Bow facing prop?

[spuggy]

Is it possible to have a prop at the bow of a sub facing forward? I am building a very basic rc 'surface' sub. The only non-standard feature is a prop at the front AND back of the sub. Is this possible/recommended with regards to: prop shaft thread, prop thread, prop design (shaft behind prop) etc?

[mfr02]

Traditional layouts are in common use because they have been found to work well. I suspect that a prop at the front pulling would create a great deal of turbulence over the hull, and might well compromise steering. I also suspect that the arrangement works well on aircraft because the disturbance is not as persistent with air as it is with water.
Most boat props are designed as pushers, and are not as effective in reverse, so you would probably have to build your own - have a look at http://www.towboatjoe.com/ in the Shafts section.

[Brooks]

Prop at front of sub thoughts:
1. rudders/dive planes work more effectively if there is fast water flowing past them.
2. if both props turn the same way, then torque reaction might be too much for the sail to counter, causing the sub to roll over and over.
3. airplanes like the prop blast flowing over the wings as it delays separation at high angles of attack. Subs probably don't need this as their depth is more buoyancy controlled than wing controlled.
4. drag is proportional to v^2, so the fast water at the bow will be causing more drag than normal. A flight instructor friend of mine was towing a dock with his motorboat. They were not making much progress....then he realized that the propwash was hitting the barrels on the front of the dock....once he lengthened the towline, the tug&tow speeded up :-).

None of this is meant to discourage you from trying your design. Nothing ventured, nothing gained :-).

[SD rc boater]

Real subs are also trying very hard to be quiet in the water so as not to be detected. Having a prop in the front would cause alot of bubbles, and bubbles are not quiet.

In regards to the other reference of why airplanes have the prop in the front is because having the engine in the front is traditional airplane design, is easier to keep the engine cool, and is easier to balance the planes center of gravity. Having the prop in the back in a pusher configuration on a plane is actually more efficient with less drag.

[Shaun Hendricks]

Putting a propeller in front of a sub risks damage to the propeller if the sub strikes something. Since a ship routinely travels forward and rarely backwards, you'd increase the possibility of fouling your propulsion system as well as damaging it.

You don't really net a performance gain by it being up front so that's why props are generally behind a boat or sub. Tugs show that a propeller can be just about anywhere on a boat and function, but for subs, you'd have to have proper spacing away from the nose of the hull so you wouldn't get back pressure on the prop. The hull creates pressure waves a distance in front of it. You could mount a pair of props on the end of dive planes and face them forward.... even fix them to the dive planes and have your own little "Osprey" under water! LOL!

An advantage of a front mount design like that would likely be that the propeller would be getting pure undisturbed water to it and that would make it very effcient on the input side. I think you'd lose that efficiency on the output side though.

This is why aircraft tend to have props at the front, undisturbed air means less vibration to the plane and greater propeller efficiency. However, many designs are currently flying with rear facing props as well that are quite effective and take advantage of pusher efficiencies.

I don't think you'd need any special designed prop for a forward application. Just realize that it will be driven from behind and you'll probably need a nose cone of some kind. I would counter rotate the two propellers to keep the sub from rolling. This might give it a tendency to try to 'rotate' itself in the water (turn around it's vertical axis) due to wheel walking. So, you'll probably need more stability in the form of stabilizer fins along the hull axis or you'll have to Kort both props.... Lot's of variables going on there so have fun and keep us clued in!

[redboat219]

Do you mean something like this
http://www.excite.co.jp/world/english/web/?wb_url=http%3A%2F%2Fhomepage2.nifty.com%2FHIRAO%2 Findex.html&wb_lp=JAEN&wb_dis=2

Here's another
http://www.excite.co.jp/world/english/web/?wb_url=http%3A%2F%2Frcsub.hp.infoseek.co.jp%2Find ex.htm&wb_lp=JAEN&wb_dis=2

Finally here are some nice videos
http://www.youtube.com/watch?v=kHZlh0CT2mI&feature=related
http://www.youtube.com/watch?v=axJfloLRAPU&feature=related
http://www.youtube.com/watch?v=4NOBTM-1Uko

[spuggy]

Thanks for the insight! A lot more to think about... The big worry for me is that the prop will basically be used in reverse. I thought there might be a specially designed prop. While you are here im going to ask another one. I am building this to tow something. I have 2x 12v 500 size motors and a 12v sealed lead acid battery. The design is constrained by the size and weight of the battery (20cm long and 2.2kgs). Is there another option to run these 12v motors to pull the load?

[toesup]

Is there another option to run these 12v motors to pull the load?

