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 Post subject: Fitting prop shafts
PostPosted: Fri Sep 07, 2018 7:13 pm 
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Joined: Sat Jan 14, 2017 4:51 pm
Posts: 93
Location: Hill End, NSW, Australia
Hello all,
firstly my apologies if this question has probably already been asked a thousand times.
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I am scratch building a 1/35 scale destroyer and am in the process of buying and fitting prop shafts. What do I need to get the job done. I have seen other scratch built ships with Hull tubes, Stern tubes and then the shaft. I have bought the shafts and tubes from a reputable model shop and they said that was all I need, apart from the A-frames. Just wanted to get a second opinion before I start the resin process. You can see the photos of what I have so far.
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And could someone advise, as the shafts are just over 500mm long am I best to put any other sort of bracing in the middle of the shafts inside the hull, or will the A-frames, resin and then the motors provide enough to stop it vibrating around.
many thanks, Will
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 Post subject: Re: Fitting prop shafts
PostPosted: Fri Sep 07, 2018 8:29 pm 
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Joined: Sat Jan 17, 2009 2:12 pm
Posts: 1958
how much length is sticking out of the hull?


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 Post subject: Re: Fitting prop shafts
PostPosted: Sat Sep 08, 2018 3:20 am 
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Joined: Sat Jan 14, 2017 4:51 pm
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Location: Hill End, NSW, Australia
Hello David,
22cm of the shaft extends outside of the hull where they meet the A-frames and props, so I guess after it has gone through the hull where the resin will hold it in place there will be about 25cm before it meets the motors. Rough guess so far though but its fairly accurate
cheers, Will


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 Post subject: Re: Fitting prop shafts
PostPosted: Sat Sep 08, 2018 4:20 am 
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Joined: Tue Aug 14, 2018 6:05 pm
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Location: Caledonia
That's a very long shaft and I would definitely fit a brace in the middle, you are also going to need a flexible coupling between it and the motor, something like this https://www.ebay.co.uk/itm/Propshaft-Co ... 2624254565 and maybe an oiler for the shaft http://www.modelboatbits.com/OILER-CLAMP-SYSTEM


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 Post subject: Re: Fitting prop shafts
PostPosted: Sat Sep 08, 2018 5:33 am 
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Joined: Mon Jan 15, 2007 12:03 pm
Posts: 164
Location: Plymouth UK
I built a 1/32nd scale Type 42 Destroyer a while back and to deliver the power to the props (5" diameter) I needed 3' long shafts 8mm in diameter. What size props and shaft diameter are you using?

The actual shaft tube was appreciably shorter than the shaft itself and only extended a short distance outside the hull with the rest of the shaft being supported by a P bracket and an A bracket I soldered up from brass strip and tube to give the support for the shaft along its whole length while retaining scale appearance.

Working at this scale involves quite high power levels and I did quite a bit of experimentation with a test tank rig of the motor, reduction gearing and prop on a shorter shaft to get the power train arrangements in the right bracket and in fact had the motors on an adjustable mounting so I could change the gear reduction ratio. Have you done anything equivalent as it is best to make sure your motor is going to be able to drive the prop before fixing the shaft in place?


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 Post subject: Re: Fitting prop shafts
PostPosted: Sat Sep 08, 2018 6:11 am 
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Location: Hill End, NSW, Australia
Thanks cannonball - definitely going to add a flexible coupling and I already have oilers for both shafts. I am thinking bracing cannot hurt - the more the merrier.
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Wow Francis, 1/32 scale, I hope there is a build thread for your destroyer somewhere here, if not I would love to hear about it.
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I am using 8mm shafts and the props are 55mm diameter. Not sure about reduction gearboxes. To be honest I still haven't tested the hull in the water to see how much ballast I will need, which I think will be a lot. How much ballast did you need?. I know I am probably going about this the wrong way but I am trying to match the props and shafts to the plans and will then ballast, and get the right motors to suit, and reduction gearboxes if needed. I am going to float my boat do the ballast and stability test.
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Any advice will be very helpful. cheers, Will


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 Post subject: Re: Fitting prop shafts
PostPosted: Sat Sep 08, 2018 6:54 am 
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Location: Plymouth UK
englishgunner wrote:
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Wow Francis, 1/32 scale, I hope there is a build thread for your destroyer somewhere here, if not I would love to hear about it.

I am using 8mm shafts and the props are 55mm diameter. Not sure about reduction gearboxes. To be honest I still haven't tested the hull in the water to see how much ballast I will need, which I think will be a lot. How much ballast did you need?


No build thread but the design and build were in an article in Marine Modelling magazine back in 2002 which I can forward the text for by pm if wanted.

