Rudder Talk

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Rudder Talk

Postby RadioZephyr » Wed Mar 20, 2019 12:25 pm

I’ve been trying to get my head around the construction of my rudder for a while, and I finally got some answers. I figured I would share what I've learned here for posterity.

I’m familiar with the traditional rudder construction—a stainless steel stock that has a number of stainless steel “flags” welded to it that extend aft into the foil, some sort of putty or foam filler around that, and a fiberglass skin—and that’s what I assumed was inside mine. However, when I dropped the rudder on my F36/38 for the first time, that setup did not seem likely. The stainless steel stock is very wide at the top of the rudder, and it couldn’t possibly extend down into fin without tapering to fit.

I had to move on to other projects at the time, but the question still nagged me. Watching Mads perform surgery on his rudder in the recent episodes of SailLife has renewed my interest in understanding how mine is constructed, so I decided to ask Paul Dennis, the final word on all things Freedom. Here’s what he said:

    -The rudders on the Mull-designed Freedoms (F28, F30/32, F36/38, F45) and Pedrick-designed Freedoms (F35, 40/40) did indeed lack a stainless steel shaft. Instead, the rudder stock was just like our masts: a mix of fiberglass and carbon fiber. (We didn't get into the rudder designs of any other Freedom models, so I can't say how they were constructed)

    -This basically eliminates the possibility of the shaft separating from the blade. It also means that even if water gets inside the foil, there’s nothing to rust or corrode.

    -At the time (early 1980’s), nobody in the marine industry was really working with carbon fiber at the same level as Freedom/TPI, so no other builders were willing to attempt such a design. The specialized processes and tooling required were too involved, especially for something most owners never see or know about.

    -The only stainless steel parts of the rudder are the two sleeves on the rudder stock, which are installed during layup. They are simply there to provide a bearing surface—they are not meant to provide any additional structure to the composite shaft. The upper sleeve has holes for two bolts to go through it, fore and aft. The upper bolt only goes through the sleeve, not the actual shaft. Its purpose is to provide an attachment point for the emergency tiller. The lower bolt goes through both the sleeve and the laminate, and is bolted through the quadrant.

    -The zerk fittings on the shaft sleeve should basically be ignored. They were added to correct an unforeseen problem with the rudder bearings. The bearings are made of UHMW plastic, and were originally machined to perfectly fit the steel sleeve on the rudder stock. The tight fit was possible because UHMW theoretically does not absorb water, so the lower bearing wouldn’t get tighter after the boats were launched. The problem is, it turns out that UHMW actually does absorb a tiny amount of water. As a result, the perfectly fit lower bearings would swell ever so slightly, and cause the steering to bind up. The fix was to take down the ID of the bearing with a drum sander. This solved the problem, but there was now a small amount of play between the shaft and bearing. They installed the zerk fittings so that grease could be introduced inside the rudder sleeve to take up that play. It’s not there to lubricate or cool the bearings.

We also discussed a couple of the failure modes for these rudders that Paul has seen over the years:

    -The upper stainless sleeve can come unstuck from the laminate stock. This is not necessarily a huge problem, as the lower bolt still goes through the laminate, so you can still steer and the stock isn’t going to fall out of the boat. However, if any play develops in the lower bolt, either from the bolt loosening or a grounding that turns the rudder hard over with the quadrant in place, the bolt can start chewing up the laminate around it. This increases the play, and in turn adds to the wallowing out of the hole through the stock.

    -Rainwater can drip through the deck plate for the emergency tiller, and collect inside the top of the stainless sleeve. This can lead to corrosion of the sleeve. The solution is to fill the shaft with epoxy until just below the upper bolt (so you can still use the emergency tiller).

    -Owners often use the wrong grease in the zerk fittings. This happened on my boat. People tend to just go to the hardware store and buy a grease gun and use the grease that comes with it. The problem is that this is usually bearing grease for trailer wheels. It is designed for high RPMs, which heat it up a bit and lower the viscosity. A rudder shaft operates at under 1 RPM. In this application, the grease basically becomes thick glue. The solution is to drop the rudder and clean it all off with paint thinner.

    -The fiberglass skin of the bottom 1/4 of certain rudders can break or shear off if you go hard aground. Apparently the rudder stock ends about a foot short of the bottom of the rudder on the deep draft F36/38. At that point, it’s just skin and filler, which obviously isn’t nearly as strong as the stock. This happened to someone in Maine last season, and they were able to leave the stock alone and just rebuild the fiberglass skin at the bottom (the owner is on this forum, so please correct me if I’m getting this wrong!). My rudder actually provided the measurements for the new construction.

Anyway, I hope this information can provide some insight for those of you with rudder issues, or those who were just wondering what’s going on inside that critical piece of your boat’s construction. Feel free to post follow up questions for me to ask Paul, as I’m likely going to be at his shop a fair amount in coming weeks.

-Josh
Attachments
Rudder stock.jpg
My rudder stock, covered with the wrong grease.
Rudder stock.jpg (163.2 KiB) Viewed 862 times
Rudder.jpg
F36/38 deep draft rudder
Rudder.jpg (144.58 KiB) Viewed 862 times
Rudder stock, rudder sleeve.jpg
Rudder stock and sleeve at the factory
Rudder stock, rudder sleeve.jpg (221.25 KiB) Viewed 862 times
Josh
Sunset Spy
F38, Hull #152
Boston, MA
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RadioZephyr
 
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Re: Rudder Talk

Postby jdpandlp » Thu Mar 21, 2019 7:58 am

Thank you for the work.
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Re: Rudder Talk

Postby RadioZephyr » Thu Mar 21, 2019 12:38 pm

My pleasure. I figure the availability of information like this is going to help maintain the relatively high value of Freedoms on the used boat market, which is a benefit to all of us.
Josh
Sunset Spy
F38, Hull #152
Boston, MA
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RadioZephyr
 
Posts: 85
Joined: Mon Jun 27, 2016 10:04 am
Location: Boston, MA


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