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Hi Ed I notice that your prop shaft sticks out from the hull which may be why the prop is so near the rudder. I treat all plans as guidance notes and trial fit the parts before final fixing. I believe we have all been in your position at some time or another! I agree with the advice already given and believe a thin washer and thinned locknut would give you the clearance you need. This isn't a speed boat so there will not be much stress on the set up but my preference would be brass, its easy to file and won't rust. I have in the past reworked the propeller boss but its not really a good idea, and does tend to spoil the looks.
Evenin' Ed, No! you need some kind of thrust washer between the prop / locknut and the end of the tube! Otherwise when full ahead the prop or nut will grind against the tube 😡 I would swap the thick nylon washer for a thin stainless steel washer. A good DIY store should have some. Should win you a mm or so. If the shaft moves back and forth more than that then something else is wrong. The movement on my Sea Scout shaft is about 20 thou max. Or as RH suggests you could use Loctite to secure the prop instead of the locknut. I would prefer the stainless washer. Cheers Doug 😎 BTW: I also fit washers at the inboard end, between a collet and the tube. As shown in pic attached of my new Sea Scout installation. New propshaft was milled to lock the collet in place (Pic 2). Cocked it up slightly so I needed extra spacing washers! 😁 no one's perfect 😉
Funnily enough, was talking about this issue earlier with other scale modelers. I faithfully reproduce the rudder position and size and then propeller shaft protrusion on my scale models. Often find when the shaft and propeller are installed they either contact or come very close to the rudder leading edge. Suspect model propellers and the boss are thicker than a scale propellers. Have resorted to trimming either the rudder or the prop boss to get them in properly. Also, have several times left the prop. locknut off and Loctited the prop to the shaft. Be interested in other's experiences. Have never lost a prop by using Loctite fortunately.
I have to agree with Peter's comments. I would also suggest that you look at the coupling and fitment of your prop shaft. It could be that the whole unit is seizing together. You also need to check it is true and free running. You need a prop and locknut followed by a thrust washer then at the inboard end a thrust washer locknut and coupling. There should be a gap between the thrust washer and bearing of a few thou', we used to use a Rizla paper, Make sure all joint are tight and that the shaft turns freely and smoothly. The motor need to be securely mounted to a good solid base and 100% aligned with the coupling and prop shaft. Personal experience tells me you don't get a second chance with brushless, you have been fortunate if it is only the prop tube has suffered. Is your hull wood, plastic, fibreglass? Whilst Araldite is a fine adhesive you may need to use Stabliz Express or UHU Acrylit Plus which provide an exceptionally strong joint. E-bay have sellers of UHU in the UK. Good luck and please keep us posted
do a test run in the bathtub you can leave the superstructure off and use the throttle while holding the boat in place make sure you wife is out so the bathroom has time to dry out afterwards. Give it a run and see how hot the motor gets. The 850 is specified such that your prop should be fine. Please remember to include a locknut otherwise if you select reverse your prop could unscrew while sailing and you may lose the prop. Let us all know how you get along and enjoy .
What ESC were you using? My experience with 600 motors is that they are power hungry, smell a lot and get very, very hot. I had two in a Slipway Trent (they advise the ECO version, no longer available) and used to be able to smell them from the shore! Could be the ESC internals circuitry shut down and may start working again when cool. Any weed in your pond will definitely overload them, which was my problem. Too big a prop will also cause overheating. I had 40mm 3 blade brass props in the Trent. It's possible that the motor is to blame if it has cooked the coils and caused an internal short. Try running direct from the battery with an ammeter in circuit. I am assuming you have checked your propshaft for free rotation and no binding, locknuts can and do come adrift and can tighten up on the shaft, which may explain the slowing down you experienced. Please keep us posted with your progress Cheers Dave
Hi cliff How are you going to attach the props to the shaft? Normally if the prop shaft has a plain and threaded end, the threaded end goes to the prop with a locknut and thrust washer, The other end inside the boat has a thrust washer and a collett with grub screw(s). Dave
Hi Richard Whilst the delamination appears local chance are the fuel has penetrated well into the laminates together with water. Use whatever you want to patch the damage but a fresh piece of ply will probably be cheaper and more resilient. Cascamite will not work well with cyano. I would, after sorting the damage, use a thin resin poured and swilled around the hull insides to seal, followed by a covering of glass fibre or cloth over the outside impregnated with polyester lay up resin. You can fill any resulting blemishes with car body filler. As the model had an ic engine chances are the prop shaft will be showing signs of its age. Even if the bearings appear ok'ish the shaft is most likely bent or twisted. I suggest whilst you are sorting out the delamination you purchase a new unit of the same size. Most modern kit is metric so your shaft should fit any props and couplings you purchase. Some use an allen key to secure the coupling so this may not apply. Don't forget to fix a locknut and thrust washer at either end of the prop tube. If you look at the blogs on this site there are several example of how others have completed similar tasks Hope this helps Please keep asking if you need any further help Dave
