Turbos and Boat engines

[FlowerPower]

There are various different ways that Turbos can "fail" - each failure will have it's own set of possible causes.

e.g.
Broken blades: Foreign Object Injestion, manufacturing defect
Corroded blades: installation problems, design problems, salt water getting into the airstream somehow
Bearing Problems: oil feed issues, repeatedly stopping without allowing to cool
Variable geometry turbos have a load of additional moving parts that can gum up or jam...

dv.

[CX54WEK]

Well to answer your original question, the turbo on our KAD 32 is almost 7 years old with no problems yet.

We have owned the boat for a year, however know her previous owner had her for 6 years trouble free and we have had no trouble this year having done over 300 hours.

So yes you can have a trouble free turbo

[aquatom]

How is the boat used? Is it thrown about like alot of jet boats are? Is the oil pump picking up air in the sump as the oil sloshes about in there? Turbos don't like any interuption in oil flow at the speeds they run at.

How is the exhaust system run? Is there any chance of sea water being able to enter the turbo when suddenly slowing down?

In my experiance the common turbo faults occur in outdrive driven boats where the sea water level always quite close to the turbo. The Volvo Kad engines seem to be most prone to this problem causing the supercharger to cut in and out just as the turbo should take over.

[FlowerPower]

...causing the supercharger to cut in and out just as the turbo should take over.

Huh?

The main situation I am of aware of that can cause a problem in a KAD outdrive boat, is if you do an "emergency stop" and power off the engines at the same time - water can come back up the exhaust pipe.

dv.

[aquatom]

Yes.

That can happen if the little rubber flaps over the exhausts are damaged.

[longjohnsilver]

Why is it that Turbos on boats are so bloody unreliable? yes I know they work in a salt water environment, but that alone cannot excuse them.

You get two identical engines with turbos lets say a Cat 3126 like on my new jet boat,
put one i a car/lorry and one in a boat. Drive for approx 350 hours and guess which one will need replacing.

By the way in this case cant blame it on the old "boat engines are under different strains" chessnut cos with waterets unlike props, the engine does not have suffer from such strains.

Is there anyone who has owned the same boat for say 3 years, single or twin, who has not had to attend to turbo problems? ................rant over

Me. Previous 2 boats both had turbos, no problems in about 15 years. And did about 300 hrs per year. But they were both Ford Mermaids so not overly stressed.

[Marsupial]

A good rant

In the 1960's I was involved with fitting and testing the ford truck engine with a turbo the results were stunning a 50% increase in power coupled with a 99% reduction in service life. Obviously that changed as we learned what broke and why but the turbo was the weakness in may respects.

They obviously put more stress on the main components because of the extra power generated and fail they do - I ask you why do you want a thing spinning at 23,000 rpm or more on a boat thats pitching and yawing? its got to fail. (Take a look at the warranty they give the turbo) So I will never have a turbo on a boat.

The trouble is designers just cant resist the power to weight ratio the dreaded turbo promises and in power boats in particular the end result is an engine (s) that must be run flat out for most of its short life in order to meet the requirement, but hey thats what the custome wanted! Ragged edge engineering.

[Tank]

Please excuse me if this is slightly off topic, why dont boat builders fit superchargers to their engines, i believe they are more reliable than turbo's, or am i wrong?
regards
Tony

[Marsupial]

Please excuse me if this is slightly off topic, why dont boat builders fit superchargers to their engines, i believe they are more reliable than turbo's, or am i wrong?
regards
Tony

You are correct as far as the booster is concerned but superchargers dont get their power for free, turbo chargers make use of the power in the exhaust stroke to spin the turbine, superchargers sap "good" power from the crankshaft so are thought to be less efficient.

Turbo chargers need high exhaust gas velocity to work hence they tend to "cut in" at higher revs, superchargers pump air relative to crankshaft revs so there is no abrupt cut in of power, the boost is present throughout the rev range. Turbos have turbo lag - but that is more noticable with road vehicles.

However what ever boost device you use a boosted engine is still producing more power than the normal aspirated version so it's under more stress and will wear out faster.

[FlowerPower]

>it's under more stress and will wear out faster.
Than what? A cruise ship engine?

You won't find many modern engines that have a turbo and non-turbo version with exactly the same cylinder heads, pistons, conrods, injection systems etc. so it's almost a meaningless statement.

If you are comparing two engines of the same output, the non turbo one will be much heavier, and of little interest to the average leisure boater.