I would advocate removeable ballast when working at this sort of size as handling the hull will be very cumbersome otherwise. On a scale displacement the model needed to weigh about 300 lbs and this came out at roughly 1/3rd hull and fittings, 1/3rd batteries (the model was built for an endurance record) and 1/3rd ballast which I made up from plastic milk containers filled with gravel.


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 Post subject: Re: Fitting prop shafts
PostPosted: Sat Sep 08, 2018 7:17 am 
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Location: Hill End, NSW, Australia
Yes, please PM the article and all details!.
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Yep I was definitely going to go with removable ballast. I was thinking of using as many batteries as can be fitted to the midsection to provide ballast and then trim fore and aft. I haven't fitted any of my decking yet till that has all been done. I have some 40 x 40 mm steel RHS that I was thinking I could fit in and out of the bow section, then batteries midsection and then more RHS in the stern area (not taking into account the motors and shafts, rudder). Have a good day, I am off to bed,
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Cheers, Will


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 Post subject: Re: Fitting prop shafts
PostPosted: Sat Sep 08, 2018 2:58 pm 
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Joined: Mon Jan 15, 2007 12:03 pm
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Location: Plymouth UK
Message sent but you may have to e-mail back to me so I can send attachments.

Having now looked at your 2.7m V&W build thread, I can see you took things in a different order to me by doing much of the detailed work first before looking at the flotation and propulsion aspects. Could you show some shots of what the hull interior looks like and what sort of motor you intend to use please as that may also affect what would work best?


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 Post subject: Re: Fitting prop shafts
PostPosted: Sat Sep 08, 2018 8:20 pm 
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Joined: Wed Dec 17, 2014 2:10 am
Posts: 156
Location: Australia
The V & W class had 9' 6" propellers. In 1/35th scale the props would be 83mm.


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 Post subject: Re: Fitting prop shafts
PostPosted: Sun Sep 09, 2018 4:02 am 
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Location: Hill End, NSW, Australia
Thanks 508, yes I am using smaller props but they were a quarter of the cost, and both fit underneath quite well. I know, I know, I will probably live to regret but hopefully I can install larger ones later.
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Thanks Francis, I found the cover of the Mag your destroyer was on - very impressive.
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Here are some pics of the stern area. You can see in my thread other stages of the hull. So do I ballast the hull and then work out what motors to use. I will be getting them through "Float a Boat" RC shop in Victoria, Australia.
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I was also thinking I could cut lower into the ribs, within reason, to get the ballast as low as possible.
cheers, Will


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 Post subject: Re: Fitting prop shafts
PostPosted: Sun Sep 09, 2018 5:45 am 
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Location: Hill End, NSW, Australia
I have more pics of the hull interior, and the 40mm RHS steel I was thinking of using for ballast. I was thinking of installing it just above the keel, meaning cutting the frames 40mm wide down to the keel on the centreline. Does that make sense?. Is it best to concentrate the ballast as centrally as possible down the centre line - will it have the same effect as a keel (obviously not as it is higher in the hull), but is that better than spreading the ballast left to right.
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I think it would help in that I could fix the forecastle deck in place and when about to get wet, all I would need to do is slide the right ballasted RHS up the centreline. Hope that makes sense,
cheers, Will


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 Post subject: Re: Fitting prop shafts
PostPosted: Sun Sep 09, 2018 9:26 am 
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Posts: 164
Location: Plymouth UK
Thanks for the pictures Will

For me the whole starting point in getting the model to sit at the right waterline level and with adequate stability starts by knowing what the maximum weight the model can be and how much the main components are going take up of that. The shots of your initial hull work suggest that you have been quite frugal with the added weight for the bare hull which is definitely a good place to me. Have you weighed how much all your work to date takes up in total as I make a V&W typical figure at full displacement (c 1100 tons) in 1/35th scale 25-26kg max?

That will give you a measure of how much you have left for everything else which may well drive future decisions, particularly on battery and motor size to give you some margin for ballast if needed. Personally, I wouldn't use the 40mm RHS steel sections for ballast but rather would use sheet lead offcuts curved so that they lie flat in the bilge areas between the hull frames. The main way to get a level trim fore and aft would be to slide the battery forwards or backwards as required then put some restraining wood strips to seat the batteries there. This will give you the largest weight margin for any problems that come to light.

I have attached a shot of the 1/32nd Gloucester that gives some idea of how I did the shafts - I matched the arrangements on the original ship as much as possible. It does strike me that 500mmshaft length is not going to give you much clearance for full size props at one end and still allow room for motors and/or gears at the other end without angling it much more steeply than the 5 degrees or so that the V&Ws actually used. Having put so much good work into the above water detail, it seems important to follow the same realism for the under water areas!
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