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Author Topic: what turn fins to use???  (Read 4329 times)

MikeA

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what turn fins to use???
« on: January 13, 2012, 05:27:11 PM »

hi all. Ive decided i need to use turn fins on my fast electric but i dont know size to use. I looked on prestwich and the smallest they do is 50mm. That seems excessive for my small boat (600 length 200 beam) as my rudder is 75mm! what should i  be looking for please?


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martno1fan

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Re: what turn fins to use???
« Reply #1 on: January 13, 2012, 10:14:07 PM »

Id say 50 mm would be fine,bare in mind Gasoline powered boats are using 80 -90 mm fins on anything from a 4 ft hull to 6 ft and more.Just be sure when you mount them theyre not too low as you want them out of the water when the boats running straight and at speed so they only come in contact when she turns.
Mart
http://www.ebay.co.uk/itm/CNC-turn-fins-54mm-x-22mm-small-electric-rc-boat-/130291246781?pt=Radio_Control_Parts_Accessories&hash=item1e55f6a6bd

similar size boat to yours using those fins
http://www.ebay.co.uk/itm/25-deep-V-electric-rc-boat-kit-w-motor-ESC-/140463254534?pt=Radio_Control_Vehicles&hash=item20b4432c06
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pompebled

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Re: what turn fins to use???
« Reply #2 on: January 13, 2012, 11:04:21 PM »

Hi Mike,

Make your own out of sheet aluminum!
Like Mart said, don't make 'm too long, which will induce drag when running straight.

I'm no fan of the 'standard' turnfin, something like this works much better on my boats:



Regards, Jan.
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MikeA

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Re: what turn fins to use???
« Reply #3 on: January 14, 2012, 10:57:22 AM »

thanks very much to both of you just guys i needed to hear from.

to mart:

I have looked through ebay and these popped up:

http://www.ebay.co.uk/itm/150540753493?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2648

i think they are the same brand as the ones you picked out. will these do it? im tempted by the cheaper alternatives but last time i ordered from china it took nearly 3 months to get here!!

to jan:

I have been seriously considering making my own. judging by your turn fins they are perpendicular to the chine i thought they HAD to be 90 degrees to the transom?

like this:

http://www.ebay.co.uk/itm/25-deep-V-electric-rc-boat-kit-w-motor-ESC-/140463254534?pt=Radio_Control_Vehicles&hash=item20b4432c06

thanks

mike
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martno1fan

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Re: what turn fins to use???
« Reply #4 on: January 14, 2012, 03:35:28 PM »

Mike i order from Frank all the time and usually only takes a week to ten days for delivery.Those fins you linked are the same ones,Prestwich gets em from Frank so yes they will do just fine ;).
Mart
yes fins need to be angled at 90 deg to work best
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MikeA

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Re: what turn fins to use???
« Reply #5 on: January 15, 2012, 05:22:16 PM »

i ordered some from prestwich. I need to learn how to set them up before i can make my own so till next time thanks to both of you
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scoop

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Re: what turn fins to use???
« Reply #6 on: January 15, 2012, 09:39:14 PM »

i ordered some from prestwich. I need to learn how to set them up before i can make my own so till next time thanks to both of you
and don't forget to file the very sharp point off....you only walk into them once when they are on your boat stand, they go very deep into your flesh....ouch  :} got the scar to prove it  :embarrassed:

Scoop
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martno1fan

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Re: what turn fins to use???
« Reply #7 on: January 15, 2012, 10:26:41 PM »

and don't forget to file the very sharp point off....you only walk into them once when they are on your boat stand, they go very deep into your flesh....ouch  :} got the scar to prove it  :embarrassed:

Scoop


Haha hope its not anywhere delicate  :o
But yea good tip lol.
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MikeA

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Re: what turn fins to use???
« Reply #8 on: January 16, 2012, 10:51:37 AM »

thanks for the tip. i wouldnt have considered that, i will probably get them today (fingers crossed).
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martno1fan

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Re: what turn fins to use???
« Reply #9 on: January 16, 2012, 04:08:55 PM »

Also when boats not in use get some bits of pool noodle and slot em to slide on them so nobody gets hurt ive sliced my hand on em before now not pretty lol.
Mart
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MikeA

