One benefit of an offset shaft is the ability to remove it worth having to drop the rudder. Low speed maneuvering could be tricky. When motoring the boat will have a tendency to drift to port

 

Another benefit is the rudder will not be constantly subject to the turbulent water thrown at it by the prop when motoring. A wheeled boat will hide this effect but try motoring in a tillered boat and you can definitely feel the "prop shake".

 

Then again, you don't get to use the rudder to direct the thrust at slow speeds either. You HAVE to be making appreciable speed to steer.

 

The photos look like Sabre installations. We've owned a Sabre 28 and 38, both with offset shafts. They were installed this way to counter the effect of shaft rotation - clockwise rotation had port offset shafts. It is certainly easy to work on the shaft with an offset installation. Regarding power underway, it is true that there is far less vibration. Due to pressure on one side of the rudder, the helmsman can definitely feel the effect and has to have a firm hand on the wheel. In reverse, there will be a definitive prop walk, depending on which side the shaft is offset. In our case, we're offset to port, so in reverse, the boat will walk to port. When backing into a slip, I line up the transom's midpoint on the starpoard piling, about 3' outside the slip. Applying strong reverse thrust will back the boat while pulling it to the port side of the slip. By the time we reach the slip, the boat is centered. From that point, I slip into neutral and glide back, adjusting the rudder as necessary to keep the boat centered. A firm shot of forward stops the boat when in in it's final position.

 

Regarding power underway, it is true that there is far less vibration. Due to pressure on one side of the rudder, the helmsman can definitely feel the effect and has to have a firm hand on the wheel. In reverse, there will be a definitive prop walk, depending on which side the shaft is offset. In our case, we're offset to port, so in reverse, the boat will walk to port.

I think this must depend on the particular boat... Our Freedom 28 has the shaft offset to stbd. It will turn to stbd on a dime if you let go the wheel under power, but its not noticeable while you are steering. As for prop walk, we get none whatsoever. Not sure if that is because of the shaft offset or the feathering Max Prop, but there is no prop walk with this installation at all.

 

As a professional, that much offset makes those boats the hardest to handle at slow speeds than any of the numerous sailboats I've operated. It's like operating a TSMY on one engine.
Our offset is minimal, just enough to sneak the shaft by the rudder. It still gives us more propwalk than a centered shaft, but this is something one can use to their advantage, once they've learned to use it.

 

I'm not sure what is meant here by " Low Speed" 0- .5kn. ? .5-1kn ? or more? I've never felt it especially difficult to maneuver my boat in tight quarters with its' offset prop ( Sabre). I can steer quite easily at idle speed or less ( coasting in neutral) Maybe I've just gotten used to it after 25 years. I wouldn't suggest that someone not purchase a Sabre, because it had an offset prop. IMHO.

 

As a non professional the photo shown looks like a lot more offset than on the Cal 33-2 I owned. The Cal had the advantages of being able to slip off the shaft easily and low rudder turbulence when cruising under power. But it also was no more or less difficult to maneuver around a dock than other fin-keel/spade-rudder boats I've been on.

 

Well, it certainly will use more fuel. The prop and the rudder will be fighting one another constantly. From a standing start, the moment you put the motor into gear that boat will want to swing to starboard and it cannot be corrected until the boat is moving fast enough for the rudder to bite. Good luck with that one at close quarters. Not for me.

 

That looks like a pretty extreme offset. It makes me wonder how they would even get the engine and transmission on centerline. Maybe it is just an illusion?

What kind of boat is it?

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CPM, What kind of boat is it ? A Sabre? I've sailed one for 25 years, along with many other sailboats. If so, It's really a non-issue in my opinion. I operate in tight quarters all the time. Between two bridges with current running. I have a Max-Prop on mine, there's no weather-helm induced by the prop. Sailing or motoring. I like the way my boat reverses, you just need to keep a firm grip on the wheel at speed to keep the rudder from slamming over, ( I think that would be true with any fin keel though) the boat is very responsive in reverse. There's no discernable increase in fuel usage. I can't speak to other manufacturers of offset prop boats. I'd talk with the actual owners though. If it's a Sabre and you like the boat for other all other reasons, I would certainly not walk away from it because it had an offset prop.

