A quick search for opinions...

[honza]

Just a few quick structural notes. Silica is quite strong in compression. For tension and sheer, you need fiber. Chopped glass strand can take some tension and sheer. Glass bubbles are good for light duty fill.

The concrete analogy works here well. Think about the resin as the cement mix and the fibers as the rebars. Simple beam or a slab loaded from the top needs the rebars (fiber) at its bottom. Continuous beam with several supports needs the fibres at the top and bottom. A column needs fibers close to the outside, around its perimeter. Fibers need some extra length (2 in.?) of embedding in resin or overlapping to get fully activated.You allways want to have fibers soaked thoroughly and covered with resin.

Epoxy is the best resin for most kind of use, definitely for a secondary bond. If used for primary and secondary bonding on a same part, it always has to be washed with water after curing and subsequently sanded before secondary bond (unless peel ply is used). Do not touch epoxy with bare skin, unless cured. If you get sensitized to it, you never be able to go close to it again (it happened to friend of mine, who could not finish building his dream boat).

Orientation of the fibers is very important. Carbon is many times stronger than glass. Do not mix carbon and glass, unless you know why you are doing it. In a lot of cases the glass will do not do any good, just adding weight.

Silica and rowing do not bond, the resin does. I think, that why with silica it feels like a stronger bond is because silica is harder to peel than fiber.

Now, we have the foam core in our decks. Think about it as a web in an I-beam ......

For the tubing to hull attachment, as you are probably limited to bonding to the outside of the tubing (inside of the hull) only, I would recommend a fat rounded corner fillet with silica mix where the tubing meats the hull and biaxial glass over ("into") it, before it is uncured. Some unidirectional fibers along the tubing, radiating out at the hull will make it even stranger - but you need to cover them with the biaxial. Finish with well soaked peel ply.

I'll be glad to try to answer questions, should any particulars arise.

[nebulatech]

Great input honza!

Re: epoxy vs polyester - I have no basis to argue against epoxy making a better secondary bond, but is it necessary? In other words, is polyester already as strong as is needed? For this project, I dont think resin selection is the most important aspect so I will digress.

Honza what are your thoughts on using a prefabricated fiberglass tube as WillieC suggests?

[honza]

Yes, epoxy is stronger (3x?, off the top of my head) and adheres better for secondary bonds. The only exemption I found was with Royalex, what Old Town canoes are (were?) made of, where polyester did better job for me.

There is definitely a way to do it with FG tubing, better carbon, but I would not want to be the guinea pig. If you could find similar design, which worked, stick with the scantling. Good fit at the top and the bottom would be important. Maybe, there are some suitable strong bushings available.

[Dieselram94]

Thank you for the awesome ideas and discussion!!!
I had a hour tonight so I went ahead and removed the rudder port. It’s stainless steel and has grooves already in it! Just none that prevent it from spinning once the bond breaks free, also no evidence of any type of sealant on the flange where it meets the hull. No wonder it was leaking lol.

So... I’m thinking at this point reinstall as the factory did, only this time I will cut some vertical grooves to help it “key” into the new layup. That should prevent it from spinning if the bond lets go in the future. Also bedding it in a generous bed of 5200 as I don’t foresee removing this again. At least that’s my plan lol. I’m thinking of using the west system gflex epoxy as it’s flexible, and advertised as superior bond to stainless...for what that’s worth.
Although I really like the fiberglass tube idea!
Here are some pictures from tonight.

[nebulatech]

It's great that the tube already has the grooves in it!

What are your thoughts on alignment? Will it be difficult or does that collar sit flush on the hull and make the alignment correct?

[Dieselram94]

I believe the color just sits flush on bottom of hull (outside) and the hole was a tight fit, I was thinking best to have rudder installed held up with the pipe head fitting to make sure everything is in a non bind situation. Also use strips of biaxial 1708 to tab two layers all around tube, then one piece covering tabs on inside of hull, filit the 90degree joint, then maybe three or four wraps around the tube. Also grinding three verticals key ways into it to make a mechanical bond to prevent future rotation. Then bilge coat

[dkirsop]

The hull laminate looks to be in good shape. The hard part will be waiting for the 5200 to fully cure before proceeding with the FRP lay up. Having the rudder in place and having the post fully supported during the cure is a good idea. Keep in mind that when everything is done the rudder hangs from the top of the post and does not rest on the lower pipe elbow. The pipe elbow serves as a steady bearing. A few extra wraps around the post log to support the weight of the finished assembly won't hurt. Also, the tiller arm will exert a bending moment at the hull joint so there needs to be good flexural strength at this location. "Strong" and "rugged" are the key words here.

[Dieselram94]

Hull laminate is in good shape, I was hoping to have got some sanding and grinding done tonight, but it didn’t happen. Kids (2 babies) take some serious time! Lol
The piece of mat that’s still bonded to the hull seems to be very well bonded, but I’ll dig deeper to make sure. If it is, I think I’ll just fill that chipped area next to the hole and sand everything really well, then start laying up. I think this repair will come out well.
I’ll definitely make sure the final fit has the rudder hanging. Next up after this is notching the rudder to clear the new shaft as I had it made slightly longer to accommodate a zinc/cutter combo. As well as repair the keel as it is cracked where the pipe fits in.

[honza]

Just a couple of notes. I would not mix the 5200 in there, I would use only epoxy thickened with silica, or better, with chopped glass to secure it in position and grinded a bit before final lamination. I do not see any need for vertical grooves. If you are worried about the thing spinning later - I am not - de-grease well and, you may consider sanding the metal under uncured epoxy mix, before final placement. Dry run for everything helps a lot. For super strength, I would consider triangular corner gussets made of high density foam covered with glass, between the pipe and the hull.

[WillieC]

"For super strength, I would consider triangular corner gussets"

Excellent suggestion.

[nebulatech]

you may consider sanding the metal under uncured epoxy mix, before final placement

I'm having a hard time imagining this. I'm assuming that you want to sand it while under epoxy to trap out oxygen and prevent passivation. Would you use wet/dry paper?

[honza]

I do not understand the chemistry of it, but it is a common procedure recommended by fine boat and airplane designers. To prevent oxidation and contamination, I guess. I always used just paper at hand and what worked. Decent dry paper should be ok. You really do not need to expose it for too long. Most wet paper I see, is kind of too fine.

[nebulatech]

I understand. I've never heard of doing that before, but I haven't done a lot of work with resins on stainless. My wet papers start at 220. Looking at the scratch pattern of 80 grit, I don't think I would want to go any finer, though for automotive and woodworking, 120-150 are the recommended grits for substrate and 320-400 between coats, which has worked well for paint, but the film build of paint is much less than resin.

I watched a video recently where the craftsman used 36 grit flap disks to prepare substrate. I think it was glass on glass.

[tribologist]

Here's my bow thruster install...

IMG_1344.JPG

The tube is straight but you can see how it got thicker at the end with my laminations to the hull. Almost like an hourglass.

I also first put a 3/4" radius fillet of thickened epoxy as a starter to bond the tube in place before I started with the laminations. Small strips first, then built up to larger strips with each lamination. I finished just by brushing gelcoat over the thing to make it pretty.

Told you I was a glutton for punishment.

Jon, What size thruster did you put in?

Ulf

[hetek]

My thruster...

Side-Power SE40/125S DC Thruster (On/Off)

I installed it in a 27' Seasport Pilot. Side-Power does make one size smaller, the SE30, but oddly it has the same size tunnel as the SE40.