|Topic Review (Newest First)|
|01-14-2008 09:50 AM|
Yes, it all needs to be matched, or near so.
If the existing motor moves the ship well, then repair it and move on.
You really do not need a turbo.
If you try to extract that 75 hp, then you are going to be ploughing water and the fuel consumption will increase, not because the motor is les efficient, but because the boat realy drinks fuel at the higher hull speeds.
If you just have top end scoring, then it should not be too expensive. You should be able to get oversizes and re-bore the barrels. Then a valve seat re-grind (or re-cut and grind if they are pitted), a new cylinder head gasket and you shuld be ok.
Yanmar spare parts are not TOO expensive (compared to Volvo that is).
Cost it out, and see.
|01-13-2008 09:06 AM|
Why would you want an engine that is badly suited for the marine environment. A turbo is more complex, more maintenance, more prone to failure, generates more heat, resists the kind of abuse a sailboat engine goes through less and so on. Usually, weight isn't all that critical an issue. If you have a 20,000 lb. boat, the difference in weight between a normally aspirated 75 HP diesel and a smaller 75 HP turbo diesel is meaningless. Why not just rebuild or replace the existing engine's block. Then you would not need to worry about modifying the transmission gearing, or the engine mounts.
As for your reasons:
The larger engine isn't going to give you better fuel economy necessarily. Once you're at hull speed, the amount of fuel it takes to go any faster goes up incredibly. Also, as a turbo engine, the engine won't be working very efficiently at the lower RPM ranges, and will suffer from turbo lag, as previously pointed out.
Since the engine will be a turbo, it isn't going to have much more low end torque, since the turbo requires fairly high engine RPMs to really kick in. This has also been pointed out.
The extra horsepower does you absolutely no good if the propshaft and prop can't handle it. Unless you're willing to spend the money on a larger propshaft and propellor, the additional HP isn't going to be all that useful. Most likely, the current prop would just cavitate, rather than generate any significant increase in power.
Proper propellor selection depends on many things—including the HP of the engine. I could go from a 20 HP on my boat to a 50 HP, but if I didn't change the prop, I certainly wouldn't get an increase in fuel economy or useable power—and it probably wouldn't affect my WOT speed significantly.
|01-13-2008 04:53 AM|
I too am personally no fan of turbo powered sailing boats. However there are some cases where it might be the only solution.
The engine room compartment is to small to fit in a non-turbo of desired HP range.
Weight might be an issue fitting a bigger non-turbo (going from 4 to 6 cyl).
However the turbo does not get glowing red in the dark, the exhaust turbine housing is water cooled! The heat emission to air does not get significant higher from same engine type with turbo, but the air consumption encrease which might call for modified ventilation . If properly arranged ventilation, the running temp in the compartment might be reduced due to encreased consumption of the air and quicker circulation. The main 'problem' might be the turbo itself, but most likely only after 1000hrs+ of running time depending of use.
The specific consumption of the turbo engine is lower than the normal aspirated one, but only in the turbo rpm range: above about 2500rpm.
However do You need more HP ore do You need more prop-shaft torque?
Have a talk with Your prop supplier and check. Perhaps a different gear ratio and new prop will give You what You want.
Unless You have a dream of sailing with a decal at the transom saying 'Turbo Powered', I would have tried something else.
|01-13-2008 02:38 AM|
first it was no #2 now it's "there all scored"?
1) Scoring alone in a diesel will not produce a zero compresion reading. Only a valve will do that.
2) Turbos are not like blowers they dont produce any boost benifits untill engine is past 60% max rpm. So you do not get better lower tork with one.
3) 80% of all our marine engine problums are realeated to cooling and cooling water problums, adding more heat in your enging compartment from your warm little round frying pan aint helping anything. Yes they do get red hot!!
4) Yes you could benifit from more horspower, but get it differently with a different bigger normally asperated engine. Whats another 1/2 gal per hour. It's a blowboat .
5) Dont be sturbon you asked for advice TAKE IT !! your getting some good advice from some knowlagable people from what I see.
6) Have the rack run on you curent engine to see if I not right on this compression issue befor you get suckkered into a new one.
I have 17 piecies of heavy equipment with a diesel engine in it. Turbos only help in some instances.
Sorry to hear about your predicament. Hind site is always 20/20
always get 3 surveys
3) Mechanical ( Hull & machanic on board at sea trial )
|01-13-2008 01:49 AM|
I like turbos.I liked them in cars and I like them on motorcycles.
