New Rudder Build for 26S

[buck_justice]

I am in the process of starting a new rudder build for my 26S. My plan is to extend the leading edge forward 3 inches and with added scallops, and add an adjustable trim tab to the trailing edge. My thought is to be able to adjust it on the fly to reduce the forces on the tiller. I was wondering if anyone else has seen this done and how effective it was? Or ideas that I have not thought of?
Buck

[Maraquita]

The only reason for having an adjustable trim tab is to sail with the rudder offset from center. You don't want to sail that way (unless you are sailing in circles, I guess). As soon as you turn the boat and are on your new course, you will trim the sails so that the rudder is streamlined and stays centered. I would not bother with a trim tab.
Putting more area in front of the rudder hinges will make it easier to turn the tiller. It can make enough difference that the tiller will actually be snatched out of your hand and that can be uncomfortable to sail. You are trying to achieve a lightly balanced rudder that will return to neutral, not go further to the stops. I don't know what 3 inches in front of the pivot point will do. There have been lots of changes, both commercially and by individuals, on Mac rudders. I'm sure someone will have an idea about how much bigger than stock is a good idea.
I understand that the MODS page is back, and there used to be a wealth of ideas in that section about rudder mods. Try searching that.

[Jimmyt]

You can look around the net for real rudder design info. This is a fairly detailed article on keel and rudder design. https://www.ericwsponberg.com/wp-conten ... design.pdf

I would stick with a smooth NACA foil shape and have around 17% max of the rudder area ahead of the pivot point. Maraquita made some great remarks about rudder design in his post. Scallops and excessive area ahead of the pivot are not likely to give you good performance. I totally agree with deleting the trim tab idea - which is basically drag. As stated, balancing the sail plan is the key to having minimal rudder effort (and minimum drag).

Please post what you come up with. There have been numerous discussions of rudder design for the various Mac models.

Good luck.

[buck_justice]

Thank you both for your input, this is exactly what I needed. The trim tab idea is probably due only to my in ability to trim sail properly. Experience will tell on that account. I was running downwind and was experiencing a stiff tiller and was holding a lot more pressure than I thought I should have been holding. That’s when I came upon the idea of a trim tab! On the mods page a sailor posted this photo of his new rudder. I was thinking of something like it.

I’ll research Maraquito as suggested, I have read that scallops act similar to vortex generators, and create a swirling effect on the boundary layer of water causing it to be more effective. My reasoning was that if it added nothing, I could cut them off, which would be easier than adding them after the fact.

[Jimmyt]

Running downwind is a different animal. I assumed you were having trouble reaching and beating. What sails did you have up? If both main and jib, were you wing on wing? Did you have following or quartering seas? Depending on the conditions, running downwind can be a handful.

If you could post a link or pic of the scallops you were considering, maybe someone here has a different take. I've never seen any performance rudders with what I would consider scallops; but once the world was thought to be flat and flight was only for birds... I'd be interested in seeing a scalloped rudder design - particularly if there is performance data to go with it.

And, if you wake up in a scalloping mood on rudder day - just do it. I agree that you can always cut them off later (assuming the rudder is constructed of wood or the scallops are a solid layup).

[buck_justice]

There was a discussion here on this forum “making rudders” with a link. And this caught my attention!

A series of wind tunnel tests were performed to investigate the stall characteristics of wings with and without leading-edge protuberances (LEP). NACA 63(4)-021 aerofoil profile based baseline smooth leading-edge and modified leading-edge protuberanced wing model featuring Amplitude A=0.1c and wavelength λ=0.25c were manufactured using 3D Printing for wind tunnel testing. Surface pressure measurements were made over the test models to obtain the aerodynamic force coefficients for a wide range of angle of attack (α=0 o to 45 o) at Re=2.0×10 5. Results demonstrated that the modified wing with leading-edge protuberances (LEP) improves the mean lift coefficient () by 25% relative to the baseline unmodified case in addition to the stall delay characteristics. Attempts were made to identify the underlying dynamics behind the stall delay characteristics associated with leading-edge protuberanced (LEP) wing using surface pressure distribution.

Buck

[Jimmyt]

You'll be the first boat in your area to sport a humpback whale fin for a rudder The study shows some interesting findings. I didn't find one with photos, and that same text though. https://arc.aiaa.org/doi/abs/10.2514/1. ... Code=aiaaj

Study was done in a wind tunnel also.

