oceansky

In Tassie, we have our fair share of cool weather. Whilst this can be pleasant to work in, it can make wetting out glass with epoxy difficult. The cooler the epoxy the thicker it gets and the harder it is to wet out cloth. To make things easier, use either a variable temp heat gun set on low, or borrow your wife's hairdryer and gently warm the resin after it is applied to a section of the glass tape. Warming the resin lowers the viscosity and it wets out the cloth beautifully. The same method is used when wetting out cloth on the hull. Try it and you'll be pleasantly surprised. It also helps to make a "hot box" in which to store your resin. Mine can hold a couple of 20 litre drums of resin and hardener and a 75 watt light bulb inside provides enough heat to keep the internal box temperature between 18 and 30 degrees during the cooler months. regards, Andrew Denman DENMAN MARINE

The first job of transferring the full size patterns to the MDF is quite a job on its own, Here's a method of making the job so easy. First get yourself a dressmakers tool and a large sheet of carbon paper. ( I got mine from Spotlight store ) 1/ Lay your sheet of plywood on a bench or floor then place the full size patterns on top of plywood. 2/ Line up the patterns on the plywood accuratley. 3/ Slip a sheet of carbon paper between the plywood and the patterns. 4/ Then scroll the dressmakers tool over the top of the pattern line. 5/ Remove the full size patterns and simply cut the bulkhead/Frame pattern out by cutting along the "dotted" line

Why is it when we're building boats, the final weight of the boat is always more than it should be? One of the main causes of increasing weight is the material we're building from. Typically, you get a set of plans and it says in the Bill of Materials to use Marine Ply. There are so many variations and plywood species, that here alone the weight can vary drastically. Even if the plans specifies a specific plywood species, the weight here can also jump even within the pack. What I'd like to do here is, show you how to work out the real weight of the ply your using ( not the manufactures figures) and then go through a simple boat example that I'm hoping, everyone will participate in. PART 1 First we need to determine the Specific Gravity of the material. (Specific Gravity is the difference between the weight of an object and the weight of freshwater that occupies an equal volume) Step 1/ Cut a length or strip of plywood ( doesn't need to be too long) In this example I've cut a length of 6mm ( 1/4") Okoume (gaboon ) plywood measuring 300mm long by 39mm wide ( 11" 13/16" by 1" 9/16" or 11.812" by 1.56") Step 2/ Sand the edges lightly to remove roughness or saw-cut strands that can hold air bubbles, wipe clean. Step 3/ Float the sample vertically in the container Step 4/ Mark the waterline Step 5/Measure the distance from the bottom of the plywood strip to the water tick mark Here my water mark measurement from the bottom of the plywood strip is 174mm ( 6 - 13/16" or 6.812 decimal inches) PART 2 Specific Gravity (SG) Calculation. Formula: Watermark distance from bottom of plywood strip/ LOA of plywood strip = SG Using our plywood strip: Metric users: 174mm water mark / 300mm length of plywood strip = .58 Imperial Users: 6.812in / 11.812 = .58 The Density of the sample can now be calculated: Metric Users: .58 SG x 1000 kg/m^3 freshwater = 580 kg/ per cubic metre Imperial users: .58 SG x 62.4 lbs/ft^3 fresh water = 36.2 lbs per cubic ft. Now what's interesting here is, Okoume (gaboon ) plywood is advertised as being 25 - 28 lbs ft^3 ( 400 - 450 kg m^3) Obviously it's not! Overall, that's a massive increase of 9.7 lbs/ft^3 approx or 155 kg / m^3 !!! So the question is - what of other plywoods out there? Are you really getting the weight your looking for? So how does all this apply to a boat your building? Boat Example: Well, let's try an example to see what happens. Here we've got "Robs Rocket ". It's got a fast name, so it must be fast ha ha We'll assume this boat is built entirely from 6mm or 1/4 plywood and it's all stitched together ready to be glassed. In other words, it's only just plywood here, nothing else. The total surface area of the boat hull only is 7.935 m^2 (85.42 ft^2) To calculate the weight of an object, the formula is: Metric Users: Thickness in metres x Total surface area in m^2 x Density in kg/m^3 = weight in Kg Imperial Users: (Thickness in decimal inches / 12) x total surface area in ft^2 x Density in lbs/ft^3 = weight in lbs Using the advertised weight (FROM THE MANUFACTURERS), the boats (supposed )weight should be: Metric Users: (6mm / 1000) =.006m ply thickness x 7.935m^2 surface area x 425kg/m^3 = 20.23 kg Imperial Users: (.236" / 12) x 85.42 ft^2 x 26.5 lbs/ft^3 = 44.51 lbs Now lets use the real and actual density we calculated from the plywood strip: Metric Users: (6mm / 1000) =.006m ply thickness x 7.935m^2 surface area x 580kg/m^3 = 27.61 kg Imperial Users: (.236" / 12) x 85.42 ft^2 x 36.2 lbs/ft^3 = 60.8 lbs That's a difference already of 7.38kg or 16.29 lbs. AND THIS IS JUST FOR THE HULL ALONE. What of frames, bulkhead, seats, false floors or soles, decking… ? The list goes on and all these weights really add up !!!. So, before you know it, the boat is 20 to 30 kg ( 44lb to 67 lb) if not more, overweight !! And this is just for this little 14 footer ! ------------------------------------- Makes you think, doesn't it What would make an interesting exercise is , if everyone who's presently building a boat, or has spare scrap plywood lying around from a previous build, is to apply the above formula's to determine the "real " Density of their plywood and then apply it to "Robs Rocket", so we can all see how "Robs Rocket" weight moves around. It doesn't take that all that long. For everyone's benefit, could you also include the plywood species ie Meranti, Hoop Pine, Douglas Fir etc. If someone does for example, Hoop Pine as a test, don't think for a minute that it will apply to all. You can get variations here as well. So it would be interesting to see even a couple of tests done by 2 different people on the same species and post it up. I hope you'll join in as it would be fun seeing the results from everyone. I think this would make for a really interesting topic.