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Re: what turn fins to use???
« Reply #10 on: January 19, 2012, 06:03:25 PM »

so ive got the turn fins installed ive had the boat out today and they havent really made no difference really. I think ive made the V on the hull to shallow so its good on the straights but wont take a turn over half throttle with bouncing. In fact i took a turn too fast today and the boat barrelled 360 deg! I fettled about with the angles a bit dont really know what im doing to be honest to get the best results.

anyway here they are installed i think theyre a good size. i managed to strip the starboard fin allready and had to put a nut on!!






what should i do to set them up, should i point them straight down to start and lift em up till im happy? I really hate these things where you have to fiddle about with them till they work best im never happy with them.
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Craig Dickson

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Re: what turn fins to use???
« Reply #11 on: January 19, 2012, 06:11:52 PM »

Hi Mike

In my opinion you need to have those fins fully down (vertical).
I have them that way on my 47" Lynx mono and they do the job well.



Cheers
Craig
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Craig Dickson

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Re: what turn fins to use???
« Reply #12 on: January 19, 2012, 06:24:58 PM »

Just a further point, my fins are quite long and mounted as low as possible at the outer edges of the transom. However they are still out of the water on the straight when running full throttle as hopefully these two images show:




Craig
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martno1fan

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Re: what turn fins to use???
« Reply #13 on: January 19, 2012, 06:26:30 PM »

Mike where does your boat balance at ? you should be looking to have the cog at arround 28-30 % of the length of the boat measured from the transom.Theres no fast way to fine tuning your boat to get the handling sorted im afraid its all about testing and adjusting one thing at a time.Try the fins all the way down as suggested and see if that helps the turns.
Mart
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MikeA

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Re: what turn fins to use???
« Reply #14 on: January 19, 2012, 09:34:27 PM »

I reckon the cog is about right i have a video on youtube i made today, if you look about 19 secs you get an IDEA of the ride attitude im afraid its not a good quality vid.

http://www.youtube.com/watch?v=qwxvfQKKzSY&context=C35bb573ADOEgsToPDskLVBJ8Dcn-Y4Wv-9eu7qagj

The outcome of the hull being shallow V was an accident, It gets on a plane very quickly but doesnt ride nowhere near as high as craigs.
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Craig Dickson

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Re: what turn fins to use???
« Reply #15 on: January 19, 2012, 09:51:32 PM »

Hi Mike

I just enjoyed viewing your clip and frankly I was impressed with your boat. From what I saw a bit of fine tuning is all that is needed.

Riding very high on the water isn't always a good thing. As demonstrated from this clip of my twin brother's lynx BEFORE he got it trimmed out and tamed!  :embarrassed:

http://www.youtube.com/watch?v=9VDx_XeFSBI

Cheers
Craig
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pompebled

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Re: what turn fins to use???
« Reply #16 on: January 21, 2012, 09:40:54 PM »

I have been seriously considering making my own. judging by your turn fins they are perpendicular to the chine i thought they HAD to be 90 degrees to the transom?
mike
Hi Mike,

I've tried various angles and vertical seems to work best for my boats, so it's a matter of trial and error, until the boat behaves the way you want it to.
I'm not surprised you didn't notice much difference with or without the turnfins, those things are waay too small to make a mark at the speed you're going, why do you think my turnfin is the size it is, small doesn't work for me, as I have to negotiate 60 corners racing around the triangle course.

Regarding the video; I didn't see much wrong in how the boat behaves, it may have run a bit too wet, but the circumstances called for that.
You didn't make any turns that were narrow, or quick enough to provoke a spin, so I could not tell if the turnfins actually worked.
The motor didn't sound like 3600KV on 3S, or didn't you go full throttle at any time?

You throttled down before every turn, that's not the way to do it with a well set-up boat, in these conditions I corner nearly at full blast, the turnfin keeps the boat pinned down, when conditions are calmer, I don't even blip the throttle when cornering.

Here's a compilation of my Arowana (purple/yellow) running with an (yellow) Xcalibur in Mono II set-up and of my white Xcalibur in a Mono I set-up (a 1700KV outrunner on 3S turning a 45K).
There was a lot of wind, so the turns were not as narrow as could be, as the risk of getting blown sideways and missing a marker was too great:
http://www.youtube.com/watch?v=I2h1kWwaFCA&list=UUQb0kIx1hJggO2SRadzYsuw&index=35&feature=plcp

Regards, Jan.

