What makes stern drives unreliable?

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At the risk of starting a war there seems to be a strong opinion that stern drives are doomed to fail and cost the owner a fortune.. I accept that shaft drives appear more "robust" for the perspective that they are pretty much entirely internal and for the most part based on ancient and well proven technology.. Looking at the schematics of my Volvo SX drive there really doesn't seem to be that much to it that can go that badly wrong..

Is it just the older ones (20+ years old) that are problematic with newer drives (say 10-15 years old and newer) being more reliable?

Is it purely a corrosion issue because they are in the water that causes problems with stern drives?

Is there an inherent design issue?

Is it simply a lack of maintenance that has given them the "unreliable" reputation?

Its certainly hard to deny the advantages of stern drives, that being apparently significantly better performance and fuel efficiency than shafts..
 
drives becomes unreliable if you pay travellers to do the work :)

seriously though, more moving parts in terms of things moving up and down, side to side and the like whilst spinning at high speed has got to be a factor when compared to shafts. things will wear, rubber will perish etc etc as said, ignore regular maintenance at your peril for this reason
 
So that's two for maintenance (or lack of) being the cause of them being branded unreliable.. Perhaps its owners who don't maintain their boats that should be branded unreliable instead.. :)
 
IMHO shafts for anything over 30' are essential. The worse fuel usage is easily compensated by reduced maintenance costs, and better steerability of twin shafts.

Ok you CANNOT touch bottom with shafts without a subsequent haul out, whereas you could possibly change props on a out drive without a lift out.

VP have had major issues with the drives on the D6s, and access for seemingly simple tasks requires moving the engines forward on many boats using these.

They are better for fast planing boats because of the higher weight distribution towards the stern, but not conducive to stern cabins.

Out drives do have a certain star quality for catching errand continental quilts floating along the Hamble too ! Took three hours to dig the mess out from between the duo props on my pals Princess V42.
 
I've done shedloads of maintenance, and still had issues.
Don't get me wrong, it's a love/hate thing.
Loving the performance and efficiency, and being able to lift them up in shallow water.
But not loving picking up a rope which knackered the shaft seal and let all the water in, and trim pistons that had to be replaced because they leaked like a leaky thing.

Early DP-H owners had their own club, membership of which included dissolving propellors, dissolving steering rams, shaft seals, etc. Merc Bravo III membership included a dissoving bearing cage. To be fair, most of these issues are now sorted. But owners wallets got a bit lighter along the way.
 
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FlowerPower said:
I've done shedloads of maintenance, and still had issues.
Don't get me wrong, it's a love/hate thing.
Loving the performance and efficiency, and being able to lift them up in shallow water.
But not loving picking up a rope which knackered the shaft seal and let all the water in, and trim pistons that had to be replaced because they leaked like a leaky thing.

Early DP-H owners had their own club, membership of which included dissolving propellors, dissolving steering rams, shaft seals, etc. Merc Bravo III membership included a dissoving bearing cage. To be fair, most of these issues are now sorted. But owners wallets got a bit lighter along the way.
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Have twin Bravo 2X, reputedly the best type for our boat. Apart from some misplaced opinions of Mercruiser engines and drives we have been fine. Parts are easy to get & cheaper than VP but any drives can fail even if looked after.
 
Had both and no question that drives are more hassle. Even if well maintained bellows sometimes fail, fishing line gets caught and trashes the shaft seal, bushes wear and are a bugg*r to replace etc, etc, etc.

Even on good years there is the worry that the annual check will reveal water in the oil or some other minor/major disaster and discovering that all is well is only ever a temporary reprieve.

Having got to understand them the mystery has gone and I was more confident in dealing with issues and I would still have them on the right boat (i.e. sports cruiser) but I am currently enjoying the simplicity of shafts.
 
Lack of maintenance is really the only culprit.

We have used ours extensively and it has not missed a beat.

