Best hull manufacturing method

[seamonkey]

[quote=cristofa]

and "It seemed from the description that a pressure bag is INFLATED to hold cloth in place,,then a vaccuum is used to pull the resin through ---is this the case?
If this is the technique then the balance of pressures would seem to be quite critical in establishing optimal resin weight %'s....but maybe I got the wrong impression altogether!!"

You are right to see an issue here. We have actually found that there is an advantage in divorcing the consolidation of the laminate from the resin infusion, and we are still working on the optimum balance. But, as soon as I can afford it, I will get a resin mixing/injection machine (such as the Plastech Megaject V, www.plastech.co.uk) to inject the resin under pressure, counteracting this with pressure in the bag.


Christoffa....yes ,it would seem that this 'one peice product' system would only be appropriate for smaller,straight closed shapes such as kayaks,,,rowing shells,,small catamaran hulls,,and pontoons like yours,,,when there is a high priority for OPTIMAL weight to strength ratios,,and no seams to speak of.---As soon as the shape gets larger to the extent of a small sailing dinghy(laser size) or bigger,,the added weight of seam bonding becomes a smaller % of total weight,and is also usually offset by the acceptance that the seam 'lip' is also useful for structure,and hull protection.
When considering a high performance rowing shell,or kayak where the total weight can be as little as ~22lbs,,with some 48' of edge seam,,,I'd consider your method as worth looking into!
I imagine that the balance between the bladder pressure,and vacuum for infusion would be quite critical for this system to be effective--I wish I lived a bit closer to Cornwall to take a look at your operation!

[Herman]

About the general production method, please do remember that many companies are looking for solutions, and many have (independently from each other) developed a technique, similar to Christophers technique. (which works wonders).

Here in Holland we have some companies that utilise globally the same technique, among other things for lamp posts (longest is 22 meters...)

To Christopher: If you consider a Plastech machine, please remind alan Harper about the lamp posts. His experience there can help you as well. The Plastech machines, especially with the new mold pressure sensors which control the machine, is very suitable and safe for your products.

To Seamonkey: The choice for your construction method is not only dependent on producability, but also strength demands, material cost, mold cost, and no of products to be built.

If a larger number of products need to be built, rotomoulding could be an option. advantage is the relative strength, but weight could be an issue. Topper Intl uses this system for the Topaz, and use a sort of PE foam core in the middle, to reduce weight.

Another possibility is to produce the hull and deck seperately and glue them together in some sort of system. Plexus Methacrylate glue can be a good option: www.itwplexus.co.uk. For example use a H-shaped PVC profile, and glue the butted shells in the profile, or make some sort of flange.

About making the hull and deck: Many options are available, from hand laminating to "wet bagging" (vacuum bag after laminating), to resin infusion under film, to VARTM (Plastech system). For a decent number of units made, I would opt for the latter.

To create 1 piece hull-deck units with the technique Christopher uses, in more complex shapes, is a lot of work with a lot of trial and error. For simple parts it is OK, but for complex parts, a lot is still to be learnt.

However, it is nice to see people develop new products, and new production systems. I hope yours will be a success.

[DuncanB]

Hi from Rojac

We came across this discussion thread and noticed quite a large amount of discussion regarding the Rojac/Rocat Moulds.

I was a little concerned to read that "Seamonkey" sent us an enquiry and we didn’t respond!!? Please could you let me know if you did actually receive a reply??

I just thought we would join in this discussion (obviously we are keen to promote our mould toolmaking skills ) but also if anyone has any questions, we are would be glad to help.

Regards

Duncan
Rojac Tooling Technologies, UK

[DuncanB]

Please check out our websites;

www.rojac.com
www.rojac-urethane.com

[B. Hamm]

Personally I think you're over engineering a rather simple boat. For large scale production rotomolded polyethelene would be ideal, though the tooling costs are high. For smaller scale production with less expensive tooling might look into vacuum forming from sheet plastics. There have been considerable advances in the materials for this in the past few years. Both of these processes would mean you'd likely be contracting the molding, since the molding machines are quite expensive, but the labor cost is then dropped to the very minimum which you need to get the costs where you'll need them to be.

Bill H.