Carbon Fiber on Student Designed Hull

Hello,

I run a college engineering competition team who is building a new carbon fiber hull. We are building a 12 x 4 monohull that was designed by one of our team members. I’ve run into an issue where I have no idea how much carbon fiber we need, and no way to know until after I buy it. I have a sheet that can run my laminate properties, but only in plane, so I don’t know my strength. There’s also no easy way to know our forces exactly to calculate our necessary strength.

I am planning on doing a hand layup on tooling. I would like to lay an initial set of 8 layers (0/45/-45/90/90/-45/45/0) on the curves of the hull, set the sandwich parts with a single layer, then run material tests using machines at my university. I am planning on doing it like this because we are running low on time due to bureaucratic issues with the clubs money, and it will give us a decent measure of what our actual properties are (I’m sure we will be weaker then data sheets).


What is the overkill thickness for a carbon fiber hull? How many layers do people generally use? What thickness of fabric are people generally using? Any help is much appreciated.

 

The normal way to describe a laminate is by weight per unit of area as the material is available in quite a range of specifications.Carbon also comes in a range of different weaves and the less crimp there is,the less the fibres are distorted.Unless the material you plan to use is light enough for model aircraft building,eight plies is a lot in terms of strength and most hulls would use a couple of plies on either side of a core material for optimum stiffness and manufacturing time.Solid carbon panels are quite rare.It also varies with the type of use the boat will see.What is the weight and weave type of the carbon in question?Not promising a precise specification,but more information would be good.

 

Hi @EllieO , welcome to the forum.
You're saying several things that could lead to complete failure. A 12x4 (feet, meters?) boat is already substantial enough to warrant careful engineering. It's not about adding many layers of fiberglass, but about using only the appropriate layers in each location. In many cases, a large thickness may not be enough to withstand the loads acting on the hull. You can achieve a very expensive and heavy combination of layers, but one that has layers overloaded beyond their capacity. It's essential to place the layer best suited to the loads present in each area.
A sandwich with only one layer of fiberglass on each side is absurd.
You must use design pressures approved by a relevant organization.
The design stresses are not those specified in the vendor's catalog. You must use safety factors accepted by best practices.
In short, if I understand you correctly, I think you should consult someone who knows about the design and calculation of naval structures.

 

You really need to find competent engineering.

The post here is far too vague to offer any help. You didn’t use units, or offer the hull shape or anything.

Hand laying CF over tooling is probably the hardest way to build and so you also really won’t have time to build a tool and the boat in any ordinary course at school.

About the only way to build fast would be over or inside a jig with the foam and then laminating, but to be fair, you also did not specify the timeframe for deliverable.

Anyhow, you’ll need to offer more details to anyone trying to assist.

 

EllieO,

Indeed, welcome to the mad-house... oh... no... I mean Forum.

All good advice above.

Going straight to carbon fibre on a prototype design is like running before you can walk.
If you insist, then just build light, if it fails in sea trials, repair it and go a bit heavier.
Repeat until it doesn't fail.

OR

Build to a proven set of plans from a proven design.

 

I have to wonder if we are providing a data harvesting bot with information of if the OP is a bit hesitant to reply.For an attempt at guidance,I will mention that for quite a few weekends in the last twenty years or more I have been racing a small boat that is essentially 450gsm glass on either side of 8mm foam and it is all held together with polyester resin (cue shock and horror from the brigade that parrot 1708 and epoxy to any enquiry!!!). It obviously has bulkheads and other stiffeners but is a little over 5 metres long. It would not be sensible to sit such a hull on a beach covered in large stones and it lives on a padded launching trolley when not in the water as light laminates over foam can be crushed by high local forces,when in other respects they are strong enough for the loads encountered.

 

The design should have the laminate schedule. Otherwise, it is a drawing. The width and length are not enough to give you a relevant answer. You need to have a description of everything the boat is supposed to do. For example, the maximum weight empty and loaded, expected slamming forces, what puncture resistance is required, type of propulsion, target speed, etc.

 

Mayuko Phillips has a post about that

 

Where?

 

Something is wrong with the OP that I could not wrap my head around it.

First he says that it will be a "college engineering competition team" but "I’ve run into an issue where I have no idea how much carbon fiber we need". Isn't it that when it is a college team competition, the professor learns first how to design then teaches the students "how to" and let them compete with each other to see how much they have learned.

Second, he is talking of of a quasi isotropic layup, carbon fiber, and sandwich construction. That is the pinnacle of composite design and it is a tall order for someone with little knowledge to start with. Exactly what BlueBell said.

 

I concur Rxcomposite. It's a very strange post and the OP hasn't been back since.
I smell a rat...

 

For a hand-laid carbon fiber hull of this size, most teams end up in a similar range: 6–12 layers of 200–300 g/m² fabric for the main shell. Your planned 8-layer 0/45/−45/90 stack is a very typical baseline and a reasonable place to start, especially if you’ll follow up with material tests. Hand layups almost always come out weaker than datasheet values, so testing coupons the way you plan is the best way to dial in final thickness. After you see your real numbers, you can add extra layers in high-stress areas like the keel, bow, and chines. In practice, a 12-foot hull built with 8 layers plus localized reinforcement is usually strong enough, and that’s considered the “safe, slightly overbuilt” range for student racing projects.

 

This is probably another student that wants us to do his homework.