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Author Topic: 1:12 BPB Whaleback advice requested please  (Read 1078 times)

Big E

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1:12 BPB Whaleback advice requested please
« on: March 19, 2018, 08:17:19 PM »

Well, here we go, I've decided to build a 1:12 RAF 63' rescue launch, the wonderful Whaleback. It's been a long time since my last model (remember Hill two-valve receivers? Yes, that long!).  It was going to be a 34" Crash Tender kit until I called in and talked to Paul at P&S Models in York for some advice on motors. On the same weekend I also went to the Elvington Air Museum and saw a Whaleback model in one of their displays.  That settled it, why build a kit at 46" when you can scratch build something much bigger and with the added bonus of a yellow superstructure? Sold.
So, for the last couple of weeks I've been gathering info and reading everything I could find on British Power Boats.  I found Model Boat Mayhem and John WE (Bluebird's) brilliant article on building a Whaleback, then onto Martin13 in Oz and finally Todd Smith in the US. Poor old Todd has been answering my queries ever since!  The more I look, the more people offer help, information and suppliers.
I have a set of Pritchard plans on the way and I've now amassed quite a lot of photos (and a cd) so I am now almost at the point of no return and committing myself to cutting wood.
The reason for this note is to beg some advice please. My knowledge of electric power stopped at Taycol Supermarine specials, after playing with Taplin Twins and an impossible to start ED Racer.  I know the latest developments in Brushless offer amazing performance, but they have quite a few drawbacks for a novice, especially one who is a Mechanical Engineer and tends to treat electronics as black magic. I can cope with brushed motors, just about, so let's stick with those for the time being.
For a 63" high speed launch model I am proposing three CEM 900. Obviously I want it to plane, hence plenty of oomph. What are fellow members opinions of this choice please?  Overkill, or about right?
John WE alerted me to the problems of steering with three right hand props.  Do you think that a pair of out-turning props on the outer shafts and a right hand on the centre shaft, combined with preferential rudder control on the three rudders (Ackerman steering principle, like a car, sorry, don't know the correct nautical term) and perhaps an idling centre drive on turns, would overcome this?
John, thanks for giving me the inspiration to double diagonal plank, I just hope I can succeed.
Martin, thanks for your input via your article and Todd, just when I thought some models displayed amazing detail, you came along and blew my socks off.  Your turret frames are a work of art.
Final question: is a 1:12 scale model a bit over the top? We shall see!
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essexbill

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Re: 1:12 BPB Whaleback advice requested please
« Reply #1 on: April 03, 2018, 06:33:22 PM »

I have always liked the whaleback, I did consider the Deans Marine a few years ago but, to do the boat justice the hull should be wood.
Looking forward to following your build.

Good luck 
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raflaunches

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Re: 1:12 BPB Whaleback advice requested please
« Reply #2 on: April 03, 2018, 07:16:55 PM »

I don't think a 1/12 scale launch is too big!!!


My Dad and I have built four 1/12th scale launches used by the RAF Marine Craft Branch/Section but not a Whaleback. We have built a Walton 65ft ASRL prototype, a 60ft General Purpose Pinnace, a Thornycroft 62ft Fast Motor Boat, and a BPB 40ft Armoured Target Boat.
They are brilliant models in this scale as they behave much like the real boats but you will end up making a lot of the fittings yourself.
I look forward to your build.
For our source of power we use 12v Bosch car heater motors and 12v 7 or 10amp/hr SLA batteries, we also use prop shop (now Protean Design) cast Bronze propellers. On our three propellered model (Pinnace) we have used two RH and one LH props to keep the model in a straight line but he turns better in one direction obviously. Our LH and centre prop we driven by a belt drive from SHG Marine, it has worked really well and is still going strong 12 years later. Its a system we are so happy with that with my current project HMS Invincible I have two drive motors driving four propellers via a belt drive system.
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Nordlys

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Re: 1:12 BPB Whaleback advice requested please
« Reply #3 on: April 03, 2018, 07:54:11 PM »

Big E ---- My collection of boats is made up almost entirely of RAF launches  - my biggest boat being the Range Safety launch at 46".
Personally I wouldn't choose anything larger than that because of weight and ease of transporting.
Just my opinion. -  but a great boat to build for sure.
Nordlys.
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Big E

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Re: 1:12 BPB Whaleback advice requested please
« Reply #4 on: April 03, 2018, 08:32:13 PM »

