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Author Topic: KING OF SHAVES STEERING problem  (Read 15291 times)

Dave J

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KING OF SHAVES STEERING problem
« on: September 18, 2016, 10:01:36 pm »

I have been running a KING OF SHAVES catamaran model which when on full power does not respond to the rudder unless the power is reduced. I increased the rudder width which gave improvement and also added two side rudders, but it will not turn until the power is off, I wondered how can I resolve this problem?
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derekwarner

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Re: KING OF SHAVES STEERING problem
« Reply #1 on: September 18, 2016, 11:10:25 pm »

Dave....a little difficult to see from the images, but it appears that the outer rudder blades are knife profiled on the leading edge and outboard side only

You note that the main [central] blade been extended in length [fore & aft]

Again, very difficult to see, but is the depth of the central rudder blade as manufactured & supplied?......the image from the WEB site questions this

When we think of the dynamics of the movement of the water, the original central rudder blade is the only one in direct flow of the accelerated water from the propeller. The outer two are only creating an angular resistance to the speed of the hull through the water

From studies too many years ago, & if the memory bank is in gear.....the issue may be too much turbulence at high RPM, and the propeller is being subjected to & causing cavitation so hence the lack of steerage at high RPM...... another part of the equation is the distance of the rudder blade from the propeller & to complicate things further many high speed drives have the rudder blade offset to the axis of the propeller [relative to direction of the drive hand of rotation]

I am sure one of the high speed drive members will offer a more concise answer

Derek
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Derek Warner

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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #2 on: September 19, 2016, 10:51:47 am »

Derek,


Thank for your comments, the main rudder has only been extended on the back edge the length as original. I agree the cavitation from the propeller must be part of the problem, I could try and increase the the distance between the prop and the rudder. I have also been looking at the underwater stern recess distance to the stern hull end, could that influence the problem? On the plane this area would be above the water?. Do other catamaran hulls have this turning problem?


Dave
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #3 on: September 19, 2016, 09:42:56 pm »

A cat only needs one rudder,sounds to me like your servo or pushrods are not doing their job properly ?,if anything at speed a boat needs much less rudder input to turn than when running slow.Its possible with the central rudder you are putting a lot of strain on your servo and it may not have the power to do the job,most people don't use rudders directly behind the prop on surface drive boats especially when using large props,they cause too much prop wash for the rudder to work well .Adding the two outer rudders isnt the solution here,you need a high torque servo and good strong pushrods if sticking with the original rudder in centre. .
My advice would be try a stronger servo on the central rudder and remove the others and if this doesn't work then go with one single offset rudder on the right like most use,then you wont have any problems turning either way and your boat will gain some speed also as the rudder behind the prop will slow you down more than you realise.
Also you have too much up angle on your prop that isn't helping either,set it so it is level so all the thrust is directed where it needs to go rather than up in the air.It also looks like its quite high up ? when the boats sat on a flat surface with the rudders hanging over the end set the strut so the bottom of the strut hub is level with it then raise it maybe 1/8" and you should find it runs better there.
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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #4 on: September 20, 2016, 11:27:39 am »

Thank you for the suggestions, I will try and re position the rudder along side the prop. looking at a side view of your system is the rudder in front, level or behind the prop, which would you suggest as the best position? I will change the servo and upgrade the pushrod setup. I can fit the original rudder bracket to the rear transom but depending on position I may have to add a suitable distance piece.
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #5 on: September 20, 2016, 01:44:04 pm »

On a cat most people seem to go alongside the prop some just behind but some cats like them sometimes closer to the transom ,having it too far back on a  cat can sometimes create strange handling .Pic isnt of my boat but a customers as i build these cats.
Heres another pic of this same style cat its a Thunderbolt but a similar setup should work on most cats.Personally i like it as in this pic it seems to give the best results on a cat .
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chrisholleyuk

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Re: KING OF SHAVES STEERING problem
« Reply #6 on: September 20, 2016, 02:32:42 pm »

