rudder plungers keep breaking!

Maybe there's just something I'm doing wrong...
Last year I took the boat out once, the port rudder popped back as though it hit something, and the plunger got jammed halfway out under the cam. It wouldn't go back in. Season over.

This year I got a new cam, and new plunger, put them in, and while on the trailer testing out the breakaway strength of the rudder cam, it did the same thing. Another broken and jammed plunger. So i went to the other side which I haven't touched, tested the strength required (nothing heroic mind you) and now that one jammed and broke too!! This boat is determined to never sail!!
what on earth is wrong with my cam system??!?!?

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78 Hobie 18.

The rudder castings may have some mold flashing inside the plunger cavity that is causing a hangup.

I have also noticed that all plungers are not exactly the same width and some are too wide to fit inside the cavity and operate smoothly. They need to be sanded down on the sides to fit correctly. Also make sure you are using the correct plunger. The H18 plungers are a rectangular cross-section whereas the H16 plungers are cylindrical.

I suspect your plunger may be getting hung up for one of the above reasons. It is a fairly simple system, so should be correctable. I would recommend you remove the cam and do a dry fit with just the plunger, spring, and adjustment screw to verify that the plunger is moving up and down inside the casting smoothly. Just push the plunger up and down with your finger to make sure it is working correctly. Also lubrication should help. I would recommend using grease on the plunger. This will last longer than a spray lube like WD-40 or silicone spray.

sm

I will clean the area out and try with new plungers. To be clear, my plungers get almost sucked up when the cam turns, and then are pulled out and up to the rear, and are then jammed under the cam, and this causes the round stem of the plunger to break half off the half cylinder top.

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78 Hobie 18.

As I mentioned in my prior post, the H16 uses cylindrical plungers. The 18 plunger is rectangular (at the top). Are you sure hou have the correct plungers installed? H18 plunger should look like this....



Otherwise it sounds like maybe your cam is over-rotating on release allowing the plunger to pop out. Are you sure you have the cam installed correctly and is it in good condition?

sm

One other thought... slight dimensional differences in castings or cam pin location? Is the can pin tight and holding the cam in the right vertical dimension. If the pin is worn or you use the sister screw replacements and that is loose or has worn the hole in the casting... the cam could be too high and allow the plunger to rise to high... not enough material in the casting to keep it in column.

You might be able to build up some material with JB weld or epoxy putty to support the plunger?

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Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

Yup, that's them. I just put in a new one too. I greased it all up. New cam and sister screw seem tight. We just bought these rudders like 7 years ago and only have like 15 hours or so on them. Stored the last 5 years then suddenly they aren't working right.

Side note; I can't find anything that shows the normal function of the cams (like which way they should be to start, how they rotate, proper way to engage them,etc.) or any instructions on how to adjust the striker plate that goes in to them. I'm sure they are out there but I can't find it.
If anyone can make a quick video showing how they are supposed to work, it would help a lot!

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78 Hobie 18.

The “hook” portion of the cam (part the slider plate engages into) should point aft when the rudder is locked in the down position and and the cam should rotate so the hook points up when the rudder is kicked up.

The casting in this pic shows the cam in the “up” position. The hook portion of the cam is somewhat hidden by the top of the casting. When the rudder is locked down, the cam will rotate (clockwise in this case) and the hook will engage the slider plate. The cam will roatate so that the semi-circular cutout visible at the bottom of the cam will engage the plunger. This is what holds the rudder down.

https://westcoastsailing.net/hobie-wave ... QQQAvD_BwE

To set the slider plate, loosen the bolt that holds the plate in position and slide the plate all the way aft. Rotate the cam into the “down” position. Put the rudder blade down and push it forward so the leading edge is fully seated against the front of the lower casting. Lower the tiller arm down so it is touching and engaged with the lower casting. Then put your wrench on the slider plate bolt and push the bolt as far forward as it will go. This will engage the slider plate into the cam. Tighten the slider plate bolt. Finally, check that the rudder/cam engages and disengages properly.

sm

Sailing FAQ area: https://www.hobie.com/forums/viewforum.php?f=18

Cam and rake FAQ: https://www.hobie.com/forums/viewtopic.php?f=18&t=467

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Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

It is becoming more and more common on H18s and H20s for the plungers to fail due to old springs.

Spring gets old and compresses... so you screw in the adjuster more... and more.

Until you don't have enough travel in the spring to allow the cam to go down all the way, then things get bad!

I've seen where the bore in the casting is bigger then the plunger and the plunger gets out of alignment (a little sideways) with pressure from the spring. This will keep it from going back into the bore hole.

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Buxton
18' T16 Silent Lightning (16' T2 Hybrid)
11' H16 White Lightning
79' H16 Green Lightning