building a sailboat using surfboard technic?

Hi,

I am thinking about building a 4.5m proa (like this:
http://homepages.paradise.net.nz/garyd/t2.html).
I know of the 2 main building technics: strip plank, and stitch&glue.
But I was thinking about using surfboard technic: foam core with wood backbone and fiberglass coating.
It looks like a quite nice way to do the job: I would have the strip planked rounded hull, and it would be easier to work out.
But as I have no experience and I haven't found anything like that on the web, I may be missing some important issues.
Anybody has ever heard of anything like this?
I know that polystirene foam is not recommanded for sandwich construction, would it be good enough here?

regards,

Pierre

ps: excuse my bad english, I french and not used to boatbuilding vocabulary..

 

Lots of issues. Polystyrene foam and polyester resin are not compatible.

I have done the glassing over foam for a long slender hull and it is not good. I could go into the issues at length but it is far from ideal. If you must go this way the best idea is to use the foam as a plug and form the lower part of the hull over the male plug. This needs vacuum bagging to do a fair job. The plug is taped over so it can be pulled out.

You will find a hard chine version of the boat will perform just as well and this form lends itself to stitch and glue with composite panels. You will find you get a a superbly light and strong hull using these panels with S&G.

You could practise the technique on the smaller hull to perfect it. About the only requirement is a large flat surface to lay up the long panels. I use veneered chipboard, covered with very smooth plastic sheet, with the boards joined and levelled on a nice solid floor. Mixing the epoxy (or resin) is the longest time involved in making a panel.

You need a good closed cell structural foam like Klegecell or Corecell.

In a large hull the weight of the polystyrene foam is significant. It is around 25 times heavier than air. So why not just use air.

Rick W

 

Really, strip-planking is ideal for the proa. It's light and stiff, and it lends itself to compound curvatures.
At your level of experience, the commoner methods are best. While some have built using the method you described, you would find that the reason they did so had more to do with the kind of complexity that would be extremely tedious and time-consuming to frame up in a one-off situation. Usually this would involve parts and pieces rather than a whole hull.
An example might be a hi-tech rudder or a carbon sprit.
Using the wood strip-over-station-frames method, once your frame is set up, there's no dragging patterns around. The work progresses more quickly. With a foam core, it's a back and forth operation.
As the foam core method is, in the end, a fiberglass boat, you're not done when the skin is finished---- glass alone isn't near as stiff as strip. Much reinforcement has to be added, and hence more engineering as well, since it has to be decided where exactly the stiffening is needed.
Add to this the aforementioned problem of incompatability between polyester (inexpensive) resin and styrene foam, and you can see why few boats are built this way.
Finally, price some foam and see if it makes sense to use up that much expensive material to build one hull.

Alan

 

Alan
I agree with what you say about strip planking. However I do not agree with the statement above on foam core. You can make a foam core boat with fewer bulkheads or frames than any timbered hull. A good structural closed cell foam with glass or other high strength skin on both sides is immensely stiff for its weight.

I have only done a bit of flat pack composite stuff but I am impressed even with what I can do with it and the ease of laying it up in the flat panels. I expect factory produced panels would be impressive.

Rick W

 

Sorry Rick,

I shouldn't have used the words, "foam core". I should have said "surfboard method". You are correct if we're talking about normal foam core, but surfboards are (I think) made by sculpting a styrene foam blank which allows building a one-off without any mold (hence my mentioning going back and forth between patterns and rasp, for example).
Using large foam blocks (which was my understanding of Pierre's comment) to sculpt a shape would, I assume, be followed by removal of that same (he mentions styrene) foam. Hence a straightforward glass-only hull now requiring framing and stringers, etc., to support it.
The other thread where I wrote yesterday had to do with a gentleman building his first (24 ft) boat ultra-light using foam core. I suggested strip-planking (glassed inside and out) as a better first build method owing to the fact that strip method was easier to do if one hadn't built a boat before. I could have been wrong too, but was imagining the relative difficulty of building the mold, vaccuum-bagging, and fairing.

Alan

 

alan and rick, you both seem to know a lot abt this why didnt you answer my thread on grp, /foam/ grp ? i needed help there?

 

Stu
I am a new player to flat pack. There was a very good thread started here on a fellow from NQ building a cat using flat pack. I have seen samples of factory made thick panels and I have done some thin layups.

I have been watching the thread you started. The panels look good. Before I used them on a boat I would want to know more about the foam core. For example is it closed cell.

Apart from the watertightness, if you are using for cabins and the like above the waterline then you would use developable shapes. Probably need to be very little curvature unless you get thinner layups than you displayed. From then on it is stitch and glue I suspect if you want a nice tight structure. You may also be able to get aluminium mouldings that you epoxy panels into but, although quick and simple, I doubt they would have the strength of S&G with nicely laid double sided joints.

I am interested in the answers you get on you thread.

Rick W

 

I think Rick knows far more than me about foam core. I'm more of a solid wood and plywood guy. This thread started with a question about sculpting a foam block to create a glassed-over hull as far as I understand it.
I think the idea of stiff foam core panels is fascinating, something to stitch and glue like plywood but far lighter.
My reservations have always been in the area of puncture resistance and safety. Great high performance materials, however.
I'll check out your comment in grp/foam/grp, but I'm no expert.

Alan

 

I've buried a lot of good urethane foam inside fiberglass. One of the drawbacks is that a strong impact can separate the 'glass from the foam, weakening the part.

 

Alan
If I know more than you about cores then should stick with wood for sure. What I know could be published on a postage stamp in large text.

However I am learning about it and I have impressed myself with the results I can get. I am getting close to making my next hull using home made flat panel with stitch and glue. My current project has flat panel deck and I have learnt a bit from that.

Rick W

 

How much bend after skinning--- must be real limited and so you must leave one side unglassed til after hanging the panel?

 

Alan
It depends on the thickness of the core and the weight of cloth. If it is only 3mm thick core with 320gsm cloth it can easily form my long slender hulls.

I am considering a design using the technique that would be made from two sheets of foam. So do one layup, cut the pieces and stitch up. It gets into efficiency similar to what I can do with aluminium but will be more robust. It surprises me how well it bounces.

If you have not tried it out then I suggest you have a go. You could make planking with it for a more rounded strip plank design. Do light skin initially then a final cover.

Rick

 

I'm thinking of constant camber. Well suited to kayaks and any small boat. what is your favorite foam core, Rick?

 

I have only used two structural foam types Klegecell and Corecell. I believe Corecell has superior properties. I think prices are similar.

I have tried Nomex but I did not lay it up in a flat panel to start with. Nomex would be good over a plug as it is more flexible but you can only glass one side at a time from what I can see. No doubt there are better techniques than I have used.

Have also done hulls with polystyrene plug and polyurethane sheet so I have had a go at most techniques.

I have noticed that there are places in North America that have specials on Corecell. It is much cheaper than we buy here.

For my lightweight stuff I feel 1/4" Corecell with a layer of 320gsm on either side offers adequate strength and rigidity bulkheads in areas of point loading. If you want to make it more damage resistance skin then go for two layers on the outside. I have not seen it but I am told it can be peeled so there is a preference to make the end sections of the boat a bit thicker skinned.

Rick W

 

That's 10 oz according to my calculator, I think.
Thanks. I'll see what it costs---- I may try it out one day soon. At this point, I'm restoring and not building, but I've got this ultra-light car I'm building on the side...