Well, firstly thanks to everyone who has offered advice on suitable motors for the Whaleback. I'm still not decided on brushed v brushless, although I would prefer brushed (being very old and staid!) but I will persevere and let you know what happens over what might prove to be a very long build!
Thanks to RAFLAUNCHES for encouragement with 1:12 scale, your collection sounds wonderful. You mention Bosch heater motors and also gearboxes, but you don't mention prop sizes or shaft revs. Are you pulling huge torque on massive props or spinning like the proverbial? Also, do your boats (sorry, ships or launches. Submarines are boats, everything else is a target! I learned this working on nuclear subs.)......where was I.......do your models plane?
Thanks also to NORDLYS and I am tempted to agree, 63" models are perhaps a tad on the large side, but it's too late now, I've bought the wood, the equivalent of a mature forest, and I've built the board, so I feel committed. Hindsight is a wonderful thing.
STAVROS didn't beat about the bush - brushless and at least 15000 revs. Thanks for that, I am looking at the details of controllers etc. What do you think of Turnigy motors and marine ESCs?
Ah well, back to the garage and marking out the 17 frames.  Thanks again everybody, keep it coming.
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raflaunches

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Re: 1:12 BPB Whaleback advice requested please
« Reply #5 on: April 03, 2018, 08:50:23 PM »

Yes they are certainly impressive models, we did once consider making a 68ft RTTL but it was going to be huge. Thatís why we didnít go past the 65ft vessels. To answer your questions about my models, the two fast launches (65ft and 62ft) do plane very well, they donít stick out the water balancing on props and the rear third of the hull but Iíd say the forward third can get some air!
Iíll have to ask my Dad which specification of prop we used but I think that they are some thing like 50-55mm diameter three bladed props. The Bosche motors arenít revvy but produce a stunning amount of torque. I have no experience at the moment of brushless motors but there are plenty of members on the forum who know their stuff and are better suited to answer anything to do with them. My advice if you want to get your boat to plane nicely is to put the weight ie the motors and batteries where the real engines and fuel tanks were fitted or vice versa as the engines were often driving v-drive gearboxes backwards. For example the engine drive shaft going forwards to a gearbox which turns the shaft backwards out of the back of the vessel. Very complicated in model form! We have a 1/12 55ft Coastal Motor Torpedo Boat which relied on balance to get to plane- type in Coastal Motor Torpedo Boats into the forum search engine and youíll find my Dadís build.
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malcolmfrary

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Re: 1:12 BPB Whaleback advice requested please
« Reply #6 on: April 04, 2018, 09:52:01 AM »

Just looking at numbers, the model has a target maximum weight of about 25 lb.  A big boat needs a lot to shove it along at the right speed.
The props will need to turn at about 8000 rpm, but Stavros' 15000 is probably better.  Smaller props and an easier life for the motors, which  will need to pull about 1KW between them, or about 350 watt each ( = 1/2 HP ).  Engines are quoted on power out at the shaft - electric motors get quoted on electric power in, so there tends to be a discrepancy to allow for the inefficiency of converting from electric to mechanical energy.  A heavily loaded motor will move out of its happy zone and, while providing power, will also convert more electric energy into heat rather than into turning force.
I'm not that well up on brushless, but I suspect that there is something out there that will do the job when allied to the right ESCs.  The  CEM 900 motors (nominally 60W on 12 volts) would do a good job of powering a tug, but this isn't a tug.  Getting performance means adding lightness.  SLA batteries were never up to the job of giving performance and run time, being heavy and inclined to warp their plates if heavily overworked for any length of time.  They only got into general use because they were the only things available back then.  LiFe or LiPo offer much better stored power for the same weight, and, because they will be operating within what they were designed to do, will last longer without damaging themselves.
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John W E

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Re: 1:12 BPB Whaleback advice requested please
« Reply #7 on: April 04, 2018, 02:40:36 PM »


Hi ya there Big E - I have been reading / watching your posts with great interest.


May I offer three bits of advice :-) first of all build your hull, building it as light as you possibly can.   Look at the build which I did for the Whaleback and notice all the lightening holes which I put in - in all of the frames, the keel and all major structures.   


When I build a hull for speed, I always think of Barnes Wallace and the way he designed the Wellington Bomber - the way the superstructure and the wings are built.   Have a look at Barnes Wallace's design to see how you may incorporate a similar design into your build.   Remember, keep the hull light.   Next thing, think about the motors after you have completed your hull  :-))   the less weight in the hull, the less power the motors will need to provide to get it up onto the plane.