 

I'm not sure because I've looked at so many but it probably is a Sabre because they are on my shopping list.
Thanks all. That pretty much answers my question of whether this was a recognizable design or some kind of weird cob job.

 

 

So the dog pulls the stern to starboard, to counteract the prop walk?

 

No, not at all. She paints the prop with her tail.

 

The very best of 1980's technology. Right up there with chevy cavalier convertibles and Beta tapes. There is no real advantage. It was just a manufacturing decision.

 

@tempest, why are the anodes painted over?

 

It's Petit Zinc coat, I experimented painting them that year. Seemed to work fine, they were still there at the end of season a little less eroded than usual. Couldn't think of a good reason not to.

 

I just had to land a slip at an unfamiliar marina, where we'll be hauled for the winter. It required a stern-to docking, as the power pedestal would not have otherwise reached. On approach, the dockmaster explained that to me, but said, if I was uncomfortable getting in the slip, then to come in bow first and they'd figure something out.

I had to get the job done right, which required coming to a stop outside the t-head of the next set of slips, backing into a 90 degree turn to port, then down another fairway, where I'd have to continue backing into another 90 degree turn to starboard, then into a finger slip.

I was a bit of a white knuckled affair, but turned out to be one of my finer moments. Being the official end of the season, I guess that was something. No freaking way I would have pulled it off with an offset prop. Moral to the story is you never know what cards you'll be dealt.

 

I just had to land a slip at an unfamiliar marina, where we'll be hauled for the winter. It required a stern-to docking, as the power pedestal would not have otherwise reached. On approach, the dockmaster explained that to me, but said, if I was uncomfortable getting in the slip, then to come in bow first and they'd figure something out.

I had to get the job done right, which required coming to a stop outside the t-head of the next set of slips, backing into a 90 degree turn to port, then down another fairway, where I'd have to continue backing into another 90 degree turn to starboard, then into a finger slip.

I was a bit of a white knuckled affair, but turned out to be one of my finer moments. Being the official end of the season, I guess that was something. No freaking way I would have pulled it off with an offset prop. Moral to the story is you never know what cards you'll be dealt.

Slips can obviously represent a challenge as far as boat maneuvering goes. It's one good reason to avoid them if you can. But for many the convenience is trumps.
I think you concern about the electrical hook up is not important. It may be possible to warp the boat. Or it may only be in the slip until hauled... no need for a hook up.

This was my first and probably my last year in a summer slip. I wanted a slip with a starboard tie and stern to... because I board from the read boarding ladder. The slip I got was perfect. My boat backs to stbd. With this slip I can come along side the main dock.. stop the boat...get off with 2 lines and warp the boat back into the slip... or back down into the slip... or a combination if some handles the dock lines and someone handles the helm. 30 amp chord is long enough for a bow in... but I lose the convenience of the stern boarding. I will keep this slip for in water winter storage and have a spot out of the water for the RIB.

 

I get why manufactures slightly offset their propshafts to allow the shaft to be removed without dropping the rudder, but looking at the extreme example the OP posted I really can't see any other advantage, aside from apparently reduced propwalk. I would be interested to see pictures of that boat from directly astern.

On the other hand one disadvantage I can see to directing the propwash off to one side rather than straight down the centerline, is that you lose the ability to vector the thrust using the rudder. That would eliminate a number of very useful maneuvering techniques that I use regularly when getting in and out of tight slips, getting off leeward docks etc. Even a certain amount of propwalk is useful once you learn how to use it.

When I got our current boat it was a little intimidating to maneuver since I was going from a 30ft tiller boat to a 40ft wheeled boat. The boat came with a fixed prop that had quite a bit of propwalk. I quickly learned to use that propwalk to my advantage. Using the "back and fill" technique I can rotate the boat on her own length. For those that don't know, that technique entails putting the helm hard over, and giving a short hard burst of reverse which stops the boat and propwalk pulls the stern to one side, then you give a sharp burst of forward and the rudder vectors the thrust at right angle to the stern and kicks the stern around. By alternating forward and reverse bursts you can spin the boat on the spot. It is an extremely useful maneuvering technique that just wouldn't be possible with such an extreme prop offset.