In short... "No"

You can run the 12v on 6v but the batteries will be approx the same size .. and you will only get half the RPM from the motors.

If we knew what you were trying to achieve by 'a very basic rc 'surface' sub' and 'pulling something', then we may be able to suggest a better option.

[mfr02]

The design is constrained by the size and weight of the battery (20cm long and 2.2kgs). Is there another option to run these 12v motors to pull the load?
There are twin prop subs out there, usually side by side. Out rigged sponsons spring to mind.
If you look at scale props, you will notice with most that the blades are not symmetrical, so there will be a difference in effectiveness depending on direction of rotation between pushing and pulling.

[spuggy]

I am building a torpedo shaped sea bait boat. As soon as i mention sea and bait boat together the responses include "LOL's" and "don't do it"... so i try to leave out the details

[toesup]

I am building a torpedo shaped sea bait boat. As soon as i mention sea and bait boat together the responses include "LOL's" and "don't do it"... so i try to leave out the details

LOL

Dont do it!...

OK, thats got that over with...

How big is this 'torpedo'?
How are you planning on being able to see something that is partially submerged / obscured... in rolling breakers?
Towing something behind a boat involves getting the towline close to the prop....

Thats just for starters... ;)

[spuggy]

The towing part will come later (kort nozzles and line and prop placement etc). I just want to get the electronics sorted.

It is 70cm long and weighs about 5kgs.

It will have an 'antenna' with a multi coloured flotation ball on top. This will be used to right itself + viz + direction indication.

[cos918]

hi there one or two question. I can see why you want a bait boat that can opearte in the sea . But it not clear why you would want a sub shape is there a reasion. All so will this sub run submerged , the reasion i ask is that when you dump the bait you will change the trim of the sub which might make problems. All so what type of sea are you intending on sailing in Ie a clam bay a an open beach with big waves. is there a stronge current etc etc as all of these will govern answer given on this forum. The more in put date you give the better the answer we all can give.

john

[spuggy]

The sub shape is not 100% accurate. The 12v battery will be mounted almost below the craft. I have attached a basic drawing of the layout.
A = Motor tubes with: 12v Mabuchi motors, stainless steel prop shaft, prop shaft seal and 3 or 4 blade power prop
B = 12v Battery in sealed plexiglass container
C = Sealed radio box housing esc, rx (i have left out servo and rudder for now)
D = Antenna (extended to increase line of site... how do I do this. I have a 2.4Ghz 3PM Futaba pistol grip system)
E = Flotation ball with 2 colours
F = Pvc tubing filled with expanding foam for rigidity. Pvc end caps.

Most of the pvc will be submerged.

Is that helpfull?

[arrow5]

Amongst others...major problems with using 2.4 gHz underwater. Check the sub guy forums.

[spuggy]

Amongst others...major problems with using 2.4 gHz underwater. Check the sub guy forums.


The antenna wont be submerged though

[mfr02]

A lower frequency system would need a longer aerial. For greater range, this is best vertical, and this can be an aid to visibility.
I assume that the bait will be in the tow?
The props might be best both at the front, but in knozzels and pushing (think B36 with shorter wings) to help keep them clear of the tow line.
It sounds not so much a sub, as a tugboat that runs VERY awash.

[arrow5]

The antenna wont be submerged though
That is going to be tricky, have you seen a 2.4 gHz receiver ?

[arrow5]

It sounds not so much a sub, as a tugboat that runs VERY awash.
Sounds like a Springer :rolleyes:

[spuggy]

I realise I still have a lot to learn. I went for 2.4Ghz thinking it was the latest technology therfore would work best. I've been asking Futaba if its possible to extend the antenna. I've paid a deposit at www.waigohobby.com. They didn't have stock of the 2.4Ghz system so I've been waiting for stock. I would really be greatfull if someone could have a look at the site and suggest a radio system that would work well for my awish norri springer tug sub bait boat (ok might need to rethink the name).

With regards to wave and current info: on days the waves can be 8foot and strong current. I obviously won't go out on those days but 4foot waves on a calm day would be ideal. I would need to get the bait out about 600feet. (add "lol's" and "not possible" here)

Thanks again for all the help!!!

[cos918]

hi there spuggey i have used rc in subs that went down to 20 foot. I used 40mhz and never had a problem. You would need to check what frequences are allowed were you live . Now i have heard that 2.4ghz is no good for subs but as you are not making a sub IE diving one the only under water time you will have is when a wave breaks over your boat/sub all so not sure how salt water effects it. You might fine 2.4 ghz might be ok.

