First boat runs better, still poor turns!

[jdwxly]

Thanks to Andrewg and others I added some turn fins to my boat to try and help it turn. It's a bit better (in fact, it turns MUCH better to the right now - more stable) but it still doesn't like to turn left at speed.

I think I found part of the reason. I have to run a bunch of right rudder trim to keep it straight at full throttle, probably due to torque. So there isn't much "left rudder" to use when I give it left rudder! Do folks running boats that turn both ways use a bunch more left rudder throw than right? A bigger rudder so less trim is involved? Or do I tweak the turn fins so it runs straight with the rudder centered?

Quick reminder details: it's a 23" V-hull, subsurface drive, ROAR Stock 05 motor on 7 cells, rudder is 1" wide and 2" tall, two turn fins.

Thanks for all the help, guys!

[Steve Vasdekis]

What size prop are you running? A picture will help alot.

[jdwxly]

Not sure on the prop size; it's whatever the guy sold me in the hardware kit. I'll measure the diameter tonight but I think it's around 30mm. All I know is it's red, fits an 1/8" shaft and seems to make the boat go pretty well :-)

I'll shoot some pics tonight, too. Might as well share what it looks like with everyone!

[AndyKunz]

If you are trimming right to go straight, something ain't right. It should try to turn right all by itself, and you would have to trim to left.

Andy

[jdwxly]

Weird. It is definitely going left on its own. I'll have to measure the trim, but I'd estimate the rudder is offset 1/8" to the right to get it to go straight at full throttle. It was the same way without the turn fins, so I must have got them on pretty straight :-)

The hull has a molded-in skeg/fairing for the driveshaft, so I don't think I could have gotten the driveline in too crooked. Maybe it's just my blunt, home-made rudder causing grief.

[Andrewg]

Can you post pics of the boat from behind; and looking straight at the bottom of the hull.

Sounds like its you rudder or your shaft isnt quite straight

Other things matter too

Andrew

[jdwxly]

Ok, here's a shot of the boat to see if I have the image size about right :-)

[jdwxly]

Now a shot from the bow:

[jdwxly]

and one from the stern:

[jdwxly]

I also measured the prop and it's 30mm diameter. I have no idea what the pitch is.

Thanks for all the help with this, folks!

[AndyKunz]

How far is Wilsonville from Portland? There are several guys there who should be able to help some. They frequent this site, so I expect them to chime in soon.

How does your boat balance in both directions?

Andy

[jdwxly]

Wilsonville is about 15 minutes from Portland (and Tammie's Hobbies, the local big hobby store), so hooking up with Portland area folks would be easy.

Balance wise it is right on left-to-right. Front-to-back CG is 9" from the transom.

[Greg Schweers]

You need to move all of the weight back (battery pack, etc.). If the cg is 9 inches from front to back, then you have too much weight forward. I know you can't move the motor. I think what's happening too is that with so much weight forward the boat is hunting to the left. If you're running a 6 cell stick pack, maybe you can put it across the back behind the motor. Plus, it looks like you could scale down the return fin and rudder. The size you have on there now you could run on a 12 cell mono.

[kyle.c]

i live in forest grove oregon i may be able to help out.

[jdwxly]

I'm running 7 cells, but it's split into a 3 and a 4 cell pack. I did a dumb thing and mounted trhe rudder servo over the stuffing box. I could move that to the right, then mount all the cells over the stuffing box and easily get the CG back. Here's a look inside:

[Garry Finlay]

jdwxly;

Hi, sorry I didn't pcik up on this until now. Andy just put me on to it. A couple of other boaters will meet @ 1:00 at the MurrayHill pond (S.W. Murray & Scholl's Fr Rd) - If it don't snow no more. We will be in Starbucks keeping warm.

Brian and Bill have more V hull experience than I. If you see this and can get there, the roads are starting to melt off, we'd love to at least do a little dry land racing. Brign your boat. It looks great in the photos. We will take a look and drink some mochas.

Garry Finlay

[Greg Schweers]

You need to move those batteries, the servo, receiver, speed controller all as far back as you can get them. You gotta remember that motor doesn't have enough power to keep the bow of the boat up. It should have been "turn" fin (not return fin)!

[jdwxly]

Garry:
I got your email too late to hook up with you guys. Keep me in the loop so I can try again! Thanks for the offer to help me with this (and thanks to Andy for pointing you my way).