"Spot Welding with a hot glue gun" ( A little trick used in the boatbuilding industry) When locating and installing the bulkheads, mark the postion on the keel as per the plans and using a hot glue gun, temporarily "spot weld" the bulkhead into postion. This will enable you to quickly install all the bulkheads at once. Since bulkheads/ringframes tend to be pretty floppy in the topsides section and more solid in the bottom section, this means you can quickly spot weld the bottom and then work your way towards the top of the bulkhead /ringframe. As a quick check, you can then temporarily lay the sole stingers (only a couple required) into their repective slots to check that the sole will sit correctly and level. Once all done, make up some glue and using your finger, push the glue under the bottom edge between the bulkhead and planking. Do the same for the other side. If your run out out time, leave until the following day to fillet correctly to its required size and then tabb. In regards to those "spot welds, fillet and tabb straight over. Also, you spot weld just enough to hold the bulkhead into postion. This little tip can be used for just about anything you want in boatbuilding. Have fun Regards Mark

G'day Everyone, Some of you are approaching the time (if you haven't aready), to start bogging your boat ready for fairing or / mixing glue and Q-cells together for squeeging between the planks, or whatever. No doubt, you've found when mixing the bog powder or Q-cells with the resin, the powder seems to "float" on top of the resin when mixing and everywhere else as you seem to spend ages trying to mix it together. Here's a hint: Using a margarine or icecream container, mix up the resin and hardner first. Then grab a hand full or three of Q-cells and throw it into the container. Put the lid on the container and shake like mad for around 10 - 15 seconds, then open up. Its basically mixed together. Now you can grab a stick and give it a good solid mixing without the Q-cells floating on top of the resin and floating up into your face. If more Q-cells are required, repeat the process. Save's time and also a mess. TOO EASY !! have fun Regards Mark

G'day all The plank thickness used in the video was 9mm by 30mm. The glue mixture is 50/50 cabasil and microballons. The design overall is not negineered as a plank boat, but as a composite boat which means we can use a thinner plank as the strength is in the laminate and the plank itself is simply a core of which we're only interested in its core shear strength. Typically when planking this method, it's easier to do it with two people, one outside pushing the glue through and the other inside telling you when to stop. The preson on the inside wipes of the excess and also fills any voids that was missed. This way the whole gluing process is very quick and easy. It took me two nights after work to plank this boat on my own and took 4 hours (two people) to glue up. Hope this helps out Mark