The Ship Model Forum

by **Maarten Sch�nfeld** » Fri Aug 26, 2022 6:32 am

Hi Bonobo,

As far as I can see from these photos it's almost right now, you can best judge for yourself. If one side is lower than the other then maybe add a sliver of plasticard of 0.25 or 0.5 mm (.010 or .020 inch) thickness, and file the excess away. That should do.

Those sponsons start looking alright!

by **Bonobo_Atho** » Fri Aug 26, 2022 5:46 am

Kind of.

The openings are all aligned now but the deck on the port side is a little low. I'm considering how effectively I can fill it without making a major mess. This is all in the second photo which is a bit blurry

by **Maarten Sch�nfeld** » Sat Aug 20, 2022 11:07 am

Nice progress!

Have you solved the unintended upsweep of the quarterdeck?

by **Bonobo_Atho** » Sat Aug 20, 2022 6:07 am

Well works have been very slow lately with work commitments and C19, however an increase in beer rations has seen an increase in productivity. The various sponsons are slowly taking shape.

by **Timmy C** » Tue Jun 14, 2022 4:02 pm

DavidP wrote:Fliger747, I think you mean the Lexington class & Yorktown class not the Essex Class that also had arresting cables near the bow.
https://www.historyonthenet.com/history ... l-aircraft

Nope, here's Yorktown CV-10 taking a TBF over the bow while sailing astern: https://www.navsource.org/archives/02/021019.jpg

Caption: The Yorktown steams full astern to land a TBF Avenger over the bow, July 1943. Though provision for over-the-bow landing was a design requirement, it was rarely practiced and the bow arresting gear was soon eliminated.

by **Fliger747** » Tue Jun 14, 2022 11:10 am

In the good old days turbine powered ships had reversing turbines, usually smaller since high speeds astern weren't usually required. An exception, though the reverse turbines weren't huge, the Essex Class Carriers during WWII had arresting cables arranged on the bow as well as stern such that it would be possible to recover aircraft by steaming astern in the case of aft flight deck damage. I am not sure if this was ever used. The movie Titanic had it's engine room reversing scene filmed aboard the Liberty ship based in San Fransisco with it's Uniflow triple expansion reciprocating steam engine. These as with railroad steam engines stop the pistons and move the valve gear to effect reverse motion. I flew a number of turboprop aircraft with reversible propellers to shorten ground roll. Reversers on turbine jets really only redirected the thrust.

I think? maybe, that the Washington State Ferries have controllable pitch props as the dozens of docking each day would appreciate more instant control.

Keep at your interesting projects! Cheers: Tom

by **NavyShooter** » Tue Jun 14, 2022 10:50 am

Tom,

My time with the RCN saw me sailing on HMCS Gatineau - which had fixed props, moving to IRO and CPF class ships that have CRPP (Continuous Rotation Positive Pitch) control blades.

The ability to switch from full ahead to full astern - without having to stop the shaft and reverse the rotation is a real game changer.

256 RPM with blades at 32 degrees, is full speed ahead. 0-12 knots is basically about 80 RPM or so with the pitch varying to control speed.

(If my memory serves me correctly....)

Brad

by **Fliger747** » Sun Jun 05, 2022 12:30 am

It is amazing that these large machines work as well as they do. Wonders of both design and industrial construction. In addition to balancing the machines moving parts propellers of any sort create considerable turbulence in providing their thrust. For aircraft with multiple engines spacing assists interference, though matching the prop phases (blade position around the circle of progression) is necessary to ameliorate airframe vibration as s speed synchronization to eliminate the "Washing machine Charlie" effect.

With ships the fluid, unlike air, quite easily transmits the pressure waves of the eddies curling off the blades, they are close enough to have interference effects which can change with the advance ratio (ships RPM and speed) such that certain speeds could give vibrations severe enough to mage optical gun laying impossible. Alaska (CB1) had large bracing for the aft main director barbettes for the MK38 director. Unlike controllable pitch aircraft props WWII ships propeller technology changing of pitch to adjust phase is not possible.

Regards: Tom

by **DrPR** » Sat Jun 04, 2022 10:02 pm

Balancing long prop shafts was tricky. They were constructed in several joined sections and supported by several "pillow blocks" with bearing journals. These bearings could be adjusted vertically and horizontally (left/right). The combined shaft, pillow blocks, propellers and hull structure resonated at certain speeds and turned smoothly at others. You might get things balanced to run smoothly at some speeds just to get significant vibrations at other speeds.

On the USS Oklahoma City CLG-5 we had two inboard shafts (aft engine room) 149 feet long and two outboard shafts (forward engine room) 185 feet long. The shafts were machined and balanced to the closest measurable tolerances. The different shafts had different masses and resonances.

