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Author Topic: 1/5 Riva Aquarama...  (Read 27742 times)

DJW

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1/5 Riva Aquarama...
« on: November 09, 2021, 09:05:52 pm »

Hi All


I'm really enjoying the build process of my Amati Riva Aquarama, it's so rewarding to see the classic beauty of the boat emerge from the component parts.  And so starting to consider what comes next, maybe the title of the post gives that away...


I'm learning a lot about the 1/10 scale Aquarama build and quite like the idea of doing it again, improving my implementation in several areas, and taking on the general challenges of scaling up.  I'm thinking that the plans I have can be generally scaled up, with some thought given to materials and hardware.


The 1/10 scale is my first real build for 30 years, so I'd welcome some input as I start to plan out how to approach the project.  I have acquired tools, materials, contacts and techniques that should carry over nicely into the larger version, but would be grateful for comments on some initial planning thoughts.  I have nothing yet in terms of specific materials or hardware, so all up for consideration.


Construction would I think stay quite faithful to the 1/10 build with suitable scaling of materials.


My current build is 860mm loa, and a beam of 270mm at the widest point.  Weight is currently 4.0kg and will end up close to 4.5kg I think.  A doubling of those dimensions would make the new build around 1700mm loa and a beam of 540mm.  First question, how to estimate the target weight...?  It's not a doubling, should I assume around 3x as a guide..? That would make a target weight around 12 - 15kg, is that a reasonable assumption..?


Then the running hardware.  Looking at other builds at this sort of size, a pair of brushless outrunners, say the Overlander / Surpass 5055 model feels about right.  1550w, so around 2hp each, 570kv and can handle up to 24v and have a 65A max rating.  So running them on say 5S lipos would spin them at around 10,000 rpm.  I'm running FrSky and really like the Neuron 40S ESCs on my current build, I'd like to go with the 80S versions on the new build, they handle 80A, 120A burst so seem about right.  An overall 4hp seems a lot to me... But I'd be happy to restrict the top end power or play with the LiPo voltage rather than end up with anything under powered.


I'm thinking 5mm exposed propshafts, I'll make up the tubes and P brackets.  No idea what props these motors would optimally drive...  Any comments gratefully received.  I'd want to use Prop Shop units, so maybe I should ask Simon what he thinks once I've arrived at the correct power and RPM targets.


What do we think...?
David.

ChrisF

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Re: 1/5 Riva Aquarama...
« Reply #1 on: November 09, 2021, 09:54:45 pm »

Hi David


My first thoughts were if I'd made such a lovely build already of a Riva I wouldn't want to do another one, but that's just me!


But having thought some more I can see where you're coming from. You've learnt a great deal from your first build and know where you want to do things differently. Having already done it is really the only way to highlight "improvements" though I think most of us would be more than happy with your 1:10 version.


Your reasoning on upsizing all sounds pretty good to me. Have you made a list of things you want to do differently and possible ways of achieving them? One thing I can think of is that reducing weight can be considered at the design stage rather than during the build.


Obviously UKMike will as usual be an excellent source of information and be able to offer constructive advice given his experience of building a bigger Riva.


Again, I will look forward to the build.


Chris
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C-3PO

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Re: 1/5 Riva Aquarama...
« Reply #2 on: November 09, 2021, 10:28:03 pm »

You may be able to extract some information from this site. I am not certain if they are still active.

http://www.exclusive-shipmodel-shop.de/Riva-Aquarama

or

http://classicrunabouts.de/


and their FB page https://www.facebook.com/BAE-Schiffsmodellbau-322562321265360/photos/?ref=page_internal

and also https://modellboote-mahagoni.de/riva.html

or

https://modellboote-mahagoni.de/riva2.html


They quote 1/6 as being 137 cm x  43 cm - they produced some awesome fittings ($$$)

I have in my fleet one of the models featured in their FB pages "ROCKET" - a beauty



Regards
C-3PO

 
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ChrisF

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Re: 1/5 Riva Aquarama...
« Reply #3 on: November 09, 2021, 10:45:16 pm »

Very nice!

Had a look at your first link - you could soon tot up some serious expense!

Chris
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DJW

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Re: 1/5 Riva Aquarama...
« Reply #4 on: November 10, 2021, 09:39:07 am »

Morning Both


Thanks for the comments, some great information in those links 3PO, I hadn't seen them before...


