The Pod Parted

BandB · Sep 3, 2015

Art said:
Every article should (or at least could) leave some sort of an impression.

OK... I change the way I say it (repeating the same thing I said, but in more words)... their objective information did not impress me toward a good feeling for pods; at least at this level of development and constant/various needs required/apparent.

No, it doesn't make you want to run out to the store and buy a couple.

BruceK · Sep 3, 2015

I`d prefer the gearbox inside the hull, than under it. I/O or sterndrives are a maintenance hassle, these seem no better in that respect, but there is the handling advantage. Even so, a month for a replacement just seems wrong.

Cottontop · Sep 3, 2015

hmason said:
The dealer for the boat called Mercury directly yesterday and asked why there was such a delay. He was told that these drives are not an off the shelf item and each was individually built to order. They said the current build time was 2-weeks minimum and shipping could take another 2-weeks. That's why it took so long for the drive to appear.

So maybe a one-month delivery time is normal. Million-dollar boats waiting for $20,000 pods, so Mercury can manage its cash flow.

Art · Sep 3, 2015

BandB said:
No, it doesn't make you want to run out to the store and buy a couple.

Honestly... and, to the best of my intuitive (as well as learned) capabilities:

For extreme/best longevity with least need-filled services - - > Nothing beats a slow moven, single screw FD hull with good ol' heavy duty nearly forever dependable NA diesel that has straight drive with full keel and rugged skeg that supports a big, badass rudder. That combo may not be too sexy to many boaters... but it sure is sexy to thems that own em!

Of course - I say tongue in cheek: Next on my list of dependability is our bullet-proof Tollycraft. Am I a bit prejudice??- Naw! - LOL :popcorn:

For reasons, I would sorta like our twin screw Tolly to have duplicate heavy duty keels with full skegs built as original design. However, I imagine that extra weight and water-friction-drag would considerably limit its easy planing capabilities, top speed of 22 knots, and 1 nmpg fuel usage at 17 knots. Also might reduce its slow-travel (5 to 6 knot while running one engine) capabilities that nearly enable 3 nmpg. :whistling:

sunchaser · Sep 3, 2015

I may have misread the article, but the table showed a 45% fuel burn improvement at 25 knots when comparing two drive systems.

Doug Zurn designs either way but likes the improved range and economy of the IPS. Like comparing fuel burn differences of gas vs diesel almost.

IPS is at 6000 units installed and climbing. Not surprising we on TF are not accepting, our cruising style and go slow desires are not the audience.

Surprising that grounding a "fast" boat with straight drives has not been mentioned. Not a cheap fix either. So do we blame the drive or driver for a grounding? I've had two expensive groundings over the years, never blamed the boat.

Anybody have a Sail drive? Not to mention the clamoring over stern drives in the middle of the last century----.

BandB · Sep 3, 2015

sunchaser said:
I may have misread the article, but the table showed a 45% fuel burn improvement at 25 knots when comparing two drive systems.

Doug Zurn designs either way but likes the improved range and economy of the IPS. Like comparing fuel burn differences of gas vs diesel almost.

IPS is at 6000 units installed and climbing. Not surprising we on TF are not accepting, our cruising style and go slow desires are not the audience.

Surprising that grounding a "fast" boat with straight drives has not been mentioned. Not a cheap fix either. So do we blame the drive or driver for a grounding? I've had two expensive groundings over the years, never blamed the boat.

Anybody have a Sail drive? Not to mention the clamoring over stern drives in the middle of the last century----.

So my wild guess on volume wasn't far off. Thanks. I wouldn't expect TF to be a big pod group, but this isn't their target audience. And the problems we're talking about are people running over and into things and that often isn't cheap or quick on any drive, especially when done at decent speed.

You're correct that the fuel efficiency is significant, more so on some than others. Plus space provided on a medium size boat. Good system for some people, not for others. Just because it isn't right for some doesn't make it bad.

