Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[Imagewerx]

Good morning everyone.


After taking my holiday in the Lake District this year and taking a tour of Coniston Water and the surrounding area,I have been inspired to build a model of Donald Campbells Bluebird K7 that he had the fatal accident in.


I am intending to make the boat to about 1/12th scale which would make it about 27 inches long,but this is flexible to allow for the chosen propulsion system.I don't have a big budget for this,so need to do it as reasonably cheaply as possible so have ordered one of these....



This particular one has a 40mm nozzle,so will hopefully be about right for this size boat unless anyone can advise me otherwise.Power will be a water cooled brushless inrunner of about 2000kv.I would really like to use one of the model jet turbine engines for the truly authentic sound,but at over £1000 it's so far out of my budget it's not funny.


The main question I need to ask for this particular boat.The original Bluebird K7 has a totally flat hull,which is obviously perfect for it's intended purpose of going VERY fast in a straight line.I'd like my model to be able to turn quickly as well,so am I right in thinking I will need to give it a V hull maybe even with chines so it can turn without having to slow right down? If so,how critical is the exact shape and angle of the V and placement of the chines,or can I just buy a cheap model speedboat and copy it's hull design?

[raflaunches]

Morning and welcome to the forum


Interesting idea but I think you’re going to struggle to get two different hull types into one model.
Bluebird K7 was a three point hydroplane which relies on it staying on its three points to achieve its high speed in a straight line. I don’t think you’ll struggle putting a V hull on to this design but I think it won’t work as effectively as you think. The outrigger/sponsons will prevent tight turning as they are there for stability and will fight you in the turn.
An idea might be to go for Donald’s previous boat K4 which was a more conventional hull which he also raced. Other than the sponsons the boats is similar in style and would be easier to control. But that’s my opinion 

[Neil]

you might be better going down the road of a ducted fan propulsion similar in theory to the pusher propeller of a Walrus aircraft.


I have seen this method used in the bluebird and with the upsurge of big high revving brushless motors, you might have far better results.


after all, such ducted fans are used on scale jet aircraft with fabulous results.

[Neil]

and as raflaunches says...……….steering is very marginal.


Bluebird had only 3 tiny rudders to steer her by, one on the aft end of each sponson and one on the aft end of the main fuselage

[Hotglove]

Shovel nose hydroplanes have flat bottoms but are fast and manoeuvrable perhaps have a look at how they behave, an onboard sound system would give an authentic jet turbine noise for less than a tenth the cost of a gas turbine motor. google Ferrari Arno X1 Sotheby's they sold this boat a few years ago and published a great little movie to display it.

[Imagewerx]

Morning and welcome to the forum


Interesting idea but I think you’re going to struggle to get two different hull types into one model.
Bluebird K7 was a three point hydroplane which relies on it staying on its three points to achieve its high speed in a straight line. I don’t think you’ll struggle putting a V hull on to this design but I think it won’t work as effectively as you think. The outrigger/sponsons will prevent tight turning as they are there for stability and will fight you in the turn.
An idea might be to go for Donald’s previous boat K4 which was a more conventional hull which he also raced. Other than the sponsons the boats is similar in style and would be easier to control. But that’s my opinion 

Thanks for the prompt reply.


I'm sort of hoping for what ever the model boat builders version of artistic licence is.It needs to look as authentic as possible above the water line,but below the water line it will be strictly functional.The sponsons could be cut down so they're higher out of the water than on the original boat,and at rest wouldn't look any different.Once the boat is moving and up on the plane,they will be clear of the water (hopefully!),or even a couple of servos that automatically lift them out of the water above a certain speed.
While up there I visited The Lakeland Motor Museum and was surrounded by enough inspiration to build a model of any of the Campbell's record breaking cars or boats.But in the end it just had to be the most iconic of all of them.....
918 by Chris Plunkett, on Flickr
908 by Chris Plunkett, on Flickr

[Imagewerx]

you might be better going down the road of a ducted fan propulsion similar in theory to the pusher propeller of a Walrus aircraft.


I have seen this method used in the bluebird and with the upsurge of big high revving brushless motors, you might have far better results.


after all, such ducted fans are used on scale jet aircraft with fabulous results.

A ducted fan was my next option and would sound almost as good as a 'proper' jet engine.I've already paid for this so want to try this way first.I used to have jetskis and this is just a scaled down version of the jet pump they use,and I know my way around them very well and how to get the best from them.As long as they stay 'hooked up' (sucking water and not air) they are way more efficient than a bare propellor and the steering nozzle is more precise in my opinion than a conventional rudder.

[Imagewerx]

and as raflaunches says...……….steering is very marginal.


