Author Topic: WWII USN Sea Mule  (Read 1195 times)

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sea monkey

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WWII USN Sea Mule
« on: January 15, 2020, 12:12:40 »
Activity has been very light on the site recently, hopefully a few members might start some new projects in the new year.
In the meantime here's something to whet your appetite. A little background first:

Immediately after Pearl Harbour the British bases in Hong Kong, Singapore and Malaysia, and the Dutch ones throughout Indonesia. then the Philipines, had fallen to the Japanese Army. The Australian bases in New Guinea, and the Solomons, and the NZ ones in Samoa, Fiji, Tonga and the Cook Islands were seriously understrength and under-manned as most Aus and NZ Army, Airforce and Navy personnel had been fighting in Europe since 1939. Some of the more remote NZ Pacific stations had been reduced to weather stations and listening posts only. One island in the Gilbert & Ellis Islands only had 14 Post Office radio staff to help protect it. They didn’t do too well against the full force of IJA. All beheaded.

There are more than 35,000 islands in the Pacific, Indonesia and the Philipines and as the US High Command planned its island-hopping strategy to move across the Pacific it realised that it would need dozens, maybe hundreds of forward bases and depots in tiny far-flung island spread right across the ocean.

Some of those places already had very basic, small facilities but most of the islands had either nothing of any use or would be badly war damaged. Each USN forward base would need to have port facilities that could handle an instant influx of ships, cargo, fuel and people. The ‘Mulberry’ style harbours that were to be used in D Day wouldn’t be any use because of the vast distances to be transported. The USN would have to bring everything they needed with them.

One thing they would need was tugs – and plenty of them. Major seagoing vessels would still require a conventional tugboat like a YTL or a YTB, but many of the operations of the Army Transportation Corps could be performed by smaller vessels: HUTs (Harbour Utility Tug). They needed tugs that could be quickly and easily mass produced, easily transported, simple to use, and cheap.

The answer, just like the Jeep, and the Marston Mat, was a design and engineering stoke of genius: the Sea Mule.



sea monkey

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Re: WWII USN Sea Mule
« Reply #1 on: January 15, 2020, 12:20:22 »
Rather than building a traditional boat, the Sea Mule was really four pontoons bolted together to form a motorised barge.The two stern pontoons each housed a Chrysler Royal Marine Straight 6 (M8) petrol engine, and the two forward pontoons each held a fuel tank of about 700 gallons. No pilot house, or any kind of protection, was provided. A basic console for the wheel and throttles was on the deck, with a rudimentary safety rail. The Sea Mule was a 41ft long and 14ft wide. Not at all good looking, but perfect for its role – robust, effective, cheap and simple to use. They could easily be transported in their crates or assembled, by road, rail or as deck cargo.

The pre-fabricated mini tug came in 4 crates and could be assembled by its crew of 3 in a couple of days, using only the tools included, and a gas welding set. I’ve attached the assembly instructions that came with the components. As you can see – assembly was very simple and could be handled with a very basic level of skill and equipment. The assembly instructions are only 42 pages and much easier to follow than anything from Ikea.
« Last Edit: January 15, 2020, 12:23:03 by sea monkey »

sea monkey

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Re: WWII USN Sea Mule
« Reply #2 on: January 15, 2020, 12:27:57 »
The tug components were built by Chrysler in Detroit, and Ingalls Iron Works in Birmingham, Alabama to a pretty standard Bureau of Shipping template. The engines all came from Chrysler. The tractor units could also be used individually and bolted onto a barge, although without a barge attached they would have been very unstable.

des

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Re: WWII USN Sea Mule
« Reply #3 on: January 15, 2020, 12:50:02 »
Hi Steve - happy New Year to you.

Are you looking at building one of these things?  It'll take you longer than it took to build the real thing.  You really do like the unusual and ugly looking things, don't you.

I also was thinking that the forum needed to be woken up after the Christmas slumber.  But I am still endlessly filling, rubbing back, applying primer, inspecting, and repeat - and repeat - and repeat for my styrene tug hull.  Hopefully by this weekend I'll get a couple of shots.

Des.

tugboyben

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Re: WWII USN Sea Mule
« Reply #4 on: January 16, 2020, 03:56:49 »
Hi Steve

Ill be watching very interesting build

Jason
kirkleesmodelboatclub

sea monkey

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Re: WWII USN Sea Mule
« Reply #5 on: January 18, 2020, 16:06:02 »
Thanks, Jason.

Yes Des, 1/50 display only. After seeing your work on the styrene hull, I thought that I might try this one all in styrene.

I like your comment about taking longer to build it than a real one, so to add a bit of a challenge for myself, I'll try to build this one from scratch in 2 days. I'll see if I can do it in 48 hours at the bench. Not all in one hit – I wouldn't want to be using a scalpel after 47 hours non-stop work, I'll limit the total build time to 48 hours. That's a couple of hours a night for 3 weeks. Should be do-able. Nothing like a deadline to focus the mind.

It's a public holiday tomorrow so that will be a good time to get started. I think I pretty much have all of the materials that I'll need. Better check the styrene cement supplies.

sea monkey

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Re: WWII USN Sea Mule
« Reply #6 on: January 20, 2020, 14:45:33 »
A little more background info:

They were designed with no concession to style at all. However, that has some appeal in itself – all function over form. – a hard working machine in a tough environment. A friend of mine did his National Service driving a $5million German tank. He said that his four 19-year old crew members spent their whole 12 months trying to ger it to do things it was never supposed to do and pushing it to its breaking point. I imaging that was the sort of life the Sea Mules had – 12 cylinders, 1400 gallons of gas and a crew of 19 year olds – what could possible go wrong?



