CARBON VS. VACUUM GLASS

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10 years 11 months ago #9156 by Rightarmbad
An infused fibreglass hull would probably be lighter than a vacuum bagged glass hull.
Infusion in it's best practice is getting fibre to resin ratios of well over 80%
Vacuum bagging as I have read doesn't approach that.
(unless there have been some developments since I did my research.)
Extra resin doesn't make it have a better strength to weight ratio, just heavier and a worse ratio in absolute terms.

The whole industry is switching en mass to infusion over bagging at the moment if they are using fibre that can be used this way.
It's only Nomex core and the super lightweight pre-impregnated carbons that stick with bagging.


So you really need to be specific about what you are talking about here.

Follow the path of the independent thinker. Expose your ideas to the dangers of controversy. Speak your mind and fear less the label of 'crackpot' than the stigma of conformity. And on issues that are important to you, stand up and be counted at any cost.--- Thomas J. Watson

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10 years 11 months ago #9157 by AR_convert
For the benefit of those not familiar with these terms lets review infusion (dry lay-up) and Vacuum bagged (wet lay-up) construction.

Courtesy of fiberglasshelp.com/2009/02/fiberglass-resin-infusion/

Fiberglass Resin Infusion

Basically, the process works as follows: Cloth is laid up ‘dry’ on either the male or the female part of the mold. The mold is assembled, and any opening or joint is sealed using clay. Vacuum lines are attached to the highest point of the part (resin outflow), and a main line (resin inflow) is attached to the lowest point. The resin (mixed with catalyst) is placed in a container that is attached to the resin inflow line. A vacuum pump sucks the air out of the part at the outflow point, creating a low pressure area where the resin will be drawn towards. The resin, flowing into the mold because of the lower pressure, will flow through the cloth and towards the outflow line. Once the mold is full of resin, excess resin will flow into a resin trap to avoid resin being sucked into the vacuum pump. Once the resin has cured, the part is de-molded and trimmed. As a female/male mold was used, the resulting part thickness is uniform, and the finish is perfect on both sides of the part. Problem areas that often arise with resin infusion are incomplete areas where the resin did not flow properly, resulting in dry areas. It is also not possible to see where problem areas might arise during fabrication as the mold is closed. Furthermore, the catalyst used is often a catalyst that works at a slower rate, giving the process more time so as to avoid any dry areas.

Vacuum bagging from ( www.miketrax.info/fiberglass/why-vacuum-bag-fiberglass-parts-2/)

One way to make light, strong and clean parts is through a technique called vacuum bagging. In general, parts made with vacuum bagging techniques show better strength and stiffness than simple molding lay-ups and they are smoother to the touch. The strength and stiffness of vacuum bagged parts obviously comes from the compression from the vacuum pressure.

In a nut shell, vacuum bagging involves placing your mold and parts, while still in the cure cycle into a flexible plastic bag. Once in the bag, all the air is sucked out at a pressure of about 15 psi.

The bag must be flexible enough to conform to all the contours of your mold, it must not be susceptible to attack by your resin, it must not interfere with the cure of your resin and it must be able to withstand the temperatures released by the resin during the curing process.

Vacuum bagging can be accomplished either by placing the entire mold into a bag or by attaching a plastic film, usually made of PVC to the flanges of your mold and then applying the vacuum draw. Note that the vacuum draw is held throughout the resins’ curing time.

Vacuum bagging small parts is easy and can even be accomplished with large zip lock type food storage bags that have been modified with a nipple that will accept the line from your vacuum source. Larger parts are more complex and difficult to set up.

Bagging larger parts that require a large volume of resin require a bleeder layer as well as catch areas for the excess resin that will be drawn out of the mold from the vacuum. The extra resin pulled out by this process is responsible for the resulting light weight parts which are such a desirable outcome of vacuum bagging.

Always looking for the next boat :)

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10 years 11 months ago #9209 by f0xxee
Replied by f0xxee on topic Re: CARBON VS. VACUUM GLASS
Hi all,

I have read this thread with great interest and can (as a complete newbie) add nothing of value as to which are the better materials for construction of surf skis.

As one who has worked at sea as a mariner for 30 years I can however tell you that ALL the skis mentioned on here are inherently unstable once you sit in them and put your feet into the foot straps.

If you are interested in the physics of all this check out the following link concerning the "metacentric height" and its relation to inherent stability. It also explains why round hulls are by their nature more tippy than V or square hulls.

Just if you are interested.

en.wikipedia.org/wiki/Metacentric_height

Lastly, I would hazard a guess that in the end price and durability will end up being the factor in most peoples decision making process.

Regards,

Foxy.

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10 years 10 months ago #9789 by Nige
Replied by Nige on topic Re: CARBON VS. VACUUM GLASS
Well after having originally started this thread,I decided to upgrade my carbon Elite to the carbon Elite SL, and had my first 15km paddle yesterday, out to sea in a 15 knot upwind - downwind route. Conditions were pretty lumpy but with good runs to be had on the way back.

The big difference with the SL is the primary stability : the ski is a lot more tippy than the Elite, but still has good secondary stability, so I never had to brace or felt like I was going to fall in, but in the lumpy seas the ski was a lot more skittish than my old Elite. My core muscles really felt it after the paddle!

Upwind the narrow entry of the ski meant it was faster and smoother punching into the chop and it felt really good. Downwind the ski behaved similarly to the Elite, but the narrower nose meant it was easier to catch a run and then push through onto the run ahead. I was pacing myself with a friend on an Elite and was comfortably able to open up a 100 metre gap on him. With less volume in the nose I was expecting the ski to bury its nose more than the Elite, but surprisingly this wasn't the case and the ski remained completely dry. Still, conditions were fairly mild, so it will be interesting to get it out in 25 knots.

All in all, a very fast ski and a definite step up from the Elite, but you need to have no stability issues in order to make use of the performance.

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