How much fiberglass layers / weight is needed when making a boat?

[LibertyMKiii]

I have sculpted a rigger from Styrofoam and looking to skin it with fiberglass cloth. The use case will be high speed SAW runs so it needs to be built up enough to handle crashes reasonably well.
Looking for experienced folks to advise how much is enough for strength without going to far and making it heavy.

My thought was something like 2 layers of 6oz cloth, but is absolutely just a wild guess. I plan to make it stronger around the boom tube attachment points and the entire rear 1/4 of the boat.
The fiberglass cloth will be done with epoxy resin (because poly will attack the foam)

Thanks!

Liberty

[sammyha]

With my little experience building my one off UL19 Experimental Rigger, I would think two layers of 6oz. cloth is enough. It's so easy to add a little here and there and get too heavy. The more important thing is use a good epoxy resin like MAS or West Systems.

I noticed two layers of 6oz. cloth ends up being about the same thickness as the ProBoat UL19 hull that I was bashing, fwiw...

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[LibertyMKiii]

With my little experience building my one off UL19 Experimental Rigger, I would think two layers of 6oz. cloth is enough. It's so easy to add a little here and there and get too heavy. The more important thing is use a good epoxy resin like MAS or West Systems.

I noticed two layers of 6oz. cloth ends up being about the same thickness as the ProBoat UL19 hull that I was bashing, fwiw...

Sent from my SM-G950U1 using Tapatalk

Thanks Sam, that seems to align with my estimation of 12oz total.

[NativePaul]

It depends, how big is the rigger, how fast are you aiming for? The bigger and faster, the heavier layup you need.

Are you using the foam as a temporary former and melting it out when you're done, or leaving it in situ? Foam with glass on each side of it has great stiffness and you need more glass if your getting rid of the foam, although if you make it the same weight without the foam it can still be stiff enough and a lot stronger, or conversely lighter for the same strength but you will lose some stiffness.

Does it have any stiffening or structure other than the glass skin? There are parts that even if you want to keep the foam in most of it you wont be able to as you need space for the electrics etc, and you need to cut holes in the skin for the hatch/s which weaken the tub a surprising amount, if you dont plan to reinforce these areas locally one way or another you will need a much thicker skin.

It might just be me, but I cant get a perfect finish on the entire tub with glass over foam and it needs sanding after, its easy to burn through a layer on a high spot, so I add an extra layer more than I think I need that can be sanded through without compromising the structure.

Do you have access to cloth cut at 45 degrees? I used to so know its available, but cant find it any more here, almost all the cloth on a rigger should be at 45, so if you have access to it without a huge price gauge, get it as you will waste a lot less cloth.

[LibertyMKiii]

It depends, how big is the rigger, how fast are you aiming for? The bigger and faster, the heavier layup you need.

Are you using the foam as a temporary former and melting it out when you're done, or leaving it in situ? Foam with glass on each side of it has great stiffness and you need more glass if your getting rid of the foam, although if you make it the same weight without the foam it can still be stiff enough and a lot stronger, or conversely lighter for the same strength but you will lose some stiffness.

Does it have any stiffening or structure other than the glass skin? There are parts that even if you want to keep the foam in most of it you wont be able to as you need space for the electrics etc, and you need to cut holes in the skin for the hatch/s which weaken the tub a surprising amount, if you don't plan to reinforce these areas locally one way or another you will need a much thicker skin.

It might just be me, but I cant get a perfect finish on the entire tub with glass over foam and it needs sanding after, its easy to burn through a layer on a high spot, so I add an extra layer more than I think I need that can be sanded through without compromising the structure.

Do you have access to cloth cut at 45 degrees? I used to so know its available, but cant find it any more here, almost all the cloth on a rigger should be at 45, so if you have access to it without a huge price gauge, get it as you will waste a lot less cloth.

The boat will be around 30" roughly.
I plan to keep the foam in some areas but mostly it will be removed. I was thinking of cutting out of wood a few stiffening structures for inside the hull once the foam is out.