Hi Grandpa Looking at the latest photos suggests the shaft and keel will be secure and if the prop is clearing the hull then the shaft may be long enough. You may need to add an extended coupling to allow for the motor. As I mentioned it would be a good idea to fit the motor, coupling shaft and prop now to make sure it all fits nice and square and runs freely. Don't forget you must have thrust washers at either end of the propshaft together with a locknut for both the coupling and prop.😁 I am in the Crewe club and Mark I believe sails with Etherow. We are both North West clubs so a few hundred miles from Canterbury. Good to hear you have a local modellers Club. Good building Dave
Do not forget to specify right or left handed the thread is the same but the direction of rotation is different and please do remember to fit a locknut ( and use locktite) so your new prop doesn't join the rest of the lost bits on the bottom of the pond
I would agree with Haverlock's advice so far and would add the BRChobbies is a good supplier of motors/Esc and batteries. I have used them in the past and their products are 1st class. I also believe you will need a much beefier motor and ESC (your wattmeter) will give you the amps and watts used so you will be able to avoid cooking and electrics. NiMh batteries give good power but for your application you need lots of power and LiPos are the best choice. Going back to my flying days it was usual the try several different sizes and pitches of propeller before the optimum was achieved. You cannot just add any prop to a brushless motor as they require a load that enables them to work within their wattage. That is why you need a Wattmeter so you can check and also make sure you are not exceeding the ESC rating or overloading the battery capacity. This is important with LiPos as they should not be discharged below about 3.3v but this should be marked on the batteries. Many ESCs have a built in cut off that can be set to the correct value. Unlike other batteries LiPos change internally if abused and there have been many instances where fires have resulted. U-tube has many examples. If you are new to LiPos then you need to be aware of the correct charging procedure using a dedicated charger. LiPos should never be charged unattended and preferably in a charging bag in an area near to an outside door should the need arise. I have used LiPos for many years without incident so correct use will reduce the chance of any accidents. As with any high speed high power setup you do need to make sure everything is securely fastened and the wiring neat and of the correct capacity. I once cooked a motor because I had not secured it correctly, I now always use bolts locknuts and washers, and check the mounting before every sail. Good luck and some pics and perhaps video on water would be good to see Dave
I have in the past threaded some brass bar and sweated this onto the prop shaft. Using a lathe you can then turn to the new die size and make a new thread. Make sure there is room for a locknut to fasten the prop. If the shaft bearings are thick enough you could buy an M5 threaded shaft and make new bearings or ream out the existing bearings. Dave
HI Les Haverlock has already answered your question relating to the thread and I agree particularly with his advice to use a locknut. The use of the correct thread is very important if you are running a very fast and powerful racing type of model where the forces acting on the prop are not small and are best used to keep the prop on the shaft, even with a locknut. The use of a locknut on a scale model where both forwards and reverse may be used frequently should help keep the prop in place. As regards two props it is beneficial to use contra rotating props as the model will be more balanced under way and will also respond correctly to the rudder in both directions, as already advised by jgs43. If you are modelling a true scale model of an original, say a lifeboat, then it will be important to replicate the full size arrangement on your model.
Most props whether left or right handed come with a right handed thread. The one company which does provide props with right and left hand threads is Graupner but only on some of the types and sizes - the thread direction is coupled to the handing of the prop so that they tighten on the shaft when running forwards. Does mean that you need to source a left handed thread on the prop shaft and I have only found one german shop/manufacturer which is able to supply M4 Left hand threaded shafts. As said by other posters easier to stick with right hand threaded and use a locknut. The props should rotate in opposite directions and the direction of rotation does create different effects on full size boats - e.g. raising or lowering the bow when running. Outwards turning props (top of prop) are also supposed to improve manoeuvering and are generally used on tugs and the like. There is also supposed to be an effect on achievable speed but you would need to search for the relevant article on the web. When the prop turns the boat tends to try and rotate in the opposite direction due to torque. Having the props on twin prop boats rotate in different directions cancels out this effect. The pilot on single prop boats is normally positioned either right or left to help counteract this effect - there are some very interesting articles to be found on the web referencing these subjects with respect to full size boats