Saildrive or shaft?

[ds797]

All other things being equal, would you have a sail drive or shaft? Most importantly, why?

Lets assume exactly the same boat, hull, rig, but there was an option for shaft or saildrive, which are you going to choose?

(For the purpose of discussion, lets assume its a 35-40ft fibreglass cruiser/racer with a fin keel and a spade rudder.

I'm guessing its going to be about 50/50 with pros and cons!

3,2,1, go!

 

[Kelpie]

Personally, I like a shaft drive, but there are pros and cons.
A shaft with a moulded log is about as robust as you can get, if you are concerned about hitting anything or getting entangled in bits of rope, and ongoing maintenance requirements and costs are low. Cutless bearing and shaft seal will need replaced every few years, and the shaft seal will always let a little drip of water in to the bilge.
However some would say this arrangement restricts prop size and can cause interference between the propwash and the hull. And of course shaft drive will always have a bit of an angle to it which slightly reduces output. Position of the engine is also quite inflexible, and that can dictate the rest of the layout.

A shaft with a P bracket may put the prop in a better position, and may be unavoidable with a more modern hull shape, but it's an extra cutless bearing to consider and somewhat more vulnerable to damage.

A saildrive gives the designer more options in engine and prop placement, although often this ends up with the prop quite far ahead of the rudder which can reduce maneuverability under power. But the prop can be perfectly parallel to the waterline, and in clear water, giving better efficiency and output. No shaft seal to drip, and no alignment issues.
The main downsides IMHO are that the whole system is a bit less robust, and more complex. A leg sticking out of the boat is a bit more at risk of impact damage or snagging on ropes, compared to a shaft. There is a gearbox which is permanently immersed in seawater. The whole unit is made from aluminium and needs suitable ongoing protection. And lastly there is the seal between the saildrive and hull, which you are advised to change every seven years, although a lot of people leave it considerably longer and actual failures are quite rare.

 

[Baddox]

The saildrive on our current boat is set deep enough away from the hull that prop-walk is minimal and we still get the benefit of prop-wash from a bust of ahead for steering. The design is appealing if you spend time manoeuvring in tight spaces.

My last boat had a shaft drive which although it had a stuffing box to drip into the boat, was far less exposed to any risk of hitting underwater debris. If it did hit anything substantial, the size of the hole it risks opening up was smaller. Drag should be lower with the shaft drive than SD. Both would tip the balance for me to favour shaft drive for longer passages or races.

It is easy to change the oil in the gearbox for both; mechanically, there is less underwater to go wrong with the simple shaft drive.

 

[scottie]

Might all depend on which anchor or apple or Android Volvo or Yanmar etc
You take your pick

 

[BobnLesley]

If you're ever planning to head off into the wide blue yonder, then definitely a shaft:
There are fishing fleets everywhere and wherever there are fishing boats, you'll also find a Fred/Pierre/Pedro/Stavros/Winston who can achieve quite amazing repairs to damaged shafts and fixed-props with little more than an oxy-acetylene torch and a selection of hammers, with an out-drive you might be waiting a long time for spare parts. Fitting a folding/feathering prop to said shaft's fine, but do be sure to bring that old fixed prop along with you too. On the same basis I also advocate traditional stuffing boxes over the nowadays more popular dripless-seals: A bad stuffing box leak might be a pain in the backside, but it'll continue to hold enough water back to take you the couple of hundred/thousand miles it might be to the next haul out yard an the engine remains usable, we've met a couple of yachts who were forced to 'clamp down' their dripless seals to stop the inflow so couldn't use the engine (or engage gear at least) until they'd been hauled and repaired/replaced said seal.

 

[noelex]

Shaftdrive.
If I was a boatbuilder, saildrive .

 

[Skylark]

Already some very thorough, objective reviews posted so nothing to add.

My current boat has a saildrive by Yanmar. Their 5 year hull membrane change recommendation is a constant source of frustration to me. Changing the membrane is more difficult than it should be due to poor engineering of an otherwise eloquent design solution. The risk of collateral damage, scratches and so on, is high during such a complex maintenance procedure, it potentially violates the philosophy “do no harm”.

 

[Seajet]

I had a boat with a saildrive - I managed to sell her before gaiter replacement was due.