Bluebird had only 3 tiny rudders to steer her by, one on the aft end of each sponson and one on the aft end of the main fuselage

Steering using a high pressure jet of water forced through a small nozzle is the new three rudders!

[Imagewerx]

Shovel nose hydroplanes have flat bottoms but are fast and manoeuvrable perhaps have a look at how they behave, an onboard sound system would give an authentic jet turbine noise for less than a tenth the cost of a gas turbine motor. google Ferrari Arno X1 Sotheby's they sold this boat a few years ago and published a great little movie to display it.

The authentic sound was just a pipedream and for me a speaker playing engine sounds would be as tacky as the fake dump valves boy racers used to to fit to their Citroen Saxos.

[Imagewerx]

So,any more thoughts on this please guys,I still need help with this? I see from the film of the original boat on the ill fated run that when the boat's up on the plane,only the very back of the sponsons are in the water.Also most of the models of it seem to be the same,but turn at speed without any problems?

[Neil]

So,any more thoughts on this please guys,I still need help with this? I see from the film of the original boat on the ill fated run that when the boat's up on the plane,only the very back of the sponsons are in the water.Also most of the models of it seem to be the same,but turn at speed without any problems?

well, i'm sorry to be so blunt and forthright, but you seem to have made up your mind that you have bought the jet drive and are going to use it for your propulsion unit, and have discarded any other suggestions,


 so unless someone can come up with a totally new suggestion such as miniature nuclear fusion or warp speed, it's your choice,...…...get on with it and show us how your expertise of jet systems on a semi planing hull, will work and adapt to a full plane hull.

[Stavros]

Sponsons Higher than where on the Original boat  is defo re inventing the wheel....I WOULD love to be there to watch as it cartwheels over when you turn and a sponson digs in...........Bluebird was a Hydroplane...clue there in the type  of boat she is, so as Neil has so politely said lets see your expertise of Jet propulsion on a semi planing hull




Dave

[C-3PO]

https://www.youtube.com/watch?v=pMlsGuv-3cE
C-3PO

[Imagewerx]

well, i'm sorry to be so blunt and forthright, but you seem to have made up your mind that you have bought the jet drive and are going to use it for your propulsion unit, and have discarded any other suggestions,


 so unless someone can come up with a totally new suggestion such as miniature nuclear fusion or warp speed, it's your choice,...…...get on with it and show us how your expertise of jet systems on a semi plaining hull, will work and adapt to a full plane hull.

Because as I already stated,this is the only part of this project that I already have any experience with,so I don't see why it's considered 'wrong' to not want to use other propulsion systems.It's not as if jet drives are never used for marine propulsion is it? I have never said it WILL work with these types of hull,I came on here to ask the opinions of people who hopefully have more knowledge of this than I do.

The chosen drive system has the advantage of a much greater downforce than any other type.This will have a lower centre of gravity than the original boat which will hopefully be in my favour.


What might not be in my favour is extreme light weight.The motor,battery,ESC,servo and receiver only weigh 1.2kg and the balsa and plywood construction of the boat (plus the jet pump) won't add more than a couple of kg to this (a wild guess as I have no experience with this).The original boat weighed over 2600kg so my 1/12th scale in dimensions is way under weight at probably 1% of the weight of the original boat! But at least it's easier to add ballast than it is to get rid of weight if it's too heavy.

[Imagewerx]

Sponsons Higher than where on the Original oat  is defo re inventing the wheel....I WOULD love to be there to watch as it cartwheels over when you turn and a sponson dig's in...........Bluebird was a Hydroplane...clue there in the type  of boat she is,so as Neil has so politely said lets see your expertise of Jet propulsion on a semi planing hull




Dave

Thanks for your support Dave.

[Imagewerx]

https://www.youtube.com/watch?v=pMlsGuv-3cE
C-3PO

Thank you!

[C-3PO]

Hi Imagewerx,

The video of the Bluebird at Wicksteed park only tells part of the story.

Somewhere I have other videos - one where the craft caught the water and became submersible instantly

One where it ran much faster than this trial.

It was an interesting experiment - I was just the cameraman...

C-3PO

[John W E]

Hi C - 3PO - its difficult to work that out.   Is that a ducted fan drive with a brushless motor and lipo set up in that Bluebird?


To go to Imagewerx queries - right - try thinking of it this way


Water jet propulsion on a boat is fairly efficient and was designed for boats to be beached on the shore and also enter areas where other propeller driven craft couldn't venture because of fouling the propeller.  These vessels tend to be a deep 'V' hull, which can only sustain a certain speed - due to the fact of water drag.  This is why designers went to the stepped hull design for water speed records - to enable them to reduce the water drag, because in theory you are only actually sitting on two stepped areas when the boat is in motion.   This only can be pushed so far as far as speed goes because then the mass of the boat becomes airborne and very unstable.