Agreed on the final finish being difficult. It takes some significant sanding work to get it all smooth. That is a good point on adding more to leave room to sand through it. Thanks for that reminder!
I don't have access to 45 deg fabric without spending more, but I can lay the fabric layers in different orientations and get a decent strength usually.

[Bande1]

The boat will be around 30" roughly.
I plan to keep the foam in some areas but mostly it will be removed. I was thinking of cutting out of wood a few stiffening structures for inside the hull once the foam is out.

Agreed on the final finish being difficult. It takes some significant sanding work to get it all smooth. That is a good point on adding more to leave room to sand through it. Thanks for that reminder!
I don't have access to 45 deg fabric without spending more, but I can lay the fabric layers in different orientations and get a decent strength usually.

do a layer of mat and a layer of strand.

[LibertyMKiii]

do a layer of mat and a layer of strand.

I believe the mat requires poly resin, which does not play well with the foam.
So I don't have to buy anything else I'll probably just stick with cloth for both layers and use the epoxy resin.

[Bande1]

I believe the mat requires poly resin, which does not play well with the foam.
So I don't have to buy anything else I'll probably just stick with cloth for both layers and use the epoxy resin.

not all foam is melted by poly. I used it to make a hatch and it didnt melt. mat or strand will work with epoxy. using both makes it as strong as possible.

[RandyatBBY]

When I build a structure that wil not have any foam behind it and want it ridigid if I have no other materials there. I will use three cloth materials a light fiberglass, in the middle a light kevlar and the other side will have Carbon fiber. The weight of the Fiberglass is flexabledepending on what I have in stock 4oz. is average use. Sonetimes I only have 2 oz., 8oz. and 19oz. FG so I will doubble up on the 2oz.. Most of thye time I only carry in stock a light fine 2 oz. kevlar and rarely use more than one layer of it ever. On the Carbonfiber I allways only have the 5.9OZ ever. This is what I use for bottoms and sides of a hull, If I want to do a deck I will use a 10.oz Plain Weave and a 10.oz and the fine kevlar and a 2oz. fg under it for the lighter deck and wood stringers.

As of latley I am just building mostly for my self and like a marriage of materials. Ie wood Be it plywood or Ultra plywood, spruce exctra with pre formed sheets of the composites above mentioned above. Of course I have a lot of molds and use glass sheets for molds too. Pictures below will help under stand my process.

71504091682--899511A4-5812-46F9-AE23-34162CD6AC1E.jpgIMG-3352 (1).jpg 71504103827--69CE93FB-F1A5-4D3D-BBB1-3893B95774E0.jpgIMG-3818.jpgIMG-3818.jpgIMG-3837.jpg

[BUMBLESPECIMOODA]

With my little experience building my one off UL19 Experimental Rigger, I would think two layers of 6oz. cloth is enough. It's so easy to add a little here and there and get too heavy. The more important thing is use a good epoxy resin like MAS or West Systems.

I noticed two layers of 6oz. cloth ends up being about the same thickness as the ProBoat UL19 hull that I was bashing, fwiw...

Sent from my SM-G950U1 using Tapatalk

Good advise.

2-layers (one 0-90, and one on the bias) for a layer that's strong in all directions is the start. If more is needed, do that again for 4-layers total. As for weight of cloth, 6oz. is a good place to start. 4oz. and 2oz. are good too for lighter lay-ups. Using stronger stiffer reinforcements (like carbon fiber), will reduce weight, becuase less of it is needed, to acheive what the glass cloth does, although costs go up as well. Always use epoxy resin too, no mater what the foam.

[lohring]

We laid up the Leecraft tunnels with 2 layers of 6 oz cloth over a layer of 3 oz cloth on the outside. We only used a single layer of 6 oz on the cowl.

Lohring Miller

[LibertyMKiii]

Thanks all!
It sounds like everyone is doing about the same thing with minor variations.

I appreciated the feedback and advice!

-Liberty