There are other techniques that utilize propwash off the rudder, such as springing off a dock. I was on a dock with large boats fore and aft of me, and a breeze blowing us against the dock. I untied everything but the forward spring, and doubled that back to the bow. I then put the helm hard over towards the dock and motored forward against the spring. The rudder directed the thrust sideways and pushed the stern away from the dock. Once the stern was clear of the boat behind me, my wife cast off the spring line, and I backed off the dock. Without propwash on my rudder that maneuver would not be possible.

If you never have to dock your boat or maneuver in tight spaces it probably doesn't matter, but for me the offset prop would be a deal breaker.




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Using the "back and fill" technique...
There are other techniques that utilize propwash off the rudder, such as springing off a dock.

From my beginner ASA coarse, I'm familiar with the Back and Fill technique (though my instructor didn't give it any name) and springing off. I know I'm getting a little off topic but since you mention it, are there other common maneuvering techniques like these that I should know about? My only techniques so far have been tailoring or crash-n-pray.

As far as the offset shaft goes, I hope I didn't start any negative feelings about somebodies yacht. I think it was a Sabre 38 I posted and if I had the opportunity to own such a stunner, I think I could get used to that particular unorthodox feature. I must admit though, I do have some of my own "deal breakers" that would be thought of as unreasonable.

 

There is a very good discussion in Francis Herreshoff's book "The Common Sense of Yacht Designs" in the chapter "Power Plants and Propellers" The discussion is fairly long and if you can find the book I would recommend reading it entirely. Here is a quote from a article that he wrote for Rudder magazine in 1943: The advantages of the offset propeller is as follows " 1. The shaft doesn't interfere with keel bolts. 2. The yacht is faster and more economical under power. 3. The yacht is faster under sail. 4. The yacht steers better under power. 5. The yacht steers better under sail. 6. If it is desired to remove the motor.. the matter is much simplified. This was written in a time when most yachts had the rudder attached to the keel so there was often an aperture in the rudder which compromised performance under sail in particular. I think these points are still valid. I am a fan on Francis Herrishoff. He was very opinionated but I am very happy to hear his opinions. He was not only completely knowledgeable about what had gone before his time but also had great ideas that were ahead of his time. I think mainly because the technology was not yet developed to make the construction feasible. Also, in my opinion, he designed some of the most beautiful sailing yachts ever built.

 

There is a very good discussion in Francis Herreshoff's book "The Common Sense of Yacht Designs" in the chapter "Power Plants and Propellers" The discussion is fairly long and if you can find the book I would recommend reading it entirely. Here is a quote from a article that he wrote for Rudder magazine in 1943: The advantages of the offset propeller is as follows " 1. The shaft doesn't interfere with keel bolts. 2. The yacht is faster and more economical under power. 3. The yacht is faster under sail. 4. The yacht steers better under power. 5. The yacht steers better under sail. 6. If it is desired to remove the motor.. the matter is much simplified. This was written in a time when most yachts had the rudder attached to the keel so there was often an aperture in the rudder which compromised performance under sail in particular. I think these points are still valid. I am a fan on Francis Herrishoff. He was very opinionated but I am very happy to hear his opinions. He was not only completely knowledgeable about what had gone before his time but also had great ideas that were ahead of his time. I think mainly because the technology was not yet developed to make the construction feasible. Also, in my opinion, he designed some of the most beautiful sailing yachts ever built.

He wrote that article 80 years ago! I don't think any of the points he makes hold true today.

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The rationals seem pretty thin. Why are owners needing to remove their prop shaft? In 36 years there has never been a need to remove the shaft. I was able to install a PSS, replace the cutlass bearing without removing the shaft.

I am unconvinced by claims of superior performance motoring or sailing. Let's see the numbers.

 

I am unconvinced by claims of superior performance motoring or sailing. Let's see the numbers.

