How to fiberglass upside down?

[kach22i]

HOVERCRAFT HULL

I would like to fiberglass over the aluminum, fiberglass shower panel, ABS plastic and wood rails/landing pads on the bottom of my hovercraft hull.

I painted the area with West Systems resin but the heaviest fiberglass cloth I selected would not stay up. A lot of the resin was soaked up by the wood, other surfaces were very wet and drippy. I have several weights of cloth I purchased a while ago.

I have some very light weight fiberglass cloth which I used on my tail cone. Will the lightest weight cloth soak up the resin better and stay on the surface upside down all on it's own?

Screws with washers are an option.

Wax paper strips/stripes and duct tape are a consideration.

I'm out of ideas - help.

[afrhydro]

small thin coats dont forget the bubble buster roller
you will have to kick it far faster than normal

[the1much]

like afro,,hehe,, said,,thin,,and small,,and 2 more guys,,,and some good arm protection,hehe,,,(upside down glassing was the first thing i did in a shop,,,i almost quit),,and alot of 3 inch masking tape,,,and roll the crap outta it,,,and too much resin will be your worst enemy.,,that stuff weighs alot,,and dont let the ry part of ya fabric pull ya wet down,,the glass really sticks up easy,,even before you wet the glass,,,wet ya area,,and tape the begining up,,then press with ya hands a foot down the line,,then wet out the glass.,and the lighter the glass the better it will stay up for ya,,some times if your gonna need "layers",,its best to do them 1 at a time.

[PAR]

There are a few different methods to work overhead. Apply a wetout coat of unthickened resin, then let this sit until it's kicking off, but still tacky, then apply the fabric, pushing it against the partly gelled goo. In this high tack state, it should stick, then you can wetout the fabric with more unthickened resin, being careful not to float the fabric off the surface with too much resin. Lighter weight fabrics will work better, because they will not get so heavy with resin that they pull off.

Another trick I use, is to very lightly dust the area with 3M 77 spray adhesive, then stick the fabric to this, which holds it in place, while you wetout the fabric with resin. The 3M 77 will not affect the bond.

ABS and aluminum are difficult to bond to, with over head work making this more critical. I think you'll have a very difficult time getting resin to stick to ABS, but aluminum will if it's etched first then has resin applied directly after it's dried off.

Stick a small patch of fabric to the ABS, give it a couple of days to cure then grab an exposed edge with a pair of pliers and yank. This will test the bond. Another method is the scratch the surface with a razor, in a crosshatch pattern. Apply some duct tape, pressing it down real well, then yank it off to see if any epoxy comes with it. If it does in either case, then you may want to consider other options.

Another note is the photo shows many crisp edges along the aluminum and plywood edges. 'Glass will not adhere well to these edges, leaving you a very weak blister or pucker. The exposed screw heads should also be faired in for the same reason, other wise the 'glass will "dome" over it and leave you with the same deal as along the crisp edges. Radius all edges, so the fabric will "lay down" and use some light weight fairing compound around the screw heads.

[KnottyBuoyz]

That's a tough one Kach. I don't think you'd be able to glass over the aluminum as was mentioned before. It's such an irregular shape you'd have a tough time getting a vacuum bag to hold.

You could try making a plywood pattern of the shape to be glassed. Cover it with poly film, lay out your glass on that, wet it out and jack it up into the space to hold it against the bottom until it kicks. I've seen this done in parking garages when they make repairs to ceilings with concrete.

Anytime I've done overhead or vertical glassing I've tacked it into place with 3M77 and vacuum bagged it. It's a bugger gettin' cured and uncured epoxy out of your hair.

[Fanie]

Is there no way you can turn it ? It's really going to be a LOT easier... For one your arms won't break off after the first two hours or so.

Maybe get a bunch of people to help you do it. Buy the beer, it's going to be worth it. Take into consideration that's a relative large area you want glassed, it's going to take a while and you probably want a couple of layers on it.

I would defenately turn it, even if I have to put scaffolding up.

[kach22i]

Thank you for all the input everyone.

Thoughts about fiberglass not helping 90 degree bends and comments about the difficulty of covering odd shapes and sharp angles are making headway with me. My goal on this part of the project is to add strength to the beveled pieces of wood lagged into the aluminum bar on the sides (at the wide part - set in place after the first picture was taken).

Yesterday I filled some gaps with resin soaked fiberglass twisted up and jambed in cracks with a screw driver. However it's still a piece of work to deal with.

I have some microballons and shredded strands which I also purchased at the same time as the cloth/matt. I've been meaning to learn how to best use them and experiment a little. The bottom of the craft with odd joints to fill will be a good place to do this.

I may leave the very bottom of the aluminum parts exposed, it was never my goal to cover them up. My goal is to secure them better, and I might be able to do this on each side without overlapping or covering them.

