Model Boat Mayhem - Forum

Dry Dock / Shipyard: Builds & Questions => Pleasure boats, Sports, Race, Power and Leisure Boats: => Topic started by: dazzle on June 19, 2015, 05:19:50 PM

Title: Help please re flexishaft and turn fin
Post by: dazzle on June 19, 2015, 05:19:50 PM
Hi All, Have a couple of ?? re a dragon shark 2 mono 1 fast electric, 1st could apply to any electric
nitro or petrol boat with a flexishaft.

1, Does a flexishaft tend to shorten when its revolving at high speed ? as I am trying to judge how much gap there should be between the dog drive, thrust washer etc and end of shaft tube.

Boat has a single quite long turn fin on the right hand side, which at the moment I have set the same as
the rudder approx 90 degrees to the transom looking side on, fin is angled inwards about approx 5 degrees looking from the rear of the boat see enc pic, Gave the boat 1 run on a 2s lipo, boat is very fast and seems to turn right ok, backing off the throttle a I can turn left in a wider turn I have not tried a
tight left turn. as know these boats are ment to turn right only, thats about sum of my knowledge as
surface drives go's.

Before I put the 3s lipo in it and after a search of the internet on rc boat turn fins, seems they angle
the fin everwhere inwards, outwards, also backwards so there is not so much of it in the water, my 2nd ? is where and what angle should the fin be set at ?

As along with my scale boats I mainly do fsrv, so  not got a clue about these flexishaft offset rudder
turn one way only little beasties, any help would be much appreciated.

Title: Re my post other pic
Post by: dazzle on June 19, 2015, 05:25:28 PM
Re my post flexishaft and turn fin, site only uploaded 1 pic here is the other
Title: Re: Help please re flexishaft and turn fin
Post by: Andyn on June 19, 2015, 05:32:13 PM
You'll probably find that turnfin is way too big, and will probably make handling non existent, could do with going outwards a bit but other than that position is fine. The flexi will need around an eight of an inch of spare room, as they do tighten up under pressure. It'll need checking for grease / oil in the shaft regularly
Title: Re: Help please re flexishaft and turn fin
Post by: martno1fan on June 20, 2015, 09:07:35 AM
The flex shaft will shorten a little under load , i always leave at least 1/8 gap sometimes 1/4".Your turn fin is way too big even gas boats only use 80-90 mm long turn fins usually and also its at the wrong angle it needs to be at 90 deg to the bottom  like this.Also turn fins only touch the water when the boat leans into a turn,you can fit one on each side to help turns both ways.Right turns are always sharper due to prop rotation ,having the rudder offset you should still be ably to make good left turns,your problem is that massive turn fin which is stopping your boat from turning left as its dragging in the water all the time.
Title: Re: Help please re flexishaft and turn fin
Post by: dazzle on June 20, 2015, 11:18:08 AM
Thank you Andy and Mart for your help, was just the info I needed, I knew  rubber/aluminium race couplings shorten by up to 3mm at high revs so had a sneaky feeling a flexi would do the same.

Also thanks for other tips, have the white and red teflon greases for flexishafts normally I use them on the rudders of my boats and oil the shafts, I shall use one of them and grease the shaft,  I will also buy a much smaller turn fin.

Your location sounds good Andy, reminds me of my second home, will buy you one or more if ever we meet,

Thanks again to you both for your help. Mick