Fiber-glassing outer hull anyone? - moved by moderator

[shawn32671]

Does anyone here have experience with fiber-glassing an outer hull? I am building a Midwest Fantail Launch II steam powered R/C boat and the instructions call for having the outer hull fiber-glassed. A tutorial would be nice along with hints/tips. The lower most picture below is where I'm at with my build up to now. Any help would be greatly appreciated. See my build log at http://modelshipworld.com/index.php?/topic/4593-fantail-launch-ii-by-shawn-midwest-products-small/

Shawn

 

 

 

Edited December 17, 2013 by shawn

[NMBROOK]

Hi Shawn

I have done this numerous times on RC builds.I have looked at your log to see what you are up against.The stumbling block is the rail being fitted around the deck edge.You need to be able to 'drape' the cloth over the hull.The cloth is left overlong at the deck edge until the resin is 'green'(set but not cured hard) and then trimmed flush.You have two options.

1,You can paint the hull with epoxy resin.This will harden the hull skin and make it impervious to water.This method means a lot last filling and sanding to get a nice finish for paint.If you buy some ZAP finishing epoxy resin and epoxy thinners.Mix the resin as suggested and then add the thinners to produce a water like consistancy.Thoroughly mix it,it will go milky and then clear when thoroughly mixed.Apply the resin to the hull using a paintbrush generously (having masked off everything else)the more you put on,the further it will penetrate into the balsa.Clean the excess off with the brush after a good soak.The cure time for this resin is 3hours,however Epoxy does not stick to itself once fully cured unless you sand it.Therefore leave it for 1 hour and apply another coat with freshly mixed epoxy again thinned.After three coats you may find most of the grain is filed at which point you can the apply more epoxy unthinned.Two more coats again at one hour intervals should give you enough build for 'knocking back' with glasspaper.Do not attempt to sand the hull for at least 48hrs.This gives the epoxy plenty of time to harden up,otherwise your glasspaper will just clog in a few strokes.It is a case of a thorough sanding and fill the low spots with car body filler.Make sure all low spots are keyed before applying filler.Looking at your build,I would also coat the interior with a couple of thin coats of resin to seal everything further because you will get some water in the hull during sailing.

2.A little different in that you use laminating resin instead.This involves cutting the 'chines' form glassfibre mat.I wouldn't use chop strand mat or tissue,but use fine woven glass fibre cloth.This is used by aircraft modellers to 'hard skin' balsa wings and fuselages.Cut the four chines out of the mat using scissors.You need to have made cardboard templates first.When applying the epoxy mix as directed(no thinning) and apply to the hull.I would work on one section at a time as you get less worktime with this resin and you haven't done it before.After applying resin for one panel(don't put loads on because you will only end up removing it)lay the cloth on the section.Then using an old bank card and making sure you hold the cloth so it doesn't move,Scrape along the surface similar to using a cabinet scaper.This 'forces' the cloth through the resin film.Keep repeating this operation with light pressure stroking the cloth to force out air bubbles and wipe away the resin build up that appears as you do this.After this resin goes tacky,but not hard,apply a further coat of freshly mixed resin without cloth.This is to avoid breaking through into the mat when sanding.Sand the hull being careful not to expose the cloth.Any low spots will need filling as before.

Hope this gives you a little insight as to whats required.Personally I would go with option one and see how 'hard' the hull becomes.When sanded you can always apply option 2 over the top.Option one is easier if you have never done it before.

One last note,ensure wherever you work is at least 16 deg c when you do this.Epoxy will lay dormant and not cure at temperatures below this.

Kind Regards Nigel

[shawn32671]

Thank you Nigel, you were a huge help and I was already thinking of just epoxying the hull and calling it good but wasn't sure if that'd work but you confirmed that it will. I had also already planned to epoxy the inner hull where I can reach to water proof the interior.Thanks again.

Shawn

[NMBROOK]

My pleasure Shawn,as long as the resin is thin enough and penetrates the balsa,there won't be any problems.Some builders use cellulose dope instead of epoxy,but I have cracking issues with this in the long term so I stick to epoxy.