My missile warhead magazine was on the second platform between the inboard shaft alleys. At normal cruising speeds there was little vibration. But when we cranked the props up to 350 RPM (32 knots) the whole space vibrated significantly. If you put a penny on the deck it would bounce around.

Phil

by **Fliger747** » Sat Jun 04, 2022 10:42 am

Almost all warships have different length shafting since the engine rooms for each shaft are en echelon. Perhaps an exception might be a small Diesel powered ship which could have both engines abeam each other. The ARL's and LST's were like this.

Sometimes the shaft lengths can be very long. The loss of the Prince of Wales was assisted to damage to a rotating shaft which caused further damage to the shaft alley, allowing flooding deep into the ship.

Keep at it! Tom

by **Bonobo_Atho** » Sat Jun 04, 2022 4:47 am

More progress on the sponsons.

by **Bonobo_Atho** » Sat Jun 04, 2022 4:46 am

I have a new toy... I mean tool... and it has already proven it's worth.

Surprisingly the deck in all of the galleries is at the same height except for that one place at the stern. I have a plan for fixing this now that shouldn't involve any deconstruction.

by **Bonobo_Atho** » Sat Jun 04, 2022 4:42 am

Thank you for the words of encouragement NavyShooter, and the offer wrt the island. I'm currently drawing the island in CAD from the plans and photos I have collected of Melbourne. I'm not in a rush for it just yet as I'm contemplating buying a PLA printer so I can print the island in polystyrene. Not too keen on printing it in resin. I may still hand build it though. But if I fail miserably I'll be sure to make use of your island.

by **Bonobo_Atho** » Fri Jun 03, 2022 6:03 am

I wonder if the vibrations on the Majestic carriers is due to the prop shaft being different lengths???

by **Fliger747** » Thu Jun 02, 2022 1:00 pm

Interesting story about the props. Both the North Carolina and SODAK class battleships had vibration issues during trials resulting in prop changes. The upshot of this was that the Iowa's had pairs of four and five blade props from the get go. A bit strange that only one shaft of the two would be affected?

Best regards: Tom

by **NavyShooter** » Wed Jun 01, 2022 9:04 pm

Having received plans...and spent some time looking at Don Linton's model ( https://www.carrierbuilders.net/element ... php?id=863 ) I have made some additional corrections to my 3D model...I'm not done yet, so I'm not printing yet...but as the days go on, I add more and more detail...and seeing Don's model helped give me some guidance on a few things that I'd missed. If you compare the diagrams...you'll see just how far this has come in a couple of weeks of off and on work.

by **NavyShooter** » Wed Jun 01, 2022 11:18 am

Here's another image from the Canadian War Museum, sadly, it's not higher resolution.

by **NavyShooter** » Wed Jun 01, 2022 11:15 am

There are 2 doors on the port side of her Island - here's a sample photo - looks like I've got the rear door a bit too far back though.

Any other corrections you can see that I should make (seriously asking - I'm looking to make this better!)

Do you have any close-ups that are better? I have some references that show that both of these doors are 'sliding' doors? Any chance you have a picture of them so I can make them look somewhat closer to real?

by **NavyShooter** » Tue May 31, 2022 10:50 am

A fascinating process - I applaud your efforts and perseverance to this build.

I'll offer a couple of points - WRT the props - here's a link to a page about HMCS Bonaventure - she also had a 3 and 4 bladed set of props, but there is a legitimate engineering explanation:

http://www.forposterityssake.ca/Navy/HM ... _CVL22.htm

Apparently, during builder's trials, excessive vibration was noted in the starboard shaft even though it was adequately supported with bearings (plummer blocks) throughout its length. The solution was to fit a four-bladed propeller on the shaft to dampen out over-all shaft harmonics. It worked!

I do have something to offer you in assistance though - I am working on a 1/96 Scale Bonnie. I received the hull/flight deck and island when I bought the project from a friend. I was not thrilled with the island as it came...so while I was 'down for the count' with C-19 a couple of weeks ago, I started on a 3D model of the island. I am (literally right now) printing Version 4 of it on my Filament printer at home, but I have uploaded an earlier version of the design to Thingiverse that you are welcome to download and print if you wish, in case it might save you some effort on your project?

https://www.thingiverse.com/thing:5391778

If you're interested, I can share the latest version (with more detail added as of last night) and upload that if you'd like to use it.

I realize that the Bonnie and the Melbourne were not twins....merely sisters....so there will be some difference.
I'll note, that since I designed it in 1/96 scale, some elements are scaled to print in 1/96...and since I have a 0.4mm nozzle, parts of it are designed to print at 0.4 or 0.8mm thickness, which, if scaled down to 1/350 would not work on a filament printer. It might, however, work on a resin printer since they have a somewhat higher degree of resolution.

by **Bonobo_Atho** » Tue May 31, 2022 12:52 am

Thank you for the advise and words of encouragement

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1/350 HMAS Melbourne R21 (1982)

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