I'd definitely go for shaft next time, the huge potential hole of a saildrive and the gaiter replacement cost and hassle mean they're only a convenience for boatbuilders as mentioned above.

 

[pandroid]

Shaftdrive.
If I was a boatbuilder, saildrive .

Exactly. Nuff said.

 

[johnalison]

Exactly. Nuff said.

Only part of the story. Quite a lot of sailors vote with their wallets for saildrive. I've had both and although I like the simplicity and lack of servicing needs of a shaft, I think that my current boat would have given me less pleasure over the last twenty years if it had not had saildrive.

 

[doug748]

To be fair to saildrives they are quiet, or rather some of the most polished and quiet installations I have seen have been saildrives. There tends to be reduced prop kick as well.
There can be problems with boats with the prop in the middle which are made worse with twin rudders, this is solved by bow thrusters of course. It's an example of how design choices can have consequences which reverberate beyond the original intention.

If you are buying new-ish there is a very restricted choice if you stuck to shaft drive. However this is probably not high on the agenda of worry if you are buying a new boat. Down the line, putting a new engine on an old saildrive cuts down your options an can shove up the cost.

 

[Praxinoscope]

I have to admit it is a completely unfounded preference but I would prefer to go with a shaft drive rather than saildrive, and definitely a shaft drive with a traditional stuffing box r
Bobnlesley’s comments on the resilience of a traditional stuffing box even when failing are certainly worth considering, I remember crossing the Irish Sea with a dodgy stuffing box, we just had to keep adding grease and keep the bilge pumps operating until we got back to our home port and spend a couple of uncomfortble hours replacing the stuffing which cost about £5.
A couple of friends have saildrives, both have had the seals replced recently at some expense and both seem to have had more problems with catching floating lobster pot lines than those of us with shaft drive, although this may just be coincidental.

 

[Kelpie]

I'm surprised the AWB brigade haven't jumped to the defence of Saildrives yet.

Does Tranona not post on here any more?

 

[Praxinoscope]

I'm surprised the AWB brigade haven't jumped to the defence of Saildrives yet.

Does Tranona not post on here any more?

Unfortunately Tranona hasn’t posted for months, I am sure most forumites miss Tranona’s input.

 

[maby]

I'm surprised the AWB brigade haven't jumped to the defence of Saildrives yet.

...

Having had both - in brand new boats - I would go for saildrive on the grounds of far better handling, but without too much enthusiasm given that the maintenance is so much more demanding. It's not just the gasket - that is only every few years and, arguably, can be left a lot longer. It's the need to change the oil - which is not cheap - and the worry that, when I do change it, it is going to come out looking like whipped cream and I'm going to find that the drive train is knackered as a result of water getting past a failed oil seal. The anodes also worry me - they are difficult to see with the boat in the water and if they fail early, you can find yourself looking at a motheaten saildrive which is expensive to replace.

 

[Baggywrinkle]

OK ... I'll bite.

Saildrive.....

Thrust parallel to direction of travel, prop walk minimal, maneuverability impeccable.
Vibration minimal, installation compact.

Fear over seal failure unfounded ... we trust our lives to pneumatic tyres daily and saildrive seals get orders of magnitude less abuse. Can't find any evidence of seal failure other than when everything is misaligned and the seal abused.

I've heard many tales of prop shaft vibration, problems with bearings, leaky seals, damp bilges and even shafts coming loose and jamming rudders or coming out completely.

Halberg Rassy abandoned shaft drive a number of years ago, saildrives are the future.

Downside is seal replacement ... but that's it IMO .... I have a dry boat with bilges full of dust and a quiet, vibration and almost maintenance free propulsion system - except for seal replacement every 7 years.

 

[maby]

...

I've heard many tales of prop shaft vibration, problems with bearings, leaky seals, damp bilges and even shafts coming loose and jamming rudders or coming out completely.

....

In fairness to shaft drives, the potential problems are all down to poor maintenance and the entire drive can be replaced for a few tens of pounds - it is just a steel rod rotating in a couple of pretty basic bearings with an overgrown rubber 'O' ring to keep the water out. The shaft drive is certainly not maintenance free, but the maintenance that is required is trivial and the entire mechanism is easily visible to check its condition.