Can I ask why it has the 3 rudders?
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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #7 on: September 20, 2016, 07:37:59 pm »

The hull originally had one rudder positioned behind the prop which would not respond to the tx stick with power on, I then added 15mm to the back of the rudder which did not have any effect. (unless the throttle was low and the hull was off plane and without thrust.) Thoughts along the lines that it also needed side control outside the central thrust line led to fitting the two linked side rudders.
This rudder arrangement was a experiment which did not correct the problem, it did give more movement but was not as successful as I expected. That is the background to my Question. I have had good advice and I am now in the process of fitting one side rudder and different servo and I hope getting the balance right.
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #8 on: September 21, 2016, 08:13:23 am »

Dave just as heads up you need a metal geared servo of at least 12-13 kg torque,normal sized will do just so long as it has enough torque,the ones i use are 16 kg and i use them on my 58" Apaches and the 50" cat .
Hope this solves your problem for you .
Another thing to check is possible signal interference ,are you using a resistor plug on the engine ? ie number should begin with an R this stops any chance the engine interferes with your radio signal . Might also be worth a check to rule out that possibility .
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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #9 on: September 21, 2016, 11:09:32 am »

I have just ordered a Hitec servo HS-5585MH 17kg standard size, the one in the hull at present is a Futaba S3003. the Zenoah engine has a Champion plug RZ7C.
I have been using Futaba radio 2.4 and have not experienced any electrical interference up to now.
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #10 on: September 21, 2016, 11:45:23 am »

Hi Dave while the Champion plug is a resistor plug they are renowned for breaking and parts going inside and destroying engines so please throw it away and get yourself an NGK plug .Glad i mentioned it now as id hate to see you ruin a good motor,its the first part most of us throw away when we by a zenoah engine .

http://www.ebay.co.uk/itm/NGK-CMR7H-3066-Standard-Spark-Plug-Replaces-RZ7C-/361558368234?hash=item542e8edfea:g:-qUAAOSwdV1XNyk8
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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #11 on: September 21, 2016, 04:40:55 pm »

I have not had a problem  with the RZ7C plug but I will change it for the type you advised.
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MichaelRanger

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Re: KING OF SHAVES STEERING problem
« Reply #12 on: September 21, 2016, 09:57:48 pm »

Hi Dave,

Just seen your article and l think that the issue has already been answered by other contributors, but l would have said straight away that the servo isn't power full enough and you are stalling it. I have experienced the same issue with a mono hull and l was advised that you need a servo with at least 20kg thrust so you may find that the new Futaba servo that you have ordered may still be marginal. I am now using a Trackstar servo from HK running on a 2 cell lipo which for £28 gives you 30kg of thrust. I made life complicated for myself as although the RX can also work on high voltage the throttle servo was a standard one and l fitted a MKS in-line BEC unit to reduce the voltage to this one servo.

I hope that my advice will resolve your turning issues.

Michael
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MichaelRanger

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Re: KING OF SHAVES STEERING problem
« Reply #13 on: September 21, 2016, 10:01:48 pm »

Dave,

Make sure that there isn't any flex in the pushrod and use a 3mm pushrod.

Michael
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #14 on: September 21, 2016, 10:21:05 pm »

Ive been using 16 kg servos in my 58" Apaches without any issues but more kg wont hurt ,that said a cat doesnt need much to turn it like a large mono hull does and much less rudder throws unless you want to spin out a lot lol .17 kg should be plenty,the one he has in it only has a tad over 4 kg torque so theres the culprit right there. .
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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #15 on: September 22, 2016, 10:09:44 am »

The rudders are now off the hull and I do intend to upgrade the servo and pushrod etc as suggested. When I look at the design of the stern of this hull (see picture oo2 on first posting) the last step on the cat hulls is at least 8 inches from the original rudder position, the hulls on other cats appear to have the last step nearer to the rudder, although the design can not be changed could this also effect the steering?   
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #16 on: September 22, 2016, 09:04:01 pm »

