ROCAT closed mould one-piece hulls

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

 

Chris,

How long did it take you to design and build the hulls plu/moulds?

Did you make any prototypes before your production mould?

How did you first get into RI? What were your major problems developing the process?

Did you have any help? or did you do it off your own back.

Buckle

 

Buckle

The first ROCAT prototype was designed and produced in about 6 months. I made most of the parts, but farmed out the hulls to save time. They were designed using Vacanti's excellent Proline CAD and beautifully hand shaped by ACMC from the resultant lines. They then made a couple of moulds from that plug. At that stage I was still thinking of moulding the two halves and sticking them together, in the conventional way. Two prototype hulls were made thus, and these were used extensively in sea trials.

Having decided to put the ROCAT into production, I looked into all the possible ways it could be made ... RI consistently came out top. Then, making the hulls in one piece inside a closed mould seemed the obvious way to exploit this technology.

The biggest problems that I have had developing the product have not been resin infusion related, but with the internal bag in the complex crossbeams mould. I had never used RI before, but have found it to be a simple, straightforward process which produces excellent, remarkably consistent parts.

I am an industrial designer with no particular boat, or composites background ... yes, I sought all the help I could get, and had to learn fast along the way. Not all the advice I received was sound, but I reckon we are on the right road now.

Christopher

 

cristofa, I built a scale model of a catamaran I plan to build, it didnt have enough bouyancy to use as a small sailing cat so I set it up to row. It looks identical to "rocat". My full size cat at it's fattest b/head is ellipse shaped 900ml x 600 ml and 12 mtr's long will your "Vacuum resin infusion" work on this scale .I havnt worried about the high resin ratio because I thought I needed bulk in the single skin to give it strength.Did you stumble upon "rocat" the same way I stumbled on "roocat" ???

 

When laying your pre-cut fabric into the mold, how do you keep it in place on the top part of the mold?

 

newo eloc

'Vacuum resin infusion' is being used widely, and successfully, for boats very much larger than 12m long. It sounds like this is a one-off project, so having moulds made from CNC machined plugs is unlikely to be a cost-effective solution.

"Did you stumble upon "rocat" the same way I stumbled on "roocat" ???"

Doesn't sound like it ... check out http://www.rocat.co.uk/about/origins.htm to see how the ROCAT originated.

 

JEM

"how do you keep it in place on the top part of the mold?"

... lightly tacked in place with spray glue.

 

Cristopher,

What kind of "gelcoat" or in-mold "paint" do you use with the epoxy? The only reliable method I've found so far is to "gel" with epoxy primer in the mold, and then sand and paint afterwards, but it's a bit more work than I would prefer.

Yoke.

 

yokebutt

I'm interested to hear that you are also using epoxy primer in the mould ... I have found this works really well and is much easier to fix any flaws in the part when it comes out of the mould. From my point of view it has two further substantial advantages:

1) the ROCAT will be 'made to order' and the customer will get to choose the colours ... as soon as the colouring and manufacturing processes are decoupled, the orders no longer dictate the manufacturing cycle.

2) as soon as you go the paint route you can choose from an enormous range of colours and spectacular custom effects ... the range of gelcoat colours is dismal, to say the least.

The downside for me, though, is that I am having to spray in the composites shop, with all the extraction ramifications. The real beauty of resin infusion is that it is free of mess and emissions. I would really like to put all the spraying into one dedicated space which would mean infusing without any in-mould finish. I will be testing the idea with various weights and compositions of surface veil soon, but would love to hear from anybody who is already infusing into naked moulds.

atb ... Christopher

 

Cristopher,

If you do come upon a method of laminating straight onto the mold-surface without getting thousands of those little frigging pinholes, do let me know. I've even toyed with the idea of putting a little bit of detergent in the resin to lower the surface-tension, but then, what if it ruins the resin?

Yoke.

 

Yoke

OK ... I expect the solution is just around the corner! Composites have come such a long way in the last few years, I can't believe this is insoluable.

atb ... Chrsitopher