Kind Regards Nigel

[shawn32671]

What can I use to thin the epoxy?

[NMBROOK]

I buy dedicated Epoxy thinners from the model shop.Any thing else I think will affect the strength.

 

Kind Regards Nigel

[shawn32671]

Thanks Nigel, I had heard about using denatured alcohol to thin it...Would this be a bad idea?

[captainbob]

Isopropyl alcohol makes a nice thinner.  I’ve used it many times, of course in those days nobody heard of epoxy thinners. 

 

A warning.  If you are not using fiber, (glass, nylon stockings,  . . .) you need to build up the thickness of the epoxy for strength.  I have seen the wood of the hull swell and shrink with moisture and/or weather enough to open the seams between the planks.

 

Bob

[shawn32671]

Cap 'n' Bob suggested using a nylon stocking in place of fiber glass...That sure sounds like a great option.

[shawn32671]

Thanks Bob and Nigel.

[shawn32671]

I found this great tutorial on fiber glassing balsa on YouTube for anyone else thinking about glassing their build.

https://www.youtube.com/watch?v=ujk-wBQDUSk

[NMBROOK]

Been out in the shop and had a look at the thinners bottle.It doesn't give a list of chemical content and may just be denatured alcohol rebranded.It is easily available for me and inexpensive as it goes along way,so I have never tried anything else.Because you are heavily thinning the resin and it is going on Balsa,the balsa is the reinforcement,so reducing the need for a binder.Had the timber been denser and less absorbent then yes I would of recommended a form of mat over any other option.Densities of balsa do vary a lot so the only way you will know for certain if giving it a go with resin only first and then mat later if necessary.One thing is for sure,if you use both processes,your hull will be like concrete,just not as heavy

Kind Regards Nigel

[shawn32671]

Thanks again Nigel, I found some denatured alcohol in my shop and a few pairs of nylons I had been keeping around to use with my swimming pool skimmer filter. I'm going to give the nylons a try and see how it turns out. Hopefully I have a posting to share later today showing positive results...I only wish I hadn't already added the mahogany trim around the hull, it will sure make this more of a challenge. 

[shawn32671]

I plan on trying nylon stocking material for my "glassing" of my Fantail Launch II but I was checking out the 3M Bondo brand fiberglass repair kit part number 420 that I have and couldn't find the "weight" of the cloth in the box...I called 3M and no one I spoke to on the phone there had any idea of what "weight" I was referring to other than the actual net weight of the cloth contained in the kit which I was told was 9 ounces...Not very helpful at all.

 

The cloth is a fairly heavy cross woven type. Has anyone here used one of these kits or possibly know what "weight" the fiberglass cloth in the kit is?

Edited December 17, 2013 by shawn

[NMBROOK]

Hi Shawn,yes been there tried that.It is heavy chopped strand mat that is included in these body repair kits.If you use this you will be filling and sanding for ever,it is far too rough for this application.This mat is only suitable when making a hull in a mould.You will find the woven material in model shops specializing in RC planes more than boats.The woven material is wafer thin.

Kind Regards Nigel

[shawn32671]

Nigel, that's kind of what I figured...I just started the process of "glassing" the hull using nylon stocking material. I had 2 and a half knee high pairs in a box (I used one stocking for my swimming pool filter this summer already) but it looks like there should be enough to cover the hull with it. So far I've just been test fitting pieces to see how they will lay down on the hull.

[NMBROOK]

You may find this material may lay around the corners of the chines,the woven cloth probably wouldn't without causing air pockets,it doesn't like sharp corners,preferring a radius instead.

I wish you all the best and look forward to seeing how you get on.

Kind Regards Nigel

[shawn32671]

Thanks Nigel, you have been incredibly helpful, you rock.

[shawn32671]

OK, I posted a quick update of my attempt of "glassing" the hull with nylon stocking in my "Fantail Launch II by Shawn - Midwest Products - SMALL" thread if anyone would like to see...Let me know what you think on that thread rather than here please.

[captainbob]

Shawn,

 

Looks like a fine glass (nylon) job.

 

Bob