On Tue, May 29, 2018 at 1:22 AM, StoneTool owly@ttc-cmc.net [harryproa] <harryproa@yahoogroups.com.au> wrote:
Rob:
The suggestion that a complex shape such as the two panels of the hull side, and the bottom on the KD 860 could be infused flat and folded at the seams is patently
absurd. The only time this can be done is when the finished seam angle will be a straight line. In this case, both of these seams is a compound curve, and therefore these structures can be built one of two ways. Either as 3 separate panels joined at the seams later, or in a mold that begins with the desired shape.
It is indeed absurd. But you are missing 2 points. 1) It is absurd to build a complicated shape when a simple one (see the video in my previous post) will suffice. 2) The shape is easy to get with a box mould, as in my last post.
Neither method is truly simple, but I personally would prefer to put the labor into the mold. Below is an image of a hull side from Pete Hill's Oryx, which is the shape I prefer due to the "wing" or knuckle, which adds interior volume, and a sense of more interior space, and the possibility of putting the ports high enough to provide useful side view from on the bridge deck. In this case they were obviously placed so the person in the galley could see out. It of course has the additional advantage of greater reserve buoyancy in a knockdown situation. This boat is 10M. Next to it is a rendering of the stock KD 860 hull. Quite obviously neither of these hull forms could simply be infused and folded as was suggested in a previous post. The compound curve of the seam is easily visible in the rendering. On the right is a Tiki 38 hull under construction.
The Oryx hull shape is unnecessarily complicated, but still possible in a box mould. The knuckle makes it difficult to build and to moor (the fenders get pushed out). The added buoyancy would make no difference in a knock down as the boat would already be heeled past zero rm. For what it is worth, Pete is selling Oryx so he can build a harryproa as it is more suitable for his requirements, which are similar to yours. "Simply infusing and folding complex hull shapes" was NOT suggested in a previous post.
I must admit that I'm completely unfamiliar with modern MDF. To me it is particle board, which is stiff and inflexible, and is often used as floor underlayment in cheap construction because of it's rigidity. I will have to make a trip to the lumber yard and have a looksee.
Similar stuff, either will do. Get it with melamine faces, which make the surface airtight. Otherwise, sealing it is a time and materials consuming job.
Obviously I'm going to have to do some small "intelligent infusion" projects in simple and complex molds............My canoe trimaran project is an ideal place to experiment, as I need to build amas for it.
Go for it. If you want advice, please ask.
I'm not sure if a catamaran is a symmetrical proa, or a proa is an assymetric catamaran ;-) My 30' criteria is pretty well locked in stone. It may not ride as nicely as a 40 footer, but will probably ride at least as well as a 40' double ender such as a proa. It's well established that the distribution of the displacement, combined with the optimal rocker, and a transom stern damp out most of the hobbyhorsing. Note in the rendering, that this hull is built specifically to these criteria. In comparison, the Wharram Tiki 38 hull is more or less symmetrical with a canoe bow and stern. I would suspect that the KD 860 would have a better motion than the larger Wharram, as well as having a shallower draft, and a generally better shape for living in. The Wharram has a LOT of bilge. area below the sole, the KD 860, almost none, and this is a bit of a liability, as the bilge is where heavy stuff should be stored, as you said.
Comparing a Wharram to a KD 860 and concluding a 30' cat will ride as well as a 40' proa is illogical. And wrong.
Hobby horsing is reduced by high prismatic coefficient hulls, and centralised weight. The longer the hull, the rarer the wave characteristics that will cause it to hobby horse. Wharram hulls have a lot of rocker and heavy ends/rigs, so pitch a lot.
It is not the symmetry of the hull that causes pitching. It is the speed at which the ends of the hull gain/loses buoyancy. A long hull with vertical ends and no rocker does this far quicker than a short, rockered hull with an angled bow.
The other unpleasant motion in a cat is upwind over waves, when the boat corkscrews. On a proa the hulls meet the waves at the same time, so the motion is more like a monohull, but without the heeling.
I'm not tall.... not much over 1.65M, and looking at this suggests raising the cabin sole to create useable bilge space, sacrificing some unneeded head space. I mentioned this previously.
Storing stuff in the bilges turns it into mouldy/rusty mush. And building the floors will take longer, and be less pleasant, than any other part of the build apart from hull fairing. Making the hulls 1.7m high instead of 2m not only reduces windage, but saves weight and cost.
You make a good and valid point(s) about beaching keels. My concern is concentrated point loads on the hull bottom, which on the flat bottom I'm talking about could be an issue........... Getting tires hauled under the hulls on a catamaran could be considerably more challenge than on a monohull.... The bridge deck kind of gets in the way ;-)
Precisely. But on a harryproa, it is simple. The loads on beaching keels are enormous. I doubt you could build them stong enough to withstand being blown sideways onto a beach with small waves. Big waves and they will either be broken off or tear a long hole in the bottom of the hull.
There are some simple sheet release systems that are extremely reliable. The simplest tension based release uses a cam cleat mounted so that it tilts under tension such that the sheet simply lifts out of the top of the cleat. There have been a number of commercially made angle based releases, at least one of which has a very good reputation, but availability is a problem. I'm interested in your version...... are there photos somewhere? As a single hander, I consider some sort of auto sheet release important. Being there to release the sheets in person is best, but.................... Let's be realistic ;-)
Releasing sheets at a preset tension is unreliable. Winches, people standing on sheets, waves, point of sail and flogging sails all add or subtract from the loads. The only reliable system is based on heeling and pitching angles. These can be electronic, expensive and unreliable, or cheap and idiot proof. No photos of the latest version (none built yet), there is an earlier version in the Files section.
