rudders

A general, non-powerplant specific, discussion on airboat technology, ie., hulls, rigging, polymer, etc..
dick2256
Southern Airboat Member
Posts: 305
Joined: Sun Jun 05, 2011 12:25 pm
Location: Carson Iowa

rudders

Postby dick2256 » Sun Aug 13, 2017 10:49 am

seems to me my rudders aren't controlling the boat like it should
when I lowered the prop 6" into the boat that put 6" out of the air draft so I cut it off
do you think I need to make new rudders and add the 6" on top of the rudders so all of the rudder will be in the prop draft
here is a picture of the rudders now
Airboat pics (4).jpg

User avatar
Deano
Site Supporter - V
Site Supporter - V
Posts: 4272
Joined: Thu Jan 06, 2005 11:16 am
Location: Inverness, FL

Re: rudders

Postby Deano » Sun Aug 13, 2017 1:41 pm

It's a shame that you didn't pose the question before you cut them off.
There is no harm and little thrust penalty to be paid for having the prop dip below the top of the transom.
Hopefully you haven't noticed a large difference in the amount of push you are seeing.

As far as your rudders vs maneuverability, I would say with little doubt that it would be improved by having them taller.
The way things are sitting right now, you look to have a measurable amount of clean air coming off your prop and moving aft without being re-directed by the rudders. This would reasonably be expected to partially negate whatever influence the rudders were having.

While another alternative may be to make them longer (deeper aft), that would not address the clean unaffected air at all.
Hence, I would first do exactly what as you propose and make them taller. However, I don't know why you would only go six additional inches in height. It would be a shame to get another prop later, and then find yourself in the same position. I would inclined to make the height of them to fit the cage rather than the current prop. By doing so the rudders won't need to have that same attention again in the future, even if you do come across a better, longer prop that will fit in your cage.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

User avatar
mojoe
Southern Airboat Member
Posts: 806
Joined: Thu Jul 23, 2009 8:55 pm
Location: Catfish Motel

Re: rudders

Postby mojoe » Sun Aug 13, 2017 1:48 pm

I have seen a number of boats with single or otherwise undersized Rudders that worked to the operators satisfaction. I have not seen any with the part sticking up behind the pivot point like you have created.
Airboating is like marriage: There are unlimited ways a person can be right, and somehow still be wrong at the same time!!

User avatar
Deano
Site Supporter - V
Site Supporter - V
Posts: 4272
Joined: Thu Jan 06, 2005 11:16 am
Location: Inverness, FL

Re: rudders

Postby Deano » Sun Aug 13, 2017 2:30 pm

MoJoe, brings up a more than passively relevant point. Thank you for pointing this out. :thumbleft:

When you said make new rudders, I was perceiving that you would loose that notch out of the top. Whether the pivot point is moved or not, that missing notch needs to be filled in. Part of the problem right now is that that section above the pivot is to far back from the prop to be effective. I do not believe extending that section only would provide enough difference to justify the effort.

My meaning was to extend the entire rudder higher, not just that extension currently above your pivot point. My bad. :oops:
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

dick2256
Southern Airboat Member
Posts: 305
Joined: Sun Jun 05, 2011 12:25 pm
Location: Carson Iowa

Re: rudders

Postby dick2256 » Mon Aug 14, 2017 8:34 am

Deano wrote:It's a shame that you didn't pose the question before you cut them off.
There is no harm and little thrust penalty to be paid for having the prop dip below the top of the transom.
Hopefully you haven't noticed a large difference in the amount of push you are seeing.

As far as your rudders vs maneuverability, I would say with little doubt that it would be improved by having them taller.
The way things are sitting right now, you look to have a measurable amount of clean air coming off your prop and moving aft without being re-directed by the rudders. This would reasonably be expected to partially negate whatever influence the rudders were having.

While another alternative may be to make them longer (deeper aft), that would not address the clean unaffected air at all.
Hence, I would first do exactly what as you propose and make them taller. However, I don't know why you would only go six additional inches in height. It would be a shame to get another prop later, and then find yourself in the same position. I would inclined to make the height of them to fit the cage rather than the current prop. By doing so the rudders won't need to have that same attention again in the future, even if you do come across a better, longer prop that will fit in your cage.
my thrust is about the same as it was and my stability is very much improved since I lowered the engine it is not top heavy at all in deep water.
as far as that notch in the rudder at the top , that was the way banks Maxwell had their rudders drawn up

User avatar
Rick McC.
Southern Airboat Member
Posts: 99
Joined: Wed Jan 11, 2017 10:14 pm
Location: Weeki Wachee, Fl

Re: rudders

Postby Rick McC. » Tue Aug 15, 2017 12:25 pm

I've never seen rudders like that before.
"Sights are for the unenlightened."
Rick
http://guntipsandtalk.com

dick2256
Southern Airboat Member
Posts: 305
Joined: Sun Jun 05, 2011 12:25 pm
Location: Carson Iowa

Re: rudders

Postby dick2256 » Tue Aug 15, 2017 1:40 pm

poor boy rudders made out of 1/4' plastic
use to make them out of 3/8" plywood
they don't have to be pretty to work but do have to be big enough


Return to “Airboat Tech”

Who is online

Users browsing this forum: No registered users and 4 guests