You said your going through 4 foot wave and out as far as 600f/ 200m that a tall order. Here some problems i think you will need to overcome.
1. the weight /power of a 4foot wave.
2. the current caused by 4 foot wave.
3 in the shallow water the boat (prop) hitting the sea bed.
4. at 600f seeing the boat.

the first one to tackel would be the range . Put an object 600f away from you then look at it .A 3foot boat going to be very small now imagina that you boat in the swell of the sea it going to be hard to see and steer a course with curents. The bigger the boat the better + very high viz colours.

Here a few iders for the rest.
You might want to think of a wave pearcing hull to get throught the wave.

In stead of props use a jet drive. The benfits are if you boat hits the sea bed in the the wash you might bend a prop shaft as with a jet drive its all in side the boat execpt for the rear nozzel. Less exposed so less to break.

Now 1200f dosnt sound a lot but when you factor in waves wind swells etc this boat going to need some power. So as far as the battery is concerned, i would hang fire on those now get a decent motor / drive set up measure the current . then this should give you an idea on what size bat your going to need.

This is one hell of a project you got on your hands.

john

[arrow5]

Another alternative is a radio controlled aircraft. You have no visibility problems at the range you talk about, no radio problems or waterproofing for total immersion except in emergency. A suitable weight carrier, say 1lb of payload based on trainer type model would be a cinch. You have to learn to fly of course. Simple fold-away Rogallo fabric wing (similar to hang glider ) would solve transport problem. "Shark Bomber" has a ring to it for a name. I dont think the wave-piercer style boat has much merit. Too much power required , not enough inertia to prevent following the wave gradients instead of going through and out the other side like a torpedo at this scale.

[mfr02]

Waves that size implies sea rather than lake, unless its a heck of a big lake. Subs can be controlled at a surprising range in fresh water, but not in salt. The ones I have seen the operator has to be almost on top of the model once it goes under.
Range is vital in this case - if it loses signal, with modern ESCs, the motor will stop. If wind + current causes the model to drift towards you, no problem, it will regain control. If not, bait boat bye-bye.
Thoughts turn to the springer sub, but with the radio mounted on top of a strong (to live through the waves) but light (needs to stay upright) pylon. Paint everything in a bright harlequin pattern so you can see which way its pointing at a distance.

[spuggy]

thanks cos918. Appreciate the comments.

I dont think the prop hitting the sea bed will be an issue. They will have korte nozzles protecting the props.

The distance 'seems' to be the biggest issue. 300ft is more realisticly the distance to the backline of waves though. We have divers diving 500ft out infront of our house. They use these orange floatation bouys measuring 20'' x 6'' x 5''. We can see them clearly. The divers reckon you can see them 1000ft away on the water. Hence the high viz paint should be ok at 300ft.

The torpedo shape is being used as it will be easy and relatively cheap to manufacture. It will also be very strong. The other fact is that it will be bouyant enough to travel over the waves rather than through them (hopefully!). You just need to time it right so that you dont go through too much white water.

I have a 12 volt 7ah battery with 2 (possibly 4) x 500 size mabuchi 12volt motors at my disposal. Do you think this battery and motor combo will give enough power? If not what setup can you suggest that has enough power? i think the power issue will be my biggest challenge. i dont want to go mad and use a car windscreen wiper motor etc. What rc battery and motor setup do you think i should use? You absolutely right... i need to get an adequate power train setup and then design around it.

[arrow5]

What you suggest is a surface running submarine with "conning tower" high enough to be "seen" by radio signal. Forget the Springer idea, that was just my little joke . The Springer hull is shaped like a brick. Regarding colour, not harlequin, even bright colours. See how effective the WW1 German lozenge camoflage was using multi colours. Better two balls/floats with solid colour, one dayglo red/orange and one black. At least one should be visible depending on water colour variations. Avoid white or yellow. See lobster pot float colours. All RAF trainer aircraft are now painted black gloss. In some conditions you will be looking at the reflection of the sky on the water. Regarding power, what is wrong with a suitable surplus motor, some are very high quality with ball races etc. Is the flying bait bomber idea no good????

[spuggy]

i loved the flying bait bomber idea... could scare the locals though.... noisy flying machine with half a fish head in tow overhead.... seagulls could also be an issue! no harm in thinking out of the box.

so you see no problems with a 12v sealed lead acid battery and 2 12v motors?

