luckytempo93

hi everyone. i am building a foam rc airboat. it is 4 feet long and 2 feet wide and is powered by a ryobi 31cc gas engine swinging a 16x10 3 blade prop. i made the engine stand by myself and carved it to the shape that i would like. now here is the issue. i have done some research and found out the the fibergalss resin used in autobody and bonding that you purchase at walmart or lows is very harmful. it will melt the foam, so i found out that epoxy with fiberglass cloth (just like fibergalssing with the resin but using epoxy) would work. the epoxy wont melt the foam. so here are my questions. would you spend the money for the epoxy ($110) and adheard to the foam itself or put a layer of tin foil over the foam mold and resin with fiberglass on top of that cause of how cheep it will be. would bonding to the foam be better? or will the resin shell tight against the foam be strong enough? im torn cause that $60 or so will fill my bass boat 2 times. please leave some feed back and let me know what you have done or what you think. or any tips that you have to help me do this. thanks, Bruce

KC36330

you can get a 1 qt West Systems epoxy kit for 40 bucks and enough 6oz cloth to cover a project that size for about 10 bucks. if the foam is porous then put a coat of the West epoxy on the foam and let it harden, then sand it with some 80 grit and then lay the glass over it and any imperfections can then be bondo'd and sanded.

Strankon

I too intend to build an airboat, but instead of glass over foam, my plan is to mold a fiberglass hull ( build a plug, build a mold, build a hull)
I'm going to use a clear gelcoat on the hull so I can use glitterflake in the mold to produce a hull similar to what you might see on a bass boat.
Once I start the build, I'll photo document the process.

luckytempo93

its the pink insulation foam that i got at home depot. is that the porous foam you were talking about? and would i be able to get any type of epoxy? and would 1 qt be able to cover it and do the glassing for the entire project. and for Strankon, what are you going to suppoer the genine stand with? i dont think that the fiberglass shell will be strong enough and you do need some weight to hold the boat to the water cause of all the air that goes under the boat. some weight is good. but i will have photos of what mine looks like and what i have done to it so far. thanks guys.

tony-howard

My Feedback: (224)

With a glass hull, be sure to put enough foam inside to make sure it floats if the hull gets breached. Some of us here have raced air boats of and on for some time. They spend more time than you'd imagine up side down, whether by getting hit or by going over on their own. Twice mine have blown over backwards on the straight away. More often it's a wave or the wind that upsets them.

Bottom line is they take a beating, racing or not. They need to be light to be fun. We've gone to foam hulls with glass as being the most practical for racing.

They're sure a lot of fun.

tony-howard

My Feedback: (224)

I forgot to mention that what works for me is to use lightweight spackle trowled over the bare foam first - one or two coats as required and lightly sanded after each coat - followed by the epoxy and glass. If the last coat is sanded down to expose the top of the foam surface, the epxoy adheres well, yet by filling the voids first, excess weight is avoided.

In the picture above, there are two 1/4 X 3/4 wide plywood strips that are inlayed into the foam and run from the edge of the aft plywood sheeting to the transom. This method of attaching the engine stand has held up well despite several full throttle blow / knock overs.

The plexiglass hatch cover makes it easy to watch for moisture in the radio bay. To access the switch and charging jack without removing the hatch, the top of a prescription bottle has been epoxied to the cover.

Because racing means collisions, the gunwhales have an aluminum protection strip. The air rudders assemblies are easily replaced. (Because we sometimes race in very shallow water, water rudders, if used, are the swing up style.)

As can be seen in the pictures, we recently added non tips to the aft hull chines. They work quite well and my partially finished new boat has them incorporated into the hull.