As to stern drives, their share hasn't been lost to straight inboards. It's been lost on the lower end to outboards and to jets, on the upper end to pods, and in the middle just to lower sales of mid sized family boats, especially express.

Moonstruck · Sep 3, 2015

Art, I think B and B was correct in saying the artice was to inform rather than impress. To paraphrase Bentley Collins with Sabre pods impress buyers, and create excitement.

Sunchaser, Bentley also said that overall fuel savings were not that great. Especially when compared to the increased maintenance costs. Here is a chart that was performed on my boat. It was the Miami Boat Show boat. There was 450 gal of fuel, 12 people, and no water on board. She was carrying a pretty good load. Lighter loaded with smoother wind and water her fuel burn is less.

Power: (2) 500-hp Yanmar 6CX diesels turning
26" by 35" bronze four-bladed props
through a ZF 280 gear with a 2.27:1 reduction.
Performance:
RPM MPH GPH dB-A
900 8.6 2.9 72
1200 10.0 6.7 74
1500 12.5 12.0 75
1800 18.0 17.5 84
2100 24.5 23.5 85
2500 30.7 35.9 87
2800 33.0 44.6 89
2950 35.6 54.9 90
Speeds measured by GPS in the Atlantic off Miami
Beach, Fla., in 10-12 mph winds and 1' to
2' waves with 12 people aboard, full fuel and
no water.

sunchaser · Sep 3, 2015

After another 4 months in Alaska, I am amazed at how well cruise ships perform during docking and maintaining position without anchoring. No tugs just commercial grade pods (and computer controlled) buried well under the WL.

At some point a recreational pod design will arrive that will hold up better under normal operation. But maybe it requires a stout enough design that weight and size are too great. I do know that very large pumps have seal designs that hold up under high pressures, so the engineering and design is well known.

But, with a a success rate of say 99% per year, that could lead to a theoretical several dozen seal failures per year and lots of expense and grief. If Volvo were to offer a maintenance agreement that would be a good thing to have, ditto Zeus.

Art · Sep 7, 2015

If pods do create better mileage per gallon of fuel... why is that? Their gear-casing unit's under water drag must be similar to an o/d. I doubt struts and rudders on straight drives have any more drag than a pod's underwater profile. Is it the way gears are set up that lessens loss?

I just can't get my mind's-eye wrapped around why pods would be much more efficient... especially so much more as mentioned might be the case in Sunchaser post # 155

CPseudonym · Sep 7, 2015

Could counter rotating dual props have anything to do with it? Also props are located forward of the pod in "clean water". Just my wag

twistedtree · Sep 7, 2015

sunchaser said:
After another 4 months in Alaska, I am amazed at how well cruise ships perform during docking and maintaining position without anchoring. No tugs just commercial grade pods (and computer controlled) buried well under the WL.

At some point a recreational pod design will arrive that will hold up better under normal operation. But maybe it requires a stout enough design that weight and size are too great. I do know that very large pumps have seal designs that hold up under high pressures, so the engineering and design is well known.

But, with a a success rate of say 99% per year, that could lead to a theoretical several dozen seal failures per year and lots of expense and grief. If Volvo were to offer a maintenance agreement that would be a good thing to have, ditto Zeus.

I image the cost savings is substantial from not having to hire a coupe of tugs every time you want to dock. That leaves a lot of money to buy pods, and a lot of value in having them.

Art · Sep 7, 2015

CPseudonym said:
Could counter rotating dual props have anything to do with it? Also props are located forward of the pod in "clean water". Just my wag

Good points!

There must be engineered calcs on this. Also, speced in-tub water-flow tests??

Cottontop · Sep 7, 2015

Art said:
If pods do create better mileage per gallon of fuel... why is that? Their gear-casing unit's under water drag must be similar to an o/d. I doubt struts and rudders on straight drives have any more drag than a pod's underwater profile. Is it the way gears are set up that lessens loss?