Yes the sponson transom is well short of where your prop is at so this can and will effect things but that said there are a few of these cats out there and while they aren't the best handling of cats it should still turn with a decent servo etc just not sharply .For comparison here's the bottom of one of my Thunderbolt hulls .Prop is much closer to the sponson transoms than on yours as you say.
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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #17 on: September 23, 2016, 08:02:45 pm »

I have now re positioned the steering post bracket to the right hand side. I had to fit a 5mm thick Ali plate to the inside of the hull to strengthen the transom this was then drilled and tapped to support the steering post. With the transom not being square I also had to put a tapered distance piece in to position the rudder so the leading edge will be at 90 degrees to the hull. ( The rudder still has the distance piece added) The push rod and servo have still to be positioned.
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #18 on: September 24, 2016, 08:34:18 am »

Should work once you get your new servo and pushrods fitted,one thing ill say is try and level your prop angle so theres no up angle,if anything on a cat you might need a tad down to keep her on the water at speed as cats create a lot of lift but start level .
Is the prop sharpened and balanced ? if not id try and do that if you know how ? or buy one thats done for you.
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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #19 on: September 24, 2016, 02:55:50 pm »

At present the servo has not arrived and the linkage will be on hold until I can line it up correctly. I will reline up the prop to the level position and I had balanced it for earlier runs.
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #20 on: September 25, 2016, 09:56:26 am »

Another good idea at some point would be to get a brass prop tube instead of just the teflon tube to avoid any chance of the cable whipping and destroying your hardware or damaging the motor .I see that setup on a lot of these Chinese rtr boats and its just not the best idea to be honest .
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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #21 on: September 26, 2016, 11:30:18 am »

Another good point, at present the brass outer tube only goes from inside the hull by the coupling through to the entry out of the hull. I have enough thin wall brass tubing the correct o/d to cover the teflon tube from the hull outlet to the prop skeg. The tube will need a slight bend in it, what would be the best way to bend it to suit the prop angle etc?
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #22 on: September 26, 2016, 01:03:19 pm »

Hi Dave all i do is install the flex into the brass tube or a spare one if you have one ? then bend it by hand using gentle thumb pressure  the flex should stop it from kinking but just do it carefully and you should be fine.Wondering if you do it as you suggest that the tube has somewhere to lock into ie will it fit inside the other brass tube or is it the same diam as it needs something to hold it from been able to move .Might be best to redo the whole thing in one piece at a later date ?.What i do is once im happy with the bend of my tube is i take the next size up cut a 4" piece and use that as the through hull fitting,i then epoxy this in place using some plumbers epoxy putty,this way if you ever need the longer tube out it will slide right out.
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Dave J

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Re: KING OF SHAVES STEERING problem
« Reply #23 on: September 26, 2016, 10:56:13 pm »

Mart, I have decided to replace the complete tube, the tube I have is 11mm OD and is a close fit over the teflon liner. The tube will not move it is rigid so I have tried to soften it with heat buI have not tried to bend it yet. I have also tried to drift out the tube in the hull but that was not successful, I will have to remove some of the fibre glass under the radio box inside the hull to release it. I could not fit a smaller dia tube at the prop skeg end because the teflon is a neat fit, the tube should give enough strength when supported at the hull end through to the inside.
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martno1fan

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Re: KING OF SHAVES STEERING problem
« Reply #24 on: September 27, 2016, 12:02:12 pm »

You should be able to loosen the tube from the hull by dremeling away some of the material holding it in place once youve done that give it a light tap with a hammer and a block of wood and it should come out , dont go too mad as you dont want to damage the hull as these hulls are quite thin as you know. As regards the strut  if you get 5/16 od brass tube and do away with the liner the tube should fit into the strut  as mine do ,might need to use some emery cloth on the end of the tube to let it slide in but it should work.You dont need a liner just use plenty of grease and your good to go.

http://www.ebay.co.uk/itm/STUFFING-TUBE-for-36-x-1-4-6-35mm-flexishaft-rc-model-boat-brass-8mm-/391244889514
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