Thirdly, think of the power supply - I, myself, would go for NiCad batteries:


Malcolm, your ballpark figure of 25 lbs may be a little on the heavy side  :-) that is equivalent to The Leeds Castle which had 3 x 24 amp batteries - it took 2 of us to lift that model into the water.    I would be looking at something of all up weight of something like 4 - 5 lb which is easily achievable if you do it right.


John
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Nordlys

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Re: 1:12 BPB Whaleback advice requested please
« Reply #8 on: April 04, 2018, 03:53:46 PM »

John,  Its not often I've been inclined to weigh my models but today I weighed my 46" Range Safety Launch out of interest!
All up weight excluding batteries was approx 14lbs on the bathroom scales!
I thought it would be more - it is an awkward lift at the waters edge for me - but do-able.
Nordlys.
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John W E

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Re: 1:12 BPB Whaleback advice requested please
« Reply #9 on: April 04, 2018, 06:48:14 PM »


Hi Nordlys


Problem with some builders they may build their models as though they are going to knock the doors down of Fort Knox with their Model  ok2 maybe over-engineered in some cases.  In a way, that adds unnecessary weight to a model.  It shouldn't be the case today with the materials available nowadays.


I think model boat people would benefit from a course of model aircraft building - but - hey ho - everyone to their own.


I have just weighed my model of the RTTL on the bathroom scales - in this model she has an ACTion sound unit, amplifier, 2.5 inch speaker, as well as the normal ACTion speed controllers - she also carries 2 x 400 NiCad's for powering the motors - plus a 1500 NiCad for the sound units.  She comes in at just under 7 lbs.


Just some examples one of the batteries for HMS Leeds Castle came in at just over 8 lbs when weighed and there were 3 of those in that model.


Couple of pics follow I hope  :-)


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Nordlys

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Re: 1:12 BPB Whaleback advice requested please
« Reply #10 on: April 04, 2018, 07:13:46 PM »

If I remember correctly the RTTL would be around 30" length?  So 7lbs would be a fair weight with Nicad on board.
Some modellers use Liteply or even Balsa for large parts of the hull.
I have only ever built with marine ply, my thinking is Balsa is for aircraft for the most part.
A friend of mine fitted Brushless X2 motors to his 46" Range Safety launch with lipo batteries and the boat nearly took off!
It was overspeed.
But yes, I agree there is a tendency to build with strength for some of my boats.
Nordlys
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Big E

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Re: 1:12 BPB Whaleback advice requested please
« Reply #11 on: April 04, 2018, 07:46:14 PM »

I'm really pleased that my cries for help are stirring up so much interest, thanks everyone.
RAFLAUNCHES, I've already read the report on your Dad's amazing Coastal MTB and understand a little better now that balance will have a major impact on to getting the bows up, it's just a shame that weighting the tail makes a mess of trying to comply with a waterline at rest. Still, I would be more than happy to have the boat with 33% nose high at full speed, it would look odd tearing along with just the props and rudders in the water!
Malcolm, I am keeping an eye on weight and take your point about getting it down, the idea of putting a kW of power onboard is somewhat sobering.
John, thanks for joining in on the debate and your point too about keeping an eye on build weight, as you mentioned in your Masterclass on the RAF launch build. Obviously I am scaling up your timber sizes to suit 1:12 scale, but I haven't got enough experience to be able to decide just how thin I can go! My brother has offered to take a mould off my finished hull and make me a carbon fibre one. Now THAT will be light, so I might take him up on the offer. Your RTTL looks superb, but I am coming to expect nothing less from you now.   I will take your advice and see what the build weight comes out at before committing to power units, I really don't think I have any alternative and asking people to stick their necks out and advise me is really not on at this stage.
Thanks again for all your patience and advice everybody, I'll let you know how it goes.

Chris.
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John W E

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Re: 1:12 BPB Whaleback advice requested please
« Reply #12 on: April 04, 2018, 07:52:17 PM »


Hi Chris
the build for the RTTL is hear, it may help you  :-))

http://www.modelboatmayhem.co.uk/forum/index.php/topic,20758.0.html


john
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malcolmfrary

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Re: 1:12 BPB Whaleback advice requested please
« Reply #13 on: April 05, 2018, 09:30:04 AM »