This is style airboat is certainly not the only way that works. But mybe there's some ideas here that will be of interest.

luckytempo93

thanks for the idea. but should i use the epoxy or resin( http://jgreer.com/ ). i found this and i think that this is a good cost for epoxy. but all the spackle does is fill in the holes to give it a good bonding surface for the epoxy right? and would i use the spackle for bonding the upper and lower halves of the boat together too? i just want this step to be right cause im not rich and i want to get the most knowledge from everyone out there. thanks

Strankon

I'm going to try to build my airboat as true to scale as possible, therefore I intend to glass in hardwood stringers in the bottom of the hull.
On full scale airboats, the engine stand and rigging are bolted to stringers.

tony-howard

My Feedback: (224)

You must use epoxy resin as mentioned earlier. Polyester resin will eat the foam. The pink foam you mentioned is extruded polystyrene. It has a somewhat porus structure and the spackle simply fills the surface voids to avoid sucking the resin out of the cloth and/or having to use too much resin. It isn't absolutely necessary and the epoxy will bond well in either case.

The spackle is a filler and would not have any strength for bonding. I use lightweight wall board spackle found at any hardware store.

It sounds like you're new to using epoxy so just one more word of advice (well two). One is to measure the two parts carefully and stir the mix for a couple of minutes (you can't over mix it but you sure can under-mix it!). The second is to put only enough resin onto the cloth to make the weave turn translucent. Don't try to make the surface smooth on the first coat - let the cloth weave show.

Don't let this put you off from going ahead. We all had to start at sometime. For me it was in the 60's.

luckytempo93

your right this is my first time with epoxy-fiberglassing. i have fixed things with epoxy but not building anything. you said for the first layer is to put on enough to make the fiber translusant. does that mean i should let that layer dry? do i sand it smooth after that or do i just put another layer of glass on top of that? or just epoxy? im getting so close and excited about this project. and do you think that this is a good epoxy to use http://jgreer.com/ ??? thanks tony-howard

tony-howard

My Feedback: (224)

You can put both cloth layers down in one pass. Wet the first layer out and smooth it down flat with an old credit card or any disposable straight edge. Then lay the second layer of cloth over that and smooth it first. Then add just enough resin to make that layer translucent too. If you get a little too much resin in spots, rather than brushing at it, try using a wadded paper towel or toilet paper to blot up the excess.

When the resin has set, wash the surface with soapy water first to remove any amine blush, dry, then sand it lightly to remove any high spots. At that point you can give it another coat of resin (I like to use a thick slurry of resin with micro balloons that I squeege over the surface). Or you can finish it with a number of other methods.

I think your resin will be OK. Follow the instructions on the can and pay attention to the temperature requirements - almost all expoxies get very thick and hard to use at lower temperatures. Resist the temptation to thin it.

Finally I encourage you to test each step first on some scrap foam. That can save you a lot of problems later. Been there, done that.

luckytempo93

thank you som much. on that page there is the red and the green. should i spend the more money for the red? the manufactor said that they make props for the real thing out of that stuff. and how thick should the glass sheets be? they sell the 6 ounce, 50" wide for $6 a yard. would that be too heavy for 2 layers? or do you have another place where i can get it better. or could you give me a link or something with what you use to purchase from and what items. but i also want to know about those 2 epoxys. with what you think is better i will purchase. it almost sounds like your almost a pro. lol.

tony-howard

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From the descriptions, I'd go with the 'green' resin. The 'red' appears to be intended to be used as an adhesive and probably is too thick to use as a laminating resin where you want it to be thin enough to encapsulate the strands of the glass fiber. (The resin holds the glass cloth rigid which is what gives the combination of the resin and fabric its ultimate strength.)

The 6 oz fiberglass cloth should be fine for your application assuming you don't have any sharp edges or corners to go around.

I get most of my supplies locally from various sources. Greer should be OK for you to use. another source might be TAP Plastics if they have a store near you.

If a master is someone who has learned from a lot of mistakes, that would be me.

luckytempo93

thanks tony. i will call him monday and order the red and the fibergalss. here are some pictures i took. i have the sides cut to round them off really nice already.

wkevinm

I personaly use epoxy resins for laminating airplane wings and fuses, to date I have use West System and East System, both have a thin viscosity nice for laminating with FG cloth. I assume weight is not as much an issue with the project you have and as such an alternate my be to seal the foam with a latex house paint then use the Polyester resin over this to reduce cost.

Do a test piece 1st to ensure this works, I am only assuming it would.