Other than the quoted article by Herreshoff, no one here has claimed " Superior" Performance. What has been said by people who own certain models with offset propellers is that it's a non-issue. ( to us) And, that there's no discernable lack of Maneuverability. increased fuel consumption etc. It's also been said that not having to drop the rudder to replace a shaft or cutlass bearing etc. can be a plus.

Between Sabreman and myself there's 55 years of owning and operating boats with offset propellers. Albeit, from one manufacturer. I too am neutral, in that, I would not base a boat purchasing decision on whether the boat had an offset propeller or not ( at least not a 38 Sabre that the OP was inquiring about) If everything else was sound. It's a fine ship.

 

Don't get me wrong, I'm not arguing against Sabre 38s. For me this is a purely theoretical discussion. Owners of that particular model are bringing real world experience to the mix.

My only experience with offset shafts are shafts that are slightly offset, just enough so that the shaft just barely clears the rudder when removed.

I wonder if the OP's original picture is even a Sabre. It does not look like the same hull shape as the subsequent Sabre pics that have been posted. In the original pic you can clearly see the rudder beside the prop. I am having troubles visualizing how the prop thrust can be directed by the rudder in that position. Perhaps the rudder will catch a bit of the wash when turning to port, but it couldn't possibly do so turning to starboard.

Again, maybe it is an illusion due to camera angle?

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I have never tried to use an AP in reverse.. only going forward.
Has any one use a course / heading controlled AP in reverse?

So let's say you have a slip which is oriented North-South with the open side to the north.
What would happen if you got the boat "aligned" with the slip bow point north.. stopped the boat, set the AP to 180° and put the tranny in reverse? Would the AP back the boat in reverse into the slip... or try to turn so the bow was pointed South into the slip? My sense is the AP couldn't steer in reverse.... But I don't know why.

Any thoughts?

 

I was talking about AP as it would normally be used... not in reverse. I'm inexperienced but not that much!
From what little I know, there are gyro sensor thingamajigs that would make the AP default to a forward position right?

Thank you @Sabreman that's much appreciated.

The propwalk is only in reverse.

I'm aware of that. The wording of my question probably made it sound otherwise though.

Don't get me wrong, I'm not arguing against Sabre 38s. For me this is a purely theoretical discussion. Owners of that particular model are bringing real world experience to the mix.

My only experience with offset shafts are shafts that are slightly offset, just enough so that the shaft just barely clears the rudder when removed.

I wonder if the OP's original picture is even a Sabre. It does not look like the same hull shape as the subsequent Sabre pics that have been posted. In the original pic you can clearly see the rudder beside the prop. I am having troubles visualizing how the prop thrust can be directed by the rudder in that position. Perhaps the rudder will catch a bit of the wash when turning to port, but it couldn't possibly do so turning to starboard.

Again, maybe it is an illusion due to camera angle?

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You haven't come across as argumentative at all. All fair points as far as I can tell.
Here is the link to the listing showing the pics that I posted.

Sabre 38 Mk Ii boats for sale | YachtWorld

Find Sabre 38 Mk Ii for sale on YachtWorld Europe's largest marketplace for boats & yachts. We connect over 10 million boat buyers and sellers each year!

www.yachtworld.com

After seeing Sabreman's pics, it does look like the listing appears to be more extreme that in reality. It's that false extreme that had me questioning my desire.
AND, it's one of the few that I've seen that has AC! It just squeaks in under my top end budget but I still have reserves for minor updates that would probably have to happen.

 

Modern yacht design didn't "begin" it is an ongoing evolution. A 1970' boat is more modern than a 1920's boat.

Personally, if I am thinking of "modern" boats I would think of boats designed in the last 20 years. Even so, there have been significant design changes over that relatively short period of time.

Good design ideas tend to persist over many years, whereas other ideas disappear as designers find better ways to do it.

Offset propshafts are one of those design ideas that has not withstood the test of time.

Yacht design has come a long way since Hereshoff's day. Holding his design ideas out as being "educational" design theory would be akin to offering Henry Ford's automotive engineering ideas as useful engineering knowledge today. In both cases they are interesting from a historical context, but are of little use when applied in today's world.