While the aspect ratio will be lower, total sail area ideally will be greater. The net result being probably less overall speed in many situations, but the ability to ghost in extremely light wind due entirely to lots of footage, and the fact that a junk rig will not flog due to all the battens.
If "extremely light" winds are those below 6 knots a tall rig is far better as, due to friction/boundary layer, there is much more breeze up high. And as force is a square functionof wind speed, 3 times as much wind (ie 6 knots 10m up vs of 2 knots 2 metres up) will provide 9 times as much power. See Frank Bethwaite's High Performance Sailing for more information.
Re length:
I post about this for the same reasons I posted about foam vs ply. It is not to try to change your mind, it is to let other readers know the options.
You are planning on building a complicated (rocker, chine, knuckle, too wide to reach all of it without a raised platform) 30' mould, then using the frames to build another complicated 30' mould. This is 60' of moulds, which will take longer to build than the rest of the boat.. The harryproa requires a 40' simple mould for the lee hull, then cut the centre section out of it to make a 28' mould for the windward hull. Each of these will take less than a day.
Rocker:
When I look at the keel of a rockered hull, I see a wing section. Lengthwise flow over this acts to pull the hull down into the water. Not a huge deal with round hulls as the 3D wing is a poor shape. But with a flat bottom on the boat, it becomes a lot more wing like. Probably more so than the sides of an assymetric hull, which generates enough sideways lift to almost negate the need for daggerboards. This much force pulling the hulls down into the water does not seem efficient to me. This and the ease of building is why harry's have rockerless hulls.
Rick,
If you want to try Intelligent Infusion next time you are building a simple hull shape, let me know.
Björn
Yes, would be interesting to know how often it fails for experts like Rob, and also for amateurs.
I have had several failures due to pushing the limits and taking shortcuts to see what can be done. There are several ways to screw up infusion, but if you follow the instructions, it is almost impossible. The worst screw up would be to lose vacuum part way through, leaving half the job not wet out. If this is likely, buy a second cheap vac pump and/or a gen set.
The other possible fatal screw up is incorrectly measured resin. This is indeed catastrophic, but less of a worry than one or several of the many mixes required for hand laminating going wrong. With the infusion, you know you have a problem. With the hand lay up, you don't, or at least not until something fails while sailing.
Non fatal screw ups would be:
Dry areas due to resin flow being impeded, which won't happen if instructions are followed. On the bag side, these are easily fixed (see Intelligent Infusion manual). If on the mould side, they will require wetting out by hand (or infusion), vacuum bagging and some fairing, although less than that required if the whole job was hand laid.
Intelligent Infusers are encouraged to do tests and make screw ups so they know what to look for.
Extra resin in corners etc where the bag is bridging a corner or edge. These are obvious during the set up and must be fixed. They are not catastrophic, but the excess resin should be ground off, if for no other reason than it will make you more careful next time. ;-)
My guess is that the risk increases with the size of the infusion since it takes more time, and there might be many hoses, clamps, buckets, etc, involved in a big infusion. And you have manually time these clamps/buckets and make sure the inlets doesn't breath air, I can imagine. So if you forget one thing...
True, but it is still all in the set up. Get that right and even the biggest job will go seamlessly
. Steinar used one hose and two buckets for his 70' lee hull half. Inlets breathing air is not that big a deal. As soon as it is clamped off or inserted in the resin bucket, any air that got in is removed.
Rob, regarding buying Finnfoam, I received one reply when asking if they can supply it. They said straight away that they could sell a custom a pallet of 10mm FF700, or any desired thickness. But after I told him I'm in Sweden, he hasn't replied for a few days. I will try to call him and see.
But I believe it is like eruttan said, that the brand of he XPS isn't important. It's only important to get the high strength/density foam. When the foam is produced, there are probably just have some knobs to turn to increase the density of that batch. So any XPS factory should be able to make it. You could maybe even ask for higher density than their highest grade, if they are making a custom batches. I have not had a reply, would like half a sq m to experiment on. My understanding is there are 2 types.
EPS is produced from solid beads of polystyrene. Expansion is achieved by virtue of small amounts of gas contained within the polystyrene bead. The gas expands when heat in the form of steam is applied, thus forming closed cells of EPS. These cells occupy approximately 40 times the volume of the original polystyrene bead. The large EPS blocks beads can be fabricated per specification to form customised shapes.XPS foam begins with solid polystyrene crystals. The crystals, along with special additives and a blowing agent, are fed into an extruder. Within the extruder the mixture is combined and melted under controlled conditions of high temperature and pressure into a viscous plastic fluid. The hot, thick liquid is then forced in a continuous process through a die. As it emerges from the die it expands to a foam, is shaped, cooled, and trimmed to dimension.
XPS is formed in large blocks when stryene monomer, steam and foaming agent are mixed.
EPS does not result in densities high enough to resist vacuum. XPS is vacuum resistant, produced in set thicknesses with smooth faces. I have emailed a couple of Aus suppliers, will let yu know if anyone has anything with FinnFoam typre properties.
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Posted by: Rob Denney <harryproa@gmail.com>
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