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[red181]

Hi all,
some (more!) help required please! Fast electic 34" aerokits fireboat, gets on the plane really nice, but it will not turn! The bow dips severely into the water when turning, if it catches a small wave  in choppy water its like understeering with a car and almost wants to go straight on, and almost acts like a submarine!
I have been told its a rudder problem. I have a standard brass rudder, I have cut the corners off, and made the gap between the hull and the top of the rudder bigger, as it was very close, but it made no difference.

Any ideas please!

[grasshopper]

Now this may sound a little stupid but is the rudder shaft vertical?  Rudder Shaft angle can sometimes be used to trim speed boats in turns.

[john54]

Might be c of g does she balance 30% (ish) from stern ?
Also has she got a chine strip ? had the same snag on my elco.

[DickyD]

I thought I was the only one to suffer from this.
My Robbe PT15 does this. It has been built as per instructions so should be OK.
Only difference is I have a slightly more powerful motor.
If I cut back on the speed when turning it is OK, flat out it wants to go straight on.

[Stavros]

My imediate thouhgt was fit a bigger rudder but also have the same problem on a Marbelhead dammed thing won't Tack if it is heeling over and the rudder is mahoosive


Stavros

[DickyD]

I have one prop and two rudders on my PT boat Stavros.

[Stavros]

Maybee it is because the rudders are not in direct line with the wash from the props and this is causing your problem Dicky,can you enlarge the rudders at all



Stavros

[DickyD]

Possibly, what do you think. Rudders came with kit ? :-\

[tobyker]

On the strength of that photo, I'd say most of the stream of water off the prop is passing below the props at full chat. The rudders may well be in a ring of turbulence from the blade tips, and hence ineffective. The options may be (a) less thrust - ie go slower, or (b) make the rudders slightly deeper, so they project into and divert some of the thrust stream.

[red181]

Rudder shaft is vertical, cog is nice and low, running flat nimh packs, bow is higher than stern in water, looks correct. I was thinking rudder was too big, not too small, is it possible that it is acting like a brake causing bow to dig in?
This video has been shown before, however here is the problem,  watch after the first couple of minutes when its going fast. The turns are exagerated to show the problem however it does it on more gradual turns also

http://uk.youtube.com/watch?v=so5Ge9CNEV4

Thanks

[Shipmate60]

Is there too much throw on the rudder acting as a brake.
Any more than 35 degrees maximum acts as a brake on faster boats.

Bob

[tobyker]

I think Shipmate is right - its only seems to do it when it is asked to turn too quickly.

[modelman66]

had similar problem with bismarck looks like your rudders are too small and too far from props it will take a week to turn .my ship turns much wider when not under power [needs wash from props to turn fast] 

[Captain Jack]

Shipmate has the answer...decrease the rudder throw, and the problem is solved. Been there, done that.

[red181]

Hey guys, there seems to be two threads going on here, and I am getting confused!

Can we please stick to the original post, its a fast electric, as in video, single screw, single rudder, bow digs in at high speed turns, and moderate speed turns, virtually goes underwater.

I have had a very good suggestion fron hs93, that perhaps the rudder is too long in the water when the angle of the boat is on the plane, so I have trimmed the rudder to resemble that used on a fast electric racing boat, much narrower, and virtually all the blade behind the shaft, will be testing later in week, lets what what happens. As for bigger rudder, it made it much worse.

Thanks

[DickyD]

Be interested to know what happens. The only difference between your boat and mine is yours has one rudder and mine has two.

[GaryM]

Hi

Would the angle of the prop shaft make a difference - just a thought from a novice, but if there was a slight incline or decline, could this push the boat up or down, increasing the problem at high speed turns?

regards
Gary :)

[grasshopper]

propshaft angle can make a difference, too steep and you'll get that 'falling off the plane' effect. 

Watching the video, the model looks great, when you get to the second part with 'me' at the controls it looked very realistic (if not a little over scale speed? - are you just asking too much of the design? After all you have built a beautiful model launch and not a gung-ho electric racing boat that is supposed to turn on a sixpence. If the skipper of the real thing drove like that he'd have lost half his crew overboard and the rest would be seasick.

[red181]

Ha hA, Well said Grasshopper, I keep getting told off for exactly the same by the people I sail with, it is going too fast! Anyway, tonight rudder problem is sorted, and with the new 9.6v (x2) 4600 nimhs, I can achieve that speed for at least 25mins!

To cure the turning, we decided the standard rudder was acting like a brake. I cut off all the blade on the prop side (looking side on), and some of the other side of the shaft, making it resemble a fast electric style. It turns beautifully now (at speed), and if I ease it back to 3/4 throttle looks very nice, wish I had the camcorder with me! I think I cut too much of, as the low speed turns are a bit big, I would never win a steering comp now, so will do the job again, but leave a bit more on

Thanks for all comments

[nightowl2912]

i must say it dose look real good when you get to the second part with 'me' at the controls it looked very realistic
LOL

Andy