Sail drives vs shaft drives? - SailNet Community
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post #1 of Old 01-21-2009 Thread Starter
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Sail drives vs shaft drives?

Hi all,

I keep seeing the vast majority of boats equiped with 'saildrives'. I have not really been able to figure out the difference between a saildrive and a shaft drive other than seeing that shaft drives are apparently 'better'. What exactly is the difference - props are obviously connected to a diesel engine via one of these two methods I assume but if shaft drives are indeed 'better' why do I not read more about them. It seems almost all boats I have seen mention saildrives.

Does it impact the prop location? Higher/lower? Does it impact weight? About all I know about shaft drives was that my old Yamaha motorcycle had one and that shaft drives on a motorbike were more reliable than chains.

Thanks and regards for any thoughts or good links!

edit...

I kept digging around I came across comments comparing a couple boats and this person mentioned the following......

"stay very very far away from anything with a saildrive" was the opinion and went on to describe that saildrives are aluminum housed below the boat immersed in seawater which, when it fails requires hauling the boat. They are easier to build and leave more room inside as well as gets an engine out of an aft bunk (or two in a cat). I gather from the comment that shaft drives though ar easier to fix, less likely to break and don't expose a prop as much (although don't go snorkeling near the back of the boat maybe or you might get sliced up??).

Last edited by yellowwducky; 01-21-2009 at 12:20 AM. Reason: found partial answer!
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post #2 of Old 01-21-2009
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A saildrive is a little like having an outboard leg sticking out the bottom of the boat and connected to an engine inside the boat.

The first thing that I reckon you have wrong (but will stand corrected) is that saildrives dominate. I think shaft drives are far more prolific.

One advantage of a saildrive is that the ones I have seen are totally watertight and the boat has a totally dry bilge whereas shafts mostly leaks a little water.


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post #3 of Old 01-21-2009
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The big disadvantage is that when you have a problem with the saildrive and have to pull it, you will have a huge hole in the bottom of your boat. A properly installed saildrive is a good thing, a badly installed one or a defective one is a nightmare.

Saildrives tend to have far less propwalk, since the saildrive is installed with the prop basically vertical... They don't have the same alignment issues that you get with shaft-drives. However, they're generally found on more modern designs—I've never seen a full-keel boat with a saildrive.

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post #4 of Old 01-21-2009 Thread Starter
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Interesting, some of the points I have seen seem to highly go against them. Glad its not a universal problem type of installation.
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OMC made a saildrive that gave all saildrives a huge black eye for many years. Yanmar has had a few problems with theirs that haven't helped saildrives out much recently as well.

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post #6 of Old 01-21-2009
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It also depends on were you live in this area Barnacle growth is a problem on units that have there water intake in the leg because you cant really paint inside the intake grates

Up here most boats are only in the water 6 months or so and this makes it pretty easy to stay on top of them BUT in areas were poeple may stay in for 2 years between hauls things like drive oil changes become and issue

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post #7 of Old 01-21-2009
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I have lived with both a saildrives and conventional prop shafts and I would say that the comparason from my experience is that Saildrives offer the following advantages:
  • Easier for manufacturers to install accurately but not necessarily less expensive.
  • Less maintenance in the short run
  • higher fuel efficiency
  • Less drag
  • No water in the bilge to deal with
  • Do not have shaft alignment, coupling and packing gland issues to deal with.
  • Easier to isolate for less vibration and quieter operation
The disadvantages:
  • Way more prop walk
  • proprietory propellors
  • need more expensive geared folding or feathering props if low drag prop is used
  • need to haul boat for almost any form of gearbox maintenance including changing lube oil
  • big hole in the bottom of the boat
  • Need special non-copper type bottom paints
  • expensive proprietary zincs that need frequent attention
Some of the old problems with saildrives have been addressed by some manufacturers. Saildrives used to have water passages for cooling water or exhaust like an outboard motor. These passages meant that sooner or later the coatings would flake loose and sooner or later spell the end of the life for the lower unit casings. Today some manufacturers have changed the design of their saildrives to eliminate the water passages. This is a plus in all ways.

The metalergy of saildrives have improved. Early saildrives used aluminum alloys that seemed especially prone to electrolysis and other forms of corrosion problems. I understand that some sail drive manufacturers are now using much better corrosion resistant alloys.

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post #8 of Old 01-21-2009
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I agree entirely with what Jeff has said but would note that there is still an open question about the reliability of even today's saildrives. OMC's did have a lot of problems but some will recall the lawsuit Gavin Stener has in progress against BOTH Yanmar and Tartan for the deterioration of 2 saildrives. This is supported by Tartan's refusal to pay Yanmar and the switch to Volvo drives and the CLAIM of many customer problems with Yanmar drives (NOTE: the claim was UNSUPPORTED in the recent MackBoring/Yanmar NJ court case). Mr. Stener's case will go to trial next month if there are not further delays and we shall see whether the claims are supported by facts and a favorable court decision.
Assuming one wishes to avoid Yanmar pending the outcome...this leave you with the sole choice of Volvo for a sail drive and that is one company whose reputation for low product support and high repair and parts costs in marine engines is well known.

Finally...if one is planning on cruising to distant shores I think it would be a very poor decision to buy a saildrive from anyone. Everything is proprietary, and finding someone qualified to make repairs can be extremely difficult and parts can take a long time to arrive and make it through customs. Someone can always fix a standard diesel/shaft no matter where you go.

Saildrives have their advantages as Jeff enumerates...but if I were not engaged in racing or coastal cruising in 1st world countries, I would avoid them entirely.

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post #9 of Old 01-21-2009 Thread Starter
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I am not sure you will get the choice though camaraderie,

'Hello, Lagoon/Foutaine/Manta/Leopard/xxxxxx, I don't want a saildrive, can you please re-engineer your boat so mine can have a shaft drive'

'click'

I could be mistaken of course but it seems its not as simple a decision as microwave or no microwave.
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post #10 of Old 01-21-2009
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That's what you get for not looking at real sailboats!
You could go for the electric Lagoon!

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