Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Pleasure boats, Sports, Race, Power and Leisure Boats: => Topic started by: Drkomen86 on October 06, 2010, 06:01:49 pm
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I'm in total confusion at the moment, I have just fitted a 3600kv brushless motor, a 60A ESC and a 3cell 5000mAh Lipo to my 42" Cat.
The only problem is I'm not quite sure what prop to put on it, I have a few here ranging from 30mm - 50mm and all they do is froth up the water behind it an not really move.
Please can some body help as it is quite upsetting when my yacht is faster than my speed boat :}
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I'm in total confusion at the moment, I have just fitted a 3600kv brushless motor, a 60A ESC and a 3cell 5000mAh Lipo to my 42" Cat.
The only problem is I'm not quite sure what prop to put on it, I have a few here ranging from 30mm - 50mm and all they do is froth up the water behind it an not really move.
Please can some body help as it is quite upsetting when my yacht is faster than my speed boat :}
3600rpm per volt and 11 volts, that prop is spinning some! :o
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if thats how its worked out then yes but I'm not to sure :embarrassed:
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Is it surface piercing or submerged drive etc.???
if its frothing the water it is cavitating, ie not gripping the water, just dragging air in from the surface, it could be a load of reasons depending on the question ie too light in the stern etc if its submerged drive etc etc, but you need to ascertain what type of drive it should have.
sub.
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here is a picture, hope it helps
(http://s3.postimage.org/R_pV0.jpg) (http://postimage.org/image/31mo1slms/)
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Hard to see from the pic but a rough guess is that your prop is way too high. Take a couple more pics, one from directly behind the boat and one of the back of the boat from the side.
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Found a pic on RCU that gives a better idea of placement.
You have removed all possibilities of trimming your cat to run at its best by not using an adjustable strut. Are you using a flex cable?
(http://origin-images.rcuniverse.com/forum/upfiles/326194/Rm38050.jpg)
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what are the other figures of the motor, just the KV is not enough info as you can get a very small 3600kv or a very large 3600kv yes the voltage will give the revs but you know the size of motor to get a prop size.
Peter
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drkomen 86 that to me looks like it should be a surface piercing set up and the prop from the pic looks way. to close to the transom. useually the are away from the transom and on flexi drives and run clever type props as per the other pic posted. the race boys should be able to help more post a pic of the stern side on. regards sub.
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Rotational Speed 3600 RPM/V
Continuous Current 45A
Max. Current 52A
Input Voltage 8 - 18V
Max. Efficiency 90%
No Load Current 1.9A
Internal Resistance 0.0119Ω
Hope thats better :-)
Its a solid shaft and was pre fitted to hull when bought so would be a massive job to change {:-{
(http://s3.postimage.org/TUFbS.jpg) (http://postimage.org/image/35i6oxldw/)
(http://s3.postimage.org/TVaCJ.jpg) (http://postimage.org/image/35is6x3t0/)
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Props way too high and looks way too small to move the boat well ,look at the size we gas boaters use for 42" cats theyre arround 65-67 mm minimum as seen in Ians pic,you def need to ditch the solid shaft and switch to a flex setup in my opinion,easy enough to do then use a strut on the transom which will allow you adjustment to get the right setting on the prop depth etc.Usually they start by sitting the boat on a table with rudder hanging over the edge and drop the strut so it sits flush with the sponsons and then the adjustments start from there making small adjustmenst after each run till you find the best setting for speed and handling.Cant help with the motor im afraid as i only run sparkies.
Mart
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Sorry but as Martin says if you want the boat to work you have no option but to rebuild the whole of the drive train and your best option would be a flex cable setup.
I can't help you with regard to whether the motor is capable of pushing the boat to a reasonable speed as electrics are not my thing. However a quick trip to and a look around http://www.xtremercboats.com/phpBB/index.php (http://www.xtremercboats.com/phpBB/index.php) coupled with a few questions should get you some good answers.
