Building another rudder (winged)

I posted about a prototype rudder I built a few weeks ago from wood. I'm trying different designs and getting tired of planing and sanding wood. I bought some styrofoam today and it's sandable. I plan on coating it with fiberglass and epoxy. Is this doable? Will the glass give it enough strength?

TIA,

John

 

If you add enough glass,you will get enough strength! You will then have the delightful experience of sanding the glass smooth and adding a coating for a finish you find acceptable.You may want to include crush resistant inserts where fastenings pass through or perhaps a longitudinal stiffener.As you can probably guess,I prefer shaping wood.There is also the ease with which you can modify the rudder,something that will not be easy with a glass skinned foam core.I have made winged rudders with a carbon T section let into the main blade and the end foil to help them remain together.You might consider something similar if you ever have the experience of going back to retrieve the tip foil.

 

endplate?

John, if you're going to use it to make an endplate like we previously discussed the styro is a bad idea because it will make the endplate too thick-and styro is not a good core in any case.. You can buy flat sheets of epoxy glass from the Atlanta warehouse of McMaster Carr in very small quantities. see: www.mcmaster.com ; phone 404-346-7000 ;e-mail: atl.sales@mcmaster.com
A small sheet of 3/16" G10 should do the trick I would think. The down side is you'll be creating fiberglass dust when you cut it and shape the edges.
Once you have a shape that you're satisfied with you could make your own quickie mold and build a shaped glass piece that would need virtually no cutting or sanding.

 

Can you explain how I'd make the mold?

John

 

DO NOT start sanding or cutting any type of glass materials without buying a, full face resperator of moulded rubber with a organic filter at the very least. Home Depot sell a very good one in their tool dept. for about $30.00. We can't get the stuff out of your lungs, John, after you put it in them. You only get 1 chance to work with fiberglass and stay healthy.

 

Getting a old brain is no fun. Cut and sand outside if you can. Or use a large floor fan by a garage door to make sure the dust stays outside forever. Walking in the dust will not save your lungs. It just takes longer to find it's way into your lungs. Yes ,I am trying to scare you a lot. I visit careless friends of fiberglass.

 

quickie mold

John, the more I think about it the least hassle in terms of finish and building is without a doubt cutting a piece from an already laid up sheet of glass IF you're going with a Bolger type endplate. Most of the surface is alreay finished!
-----------
Assuming that you would use an endplate shape similar to Bolgers with one flat side and one shaped side you could start with a flat untwisted,non flexible piece of aluminum, fiberglass or steel about an inch bigger than the part. You could then cut and shape a piece of plywood and glue the shaped piece to the base piece. You could finish shaping the piece using a putty like bondo being carefull not to blurr the edge between the finished shape and the base piece. When shaped to your satisfaction the whole thing should be coated with Partall Paste wax and you can spray or pour on two coats of PVA. I use pouring on rc boat molds up to around 5' in length. You need a clean recovery pan of some kind and you stand the whole plug up in the pan and pour on the PVA. You remove the plug from the pan and allow to dry vertically(with newspapers underneath to catch residue). When using bondo as a finishing material two coats of PVA is advisable.
Pouring the PVA creates a surface that is free of imperfections and very glossy-a much better finish than spraying PVA.
You can then layup a mold-w/o gelcoat if you're just going to pull a few parts using Partall and PVA as the release agent..If you use epoxy resin you can lay the whole thing up at one time using 6 layers of 6 oz. cloth( you'll need to keep the temperature around 68° if you use Fibergalss Coatings 4/1 epoxy). Bond a piece of wood or preferably glass or metal to the mold to stiffen it before you pull it.
When the mold is pulled you'll have the one side of the part; you'll need a waxed and partalled flat sheet about the size of the original plug base to make a finished part.
Asumming the finished part thickness is no more than around a quarter of an inch you can lay up the flat sheet and the mold with say three layers of cloth(placed in the mold 45°/45° to the centerline) and fill the cavity with resin and micro ballons(mixed thick) to serve as a core. Clamp the two pieces together and then pull in 24 hours. You'll have to trim the flash around the edge and you'll have a finished part. This can be a very quick process; it almost takes longer to describe it than to do it.
But, again, the simplest way is to cut the part from a finnished sheet of G10....

 

I built a pram a year ago with glassed over fir. I work with the glass outside with a mask and suit, and sock type thing on my head. I looked like a space man as the car drove by my front yard.

Why is styrofoam a bad core? What kind of foam do boat builders use? Lastly, does West Marine carry the releasing wax and PVA?

I'm not sure if it would be easier to just build it out of wood and put a coat of epoxy over it. I'll just be building one once I find the shape I want. And... yes it's a Bolger type wing.


John

 

styro

White stryo at 1 lb. per cu.ft. has big "beads" and is hard to sand well w/o leaving surface that absorbs a lot of resin. You can't use polyester resin with it or it will melt and it has very low compresive strength.Even though it is closed cell it will absorb water over time.I've used it for quick plugs that were covered with a lot of epoxy/glass. The 2lb stryo is slightly better and 2lb polyurethane can be glassed with polyester but is nasty to sand.
Some cores are PVC but the best ,I think, is Core Cell. 4-6 lb. density Core Cell is specified in alot of laminates but you really should have a Naval Architect and /or marine engineer help with the specs on any large laminate.
You might do better to call Fiberglass Coatings in St. Pete; they carry everything and ship it. But you might find a local boat , glass shop or body shop you can get what you need in small quantities.
Epoxy coated ply might be strong enough though it's questionable at 1/4" thix; with solid glass 3/16" is probably thick enough. For a simple endplate I'd keep it thin.

 

Thanks for the answer. I was going to build the entire rudder of styrofoam but I guess I'll stick to wood.

John

 

I wouldn't give up on the foam so early. You can by blue or pink styrofoam that does not resemble the stuff mentioned above. It is easy to work and sand, and you can get it through Mcmaster-Carr; it is marketed as "square edge" and I think Dow manufactures it. I use it for making quick plugs all the time, and I have used it as structural core in many instances as well. In the structural cases, the stringers were always oversize, so I never really worried about the fact that the foam has really poor structural characteristics. If you use it on your rudder, I would make sure your laminate is up to the task...

www.eliboat.com

 

hot wires

You can make really neat stuff using hot wires and "flotation billet."
This is the blue or orange foam that is under floats and such.
Dig around the web, and you can find out all the fun ways one can pull wires along templates to make really accurate cores, and use the cut off peices as molds to push the laminate onto the core. Model airplane stuff, very cool.
On the other hand, shapingf a suitable peice of wood ands adding some glass is a pretty direct and satisfactory method. Almost fool proof as well.
SHC

 

What type of laminate would be up to the task?

John

 

Sall boat rudder laminates

Making a bunch of guesses and assumptions:
That the blade is about 3/4" thick and about 16"deep
I would guess a layer of 9oz cloth , a layer of 13oz uni over the whole blade and a second layer of 13oz uni on the top half.
Sheer properties of the foam aren't very good, so you may want to cut in a peice of wood as a sheerweb down the max thickness.
This is not gospel, test the part by bending it before you bet your life on it.
SHC

 

Hi John,

I agree about the hot wire method. Years ago we built these R/C aircraft combat wings out of foam using a hot wire. Just clue your end templets to the end of the foam and use the hot wire to cut it. We used .021 wire. Keep it tight and go steady. It takes a few times to get the hang of it.

Delane