Hi Rowen, I have had water cooling on all my patrol boats running at 12Volts, whether brushed or now brushless. For the brushed motors I have used aluminium tube coils with water pickups between the propellers and rudders. I did try water jackets a couple of times but found too much friction loss and therefore lack of flow. For the newer brushless outrunners I use a brass tube soldered to a brass plate across the front of the motor fitted between it and motor mounting bracket. I agree with Doug with regards to the disconnection of the red wires on the ESC's. This is now common practice, especially if you have an external receiver battery.
This Higgins PT boat was built and sailed by a good friend of mine. It is scratch-built. It uses a single Turnigy 3639 1100kV brushless motor and LiPo battery. It is pretty new and has not had its number painted on as yet. Its performance is excellent.
[Score: 9/10] 58"/9000g MTB741 Fairmile D Capable of 9mph and a runtime of 65mins Twin Propellors (2 Blade S Type 40mm) Direct Drive to a Graupner 700BB 12V (2 Blade S Type) Powered by NiMH (12v) 9Amp/h Batteries Controlled Through MTroniks 30A Tio x 2 (10Amps) ESC - Comments: 1/24 Scale. Scratchbuilt from John Lambert Drgs & photos. It took 3.5 years. Plywood bulkheads, pine stringers & balsawood planking, then fibreglassed. Superstructure balsawood. Guns scratchbuilt from tinplate and brass. There are 2 motors and drive trains powered by 2 x 9cell NiMH D cells x 9Ah. 6 pdr guns rotate. 20mm oerlikon rotates and elevates. Radio is Futaba 2.4 GHz
Mr. Grumpy - The reason for a hovercraft skirt is to provide a flexible seal between the craft and the ground/water surface. If everything was flat and smooth, then a shirtless hovercraft would probably work, as a uniform cushion of air could be maintained. Unfortunately this is not reality. I used to like the concept of a hovercraft and once keen to model one, but having seen real ones and models lack of directional control have gone away from the idea. Another reason for the skirt - bouncing off nearby objects in the vicinity of the hovercraft.
I have scratch-built a Fairmile D in 1/24 scale. if you look through my posts/videos you will see it. I used the Lambert-Ross Allied Coastal Forces book for the plan that I scaled up. Perhaps I should enter it in my boat harbour. Anatomy of a Ship is also a good source of information. I built mine from Balsawood/Pine and fibreglassed it. Attached are a few photos. Watch the videos. They may inspire you. I have previously posted these links under videos. https://www.youtube.com/watch?v=a3KotucrlzE&t=20shttps://www.youtube.com/watch?v=Ny718cnD6sQ&t=166s
Hi Graham, There have probably not been any answers so far because we are most possibly speechless. If you go back and read through the comments above you will see that most of the problem has been the large overpowering of your boat (1690 Watts - according to info provided by DaveM), coupled with an inadequate drive train. So with all this knowledge available you have asked our opinion of the Graupner 500ECO - one of the largest motors in that range. This is quoted at 1440 Watts. This may not rip the drive train out as quickly as the other motor did but has enough torque to do so. In my opinion I think you could try a motor producing under 500 Watts and see how that goes - with a 5mm shaft.
Thanks Dave, Eventually we will have put together a body of knowledge that model boat builders can use with some certainty. At present the information is sketchy, hard to find and sometimes ambiguous. The motor designers and manufacturers have not been very helpful. For my La Combattante iii missile boat I used two Hobbyking Keda 720kV motors rated at 215 Watts and 19.3amps max. They were the first brushless motors I tried. I was not sure how many amps they would draw, so I connected an ammeter and fitted my video camera so it read the amps whilst operating. At full speed they used only 8 amps each. Each of the batteries is from 12V made from 9 x NiMH 9Ah D Cells. I easily get over an hour run time at good speed. The boat is 1605mm long so not small. This information may help someone.
