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Old 13-07-2013, 00:25   #1
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Direct drive as opposed to skeg leg

One of the vessels I am considering getting for a Blue Water cruise has a skeg drive, honestly its not my preference as Iím more familiar with straight drive. But Iíve heard of skeg legs being replaced after 25years for the only reason that it got damaged when there was a loose rope and the Engine was inadvertently run. Would others comment on advantage, disadvantage of skeg drive. Iím hoping to determine that a skeg leg is more suitable for the racing circuit. Or it doesnít really matter


Skeg leg, I mean the type of drive that a lot of volvo engines have, like an outboard.
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Old 13-07-2013, 08:04   #2
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Re: Direct drive as opposed to skeg leg

That is called a saildrive. They are very common and have their pros and cons. Search the forum for many threads on them.

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Old 13-07-2013, 08:19   #3
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Re: Direct drive as opposed to skeg leg

They (skeg leg/saildrive) are high maintenance. It's like keeping an out board in the water full time.

The disadvantages out weigh the advantages for cruising boats. Racing boats generally don't set in the water for long periods unattended.
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Old 13-07-2013, 09:02   #4
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Re: Direct drive as opposed to skeg leg

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Originally Posted by delmarrey View Post
They (skeg leg/saildrive) are high maintenance. It's like keeping an out board in the water full time.

The disadvantages out weigh the advantages for cruising boats. Racing boats generally don't set in the water for long periods unattended.
Do you have a lot of personal experience with them to make this an informed opinion? Our two have been trouble free for 15 years of cruising, and that is not unique - lots of long term cruising boats using them.

The maintenance consists of every two years changing the oil and zinc. Nothing else at all. And it is nothing like keeping an outboard in the water - they are different beasts altogether, other than they look vaguely similar.

Like I said, there are pros and cons. The cons do not outweigh the pros, nor vice versa. It is a matter of choice, and sometimes a matter of vessel design.

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Old 13-07-2013, 10:14   #5
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Re: Direct drive as opposed to skeg leg

Experience no! Just my opinion! Personally, I wouldn't take one if it were free, unless I could sell it in short term. I really don't like having a large hole in the bottom of a boat with an appendage hanging out to take a hit. Rudders are bad enough.
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Old 13-07-2013, 10:20   #6
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Re: Direct drive as opposed to skeg leg

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Experience no! Just my opinion!
Sorry, but you posted as though what you were saying was a fact. Being the internet, one needs to specifically ask, so I did. I now know it is an opinion with no underlying basis of fact other than gut feeling.

My impression was the OP was looking for facts, or at least direct experiences.

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Old 13-07-2013, 10:46   #7
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Re: Direct drive as opposed to skeg leg

One factual difference: If one has a fault in the saildrive that requires mechanical work, one must slip the boat and remove the drive to access its innards. This can be difficult to accomplish in many cruising areas. With a conventional shaft drive the tranny can be removed with the boat in the water.

Real life experience: A pal with a Seawind 1200 cat had an unfortunate experience in NZed. In the middle of the night the boat swung over an unexpected rock, and the tide went down. Unfortunately one saildrive was over the rock, and as the boat descended, the drive was forced upward, rupturing the seal and flooding the hull. Nearly lost the boat, but managed to partially block the inflow and eventually made his way to a (distant) slipway and repair. While a shaft drive might have been damaged in such a situation, it would likely not have threatened sinking the boat.

Another real life experience: A different pal with a Knot 40 cutter and Bukh saildrive spent a month in the old marina in Ketterting, Tasmania. There was a fault in the marina wiring, and his saildrive's aluminium housing was corroded to the point that it required replacement.

Fact: Some models of saildrive require the boat to be slipped to change the oil in the drive.

It is certainly true that there are lots of boats out cruising with saildrives, so it can be done. None the less, I considered a saildrive to be a dealbreaker when we were seeking our various cruising yachts.

