Thread: Material for Rudder Repair query

Originally Posted by redx

Hi,
I am posting my query on this forum because it involves the repair or replacement of a rudder for my 20 foot fibreglass boat. I would like to repair the existing fiberglass rudder but if that is not possible I will need to make a new one from wood.

My existing rudder was in such a sorry state that I removed it from the boat and in the process of cleaning it up I ended up pulling it all apart with the intention of repair it from scratch. It was made of two fibreglass shells bonded together and filled with some kind of orange putty/filler substance. (see photos)

http://img.photobucket.com/albums/v4...ingRudder2.jpg

http://img.photobucket.com/albums/v4...ingRudder4.jpg

The material was very heavy making the whole rudder weigh about 15 Kgs. I have separated the two halves and removed all of the orange material and now want to glass the two halves together again and fill the intervening cavity with a similar material.

My question is - Does anyone know what the orange filler substance might have been? Or is there anything I can use as an alternative? Whatever I use will need to be pourable and must set hard and be waterproof. I've considered using closed cell expanding urethane foam but I think it will be too lightweight for use as reinforcement in a rudder. Can someone help me with suggestions please?

redx.

Looks like the 2-pack foam used for packaging heavy but delicate items such
as jet engine shafts & etc back in the '80s when I rubbed shoulders with such
things. Reasonably tough in compression but little strength in tension. Did the
buoyancy foam in a kayak with it once (International Marine purchased from
Glascraft Adelaide). Never again. Absorbed water.
That bottom mount area looks particularly scungey.
How much of the 15kg weight do you reckon was absorbed water?

You are in a wooden boat forum
Obviously someone (starting with me) will recommend using your glass shells
as a template to produce a plywood rudder, and coat it in epoxy/glass. Then
put away the old shells. The thing with wood is that it is lighter than many
alternatives, and has intrinsic strength, both in compression & tension.
Especially tension. Far more so than foam. Of any type. A strong core
reinforced with a glass skin, vs a glass skin with an insubstantial core...

Done properly, plywood would probably outlast your existing system by a
decade or two. Epoxy is a much more water-proof system than polyester.
Done badly, it would probably be only a year or two shorter lived than the
filled shells approach.

Fair winds
AJ

I agree with AJ -wood will be better. But I understand that you might want authenticity which in this case is using fiberglass with foam inside. I suspect that the foam was used as nothing more than support for the fiberglass shells. The strength for the rudder comes from the shells and the foam just helps to keep the shape especially in compression. So any foam will probably do so long as it is good in compression.

I'm sorry gentlemen, but wood is no where near as good as modern composite materials when it comes to building light and strong. Do we see wooden boats in the America's Cup, Transpac, VOR or any other races of note? I guarantee that if old Nat was around nowadays he would be up to his elbows in carbon and whatever the latest you beaut epoxy resins are available, don't forget he was one of the first to use aluminium masts.

Not to knock wooden boats, I love them, but let's be honest and accept that modern composites are lighter, stronger and more efficient. They just don't have any soul.

Redx, your rudder would most probably have been made by glassing over a shaped foam blank. Your problem now is to replace the foam which you have removed without leaving any voids and remaining light. I would be looking at one of the expanding foams (can't recommend one of the top of my head) and fill each half of the rudder. You may need to drag a hotwire across the top to skim the foam flat and level. I would then glue the two halves together with thickened epoxy then tape and fair the joins as well.

You may like to try this forum here which deals specifically with composites.

Redx, I've offered an answer to your questions on the forum linked above, also where you've posted the same set of issues.

I wasn't able to open the link there, but here I can see your orange stuff is foam. It may be two part polyurethane or something else like polystyrene, who knows without hands on. If it was holding moisture, it wasn't polyurethane.

Again, and supporting Darce (not that I would usually ) a blade of inert materials is far superior to wood in appendage applications. If you're forced to use wood, that's one thing, but other wise . . .

Since your rudder isn't a kickup style (which I assumed on the other forum) you don't need to worry about weight, so long as you have a "keeper" mounted above one of the gudgeons (usually the top one), to prevent the rudder's pintles from floating up and out.