Graham, I have attached the same table that Doug sent me. This has the relevant information you seek. According to the table attached the Graupner 500 kV ECO has a specified output of 1440 watts and 80Amps. Strangely the 400 kV ECO has a specified output of 2010 Watts. So the 1440Watt output is questionable and may be a typo based on the other entries in the table. more likely to be 2440Watts In any case you need a 5mm diameter propeller shaft. For shaft alignment i use a brass tube that slides snugly on the propeller shaft and then on the motor shaft. When the tube rotates/slides well on both then the shafts are aligned. I then fit the motor mounts, check and tweak the alignment if necessary, remove the tube and replace with a universal coupling. If the motor or propeller shafts are a different diameter then I insert the relevant size smaller tube inside the larger of the tubes. This method is simple and has served me well, including for larger IC engine powered boats belonging to friends. Haig
Thanks Dave, In common car language that is a V12 in a Ford Fiesta, with the Fiesta drive train. In some ways I believe the brushless motor manufacturers/sellers are responsible for the confusion. Mostly we see the kV, physical size and the number of Lipo cells required. You need to dig deeper to find out the Watts. The kV basically gives the RPM only. No mention of amps and power. We don't buy cars and motorcycles based on the engine RPM do we? Typically if you look at the reputed Graupner Speed Brushless range, they have low kV specs, but the differences between a 400kV 7.4V, 400kV BB 11.1V and a 400kV ECO 14.8V are 130W, 1100W and 2010W respectively. A huge difference. When viewing the on-line retail sites, including Graupner, they all look the same (maybe the same photo), but they are all very different motors. Without the rated amps and Watts (not published) the buyer is left unclear as to what they should buy. Brushed motors are more clearly defined. I must thank Doug for helping me out with Graupner brushless specs when I required assistance.
I get my Raboesch propellers from Cornwall model boats - and I am in Australia. It would be very interesting if there was a video made at the start of this post. How many Watts of power is that motor producing. That is the question I would have asked at the time.
[Score: 8/10] 64" HS Smitzopoulos Twin Propellors (3 Blade 35mm) Direct Drive to a 2 x 720kV (3 Blade) Powered by NiMH (12v) 9Amp/h Batteries Controlled Through 2 x Turnigy 30A (15Amps) ESC - Comments: La Combattante IIIB Class Guided Missile boat of the Hellenic Navy. It has two brushless motor systems (each described in the table, drawing 8 amps max). All four gun turrets can rotate and the main guns can also elevate. Radars both rotate. LED running lights. Hull is from balsa and marine ply with a fibreglass skin. Deck and superstructure is balsa. Masts are from brass tube.
Vosper 73ft Type 1 MTB - Scratchbuilt. Now running two brushless motors and NiMH batteries. Photos previously posted. 1/24 Scale Fairmile D MTB623 belongs to a good friend. This boat was also featured in a previous video with my Fairmile D. The lake was a bit choppy with realistic sea conditions.
Scratchbuilt WW2 1/24 Scale Vosper 73' Type 1 MTB. Built in 2016, in company with a friend's 1/24 scale BPB MGB. The Vosper hull is built from balsawood and fibreglass. The upper deck and superstructure is from balsawood. The weapons and fittings are from brass, aluminium and plastic. The 20mm and gunner can rotate.
1/35 Scale model of the La Combattante IIIB Class Fast Missile Boat of the Hellenic Navy. The boat is scratchbuilt. It is 1606mm long. It has 2 brushless 720Kv motors and NiMH batteries. The 76mm guns can traverse and elevate. The 30mm guns can traverse. Both radars rotate and there are LED running lights.
I tried a few different grades of oil and found that if the inside end of the prop tube is close to or below the waterline then some water always seemed to enter the boat, as well as leaving an oil slick in the lake. You also need an oiler tube. Light grade marine grease - whilst offering some friction initially soon eases off on the friction (via a quick run-in), whilst offering a good seal. I have ships, patrol boats and submarines and they all have marine grease. I re-grease the prop tubes/shafts once a year for the frequently used models and others once every few years. I also tried Lithium grease, but it always remains sticky and so does the friction load. In most cases this is great grease except for prop shafts. Choose what ever you are happy with.
Hi Seafarer, I have a few ships with rotating radars I have a few of these motors per the link below. They rotate quite well with one cell (1.4 volts) Gear Motor 3 - 224:1 90 Degree Shaft https://solarbotics.com/product/gm3/ I also have some of these, but they require a bit more vertical space. MFA 951 Series Motor and Gearbox 298:1 6volt (from CMB in the UK). I run these on 3 volts. Both are quite small. I have also used old servos in a couple of places.
Richard, If as you said each blade from shaft centreline to tip of blade is 30mm then it would not matter if you had two blades or ten. If the radius (your measurement) is 30mm then the diameter is 60mm. Perhaps you can remove the prop and place it on a flat surface so you can see the swept circumference when rotated.
Hi Richard, If each blade is 30mm from the shaft centre, it is a 60mm diameter propeller and is far too big for that size motor. For performance you need a larger motor say a Graupner 700 and I would still recommend a smaller propeller.