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Old 09-07-2015, 09:42 PM   #161
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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.
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Old 09-07-2015, 10:07 PM   #162
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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??
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Old 09-07-2015, 11:10 PM   #163
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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.
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Old 09-07-2015, 11:14 PM   #164
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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.
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Old 09-07-2015, 11:23 PM   #165
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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??
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Old 09-08-2015, 12:07 AM   #166
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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.
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Old 09-08-2015, 01:54 AM   #167
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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.
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Old 09-08-2015, 07:26 AM   #168
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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!
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Old 09-08-2015, 08:13 AM   #169
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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.

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Old 09-08-2015, 08:20 AM   #170
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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
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Old 09-08-2015, 09:08 AM   #171
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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.

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Apples to oranges.

Pods are mostly found on boats that would not have a keel otherwise. But have exposed shafts, props and rudders.
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Old 09-08-2015, 09:50 AM   #172
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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.
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Old 09-08-2015, 10:39 AM   #173
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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.
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Old 09-08-2015, 10:54 AM   #174
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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.
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Old 09-08-2015, 11:07 AM   #175
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Wow, how did a trim tab get into the equation? Meridian design, Zeus or knocked off during the grounding?
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Old 09-08-2015, 12:11 PM   #176
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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
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Old 09-08-2015, 12:44 PM   #177
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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.
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Old 09-08-2015, 12:47 PM   #178
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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.
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Old 09-08-2015, 07:54 PM   #179
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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!
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Old 09-11-2015, 07:47 PM   #180
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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."
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