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Turn Fins

Old 08-06-2008, 02:21 PM
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VFR_RC
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Default Turn Fins

I am trying to find a good description of the purpose of the turn fins. What do they do and what happens when you don't use them?

I'd like to know this for a mono V hull.

Thanks
Old 08-06-2008, 02:49 PM
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mopartybob
 
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Default RE: Turn Fins

by using the SEARCH bar provided at the top left of the page,I was able to easily pull up numerous related threads..... , here ya go... http://www.rcuniverse.com/forum/sear...ilter=0&top=10
Old 08-07-2008, 08:54 AM
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Default RE: Turn Fins

Did you read the links you posted?
None of them answer my question. All the threads ask if turn fins are needed or how to place them. What I am looking for is "how do they affect the boat while on a turn"? I understand they benefit stability control during turns but how do they?
Old 08-07-2008, 11:45 AM
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Default RE: Turn Fins

Sorry I can't give you a textbook explanation,but from what i was able to gather AND DEDUCE from those threads is that the fins act like a rudder extension,as the hull leans more into a turn,less and less of the rudder is in the water becoming less effective,as the hull leans into the turn,more and more of the fin is in the water compensating for the lack of rudder which creates another pivot point and drag that helps induce and stabilize the turn....the deeper the fins are the more drag is induced, which equals more turning stability, but by the same token,drag bleeds off speed,which is why its also important to "tune" the depth of your fins to your hull characteristics ie:shallow-vee,deep-vee, semi vee,flat bottom,etc...., if you have too short a rudder,you will be able to lean only so much into the turn that should it lose contact with the water/pivot point,the stern or "back of the boat" will "break loose" and try to right itself, causing a very undesirable stability issue especially at hi-speed, whereas a longer rudder might be more beneficial in lieu of "no spin fins",this is not true as it's more beneficial to have a corner solidly planted in the turn that is created by the drag of the fin...I hope this helps you,....if you find out different ,let me know..... [8D]
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Old 08-07-2008, 02:00 PM
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VFR_RC
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Default RE: Turn Fins

your answer makes a lot of sense. in doing some research, i found another theory that says they are supposed to counteract the "lifting" tendencies of the rudder while on a turn. It says that when you are turning the angle of the rudder will make the transom lift.

Your theory makes sense, period. The other one makes sense what the rudder does but i can't see how the turn fin would reduce the lift created by the rudder.

http://www.rcboataholic.com/hardware/turnfin.htm
Old 08-07-2008, 03:02 PM
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mopartybob
 
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Default RE: Turn Fins

ORIGINAL: VFR_RC

your answer makes a lot of sense. in doing some research, i found another theory that says they are supposed to counteract the "lifting" tendencies of the rudder while on a turn. It says that when you are turning the angle of the rudder will make the transom lift.

Your theory makes sense, period. The other one makes sense what the rudder does but i can't see how the turn fin would reduce the lift created by the rudder.

http://www.rcboataholic.com/hardware/turnfin.htm
the fin does not really counteract the lift of the rudder,UNLESS there swept forward or back,but also acts as another pivot point for the hull to turn on, the angle of the rudder,whether swept forward or backward determines how much lift is generated as it sits deeper in the water than the fins,for instance, with the rudder swept backward,this will cause a "bow up" attitude when turning,whereas a swept forward rudder would create more lift at the stern,forcing the bow down,all this PLUS the relationship of the drive angle,whether pos.-neg., determines in the overall fine tuning of the hull for speed and stability... it is a fine act of balancing all these factors when setting/tuning your hull.... [8D] I always start out by zero'ing all to a neutral setting,(rudder,strut,tabs,fins...) as my baseline, then log and record small adj. (one at a time) whilst checking for desired results,...... also prop size,pitch,#blades will also play a big part in the overall tuning of the hull..... [:-] stick with one prop size when doing all these adj.as any change in props will negate these efforts,drive you crazy,and require you start from a baseline setting all over again,just to regain your sanity..... [:-]
Old 08-08-2008, 04:29 PM
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Default RE: Turn Fins

thanks. it makes a lot more sense now.
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Old 08-08-2008, 04:45 PM
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Default RE: Turn Fins

whew..... I was just about out of B.S. there buddy....lol... but seriously,if you make small adj., one at a time,you'll be able to keep track of it AND your sanity........

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