Fish tail rudder idea!!!

[funangler]

I run and repair the tow boats off/on and I have above average boat handling skills. With that being said I would not try it with a million dollar cruiser sitting there. I will try to take a video of the boat turning at cruising speed this week.

 

[funangler]

Interesting design. However, you imply that you can put the helm hard over at full speed AND turn with less than 5 feet of forward travel. I think you meant that you meant to replace the AND with OR. If I might summarize (correct me if I'm wrong) there are at least 3 features that are important: 1. The leading edge is fairly blunt. This might cause a little more drag, but at trawler speeds, I doubt it. It mostly increases the stall angle so that at higher turn angles the flow tends to stay attached to the "back" side, increasing the rudder power during aggressive maneuvers. 2. The leading edge extends further than normal ahead of the axis. While this might make the steering effort too light, or even negative (making it unstable), it does have the advantage of capturing more of the propwash, increasing the effectiveness at high angles. 3. The endplates increase the effective length of the rudder by reducing the "spillage" of water around the ends. However, a longer rudder, though not usually practical, would be a more efficient way to do this. Further, the concave section toward the rear might make the steering more effective at small angles.

I like the overall idea. Worthy of implementing, although the forward overhang might be a little excessive.

If I redid I move it back about 1 inch it is about as light as would dare want it. Makes for easy steering overall.

 

[funangler]

Did this mod add more torque to your steering (wheel feels "heavy"...hard to turn over) when traveling at cruising speeds (7-8 knots)?

I would back and fill 6 times to make that 360 turn with my original large flat plate rudder that was bigger then the current rudder. The wheel did become lighter with this change. I change the steering piston to one that has twice the travel the year after the install to get more angle on the rudder.

 

[North Baltic sea]

Hi,

I remember reading earlier articulating rudder systems, in this video two NT37 the same speed and another modified rudder. A big difference in the radius...

This is certainly quite tricky to install and costly vs. earlier examples of a modified rudder, but can see the big difference between a standard rudder.


NBs

 

[funangler]

Post a new video just can’t link to the forum with my I phone. If someone wants to that would be great. No buoys where harmed and heavy chain holds the line straight down I know from personal experience with them.

 

[funangler]

I would bet that the reduce "vibration" is due to the better (although I'm not sure what it was like to begin with) airfoil shape and the smooth rounded leading edge that is bothered less by the pulsations in the propwash. Going by airfoil characteristics, the center of pressure is usually in the 25 to 35% of chord. If the center of pressure is ahead of the rudder post the load on the rudder goes the "wrong" way - turn the rudder a little and it wants to turn more. It just looks like the pivot is even further back. How far back is it? Another question - how did you construct the shape? On mine I used a .060 stainless steel sheet that I bent around the leading edge of the original 3/8 flat stainless steel plate.

I had a shop cut 4 plate that look like the fish shape with a centering hole. Then mounted them on a 2 inch shaft and wrapped the steel around them. The rudder is filled with vegetable oil when finished. I don’t have the measurement on the balance point but I remember doing it less aggressive then what was called for.

 

[Sabre602]

Post a new video just can’t link to the forum with my I phone. If someone wants to that would be great. No buoys where harmed and heavy chain holds the line straight down I know from personal experience with them.

Here ya go!

 

[Benthic2]

This has been really interesting....but one thing keeps me from being a believer. If there was a very simple cost effective mod to be made to your boat that had all upside and no downside, why didn't the builder make it ? They have access to all sorts of test equipment, and machine shops, and engineering expertise......but some home grown boater with a welder can make a better rudder ? Don't you have to be incredibly arrogant to think you can make a better rudder than Mainship, ( or any other mass market builder ) ???
Some boat mods make sense because the builder builds a boat for mass market appeal. If your use differs from the intended use, you can improve on design. For example if 75% of your use is slow speed trolling, maybe a different prop makes sense or you...but what manufacturer doesn't want their boat to steer as well as possible !?!?! Sometimes a manufacturer knows how to do something better, but doesn't because its cost prohibitive. Adding stabilizers for example...they are great, but may not be cost effective for everyone...... But these mods are cheap and everyone wants better handling.

So...If this is such a great idea, why didn't your manufacturer do it ??

 

[funangler]

It’s only practical for displacement hulls and there just not that many single screw displacement being made. Your boat yard and naval architect I bet would add at least 25000 for it. Then if doesn’t turn out well they have to figure out how to fix it. Cheaper to sell a bow thruster and stern thruster. I have less then 1600 dollars in mine including steering piston and it is all my problem if it did not work. I have 10 inch bow thruster in my boat that does not like to stay working. This was the cheaper option. My boat has a longer learning curve to become an expert. Most single screw boats you turn it over hard and deal with it. My boat will just do circles you have to straighten it to make forward progress. Just some random thoughts.

 

[markpierce]

With a bow thruster, we can turn on a dime without forward movement. People with twins can do the same.

 

[dhays]

With a bow thruster, we can turn on a dime without forward movement. People with twins can do the same.

Still would be nice to have a rudder that is effective at low speed regardless if you have a thruster or not.

 

[markpierce]

Still would be nice to have a rudder that is effective at low speed regardless if you have a thruster or not.

Start with a "barn door" sized rudder.

 

[Sailor of Fortune]

This has been really interesting....but one thing keeps me from being a believer. If there was a very simple cost effective mod to be made to your boat that had all upside and no downside, why didn't the builder make it ? They have access to all sorts of test equipment, and machine shops, and engineering expertise......but some home grown boater with a welder can make a better rudder ? Don't you have to be incredibly arrogant to think you can make a better rudder than Mainship, ( or any other mass market builder ) ???
Some boat mods make sense because the builder builds a boat for mass market appeal. If your use differs from the intended use, you can improve on design. For example if 75% of your use is slow speed trolling, maybe a different prop makes sense or you...but what manufacturer doesn't want their boat to steer as well as possible !?!?! Sometimes a manufacturer knows how to do something better, but doesn't because its cost prohibitive. Adding stabilizers for example...they are great, but may not be cost effective for everyone...... But these mods are cheap and everyone wants better handling.

So...If this is such a great idea, why didn't your manufacturer do it ??

you answered your own question "Sometimes a manufacturer knows how to do something better,but doesn't because its cost prohibited"
The same reason why some builders don't decore around thru hulls on cored hulls.
The same reason why builders use screws rather than through bolt hull to deck joint.
The same reason why windows aren't sealed to cabin side.
etc, etc.

 

[Xsbank]

I have been “enjoying” my single screw, no-thruster boat for 5 years and the only thing I can’t do consistently is control the bow. Unless I have way on, the wind blows it thither and yon. Pulling the anchor in a 30 knot blow, I have to sprint to the wheelhouse the moment the anchor lets go as the bow does an immediate 90 degree turn across the wind and until I get way on, she’s just like a leaf on a pond. My rudder mod has made it easier to control the bow and support my wallet’s continued health as a jet-type bow thruster system, hydraulic, is about 10 boat dollars if I do it myself. The rudder mod was maybe $100. Having blathered all that, this thread is about rudder mods, period.