New build Dingo3

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.


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.

Dingo -
might want to seek scrap foam from various construction sites. Up here in Northern USA, it is often used under roofing materials for insulation, Being extruded (not expanded) it has a lot of resistance to compression. Usually a discussion with the supervisor on a building site would result in a pile of cut-off stuff laid next to the disposal bin. In a couple of cases, they often would provide a full size sheet or two of the stuff - especially if you tell them what it is for, and maybe show them a completed project.

The only extruded kind I have had to purchase was the thin stuff in sizes I couldn’t cut down on my table saw.

Good luck - and thanks for the postings.


Hi Tony

Nice foredeck section!

Hi Guys,
Dick I really did scour for the stuff. I found quite a bit of the expanded foam on building sites where renderers were using it, but no extruded anywhere. Not for free anyway.

Wolfgang, one of my sailing mates looked at it (the foredeck) and said “whats with the dance floor?”

A couple of pics to show where I am up to. The first one is upside down. :spin:

The strip of glass is made up of offcuts out of the bin, it’s ‘layed up’ on the plug along the deck/hull seam. The line underneath the strip was used to trim both the hull and the deck sections and its traced onto the strip. I’ve made the strips in four sections: for and aft for each side.

Once set, its trimmed neat, rough sanded and epoxied to the inside of the hull gunwhale (which also got a course sand) using the traced line to match the hull.

Both forward strips in place and deck attached too. You can just make out, amongst the mess, the angled strips formed on the plug for the aft deck which is flat. I have CA glued twigs inside spacing the hull apart to get the right beam so the deck and hull are the same shape and match together.

Sorry for the missing stages, but here she is:

The hull is a layer 6oz cloth sandwiched between two 4oz layers, each layer 120 degrees apart, like a spiderweb - much stiffer than D2.
I wanted a narrow beam, plenty of buoyancy in the bow with ‘water-shedding’; you can see its quite full at the water line and narrow on the deck. The chine, well I had to have a chine…at its deepest point it sits about 5mm above the WL. Tumblehome the full length, I think it reduces windage and weight.

Trawling through some of the RC forums led me to some of Claudio’s calculations. (He has contributed lots of great material, thankyou Claudio). I decided I would aim for the following specs:

Beam over all : 164mm
Transom beam : 88mm
Design draft : 56 mm
Prismatic coefficient : 0.58
Wetted surface area : 0.151 m^2
Longitudinal centre of buoyancy : 470 mm from stern

Hull (including fittings) weight 550gm

Should be fairly good in a wide range of winds.
I did manage to sail her the other day in B-Rig conditions but had frustrating range problems (still to be resolved) and then while out of control the jib sheet tangled around the winch and burnt the winch motor out. I’ve since built a little drum cover – too impatient to sail.

The encouraging thing was that she lead the first two legs of her maiden voyage (before retiring). The new home-made sails went well. High and fast tracking up wind and actually pulled away from some very good boat/sailors downwind. As can be imagined I am itching to get these problems fixed and get back out there.

Hi DingoMack,
nice construction job all togheter ! Waiting for sailing movie…