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S

Modern yacht design didn't "begin" it is an ongoing evolution. A 1970' boat is more modern than a 1920's boat.

Personally, if I am thinking of "modern" boats I would think of boats designed in the last 20 years. Even so, there have been significant design changes over that relatively short period of time.

Good design ideas tend to persist over many years, whereas other ideas disappear as designers find better ways to do it.

Offset propshafts are one of those design ideas that has not withstood the test of time.

Yacht design has come a long way since Hereshoff's day. Holding his design ideas out as being "educational" design theory would be akin to offering Henry Ford's automotive engineering ideas as useful engineering knowledge today. In both cases they are interesting from a historical context, but are of little use when applied in today's world.

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Not a satisfying answer.
Can you list features in modern design? Would they include:
wing keels
fin keels
spade rudders
folding / feathering props
plumb bows
fractional rigs
walk thru transoms
swim platforms
self tailing winches
"high tech" sailcoth
asymmetrical spinnaker
full battened mains
roller furling
in mast furling
behind mast furling
stow booms
large roach mains
flat topped mains
biminis
solar panels
wind gens
high tech running rigging
rod rigging

 

Modern boats are just contemporary. Many older built and designed boats would be too expensive to build today. Just look at the replacement monetary evaluations as stated in resent boat surveys. One reason that I don't own a wooden boat is that I couldn't get an acceptable large yellow cedar plank at any cost. The virgin old growth forests have been mostly decimated on our lovely planet. If you think modern designs do everything better you try to get a ride on Sparkman Stevens Bolero or Stormy Weather, an Alden Malibar II schooner, or Francis Herrishoff's Ticonderoga, William Hands motor sailer, etc. It is still the same ocean and we are still our parents sons and daughters. We are not doing everything better. Not even close.

 

Modern boats are just contemporary. Many older built and designed boats would be too expensive to build today. Just look at the replacement monetary evaluations as stated in resent boat surveys. One reason that I don't own a wooden boat is that I couldn't get an acceptable large yellow cedar plank at any cost. The virgin old growth forests have been mostly decimated on our lovely planet. If you think modern designs do everything better you try to get a ride on Sparkman Stevens Bolero or Stormy Weather, an Alden Malibar II schooner, or Francis Herrishoff's Ticonderoga, William Hands motor sailer, etc. It is still the same ocean and we are still our parents sons and daughters. We are not doing everything better. Not even close.

I guess it all depends on what you expect from a boat. I haven't got a ton of experience on classic yachts. I did spend an afternoon sailing Sydney Harbour on my brother in law's classic 1940's 45ft wooden Yawl. It was a pleasant sail, but from a boat handling perspective it was very cumbersome and the ergonomics were not good. The interior was cramped and dark. The wood hull apparently is a huge amount of maintenance. It has to be a labour of love. The boat has a long history of racing in the area, but would not stand a chance against "contemporary" competitors.

Certainly building yachts out of wood is expensive, but that is not the only reason nobody is building those old designs. They could easily be replicated in fiberglass.

I don't really want to get into a debate about classics vs modern. People who love those old boats LOVE them, and as we all know, love is blind!

I am more interested in the theories as they pertain to the offset propshafts. The points you are citing Herishoff on:

It keeps the shaft clear of the keel bolts? Not an issue these days. Modern keels don't come back that far.

The boat sails faster? I doubt it, but perhaps on his designs that is true. Modern technology has all but eliminated propeller drag.

The boat motors faster and is more efficient? I doubt it. How can it be more efficient to point the thrust 30° off centre, and then counter that off axis thrust with the rudder and call it more efficient? Perhaps compared to a propeller in a keel aperture, but nobody does that any more, so again, the problem is solved differently with modern design.

It makes engine removal easier? Well these days the engine can be decoupled from the prop shaft, so shaft angle makes no difference, however it IS easier to remove the shaft, which is why that design element lingers to this day, albeit to a much lesser degree in most cases.

