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Tail Rudder

Thepwood

Member
Hello all, Pat from northern Alberta here. I bought an old airboat last week and I thought this would be a great forum to join to profit from multiple years experience. I notice the boat doesn’t turn real great at slow speeds and I believe it’s because the tail rudders aren’t long enough. I started drawing out a pattern to extend them but I’d sure appreciate some feedback to see if I’m wasting my time. Thank you in advance
 

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What do they measure now, (height by depth)?
How far apart are they? What is the distance from the leading edge of them to the prop?
Understand that the air coming off the prop moves up the blade toward the hub before going aft to the rudders.
The thrust column you are generating is mostly centered around the hub and nearly nonexistent at the ends of the blades.
What you have there would work much better moved up to be centered in the prop wash, as is, the bottom third third is mostly ineffective.
I would expect that extending them as is, would most likely, not make a noticeable difference.
 
I see a fold down top section of your cage, (which I'm guessing set the height of the rudders).
Does the boat still go under bridges or other obstacles warranting the fold down cage?
If so, the suggestion Deano made, (to which is valid) you probably couldn't do?

Would like to see more of your "long belt drive", (are those automotive style V-belts)? What kind of powerplant?
And does the transom lower, is that polymer on the transom?
 
X2 on Deano's input for sure.

This boat is set up for either passing under low obstructions or duck/goose hunting (probably the later). The Utah crowd just cuts their cages and mounts the rudder low so they have a lower profile in the decoy spread and can throw camo over the whole rig. If neither of these situations apply, centering the rudder will be a good move.

Deano said:
What do they measure now, (height by depth)?
How far apart are they? What is the distance from the leading edge of them to the prop?
Understand that the air coming off the prop moves up the blade toward the hub before going aft to the rudders.
The thrust column you are generating is mostly centered around the hub and nearly nonexistent at the ends of the blades.
What you have there would work much better moved up to be centered in the prop wash, as is, the bottom third third is mostly ineffective.
I would expect that extending them as is, would most likely, not make a noticeable difference.

What has not yet been said is that airboats as a rule do not turn or handle well unless you are in the power. The only way to have control is to be in the throttle, otherwise it's inertia, wind and luck. A few years back my son got a kick out of my brain fart, came up on a crossing trail where I needed to take a hard turn to Stbd. Brain disconnected and I let off throttle while pushing stick forward. Slid right through the junction. Had to make a U turn, but Under Power the second time for sure.

Thepwood said:
I bought an old airboat last week and I thought this would be a great forum to join to profit from multiple years experience.

As it looks like this is your first airboat, you are gonna have to temper your expectations, this ain't any boat you have ever run, it goes straight until you make it turn. First rule, if you ain't on ground or in the throttle, your sinking. If you search the forum options you will find an entire forum dedicated to Airboat Safety. For starters read this full thread. Next, go get enough survival suits to match your seat count plus one. Finally, spend this summer with no riders, you should have sunk or flipped by then and can spend next winter fitting a new engine. By next summer you will be getting the picture.

https://southernairboat.com/phpBB3/viewtopic.php?f=132&t=30116
 
Finally, spend this summer with no riders,

This to me should be the n umber one rule to all new air boaters.
 
Gary S said:
Rudders look big already. How far do they turn?

To turn Left the fins just about close. id say 75-80 degrees, to the right its about 45 degrees. i can see it can benefit from a bit of
haha
 
To turn Left the fins just about close. id say 75-80 degrees, to the right its about 45 degrees. i can see it can benefit from a bit of
haha
 
Deano said:
What do they measure now, (height by depth)?
How far apart are they? What is the distance from the leading edge of them to the prop?
Understand that the air coming off the prop moves up the blade toward the hub before going aft to the rudders.
The thrust column you are generating is mostly centered around the hub and nearly nonexistent at the ends of the blades.
What you have there would work much better moved up to be centered in the prop wash, as is, the bottom third third is mostly ineffective.
I would expect that extending them as is, would most likely, not make a noticeable difference.

What you say makes a lot of sense, i am going to try and centre them with the hub
 
JLP3314 said:
I see a fold down top section of your cage, (which I'm guessing set the height of the rudders).
Does the boat still go under bridges or other obstacles warranting the fold down cage?
If so, the suggestion Deano made, (to which is valid) you probably couldn't do?

Would like to see more of your "long belt drive", (are those automotive style V-belts)? What kind of powerplant?
And does the transom lower, is that polymer on the transom?

To be honest I don't know the history of it. Its a 77 and i can see that its had many modifications over the years. i think it might of been converted to an airboat at some point. It has nothing but a huge shallow lake and a bit of river to run in. I love the belt system it puts the engine low and this thing isn't tippy at all. i can whip it around like a seadoo. The belt just started separating and Im waiting for a new one but it was pretty cracked up when i purchased it.
 
JLP3314 said:
I see a fold down top section of your cage, (which I'm guessing set the height of the rudders).
Does the boat still go under bridges or other obstacles warranting the fold down cage?
If so, the suggestion Deano made, (to which is valid) you probably couldn't do?

Would like to see more of your "long belt drive", (are those automotive style V-belts)? What kind of powerplant?
And does the transom lower, is that polymer on the transom?
 

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To turn Left the fins just about close. id say 75-80 degrees, to the right its about 45 degrees. i can see it can benefit from a bit of
haha

I can see that actually being dangerous, (think jumping out of the seat like most of us do to grab something or many other reasons we're at idle with no hand on the rudder-I know guys I didn't say that right LOL?). The rudder all of a sudden decides to slam over to the side putting the boat into a hard turn. I just wouldn't trust it.

Hard to tell if it's old skool dogleg mechanical steering but would benefit you to slap a teleflex cable on it and some rudder stops.
Here's a pretty good thread on steering:

https://southernairboat.com/phpBB3/viewtopic.php?f=85&t=71212&p=686002&hilit=dog+leg+steering#p686002
 
I will take dogleg steering over cable anyway. Never had dogleg break,or had it slam over when I let go. If it slams over you have some other problems.
 
I adjusted the steering so it turns the same both ways. I also lifted the fins 4", excited to try it but i have to wait for belts
 
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