@Chris, you're right.  I think that building the same boat again allows the benefit of hindsight, how it should have been done in the first place.  As you point out, weight is a major one of those things.  I now know that so much can be taken out of the frames, a lot of the wood is overkill once the planks are on and the hull shape achieved. The bow is a particular issue as its pretty much inaccessible once the first frames are installed. I know that a better engine / shaft arrangement can be arrived at that runs quieter. Most of all I have just run out of room on the 1/10th everything is constrained by the space available. If I want to take out the Rx, almost everything else has to come out first.  I enjoy the electronics side, I know I can improve the sound system.  I'd like to integrate the vapour system in the 1/10th, but have run out of room...


And in terms of cost...  It would be a lengthy project I think, so a spread cost.  And I've probably spent 3x more on tools than the cost of the 1/10 Riva kit, so would be good to give the tools a bit of a workout..!  And thinking about it, I've binned a lot of the kit fittings to make up my own, practice for the next one...  UKMike has indeed led the way with techniques and fabricating Aquarama hardware.


@C-3PO, the links to the German sites are very interesting indeed, some techniques there that I've not seen.  Interesting discussion of materials and running hardware used. I like the method of creating the padding effect on the upholstery, will be looking at that for the 1/10 upholstery.  Interesting motor mounts too.


And love the 'Rocket'..!


Best regards
David.

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Re: 1/5 Riva Aquarama...
« Reply #5 on: November 10, 2021, 10:07:11 am »

Hi David,

I will follow your "large scale" Aquarama project with interest.

Somewhere I have plans for a large scale model - I will dig them out and post an update.

My Rocket is currently in dry dock undergoing some upgrades and an installation of a "full on" sound system :)



Regards
C-3PO
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tonyH

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Re: 1/5 Riva Aquarama...
« Reply #6 on: November 10, 2021, 10:46:17 am »

I'd check on your weight calculation. It's based on the cube of the scale so if the 1/1 Riva weighs 4000kg, then the 1/10 model comes in at 4000/10x10x10 = 4kg BUT at 1/5 it's 4000/5x5x5 = 32kg. ok2
The general dry weight of the real Aquarama Riva is about 3000kg, so it might be worth aiming at 3000/5x5x5 = 24kg
Have fun!Tony
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mrlownotes

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Re: 1/5 Riva Aquarama...
« Reply #7 on: November 10, 2021, 12:21:17 pm »

If you would rather skip the hull build then MHZ have a 1485mm Riva just waiting for a fitting out and paint job :-


https://www.mhz-powerboats.com/shop/en/hulls/mono-hulls/l-1800-mm/257/riva-modellboat-1485mm-58-46-gfk?c=56
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DJW

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Re: 1/5 Riva Aquarama...
« Reply #8 on: November 10, 2021, 07:55:45 pm »

Evening All


More very interesting points raised. I didn't realise that was the calculation for scale weight. 24kg sounds pretty heavy to me, but I guess it's important to try not to go over it, then if it needs ballast to get the correct waterline. Well that's fine.


The GRP version of the hull is interesting,  and at 1.4m it's substantial. But I think the Aquarama is all about the woodwork, and finish. I enjoyed the hull taking shape from it's component parts...


Regards to all.
David.

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Re: 1/5 Riva Aquarama...
« Reply #9 on: November 11, 2021, 10:19:58 am »

At least you're going in the right direction David! It can get a bit scary if you're going the other way so, using the same numbers, 1/20 gives a displacement of 4000 / 20x20x20 = 0.5Kg  {:-{
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Re: 1/5 Riva Aquarama...
« Reply #10 on: November 11, 2021, 01:46:55 pm »

I think and feel so fundamentally about the way of thinking though I'm not sure... {:-{ ?
4kgx1/2x1/2x1/2=0.5kg...1/20 scale
4kgx2x2x2=32kg.............1/5 scale
If 1/10 model is 4kg....??? {:-{ ?
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Re: 1/5 Riva Aquarama...
« Reply #11 on: November 11, 2021, 02:17:45 pm »