Saildrives are a lot more demanding as far as maintenance is concerned. The mechanism is enclosed and spends most of its time under water. Replacement costs thousands of pounds and almost all maintenance work beyond an annual oil change requires significant engineering skills. What it does do is to significantly improve boat handling and permit an engine layout that often results in better usage of space within the boat. All our boats apart from the first have been purchased new and we have not yet kept one for more than five years - I have not worried too much about maintenance. I do anticipate that our current boat will have to last us out - ten years, possibly fifteen - maintenance is more of an issue. I would think very carefully before buying anything with a saildrive more than ten or fifteen years old - I'm not sure how much longer to expect it to last and I would have to factor in a fairly high maintenance bill.

 

[Baggywrinkle]

In fairness to shaft drives, the potential problems are all down to poor maintenance and the entire drive can be replaced for a few tens of pounds - it is just a steel rod rotating in a couple of pretty basic bearings with an overgrown rubber 'O' ring to keep the water out. The shaft drive is certainly not maintenance free, but the maintenance that is required is trivial and the entire mechanism is easily visible to check its condition.

Saildrives are a lot more demanding as far as maintenance is concerned. The mechanism is enclosed and spends most of its time under water. Replacement costs thousands of pounds and almost all maintenance work beyond an annual oil change requires significant engineering skills. What it does do is to significantly improve boat handling and permit an engine layout that often results in better usage of space within the boat. All our boats apart from the first have been purchased new and we have not yet kept one for more than five years - I have not worried too much about maintenance. I do anticipate that our current boat will have to last us out - ten years, possibly fifteen - maintenance is more of an issue. I would think very carefully before buying anything with a saildrive more than ten or fifteen years old - I'm not sure how much longer to expect it to last and I would have to factor in a fairly high maintenance bill.

Taken out and sold due to a worn out engine at 16 years, 4500 hrs. Boat was repowered with a VP D1-30 + new saildrive. Other than regular oil change, anode and anti-fouling it was still running problem free. Seal was changed once by me. Don't understand what people are afraid of. Aren't most problems down to neglected maintenance?



Last year in service ....

 

[Seajet]

No,

the concerns are a whacking great hole if the exposed leg gets hit by serious flotsam etc, and the gasket is a time lifed item which has to involve an expensive, serious hassle replacement.

The leg in the water all the time is not going to last forever either, no matter what one does with anodes.

A nasty I had on my Volvo 13hp saildrive ( I forget the designation, long time ago ) was that one of the prop' boss hinge points for the 2 blade folding prop cracked.

I gave the boss to chums at BAe Kingston where they had 6 various welding departments ranging from standard to exotic but they couldn't do anything with the nasty zinc casting - £ 480 in 1989.

 

[Baggywrinkle]

No,

the concerns are a whacking great hole if the exposed leg gets hit by serious flotsam etc, and the gasket is a time lifed item which has to involve an expensive, serious hassle replacement.

The leg in the water all the time is not going to last forever either, no matter what one does with anodes.

A nasty I had on my Volvo 13hp saildrive ( I forget the designation, long time ago ) was that one of the prop' boss hinge points for the 2 blade folding prop cracked.

I gave the boss to chums at BAe Kingston where they had 6 various welding departments ranging from standard to exotic but they couldn't do anything with the nasty zinc casting - £ 480 in 1989.

That prop failure could just have easily happened on a folding prop on a shaft? Sounds like a prop failure, not saildrive.

How often does a car tyre tear itself apart due to hitting something at 8mph? ... and a saildrive is normally travelling along sheltered behind a keel (except in a cat.).

I challenge you to find examples of saildrive seal failure ... for every seal failure you post, I'll post a shaft seal failure (with verifiable links) - see who runs out first.

I'm brand spanking new at sailing and boating so pardon the novice questions and wrong terms. I recently took my S2 27 (8.1) out for a sail, at some point we started taking on water (ankle high), needless to say it was quite the ordeal. Anyhow all turned out ok, made it back to the marina under sail (no propulsion) and figured out that the prop shaft had come completely out.

https://forums.sailboatowners.com/i...eller-shaft-fell-out-while-under-sail.144270/