Thought I’d post a progress report on my latest build and third IOM the Dingo(3). Sorry I don’t have photos for some these steps, I hope my explanation is clear enough.
I designed her on FreeShip software which turned out quite easy and fun although initially it seemed a little complex.
This is the resulting line diagram:
The method of construction I used is similar as that for D1 and D2: polyurethane foam shaped into a male plug, covered in packing tape and lay-up the hull and deck over it.
D2:
The recommended foam is extruded polystyrene (not expanded) but I don’t have a nearby supplier (I hunted high and low). The good thing about polyurethane is that its easy to scrounge free stuff. Last time i got some of a refridgeration repair place, this time a local manufacturer of DC powered camping ice-boxes. They conveniently had a huge pile of 50mm off-cuts. Exactly what I needed.
There are a couple of drawbacks with polyurethane (see the green foam I’m using as a stand in the photos), it is quite fragile so unless the mould is given a hard coating it is easily dented also it is quite porous so tricky to glue one piece to another.
It is very easy to shape and sand. For the previous two Dingo plugs I used slabs of the foam and built up a block 200mm X 200mm X 1000mm. Then with a thick felt tipped marker traced a ‘plan’ outline on top, a profile on the sides and hacked out a basic shape with a handsaw, thinner slices with a hacksaw blade. Then it was just a matter of sanding down to what I thought was a nice shape, pretty well by eye.:blkeye:
Ok, but not really very precise.
For Dingo3 I cut 20 blocks of foam: 180mm x 180mm x 50mm, printed out all the stations of the linesplan and pasted one shadow on each block. Let them dry for a day or so then glue the blocks together.
BTW I had a close look at some other ways to do this, particularly Claudios from another thread but I don’t have a bandsaw.
Tip: I had to fiddle around to scale the shadows so that the maximum beam was 165mm. Then when you print out 10 copies of the forward shadows you can match up the bottom edge of the paper of each shadow with the bottom edge of each foam block. That way you create a ‘datum’ height and all the shadows will have have their waterlines on the same plane.
Another tip: try to make the blocks the identical size, that way they stack together better when you go to glue them. The maximum draught of my design is 165mm hence the choice of 180x180.
On each shadow I made sure the waterlines and vertical centrelines were extended to the edge of the foam block, that gave me a way to line up the foam blocks accurately as I glued them together. Also trace around each shadow with say a red felt pen as a ‘spy’ line so you know when you are getting close, as suggested in Claudio’s build thread. (Yes, go and re-read his too)
Don’t have any photos of this but you can imagine 20 foam blocks, face to face with the shadows sandwiched between. I just used lots of PVA glue to stick it all together.
Tip: Lots of glue but keep it away from the zone you are going to eventually sand because the glue, even when dry, is difficult to sand. In other words: plenty of glue in the middle and some around the outside on the area that will be sliced off as waste to help bond the blocks together but none close to the edge of the paper shadow. Clamp the whole thing firmly on a flat bench by ‘bookending’ it somehow and leave it for a good 48hrs to dry completely. That way you will get a nice rigid block to work with.
You can carefully slice down fairly close to the spy-line with a saw to get rid of the bulk of the waste, then gently sand down to the shadow depth.
Use wall filler (here, a common brand name would be Spakfilla) to fair the plug. Make the mix slightly wetter than recommended and 'paint it on. When dry gently sand back. Repeat until your happy with the result. You can put a bit of colour in the mix to contrast the layers.
Wrap the whole thing in packing tape and slap on the fibre glass and epoxy. I used three layers for the hull: 4oz, 6oz and 4oz and for the decks: three layers of 4oz.
Tip: Draw the gunwale (hull/deck intersection) line on the taped up plug with a felt marker. Use that line as guide when laying up the hull cloth and when the epoxy has set trace the line onto the layup and cut along with scissors and lightly sand of any rough bits. Voila, one new hull. Same for the deck/s.
Now heres the trick. Wipe the line of the taped up plug, slip the newly hatched hull back onto the plug and use the cut line to trace a new, accurate line onto the plug. Place the deck on, trace the line and cut out with scissors. Perfect match!
I’ve painted a thinned down epoxy solution onto the insides of the shells to fill the numerous pinholes.
Here is one I prepared earlier:
This is kind of where I am up to. The photos are of the hull and two deck sections with the plug inside. Next I’ll install the transom and bow which I made on a flat ‘taped’ surface with the excess epoxy I had left over from laying up the hull.