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 )

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.

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.

Saildrives

https://www.boats.com/reviews/all-about-saildrives/

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.

BruceK said:

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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Particularly salt water.

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.

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.

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.

For a novice , sail drives can make the boat self docking , but at huge cost.

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).

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.

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.

psneeld said:

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.

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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.

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.

rslifkin said:

A lot of sterndrive boats tend to wander at low speeds, for example.

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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.

Gdavid said:

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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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.

Benthic2 said:

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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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.

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!!

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.

Art said:

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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For handling, single or twin shaft drive with good rudders and a good hull design wins. Nothing will beat swiveling pods with thrusters for maneuverability though. Watching what some of those pod drive boats can do when docking is downright impressive.

Sometimes it doesn't take much to cure a small boat's low speed wandering habit. I've cured it with homemade or store bought skegs. Maybe get a couple of these PVC Material Skeg Integral Fin Simple to Attach for Kayaks Rowing Boats Canoes and temporarily attach them to the bottom with something like Gorilla tape. It's a cheap experiment. If they work then permanently mount them so you can run at higher speeds without loosing them.

Gdavid said:

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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BruceK said:

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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saildrives use a mechanical shifter/clutch above the water line. There is a 90 deg gear set u/w. Also, saildrives do not pivot, they rely on rudders for high speed steering, using in front of the prop. Mine are electrically isolated from the engine, and last survey showed no corrosion. I'm in salt water. They do have zinc collars around the shaft area. These are not IPS, i/o, etc...

Portage_Bay said:

Sometimes it doesn't take much to cure a small boat's low speed wandering habit. I've cured it with homemade or store bought skegs. Maybe get a couple of these PVC Material Skeg Integral Fin Simple to Attach for Kayaks Rowing Boats Canoes and temporarily attach them to the bottom with something like Gorilla tape. It's a cheap experiment. If they work then permanently mount them so you can run at higher speeds without loosing them.

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I considered both tabs and adding a tracking fin like inboard ski boats use but ultimately we outgrew the boat and I need to sell it. I believe mine is particularly bad because it has a short waterline, wide beam and shallow draft. It excels at planning at low speeds and can carry a pretty good load for only a 4 cylinder but it just isn't good any amount of chop or slow cruising.

psneeld said:

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.

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I could not agree more! My Duffy has a "power rudder" which means the prop is on the trailing edge of the rudder. Just like an IO & outboard motor. Since all turns are initiated by the thrust of the prop, slow steering is excellent because you don't need a good flow of water over the rudder to initiate a change in direction. The Duffy is the best manuevering boat I've ever had!


https://www.duffyboats.com/power-rudder/

Codger2 said:

I could not agree more! My Duffy has a "power rudder" which means the prop is on the trailing edge of the rudder. Just like an IO & outboard motor. Since all turns are initiated by the thrust of the prop, slow steering is excellent because you don't need a good flow of water over the rudder to initiate a change in direction. The Duffy is the best manuevering boat I've ever had!


https://www.duffyboats.com/power-rudder/

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Since we r so far off topic anyway. Try a carolina skiff with a 40 hp on it. Skid training boat. [emoji23]
But if u absolutely, positively need a heavy load pushed thru 12” of water at speed, thats the rig.

When maneuvering a straight drive twin screw boat in close quarters I leave the rudders in straight line. The forward/reverse operations of the trany and each engines desired rpm is all I need. Unless, of course, I want to move the boat sideways [not forward or reverse]... then each engine's independently different rpm and different trany position in conjunction with rudders' position becomes my friend. Seldom do I want to go just sideways.

I’m still trying to adjust to a boat with no rub rails. Thats a pain.

jgwinks said:

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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It is not true that their only advantage is installation cost on a sailboat. They have less prop walk, greater efficiency, and less drag under sail (you will get a rating hit for a saildrive vs. a shaft). In addition, the bilge is dry and there is greater freedom in planning the accommodation. You will see them in some very high end sailboats where cost was not even a small consideration.

Very little of this applies to a trawler though (except for perhaps in small sizes). Even the biggest saildrives can only swing a 20" or so prop. IPS drives are made somewhat bigger and seem to have counter rotating twin props (which can be smaller). A friend of mine brushed his off on a light touch on a reef, the bill was >$200K.

DDW said:

IPS drives are made somewhat bigger and seem to have counter rotating twin props (which can be smaller). A friend of mine brushed his off on a light touch on a reef, the bill was >$200K.

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Some friends had their season interrupted for a while due to fishing line getting wound into the seals of the IPS pods on their Palm Beach.

The efficiency and how flat their boat runs is really remarkable compared to the tsunami of a wake we tend throw with the inboard props on our EB47.

But when I ding a wheel it's only a few hundred dollars to have the pulled and turned. I never asked what the pod adventure cost them.