I just can't get my mind's-eye wrapped around why pods would be much more efficient... especially so much more as mentioned might be the case in Sunchaser post # 155

A few reasons, at least:

1. No angle on prop shaft; all thrust pushes the boat forward, not "up."
2. No rudder drag.
3. Counterrotating dual props.

BandB · Sep 7, 2015

CPseudonym said:
Could counter rotating dual props have anything to do with it? Also props are located forward of the pod in "clean water". Just my wag

It's a combination of factors including those. Now from that point Zeus and IPS have different approaches. Shaft angle plays a role, much like surface drives, but the two of them approach it differently. Same thing with pull vs. push as IPS has forward facing props.

Art · Sep 7, 2015

Conjecture and what-ifs are nice... but... as I said in post 162:

There must be engineered calcs on this. Also, speced in-tub water-flow tests??

BandB · Sep 8, 2015

Art said:
Conjecture and what-ifs are nice... but... as I said in post 162:

There must be engineered calcs on this. Also, speced in-tub water-flow tests??

There certainly are. Volvo and Zeus obviously don't release their internal engineering calculations. They just quote percentages.

There are real world comparisons as well. The efficiency variations do change from boat to boat. Commercial shippers are thrilled with a 7% gain in efficiency. Various boats gain as much as 15-20% at some speeds. At slow, displacement speeds the design actually makes some boats less efficient though. Boats like Delta Powerboats designed for pods and Sabre with a lot of pod experience gain more too than boats that have just used pods on an existing design.

THD · Sep 8, 2015

Art-I searched and searched and cannot find anything published independently that (1) explains why there should be such a significant difference in efficiency or (2) has any independent verification or testing to support the claims made by either Mercury or Volvo. I did find several discussions of the increased maintenance needed including the corrosion issue. One Mercury tech noted one installation where the plates corroded away because the owner "did not know" about the need to check and replace sacrificial anodes. Hard to believe that an owner just "would not know"! For my part, I would not have any major system on my boat that (1) was a "one off" or built to order system, or (2) could not be readily be repaired by any reasonably competent yard, or (3) required company techs to fly in with custom parts and on their, not my, schedule, and finally (4) that I cannot perform routine maintenance to keep it functioning. Whatever savings there may be in fuel, even if real, cannot make up the costs involved with 1 though 4. And that does not even address repairs if the unit is damaged.

Art · Sep 8, 2015

THD said:
Art-I searched and searched and cannot find anything published independently that (1) explains why there should be such a significant difference in efficiency or (2) has any independent verification or testing to support the claims made by either Mercury or Volvo. I did find several discussions of the increased maintenance needed including the corrosion issue. One Mercury tech noted one installation where the plates corroded away because the owner "did not know" about the need to check and replace sacrificial anodes. Hard to believe that an owner just "would not know"! For my part, I would not have any major system on my boat that (1) was a "one off" or built to order system, or (2) could not be readily be repaired by any reasonably competent yard, or (3) required company techs to fly in with custom parts and on their, not my, schedule, and finally (4) that I cannot perform routine maintenance to keep it functioning. Whatever savings there may be in fuel, even if real, cannot make up the costs involved with 1 though 4. And that does not even address repairs if the unit is damaged.

My feelings exactly! Well stated.

Who in TF has first-hand personal experience with pods (on pleasure boats...not commercial boats)? Experience where two, three, or more years of use and records have been experienced and duly noted. I'd love to hear from you what you actually think about pods.

I too have found no verifiable data that conclusively proves pod's extra "fuel" efficiency as an overall factor. With use-factor-expenses and hassles (such as you mention above) it seems to me that pods have limited market scope regarding pleasure boating. For commercial boating I think pods may be a bonanza!

ranger58sb · Sep 8, 2015

There were a bunch of magazine articles... IIRC most at least mentioning efficiency improvements... and lower power requirements for the same performance of a non-pod installation. But I'd guess they got most of their spiel from the boat and engine/pod manufacturers.

