possible for failure to cause the turbo's lubricant to bleed into the engine, causing runaway combustion. Both are very rare: turbos are highly reliable and usually give audible warning of impending failure (bearing whine, exhaust smoke, etc). But I still don't want one
Why? Why don't people want something that essentially improves your engines performance? If we are saying it is a complication that never really goes wrong and if it does go wrong 99 times out of a hundred the engine still functions at a lower output it doesn't make much sense to me to say that it is too complicated. No more so than an extra cylinder or any of the modern changes to engines in the last century.
Bobc
Well-Known Member
To be honest, I would be far more worried about having an ECU in a boat than a turbo, which a lot of modern engines seem to have.
pmagowan
Well-Known Member
I would not mind an ECU if they were not locked to dealers. If I have a computer I want to be in charge of it and I don't appreciate cryptic messages that only a dealer with an expensive bit of kit can decrypt. Bottom line is, if you can tell me there is an error you can tell me what it is. In a boat I think you need fail to safe and that means you might need to be able to flog an engine even if it will damage it. I don't want some computer telling me I can't do that. I don't mind a computer that warns me of the consequences but I should be free to ignore them.
sailorman
Well-Known Member
The Spec for thr Beta 45 & my Nanni 37.5
The 45 is certainly using more fuel as would be expected.
I generally cruise @ 2000 RPM which gives 6.6 6.7 boat spd, this is approx 29 / 30 hp used, the Beta is nearer 33 hp at the same RPM
http://betamarine.co.uk/wp-content/...al_data_sheets/seagoing_data/B45-SDS-0915.pdf
The 45 is certainly using more fuel as would be expected.
I generally cruise @ 2000 RPM which gives 6.6 6.7 boat spd, this is approx 29 / 30 hp used, the Beta is nearer 33 hp at the same RPM
http://betamarine.co.uk/wp-content/...al_data_sheets/seagoing_data/B45-SDS-0915.pdf
Tranona
Well-Known Member
There is no need for turbos on small diesels as the power requirement is modest - typically specific outputs of 25hp/litre compared with road vehicles where double that or more is the norm. Remember we only use a fraction of the available power to drive the boat, typically around 50% maximum. It is the propeller than pushes the boat and they typically require a shaft speed of less than 1500rpm so high revs and power cannot be used on a small displacement boat.
As you move up in boat size and particularly displacement the power required in relation to displacement increases and when you get above say 50hp the bulk of a low output type diesel rises significantly and adding a turbo to increase power in relation to bulk becomes possible. However the specific output remains roughly the same - so a 45 Beta with a capacity of 1500cc still only has a specific output of 30. The 50 hp Volvo is a 2l engine, and its turbo version is 75hp. A far cry from outputs of road vehicle engines, but higher than for example a Perkins 4 236 which offered similar power ranges in the past, but out of 3.6litres. Physically huge compared with a Volvo 75 turbo. important to note that the new style turbo engines still run at lower revs, typically 3500 compared with road engines which, even in "simple" form will rev to 4500.
Physical size is important for modern yachts as they don't have the space (or don't want to allocate it) to fit old style diesels in that power range (50hp+) making turbos at low boost much more attractive.
As you move up in boat size and particularly displacement the power required in relation to displacement increases and when you get above say 50hp the bulk of a low output type diesel rises significantly and adding a turbo to increase power in relation to bulk becomes possible. However the specific output remains roughly the same - so a 45 Beta with a capacity of 1500cc still only has a specific output of 30. The 50 hp Volvo is a 2l engine, and its turbo version is 75hp. A far cry from outputs of road vehicle engines, but higher than for example a Perkins 4 236 which offered similar power ranges in the past, but out of 3.6litres. Physically huge compared with a Volvo 75 turbo. important to note that the new style turbo engines still run at lower revs, typically 3500 compared with road engines which, even in "simple" form will rev to 4500.
Physical size is important for modern yachts as they don't have the space (or don't want to allocate it) to fit old style diesels in that power range (50hp+) making turbos at low boost much more attractive.
macd
Well-Known Member
I presume the "Why?" refers to my "But I still don't want one", yes?
Well, one reason amongst all this tosh about turbos giving you something for nothing is, as I suggested earlier, that the opposite is true, at least until they start giving turbos away. We re-engined two years ago. One of the considerations, as it would be for 99% of us, was cost. Turbo engines cost more up front. Besides, as several others have suggested, for the sort of power output required by most yachts, they actually don't make a lot of sense. This may very well change if the trend to ever-bigger yachts continues.
I've been on a few turbo-equipped sailing yachts owned by friends. They generally lived in dread of the turbo kicking in. You could almost see the pain in their wallets.
I'm very happy with my current engine, as I hope everyone else is with theirs.
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