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Author Topic:   Chopper Gun Hull Layup

JaySul posted 09-18-2002 01:32 PM ET (US)
I am new to all this and have read about a chopper gun hull layup on my 1978 V-20. What is it?
Jay
JFM posted 09-18-2002 02:17 PM ET (US)
Jay, could you add more detail to your question??? We may then be able to help you. If your question is did Boston Whaler use chopper guns the answer is yes. Is there any thing wrong with that, the answer is no.
Regards, Jay
Taylor posted 09-18-2002 02:22 PM ET (US)
Me, me... I'll take this :)
There are several ways of putting fiberglass into a mold. The tried and true way is hand layup where you take fiberglass woven cloth, Omindirection mat, kevlar, carbon fiber etc etc etc, and lay it in the mold, wetting it with resin and using brushes and squeegies to uniformly saturate the fiberglass. Extra resin makes it heavy, not enough will make it weak.
Vacuum bagging offers better quality control than hand layup, a plasic bag is placed over the mold and the vacuum pull is regulated to keep just the right amount of resin in the fiberglass for maximum strength/weight ratio. (My experience is kayak related, I don't know that many big boat builders use vacuum bagging, although I'm pretty sure that the Hinkley picnic boat is build that way)
Problem with vacuum bagging is that it costs a lot to do. But hand layup requires experienced people to do right, and experienced people burn out fast in the industry... if they don't quit, the fumes toasts there faculties.
Which brings me to chopper gun. With a chopper gun resin is fed through a hose along with chopped glass strands which then spray out on the mould in a random pattern (like mat). The resin to glass mix is adjusted as you spray out material. Its probably the fastest way to get fiberglass and resin in a mold. It requires less experience to use, although it takes more experience to do it well. Chopper guns generally produce heavier and thicker hulls than hand layup, but sometimes that does not matter.
It all boils down to the skill of the operator for both hand layup and chopper gun.
Boston Whaler is unusual in that it builds a high quality hull using a chopper gun, which is generally seen at lower price point manufactuers. I think they can do this because the strength of a whaler hull comes not just from the glass but from the foam filled construction with skins on either side. The glass skins on classic whalers are fairly thin compaired single hull boats. This helps to keep the weight down.
I've also been told that with thin skins, the weave pattern from hand layup of fiberglass cloth will show, and that chopper gun (or mat) will produce a smoother hull. I'm not sure I believe that.
Anyway, when I first heard whalers will built with a chopper gun it surprised me.
JaySul posted 09-18-2002 02:27 PM ET (US)
Taylor, thanks for the fiberglass lesson. I had read on some other threads about complaints with the use of chopper guns and the design of this particular hull and wanted to know just what the heck I was getting myself into. So far so good
jimh posted 09-18-2002 08:59 PM ET (US)
The Boston Whaler laminate schedule is rather thin compared to other boats, but as mentioned, the composite struture of the UNIBOND hull creates the strength, not the thickness of the laminate.
I have also heard that it is possible to get higher consistency with a chopper-gun layup than with a hand layup with lower skill level operators. This may also be the key. If a plant only makes a boat or two per day, they can be hand-laid. The operators can take their time and they are probably quite skilled. If you want to mold ten boats a day, perhaps a chopper gun is faster.
The hand-layup laminate must be carefully done so as not to get too much resin--that adds weight, cost, and no additional strength. I have heard stories that in some plants the layup crew is only allowed to use a certain amount of resin to lay up each boat. The QC people weigh out the resin and only so much is provided for each hull.
In the chopper gun technique the resin/glass mixture is more controlled.
Hey, however they're making them, the Whaler hull seems to last!
JaySul posted 09-19-2002 01:47 PM ET (US)
Amen! I have a 78 with few fiberglass problems...as far as I know.
Taylor posted 09-19-2002 05:17 PM ET (US)
Clearly weight is related to the amount of resin used; there is an optimum point where high strength is reached beyond which extra resin just makes it heavier. You can hit that with either a well adjusted gun, or a skilled layup guy, or a perfect pull on the vacuum bag.