I forgot to mention that I will be fiberglass covering the modified plow plane. If I have to I will use a combination of screws, wax paper and duct-tape in some sort of band pattern and multi-step process.

Peel-Ply was mentioned in a hovercraft forum, I'm going back to the hardware store where I picked up the West Systems and see what they have. I read in an aircraft forum to stay away from the cheep knock off Peel-Ply they sell at Walmart. It does not work they said.



The white fiberglass shower panel (I should be able to bond) is on the bottom of the ABS hull was because the hull was ripped open from front to back (6 inched from the side edge) in an incident approx. seven years ago. The fiberglass shower panel sheet was the only way at the time that I could figure out to get some sort of hull continuity, and I was not having much luck with test samples in bonding to ABS plastic. This was all done long before I had access to the resources of this forum. It is secured to the ABS with heavy duty contact cement and over one hundred S.S. screws. I did this with the craft on it's side and leaning on my house - a crazy thing I do not wish to repeat.

[afrhydro]

kach
i hate to say it but you should have left that job to a pro
i am afraid you have a mess now that is not recoverable
you really need to flip it over and glass it all up that way (tow truck crane something)
i cant tell 100 % of what you have there but a 3 mil or so shower panel is not very strong and most of them have a plastic coating over the fiberglass and gel
does it melt if you put a grinder to it

[kach22i]

Originally Posted by afrhydro

3 mil or so shower panel is not very strong and most of them have a plastic coating over the fiberglass and gel
does it melt if you put a grinder to it

The shower panel has been on for many years and has gone through many test flights without any problems. It's doing it's job of connecting the two lower hull pieces of ABS hull under it. It is in theory only being asked to take small forces in tension distributed over a very great area.

I don't see a reason to grind it and would expect it to melt like you said. If I grid over it to polish off some stray hardened strands I have a sandpaper wheel in addition to cutting and grinding stone wheels.

One thing for you boat guys to remember is that the hull of a hovercraft is not in the water. All the typical quality of finish for hydrodynamic reasons are pretty much out the window. I'm much more concerned about sharp edges though because if the hull impacts something and pins the skirt between the hull and a hard place it may damage or cut the skirt. Trust me, I've done this several times and have plans/design solutions to avoid it.

I now have S.S. self tapping screws and S.S. fender washers and masking tape. I plan to tape as much as possible after using the tacky resin method. I will then use the screws and washers to help hold things in place before I roller a light coat of resin. I plan to leave the screws in place and may apply liquid tool grip rubber over the heads when I'm done.

I also have a little Peel-Ply cloth and may experiment with that method in larger areas just to get the feel of it.

I'm not glassing the whole hull, I'm just doing the spot areas of plow plane and landing pads. If I get around to it; all exposed foam will get get resin or resin and a layer of fiberglass cloth.

[afrhydro]

oh sorry i didn't catch it was a hover craft
we had one once in the shop for repair just a little yellow thing it had a prop on the back as i recall kinda like a air boat
anyways we all tried it out i was the only one who could drive the thing around
they we got in trouble cause we blew dirt all over the place and the boss got mad made us leave it alone before we broke it


way way long time ago back in my first few years of fiberglass repair

lol

[kach22i]

Originally Posted by afrhydro

we blew dirt all over the place

Yea, that's what they do best, blow dirt on land and water spray over water around.

I just tried those brick red micro-bubbles. I made it just a little too thin but I like the way they work.

I also tried the chopped strands of fiberglass. Too darn slippery for horizontal surfaces, but I managed. It's slippery nature makes it almost self leveing on horizontal/flat surfaces. I'm worried about sanding and finishing it. I suspect that a layer of micro-bubbles or cloth will be required.

I also have some white 3M ballons which are next on my list to try.

I'm still having fun.

[ondarvr]

Glassing the under side is going to be difficult for a first timer, this looks like job for a spray on truck bed coating product. It's fast, easy, waterproof and sticks to almost every thing. It will most likely cost less too.

[the1much]

Originally Posted by ondarvr

Glassing the under side is going to be difficult for a first timer, this looks like job for a spray on truck bed coating product. It's fast, easy, waterproof and sticks to almost every thing. It will most likely cost less too.

and SLOW the craft down by ALOT. that stuff is heavy, and will cause so much drag and friction,,that he may not even get it off the ground,,hehe,,k thats a little overboard,,but,,it does do that stuff.and im not sure how the stuff would handle being in the water all the time

[ondarvr]

Glass is very heavy also, and it depends on how much of each is applied. Friction is not an issue, there's nothing coming in contact with this surface during normal operation, only when things go wrong.

If it was flipped over and he could cover the whole surface easily, then epoxy and glass would be much easier to do, but with all the angles, different substrates, then doing it upside down, I think he'll end up with a mess.

[northerncat]

stianless staples around the edges fired only halfway in so they can be pulled out or tapped in as needed and start rolling from centre out
sean