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rudder question 3 small or 2 big ?

patriot

Member
using this cold spell to work on my new boat, I`m wondering which will be better 2 large rudders or 3 smaller ones ? also what is a airfoil rudder ? is it shaped like a plane`s wing ? Thanks in advace



patriot
 
I know a lot of the guys who jump dikes (that just don't sound right) prefer to stay away from those long single rudders because when they re-enter the water the quick change in direction can have that extended rudder hitting the ground.

Or any obstacle for that matter. A log or rock too.

JD's triple rudders barely stick out the back of his boat.

Airfoil rudders are not shaped like a traditional wing cross section. They are like the top on both sides. Fat in front grabs more of the prop's wind. It grabs the wind from even the trailing side.

One of the engineers here will have a better definition with the same result. I sure ain't no expert on that. But my dad made me a wind tunnel out of a couple old marching band bass drums when I was about 7 years old. I learned a lot playing with that thing!!!

Airboat dads - I'll bet you never thought of giving your kid a wind tunnel as a present! It could change their life.

matt.
 
I never jumped any dikes, but I have bailed off levees into canals.

It's all in what you want.

The big single rudder on this boat has been hanging there for 30+ years.
It still works just fine.
MVC-035S.JPG


If it did'nt work, it would'nt have withstood the test of time.

Dual, or triple rudders will work also.

In my opinion, it's all in thier placement, and how they are rigged that makes ALL the difference for how effective any rudders are.



JMO
 
Cowboy thats a good looking boat. I don`t really have the need to jump off or over any thing yet, but I do want to turn as sharply as possible , with as much steering respose as possible..............

so within the diameter of thrust that comes off the prop...say 60 in,.....is it more effective to try to "cover " the area of thrust with 3 rudders about 50 in tall and 18 in wide or go with 2 50 in tall and 32 wide.........................javascript:emoticon(':shock:')
Shocked


patriot
 
darn cowboy looks like you spent the weekend polishing that critter :lol:

I have a single on mine and it turns the boat just fine but they say the triples are nice never drove one though
 
What you propose would certainly work, but may be way more that actually needed.

Here's a photo of some nice rudders hanging on a new boat.
You will notice that they cover better than half of the prop blast.
Adams_boat_2_001.jpg


They are mounted low.
I don't think they are in any real peril from any thing.
This boat is being rigged by folks who know what they are doing.

Just remember that the higher they are mounted, it make the path for the forces generated longer through the rigging, so it can be applied to the hull.
These forces could be substantial if the boat was stuck.

I have seen prop guards visably twisting under these forces.
Makes me run for cover!

100_0076.JPG


100_00751.JPG


Here's a picture of Jdotson's boat with triple rudders.
He seems more than happy with how it works.

I would envite you to study the pictures in the gallerys here, and decide what you think is best for your airboating.

Also,
Many believe that one big rudder is a thing of the past.
A relic from times gone by. Perhaps that's what I am too.

We have boats with dual rudders also.
They run great.

Just take your time, and make sure your rudders are rigged well.
There's alot riding on it.

Later
 
I was thinking that multiple rudders would decrease the crosswind signature of the boat, What do you think? :?
 
Cold........ I believe that`s a very good point...........................


Cowboy, look at the picture you sent of the rear view of the 3 rudder boat, why do you think they didn`t cover more prop area by spacing them further apart ? the way they are spaced a lot of air will not be re- directed..............this seems like a waste to me, however as a newbie I`m wondering if there is a reason for this ?



patriot
 
Patriot,
Perhaps JD can tell ya the answer to that one.

I can say this...
I personally don't believe the rudders need to be lined up further out on the propellers blade.

The bottom of the props circular arc will gather plenty of the thrust.

JMO. Everybody has one.

I'm not claiming to be an engineer, or expert on anything.

Just try'in to help man
 
Cowboy...........yourself and the others here have been a great source of info, thanks again.
I am surprised that there is not more "hard " info out there...(like for auto stuff )....a lot of what I see appears to be more of a "cut and try it " sort of thing, I have always been a big fan of learning from someone else`s mistakes. I have a 60x34 prop coming any idea on how to figure the thrust from it ? I would assume if you knew the pitch, size and rpm you could figure it out........ This airboat project has been hard on my crayons with all this figgerin.


patriot
 
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