If the actual boat weighs 4 metric tons i.e. 4000 Kg, then if the scale is 1:10 the target weight for the model should be 4000 divided by 10x10x10 i.e. 4000/1000 = 4KgIf the scale is 1:5 then the target weight should be 4000 Kg divided by 5x5x5 i.e.4000/125 = 32KgIf the scale is 1:20 then the target weight should be 4000Kg divided by 20x20x20 i.e. 4000/8000 = 0.5Kg
If you're changing scales, then I find it's best to work back to the actual weight of the boat because it's less prone to error. You can work back, of course, but it's always going to be working with the cube  so going from 1:20 to 1:10 you're doubling the scale so in this case your target weight is 0.5 x (2x2x2) = 0.5x8 = 4Kg 0r from 1:10 to 1:5 you're doubling again so it's 4 x (2x2x2) = 4x8 = 32Kg
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DJW

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Re: 1/5 Riva Aquarama...
« Reply #12 on: December 02, 2021, 02:38:44 pm »

Afternoon All


Having realised there's more to scaling than I'd initially appreciated, I've taken on board the comments with respect to weight and done some more digging.  As a sanity check I'd appreciate comments on the following approximations for scale speed and power.


I'm running same calculations for my 1/10 build of the Aquarama as a check that the right numbers come out, which generally they seem to.


Firstly Speed.  I've looked at two approaches, what the scale speed should be, and then what it would take in terms of propeller pitch and shaft RPM to get to that kind of speed.


I saw this scale speed formula in March 2021 Model Boats, so for 1/10 its:





And my current 1/10 build is set up like this:





So that's a scale speed of 23.4km/h and a real world that's at best 20.86, but a bit less with some slip.  And that feels about right, I'll get some hard numbers from the GPS on next outing...


For the 1/5 same calculations look like this:










So that's a scale speed of 33 km/h, and a combination of shaft speed and pitch that gets close to 33 km/h too, depending on real world slip...


I worked on a ratio of 1.2 for pitch to diameter on the prop which I think is quit conservative in terms of motor loading.


And then on a second related point, what power would one anticipate is needed to get to the scale speed, given scale size and weight, and to turn that size of prop at that shaft speed...


Seems the power calculation is quite straightforward and involves cubes again, so firstly for the 1/10th build.  Its the full size power in HP (700), divided by the scale cubed (10x10x10 or 1000), so that's 0.7hp which is about 520 watts.  My build actually has 2 x 340w (so 680w in total) motors, which on the face of it would appear to be slightly overpowered.  I think they reach max rpm with ease, so basically aren't fully loaded and could take courser pitch props if I felt the need, which I don't.


Same calculation with the 1/5th goes like this. Full size power (700), divided by the scale cubed (5x5x5 or 125), and that's 5.6hp...  Which is just over 4,100 watts.  So that implies 2 x 2,000w ish motors are required to reach scale speed of 33 km/h.


And my feeling right now is A) that's a lot of power, and B) I think a 1/5th scale can be built at a lower weight than the 'scale' 32kg allowance. And that weight saving can be trade off against the predicted power requirement.  So I'm inclined to look at 2 x 1,600 w motors and accept a real world speed a shade lower than true scale.  But still quite perky I think.


Does this all sound realistic..?


Regards to all.
David.

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Re: 1/5 Riva Aquarama...
« Reply #13 on: December 02, 2021, 04:51:07 pm »

All looks good to me David. Yes, the power for the 1:5 build does seem a lot but the faster you go the more power you need and I think that your approach to accept a lower top speed using less power is sensible, and I wouldn't be surprised if the top speed isn't far off in reality.

How often are full sized boats run at top speed anyway and 700hp is a lot! I bet that "even" with 500hp it would go well!

And you have the advantage of your passengers weighing a lot less pro rota!

As long as it gets onto the plane easily and is quite brisk it should all be good.

Chris
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DJW

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Re: 1/5 Riva Aquarama...
« Reply #14 on: December 02, 2021, 05:19:00 pm »

Hi Chris


Thanks, and agreed re top end speed. Its proving interesting to scope out a project like this.  Just trying to get all the main components in the right ballpark in terms of functionality, but then also establishing what the financial outlay may need to be...


Best regards
David.

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Re: 1/5 Riva Aquarama...
« Reply #15 on: December 07, 2021, 11:49:48 am »

Well the DPD guy has just delivered a pair of these bad boys from Overlander...








Decided to go with the Overlander brand versions as I had great tech support from them earlier this year when they sent out test ESCs to troubleshoot problems I was having.


Going to need to build a hull to put them in now... 


I wanted the motors early so I can start looking at building the motor mounts, so I know what mods to make to the hull frames when the time comes. 


Best regards
David.


