The Ship Model Forum

[quote="Tracy White"][quote="Vepr157"]The I3B and I3M are your classic skewed propellers (skewback is an ok term, but I think still slightly colloquial). The I3B is the original 688 propeller, and the I3M is quite similar. I suspect the difference is either that the I3M has improved blade tip geometry or it can mount the hub vortex diffuser.[/quote]

I've been doing some digging here and there to try and come up with "definitive information" (I'm not holding my breath) and came up with interesting information in [url=https://www.google.com/url?esrc=s&q=&rct=j&sa=U&url=https://www.history.navy.mil/content/dam/nhhc/research/archives/command-operation-reports/ship-command-operation-reports/c/columbus-ssn-762-v/pdf/1994.pdf&ved=2ahUKEwiugP6z08T1AhWUKH0KHchtDa8QFnoECAkQAg&usg=AOvVaw22HL1kFu3rnwtrRYB-y-MQ]SSN-762 Columbus Command History for 1994[/url] (on page 4) of the [url=https://www.history.navy.mil/research/archives/Collections/command-operations-reports/ships/c/columbus-ssn-762-v.html]Command Histories for Columbus[/url] on the Naval History and Heritage Command site.

Essentially, Columbus had the I3M propeller and "dihydrals" (page 3, paragraph 3 "narrative") installed in the first half of 1994 and when she reached the Pacific afterwards , she performed extensive testing in September. I'm not sure if the baseline they established was for her or for 688i's in general, indicating a rough timeline of when the I3M became available.`[/quote]

I suspect that the I3M was developed in the '70s. The official history of DTMB ([i]Where the Fleet Begins[/i]) mentions that in the '70s DTMB developed a modified blade tip for the 688 propeller to improve tip cavitation, and that older propellers had their tips cut off and the new ones "bolted" on (must have been flush fasteners or something). Also the SKU of the I3M has a similar number to other 688 propeller developed in the '70s.

The 688I was intended to have a hybrid propeller from the start, as evidenced by congressional testimony (the Navy just said they would have new and quieter propellers, but the artists' impressions show a hybrid propeller). I would guess that most, if not all, 688Is had hybrid propellers when they entered service.

So I would guess that in the case of the [i]Columbus[/i], the newer hybrid propeller was removed and the older I3M installed for testing purposes. The early '90s was a time of intense propulsor development in preparation for the [i]Seawolf[/i] and NSSN. The [i]Philadelphia[/i] even tested a few varieties of pumpjets.

Jacob

Many thanks, Tracy! I too thought I had tried that link permutation!
Frankly, the instructions for revising the relocated link files on the website are...obscure at best.

I had seen that when I went through this thread recently but to be honest, there's so much link rot because of the age of the earlier posts (all of the image posts in the first two pages of this thread have been removed from the Navy servers) that I didn't think much about it. That said, I did find it on the wayback machine and managed to pull these images in case it disappears again:

[attachment=2]1971 Skewed Propellers 01.jpg[/attachment]

[attachment=1]1971 Skewed Propellers 02.jpg[/attachment]

[attachment=0]1971 Skewed Propellers 03.jpg[/attachment]

*Edit*, I searched for the title after finding it on the wayback machine and it's still on the DTIC site, at an address that I thought I had tried:
https://apps.dtic.mil/sti/citations/AD0732511

I note that the above link to propeller design:

This paper:
https://apps.dtic.mil/dtic/tr/fulltext/u2/732511.pdf
shows how the appearance of the propeller changes dramatically as skew increases.

Is broken. It redirects to a site that supposedly tells you how to fix the link (add AD to the accession number), but after trying several various attempts at redirection, I could not access it.

[quote="Vepr157"]The I3B and I3M are your classic skewed propellers (skewback is an ok term, but I think still slightly colloquial). The I3B is the original 688 propeller, and the I3M is quite similar. I suspect the difference is either that the I3M has improved blade tip geometry or it can mount the hub vortex diffuser.[/quote]

I've been doing some digging here and there to try and come up with "definitive information" (I'm not holding my breath) and came up with interesting information in [url=https://www.google.com/url?esrc=s&q=&rct=j&sa=U&url=https://www.history.navy.mil/content/dam/nhhc/research/archives/command-operation-reports/ship-command-operation-reports/c/columbus-ssn-762-v/pdf/1994.pdf&ved=2ahUKEwiugP6z08T1AhWUKH0KHchtDa8QFnoECAkQAg&usg=AOvVaw22HL1kFu3rnwtrRYB-y-MQ]SSN-762 Columbus Command History for 1994[/url] (on page 4) of the [url=https://www.history.navy.mil/research/archives/Collections/command-operations-reports/ships/c/columbus-ssn-762-v.html]Command Histories for Columbus[/url] on the Naval History and Heritage Command site.