The designers then went onto the next stage which is the three point hydroplane; in which you can obtain greater speeds.  This is because you only have three small areas of contact at speed.   Now, what you are wishing to do is to try and draw water into the hull to supply your jet at speed and this will greatly increase the drag of the hull.  This is because you are actually taking water inboard - and to make it simple - the effort of drawing water inboard is more than the output effort of the propulsion unit.   In other words you wont be able to bring in sufficient volume of water to supply the motor to give you the speed you want on a three point hull.


Hope that makes some sense without becoming too technical.

[C-3PO]

Hi John W E,

From memory it was not a ducted fan unit as such

It was a brushless motor with a prop blade running on 6s Lipo.

From memory the rerun (not in the published video) was using 12s and performance was significantly more impressive - that's after it had all dried out!!!

C-3PO

[John W E]

Hi C-3PO - thank you for that - I bet that is pretty awesome that - I would have liked to have seen it running.   


Hi ya Imagewerx - do a Forum Search on here and there is a lad who built a Bluebird, running on Lipo's and brushless motors and a surface piercing prop.  It is pretty good build and very entertaining read.   But, when you do the search, you will get a load of Bluebird's up.   This guy used to be a bit of a pain I have just found the link here it is for the build http://www.modelboatmayhem.co.uk/forum/index.php/topic,48395.0.html

John (aka ex - Bluebird ) 

[C-3PO]

caveat emptor
Imagewerx - You might find some more info interesting on this link - https://www.modeljetdrives.com/bluebird-k7-hydroplane.html


John W E - I will see if I can locate the video and publish on here


C-3PO

[John W E]

Hi Imagewerx  have an eye ball at this it is an interesting read
  https://www.boatdesign.net/threads/jet-vs-prop-efficiency.19655/


john

[Imagewerx]

Hi C - 3PO - its difficult to work that out.   Is that a ducted fan drive with a brushless motor and lipo set up in that Bluebird?


To go to Imagewerx queries - right - try thinking of it this way


Water jet propulsion on a boat is fairly efficient and was designed for boats to be beached on the shore and also enter areas where other propeller driven craft couldn't venture because of fouling the propeller.  These vessels tend to be a deep 'V' hull, which can only sustain a certain speed - due to the fact of water drag.  This is why designers went to the stepped hull design for water speed records - to enable them to reduce the water drag, because in theory you are only actually sitting on two stepped areas when the boat is in motion.   This only can be pushed so far as far as speed goes because then the mass of the boat becomes airborne and very unstable.


The designers then went onto the next stage which is the three point hydroplane; in which you can obtain greater speeds.  This is because you only have three small areas of contact at speed.   Now, what you are wishing to do is to try and draw water into the hull to supply your jet at speed and this will greatly increase the drag of the hull.  This is because you are actually taking water inboard - and to make it simple - the effort of drawing water inboard is more than the output effort of the propulsion unit.   In other words you wont be able to bring in sufficient volume of water to supply the motor to give you the speed you want on a three point hull.


Hope that makes some sense without becoming too technical.

Thank you for being the first person to take the trouble to answer my question properly instead of making facetious remarks and treating me as if I'm stupid.


I should have made it clearer in the first post what I want from this model boat.I won't be going for any speed records with it,nor will it be raced.The water I use it on could be quite small so it needs to be able to turn quickly.


If you think a jet drive will never work with this type of hull then I won't even try to make it work.I've been wanting to build a jet driven boat for some time now,and after spending time on Coniston Water and being inspired to make a model of one of the most iconic speedboats in history,it was logical to do both at the same time.If this won't work in your opinion,then the jet drive will be fitted to a more suitable boat.

[Imagewerx]

Hi C-3PO - thank you for that - I bet that is pretty awesome that - I would have liked to have seen it running.   


Hi ya Imagewerx - do a Forum Search on here and there is a lad who built a Bluebird, running on Lipo's and brushless motors and a surface piercing prop.  It is pretty good build and very entertaining read.   But, when you do the search, you will get a load of Bluebird's up.   This guy used to be a bit of a pain I have just found the link here it is for the build http://www.modelboatmayhem.co.uk/forum/index.php/topic,48395.0.html

John (aka ex - Bluebird ) 

Thank you and I'll try to read through it when time permits-if I decide to go ahead with this project.

[Imagewerx]

Hi Imagewerx  have an eye ball at this it is an interesting read
  https://www.boatdesign.net/threads/jet-vs-prop-efficiency.19655/


john

Thanks.It seems that this sort of argument can be pushed in which ever direction the opposing sides of it want it to go.