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PostPosted: Mon Aug 29, 2011 11:56 am 
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I am going to swap out the "old style" lower rudder castings on a 1981 H18 with a set of the redesigned-post-1987 rudder castings and tiller arms.

I have a few questions about the conversion. I know this has been covered piecemeal before, but I couldn't find a comprehensive post about the procedure.

This is the current "old style casting" (click on any photo for a full size version)

Image

As seen below, the issue is that the post-1987 rudder casting conflicts with the "old style" lower gudgeon placement, and the lower gudgeon has to be moved up.

Image

Also, it seems that the post-1987 rudder castings use two hole gudgeons, not the four hole that earlier lower casings used.

Image

My main source of confusion is where to place the new gudgeons, and if they need a backing plate. As you can see below, if you try to line up the gudgeons with the old holes they will not fit. You could drill new holes for the two hole gudgeon there, but because they are so close to the old holes I am afraid it will weaken the fiberglass.

Image

Where should the replacement gudgeons be located? If you move them up I think they will be too high, leaving play in the bottom of the lower casting.

MAIN QUESTIONS:

Where should the gudgeons be located?

Should four hole gudgeons be used, or two hole gudgeons?

Is a backing plate necessary, or can the gudgeons be tapped into the fiberglass?

what is the best way to seal the old holes?

In my opinion the best placement would be like this:

Image

To use only four hole gudgeons, seal the old holes (somehow), and use a backing plate, which will necessitate adding two inspection ports on top of the hulls.

Kindly let me know what you guys think.

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1981 Hobie 18
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PostPosted: Mon Aug 29, 2011 12:40 pm 
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Use four hole gudgeons for both the top and bottom. You should not use two hole gudgeons anywhere on an 18.

Move the bottom gudgeon up so that the existing top mounting holes become the new bottom mounting holes. Then drill and tap new top holes. There is an aluminum backing plate laminated into the transom, so you are not just tappig into fiberglass.

There is also an updated gudgeon that you should install which is stronger than the original H18 gudgeons (I'm not talking about the new cast aluminum one piece gudgeons, but those would also be an option). Seal up all the holes with silicone caulk.

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PostPosted: Mon Aug 29, 2011 1:14 pm 
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Thank you. Adding a backing plate would have been a pain. Now I just have to get a tap for the screws.

Two problems.

1) The old gudgeons are seized onto the old pins. I tried twisting them loose with vise-grips, and banging them out with a mini-sledge, but they won't come off. The only thing left I can think is torch? Unfortunately, I don't have one.

Image

2) The bottom hole doesn't line up, so once I fill it the new hole will be half in the filled hole. I think that's going to make the connection weaker.

Image

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PostPosted: Mon Aug 29, 2011 1:47 pm 
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Quote:
2) The bottom hole doesn't line up,


You need to file off some of the casting to fit... that is a normal part of the conversion. File to top of the lower part of the casting.

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PostPosted: Mon Aug 29, 2011 2:30 pm 
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If the rudder pins are seized to the gudgeons, I'd assume that's because you have aluminum pins. You're probably better off just replacing the pins with stainless steel pins anyway. The aluminum pins have a nasty habit of breaking, stainless doesn't break.

In any case, if you can't get the pins out, you may just have to replace them. Rudder pins are relatively inexpensive.

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PostPosted: Tue Aug 30, 2011 8:56 am 
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Me thinks it is a case / requirement for the angle grinder ... LOL :mrgreen:

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PostPosted: Tue Aug 30, 2011 10:26 am 
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Ok. The local machine shop got the gudgeons free, and I got the gudgeons lined up. Do you have to tap the screws, or can you use self tapping ones?

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PostPosted: Tue Aug 30, 2011 10:50 am 
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If it was me, I'd be curious how the backing plate was; seen some completely corroded. Then while in there (via porthole), use a backing locknut. But thats more work (of course). I just hate rudder issues.

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PostPosted: Tue Aug 30, 2011 11:02 am 
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divimon2000 wrote:
If it was me, I'd be curious how the backing plate was; seen some completely corroded. Then while in there (via porthole), use a backing locknut. But thats more work (of course). I just hate rudder issues.


Yeah, that was my original thought too. It think that's really the best way to go, except of course I will have to cut in two inspection ports.

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PostPosted: Tue Aug 30, 2011 11:10 am 
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Quote:
Do you have to tap the screws, or can you use self tapping ones?


You must tap the hole for the threads. 12-24 is the current thread if using new screws.

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PostPosted: Tue Aug 30, 2011 11:17 am 
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I put a bottle port drink holder in one of mine. :lol:

My dad would tell me to tap AND locknut.

http://www.apsltd.com/c-4513-inspectionports.aspx

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