Essentially, Columbus had the I3M propeller and "dihydrals" (page 3, paragraph 3 "narrative") installed in the first half of 1994 and when she reached the Pacific afterwards , she performed extensive testing in September. I'm not sure if the baseline they established was for her or for 688i's in general, indicating a rough timeline of when the I3M became available.`

Vladimir of Micro-Mir informed me that they are going to begin working on a new 1/144 kit of a 688 class boat later this year. Unfortunately, he did not say which Flight they would model, model, but I hope that it will include parts for all three. Tom Dougherty provided drawings and I have provided information on the Flight differences. I also provided information about which boats have appeared in movies and TV shows, as well as those boats that launched cruise missile attacks against Iraq because he asked about any particularly famous boats. I am really looking forward to this model!

Bill

Hi John,

Have any of the 688Is gotten MIP? All of the photos I can find in the past few years still show the SHT tiles. So the Seawolf (and Virginia) MIP isn't painted, it's just black?

Jacob

Hi all,

I'm aware that as of late, 688s are all black, but I haven't done any research into it, so I assume that only came about when they began applying anechoic tiles to the hulls. In my limited knowledge of the subject, I also assume that the tiles covering the hull were not painted as I have worked with Seawolf Class SHT (Special Hull Treatment) in the recent past, which is similar. I thought I'd throw the question out on this forum because there are a lot of knowledgeable people here. It's more a matter of curiosity for me at this time, but it does come up sometimes in conversations.

Thanks in advance for any info you have.

John :wave_1:

[quote="ModelMonkey"]Received a pair of Mike's 1/350 scale 688 screws with vortex attenuators. I am delighted.[/quote]

Great, glad you like them!

Received a pair of Mike's 1/350 scale 688 screws with vortex attenuators. I am delighted.

[quote="ssn705"]
So you're the guy? You and I are the only ones in the world with 1/350 models of the Ula class then! That's been up for a year and no one bit. I get it, it's pricey. I literally have a 3$ markup on it. Yup...this shows you the limits of Shapeways model volume base pricing algorithm + markup vs marketability. Well thanks for that, honestly. And I'm always happy to consider new topics, especially if related! Though right now I've dived off into 1/48 WWII props land...1/48 scale model of the Pratt & Whitney R4360 is giving me fits at the moment...[/quote][/quote]

Proud to be part of an exclusive club then. I just did an exercise with UTSIRA a few months ago and I had thought for a while beforehand about getting your 210 but actual time with her put me over the hump. U36 as well, but I have to mod the HB 212 kit for it. At least I have your awesome screw for it.

BTW, I wouldn't expend time or resources on the propulsor. Wouldn't really see any of the good stuff.

Cheers,

Dave[/quote]

I'm certainly happy to speculate, but with the pumpjets it's a deep dive into speculation land. I've sketched out a Seawolf, but it really doesn't offer much more than what the Bronco kit already has. So I'm on the fence on taking it any further.

[quote="EJFoeth"]> Though I suspect by now a lot of that empiric work as moved onto the digital landscape?

Hull forms, propellers are CNC-milled, many details 3D-printed, but fitting out is still the model makers job. We recently developed a new autonomous submarine model but can't find any pics online...

> However, we're still plugging away with wind tunnels and models in motorsports as with increasing computing power, the CFD demand becomes more detailed CAD models, which means the average case solve time really hasn't changed that much (in fact, it's gone up!)! And in any given day in the wind tunnel, we can bang through dozens of iterations, each being subjected to a full ride height map.

One of the reasons towing tanks and cavitation tunnels still exist. And when you are going to unsteady conditions (maneuvering and sea keeping) CFD will quickly become prohibitively expensive (for non-navy work, that is). CFD has become critically important in the design stage though and is gaining ground quickly in most aspects of design.

> Point being, for what we're doing we still see the point of physical models and wind tunnels even in light of massive increases in computing power and CFD over the past 20 years.

There are many difficulties with CFD with capturing critical flow details, plus, you need high-quality measurements to validate your CFD codes with. People are moving to so-called scale resolved-turbulence models, meaning that you try capturing as many of the smaller structures in the flow at an enormous computational cost. Capturing all flow details on a propeller remains difficult, especially when you include fluid-structure interaction for estimating blade tonals (acoustics) or deformations (the latter are becoming increasingly more important with composite propellers/rotors).[/quote]

Doesn't sound too different from where we are in automotive/motorsports.

[quote="Woodstock74"][quote="ssn705"]
So you're the guy? You and I are the only ones in the world with 1/350 models of the Ula class then! That's been up for a year and no one bit. I get it, it's pricey. I literally have a 3$ markup on it. Yup...this shows you the limits of Shapeways model volume base pricing algorithm + markup vs marketability. Well thanks for that, honestly. And I'm always happy to consider new topics, especially if related! Though right now I've dived off into 1/48 WWII props land...1/48 scale model of the Pratt & Whitney R4360 is giving me fits at the moment...[/quote][/quote]

Proud to be part of an exclusive club then. I just did an exercise with UTSIRA a few months ago and I had thought for a while beforehand about getting your 210 but actual time with her put me over the hump. U36 as well, but I have to mod the HB 212 kit for it. At least I have your awesome screw for it.

BTW, I wouldn't expend time or resources on the propulsor. Wouldn't really see any of the good stuff.