If I remember correctly the RTTL would be around 30" length?  So 7lbs would be a fair weight with Nicad on board.
Some modellers use Liteply or even Balsa for large parts of the hull.
I have only ever built with marine ply, my thinking is Balsa is for aircraft for the most part.
A friend of mine fitted Brushless X2 motors to his 46" Range Safety launch with lipo batteries and the boat nearly took off!
It was overspeed.
But yes, I agree there is a tendency to build with strength for some of my boats.
Nordlys
A 1:12 model of a 63 foot boat will be 63 inches long, proportionately wider and deeper, and, other things being equal, about 8 times as heavy as a 1:24 one, and needing power to match to make it go the right speed for the increased size.
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canabus

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Re: 1:12 BPB Whaleback advice requested please
« Reply #14 on: April 05, 2018, 01:29:58 PM »

Hi Big E
For that size boat brushless and Lipo batteries to get the speed you require.
This is a club member's heavy Fantome on G60 twin motors and FPV camera setup.

 https://www.youtube.com/watch?v=xwp5jBnUE_A
https://www.youtube.com/watch?v=2J9Ltzl5gNw

Canabus
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Crazysniper

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Re: 1:12 BPB Whaleback advice requested please
« Reply #15 on: December 05, 2018, 06:09:21 PM »

Do you have photoes or video of your Leeds castle build
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Big E

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Re: 1:12 BPB Whaleback advice requested please
« Reply #16 on: December 06, 2018, 11:33:41 AM »

Thanks again for your comments everybody and I note your suggestion on motors Canabus. The Whaleback has progressed quite a bit in the last 6 months.  I had to make a decision on the motors a while back and eventually decided to use three 850 Torpedos running on five 2200 LiPos in parallel using Action Electronics controls.  I wanted a scale speed with the boat planing but I wasn't after a hydroplane (difficult to decide what speed would be 1/12 scale for 36 knots!) but of course there is always the possibility of changing the Torpedos over to brushless if it resembles a tug boat when it eventually hits the water.
The build has been fascinating, I loved the double diagonal planking although it uses a LOT of wood and is very slow. The first layer is lime and the final layer mahogany, hull and deck.  I was worried that after sanding I would lose the planking detail, but not so, the hull is dead smooth but you can see every plank under the paint and the deck clearly shows every line, just like the real thing. BPB bashed these boats out pretty quickly, so not too much time was spent on sanding down unless performance was affected, hence a smooth hull but a fairly rough deck. The cabin top was built using a composite skin, presumably ply, over a light frame, so I did the same and have gone for a smooth finish. I've not started the turrets yet, but I have got some clear 80mm Christmas tree baubles to use for the domes.
The biggest problem I've had so far has been the 3mm outlining on the numbers on the foredeck.  What a nightmare! I masked the lines as much a as possible but ended up having to paint free-hand. After much touching up I managed, but the finish is dreadful thanks to some Humbrol enamel which was obviously very old.  It went on like milky pond water.  The Tamiya paint was just as bad. Never mind, the hull numbers are sprayed on and look great.
Next step is ballasting and then water trials without the finished cabin, so I'll soon know if the Torpedos are up to the job or not.
Weights so far:  Boat plus motors, radio and batteries - 12.2 kg (27 lb)  Ballast estimate 1.5 - 2 kg (3.3 - 4.4 lb)  Total around 14 kg (31lb).  That's sobering, I thought I had built light as John suggested!
I've managed to reduce some photos down to a manageable file size, so I shall now try to attach them to this message.
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Perkasaman2

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Re: 1:12 BPB Whaleback advice requested please
« Reply #17 on: December 06, 2018, 02:10:40 PM »

Your Whaleback looks superb. Well done.
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Neil

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Re: 1:12 BPB Whaleback advice requested please
« Reply #18 on: December 06, 2018, 04:16:31 PM »

Your Whaleback looks superb. Well done.



absolutely gorgeous...ÖÖ.a superb model.
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malcolmfrary

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Re: 1:12 BPB Whaleback advice requested please
« Reply #19 on: December 07, 2018, 09:35:40 AM »

Quote
I wanted a scale speed with the boat planing but I wasn't after a hydroplane (difficult to decide what speed would be 1/12 scale for 36 knots!) but of course there is always the possibility of changing the Torpedos over to brushless if it resembles a tug boat when it eventually hits the water.
When it looks right, you will find that it is doing what the formula suggests, 10 and a bit Kt.  Divide real speed by the square root of the scale.
Unless there is a really serious trim problem, ballast should not be needed.  Lighter boats go fast more eaasily.  Boats like this sat differently in the water depending as much as anything on the fuel load.  Sitting at a "showroom waterline" was probably very rare.
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