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MikeA

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Re: what turn fins to use???
« Reply #17 on: January 22, 2012, 01:12:01 PM »

on that perticular video the fins were not pointed down to much. I went back to the lake yesterday and pointed them down near vertical then gradually reduced till they were affective. The boat does run a little wet but its not as bad the video makes out.

Im not sure but i think the additional weight of the turn fins hanging off the back has pulled the prop under a little making it rpm slower, but i also had to keep slowing down in the video so the boat would keep in camera shot.

The turn im taking had to be that wide and had to be slowed down. The boat gets onto a slide and starts to skip in most occasions completely flipping onto its back. The other day it rolled over completely and landed right side up again which was fortunate.
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pompebled

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Re: what turn fins to use???
« Reply #18 on: January 22, 2012, 01:31:02 PM »

Hi Mike,

I must admit I'm a bit confused; you tuned the turnfins to be effective and still you have to throttle down to prevent a flip?

I'd say the turnfins still don't do a very good job.

I had a similar issue on my Arowana, when I mounted a 'traditional' turnfin on the transom; the boat would not corner at full speed without breaking away, often ending in a flip.

Once I mounted the larger turnfin on the side, I could corner at full throttle (on relative smooth water) without the boat spinning out.

Something else; in the pictures it looks as if your strakes run all the way to the transom.
Do you have a picture of the bottom?

Usually, the strakes leave a triangular space free on most designs.

With the strakes all the way back (and rather high for this size boat) the lateral resistance will be considerable; great for running straight, but when cornering, the hull will sort of dig in and when the forces become too great, it'll skip sideways quite sudden and violently.

Regards, Jan.
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MikeA

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Re: what turn fins to use???
« Reply #19 on: January 22, 2012, 04:26:14 PM »


With the strakes all the way back (and rather high for this size boat) the lateral resistance will be considerable; great for running straight, but when cornering, the hull will sort of dig in and when the forces become too great, it'll skip sideways quite sudden and violently.


That is exactly what happens!! I have no idea what made me put the strakes all the way to the back, i was following a thread/plan on the internet which explained strakes and they should be angled etc, this was part of my research:

http://forums.offshoreelectrics.com/showthread.php?2440-Darin-s-Wild-Thing-32-quot-P-Mono-Build

On my previous FE (the one i lost) I dont think the centre strakes went all the way back and they were definatly not as pronounced as the ones on this boat. I cant remeber why they do go all the way back of this boat, mightve been a picture id seen somewhere or just not watching what i was doing when building the boat.



When i lost the previous boat i was half way through building another and so i rebuilt this FE with salvaged parts from the lost one. I didnt want to put much money into it as i allready had spent a lot of my hobbies so i made the strakes out of strips off wood and they turned out rather large :embarrassed:

This would figure but the handling on the old boat wasnt much better and that didnt have the centre strakes all the way back, this clip shows that boat but its running 8.4 nimh not 3s lipo:

http://www.youtube.com/watch?v=MgPKYpQMF_k

Since i made the clip of the new boat i went back to the lake and re adjusted the fins, they are pointing lower now not quite vertical but definatly more than the they were when i took the clip. The handlings a little better but could do with somre more fiddling. I only have the one lipo and the moment and get about ten minutes before i have to come home lol
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pompebled

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Re: what turn fins to use???
« Reply #20 on: January 22, 2012, 07:23:21 PM »

Hi Mike,

You might consider removing part of the strakes, or at least trim them down in the rear part.

Regards, Jan.
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MikeA

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Re: what turn fins to use???
« Reply #21 on: January 22, 2012, 08:07:12 PM »

This boat was my 3rd attempt and making an FE. The mistakes i made on my first one was rectified on my second and in the process new mistake were made rectified on my 3rd. There is so much stuff to change on this boat that it would warranty an mk4 attempt. So im going to leave it as is instead of putting more time and money in it.

After all its ONLY me that sails them round here and turning in a large circle isnt much of a problem on a 1/4 mile wide lake
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