Here's one done in water with photos. It is a water study, but apparently not the same finding mentioned. If you find the exact link, please post it. Interesting topic. https://www.sciencedirect.com/science/a ... via%3Dihub

[buck_justice]

The second study you mentioned was done using the NACA 0063 plan form, that in other multiple studies has been shown to stall at lower “angle of attacks” I was surprised they used that profile. Suspect they were thinking it would improve the stall? But it did not! Obviously! I was a good read also. My plan was to use a 0010 profile, and build two rudders one scalloped and one plain, then sail a fixed course on the same day using both rudders. Then seeing which one I liked the best!!!
So here is a photo of my raw stock that I am starting with.
Yellow Pine should be fine for a test bed. No reason to spend big bucks on an experimental project.

As you can probably tell, I like doing R&D and if it works I may move to the next level???
Buck

[Jimmyt]

Cool!

Looking forward to following your prototyping and testing.

If I remember correctly, the standard 26m rudders are approximately 0012 (just an FYI).

[svscott]

I have a stock 26d rudder that I've modified to a NACA 0012 profile. I extended the bottom edge by 6" and the leading edge 3". The modified rudder needs to be final faired and wrapped with glass/epoxy. I started this project a couple years ago and progress stopped after realizing I need to beef up my tired aluminum rudder post where the pintle holes are ovalled out. While on the phone ordering new standing rigging for Three Hour Tour, I discussed my project rudder and my concern about it being much heavier than stock. I was told the gudgeons and pintles at the stern should be fine with the added load but during conversation I learned about a super fast and easy mod to the stock rudder that seriously improved weather helm and greatly reduced the physical effort required at the tiller. By simply redrilling the pivot bolt hole and the lock pin hole in the fiberglass, the steering characteristics were really improved. Unbolt your rudder and angle the blade forward so the lower leading edge is about 5" (I'd have to double check) in front of the pivot point on the pintles then redrill, rebolt, and head back out. The difference was incredible!
I'm still going to finish my oversized rudder and I expect the gains to be even better than the angled rudder blade, but for a free, fast, and easy project, it's worth a try before committing the bunch of hours building a new one.

[buck_justice]

Svscott;
Are you saying to redrill the rudder where it will angle forward under the boat???
Buck

[buck_justice]

Here is a photo of my rudder. The PO plugged a hole in the top portion with a dowel. Not sure what happened there? But I have been using the hole with the arrow beside it “center” for my pivot.

As you can see there is quite a bit of wear around it.
Thanks
Buck

[svscott]

Svscott;
Are you saying to redrill the rudder where it will angle forward under the boat???
Buck

Yep, that's exactly right! It really is like having power steering. My only negative feedback is that the rudder or prop is somewhat affected when turning hard to port with the outboard running. It only happened a couple times while motoring and trying to do a fast u turn. It was like the turbulent water from ther prop made the rudder go funny... either stalling the prop or the rudder. I don't know exactly and it only happened a couple times.
I'll go out to the shed and measure how far forward I angled it and report back.

[svscott]

Here is a photo of my rudder. The PO plugged a hole in the top portion with a dowel. Not sure what happened there? But I have been using the hole with the arrow beside it “center” for my pivot.

As you can see there is quite a bit of wear around it.
Thanks
Buck

It'd be easy enough to repair those bolt holes with some thickened epoxy. Drill out the holes and grind the surfaces to get clean material. Wipe with acetone then fill with epoxy, sand it, and redrill. West System epoxy is expensive but the dispenser pumps that put out the right ratio has given me much more confidence tackling composite work.
Edited to add - use large stainless steel fender washers to take up the sloppy gap between the rudder and the aluminum rudder post to minimize the rudder's twist and maybe cut down on future wear. I'm considering adding a stainless or bronze bushing around the pivot bolt.

[buck_justice]

Yes the repairs on the rudder would not be hard at all. And it actually looks worse that it really is. But I think I would like to play with the new rudder design a bit. An inlaid Stainless doubler that wrapped around the leading edge would fix the problem completely. But would be an overkill on a stock rudder. When I decide on my final design I’ll build that option into it for sure. That area of the rudder does not even need to be profiled it fits into a square bracket on the back of the boat.
Buck