(Just over 2hp each..! But I think the reference to 16 inch props is a bit optimistic...  %) [size=78%] )[/size]


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Re: 1/5 Riva Aquarama...
« Reply #16 on: December 07, 2021, 11:55:46 am »

I think they mean a 16 inch airplane prop  :-))
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DJW

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Re: 1/5 Riva Aquarama...
« Reply #17 on: December 07, 2021, 12:04:54 pm »

Hey Russell


I think you might be right..!


David.

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Re: 1/5 Riva Aquarama...
« Reply #18 on: December 07, 2021, 02:24:25 pm »

Nice David.

I use Overlander in all my builds. The biggest I've gone upto though is a 42 diameter in my Swordsman. Those really are bad boys!


The kv is pretty low, will you be gearing them up to give sufficient revs?

Chris
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Re: 1/5 Riva Aquarama...
« Reply #19 on: December 07, 2021, 04:35:42 pm »

Will you need the revs? If you end up close to the 60lb weight to get down to the theoretical waterline wouldn't the torque be more important, after all with a pair of coarse 2.5 inch handed props and potentially 7000 revs.........?
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ChrisF

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Re: 1/5 Riva Aquarama...
« Reply #20 on: December 07, 2021, 05:33:05 pm »

Yeah, I usually reckon on around 10k. rpm for good planing performance but that's with normal sized boats!  :-)


With bigger, coarser props the required performance could well be achieved. Obviously 6S will be required to give 7k. rather than 8S for 10k. without gearing.


What revs were you achieving with the 1:10 David out of interest?


Chris
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Re: 1/5 Riva Aquarama...
« Reply #21 on: December 07, 2021, 07:31:31 pm »

At this stage I'm thinking that I'd rather prop up for the 7k rpm / 6S configuration.  I think a conversation with Simon at the Prop Shop would be in order before making decisions.  I'd rather have the power delivered at lower rpm and use the torque of these motors, I've been looking at 8,000mAh 6S Turnigy graphene lipos. I guess the option would remain to go for 8S if the revs just aren't there... But ideally not.  No gearing planned, but I do want to look at isolating the motors, so will be looking at mounting options.


The 1/10 build motors are spinning at 12k at full speed, and drawing less than 10A when doing that during testing, so not fully loaded. (Say 12v at 10A gives 120w, they are 340w motors.) That current might go up as the final weight goes up and I have set of coarser pitch props to try.  These motors are on 3:2 reduction gearing (belts) so shafts are running at 8k.



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Re: 1/5 Riva Aquarama...
« Reply #22 on: December 07, 2021, 08:14:41 pm »

Part of the trouble is that, apart from the Lambo powered monsters, the standard and apparently unreliable Riva motors were petrol but they were often replaced with diesels, so the power profiles were totally different. The Yanmar diesels were rated to 3800rpm it seems but what was the gearing? If it was 2:1 then you're spot on. The Riva Crusader 270hp, for example, was allegedly a small-block Chevy, some of which used 1.9:1 gearing which revved to????It's an interesting problem you're facing and I suppose you'll only find out whether it's a gentlemans' runabout or a cads' speedster when you first sail it!
Nice one David :-))
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Re: 1/5 Riva Aquarama...
« Reply #23 on: December 07, 2021, 09:09:33 pm »

......"isolating the motors" ...... David, if these T5065/08 were designed primarily for aero applications, it may be worth understanding how or what type of mounting is used in these cases

Do these [non brushed] motors have absolutely equal characteristics with alternate [or opposite] rotation?.....do these motors have an internal thrust load bearing? 

To have 2 x 2HP acting as gyros <*< , may need absolute security of mounting and let the aero frame absorb the effects, so you could consider a similar concept %)

The other question is how to harness the near-instantaneous torque of a 1600W motor on a 6.0 diameter shaft, both at the motor, and also the propeller.....[tapered bushes {courtesy of George - ooyah/2} come into mind here, although I have not seen them applied to miniature electric applications ]

Derek
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Re: 1/5 Riva Aquarama...
« Reply #24 on: December 08, 2021, 04:19:27 am »


David........following and attached is detail from Translock........


Stainless steel M6 bore tapered locking bushes.......if you go back to the Minilock TRMINI6x16 [carbon steel] shows transmission torque values


Two of these back to back as a solid attachment between the motor & propeller shaft, with a 3rd tapered bush in the hub of the propeller  %)


https://www.transdev.co.uk/hardware/bushes/translock-bushes/translock-stainless-steel-bushes/


Derek
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