« Last Edit: January 20, 2020, 14:49:21 by sea monkey »

sea monkey

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Re: WWII USN Sea Mule
« Reply #7 on: January 20, 2020, 14:47:55 »
Thousands of Sea Mules were delivered (I read somewhere: 8000 but I don’t know if this is correct) and used throughout the Pacific and Europe but only a few still survive. After the war some more up-market versions were made for the US and export markets, with a few added luxuries like wheelhouses, and even accommodation.


sea monkey

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Re: WWII USN Sea Mule
« Reply #8 on: January 21, 2020, 11:26:57 »
Before I get started on the model I should say that for a design that had thousands made it is very hard to find any information or reference about them. The once mighty Sea Mule – just like the Dodo and the Passenger Pigeon, has just disappeared and has almost been forgotten. I have however managed to find a very basic GA and enough photos make a model.

Sea Mule design varied between the main US manufacturers so a Chrysler Sea Mule was a little different to an Ingrams one, and they had numerous developments and variations as the war went on. I plan to base my model on the Chrysler version that was produced in Auckland, in 1943. Several local boat yards made them for the USN, and this particular boat came from Mason Bros. of Mechanic’s Bay, Auckland. They made 75 in total, along with quite a few YTLs and workboats.

The pictures show some USN workboats being launched at Masons' yard, and one of the YTL being launched.


sea monkey

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Re: WWII USN Sea Mule
« Reply #9 on: January 21, 2020, 11:28:49 »
As usual this will be 1/50 display only.

Any info or insights you can offer – fire away...

The GA I have is a 1946 Ingalls version which is a bit different to the versions produced in NZ. Using some photos and the GA as a basis I was able to draw up some plans for an earlier 1943 Chrysler model. This version is much more basic than the 1946 version, and a lot cooler, I think. It’s the one featured in the diagrams in the first post. Unlike the later versions it has a central steering console, 2 very raised engine room hatches/intakes, and exposed radiators and steering gear.

Usually I make my hulls and superstructure from laser cut ply, it’s very easy, forgiving and predictable. This time I’ll try making the hull from hand cut styrene because I bought a lot of styrene at a great discounted rate about 18 months ago and I’ve got plenty of it left. The Sea Mule is all straight lines and 90º angles so it should be perfect for styrene construction. I like working with styrene but haven’t made a hull with it for over 20 years. I generally dont trust it in direct sunlight and have had a couple of disasters in the past with unpainted styrene left too close to a window. That was years ago and hopefully I’m now older and wiser – touch wood. To be on the safe side I’ll brace everything pretty thoroughly and keep the curtains drawn.

sea monkey

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Re: WWII USN Sea Mule
« Reply #10 on: January 21, 2020, 11:31:38 »
So, on with the build...

I spent a couple of hours over the weekend sorting through my reference and figuring out the build process. Sometimes the build process isn't as straightforward as first imagined. R&D doesn't count in the 48 hours.

First thing here was to form the basic carcass of the hull. This is all 1.5mm styrene with some balsa blocks for spacing and bracing. A few gaps need filling but nothing too bad.

That was 3 hours gone.

des

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Re: WWII USN Sea Mule
« Reply #11 on: January 21, 2020, 13:00:44 »
Hi Steve

You've mentioned a couple of times now about issues with syrene hulls when exposed to direct sunlight.  My hull has gone through several 42+C days now (probably up to 48C in my shed - I don't go there on those days) without any problems;  but admittedly not in direct sunlight.

The difference could be in the method of construction - I have frames every 40 mm which keeps everything nice and straight.  On the other hand, for a boxy display model you've probably got only minimal internal framing, and rely more on reinforcing joints to keep things straight - right?

Des.
« Last Edit: January 22, 2020, 12:10:10 by des »

sea monkey

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Re: WWII USN Sea Mule
« Reply #12 on: January 22, 2020, 12:28:22 »
Direct sunlight is the problem. Strangely enough we're not getting too much of that this summer. It's been overcast for about 2 months.
I moved my workroom which had all day sun to the other side of the house. Had the same issue as your shed – too hot. Can't leave the windows open as the famous Wellington wind would wreak havoc on any bits of paper etc,

sea monkey

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Re: WWII USN Sea Mule
« Reply #13 on: January 28, 2020, 20:45:52 »
Had a bit more time over the weekend and started adding details to the hull carcass.

Firstly a chequer plate steel deck – the gap is for planking in the crew working area.

Then the side 'bumpers'. These were stamped out of the hull steel to strengthen and stiffen the large area of thin steel.

Just when I thought everything was going according to plan, the guard rail protecting the steering gear caused a few problems.
Ii is a semi-circular section of channel steel and I had planned to make it from a sandwich of styrene/brass/styrene to give the unsupported shape some rigidity. The brass acts like a backbone and holds the styrene in shape. It's a method I've used before.

This time nothing went to plan. The styrene is CA glued onto the brass, the styrene is attached to the hull with styrene cement – in theory.
For some reason the combination of styrene cement and CA glue reacted badly and the styrene channel snapped for no apparent reason. This happened on 3 attempts . Finally I got it to work and then managed to snap one off the hull with a bit of rough handling.

Eventually I decided to use 2 part epoxy instead of CA glue and started again. I usually have no problems with CA glue and didn't even have any epoxy in the house. it's all sorted out now but that chewed up another 2 frustrating hours.
« Last Edit: January 28, 2020, 20:53:01 by sea monkey »

sea monkey

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Re: WWII USN Sea Mule
« Reply #14 on: January 28, 2020, 20:51:10 »
The deflector at the rear of the bow pontoons was made from planks bolted onto bracing struts. Easily made from styrene. The bolts are hexagonal styrene rod – but who can tell at that size?

There are beams under the deck to hold the section of deck planking, and beneath them is I beam bracing for the tow bitt footing.
3 hours for all that.