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Old 06-16-2021, 07:30 PM   #1
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Why aren't sail drives more common ?

I just learned about sail drives today and they seem like a great idea ? You can move the engine(s) to the stern for noise and space reasons, you don't have the inneficiency of a propeller angled downward and you avoid drive shaft/cutlass bearing/stuffing box issues.

So...I have to believe that if they really were better they would be more common. I am always curious when there is one technology that doesn't dominate or die, kind of like Mazda's rotary engine.

So, why aren't they more common ?

( thanks in advance )
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Old 06-16-2021, 07:36 PM   #2
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Have you seen the Volvo IPS? Pretty much like a saildrive but more powerful and way more expensive. And they are Volvos…. Parts are expensive if you can get them. The drives have to be resealed periodically or else.
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Old 06-16-2021, 07:53 PM   #3
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corrosion.... by now though.... if made from composite housings a lot of issues could be eliminated.


and hard to check for water intrusion into the lower gear area.
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Old 06-16-2021, 08:12 PM   #4
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Saildrives

https://www.boats.com/reviews/all-about-saildrives/
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Old 06-16-2021, 08:12 PM   #5
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Sail Drives suffer from the same issues as outdrives/sterndrives. It`s keeping water out and oil in, and why locate the gearbox under water.
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Old 06-16-2021, 08:17 PM   #6
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Sail Drives suffer from the same issues as outdrives/sterndrives. It`s keeping water out and oil in, and why locate the gearbox under water.

Particularly salt water.
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Old 06-16-2021, 09:38 PM   #7
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A sail drive is superior in all aspects except simplicity. Here is were it all comes a part. The complexity suffers more maintenance in wear and corrosion which means more cost and more break downs. Add to this that sail drive manufactures were quick to abandon their product in the past, leaving boat owners with a hole in their boat not easily filled. Quickly the end user learned to avoid all these issues and sail drives ended with a bad reputation that was well deserved.

Here we are again with the old timers wondering if history is about to repeat itself.
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Old 06-16-2021, 10:12 PM   #8
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My introduction to sail drives was when I was reading about the Marlow Mainship 32 and thought that the 6 miles per gallon at 9 mph was impressive. The Boattest.com article pointed out that pods can be 30-50% more efficient than shaft drives but admitted that some of that is due to reduced drag from the absence of rudders.
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Old 06-17-2021, 12:11 AM   #9
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IMHO

In Saltwater: Out drives, saledrives, pods - are similar to Alka-Seltzer in water... they fizzle too easily!

Not to mention too many other product complications.
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Old 06-17-2021, 05:33 AM   #10
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For a novice , sail drives can make the boat self docking , but at huge cost.
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Old 06-17-2021, 07:44 AM   #11
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Sail drives, pods, stern drives all have some efficiency advantage (particularly if the rudders are eliminated), but it's not worth the maintenance headaches in my mind. And low speed steering is usually not as good with no rudders, as you're only steering with thrust (and you lose that as soon as you take the engines out of gear).
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Old 06-17-2021, 07:49 AM   #12
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Talk to some sail drive owners that wet slip their boats and ask their opinions. They are not very robust and you have no way to check for water containination without pulling the boat. They are well suited to boats kept on a lift. IPS drives look like a risky proposition to me best suited to folks with deep pockets that can replace them without thinking twice of the cost. The fuel savings realized over several seasons could be wiped out with one log and who knows what the availability of those drives will be in 10 years. Outdrives can be pricey enough to replace and they are much more common, I would hate to spend $1-2M on a boat only to lose a drive and find it is no longer made and now I need to retrofit the whole system to get operational again. Doesn't seem worth it for a trawler style use.
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Old 06-17-2021, 07:54 AM   #13
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Completely disagree that directed thrust boats (I/Os and outboards) are less maneuverable....with the exception maybe some/many jet drives and that depends dramatically on hill shape


If talking singles, I find driving I/Os by far the most maneuverable, outboards a little less so because they physically don't turn as far and smaller profile in the water. A good sized I/O is much like a rudder even out of gear...but you don't need to use it like that once you get the hang of them.


Many single I/O's properly driven can do a 180 in almost a boat length... much like pivoting with twins. Try that with a single conventional shaft/prop and no thruster.