KM

luckytempo93

so will 1.5 quarts be enough to cover the entire airboat?

luckytempo93

and would 2 layers of 4oz cloth be better? .... im sorry. i want this right.

beenie

My Feedback: (9)

Several years ago I made a similar boat for a 50cc weed whacker engine. It was also made of pink foam. It was significantly overbuilt and was heavy. 35# if I remember correctly. I used some cheaper epoxy resin from West Marine, 1 quart was just a bit shy, 1.5 qts should cover you. I used 1 layer of the 6 oz all over and it was ok. The bottom took damage ok, for increased durability you may want to double up down there. The previous advice about wetting out and not making a smooth surface on the first coat is right on. I use resin thickened with West Systems 410 microlight for filling the weave, but I am usually working on airplanes. The microballoons will work well. I used filler on the bottom and left the top of the hull the fabric texture and just painted it. Just don't use Bondo over the epoxy. I don't use any spackle before the fiberglassing, I didn't find that the pink foam soaked up too much. The big boat was fun, not terribly fast but a real good time.
Ben

tony-howard

My Feedback: (224)

Two layers of 4 oz would be fine with maybe a 3rd layer on the bottom. 4 oz cloth is usually a tighter weave which is good from a weight standpoint (less resin and better strength) and 4 oz plain weave drapes around corners more easily. Beenie's boat is closer to your size so it may be that a quart and half is needed. Besides, you can alway use any left over for other projects.

By the way, you don't need to do the whole hull with one batch of resin and shouldn't try. I suggest doing small resin batch and when it starts to congeal in the mixing container, start a fresh batch and keep going. The set up time for epoxy is slow enough to give you plenty of warning to mix a new batch. Just work each cloth layer down before starting the next layer. One trick to extend the pot life is to pour the mixed epoxy into a shallow container - this keeps the reaction heat lower and that's what entends the working time. I'd do the top in one session, trim the overhang, and do the bottom.

Beenie, 35 lbs kinda suprised me, but your boat is quite a bit larger than mine which is 30" long by 11" wide. With a 25 it weighs 4-1/2 lbs. We race these as if they were a class and with this hull a 25 is more than enough. I tried a Norvel 25 on mine and it was wild. I had several blow over's, but when it was upright it outran the rest of the group. After hearing some negative comments I went back to my OS 25. The fun in our racing is not being faster than everyone, but being evenly matched so we can bang into each other and just plain duel, yelling at one another in the process. The post race bench talk gets really funny at times.

But this is just one way to do it.

beenie

My Feedback: (9)

I would love to race these things, but nobody to my knowledge races them here. I didn't even know that there races until I saw your post. I have had several in the 33" range, and they weighed about or 7 or 8lbs, powered by a 40 or 46. They looked a lot like yours. To me they were more fun than the large one because they were more portable. Taking the big one out to the lake was an event. The reason that it was so heavy is that it was 48"long with a 30" beam and the hull was 6" of solid foam. There were 1x2 rails in the deck that were tied in to 1x2 rails in the bottom. If you look at the pictures you can see them under the glass as I made little attempt to achieve a smooth surface on the deck. The engine was quite heavy, I never weighed it, but it was somewhere between 5-10#. It was from a line trimmer that was similar in design and operation to a regular push lawnmower. I was in college and had never worked with an engine that large and overbuilt it just in case. The engine was not a smooth runner and all of that wood and steel was probably justified. Luckytempo's engine looks more civilised.

luckytempo93

well today i did alot. i ordered the green epoxy and than 7 yards of 4oz cloth. than i was stupid and epoxied the two halves of the boat together. its not time to do that yet. but oh well. i think thursday im going to cover it with the drywall spackle and have to wait for the stuff in the mail. monday to the hobby shop and get the engine prop cone and the pushrods. i cant wait. and let me get your ideas. im thinking of adding a spoiler to the front that i can actuate with a 3rd channel (t-maxx radio) so at high speeds of windy conditions i can lift up the spoiler and it would push the front of the boat to the water. im thinking it would work. should i use a high torque servo for that or just a regular servo. let me know what you think.

Spectura65

hey hey and hav you didit build this self ??? i hope you can answer me soon ??

Gretting Steve jung