Greg:
I can move the rest of the innards back easily to move the CG.

Do you think more power would help get the bow up? I also have some more powerful motors I could drop into it if that would improve things. But then I'll bet I get to learn about water cooling :-)

[MikeC]

Here is a good layout from Fullers website.It should work on any V hull

[jdwxly]

Thanks, Mike. My motor is WAY farther forward - it's 9" from the transom to the coupler.

I just measured and I think I can get a 4 over 3 battery pack between the rudder servo and the transom. This would move the cells back a bunch.

[Greg Schweers]

You're pretty much stuck with where the motor is going since you have a straight shaft. If you put a flex shaft in it, you could probably move the motor back, but before I'd do that I'd make the boat surface drive. Putting a modified motor with a subsurface drive would just overpower the boat--turning it into a handfull to drive, and you'd probably have to put trim tabs on it.

[jdwxly]

Going to surface drive would mean moving the rudder too, correct? Should I also cut off the sub-surface driveline fairing and fill in the slot?

I may end up going that route. But if that looks like the best solution I may just build a real FE Deep V and put a little motor in this for the kids to play with :-)

I just built a couple "3 over 4 cell" packs that will go all the way against the transom, so we'll see how it runs with those. I also built a new rudder that has a sharp leading edge instead of a blunt piece of 1/8" music wire!

[Paul]

Hello,

OK, now that I've seen the pics I can give some feedback here. I have built subsurface monos and have these suggestions for you.

1. Loose the turn fins! Belive me, you don't need them.

2. The prop is a x431, that will do just fine for sport running. if you want a metal prop go for the x430.

3. The boats CG should be roughly 6.5 inches from the transom. You "should" be able to do this by moving the batteries only.

Here's some pics for you.


http://www.fastelectricrc.com/gallery/omtrans.jpg

[Paul]

Another pic,

http://www.fastelectricrc.com/gallery/omrup.jpg

[Paul]

Shot of the inside.

http://www.fastelectricrc.com/gallery/ominteriorlayout.jpg

[Paul]

So, to sum up.

Put trim tabs like you see in my pics on your boat, you'll need them. ;-)

Remove the turn fins.

Move your electronics to the rear of the boat, servo should be fine where it is. Your weight is so far forward and much of it's on the left side of the boat that it will want to run left.

Once you make these changes I think your going to be really surprised at how it runs, mine was a blast on 6 cells and a stock motor. That boat took a first place in N1 mono running against all kinds of surface drive boats. It turned left and right equally well.

Let me know if you need some other help.

Paul.

[jdwxly]

Paul, thanks for the input and the pics. It helps to see a typical setup. Several folks have mentioned the trim tabs, so I guess I need to make a set of those. No problem there. Are they usually 1/16" aluminum or something like that?

I have new battery packs ready that should move the CG back a bunch. I'll let everyone know how it runs with those.

[Dan Proulx]

This might be a little off the wall but... the original Kyosho Vipers had a goofy little rudder that made the boat exhibit the same characteristics that you are complaining of.

We tried everything mentioned in this post - moving c.g., trim tabs, and turn fins on the right, left, and both sides - all to no avail.

The solution was to replace the stock rudder with either a wedge style rudder (we used the plastic wedge rudder from DPI) or a Hughey blade type rudder.

Then, magically the boat would turn either direction - no problem.

It looks like the bracket that you have on your transom would accept a Hughey rudder no problem.

Just a thought.

[jdwxly]

Thanks for the rudder info, Dan. I actually have a more "traditional" rudder ready to try as well, but I wanted to move the batteries first and see if that helped. One change at a time :-)

I'll check out the Hughey rudder if this doesn't work.

[jdwxly]

Ok, so I didn't make "one change at a time" :-) I threw on the new rudder and moved all the cells to between the transom and rudder servo. CG is now 6.5" ahead of the transom.

And it worked! Turns nicely both ways, runs straight with just a touch of right trim and goes pretty fast, too. The motor was very hot afterwards, so now I need to do some water cooling stuff.

Thanks for all the help guys. I'll try to get a picture of it running sometime soon. Shouldn't be too hard - my wife won't give me back the Tx!

[Paul]

Cool, glad to hear it worked out for you.