[cos918]

hi there if it was me i would use 12v sla batterys. Size depends on current used by motors . AS for the 500 you might find they ant man enough. Ie the bigger the motor the bigger the prop the more power you can put down. You dont want to be in a situation were you are using 100% power and require more power to get out of a bad situation. In the break of the waves the situation is going to be changing by the second. So you would be better placed to have your boat with enough power so it can do this run throught the waves on say 60% of full power so you have 40% in reserve for bad situation. I am not sure you will get this with a 500 motor. I would be looking at 700 bb turbo . I know there heavy on battery power but the this boat is going to be going through tough situation.

john

[arrow5]

I wouldnt aero-tow a fish-head unless you want to catch a seagull. :rolleyes: Box with bomb-bay doors, simple enclosed cargo. Surplus motors are normally cheap and as I say quality beyond model store Mabuchi standard motors (unless you pay much more for a quality,read expensive, model motor). Flying would be all cheap LHS off-the-shelf (even "ready-to-fly" ) equipment and craft.

[cos918]

spuggy one question .
how big and how heavy is the bait you want to take out.

john

[spuggy]

The lead sinker is between 5 and 8oz. The bait can be as small as a pilchard (5oz / 150gm) and as large as a bonito head (20oz / 600gm). I dont think the bonito head will be realistic though. I would be very happy if i could push it to 10oz (300gm)

[arrow5]

Aha ! so you want to take a baited line out to the target area. Slightly different to what I understood a bait-boat was used for ie dropping bait. You`ve guessed I`m not a fisher. You want to build a sub-surface line towing craft ?

[spuggy]

yes thats right. sorry i thought you knew that and were joking about the bait bomber idea. the craft cannot be too submerged as you would need to see it from a distance.

[arrow5]

I was having a senior moment and presumed you were towing a barge or similar that contained bait to be deposited to attract fish and you would then cast your line from the beach. Silly me. Keep us informed on progress...tight lines etc etc.

[cos918]

Hi the spuggy so i got this wright.your total weight the will be deployed is not more than max 1kg/2.2lb. Now you mention a led sinker and some fishes head. How does this work Ie can the be dragged throught the water or do they have to be in a box and tipped at the spot. Is the bait next to the lead weight or is there some line between them.
The reasion i ask is i not a fisherman and not to sure what you mean by this. A photo/digram of your hook/weight set up would be great as then i can visualise what is trying to be achived . This would help to give you better idears and not wrong ones. john

[spuggy]

There are 2 ways the bait can be taken out.
Option 1: a 6oz sinker AND the 10oz bait (small fish or fish head) can be taken out and dropped (im not sure if i need a servo release for this or if i can use a clip and jerk the line which would release the bait)
Option 2 (ive just thought about this): an 8oz sinker can be taken out and dropped and then slide the bait out. the sinker anchors in the sand out at sea. the bait is then clipped onto the line from shore and it slides to the sinker. i have attached a pic of this rig. it is quite common

the bait setup wont be more than 800grams.

there is line between the bait and sinker (second pic attached)

I need some advice on the motors, battery and esc needed. sla vs nicad. 12v vs 6v motors. 2 or 3 12v motors running on 1 12v 7ah battery (how will effect esc).

[arrow5]

Some more lateral (senior moment )...how about a submerged tractor based on an R/C buggy. Big wheels for traction on sand(?) bottom, avoids most if not all of wave action. All the mechanicals are standard gear just need 100% water-proofing.

[spuggy]

how would you see where it is?

[cos918]

Hi there . there is an idea starting in my head just got a few more question to ask to sort out some nigels 1 what is the max current speed you would operate the boat in . is windy when you fish ie speed mph. 3 is the a lot of surf (white water) / breakers. 4 is it a shallow beach with gentle slope. photo of the sea would be great to see what we are up against. 4 what sort of depth are you talk of at the drop zone.

john

[arrow5]

how would you see where it is? Coloured floats might be accurate enough. I presume this is on a moderate budget, scuba and treasure hunters , oil industry, pollution control and other big money folk have underwater devices with navigation, GPS positioning and live video via umbilical cable. Big bucks of course but a budget version might be within an amatuer`s scope. I fear the surf may be the main problem for a model on or near the suface. Interesting challenge. Look for ideas from sub sea and ROV vehicles, Wood`s Hole etc.