Hello Par, Darce and everyone else,

Many thanks for the replies to my query. I realise I was committing an act of blasphemy by asking a fiberglassing question on this woodwork forum, but I was hoping to get opinions on which might be the better way to go, repairing the old rudder or building a new one from wood.

I posted my rudder question on several of these forums because I am trying to get as many opinions as I can regarding the rudder filling material.

Par, I have read your replies to my message on the other forum, Thanks very much for the advice. I don't think the orange filling substance was an expanding urethane foam. It was very heavy and very dense and brittle, but I do think it was poured in as a liquid because there were air bubbles in it here and there, and it was firmly adhered to the fiberglass shell. When I started removing the material I found that it was not waterlogged, in fact it was not even damp. Where the rudder was damaged the filling was stained from water ingress but only for no more than a half inch into the material, and where the bronze pintles were attached it was stained green.

Building a new rudder from scratch using timber is a good option, but I'd prefer to have the boat fitted with it's original f/glass rudder. Whatever I do I can only do once because of the cost of materials.

Thanks again to you all for the valuable advice.

redx

The 'glass shell halves seem in good shape, other then the leading edge damage. I'd repair the leading edge, possably reinforcing it with more material in case of future "attacks", then calculate about how much volume she has. This will give you an idea of how heavy she needs to be for neutral buoyancy (neither floating nor sinking). I don't suspect it'll need much weight. A highly buoyant rudder will test the gudgeon attachments the whole time she's in the water. This is an necessary strain, so just enough weight to make her have no weight on the gudgeons.

The filler used may have served this very purpose. Use polyurethane foam from the local big box store. It's used under siding as an extra layer of insulation on houses and is closed cell. Fill the majority of the interior void with this stuff, epoxied in place of course. Fit it around any weight you employ. Fill the remainder with thickened epoxy and bond the two halves together. It'll be bullet proof and can't warp, absorb moisture, etc., like wood can.

Everyone here knows how I feel about wood, but this is an ideal application for inert materials.

Hi Par,

The method you describe sounds like an easier way to go about the repair, I'll give it a go. Thanks for your help in this matter, much appreciated.

Cheers,
redx.

Hi,
Just an update to let you all know how I got on with my rudder repair.

After a few attempts at repairing the old f/g rudder I decided to make a new one from wood. As the pics show it seems to be turning out ok. I have compensated for the weight difference by using sheet lead inside it and all I need to do now is seal with several coats of epoxy and fit thr gudgeons etc.





Cheers,
redx

Nice job. With all that end grain exposed, 3 coats of epoxy minimum, better if there's more. That end grain will act like a sponge if it's coating is breached and with the epoxy on it, the moisture will not have a way to escape, so . . .

Thanks for the good advice PAR.

I had planned to give it 4 or 5 coats of epoxy and I will also be painting it with Epoxy primer and two pack polyurethane paint. Hopefully this will be enough to make it watertight.

Cheers,
redx

Someone, I think it was Duck Flat W.B. in Adelaide, recommended cutting off the bit
of a centreboard or rudder that cops impact abuse - usually the bottom front corner,
and glueing it back on before glassing it. That way the glue join forms a barrier to
water ingress to the rest of the board. If damaged, it can always be cut off & a new
small corner glued in & shaped.

Make sure you apply the epoxy coats wet on wet. Roll out a coat, let it go tacky, mix and apply another coat. If you let it cure between coats you will need to give it a good sanding before each new coat, and even then the bond of subsequent coats won't be as good as wet on wet application.

Yep, that's a good trick AJ. I don't glue the piece back on, I make a new one from pure thickened epoxy. The logic being, it can take a whole lot more abuse to the bottom of the blade. Both methods work well at saving the rest of the blade.

Originally Posted by Rick_Tatum

Make sure you apply the epoxy coats wet on wet. Roll out a coat, let it go tacky, mix and apply another coat. If you let it cure between coats you will need to give it a good sanding before each new coat, and even then the bond of subsequent coats won't be as good as wet on wet application.

Thanks Rick,
I'll make sure I do as you advise, thanks.