Cheers,

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Old 13-07-2013, 11:35   #8
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Re: Direct drive as opposed to skeg leg

If there is a fault in the lower unit, it is true that the boat must be out of the water. If the problem is in the upper unit, which contains the gearbox, clutch, main bearings, damper plate and shifting mechanism, the drive can be repaired in place without slipping. The lower unit only contains two fixed gears and a shaft riding on two bearings and a couple of lip seals, so not much to go wrong there.

Like I keep saying, there are pros and cons. If one wants to see only cons, that is what they see. For every saildrive example of a problem, one could find an equal example from a shaft system. For example, I know of boats with shaft systems that have gone down because the shaft slipped completely out of the boat and flooding happened so fast that nothing could be done.

Likewise, I have seen aluminum boats eaten by marina wiring. That should be recognized immediately and remedied. Not catching the problem is not a disadvantage of saildrives, no more than it is a disadvantage of aluminum boats. It is something to always be aware of, though.

All older models require slipping to change oil. Newer models do not. Ours requires it, but the 2-year time period coincides perfectly with needing antifoul. If necessary, I can retrieve 75% of the oil from the dipstick hole.

I have no problem with it being a deal breaker for you, I am just trying to present a balanced opinion. Your choice of phrasing -"so it can be done" - is telling, since it IS being done on a large scale.

The phrase "well, it CAN be done..." is also quite common in threads discussing cruising on multihulls.

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Old 13-07-2013, 11:49   #9
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Re: Direct drive as opposed to skeg leg

Just say "NO" to saildrive.....
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Old 13-07-2013, 12:05   #10
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Re: Direct drive as opposed to skeg leg

For the most part saildrives are quite reliable these days provided they are maintained, just like any other piece of mechanical kit.

The main disadvantage as I see it is the inability of even a reasonably competent do it yourselfer to repair/rebuild them without specialist tools and knowledge.
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Old 13-07-2013, 12:14   #11
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Re: Direct drive as opposed to skeg leg

Jim mentioned a few of the problems we've seen with saildrives over the years. And yes, they're so convenient for boatbuilders to install that heaps of boats come with them.

Our friends with the Nought 40, had huge slip fees in Botany Bay, Australia, where they had to haul out for Bukh to work on theirs. It was not the first time. In fact, frugally, they made a marine grade plywood insert that they could install so they could be relaunched in order to avoid lay day fees over the month they were out. Fortunately, the owner is a naval architecht and was able to plan it and make it; but it was a hassle.

So if you want to buy a boat with a saildrive, you might want to look at lay day fees in the places you want to visit.

Another issue is that the "Z" drive configuration cannot help having power losses that the straight drive does not.

You have to use a different type of antifouling on the aluminum part of the saildrive, so you have to plan around that, not a biggie.

Saildrives are also infamous for dissimilar metals problems. Like someone above suggested. This was all hashed over ad nauseum within the past year.

In the instance above that Jim mentioned, in case it was not clear, the aluminum skeg got so eaten by the electrolysis in that marina, that the vessel required an emergency haulout when the prop dropped off. So the incident itself occurred in Tasmania, when they were bound for the mainland of Australia. If it had occurred where there was no haulout facility at all, the story could have been very grim. As it was it was about a $10,000 fix, IIRC.

FWIW.

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Old 13-07-2013, 12:26   #12
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Re: Direct drive as opposed to skeg leg

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The main disadvantage as I see it is the inability of even a reasonably competent do it yourselfer to repair/rebuild them without specialist tools and knowledge.
And that is true for many other transmission types as well - especially for the average cruiser.

But they really are not that complicated, and not much different from a shaft tranny. The gearboxes are almost identical. The only real difference is the way the prop is connected to the gearbox - one long direct shaft vs. two indirect shafts. They are actually simpler than some shaft trannies.

Replacing clutches, shift dogs, damper plates, bearings, etc require no more skills, knowledge or specialist tools than most other transmissions.

