Rudder repair - should I taper the core?

[andreas.mehlin]

Would u suggest Im tapering the core? If so how much and with a 45 degree cut or a 50% deep 90 degree cut?

Or other suggestion that would help


Thanks

[Singularity]

I suggest refining your question a bit (I'm curious about the answer).

Are you meaning tapering the aft edge of the forward core...like a scarf joint? What kind of boat is this from?

What is your layup schedule to be? How many layers of what ounce what? Will this layup fully envelope the rudder, or are you just laying up one side? Any idea on the skins on their in the first place?

[andreas.mehlin]

Since before it's abot 2-3mm fiberglass.
Although there is about 5-6 mm gelcoat/fairing compund....so I could go thicker on with fiberglass.

Only planning to lay up this side. With about 1-1 1/2 of solid fiberglass on the trailing edge. Will be using epoxy.



Boat 46ft trimaran

[Bill O]

What are you trying to do here, change the overall rudder shape? What foil type was it before?

[Chotu]

Why not just make the core the same taper as the bottom (deepest) part of the rudder? Ie: make the core the proper shape of the foil.

Then put the normal amount of glass on all the way through the whole rudder.

It’ll save weight and be easier than trying to fair the outside.

[andreas.mehlin]

Originally Posted by Bill O

What are you trying to do here, change the overall rudder shape? What foil type was it before?

haha, sorry...I forgot to say.
It had rotton core, so I cut out the rot and the damp core.

...Im just looking to replace what I have taken out.

[psk125]

What Chotu said.

[andreas.mehlin]

Originally Posted by Chotu

Why not just make the core the same taper as the bottom (deepest) part of the rudder? Ie: make the core the proper shape of the foil.

Then put the normal amount of glass on all the way through the whole rudder.

It’ll save weight and be easier than trying to fair the outside.

I think you misunderstood me...and maybe because I used the word "taper" wrong. What I mean is how to make the joint between the new and old core. Scarf joint or just put in the new core in the pocket as it is now.

[Rucksta]

Scarf

See if you can find something better than wood as core material.

[andreas.mehlin]

Originally Posted by Rucksta

Scarf

See if you can find something better than wood as core material.

Problem is getting it here in Mexico. Shipping foam sheet from the states down here is sort of impractical.

How about strip planking and coating each strip with epoxy? Water shouldn't be any issues at least?

[Rucksta]

Originally Posted by andreas.mehlin

Problem is getting it here in Mexico. Shipping foam sheet from the states down here is sort of impractical.

How about strip planking and coating each strip with epoxy? Water shouldn't be any issues at least?

You could try and find a door with a cardboard honeycomb core.
Strip the skins and remove the core.

The following steps describe how to make ghetto Nomex.

The honeycomb will be too coarse to take the compression loads encountered on the trailing edge of a rudder.
Cut the core to the shape of your project with a box knife.
Test fit - it will be nice and flexible.
Cut somewhat circular plugs from the excess core and spiral them into alternate holes in the core as a test fit.
Remove the plugs.
Apply a slurry of thickened epoxy (glue ) to the work area on the rudder.
Allow epoxy to get sticky.
Apply honeycomb to rudder.
Use masking tape to hold in place.
Allow epoxy to set - no need to wait for cure.
Remove tape.
Spray coat of epoxy over and into the honeycomb.
Insert plugs whilst epoxy is wet
Spray another coat of epoxy over the combined core material.
Allow to set
Clean up knock off and have a beer while the sun goes down.

Fair to final shape.
Cut a layer of non emulsion Chopped Strand Mat to fit.
Wet out the CSM and allow to gel (sticky)
Apply CSM to work
Allow to set (not cure)
Apply thickened epoxy (glue) to CSM
Allow to Gel
Apply on a layer of laminating resin.
Apply bi directional cloth , roll , add resin
Repeat.
Allow to gel
Fair


Job done by beer thirty on day two ready for final sand barrier coat and antifoul on the same schedule as the rest of the hull/appendages.

Best not to use 5:1 or 7:1 resins.
4:1 is OK but 2:1 is best for non blush formulations that allow the work flow to continue without curing and sanding.

If you are stuck with a blushing resin (West?) brown vinegar will remove the blush at any stage from gel to cure without sanding.

Strip planking would take me 3-4 days.
Expanding foam about a day and a half.

[Chotu]

Originally Posted by andreas.mehlin

I think you misunderstood me...and maybe because I used the word "taper" wrong. What I mean is how to make the joint between the new and old core. Scarf joint or just put in the new core in the pocket as it is now.

Oh!!!

Now it all makes sense.

I’d do a scarf joint. Taper as large as you can possibly do. Bond with epoxy.

It is not the best rudder for your trimaran with a wood core, but I read your other posts and I understand the options for a core are limited. Foam is, of course, best. But I see it is not available where you are.

[GordMay]

Originally Posted by andreas.mehlin

... How about strip planking and coating each strip with epoxy? Water shouldn't be any issues at least?

Do I understand correctly, that you’re (partially) replacing a rotten core, but don’t think water might be a problem?

[andreas.mehlin]

Originally Posted by Chotu

Oh!!!

Now it all makes sense.

I’d do a scarf joint. Taper as large as you can possibly do. Bond with epoxy.

It is not the best rudder for your trimaran with a wood core, but I read your other posts and I understand the options for a core are limited. Foam is, of course, best. But I see it is not available where you are.

If you would have chosen. What material would u have used? Expandable foam?

[Sherpa17]

Does it need a core? Could you lay it up?