'C' Class Boat Stability

Re: 'C' Class Boat Stability

feeds@yuku.com (toadtoad) — Mon, 07 Jul 2008 07:40:46 GMT

Raced at the weekend with a total of 470grams and the CG set to 435mm from the rear transom. Much better around the centre buoy and down the straight with the CG set correctly. Thanks everyone.

Re: 'C' Class Boat Stability

feeds@yuku.com (Dave Marles) — Thu, 26 Jun 2008 02:06:04 GMT

The reason the boat can be at its fastest at that point between 3 and 4 is because the gentle right turn will usually increase the speed of the boat and so coming off buoy 3 it will be faster than it will off all the other buoys. Hope this helps.

Re: 'C' Class Boat Stability

feeds@yuku.com (toadtoad) — Wed, 25 Jun 2008 23:34:29 GMT

Many thanks - I will add some weight before the next race.

Re: 'C' Class Boat Stability

feeds@yuku.com (Dave Marles) — Wed, 25 Jun 2008 10:46:43 GMT

If its between the 2 buoys then thats just propeller torque and 300 grams is not enough. 400 grams is the minimum, possibly 450 is needed but you can only find out by testing in a race. If you put too much weight on the left side, the boat will be very nervous on the straights, possibly rocking from side to side. Its also a good idea to use some throttle control at that point on the course anyway because often the boat will be at its highest speed after the right turn

Re: 'C' Class Boat Stability

feeds@yuku.com (toadtoad) — Wed, 25 Jun 2008 10:14:04 GMT

The problem is between buoys 3 and 4 and I currently only have 300grams of added weight. The boat runs a 2127 at present but could take a larger prop and has a 13kg rudder servo set correctly. Should I add 100grams to take the total added weight to 400grams?

Re: 'C' Class Boat Stability

feeds@yuku.com (Dave Marles) — Wed, 25 Jun 2008 07:58:15 GMT

It depends if this is directly after the buoy or on the straight between number 3 and number 4.
If the boat is turning in directly after the buoy then its most likely to be a problem of rudder shape or insufficient servo power. Generally the blade area in front of the rudder will be too small and/or the linkages are set incorrectly so that the rates are reduced too much and/or servo power too low. 13 kg torque servo is needed on 15cc boats with a good 6 volt 5 cell nimh or nicad pack....

Re: 'C' Class Boat Stability

feeds@yuku.com (Teslaboats) — Wed, 25 Jun 2008 00:34:05 GMT

I have a Tornado MK1, it does not show this problem so I do not think it is a problem with the design. How is the boat down the fast straight? is it stable? If it only happens when the boat is on the straight after the right hand turn only it could be a problem with the steering servo or linkage binding. Try to set the right tab level on the right turn and see if there is a change.

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Re: 'C' Class Boat Stability

feeds@yuku.com (BoBoKwok) — Tue, 24 Jun 2008 22:02:34 GMT

I don't have this problem on Tornado 1, 2000, EVO4 and EVO5
Too many reasons can be the cause of this sudden turn.
How much extra weight you have on the left side and which prop u are using?

Re: 'C' Class Boat Stability

feeds@yuku.com (HendricX) — Tue, 24 Jun 2008 14:38:46 GMT

Had the same issues with Tornado II and III .
I don't use trimtabs (anymore) ... because when I have them .. I'm alway's using them the wrong way.
Do you have the by Dave recommended 400gram (or more) on the left ?
I made a 5mm high 50mm long 'step' with 15mm flat , on the right side just on the balance-point.
This forces the hull to lean over left , on my hulls it helped.

'C' Class Boat Stability

feeds@yuku.com (toadtoad) — Tue, 24 Jun 2008 10:14:37 GMT

My boat (early Tornado) can suddenly turn right after turning the centre buoy, this only happens occasionally. Not sure why it only happens just after the center buoy when the boat is already travelling in a straight line. Is it a weight shift (i.e fuel) or just a torque reaction. I do have a right-hand tab which is raised when turning right. What is the technical reason for suddenly turning right and any suggestion how to reduce the problem?