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Old 13-07-2013, 12:38   #13
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Re: Direct drive as opposed to skeg leg

True enough but they are a lot more involved as regards setting gear lash and rolling torque in comparison with hydraulic or gear transmissions.
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Old 13-07-2013, 12:39   #14
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Re: Direct drive as opposed to skeg leg

Many designs do not lend themselves to direct/shaft drive: some cats, many flat bottomed paper boats, etc. I think saildrive is a good choice then. I have not seen much accidental damage on saildrive boats.

I think saildrives may require more meticulous maintenance schedule - when things go wrong, they tend to go wrong big way - a boat may be left without her aux propulsion.

Because of the way the drive passes thru the hull, I would possibly consider a proper watertight bulkhead, if I imagined that the drive may at any point come in direct contact with any obstacle.

But otherwise, if my boat were the type that lends itself to a saildrive, I would have a saildrive in her.

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Old 13-07-2013, 12:48   #15
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Re: Direct drive as opposed to skeg leg

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Originally Posted by Ann T. Cate View Post

So if you want to buy a boat with a saildrive, you might want to look at lay day fees in the places you want to visit.
This is simply silly. You are actually suggesting that because one boat hit a rock and had enough damage to need to be hauled that all saildrive owners should expect their drives to go bad anywhere, anytime and should plan their cruising around less expensive haulout areas? Again, plain silly, if incomprehensible, logic.

Quote:
Originally Posted by Ann T. Cate View Post
Another issue is that the "Z" drive configuration cannot help having power losses that the straight drive does not.
I presume you are attributing power losses to the fact that there is one more orthogonal shaft in the saildrive? While there may technically be some power loss, that is more than gained by having a straight prop attitude in free, clear water. Much more power is lost on shaft drives from poor prop angle, being in apperatures, or being behind skegs than is lost on saildrive power transmission.

Quote:
Originally Posted by Ann T. Cate View Post
You have to use a different type of antifouling on the aluminum part of the saildrive, so you have to plan around that, not a biggie.
Yes, but so do aluminum boats. Nobody goes off on them because of it like they do regarding saildrives. And it is possible to epoxy coat the drives and use copper paint. Many people doing that, although I personally don't like it.

Quote:
Originally Posted by Ann T. Cate View Post
Saildrives are also infamous for dissimilar metals problems. Like someone above suggested. This was all hashed over ad nauseum within the past year.

In the instance above that Jim mentioned, in case it was not clear, the aluminum skeg got so eaten by the electrolysis in that marina, that the vessel required an emergency haulout when the prop dropped off. So the incident itself occurred in Tasmania, when they were bound for the mainland of Australia. If it had occurred where there was no haulout facility at all, the story could have been very grim. As it was it was about a $10,000 fix, IIRC.
The problem is not dissimilar metal. The problem is electrolysis from poor wiring. This should be checked for and rectified before ever plugging in.

Aluminum boats have this same issue, as do most boats to some extent. But again, no one ever lights off on aluminum boats like they do saildrives.

And a saildrive boat will not sink if the leg is eaten away, so there is no "emergency" haulout necessary. You would need to haul out to replace it, though.

I am always amazed on saildrive threads when the haters come out spouting fear and dread. I get it - you personally do not like saildrives. No problem. Just please speak from facts and actual personal experiences and not just about "I heard", or "I know this one-off thing that happened" - ergo all saildrives are bad in all situations.

Go to the multihull forums for that

The OP asked a simple question: "are (saildrives) more suitable for the racing circuit"

In general, yes they are because they present the least drag, weigh less than shaft drives and allow the most favorable positioning of the engine in the boat.

As for cruising, some of those very traits are also advantageous. The proportion of boats cruising with saildrives that have problems like you mention is most likely the same proportion of shaft drives that have similar problems.

So far, I seem to be the only person responding on this thread that actually has any experience with saildrives.

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