I wonder what Roger Heweson's reasoning for using such an extreme offset when designing the Sabre 38? I'm no expert, but if I were to guess I would say it likely had something to do with where he wanted to place the engine to accommodate the interior design. Maybe it was a compromise he made in order to move the engine further aft to achieve balance?

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Romance and philosophy aside, I'm certain that SchockT can answer much better than I can but c'mon, you guys can't accept that there have been fundamental scientific marine design improvements in the past 200, 100, 20 years? More efficient hull design and construction materials alone. Cost was mentioned. Wouldn't more efficient and cost effective building processes constitute design improvement? Henry Ford was a boon to humanity but we've surpassed even that now. Survival of the fittest seems to touch everything.
Granted, the boat in question, Sabre is a beautiful design and I accept that the offset shaft may not add significant negative affects but it would have been adopted as a standard design if it was such an important improvement right? If that were the case, I wouldn't have had to ask my opening question.
But, @Michael Bailey I'm fully with you on the romance of a wooden classic of olde. I'm the same way with cars too.

 

Romance and philosophy aside, I'm certain that SchockT can answer much better than I can but c'mon, you guys can't accept that there have been fundamental scientific marine design improvements in the past 200, 100, 20 years? More efficient hull design and construction materials alone. Cost was mentioned. Wouldn't more efficient and cost effective building processes constitute design improvement? Henry Ford was a boon to humanity but we've surpassed even that now. Survival of the fittest seems to touch everything.
Granted, the boat in question, Sabre is a beautiful design and I accept that the offset shaft may not add significant negative affects but it would have been adopted as a standard design if it was such an important improvement right? If that were the case, I wouldn't have had to ask my opening question.
But, @Michael Bailey I'm fully with you on the romance of a wooden classic of olde. I'm the same way with cars.

About the offset propeller. I was thinking that you wondered if it would be a disqualifying feature in respects to purchasing the boat. My view is - probably not. Issue that you may find is that the prop, its strut and shaft are more exposed. It is not behind the keel. We have made a couple of trips to Alaska. There is a lot of debris like wood, even logs and ice in those waters and we found it impossible to not hit some of them. Losing your propeller would be no small thing in those waters. You could say the same thing about a spade rudder and many sailors there do prefer a more protected rudder. Most modern power boats have very exposed rudders and propellers. In crossing the Pacific ocean from Honolulu to Bellingham we hooked plastic three times. The skipper had me stop the boat to clear the mess. We were too far from any assistance if we broke something. So, it is something to consider. I guess that "you pay your money and take your chances."

 

I am the owner of a Sabre 42. One of the other things I have read about reason for the offset prop shaft is the effects while motoring on the semi balanced rudder. Supposedly the prop wash would create a lot of disturbance with the rudder.

As others have said with experience in this design, it is just a nuance you get used to. I can only use prop wash to assist in slow maneuvering while turning to port. To port it is still effective. All designs have their disadvantages. Nothing one doesn't get used to.

Foster

 

I am the owner of a Sabre 42. One of the other things I have read about reason for the offset prop shaft is the effects while motoring on the semi balanced rudder. Supposedly the prop wash would create a lot of disturbance with the rudder.

As others have said with experience in this design, it is just a nuance you get used to. I can only use prop wash to assist in slow maneuvering while turning to port. To port it is still effective. All designs have their disadvantages. Nothing one doesn't get used to.

Foster

Thanks Foster for your first hand knowledge.
Is it your experience then that the below statement is accurate?
"but you certainly couldn't use forward bursts to kick the stern to port because there is no propwash at all on the starboard side of the rudder. Same with the springing methods I described. They would probably work well on one side, and not at all on the other."
If this meets your experience, I still wouldn't consider it a deal breaker, just something to think about.

We have AC. Mandatory here in the Chesapeake. If you have Sabre questions, PM me. I'd be glad to answer them. We've had wonderful experiences with our Sabres. Of course, with any boat of this vintage, there are specific things of which to be aware. But they're great boats and worth investing in the updates.

The several that I've looked into, being in New England, don't seem to have come from the factory with AC. Hell, growing up in the Adirondacks I never had central AC in the house.