My guess is that chopper gun tends to err on the high side of resin use.
I think the main difference between hand layup and chopper gun is how the fibers run in the fo the hull when you are done. In chopper gun, the fibers are short, perhaps 1 to 2" and in a random patterm, while with hand layup you can control exactly what kind of fibers, which way they run and how many there are.
I checked, the Hinkley Picnic boat is built with Kevlar and E-Glass with and a propietary(?) system called 'SCRIMP' a 'resin infusion technique that reduces the resin weight by 50%".
http://www.hinckleyyachts.com/yachts/picnic.html Way off topic, but very pretty.
pglein posted 09-20-2002 07:46 PM ET (US)
without the foam core, a chopper gun hull would be crap. but in the whaler, it is not of concern.
Family owned a fiberglass company for 20 years. Chopper gun is the cheapest and crappiest way of building fiberglass. This is a process that should be reserved only for cheap imitation automotive body panels on ricer honda civics, not the hull of a boat on which your life depends. Again, however, due to the foam core, the whaler hull is mighty high quality.
I am honestly surprised to learn that it uses chop-gun method.
jimithing posted 09-22-2002 09:30 PM ET (US)
isnt the real concern here that no matter what technique used if voids are created anywhere in the process that is where the weakness is? Voids create places for water to collect and creates a weak point in what would ordinarily should be a strong and sound hull. Question remains: Which of these methods for laying up fiberglass hulls has created fewer voids in hulls over the history of its use.
For me that determines which is the better method.
PressureDrop posted 09-24-2002 08:33 PM ET (US)
i too, would be very concerend if a chopper gun was used for the hull, or any structural members for that matter. all of the strength in a GRP (Glass Reinforced Plastic) composite is in the lenght of the fibers, a boat hand laid with woven roven that runs the length of the hull will be rock solid, however a boat laid up with a chopper gun will not be cuase the fibers are only a few inchs long, providing no strenght, think about it... if you wouldnt want hull hand laid with mat, what good it one that was machine laid (with mat)??

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Author	Topic: Chopper Gun Hull Layup
JaySul	posted 09-18-2002 01:32 PM ET (US) I am new to all this and have read about a chopper gun hull layup on my 1978 V-20. What is it? Jay
JFM	posted 09-18-2002 02:17 PM ET (US) Jay, could you add more detail to your question??? We may then be able to help you. If your question is did Boston Whaler use chopper guns the answer is yes. Is there any thing wrong with that, the answer is no. Regards, Jay
Taylor	posted 09-18-2002 02:22 PM ET (US) Me, me... I'll take this :) There are several ways of putting fiberglass into a mold. The tried and true way is hand layup where you take fiberglass woven cloth, Omindirection mat, kevlar, carbon fiber etc etc etc, and lay it in the mold, wetting it with resin and using brushes and squeegies to uniformly saturate the fiberglass. Extra resin makes it heavy, not enough will make it weak. Vacuum bagging offers better quality control than hand layup, a plasic bag is placed over the mold and the vacuum pull is regulated to keep just the right amount of resin in the fiberglass for maximum strength/weight ratio. (My experience is kayak related, I don't know that many big boat builders use vacuum bagging, although I'm pretty sure that the Hinkley picnic boat is build that way) Problem with vacuum bagging is that it costs a lot to do. But hand layup requires experienced people to do right, and experienced people burn out fast in the industry... if they don't quit, the fumes toasts there faculties. Which brings me to chopper gun. With a chopper gun resin is fed through a hose along with chopped glass strands which then spray out on the mould in a random pattern (like mat). The resin to glass mix is adjusted as you spray out material. Its probably the fastest way to get fiberglass and resin in a mold. It requires less experience to use, although it takes more experience to do it well. Chopper guns generally produce heavier and thicker hulls than hand layup, but sometimes that does not matter. It all boils down to the skill of the operator for both hand layup and chopper gun. Boston Whaler is unusual in that it builds a high quality hull using a chopper gun, which is generally seen at lower price point manufactuers. I think they can do this because the strength of a whaler hull comes not just from the glass but from the foam filled construction with skins on either side. The glass skins on classic whalers are fairly thin compaired single hull boats. This helps to keep the weight down. I've also been told that with thin skins, the weave pattern from hand layup of fiberglass cloth will show, and that chopper gun (or mat) will produce a smoother hull. I'm not sure I believe that. Anyway, when I first heard whalers will built with a chopper gun it surprised me.
JaySul	posted 09-18-2002 02:27 PM ET (US) Taylor, thanks for the fiberglass lesson. I had read on some other threads about complaints with the use of chopper guns and the design of this particular hull and wanted to know just what the heck I was getting myself into. So far so good
jimh	posted 09-18-2002 08:59 PM ET (US) The Boston Whaler laminate schedule is rather thin compared to other boats, but as mentioned, the composite struture of the UNIBOND hull creates the strength, not the thickness of the laminate. I have also heard that it is possible to get higher consistency with a chopper-gun layup than with a hand layup with lower skill level operators. This may also be the key. If a plant only makes a boat or two per day, they can be hand-laid. The operators can take their time and they are probably quite skilled. If you want to mold ten boats a day, perhaps a chopper gun is faster. The hand-layup laminate must be carefully done so as not to get too much resin--that adds weight, cost, and no additional strength. I have heard stories that in some plants the layup crew is only allowed to use a certain amount of resin to lay up each boat. The QC people weigh out the resin and only so much is provided for each hull. In the chopper gun technique the resin/glass mixture is more controlled. Hey, however they're making them, the Whaler hull seems to last!
JaySul	posted 09-19-2002 01:47 PM ET (US) Amen! I have a 78 with few fiberglass problems...as far as I know.
Taylor	posted 09-19-2002 05:17 PM ET (US) Clearly weight is related to the amount of resin used; there is an optimum point where high strength is reached beyond which extra resin just makes it heavier. You can hit that with either a well adjusted gun, or a skilled layup guy, or a perfect pull on the vacuum bag. My guess is that chopper gun tends to err on the high side of resin use. I think the main difference between hand layup and chopper gun is how the fibers run in the fo the hull when you are done. In chopper gun, the fibers are short, perhaps 1 to 2" and in a random patterm, while with hand layup you can control exactly what kind of fibers, which way they run and how many there are. I checked, the Hinkley Picnic boat is built with Kevlar and E-Glass with and a propietary(?) system called 'SCRIMP' a 'resin infusion technique that reduces the resin weight by 50%". http://www.hinckleyyachts.com/yachts/picnic.html Way off topic, but very pretty.
pglein	posted 09-20-2002 07:46 PM ET (US) without the foam core, a chopper gun hull would be crap. but in the whaler, it is not of concern. Family owned a fiberglass company for 20 years. Chopper gun is the cheapest and crappiest way of building fiberglass. This is a process that should be reserved only for cheap imitation automotive body panels on ricer honda civics, not the hull of a boat on which your life depends. Again, however, due to the foam core, the whaler hull is mighty high quality. I am honestly surprised to learn that it uses chop-gun method.
jimithing	posted 09-22-2002 09:30 PM ET (US) isnt the real concern here that no matter what technique used if voids are created anywhere in the process that is where the weakness is? Voids create places for water to collect and creates a weak point in what would ordinarily should be a strong and sound hull. Question remains: Which of these methods for laying up fiberglass hulls has created fewer voids in hulls over the history of its use. For me that determines which is the better method.
PressureDrop	posted 09-24-2002 08:33 PM ET (US) i too, would be very concerend if a chopper gun was used for the hull, or any structural members for that matter. all of the strength in a GRP (Glass Reinforced Plastic) composite is in the lenght of the fibers, a boat hand laid with woven roven that runs the length of the hull will be rock solid, however a boat laid up with a chopper gun will not be cuase the fibers are only a few inchs long, providing no strenght, think about it... if you wouldnt want hull hand laid with mat, what good it one that was machine laid (with mat)??