Beneteau 361 Rudder Cracking

[C420sailor]

Hi all! First time poster here. A little background first.

2001 Beneteau 361. I've owned it since 2015, and I've been slowly fixing it up. The bottom paint was getting thick and beginning to flake off the underlying barrier coat in places, so I elected to have the paint blasted off in preparation for a sanding, epoxy barrier, and paint.

Anyway, I just had the dustless blasting done, and the front 30+ feet of the boat looks great. Behind that, there are some small voids in the gelcoat that I'll fill. The rudder however...

There appear to be wide and deep crevices in the gelcoat and underlying epoxy fairing on both sides of the rudder. There is no method to the madness, and they do not appear to be stress related. The rudder sounds great when knocked, like a solid, dry rudder should. These cracks looks more like gouges than anything, but were not present until the rudder was blasted (I assume the blasting opened them up).

My uninformed impression is almost that the epoxy fairing done at the factory was done with a bad batch of epoxy fairing compound. It looks almost porous---very odd.

Anyway, my plan is to drop the rudder (the bushings are shot anyway), aggressively sand the rudder down until the gouges are gone, drill holes to check for moisture/delam, assess the fiberglass and re-glass if required, then re-fair and epoxy barrier.

https://imgur.com/a/q8m35WI

Thoughts? Has anyone seen this before?

Ryan

[C420sailor]

Close-ups:

https://imgur.com/a/oJOR4Ne

[tkeithlu]

Welcome to the forum, C420.

My immediate thought on reading your description was "This is going to be impact damage," but the pictures don't look like that. Has it been exposed to heat?

Consider as a first step digging (grinding) into one of those cracks to see how deep it is. The danger I'm seeing is that the cracks, whatever their source, might be structural, such that filling from the outside is really just a bandaid and you're in for an attention getting and unfortunate experience once you are in the water.

Another approach: Restrain the trailing edge of the rudder, and then apply full force through the steering. Do the cracks expand/compress?

If it is superficial, then filling works. You just need to be sure before you fair it and move on.

Congratulations on progress with your very large project.

[C420sailor]

I sent the images to the company that built the rudder (apparently, some of the early B361 rudders were produced by a company called Tides Marine).

They aren't sure, but the consensus seems to be that it may be the result of some kind of chemical attack. I don't know when or how that would happen, and it would seem to me that a decently strong acid/base would be required to do such damage. It makes me wonder if the rudder was previously stripped, and such a chemical was used during prep but never neutralized before barrier coating? Who knows.

Anyway, plan stands. I'm to strip down as far as necessary to remove the poor epoxy, hoping that the issue doesn't extend into the underlying glass.

As for your question, I don't notice any flexing of the rudder or expanding of cracks when force is applied, but the crevices are so wide and deep that it would be very difficult to notice anyway.

[tkeithlu]

I'm looking forward to hearing what you find out. I've never seen anything like it, so it should be a good story.

[Spot]

Hi Ryan,

I am not even sure what we're seeing for a material here. Cracked glass mat? HD foam? Fairing mud?

[C420sailor]

What you're seeing in that picture appears to be unthickened epoxy. I was able to sand those crevices out. Weird construction for sure, see below.

Dropped the rudder.

I started taking one side of the rudder down today. Attacked it with 36 grit paper and a long board sander. Tough work. The white is an epoxy barrier, it appears. Underneath is some fairing compound, then it appears to be epoxy. I don't see a fiberglass weave in the material. It's very strange.

The post is entirely composite, square section, and appears to be carbon fiber.

Anyway, most of the crevices seem to be in the fairing compound. By the time I get to the underlying epoxy, most are gone, and the few that remain on the sides of the blade are very shallow. The deeper ones that remain are around the edges, bottom and trailing primarily, where the blade profile is thin, and the upper corners. No method to the madness. It makes me think that perhaps the blade got too hot while curing during manufacturing? Exotherm possibly?

I will say, this thing is lighter than I expected, and very stiff.

Gameplan at this point is to heavily coat with epoxy to penetrate the remaining cracks and lay glass for good measure. Ain't no kill like overkill.

[tkeithlu]

That's entirely possible. I once had polyester resin get so hot during curing that it destroyed the fabric (Dynel, we don't use it any more) layers in the block I was building. The layered blocks shattered in a charpy impact test - no fabric strength whatever. I would guess, without asking my chemist/admiral, that epoxy is also exothermic. Perhaps someone used too thick a layer and overheated it?

Sounds like a super rudder and post underneath it all.

[C420sailor]

Got the rest of the rudder taken down. Ended up buying a belt sander and a 36 grit belt—a total godsend.

Other side looks equally rough. I was able to take the top epoxy layer down to the underlying glass and the cracks that remain are much, much smaller. Not very happy, as cracks are stress points, but hopefully this repair lasts...

I got the whole rudder ready for glass, and I’m in the process of laying two layers of 10oz fiberglass cloth with epoxy. I forgot how much worse epoxy is to work with, compared to poly resin. What a pain.

[Spot]

Originally Posted by C420sailor

Got the rest of the rudder taken down. Ended up buying a belt sander and a 36 grit belt—a total godsend.

Other side looks equally rough. I was able to take the top epoxy layer down to the underlying glass and the cracks that remain are much, much smaller. Not very happy, as cracks are stress points, but hopefully this repair lasts...

I got the whole rudder ready for glass, and I’m in the process of laying two layers of 10oz fiberglass cloth with epoxy. I forgot how much worse epoxy is to work with, compared to poly resin. What a pain.

Are you saying that there are cracks in the glass and not just in the 'mud' or fairing compound? The rudder sounded pretty well built, stiff and light. Could some of this be a bodged repair and fair job from before your time with he boat? 2 x 10oz plain weave should add quite a bit of strength. Were you thinking wrapping a layer around the leading and trailing edges?

My experience was the other way, started with polyester and ended up liking epoxy better. Now I am doing some repairs that might be better as vinylester and I am wondering if I should 'stick' with one of the other devils I know...