Trimming a tunnel

[GRoth265]

Here's a story. Last weekend I ran my new B stock tunnel for the first time. I put on a prop that I knew was going to work. I ran the boat a couple times to get the needle right and when the motor came in I noticed the boat was a little loose. I brought it in and added 2oz. of lead to the tip of the sponsons this brought the total weight up front to 8oz. I ran it again and felt it was running as good as any B stock in the district but after 5 hard laps it blew off in spectacular fashion breakining the one servo horn and the throttle servo. When I retrieved the boat I noticed the weight I had stuck on was missing. So I think I found my set up after things get fixed. My question is what do the rest of ya all do for set up? I'm posting this in the hope that some of are less experianced modelers will benefit Greg Roth B)

 

[Watercadet]

This is a great thread idea Greg!! Myself being a beging tunnel racer had a question allong those lines: What would you do if your boat is great - maybe even a little wet - with the wind, but at the end of the straight into the wind, will do a 720*? It is usually twords the end of an 8oz fuel tank. Would you leave it alone and DRIVE (let off) it, or add weight, or trim change? My set up is a DPI hull with a externaly stock ( ) SS, 1440 prop by Sholund.

Adam

 

[jydracing]

Hi All i always set up my tunnels a little tight just for the fact that when you go to a race you are running with other boats and the water gets rougher and it will loosen up the boat. I always run as big a fuel tank as i can in my tunnels in my 3.5 i run 8 oz and in my 7.5 and 11 i have 14 oz this way i do not worry about the boat getting looser as the fuel runs out. try this if your tunnel gets looser as the fuel runs out than put a few oz of weight where the fuel tank is and see what happens if this helps replace the weight with extra fuel. see ya jimmy

 

[Russell Bear]

I have a Word document that was compiled a few months ago by the fine people on this board. Lot's of good information here. It's too big to post, so PM or e-mail me and I will send it to ya.....

 

[GRoth265]

Adam; I don't even consider the weight of fuel in my set up. I balance the boat with a empty tank. If anything I would expect the boat to tighten up as I run it because the fuel is in the rear witch would make the CG move forward as I burn fuel. My B stock is a Hornet and it has excellent set up instructions that I follow closely. Theres a ton of factors that affect trimming,motor angle,motor depth,prop selection,dressing the sponson bottoms and balance just to name a few. I do agree with JYD that I want the boat a little tight when testing because thats not race water.If we explore this thread to its potential we could be going for weeks. I hope this topic stays alive because your going to find theres several roads to get to the same place. With all my tunnels My initial set up is proper balance, motor prop shaft bottom even with the bottom of the sponson and 1/4 degree negetive angle (pitched up) on the motor angle. Almost any boat I know of will run fairly well with this and then if the boat flies set the angle to 0 degrees on the motor and start adding lead.Hpoe this helps Greg Roth

 

[VansRacing]

GRoth,

Watch your boat all the way around the track as you drive it for signs of over-lift.

You want to tack it down enough so that when the water raises up, you still are within your trim window. Some designs have a narrow trim window and this is where boat selection is important. The Hornet will give good warning before it blows off if trimmed correctly. If it snaps off the water with little or no warning, you are not on your setup.

The art of trim is, being able to read your hull and put just enough negative thrust, prop height and nose weight to keep your boat on the water but maintain an acceptable speed. For heat racing, setting up tight is the way to go. How tight will come from experience. This is all based on conditions. Conditions such as, the number of wind breaks around the race site, overall pond size, bank angle and size of heats etc.

The biggest mistake I see people make is, coming to a race with their boat set up to run its maximum on "the pond at home" on slick water, and running by them selves. These are the boats you see upside down before lap 2 is complete. Then they chase their setup all weekend long trying to stay in the race.

-Carl

 

[Grimracer]

Well said Carl

We call test water.. The MUD. Its great for playing on but thats about it..

I, like Carl keep a close eye on my boat the first heat of each race i attend. If need be i make an adjustment after that.. The first heat "if you do not know your setup well" is a good time to back off, take your licks and after, tune the boat.

ROCK ON

Grimracer

 

[user 115]

Greg,

Don't you mean positive angle? If the engine is pitched up(prop pulled away from the boat) you have postive angle.. If the prop is tucked under the boat, you have negative angle.. Perhaps I read that wrong but you said if the boat flies off you then set the prop to zero, so I am assuming you initially set the boat with 1/4 degree Positive angle.

Charley

 

[user 115]

By the way.... That was quite a flip.. The boat was definitely moving at the time..

Charley

 

[Mark Anderson]

The first secret that most completely miss is to read and follow the directions that came with the boat!