To help you on your way here is a build thread for a catamaran that should help answer questions about the installation of the necessary hardware http://www.modelgasboats.com/Magazine_Content/Boats/AC_R-42_Cat/ (http://www.modelgasboats.com/Magazine_Content/Boats/AC_R-42_Cat/). I'm afraid it is a gas build but the principles are the same.
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Martins spot on :-)) Also point of balance (c of g) i found 50% (ish) works for me ok2 Again you must be able to alter the height to get it right !
(http://s2.postimage.org/qSrb0.jpg) (http://postimage.org/image/1ijqehzms/)
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(http://s2.postimage.org/qSQ7r.jpg) (http://postimage.org/image/1ik6xvgkk/)
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thanks for all the help, looks like I have alot of work ahead of me then {:-{
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CG at 50% :o :o :o Wow, that is high...... More normal around the 30-35% mark.... Are you measuring from the absolute back of the overhang or the back of the running surface?
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Works for me ok2 To far back & she porpoises & trys to fly {:-{
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thanks for all the help, looks like I have allot of work ahead of me then {:-{
I am no expert on these type of boats (as I run deep V hulls with glow motors and fully submerged props) - however I don't think adding a suitable prop tube & flexi shaft, plus the adjustable strut shouldn't be too much of a job :-) - A bit of dremmelling and some fibreglass = a pleasant way of spending a wet weekend :-))
I take it you know where to get a shaft & strut from ?
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CG at 50% :o :o :o Wow, that is high...... More normal around the 30-35% mark.... Are you measuring from the absolute back of the overhang or the back of the running surface?
I agree with Ian :o :o
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Well Iam Happy with it ok2 And thats the main thing %)
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You would be even more happy if the cog was at 30-35 % its where most fast boats balance at ,if you go further forward they run too wet so your losing a lot of speed.If its flighty then its down to adjusting the strut angle to trim the nose down a bit.But if your happy with it its your boat ;) ;)
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She does run flat ok2 Turns Very well & goes like stink on lipo 4s :-) On 6s :o :o %% %%
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Almost as quick as this one :-) More than fast enough for an old f*rt like me :}
http://www.youtube.com/watch?v=KMqcX8Oy_Mg&feature=related
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I'm buying it all from ebay as a kit for £38 unless anybody knows where I can get it cheaper :-))
I realy need cheap as this project was ment to cost nothing and with no job at the moment keeping my hobby alive is very hard <:(
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How about a link to this kit then we can have a look ?,i know a good place in China for hardware if you dont mind waiting a week or so.
Mart
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here is a link to the kit Ive seen, I dont mind waiting aslong as it is good kit at a very good price :-))
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120629530229&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en
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I deal with P.M.B Fast dispatch 2/3 days ok2
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I would question whether a 4mm flex will cope with the propeller size I suspect you are going to need. As Martin said at that size of boat we (gas boaters) are looking at 65mm and upwards in diameter. But as said no idea when it comes to electric so the props in use might vary enormously. I would seriously try contacting people that are dealing with electric in that size of boat to see what they recommend before buying.
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http://www.astecmodels.co.uk/index.php
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ok, thankyou people
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ok little question, I'm fitting a 3/16 flex-shaft with drive dog.
what I want to know is can you get a 65mm prop in anything but brass, I want a cheap prop so I can swap and change very cheaply.
any ideas?
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Carbon propellers from MHZ http://www.mhz-powerboats.com/shop/shop.htm (http://www.mhz-powerboats.com/shop/shop.htm) in the larger sizes. You can also use a bushing to allow the use of 1/4" drive propellers.
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ok so what prop size would you start with?
the boat is 34.5" long and weighs about 7.5lbs with a 3600kv motor running at 11.1v and a 60A ESC.
Any ideas ?
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42mm,X442. any larger is gunna use a ton of amps in your setup and burn.
http://www.prestwich.ndirect.co.uk/octurapropellers.htm
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ok thanks, atleast its a start position :-))
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I'm in total confusion at the moment, I have just fitted a 3600kv brushless motor, a 60A ESC and a 3cell 5000mAh Lipo to my 42" Cat.
ok so what prop size would you start with?
the boat is 34.5" long and weighs about 7.5lbs with a 3600kv motor running at 11.1v and a 60A ESC.
