Great News from the North: 14 metres x 2.4 metres in one piece!
Bruce Hodgens 11th March 2007.
Hi Maggie & Bob
Just thought I would let you know how I was getting on with the Polycore panels you supplied for my 14 metre powercat.
I received 130 sheets (in 19, 25 & 30 mms) a few months ago and I have started making all the components such as bulkheads, bridgedeck floor, roof , furniture, decks, floors and all the upper hull skins.
Basically other than the hulls below the waterline all the boat will be made from Polycore flat panels, some of which will be bent to 2D curves.
As you are well aware I spent considerable time researching different materials for the boat and now that I have started working with Polycore I am convinced that I chose the best product.
I will save nearly $34,000 using Polycore versus foam or balsa pre-made panels. As a back of envelope calculation a 19 mm panel of Polycore costs $100, and then with one layer of 600 grams/metre2 knitted glass on each side with vinylester resin costs about another $40. Pre –made balsa or foam panels cost >$400.
I know this doesn’t take into account the labour to make the panels, but you can sure get a lot of panels made for $34,000 worth of labour.
There are plenty of advantages to making your own panels other than cost savings.
Originally I was going to use balsa panels but when I experimented with this there were all sorts of problems. For example the balsa soaked up a lot of resin into the end grain so I found I had to apply a thick coat of fast curing resin and then when that had gone off I could then glass over.
The next problem was that large sheets were impossible to turn over because the balsa had no inherent strength, so then I had to look at making a flat table and glassing one skin then vacuum bagging the core on, then glassing the other side. What a drama, and also a huge expense for the vacuum bagging gear, moulding table and consumables.
With the Polycore I just glass one side in the morning and turn it over and glass the other side in the afternoon. I found we could use AutoCAD to nest all the components and then join multiple sheets together reducing the wastage. I then glass them and turn them over, none of which I could do with balsa. This is working so well I built the bridgedeck floor in one piece – that was 8.4 metres x 2.4 metres (i.e. 7 sheets joined together) and I have just finished the first of the topsides for the full length of the boat which will be 15.6 metres x 2.4 metres in one piece (13 sheets). It takes 6 or 7 people to turn these over to glass the other side, but it is no drama.
I will have the complete side of the boat in one panel with no joins and it can be faired and undercoated ready to stick on. What a joy to have all the fairing and undercoating with gravity to help you instead of doing all this on the boat. Making these large panels has reduced the time spent joining multiple panels with fibreglass tapes, creates less work for fairing because the joins always make more work, and we have a lot less waste.
Of course there are other benefits for Polycore panels.
I was concerned about balsa panels because we have had a few problems with boats here in Townsville getting water in the balsa core, leading to rot. All the claims that the water will only go to the next glue line in the balsa i.e. at the most 100 mms aren’t quite what happens in all cases. If water gets into panels it can also move along under the glass delaminating it from the core and spreading the rot to a much larger area. Polycore is polypropylene plastic and so rot isn’t a problem.
One of the tests I have done with sample panels is to beat the living daylights out of them with a hammer. This is my crude impact-testing regime. The first time I did this was when a couple of local boat builders dropped in and were asking about Polycore’s strength.
We grabbed a 25 mm scrap that had been glassed with 2 layers of 600 gram fabric on both sides – it was part of a main bulkhead lay-up. We placed it on the concrete and then swung the hammer hard onto it. Not a scrap of damage. In fact the hammer just sprang back off the panel. After about 5 or 6 hits on the same spot the glass started to get damaged but certainly not as much as any of us expected.
This led to all sorts of further “highly scientific” testing such as driving the car over it repeatedly, putting it between blocks of wood and jumping on it, and suspending it between stools and dropping heavy steel pipes end on from the roof of the shed.
I am impressed with the results. Particularly interesting was the steel pipe dropped onto the suspended panel. The glass in the impact side eventually got damaged but the lower surface glass remained intact until eventually we managed to butcher that as well. At all times we were very impressed with the core strength. It seems to absorb a lot of impact rather than just transferring it to the inner skin and damaging that. Delamination of the tissue or the core wasn’t a problem either.
I would be very interested to see some test results that compared Polycore to other types of cores such as balsa and foam. However for the use I have for the panels I am more than happy with our results. I will certainly be recommending Polycore panels to all my friends who are building or planning on building boats.