Then test to alter the set up to your driving style. Get it close at the test pond then take it to a race. Watch what the boat is doing. If possible get a co driver that can give you reliable input as to what the boat is doing. Then make small changes one thing at at time and pay atention to what the change does. It may take a couple of race days to really dial a boat in or it make take one heat. Record your set up so if you go wrong you can get back to a base line. On test days I may try different set ups to learn how the boat reacts to different changes. Once a boat is dialed I rarely find a need to change anything other than possibly adding weight to the c.g if the water is really sloppy.

One very important tool to have is a set up board. Take a piece of plywood or mdf big enough for the boat to set on and cut a slot for the lower unit to set in on one end. Use this board to measure engine height and angle and record your measurements.

Mark

 

[jydracing]

hi greg i do not set my cg with fuel in the tank. the fuel is a moving weight the more you run the less weight you have. i have walked around the ponds during openwater and watched the diffrent boats running. in your first post you said that after running 5 hard laps the boat flew off. i would suggest to set the engine angle to 0 and add the weight back to the nose of the hull and if it still wants to lift try putting some weight on the cg of the hull that way you are weighting the whole boat insted of just the nose. see ya jimmy

 

[Mike Hughes]

Here is a little tip. Last year at nats a buddy of mine was having trouble with his setup on his 7.5 stock. He had lost his motor setup at the previous race and had not quite got the sweat spot back again. He was close. About 5/8 of the way down the shute the boat was having a little hop. He was concerned it was going to catch to much air and blow off. He needed to keep it pegged cause he had drawn a couple of fast guys in his heat. I suggested that he give it a slight left to right waggle down the shute. Not much. Just a touch. The boat settled and did not scrub speed. He ended up winning that heat.

Mike

 

[VansRacing]

Mike,

There are a few things that can cause that problem. The most commom is: too much negative thrust angle. Sometimes too much nose weight can cause it and even having the prop too low can cause the same little hop.

If he can feed a small amount of steering in it and save it as you said, then his trim is very close to being perfect. At this point, he only needs a very small amount of one of the things mentioned above to fix it.

-Carl

 

[Mike Hughes]

Carl

It was one of those last minute deals. With everything going on, he had not found time to get out and get it right. Open water at nats is not a place to be doing your testing. 1 or 2 laps and put it on the shelf to the start of first round. He is a little high strung when it comes to his B stock and was a little wound up about it not being perfect. Having him do the input to the steering calm him down enough so that he could run his race.

Mike

PS Cool avatar!!!!

 

[GRoth265]

Hello all; I ran my boat today and after the repairs I'm very happy with the way its running. I started this to hopefully get some of the ideas and technology out there for everybody to share. Theres been some good advise put up like Mark's board that we all borrow from time to time and the placement of weight. Carl said it though. FOLLOW THE INSTUCTIONS I set mine up just like it say's and only needed 2 ounces of lead to make it happy. If I had the terminology wrong for the motor angle sorry Charlie it goes back to my RC airplane days and as you will find out I'm easily confused. Greg :huh:

 

[gene gager]

Greg, how many times do I have to tell you not to ask these silly questions?? one more time on set up!!! you must untuck the motor ,go to bigger prop, remove all forward weight, add minimum of 60% nito,pull out all head shims, raise the exhast port, put an on/off throttle switch on the transmitter, then do as I do ," USE THE FORCE" with the force you can do this. if the force is not with you, well then you should probably ask a few more questions. 30 seconds till the start. geno :lol:

 

[GRoth265]

Gene I know all about the force, Why do you think big dog gave me the nickname OBI-WON?. I should probably do what you say maybe I'll add some down force in the form of what? Greg :blink:

 

[bbnate804]

when you guys are setting up your outboards, i've got my basic starting point but how do i know if my motor is too high or too low? same with the pitch of the motor, how do you you know if your tucked in too far or not out far enough?

nate

 

[waterbug]

If the motor is to high, you will hear the engine rpm go up and boat speed goes down... going into and through a turn all you can hear is prop slip {RPM goes up high!!}

If the motor is to low, you will be overly wet and the RPM will be low and boat will be slow...

Trimmed out too much, you will have the nose very high and porpoising, broken flex shafts..

Trimmed in too much, the boat will stuff on the slightest ripple...{nose steering}

There's no one close to you running boats !!!???? that can help you ???

 

[bbnate804]

so far the only person i know of that runs boats and might even be mildly interested in spending a day with a retard is tunnelbill. he's about an hours away and then i'm not sure what the closest water is to us. the aeromarine guys are right in my home town (20mins) but they don't have a test pond or anything on sight either. is why i post a bunch of questions here.

nate