I recently bought some spare parts and a port side adjustable upper rudder casting from a used parts dealer. My boat has an adjustable casting on the starboard side, and I wanted to just get a matching set. Well, the casting arrived with the tiller tube on it. I went to install it and realized my tiller tubes have a bend in them. I looked around at the other cats at the club here and noticed a mixed bag of straight and bent tubes. Actually, mine look a hair more bent than any of the others, but I see no material evidence of any damage to my tubes. Well, I'm going to pull the bent tube off my current casting and rivet it onto the adjustable one I bought, but it has sparked my curiosity. When did this change in design happen? Is there an advantage to the straight tube? Is it wrong of me to use a bent tube with the adjustable casting?

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Josh Pepper
Hobie 16
Madison, MS
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Josh,

http://en.wikipedia.org/wiki/Ackermann_steering_geometry

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Ron
Nacra F18
Reservoir Sailing Assn.
Brandon, Mississippi
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Ron,

I understand Ackermann steering, but I don't think that's it. It's the difference between the tiller tube here:

http://www.thebeachcats.c…pictures/?g2_itemId=2358

...and here:

http://www.thebeachcats.c…pictures/?g2_itemId=1980

...unless perhaps you are suggesting the straight tube provides a better outer angle than the bent one, but all I can really figure it does is put the tiller crossbar further below the rear frame crossbar. It seems like the rudders would still respond the same with either setup.

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Josh Pepper
Hobie 16
Madison, MS
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Google "ackerman steering catamarans" there is an article from Aquarius Sail Owners that should explain everything.

I'm surprised some of our Hobie 16 sailors didn't respond, but it does look like Hobie changed from curved to straight tiller tubes in 1995 at the same time the upper castings were converted to adjustable.

Take a look at the Hobie 16 parts diagram.
http://2010.archive.hobie…ort/pdfs/PARTS_14-16.pdf

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Damon Linkous
1992 Hobie 18
Memphis, TN

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Most of the boats at the club are 78-82, Jerome's is late 90's or early 00's. The newest boat is an 09.
From what I've seen there is no rime or reason and hobie switched a lot thru the years on the 16.

Most of the boats (Nacra, Hobie and Prindle) have some degree of Ackermann steering. The big thing is to have both tiller arms the same and check the toe and by all means do not put the rudders on backwards.

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Ron
Nacra F18
Reservoir Sailing Assn.
Brandon, Mississippi
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On the Hobie 16, the original tiller tubes were bent upwards. This had the effect of keeping the tiller crossbar above the rear beam at all times regardless of whether the rudders were up or down. According to Matt Miller of Hobie Cat, they went to straight tubes in the late 80's. Having the crossbar above the rear beam when the rudders were up was somewhat of a nuisance when the boat was on the trailer as the mast had to be elevated more so as to not rest on the tiller crossbar. I bought my first cat in December 1978; a new '79 H16 with Tequila Sunrise sails. I have owned both a '79 and '84 boats and they both had bent tiller tubes. This seems to be a pretty minor change to me but likely eliminated a step in the manufacture of the boat.

The adjustable upper rudder castings were introduced in 1983. The rake adjustable castings have the bolt head on the top of the upper rudder casting. The adjustable casting allows you to adjust the fore and aft rake (and easily remove fore/aft slop) of the rudder which affects the helm of the boat. This was a very nice improvement in my opinion. My '79 had fixed upper castings and my '84 has adjustable ones.

Note also, that if you check, the upper rudder castings are not interchangeable from port to starboard. They should angle inward to allowing the inboard rudder to turn more sharply then the outboard rudder in turns. This "Ackerman" effect is provided by the upper casting alone not the tiller tubes. The bend in the old tiller tubes was upward only not inward.

Over the years Hobie has made a quite lot of refinements in the H16. Many were seemingly minor. But the total effect is significant and todays H16 is a much different animal then ones from the 70's or 80's. There are reasons for the changes. We just may not always know what they were.

Hope this helps.



Edited by DaveW70 on Jun 10, 2011 - 06:17 AM.

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Dave Wilson
Hobie 16, Hobie 14
Tampa, FL
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Excellent information Dave! Thanks for the details.

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Damon Linkous
1992 Hobie 18
Memphis, TN

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Thanks Dave! I was careful to request a port side one because I knew there was an angle to them that made it important to get the correct side. The tiller tube surprised me, though. I guess now I can set that straight one aside in case I happen upon another one to go with it. :)

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Josh Pepper
Hobie 16
Madison, MS
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Alright, so I have a new problem. From the previous posts, I had decided to take the bent tube off my current casting and put it on the adjustable one I bought, since I didn't have two straight tubes to use. However, the straight tube that came on my adjustable one seems to be stuck in the casting. I drilled out the three rivets, and the tube won't come out. I'm guessing they have oxidized together. I tried beating on it with no luck. I tried heating the parts up with no luck. I tried some WD-40 with no luck. Anyone have any suggestions? I suppose I could always try to get my hands on another straight tube and just go straight on both sides, but that's no fun.

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Josh Pepper
Hobie 16
Madison, MS
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