Totally confused!!!!!!!!!!! What size is the boat????
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That motor and esc will not work in that hull the hull is to big for that set up,i ran the same in a 24" F1 using a 34mm prop and the esc kept shutting down to half power as the motor drawing more amps than the esc can cope with,any bigger prop will simply fry all your electronics
I have a video which shows this if you wish to see it.
also would defo change that hardware for more adjustment and better controlabilty otherwise will be a right pig to get right
Cg on thses hulls should be between 27%-35%.
Also start with small props and work your way up in size checking the temps but you wont be able to run any bigger than a 30mm on that setup and all you will have then is cavitation and the boat wont move.
If i was you i would get a lower Kv motor and bigger esc,swing a bigger prop on more volts,less amps,cooler running and longer run times and reliabilty
Hope you take note otherwise you ll be throwing your money away
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its a 34.5" hull, memory is rubish sorry.
I bought the motor and ESC for a smaller boat and when I put it on this it did as you said and shut down quite quickly, I guessed it was draining the battery having never use this type of system before {:-{
what hardware would you use?
I think I will keep the motor but buy an ESC with about 125A, what do you think?
Chris
PS thanks pal your a life/ESC saver :-))
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its a 34.5" hull, memory is rubish sorry.
I bought the motor and ESC for a smaller boat and when I put it on this it did as you said and shut down quite quickly, I guessed it was draining the battery having never use this type of system before {:-{
what hardware would you use?
I think I will keep the motor but buy an ESC with about 125A, what do you think?
Chris
PS thanks pal your a life/ESC saver :-))
Defo need a bigger esc as for hardware i would get 1 of these and youll be set,but you will still only be able to run a smaller prop or it will just burn the motor out i would say 36mm max but this would also let the motor rev due to the high Kv.
Hardware:
http://www.astecmodels.co.uk/catalog/product_info.php?cPath=1_79&products_id=748
hope this helps
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Cool, what would I need to get the highest speed possible out of the hull ?
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Cool, what would I need to get the highest speed possible out of the hull ?
you need to run lower kv and more volts to spin a bigger prop.
What hull is it and have you got more pics of the hull,then i would be able to be a little more specific
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The same design as this just 34.5" not 42" http://www.prestwich.ndirect.co.uk/Mercury.htm
And I have just noticed that the motor says Kv
3600Rpm/V
does that help?
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Maybe a trip here http://www.rumrunnerracing.com/feforums/ (http://www.rumrunnerracing.com/feforums/) would be of further help. Just electrics..... Here's a 36" mono for instance http://www.rumrunnerracing.com/feforums/showthread.php?t=30766 (http://www.rumrunnerracing.com/feforums/showthread.php?t=30766)
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The same design as this just 34.5" not 42" http://www.prestwich.ndirect.co.uk/Mercury.htm
And I have just noticed that the motor says Kv
3600Rpm/V
does that help?
The kv rating is is 3600 pre volt you put through it,for instance:
3600 x 7.4 volts = 26640 rpms unloaded or
3600 x 11.1 volts = 39960 rpms unloaded
The motor is 2845 so is a small motor,to small for what you want really.
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Cool, what would I need to get the highest speed possible out of the hull ?
Right i would use (option 1) Leopard 4074 2200kv 0r 2000kv on a 150 amp esc or bigger spinning a 42mm prop on 4s 14.8 volts.
(option 2) leopard 4074 1500kv on same esc as above on 6s 22.2 volts on 45mm prop maybe bigger depending on temps of motor and esc.
(Option 3) scorpion 3026 1600 or 1400 on 6s 150 esc,on 6s 22.2 volts and 45mm or 47mm prop.
I have run the scorpion setup in a 37" mono and must say i had longer run times and cooler running and is reliable punchy and quite fast.
Iv just ordered the leopard motors iv not run them yet but know some1 who is and said the motor for the money,ill let you know how i get on with them