Had the odd bit of fishing line in the seals letting water into the oil but a new set of lower seals isnt expensive and are easy to fit. The only other slight problem we have had is a slight weep from the trim ram but this is easily sorted by cleaning the limescale off the ram. Once cleaned the seal fits again and it stops weeping.

Yes bushes eventually wear but so do items on shafts.
 
Same here, maintenance is key.

I also think it depends on cruising area and habits. I have got 290 dp drives which seem to be more reliable than newer ones. I like the ability to go in shallow creeks in holland. I allow me to do things you cannot do with a shaft boat. That said if I kept a boat on the coast I would probably go for shafts as the savings in fuel on a outdrive boat are probably eaten by the maintenance cost. If you do go shaft read up on them on internet forums and it will help you spot problems in advance so you can sort them out of season. I more than 10 years the only real failure was a shaft seal due to a fishing line. All the other isssue were age an once you knew I knew the drives this could be sorted in advance: shift cable replacement, clutches after approx 1000 hours, bellows etc. Oil check every winter.

Rob
 
I have had 3 boats with drives, and as others have indicated, maintenance is the key. They have been perfect for the boats I have owned and the cruisiing I have done.
 
I think they're the devil's own work. The two sterndrive boats i've had have cost me big money in repairs despite annual servicing, and most people I know with them have also had issues. I think one problem is that small failures can cost so much to repair. I had some slight pitting around the drive shaft seal, and the solution was a new lower drive leg at over £3k! Shaftdrives on the other hand are virtually fit and forget, and i've not had a hint of an issue in 10 years of shaftdrive ownership.

It's often academic though, because on most sizes and types of boats you don't get the choice. If you want a 25-40 foot sport cruiser for instance, it's going to be on sterndrives.
 
those claiming that regular servicing and maintenance of an older (10 years +) outdrive will guarantee you trouble free service year in year out are either very very lucky or living in a dream world.
Shafts will deliver this with virtually no maintenance at all.
have had both and drives bled me dry with massive repair bills despite full professional maintenance.
Shafts have cost me nothing and any fuel efficiency trade off is fine by me.
Its not just the financial cost either - you can't put a price on lost weekends and spoilt holidays spent in boatyards.
If you have the choice shafts shafts, shafts.
 
what Volvo need to do is design an outdrive that is lubricated by seawater, with all the hydraulic bits inboard. Then it might be a reliable design.
 
I have VP 290DP's. 12 years old 1100 hours and never had an issue. Oil change every other year along with bellows. Just to make sure I wasn't riding my luck I had both legs fully serviced this year, pressure tested and all seals replaced. £400 each inc parts. Me personally, given the choice would only go to shafts on something over 42'. Outdrives are just so convenient.
 
KevB said:
I have VP 290DP's. 12 years old 1100 hours and never had an issue. Oil change every other year along with bellows. Just to make sure I wasn't riding my luck I had both legs fully serviced this year, pressure tested and all seals replaced. £400 each inc parts. Me personally, given the choice would only go to shafts on something over 42'. Outdrives are just so convenient.
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12 YEARS 1100 HOURS?? YOU ARE NOT USING THEM!!! We do that in a year no problem.
 
omega2 said:
12 YEARS 1100 HOURS?? YOU ARE NOT USING THEM!!! We do that in a year no problem.
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Hats off to you if you do that amount of hours per year and not business related. Unfortunately for me work gets in the way..... And the cost of fuel....

Actually you've made me think about our usage. For the first few years we owned the boat we averaged around 180 hours a year, but since fuel prices have gone through the roof we're lucky to do 70 hours. Still use the boat as much, just differently.
 
KevB said:
I have VP 290DP's. 12 years old 1100 hours and never had an issue. Oil change every other year along with bellows. Just to make sure I wasn't riding my luck I had both legs fully serviced this year, pressure tested and all seals replaced. £400 each inc parts. Me personally, given the choice would only go to shafts on something over 42'. Outdrives are just so convenient.
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The first 12 years of an outdrive's life should befairly trouble free, shouldn't they? The next 12 years could be VERY different. Good luck!
 
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