cristofa
10-10-2004, 06:02 PM
The closed mould one-piece hull technology, that we are using to make the ROCAT rowing catamaran hulls, seems to be generating some interest. I therefore thought I might as well start a new thread, continuing on from the posts already in 'best hull manufacturing method'.
The ROCAT website www.rocat.co.uk has a fairly detailed description of the process (on 'the boat – technology' page), and I will be adding to it over time.
Briefly, we are making 5 metre rowing catamaran hulls in one piece, inside a closed mould, using vacuum resin infusion.
I have chosen to share my knowledge of this novel process, so am content to answer as many questions as time allows.
Tom McGuinness sent some to kick off:
Q1 Are you using one of those CNC cutting machines (eg. Eastman) to cut your fabric before laying it up?
A There is someone over here (surely in the US too) who will make up one's reinforcement program and provide cut kits very cost-effectively ... I've always reckoned that this is the way to go.
Q2 Do you do multiple sandwich-type layups...say, with a nomex honeycomb inner ply....or just a single cloth/mat layup? Do you use a special permeable layer to assist resin distribution?
A OK, that's covered in my previous post in your thread ... the layup is 190gsm stitched biaxial (very nice supple cloth) either side of 2mm Lantor Soric resin infusion medium/core material. Once I have removed the bag, the 5m hulls weigh 8.1kg!
Q3 Have you tried using aramid or carbon fiber and/or epoxy resins with your set-up?
A The reinforcement material would have no bearing on the success of the system, and I use both glass and carbon fibre as and where appropriate. And, as strength to weight ratio is very important, I only use epoxy resin.
Q4 How many resin feed lines do you need for a long hull like yours? Are there any viscosity limitations?
A One central resin feed on the keel, with a resin gallery running 2/3rds the length of the hull. The vacuum is pulled from the extreme ends. We use Sicomin 8100 resin, and have no flow problems at all ... infusion time is about 20 minutes.
Q5 Do you use a specially constructed inner bag? How do you remove the bag after molding, or do you just leave it in there?
A We use regular tubular bagging material, heat-sealed at the ends. Before we seal the bag, we pass a cord down the inside and attach it to each end. When we cut the slots to mount the crossbeam sockets, we simply grab the cord and peel the bag out. We could leave it in, but it weighs 436 grams and we are very weight conscious.
Q6 Approximately how much did the mold and plug cost?
A about £15.5K
Q7 What kind of savings vs wet lay-up can you achieve....in percentage terms?
A Sorry, can't answer this one as, a) I can't see how you could achieve it using wet layup, and b) why on earth would you want to?! I suspect that, as more people become aware of the advantages of vacuum resin infusion, and styrene emissions regulations become increasingly strict, wet layup will disappear as a method of manufacturing composite boats quite soon.
I do accept that not everybody in the boat-building industry would agree with this viewpoint – yet!
atb ... Christopher
The ROCAT website www.rocat.co.uk has a fairly detailed description of the process (on 'the boat – technology' page), and I will be adding to it over time.
Briefly, we are making 5 metre rowing catamaran hulls in one piece, inside a closed mould, using vacuum resin infusion.
I have chosen to share my knowledge of this novel process, so am content to answer as many questions as time allows.
Tom McGuinness sent some to kick off:
Q1 Are you using one of those CNC cutting machines (eg. Eastman) to cut your fabric before laying it up?
A There is someone over here (surely in the US too) who will make up one's reinforcement program and provide cut kits very cost-effectively ... I've always reckoned that this is the way to go.
Q2 Do you do multiple sandwich-type layups...say, with a nomex honeycomb inner ply....or just a single cloth/mat layup? Do you use a special permeable layer to assist resin distribution?
A OK, that's covered in my previous post in your thread ... the layup is 190gsm stitched biaxial (very nice supple cloth) either side of 2mm Lantor Soric resin infusion medium/core material. Once I have removed the bag, the 5m hulls weigh 8.1kg!
Q3 Have you tried using aramid or carbon fiber and/or epoxy resins with your set-up?
A The reinforcement material would have no bearing on the success of the system, and I use both glass and carbon fibre as and where appropriate. And, as strength to weight ratio is very important, I only use epoxy resin.
Q4 How many resin feed lines do you need for a long hull like yours? Are there any viscosity limitations?
A One central resin feed on the keel, with a resin gallery running 2/3rds the length of the hull. The vacuum is pulled from the extreme ends. We use Sicomin 8100 resin, and have no flow problems at all ... infusion time is about 20 minutes.
Q5 Do you use a specially constructed inner bag? How do you remove the bag after molding, or do you just leave it in there?
A We use regular tubular bagging material, heat-sealed at the ends. Before we seal the bag, we pass a cord down the inside and attach it to each end. When we cut the slots to mount the crossbeam sockets, we simply grab the cord and peel the bag out. We could leave it in, but it weighs 436 grams and we are very weight conscious.
Q6 Approximately how much did the mold and plug cost?
A about £15.5K
Q7 What kind of savings vs wet lay-up can you achieve....in percentage terms?
A Sorry, can't answer this one as, a) I can't see how you could achieve it using wet layup, and b) why on earth would you want to?! I suspect that, as more people become aware of the advantages of vacuum resin infusion, and styrene emissions regulations become increasingly strict, wet layup will disappear as a method of manufacturing composite boats quite soon.
I do accept that not everybody in the boat-building industry would agree with this viewpoint – yet!
atb ... Christopher