[spuggy]

hi cos.
current: changes constantly. on a particular day i got caught in a rip while swimming and really really struggled to swim back to shore. the same day took my kayak out and managed to get in and out without any problem.
wind speed: +-10mph
surf/breakers: the surf can get big and ugly depending on wind speed and direction (there are a lot of days i wouldnt even take my kayak out). i have attached some pics of ideal conditions.
the slope of the sea bed is not too dramatic. 200meters out it is about 3 - 4meters deep
ive attached a pic of the boat we normally take out


hi arrow.
the rov guys have been really helpfull particullarly rand3289

[spuggy]

i just want to say that i dont want to reinvent the wheel... just adapt it a little. i think i need to decide on a strong motor, battery and esc combo. then i will design around that

[cos918]

hi there. looking at what you have said+ the photo 12v high power is the way foward. The only motor i would think about is a 700 bb turbo. Very greedy on power 15/20 ahm each but high rpm+torque . As for how to get this power down not sure yet on what root to go do Ie water jet or prop. As in you photo 1 on the second breaker there a fair bit of white water not sure how a prop would cope with that. As for the amount of motors on some thing like this i would go for 2. The reasion beeing ,1 it going to have to be a fair size boat to take the bait + conditions. 2 2motors are better than 1. ie a failer on one drive means you still have 1 motor and 50% power left.
One thing i can see is if you did not hit the waves square on your boat could easily be spun a round or worse still flipped over. So on the not ie 100% require to be self righting .

john

[spuggy]

it will be self righting. i pretty much have the design sorted. what esc can handle 2 x graupner 700bb motors? what battery do you think would be best?

[arrow5]

How about a mortar to lob the line out ? Breaches Bouy idea. Rockets are fairly cheap.

[mfr02]

How about a mortar to lob the line out ?
There might be some local killjoy ordinances about letting off artillery pieces.
Looking at the pictures, I think "One small wave for a man, a huge destructive wall of water for a model"
Foreshore waves often happen over bars where it it shallower, so prop protection will be important, apart from avoiding tangles because there is always the possibility that the boat could be thrown back when meting a wave. Perhaps it needs something along the lines of a self guiding system to get out, then release bait, hook etc and steer home?

[arrow5]

Same question , how about a rocket with line attached (4th of July practice, Officer). What is the most/highest surf anyone has sailed a model size,say 48", craft in?

[spuggy]

Great idea mfr02... self guided system. How would a newbee like me even start to research something like that? Do you have any ideas about battery, esc and motor choice?

[cos918]

hi there . here 2 links one for the graupner 700 bb turbo motor and another for a speed controler. I am going to a boat show tomorrow and will ask some people there thoughts on you idea. john

https://shop.graupner.de/webuerp/servlet/AI?ARTN=6306

http://www.howesmodels.co.uk/RadioControl/viewProduct.php?ProdID=3157

[jeno]

In short, YES. While there are a lot of negative responses in this thread, I have to disagree.
Here's why. During WW2 the Italian navy developed several mini subs for infiltration. They proved very successful. They also were developing and AIP mini sub with counter-rotating TRACTION propellors. After the war both US and British investigators were very surprised and impressed by the efficiency and manueverability of these boats. These boats, called "Sandokan" had a 350hp and acheived 15knots submerged.
The US boat, X-1 bore significant resemblence despite having a pusher prop.
Try it and keep us informed.
Jonathan

[jeno]

Sorry if I wasn't clear in my previos. Sondokan's props were mounted like a torpedoe's, but at the bow. Counter-rotating about a single shaft, with control planes stern mounted.
Jonathan

[spuggy]

thanks Jeno!

[cos918]

hi there went to the boat show to day and spoke to a fair few modlers bout your boat. This is what the genral concencus is.
1 Forget jet drives as soon as the in take is out of the water or in white water you will lose drive.
2 this boat is going to have to be so over enginered and over powered if it has any chance in 4 foot waves.
REC 700 bbb turbo motor x2
brass 4 or 5 bladed props 50 mm
Do an amp test when motor/props fitted to your boat buy the apropirate speed contole. ( M tronics viper 40ah) pos
As many water tight coparments as possibel.
Here the one that split the crowd 60/40 the shaape of the hull. Most thought a wave percing hull was the way to go the rest said your tube hull would do but did say to watch out for roll.

john

[spuggy]

Thanks John. It seems this project might not be worth it in the end. Just for interest sake... what batteries would power twin 700bb motors?

[cos918]

A 700bb with a good prop will pull about 15 to 20 ah (all ways check). So x2 motors will about 40 ah. so a 12v 7 ah battery will last about 7 to 15 min depending on throttle setting. But at full power she will power some power and go some.
if you were making a bait boat for a pond/lake you would not need as much over engineering / cost. Model boats were not made to go through 4 foot wave thats not to say the cant ,but to make it so they can do with the risk of lossing the lot you have to over engineer which cost.
john

[mfr02]

Great idea mfr02... self guided system. How would a newbee like me even start to research something like that?
The electronic gyros that the helicopter lads use might do the job, or part of it. An alternative might be to wire-guide it.
Just thinking aloud, sort of "run it up the pole and see who throws a brick at it".