I don't think they are applicable in a tight engine compartments of most sailboats. I don't believe there is enough airflow in these compartments.
A good turbo system will glow a dull red when operating under a load and the propeller is a constant load.
My two cents
|01-13-2008 12:50 AM|
The oil was new, and the likelihood of getting an accurate indication of the engine condition from a lube analysis was quite low.
So, was the oil new before or after the sea trial, before or after the fuel filter change. If before the seatrial, and there was damage, the scoring (chromium, rust, all sorts of bad things) would have shown up after 10-15 minutes of operation. I just have no idea of a succinct timeline here.
Oil was new at the sea trial? did it make the noises at the sea trial? I'm trying to asctertain WHEN the first time this bad stuff happend.
So the engine rpm is lower with the turbo.
maybe I missed something but with the turbo'd engine, would it be within the operating efficiency range of the turbo engine?
I would expect that there would be less heat generated.
actually, no, exhaust temp will be the same OR higher, plus the added cast iron side of the turbo acts as a nice round griddle in your engine room, just heating everything up nice and toasty.
yes, of course you can insulate, then all those hotter exhaust gases just go down stream a bit further.
maybe I need to state this again.
a turbo'd engine has no place in a sailboat. (unless its VERY large, like those 100 ft beheamoths)
here are just some off the top of my head reasons. (in addition to the above)
diesels love to, need to be run at operating temps to be efficient, and for long life. Motoring off a ball out of the bay for 15 - 30 minutes ain't gunna cut it. Add a coke producing turbo to the mix and you're asking for trouble in the turbo bearings, oil turning to tar in the area of the separator bearing, sludging up the works.
turbo "lag"- you WILL have a 1-3 second delay in turbo wind up, this could prove dicey when motoring in close quarters.
but hey, this post might be pointless, an its your money, do what you want.
|01-12-2008 10:49 PM|
"So the engine rpm is lower with the turbo."
Is that lower rpm still in the optimum speed range for the more powerful engine? I would expect it to be running at only 60% power, which is generally not a good point to run diesel engines.
|01-12-2008 07:58 PM|
Turbo vs conventional
Thank you all so far for you input. I am on a time line, and trying to make the right decisions, so your input really is valuable.
To clarify some questions raised, the engine sounded like the 3 cylinder Universal on my 1986 Catalina... thump thump thump... like an old fishing boat (or the diesel from the Humphrey Bogart movie African Queen)
The cylinders are scored, and well outside Yanmar specs max specs. The oil was new, and the likelihood of getting an accurate indication of the engine condition from a lube analysis was quite low.
Please comment on my rational for a 75HP turbo:
I am comparing a Yanmar 4JH4-TE 75 VS 4JH4E 55 HP
Based on the sea trial shaft speed of 2750 RPM, I was close to hull speed. From the factory performance curves, this requires a propeller power of 40 HP and generates a torque of 97 Ft-lb and 2.5gal/hr fuel consumption.
Going to the 75HP engine, the same 40HP prop power requires 2500 RPM crankshaft speed, thus a different gear ratio is needed to get the correct prop rpm. So the engine rpm is lower with the turbo. My crankshaft torque goes to 140 ft-lb, and fuel consumption drops to 1.8 gph, almost a 30% reduction! With this improvement in efficiency, I would expect that there would be less heat generated. The gearing on the new engine is also over sized for the typical load.
The Yanmar 3JH4 is a 75HP engine that runs at a higher speed, and is not one I am considering.
The advantage for extra HP is fuel economy, more low-end torque, lower rpm for normal operation, and the extra HP if needed to fight a heavy headwind, or pull off a soft grounding. I have the power curves and can send them out if anyone wants them, or you can find them on Yanmarmarine.com
Please comment on my logic, Thanks for the help
|01-11-2008 10:33 PM|
Do not, do not, do not put a turbocharger on a marine diesel, unless you need it for a powerboat or something. Weight is a secondary consideration for a sailboat motor, and you do not need a turbo on there. They rev like crazy and are expensive when they blow.
Moving up from 54 to 75 hp is a heck of an upgrade. What prop? What gearing? Can the prop take it the extra power? Does it mean a big three blade that you have to drag around with you when you sail?
|01-11-2008 09:38 PM|
FWIW, (and that may not be much), I'd stay away from turbos too.... who needs the potential extra problems, why do you feel you need so much more power?
Shame the way things have gone, but there may be a less expensive way out than full out replacement. I suspect any real cost recovery would be a long shot.
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