RC Boat Construction

[TimClark]

I have finished building the mold for the RC boat that I am planning on building, now I have come to the time where I need to decide what kind of glass I am going to use. My friend built his using two layers of 12 oz glass with a layer of epoxy down over the mold, then the glass, then another layer of epoxy, then the last layer of glass, then the epoxy.

Now, I was wondering if this was the way to go about building my boat and what kind of fiberglass I should use. I would think that 12 oz. would be overkill for a 4 foot RC boat but I have not built one yet so I won't judge. How would 6 oz. cloth hold up and should I use the same technique of laying down the glass like my friend did? Thanks.

TC

Tim,generally in building production models one builds a plug first. A plug is an identical replica of the finished hull. Then a mold is layed up on the plug and pulled off; the mold is built thick and strong so it won't distort.
On models-particularly multihull models- this can be important because it allows all the finish sanding to be completed on the plug so that once the hull is pulled out of the mold there is no finish work(sanding and painting) necessary. This saves weight. If you're using epoxy you can even spray Kyrlon(original) in the mold and layup on top of it which allows the hull to come out of the mold already painted. This is similar to the way gel coat is used on full size boats but much ,much lighter.
If you have a female mold as I've just described one layer of 1.5 oz. kevlar and one layer of 5.7 oz woven carbon are sufficient. If your mold is actually the plug as described above then you might want to go with two layers of 5.7 oz carbon or two layers of 6oz glass with one layer of something like 3oz glass to serve as a sacrificial layer for final sanding. The carbon will make a stiffer hull and for the amount you need may not be too expensive. Make sure that whatever you use is put in/on double diagonally; that is so that both directions of fiber in the cloth go up to the sheer line and down to the centerline.
Another advantage of building a plug first and female mold is that if designed properly the hull and deck can be bonded together while still in their respective molds assuring perfect alignment.
Good luck...

[TimClark]

Doug, how hard is it to make a female mold? I have a plug all ready to go, I could always just sand it down a little more to make it smoother for a female mold. I was considering it but I was worried that it would be harder to push the glass down into the mold and work on the bow of the boat. Thanks again.

TC

Tim, its not hard to make a female mold once you've had some training. You'll probably be better off just making a "one off" off the plug. I'd suggest you get an experienced glass person to help you with it.
The hardest part of model boat plug/mold making is designing the hull/deck flange system-that can be a bit complicated depending on the system you use. Again, try to get some experienced help the first time around...

[TimClark]

I am probably going to just use the "one-off" method and just use a plug and not go for a female mold. The week after next I am going to be spending every day at the local Maritime Center while my dad is building a kayak so I will have access to everything I could possibly need and will have all day for 5 days to work on the boat.

I actually did the deck/hull flange system for my friends boat and it ended up working out really well. I just used a really thin layer of balsa to shape the deck and then put a really thin layer of glass over the balsa. The back section can be opened to access the servos for the rudders.

TC

[Steve Clark]

Tim, For a 4' model catamaran hull, a single ply odf 9oz colth or two plys of 6 oz would be just fine.
I would go for the 6 0z because th weave is finer and so it will be easier to get the surface.
In general more plies of finer weave gets you a higher fiber density.
SHC

[TimClark]

Thanks Steve, I went to West Marine today and they only had 6 oz. so I just got a couple yards of that. Hopefully, if the director of the local maritime center allows, I will have all week to build my boat in a boatshop while my dad builds his kayak. I'll post some pictures once I'm done. Thanks again.

TC

[TimClark]

I popped the hull off the plug today and I did 2 layers of 6 oz. glass and it seems pretty flimsy. Would balsa supports make the hull stiff enough? Thanks.

TC

Tim, that illustrates one of the reasons to bond the hull and deck while both are still in the mold(difficult to do on a one off, though).... Did you use polyester or epoxy?

[TimClark]

Epoxy...I am putting in balsa supports right now, and so far I think it will work pretty well.

Balsa or foam should work; foam is less likely to gain weight but in a model it won't make a whole lot of difference.
You'll install the trunk and reinforcing for the cross arms and then the deck ,right? Are you going to use an external rudder? How will you do the deck?

[TimClark]

Right now I am reinforcing the lateral flex of the boat. I am installing beams on the boat the will shape the deck. For the deck I am doing a 4 oz layer of glass over the top. I am planning on doing a stern mounted ruddder, I would like to do a rudder that is thru-hull, but I don't know how to keep water from flowing in the hole that is for the rudder shaft.

TC

Tim, it's easy to make a thru hull rudder system: just use brass tube matched to a ss shaft. You can get the ss shaft(.156") from Berg in NY and the brass tube at any hobby shop.You can make gudgeons for a transom hung rudder out of the nylon nose gear mounts sold by Dubro and available in most hobby shops. Get the ones for 5/32"(.156") shafts.You can use carbon shafts
if you have a hobby shop that sells small carbon rod or even tube. You'll need a way to clamp the rod and Berg sells very small shaft clamps as well. Be aware that most small carbon rod is not torsionally reinforced so keep the force required low on a thru hull installation by putting the shaft at about 19% of the chord aft of the leading edge. It won't matter on the transom hung version since the shaft won't have any torsional load at all. You might find a pix of a transom hung rudder installation on my website( www.microsail.com ) under either the F3 or the microMOTH...

[Laursen]

For all things power models I found a website its called Jim's Rc boatdock there is an entire industry on making power and hardware for these things

http://www.jrcbd.com/index.shtml

if you look in the forums there is all the info you could ever need and under the manufactors sections

anyways just go there you will see what I am talking about

Frank

Here's a picture of America One-the first production rc spinnaker boat and the first with a square top main-even before the real boats had it: