chopper gun vs. hand laid

I have seen a lot of argument over the strength differences between a hand laid boat and a boat that is sprayed with a chopper gun. Have there been any studies that show the differences in strength between the two methods? Any direction to this information would be greatly appreciated. Thanks!

 

The main diff. is the people doing the work and as long as the boat is not all chop. If done correctly It could be close but the hand laid boats for me are always lighter and stronger.

 

The main factor affecting the strength of a layup is the glass to resin ratio. The higher, the better. If the skin is vacuum bagged, the chopper gun can get pretty good but otherwise it has a high amount of resin which makes it weaker. Non woven, unidirectional or knitted fabrics can make a stronger layup than woven glass material.

 

Thanks for the replies, do you know if there are any tests that have been done with regard to this question?

 

No, sorry! Some good points Tom.

 

Stumped again guyz!!!

 

Maybe it's hard to find test data because it's like comparing apples to oranges ... like tests between a Porsche and a Chevy

Would the test show strength per weight, or weight per boat, or blister problems or ...

There must be some data available (maybe in an archive at Bayliner ), but I must confess I never considered using a chopper gun so I don't know where you would find test data.

 

lol

 

laminates

To start I would say that the size of this project would dictate the laminate schedule. If this were a 10' dory/dinghy or a shower stall you could probably go ahead and chop it out, keeping in mind that chopped strand or 1.5 oz mat on a roll offer minimal puncture resistance. Lets say this was a 22' project. After applying the skin out in either chopped strand or rolled mat you have to have structure. It matters not, cored or solid glass construction. When comparing "hand laid" glass to something,It usually is against prepreg, scrimp,or custom vacuum assist infusion processes. These processes insure a strong glass to resin ratio. A skilled laminator can deliver a strong hull but it won't compare to a scrimped cored hull. The latter will be stronger,lighter and more uniform than a hand laid cored hull.
Happy boating Phil

 

Years ago while working for Caver Yachts (mid 80's) we did run some tests, and surprise the chopper won, but, and this is a big one it depended soley on the operator. You could almost tell who made the lay up by the test results. This is all well and good but you can't chop a full lay up. It saved time and labor for small parts and doing intricate things but in the end you need the directional strength the weaves give you. Thinking about it it seems I might have read about some other tests done in Professional boat builder not sure though. And unfotunatly i no long have access to the Carver data.

 

I am curious as to what types of tests were done what were they simulating?

 

In my personel experience as a laminator i would never have a boat made with a chopper gun having worked once where it was tried,we soon went back to hand lay up, and i would never do it again and this is also the general opinion of any decent laminator i have worked with over the years.Sure it may be quick , on a flat surface but try spraying somewhere more tricky and getting the correct thickness of glass down, no one can spray as accurate in weight as to when it comes of a roll ie,one part of a square meter might vary considerably to another and any parts you cant get the gun to spray you have to hand lay anyway.Also as someone has said you can't spray a cloth or woven roving etc.The resin ratio can be set but the operator can spray more resin alone if required{all glass needs a certain amount of resin otherwise it is starved and is then weak}.what about the matter of health and safety?I could go on.The only good thing is the percentage of waste goes down.
ps. Someone once told me you can't get a lloyds moulding certificate using this method don't no if this is true however,so perhaps someone could clarify?

 

the main problem with the gun is getting the thickness uniform,throughout the hull. However assuming that the thickness is uniform, and so the fibre content can be considered to be the same as if it were laid up in chopped mat then you would say that the gun would be more resin rich and therefor heavier for the same strength. really the best and lightest option is to lay up woven rovings over pvc (or any other foam) cores simply for the impact resistance the roving give the skins.

of course like most of the boating industry i have nothing but a little experience to make these conclusions. maybee someone has some homework to do with testing some pannels. id go a 3 point bend(stiffness), repeditive cycle fatigue (not sure how id test that though) and toughness (impact resistence equals ability to absorb kinetic energy). you may want to cut up some chopper gun pannels and see how the thickness varies?

 

your choice

Hand laid glass or mat is much stronger if it is applied properly. The essential part of hand laid is to get all air out of the resin and mat. A very good comparison of the two processes is particle board vs solid oak. The less pourous the material the stronger.