How do you "dial in" a 50 inch mono?

[Andrewc]

Hi all

I have a 50 inch P1 mono which keeps spinning out at both high and low speed. By high speed I mean 53 kmph as per video. https://www.youtube.com/watch?v=41OyTU36g2Es.

The boat is powered by two Leopard 5692 1090Kv motors controlled by two Swordfish Pro + 200 amp HV Esc. Running 9 cell per motor.

The props are Octura X457 counter rotating outwards but in the video they were inward rotating. I also have a pair of Octura 3 blade X450 props which I can change to.

The hull has turn fins and trim tabs. The twin trim tabs are set 2mm above the bottom of the hull. The stingers have the front of the props 130mm away from the transom. I currently have the stingers set flush with the hull.

I have no idea which adjustment to start with. I was thinking of perhaps removing the turn fins and the trim tabs?

Can anyone tell me what sort of settings I should start with and then which one to adjust first to stop the spinning out?

3cm To Start of turn fin.jpg2014-11-11 12.45.12.jpg2014-12-02 16.50.43.jpg



Many thanks for any help offered

[kfxguy]

I'm pretty sure your rudder is too small. I can't tell by the angle of your pics because your looking down upon the props and rudder but it looks too short for that size boat.

[RaceMechaniX]

A couple of suggestions:

Place a straight edge hull and adjust the trim tabs so they are parallel to the straight edge and ideally slightly 1/32" above the straight edge. i.e. parallel, but lifted up.
Rotate the turn finsso the leading edge is as close to vertical as allows from the mounting. In your case try the trailing edge of the fin dead vertical.
Take a straight edge and make sure the stingers are also parallel to the bottom of the hull.
Make sure your controllers have equal sync to them. i.e. if you have to program neutral and full throttle, make sure they are identical as best as possible.

From the video it sounded like one motor accelerated quickly and the other was lazy right before the spin out. Perhaps a loose collet or drive dog.
Your rudder may also be a tad short under the props, but it should not spin out at low speeds when it is buried.

TG

[jaike5]

A few more suggestions,

You also may need a 1/4 scale servo on a separate power supply (not the bec ) from the esc. you may be getting a lot of turbulence from the thrust cone of both stingers causing it to hook if the servo is week, and the steering rod is to small a dia. So a chrome (won't rust) welding rod for the steering linkage is in order. Also relax the outside trim tabs quite a bit they push the bow of the boat down while in the corners.

Cheers, Jay.

Cheers, Jay.

[Andrewc]

Many thanks for all your replies. I am starting to think the rudder is not deep enough into the water. It is only 20mm below the keel (4/5ths of an inch). My fault as I moved it but I can fairly easily move it down by 25mm which would give me 45mm between the keel and the bottom of the rudder. What is the ideal depth below the keel the rudder should be?

With regard to the turn fins if I am reading the replies correctly then Tyler is suggesting positioning them deep as possible and Jay is saying decrease the depth. Which way should I go initially as I can try both!!

I have attached some more pictures which may help. Sorry for the apparent delay in replying to your speedy replies but there is a big time difference between us.

Thanks everyone.DSC04522.JPGDSC04523.JPGDSC04524.JPG

[jaike5]

Many thanks for all your replies. I am starting to think the rudder is not deep enough into the water. It is only 20mm below the keel (4/5ths of an inch). My fault as I moved it but I can fairly easily move it down by 25mm which would give me 45mm between the keel and the bottom of the rudder. What is the ideal depth below the keel the rudder should be?

With regard to the turn fins if I am reading the replies correctly then Tyler is suggesting positioning them deep as possible and Jay is saying decrease the depth. Which way should I go initially as I can try both!!

I have attached some more pictures which may help. Sorry for the apparent delay in replying to your speedy replies but there is a big time difference between us.

Thanks everyone.[ATTACH=CONFIG]127737[/ATTACH][ATTACH=CONFIG]127738[/ATTACH][ATTACH=CONFIG]127739[/ATTACH]

Tyler said turn fins, Jay said trim tabs.

Cheers, Jay.

[photohoward1]

Definitely the rudder. 4/5th below the keel? I would say start at 2 inches below the keel. Do a test. Put the boat on a flat surface with the hardware hanging off the end of the table. When you lay the boat on its side. (like in a turn) the rudder probably comes out of the water. I just measured and mine are about 2.5" down from the keel. The Ideal amount is just enough so it does not spin out. Its not the tabs or the turn fins.

[Luck as a Constant]

4/5 doesn't make sense as a fraction...

I'm no mathematician tho.... maybe I'm wrong. I suppose it is, but why use it when measuring something? i understand if you're counting apples or something ... but 1/8's, 16's, 32's, or 64's weren't accurate enough? 4/5's is essentially what 7/16's? sorry for the rant here... but its just so vexing to me lol
is there even such a thing as a ruler that measures 5th's? I'm sure it was a type-o btw. i just like typing....
lower your rudder to start

[Fluid]

How anal. 5 mm is 1/5" (0.20") so 20 mm is 4/5". Got it now 'fingers'?





.

[Make-a-Wake]

Rudder not nearly far enough into the water. When you get it down...........a whole inch more at least, tuck it in at the bottom a bit to reduce spin outs in corners.

[Andrewc]

Well from the sound of things the rudder is the problem. Next question, where can I purchase a much longer rudder blade from as I cant seem to see anything longer than the 160mm (6 1/2") rudder I have.

Thanks to everyone for their advice.

[Make-a-Wake]

Cant you just lower the whole rudder where it is mounted??

[Luck as a Constant]

How anal.


.

boy thats the pot calling the kettle black lol

yeah sorry, I've just NEVER heard anyone use the term 4/5 to measure any type of distance before. are you saying that the 5th is counted as the whole? i still don't understand the math. your lesson didn't help me understand how 20mm is 4/5ths.... math was always a tough one for me

[rickwess]

boy thats the pot calling the kettle black lol

yeah sorry, I've just NEVER heard anyone use the term 4/5 to measure any type of distance before. are you saying that the 5th is counted as the whole? i still don't understand the math. your lesson didn't help me understand how 20mm is 4/5ths.... math was always a tough one for me

The OP used the term 4/5th as a close approximation to 20mm. 20mm = .79"...........close enough. I don't understand why you're having an issue with this.

[kfxguy]

1/5 of an inch is .200. .200 x 4 = .800....not too hard to comprehend, I agree is not a common fraction used, but it's still legit.