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Old 28-11-2020, 04:37   #16
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Re: Rudder repair - should I taper the core?

Leave the trailing edge hollow? Make some fiberglass flat stock and laminate it to the trailing edge?
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Old 28-11-2020, 05:41   #17
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Re: Rudder repair - should I taper the core?

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Originally Posted by andreas.mehlin View Post
If you would have chosen. What material would u have used? Expandable foam?
Structural foam.

Corecell, Airex, divinycell, etc. it’s easy to sand it into the foil shape quickly.

Also Gord is right about the water. You should address whatever problem allowed the water in in the first place.

Sherpa has a good idea too. And you could even make “bulkheads” inside there and make them the shape of the foil section if you can’t get any structural foam.

Lots of ways to go. I guess it really depends on what you can get where you are
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Old 28-11-2020, 06:11   #18
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Re: Rudder repair - should I taper the core?

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Structural foam.

Corecell, Airex, divinycell, etc. it’s easy to sand it into the foil shape quickly.

Also Gord is right about the water. You should address whatever problem allowed the water in in the first place.

Sherpa has a good idea too. And you could even make “bulkheads” inside there and make them the shape of the foil section if you can’t get any structural foam.

Lots of ways to go. I guess it really depends on what you can get where you are
Thanks
Yeah building a framework inside could do. Would I need to make these scarf joining the wood or just butt join?
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Old 28-11-2020, 06:25   #19
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Re: Rudder repair - should I taper the core?

Re: the shape of the old rudder.
Would most likely go back to that shape if there wasn't any issue w/lift or the rudder stalling in heavier air.

If you want to shape/more lift could look here for different shapes.
For more info on rudder design here is a paper discussing how to make a better rudder/more lift.

Re: the internal foam
Is the rest of the foam in the rudder wet? If the trailing edge was wet, would suspect the rest is also wet. If so would want to remove that wet foam also.
Typically one would cut a rectangular portion out of the side, dig out the foam and then only have a side patch to glass. Have seen many use a medium density 2 part pour in expandable foam as a replacement foam. This is the easiest way to repair an existing rudder.

We used a structural foam to make a whole new rudder for our boat after a PO put on a different rudder w/no lift (a flat rudder). The new rudder works well, but IMO don't think you need to go that far to repair your rudder. If you wanted to radically change your rudder design then it could be worthwhile to use structural foam to make a new rudder blade.

A final thought is if you had salt water intrusion into the rudder core, while you have it out and apart, you may want to double check the rudder shaft/internal welds holding the rudder stock extension plates/rods.
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Old 28-11-2020, 06:37   #20
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Re: Rudder repair - should I taper the core?

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Thanks
Yeah building a framework inside could do. Would I need to make these scarf joining the wood or just butt join?
So are you saying the core was wood/plywood that you removed? Maybe I missed that fact, but would have been good to know.

Could use a structural foam like coosa or a medium density HDU then epoxy it in to the old wood (as long as its dry) and skin. These should be easy to shape and after you glass it will be extremely strong.

While I know wood core rudders are easy to build and cheap, they are very heavy especially after they get wet. Our old rudder w/an internal wood core was extremely heavy and was happy to build a new rudder w/materials that will never absorb water.
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Old 28-11-2020, 06:42   #21
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Re: Rudder repair - should I taper the core?

-Is marine pour foam available where the repair is taking place?
It does not look like too much volume to replace.

You could also find an old PU (polyurethane- MDI or TDI) surfboard and strip it for the foam (check that it is not a collector's item first...) EPS (styrofoam) would work with epoxy too but would be slightly more prone to becoming waterlogged in the future.

The glassing will be bearing most of the forces rather than the foam, getting new joined to old and all sealed is most important.

-Have you been looking online for how-to's?

https://www.boatworkstoday.com/video...rudder-part-1/
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Old 28-11-2020, 10:20   #22
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Re: Rudder repair - should I taper the core?

I would not used most expandable foams. the polyurethane ones tend to absorb moisture. There are epoxy foams but not so readily available. Best luck.
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Old 28-11-2020, 15:02   #23
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Re: Rudder repair - should I taper the core?

If you care at all about the performance of the rudder, i.e., drag/tendency to stall/ steering authority, etc., I suggest you search "sailboat rudder profiles" and review the results. I see there are some sites with information you might scale to your use.
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