Cheers,

Dave

> Though I suspect by now a lot of that empiric work as moved onto the digital landscape?

Hull forms, propellers are CNC-milled, many details 3D-printed, but fitting out is still the model makers job. We recently developed a new autonomous submarine model but can't find any pics online...

> However, we're still plugging away with wind tunnels and models in motorsports as with increasing computing power, the CFD demand becomes more detailed CAD models, which means the average case solve time really hasn't changed that much (in fact, it's gone up!)! And in any given day in the wind tunnel, we can bang through dozens of iterations, each being subjected to a full ride height map.

One of the reasons towing tanks and cavitation tunnels still exist. And when you are going to unsteady conditions (maneuvering and sea keeping) CFD will quickly become prohibitively expensive (for non-navy work, that is). CFD has become critically important in the design stage though and is gaining ground quickly in most aspects of design.

> Point being, for what we're doing we still see the point of physical models and wind tunnels even in light of massive increases in computing power and CFD over the past 20 years.

There are many difficulties with CFD with capturing critical flow details, plus, you need high-quality measurements to validate your CFD codes with. People are moving to so-called scale resolved-turbulence models, meaning that you try capturing as many of the smaller structures in the flow at an enormous computational cost. Capturing all flow details on a propeller remains difficult, especially when you include fluid-structure interaction for estimating blade tonals (acoustics) or deformations (the latter are becoming increasingly more important with composite propellers/rotors).

[quote="Vepr157"]I suggest you look into some of the DTMB reports here:
https://dome.mit.edu/handle/1721.3/48001
which may give you a better understanding of the techniques used to design marine propellers, particularly in the era (late '60s, early '70s) when the original 688 propeller was being designed. This historical context is a better guide to understanding how a give propeller was designed than looking at blurry photos.

This paper:
https://apps.dtic.mil/dtic/tr/fulltext/u2/732511.pdf
shows how the appearance of the propeller changes dramatically as skew increases.

Jacob[/quote]

These are really interesting, BTW. Thanks for directing me to them. Wonder if they're hiring! Would love to work as a model maker in that industry. Though I suspect by now a lot of that empiric work as moved onto the digital landscape? However, we're still plugging away with wind tunnels and models in motorsports as with increasing computing power, the CFD demand becomes more detailed CAD models, which means the average case solve time really hasn't changed that much (in fact, it's gone up!)! And in any given day in the wind tunnel, we can bang through dozens of iterations, each being subjected to a full ride height map. CFD: one iteration and one ride height...many, many hours later you have your answer. Point being, for what we're doing we still see the point of physical models and wind tunnels even in light of massive increases in computing power and CFD over the past 20 years. So I wonder if the same can be said for the marine industry, any insight there Jacob?

[quote="Vepr157"]Also, not that it matters really, but the most proper terminology is "skewed" whereas "skewback," though widely used, appears to be more colloquial.[/quote]

Yes; as skew is nearly always backwards; we had some forward-skew propellers for testing but it never materialized for an actual application (fear for catching rope being one reason for cautious owners). Interesting to see the Boswell paper here... :smallsmile:

[quote="Vepr157"]You could probably make a fairly decent Virginia pumpjet based on the material online (psst, Newport News, you might want to cover up your spare rotors a bit better). But there are quite a few varieties of propulsors, and the new ones probably have composite "hybrid" rotors.

Jacob[/quote]

Looking down on NN just now, no idea what this is...

[attachment=0]Annotation 2020-10-16 074331.jpg[/attachment]

I've spied these up at Groton, wasn't sure what they were or if they were related:

[attachment=0]Annotation 2020-06-22 1634.jpg[/attachment]






[quote="Vepr157"]You could probably make a fairly decent Virginia pumpjet based on the material online (psst, Newport News, you might want to cover up your spare rotors a bit better). But there are quite a few varieties of propulsors, and the new ones probably have composite "hybrid" rotors.

Jacob[/quote]

[quote="ssn705"]I happily received a set of Mike's 688, Oscar, Delta and Type 212 screws a few days ago. For the scale, and having seen 705's screw up close and personal as a reference, I am impressed and can't wait to put the speed screw with dissipator on my 705 model in the next week or two.

Jokingly, are you going to do propulsors I can use on 774, 778, 780 and 789?

I also just received one of Mike's Type 210 models that I might dive into next.

Cheers,

Dave[/quote]


So you're the guy? You and I are the only ones in the world with 1/350 models of the Ula class then! That's been up for a year and no one bit. I get it, it's pricey. I literally have a 3$ markup on it. Yup...this shows you the limits of Shapeways model volume base pricing algorithm + markup vs marketability. Well thanks for that, honestly. And I'm always happy to consider new topics, especially if related! Though right now I've dived off into 1/48 WWII props land...1/48 scale model of the Pratt & Whitney R4360 is giving me fits at the moment...

You could probably make a fairly decent Virginia pumpjet based on the material online (psst, Newport News, you might want to cover up your spare rotors a bit better). But there are quite a few varieties of propulsors, and the new ones probably have composite "hybrid" rotors.

Jacob