As I recall from my material science studies, a resin coat on its own will strengthen a thin wood panel but it is prone to cracking. Once it has cracked to a certain extent, any strength it has imparted will have evaporated and all you are left with is extra weight.
Glass fibres added to the resin act to prevent cracks propagating through the material and add to its toughness.
So resin adds strength, glass fibre adds toughness.

I have been puzzled by conflicting statements on the web, some stating that adding resin and fibreglass will strengthen wooden construction, and others stating that it will not. For my own understanding I did some tests, which others may find interesting. These are not by any means scientific, and meant only as a guide for me in model construction. The results show that coating balsa with resin and fibreglass cloth does strengthen it.
For those who want to see more detail, these are the results. Three separate strips of balsa, each 18" long by 1.5" wide were cut from a single sheet 36" long by 3" wide, 3/32" (2.4mm) thick. Each strip was placed on top of two supports 10" apart. A load was applied in increments to the centre of the span. After testing each strip in its uncoated condition, each one was coated with Deluxe Materials Eze-Kote resin, according to the maker's instructions, and a layer of fibreglass cloth applied on each side. The cloth was a piece I had spare so I don't know what weight it was, but I estimate between 1 and 1.5 oz per sq yd. After coating each strip was tested again. The results are shown in the chart. The lower the deflection when loaded, the stronger the strip.
Although all strips were cut from one sheet, strip 3 was clearly stiffer and stronger than the other two in its uncoated state. it benefited least from the addition of the fibreglass. Strips 1 and 2 showed a significant increase in strength.

Thanks for that tip. I've discovered that Deluxe Materials products are now available on this side of the pond, so I'll have to give it a try.
Roy

I find Eze-Kote from Deluxe materials a much better material to work with than epoxy or polyester. it's a water-based resin which provides a waterproof and fuel-proof finish. you may need three or four coats but that's not a chore as it's easy to apply, there's no wastage as the pot never 'goes-off' and it's dry to a paint-able surface in half an hour.

You clean up with water as well.

I should clarify my comment about 'no sanding' since it's not all 'plain sailing'.
The first coat goes on easily and did not, and should not, require any sanding. For the second and subsequent coats, the fibreglass is essentially smooth and does not hold the resin in place so well. So these coats will be fine on a horizontal surface, but on a slope the resin will tend to run, and overlap on a hard edge. if you can ensure that you don't apply too much resin it's fine, but if you get runs, you'll have to sand.

Having now completed fibreglassing a hull using the method shown in the video mentioned earlier, I can say that this has been, by far, the most satisfactory fibreglassing I have attempted. A smooth hard finish with no bubbles, no ripples, and no sanding. So for anyone who has been struggling using the technique of undiluted resin and credit card spreaders, I can thoroughly recommend the video'd method.
Roy

Resin alone gelcoat alone and tissue alone or a mixture of any of the above has no strength.

However resin used with a matting or woven roven give the strength

I have read on this forum and others that fibreglass has no strength and am puzzled by these comments.
Fibreglass is commonly used for building the hulls of full-size boats, including lifeboats, which implies that it has considerable strength. Admittedly, their hull walls are much thicker than on a model boat, but the strength is there.
I have seen a fellow model boater take a hull made of balsa, which had been coated with fibreglass and bang it on the edge of a table, with no damage. As we all know, you can poke a finger through untreated balsa.
Finally, some data is provided on wikipedia that fibreglass impregnated with polyester resin has a tensile strength of 8000 pounds per square inch.
So some clarification of the 'no strength' comments would be appreciated.
Roy

Hi chugalone 100 Welcome to the site.
You can fibreglass with different types of resin and cloth. if you are making and casting a fibreglass hull use fibreglass matting but to cover a hull lightweight fibreglass cloth is best. This is the type shown in the suggested video.
Resin can be epoxy or polyester based but the latter is generally cheaper and in my opinion is easier to use and doesn't require thinning with alcohol. it is sold as layup resin and is supplied with hardener. Do follow the instructions re quantity of each part and mix thoroughly.
If you are using epoxy iso Propyl Alcohol is the type to use and is clear.
The video shows using a brush to apply the resin and whilst this is OK it will give a very thick and heavy coating. I use the brush to apply and then a credit card sized piece of plasticard to spread the resin over and into the surface of the cloth resulting in an almost opaque finish with the weave showing through. You do need to have a good surface to work with as any imperfections will show when the resin hardens. Once dry give a light sanding all over to remove any imperfections and fill any holes with car body filler and sand smooth. I then apply a very thin top coat of the resin using a brush. When dry use wet and dry to sand and if necessary apply further thin coats until you have the finish you require. I have a local supplier and if you visit the site http://www.resin-supplies.co.uk/product.htm all the resins/cloths etc are listed. Using Google should bring up a local supplier.
you do need to follow the safety instructions to protect yourself and wear appropriate protection for your hands, eyes and breathing, it is also best to apply in a well ventilated area and not on a cold day.
The end result will be well worth the effort to keep your tug waterproof. You could also paint the resin over thye inside of the hull to protect the wood from any water that doeos find its way inside.
Dave

Some can do fibreglassing as easily as shelling peas. I have fibreglassed 3 models so far and have yet to master the technique. I've spent far too much time sanding the results to make them smooth.
For my next project I plan to follow the guidance shown here:.
He talks about 'denatured alchohol' which, in the rest of the English-speaking world is referred to as methylated spirits.

Resin and Glass fiber Tissue.

The tissue will just hold the resin and give a good seal.
Wet the area with resin first..... then lay over the tissue.
The tissue does have a certain amount of stretch to it.
Easy to join just tear the edges and dab on with resin using . soft brush.

Very soft stippling required.

The grp Tissue has NO strength to it as is NOT structural just used to get a smoother Finish when Laminating Grp
Not Easy to apply but easy to sand off if you make an error.