OTOH, when they do the on-water tests, I think they now mostly use read-outs from the electronic engine displays... so if they included speeds/GPH/NMPG in their tables... I'd suspect they were in the ballpark of accurate. There may have been a few "comparison" reviews where a magazine tested essentially the same boat with a pod and a non-pod set-up. Otherwise, might have to find a way to compare those numbers with a non-pod installation in the same boat...

All this from memory, mind you, and mine isn't what it once was.

And this was from casual reading, passing the time, not info I was actively seeking out at the time... And everyone knows how useful magazine reviews are.

-Chris

Art · Sep 8, 2015

ranger42c said:
There were a bunch of magazine articles... IIRC most at least mentioning efficiency improvements... and lower power requirements for the same performance of a non-pod installation. But I'd guess they got most of their spiel from the boat and engine/pod manufacturers.

OTOH, when they do the on-water tests, I think they now mostly use read-outs from the electronic engine displays... so if they included speeds/GPH/NMPG in their tables... I'd suspect they were in the ballpark of accurate. There may have been a few "comparison" reviews where a magazine tested essentially the same boat with a pod and a non-pod set-up. Otherwise, might have to find a way to compare those numbers with a non-pod installation in the same boat...

All this from memory, mind you, and mine isn't what it once was.

And this was from casual reading, passing the time, not info I was actively seeking out at the time... And everyone knows how useful magazine reviews are.

-Chris

Almost as useful as forum reviews??!! - LOL :facepalm:

Capt.Bill11 · Sep 8, 2015

hmason said:
If you are following the "Rudders" thread you might have noticed the post by Pgitug:

"Just finishing running the Erie Canal. There have been at least two boats with PODS that will give you $16,000 reasons they may not be as protected as keel/shaft drive vessels."

Interesting and relavent to say the least.

Howard

Apples to oranges.

Pods are mostly found on boats that would not have a keel otherwise. But have exposed shafts, props and rudders.

BandB · Sep 8, 2015

Art said:
I too have found no verifiable data that conclusively proves pod's extra "fuel" efficiency as an overall factor. With use-factor-expenses and hassles (such as you mention above) it seems to me that pods have limited market scope regarding pleasure boating. For commercial boating I think pods may be a bonanza!

What about the Sabre tests pod vs. straight?

Here is a Meridian 441, pod vs. straight.

Meridian YachtsÂ 441 Sedan Bridge (2011-)Â 2011Â Reviews,performance,compare,price,warranty, specs,Reports,Specifications Layout, video | BoatTEST.com

Seavee has their 390 in outboard, straight inboard, and pods. I'll try to find the performance data. I was shown it at one time and pods were clearly more efficient but I told them I had no interest in them.

Here is a Cranchi comparison.

Testing the Volvo Penta IPS -- boot Trade Fair

I've only run pods once and wasn't impressed or unimpressed. However, I do know a couple of people who have them and love them and have a captain friend who has run every type propulsion available and pods would be his choice based on his experience.

Here is what Volvo attributes their efficiency gain to.

Part of the improvement in efficiency is due to the fact that
the system has a state-of-the-art engine – the Volvo Penta
D4 and D6 – but almost all is due to the propulsion unit. If
we look at what happens beneath the surface, we get the
explanation:
– Volvo Penta IPS patented propellers means increased
blade area, half the load on each propeller, and smaller
propeller diameter with minimized tip losses and cavitation.
– Furthermore, the propeller system prevents rotational
losses and does not create any side forces.
– The thrust the propellers produce is horizontal with all the
force driving the boat forward.
– The propellers are at the front of the propulsion unit,
working in undisturbed water with a minimum of pressure
pulses affecting the hull.
A conventional shaft system loses efficiency with the thrust
angled downward and the propellers working in water disturbed
by the propeller bracket and shaft.
Selecting propellers is also very easy, since Volvo Penta
provides optimized gear ratios and a complete and systematic
series of propellers

I'm actually not sold on pods at all due to the maintenance issues. However, I've seen more than enough comparisons and talked to enough users to believe the efficiency gains at speed.

sunchaser · Sep 8, 2015

There is a new escort tug named the Buckley McAllister with 3 Z drives working off the East Coast. Fun read if one has the interest.