Twins are of course a different animal and can vary between setups.
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Old 06-17-2021, 08:00 AM   #14
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Completely disagree that directed thrust boats (I/Os and outboards) are less maneuverable....with the exception maybe some/many jet drives and that depends dramatically on hill shape


I find driving I/Os by far the most maneuverable, outboards a little less so because they physically don't turn as far and smaller profile in the water. A good sized I/O is much like a rudder even out of gear...but you don't need to use it like that once you get the hang of them.


Many single I/O's properly driven can do a 180 in almost a boat length... much like pivoting with twins. Try that with a single conventional shaft/prop and no thruster.



Twins are of course a different animal and can vary between setups.

They're maneuverable, but when I say they don't handle well, I'm referring to tracking, steering authority, etc. when just cruising at low speeds. A lot of sterndrive boats tend to wander at low speeds, for example.
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Old 06-17-2021, 08:01 AM   #15
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You see quite a few of them on sail boats, but their only advantage is installation cost. Probably a quarter the labor of a traditional shaft. So cheaper sale price and/or higher profits for the builder. Higher maintenance costs but the builder doesn't care about that, not his problem. True there's no shaft alignment to worry about but having to periodically replace the rubber seal greatly out weighs that and it's a haul out job.
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Old 06-17-2021, 08:07 AM   #16
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A lot of sterndrive boats tend to wander at low speeds, for example.
I have a little bowrider with a stern drive that wanders so bad that I'm afraid of being pulled over in the harbor under suspicion of being under the influence. It is really beamy and shallow draft and I believe it is caused by vortexes being shed off of the transom corners at a frequency. It will drive you crazy.
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Old 06-17-2021, 08:11 AM   #17
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I have a little bowrider with a stern drive that wanders so bad that I'm afraid of being pulled over in the harbor under suspicion of being under the influence. It is really beamy and shallow draft and I believe it is caused by vortexes being shed off of the transom corners at a frequency. It will drive you crazy.

Yup, that's exactly what I'm thinking of. Some say dropping the trim tabs all the way stabilizes things a bit, but so does having rudders.
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Old 06-17-2021, 08:14 AM   #18
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Quote:
Originally Posted by Benthic2 View Post
I just learned about sail drives today and they seem like a great idea ? You can move the engine(s) to the stern for noise and space reasons, you don't have the inneficiency of a propeller angled downward and you avoid drive shaft/cutlass bearing/stuffing box issues.

So...I have to believe that if they really were better they would be more common. I am always curious when there is one technology that doesn't dominate or die, kind of like Mazda's rotary engine.

So, why aren't they more common ?

( thanks in advance )
They are very common with sail cats. I would say the majority of volume of production sailcats use either the volvo or the yanmar saildrives. Mostly driven by increase efficiency of space, ease of production/installation, and elimination of the stuffing box failure point.
Another advantage is elimination of rear stateroom heating, after a run.
I'm getting 5.5nm/gal in my boat @ 6.x knots, no sails up.
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Old 06-17-2021, 08:15 AM   #19
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Soooo... by reading posts here and from my years [decades] of experience - IMO:

Widely spaced twin engines' straight shaft-to-prop drives, with twin rudders of ample size, win the contest for general boat maneuverability during the full range of [slow or fast] speed conditions. Add bow and/or stern thrusters [both of which I feel unnecessary on a twin engine boat]... then the water-floating boat becomes similar in [level-plane maneuverability] to an air-floating "helicopter".

What's not to love - Twin Screws for Me!!
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Old 06-17-2021, 08:17 AM   #20
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Many smaller vessels with outdrives do suffer from tracking ability...that's because they are designed for watersports not really "cruising". Bowriders are often way too bow heavy due to loading and thus wander at low speeds quite a bit. Put everyone aft and it improves on many bowriders.

Loading of these vessels is often critical for the wandering issue and also is trimming to eliminate porpoising and chine walking at higher speeds.

Jet drives with mostly flat bottoms are really a handful to handle till you learn their habits....but they are designed for purposes that really aren't slow speed tracking or long distance cruising.

Outdrives in large vessels dont have these issues as the hulls are more "cruiseworthy" designs, not sportsters.

Once above 30 to 35 feet and heavier type hulls (no go fasts)....are there that many I/Os? I haven't been looking closely. In fact, I think Sea Ray all but eliminated I/Os and went outboards in their smaller boats. At least they started to when I worked for a dealership back in the early 2000s.
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