Rudder Replacement Is HDPE Worth it?

Aug 2, 2021
3
S-2 6.9 Rocky Bayou
I own a S2 6.9 and I was out sailing my 22ft boat a few days ago in 15-20 knots of wind with 3-4 ft rollers. During the sail, my rudder broke barely above the waterline. I am looking at replacing it and I have had a few quotes on some glassed rudders. However I saw a kick up rudder from rudder craft made of HDPE and it caught my interest. I was wondering if anyone can give insight on their experience with these style of rudders. I mainly use my boat for racing with the occasional cruise. I stay inside of barrier islands and bays and rarely if ever venture out into the gulf/ocean. I see winds speeds regularly from dead calm to 20kts with average being somewhere between 9-14. I would not intentionally bring out the boat in anything higher than 20kts. How much of a performance increase or decrease would be expected from a rudder like this what would I need to expect and what limitations might I need to account/watch for?
 
Aug 2, 2021
3
S-2 6.9 Rocky Bayou
In a word... Yes
I appreciate you responding to this thread. Can you please elaborate though a little bit? I don't want to jump on this rudder just because it is a cheaper price than alternatives, I care about reliability, maintainability and performance.
 
Oct 22, 2014
20,989
CAL 35 Cruiser #21 moored EVERETT WA
Sure. Using your idenetified use and priorities.
I do not have a rudder made of HDPE. I do understand the properties of the material and the application. I have helped a friend install one on his 36ft Catalina. He is pleased. No noticable speed change during his cruising. The proposed no need for bottom paint of the rudder is still in observation.

Your Priorities and the application:
  1. I mainly use my boat for racing with the occasional cruise.
    1. The material is slippery in the water. Racing boats seek to optimize their water surface area
    2. The material is resilient and maintains it's shape. Once shaped the material tends to take a ding and rebounds unlike wood or fiberglass which cracks.
    3. It is easily shaped. You can sand out blemishes. HDPE is easily shaped like wood.
    4. When you eventually damage the product beyond repair (as will happen using a boat in races) It is less expensive to replace.
  2. I stay inside of barrier islands and bays and rarely if ever venture out into the gulf/ocean. I see winds speeds regularly from dead calm to 20kts with average being somewhere between 9-14. I would not intentionally bring out the boat in anything higher than 20kts.
    1. All of this is fine but not relevant to the discussion of materials. Wood, Fiberglass, and or HDPE will all work under these conditions
  3. How much of a performance increase or decrease would be expected from a rudder like this what would I need to expect and what limitations might I need to account/watch for?
    1. I do not have any hands on or engineering knowledge about the company you are planning to buy the rudder from. Your question is a good one and perhaps should be directed to them.
    2. The HDPE material is identified as slippery in water, much like a polished, waxed surface.
    3. It is said to resist fouling by marine life. These are all promising attributes to help to increase the performance of a rudder on your boat.
    4. HDPE can be shaped easily like wood. This is likely going to have the greatest impact on performance. The way the rudder is shaped to provide lift and control will have the greatest impact. The manufacturer is the determiner of this outcome.
    5. Rudders are susceptible to lateral wear and damage. I would ask the manufacturer for information about the lateral strength of the rudder. Is it a solid piece of HDPE or is the HDPE used as a skin over a inner structural system? Small rudders were originally made of solid wood. The strength of the long wood cells held the rudder together. Then builders used the wood as a core and laminated fiberglass over the wood. The wood provided shape and the glass fibers provided the strength. HDPE does not work well with fiberglass/resins. Too slippery, no hold.
Those are my thoughts about the issue. If the info from the manufacturer is solid and I can find others to collaborate their use experience from current buyers (asking the manufacturer for references even if not the same boat as you have) then it appears to be a reasonable way to go. I understand it is not easy being on the cusp testing out a new product. But that is kind of what racers do. They invest in new ideas to see if they can get a little bit of better performance from their boat.
 
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Jul 7, 2004
8,402
Hunter 30T Cheney, KS
In the case of my IdaSailor HDPE rudder on my old Mac 26S, they improved the shape as well for better performance. I pretty much had one since day 1 so I can't report on the difference between old and new. John's comments make a lot of sense.