The new Pilot Boats for the Columbia Bar work have 3 jet drives.

Numerous articles and data are available in the public forum about marine propulsion innovations both commercial and recreational. Homework and research reveals some real world progress and successful application.

hmason · Sep 8, 2015

Update from the OP. My friends boat received its new drive and was splashed on Saturday. It was driven a couple of miles to his home slip. As he backed into his slip, there was a sudden noise and a terrible vibration from the drive that was just replaced. The boat has been hauled again. The trim tab located directly over the drive had broken its mounting. In forward, water flow held it up, in reverse, the water flow pushed it down into the dual props damaging the new $2,500 props. More to come. You can't make this up.

sunchaser · Sep 8, 2015

Wow, how did a trim tab get into the equation? Meridian design, Zeus or knocked off during the grounding?

Art · Sep 8, 2015

Damn - Some drive trains on some boats can sure cost too much time and super-oodles of $$$$$!

Sure glad we have our classic Tolly tri cabin. Just experienced our umpteenth consecutive and much enjoyed Labor Day weekend

Hawgwash · Sep 8, 2015

hmason said:
More to come. You can't make this up.

Several years ago I had an Oldsmobile that kept getting hit. I don't mean parking lot dings but courtesy car for a week hits. It clearly was jinxed. I'd be inclined to remove my wallet from this boat.

BandB · Sep 8, 2015

Art said:
Damn - Some drive trains on some boats can sure cost too much time and super-oodles of $$$$$!

Sure glad we have our classic Tolly tri cabin. Just experienced our umpteenth consecutive and much enjoyed Labor Day weekend

Just like some cars, some of anything. I guess though that if all were like me, progress wouldn't be made as I say, "If it ain't broke, don't fix it." However, the most successful inventions address a need. Pods went after a certain market segment that had a need for greater speed and more efficiency plus added space. I see boats like Sabre and Delta and I'm very impressed. I suspect as they improve over time, I'll one day buy something with pods.

It's a bit like I am with new computer technology. I use to tell IBM on mid range computers come talk to us after they've been installed at other places for six months. I never wanted to be one of the first users. Yet, had there not been others wanting to be, there never would have been an opportunity for me.

So, I'm glad there are pods and follow the development of pods in recreational boating. Meanwhile I'll sit back and wait until the time is right for me.

Art · Sep 8, 2015

BandB said:
Just like some cars, some of anything. I guess though that if all were like me, progress wouldn't be made as I say, "If it ain't broke, don't fix it." However, the most successful inventions address a need. Pods went after a certain market segment that had a need for greater speed and more efficiency plus added space. I see boats like Sabre and Delta and I'm very impressed. I suspect as they improve over time, I'll one day buy something with pods.

It's a bit like I am with new computer technology. I use to tell IBM on mid range computers come talk to us after they've been installed at other places for six months. I never wanted to be one of the first users. Yet, had there not been others wanting to be, there never would have been an opportunity for me.

So, I'm glad there are pods and follow the development of pods in recreational boating. Meanwhile I'll sit back and wait until the time is right for me.

Well put!

Hawgwash · Sep 11, 2015

hmason said:
A friend has a boat with pod drives. Methinks Volvo. Last evening he hit a rock and one of the drives sheared completely off (as it should).

And another.
I have few details other than there was a rock, the bot cleared it but the Zeus Pods didn't. They too separated as spec'd but in the process did considerable damage to the stern section. "Fortunately this was a well built boat or it could have been a lot worse."

The Pod Parted

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