1999 Mac 26X, twin retractable rudders, 48"L X 9" tappered to 8", poor control at low speed, no bite in low wind under 2 mph when tacking...must use motor foot (50 HP Merc big foot) for additional rudder. Replacement rudders approx $500, but don't know if they will be any better. Considering having a metal shop ( form fit) wrap lower rudder from waterline down with 1/16" stainless sheet metal to 12" width for more rudder surface. Approx cost $150. Any suggestions? papamills
Rudder improvement
- Thread starter papamills
- Start date
- Status
At higher speeds it will add huge loads. Due to the unbalanced design of the rudders, this load will be passed to the steering mechanism, as well as the pintles. Because your plan is to only widen/strengthen the waterline down, it will add to the torque (twist) loads on the blade above the WL. Most often Mac gear is designed as a whole to handle a certain amount of load. I'd be very careful upsetting that balance.
I don't know if it can be done on the X or M models, but I added 2 1/2 inches to the leading edge of my rudder. Because all the load is behind the pivot point, it put a lot of strain on the tiller especially as the speed and wind picked up to control weather helm. Not only does this increase your rudder surface, it adds balance to the helm. On aircraft its called a trim tab.
That's a great idea and that's actually called a balanced rudder, where part of the control surface is in front of the pivot. It's also why spade rudder have become so popular on bigger boats as they allow this design feature.
A trim tab is a servo-based control surface behind the pivot, like on on an aircraft wing. Some fighter jets do have balanced control surfaces.. Like the rear stabilizers on a f16.
I went overboard, no pun intended, in a previous life I built model sailplane wings using vacuum bagged foam covered with epoxy and fiberglass.
I cut a NACA 0012 airfoil out of foam, vacuumed bagged it, removed the foam and used marine plywood to fill void. The plywood was a loose fit so I used Polyester resin and glass to fill the rest. Its 4” longer with about 3.5” wider than the stock M25 rudder. 2.5 inches of the added width is forward of the hinge line.
That being said there are lots of very good post on this site with detailed instructions on how to build a better rudder. I think the true airfoil shape contributes a lot to the improvement in performance. These boats have basic controls, anything you can do to upgrade them helps. Placing rudder area in front of the hinge line takes a lot of load off the tiller and helps weather helm. If I can figure out how to post a picture I’ll send one along.
I cut a NACA 0012 airfoil out of foam, vacuumed bagged it, removed the foam and used marine plywood to fill void. The plywood was a loose fit so I used Polyester resin and glass to fill the rest. Its 4” longer with about 3.5” wider than the stock M25 rudder. 2.5 inches of the added width is forward of the hinge line.
That being said there are lots of very good post on this site with detailed instructions on how to build a better rudder. I think the true airfoil shape contributes a lot to the improvement in performance. These boats have basic controls, anything you can do to upgrade them helps. Placing rudder area in front of the hinge line takes a lot of load off the tiller and helps weather helm. If I can figure out how to post a picture I’ll send one along.
Hey Erik,
I'm also a sailplane builder in a past life. FYI Michael Selig did produce several sections aimed at sailboat rudders and keels.
For those that don't know, Michael Selig (Dr Selig now) did extensive se search on low speed, low Reynolds number airfoils that were used with great success by the model sailplane crowd.
Most sailboat rudders are built exactly the same way as foam and glass aircraft wings....
Chris
I'm also a sailplane builder in a past life. FYI Michael Selig did produce several sections aimed at sailboat rudders and keels.
For those that don't know, Michael Selig (Dr Selig now) did extensive se search on low speed, low Reynolds number airfoils that were used with great success by the model sailplane crowd.
Most sailboat rudders are built exactly the same way as foam and glass aircraft wings....
Chris
- Status