how to get the exact shape of the section of a completed hull ?

Hi, I’m looking to add foilers to my Mini40 to reduce nose diving and I was looking to epoxy in a carbon tube in which I slide it the carbon rode of the foiler into but I want to make sure the angle is correct so the I was looking to get an exact drawing of a specific section of the hull where I want to fix the tube so I can position on paper the exact location of the holes I’ll drill to slide in the cf tube at the right angle.

any idea how I can do this ? :confused:


When I have needed to do something like that I draw it in cad and then print out a full sized print. Lay it on what I need then mark the dimensions.

Obtain a laser level (one of those things that projects a line) and a camera with a manual exposure control. Set up the hull and the level so it throws a vertical line at the desired station. Position the camera dead center and bracket exposures. Chances are one of them will give you a perfect section line. Measure, scale with a photo processing program, and print.



what about covering the section in question with some cling wrap, and then either use modeling clay or some plaster of paris/drywall mud this will give you a mold of sorts. uch you could then create your line drawing… or use it to make a template for the drill

or find the center line of the hull on the top and bottom and then measure to your specific point on one side. drill hole. now you know exactly where the next hole must go IE measure and transfer those measurements to the opposite side of the hull… ensuring you are perpendicular o the center line…

I have used the following methods which proved satisfactory to allow me to see the cross section of a hull (template) with minimal cost/effort.

  1. You can use a piece of lead (wire) solder. Cut a piece off the roll in the length needed. Bend it around the hull where you need the cross section. Use a knife and l(lightly) mark your center-line of the bottom of hull.

  2. Some lumber centers sell a cheap item to duplicate shapes for turning wood items on a lathe. It consists of a series of many straight pins of wire. Pressing it against an object provides a mirror image of the shape from which you can easily trace the hull section.

Either of these work great for getting a shape for making a travel cradle for a boat hull as well.


great Idea with the solder Dick…

Thanks - and if you need a stiffer wire - visit a local art glass store/glass shop and ask for a length of “Lead Came” which is the lead used between pieces of leaded glass. It has an “H” shape, thicker, and will hold the shape a bit longer/better than the solder.

Thank you all for your ideas - I tried the shape comb but too small for the hull shape but I really like the idea of the solder wire - will definitely try this.

found the centre line of the hull by pulling a line from bow to stern and with the help of my wife managed to mark the centre line.

I don’t think it will be a big deal if I’m a few degrees out (3/4) as long as I have the same angle on both side. boat not for competition but more for show but very tricky to helm at the moment as volume is too far back (inspired by orma60 of the 80’s).

When competitive racing my big beach catamaran, I built a similar “tool”, except I used a length of wood to sandwich wooden dowels. (dowels acted as the wire pins) I was able to copy any part of an 18 foot (5.5 meter) hull using this tool. I just had to make sure the total length was just slightly longer than the distance from keel to deck at the center line of the hull to allow me to get half-templates. Obviously too big for our smaller R/c sized boats. You can also take strips of stiff paper and hold two against the hull - then tape together. Repeat the process as needed and adding strips to get the desired level of detail needed. This is what kitchen counter-top or vinyl flooring guys will do to get exact room/counter dimensions and layouts . They then transfer external lines to material to cut. Just a few more ideas.

It happen once to find the shape of a class M and I built up a wooden tool as in the sketch . I cut various pieces of 1cm wide out of carton/bristol and glued in with loctite/cyanolite.
The plywood square is then transferred with the various arrows to a paper to marks the arrow index and join them with pencil.
This operation was repeated every 1/10 of the Hull length. The hull was initially standing onto small supports on the table .

even more idea - brilliant thanks Claudio and Dick.

I left the mini40 cobra platform aside for now as I am building a new carbon rig for it and having some glueing issues - I think it is greatly due to the humid air we’re having at the moment here in Ireland !!! we’re still to have our summer. and rain rain rain every day - haven’t been able to cut the grass in a few weeks either… I use a 2 hours setting epoxy from evostick which is in a seringe to glue the tubes together and various parts to the mast but even after leaving the parts to dry over night they’re still slightly tacky to the touch. I have a small rad on termostat but difficult to get my shed over 20. Hence why I think it is the humidity that mess up the curing process.

Hi Gilbert -
is the “Cobra” a new mold - or is it an older build that are you just getting it ready to finish? From whom did you purchase the hulls? I have a set of “PULSE” plans sitting in my “model room” but haven’t had a chance to get to them yet. Too many started projects and not enough finished ones. Would appreciate any photos you can take and post of the COBRA as I have only seen a few photos of the design. Seems a few Germans have been making extensive strides in getting the newer designs right, as the new videos like Rowland’s seem to support the better designs have made for better and more forgiving sailing.

Best wishes. Dick

Sure I’ll try to post some pics of the cobra - as far as I remember it is a French design and I bought it over 20 years ago when I was still living in France as I wanted to sail and learn to sail these whilst building my own Mini40. It was heavily inspired by the Orma60 of the time hence the narrow bow lines which requires to be quick to react in acceleration or you pay the price (capzise). It is heavy and did relatively alright in racing at the time but was quickly outpaced by lighter designs with more volume forward. Anyhow it is still “sailable” and still give some thrills even though it is not competitive any more - which is not a problem for me here as I’m the only one with multi here. So it is more for fun and exhibitions to attract people to RC sailing.

Like you many projects and few not finished so now - victim of the recession - I have a bit more time in my hand so try to get this one ready to sail, then finish the other one a Coyote design, again from 20 years ago but with more modern shape and more volume forward. I’ll post some pics in the next few days once I’ve taken the photos.

Atb, Gilbert

Here are the pics of my Cobra I took today - I had just finished building a new rig for it - a much stiffer cf mast (diam 14 & 12mm) vs the original 10mm too soft to control the leech of the main.

you can see from these pictures that the bow has not enough volume - not a big issue in the light wind but its weight makes this design not the best performing tri in light wind and extreme to helm in more windy conditions. Having said this I don’t really care cos this is really for fun and for show - planning to put up foilers to reduce its bow digging issue later. Once I’m happy about the rig.

still some work to do before getting it back on the water: sheeting system, winch, electrics for phase I, new rudder, foilers and improvements from phase I for phase II.

Enjoy !

Thanks so much for sharing the photos. Are the beams permanent or can they be removed from floats for travel? I think I may move my mast further aft on the “Water Resist” design, and I’ve already reshaped the hulls to have a flatter underwater section with the thought to induce “climbing” as speeds pick up. I too am moving to a more sturdy (stiff) carbon mast, however just completed a wing “MAST” (not sail) with some extra sturdy spreaders. A fellow contact from Britain was building a two masted Mini40, and sold me a set of his two sails which are much smaller - but I haven’t put in any effort to build a mast to go with them. They are not as high-aspect ratio as most, so coupled with the reworked shape of the underwater section, I am hoping for good performance in higher winds.

Thanks again for sharing.


you’re welcome :slight_smile: the beams are permanent, making the whole platform very stiff - not too much of a problem with a mini40 as it fits in my car no problem. Yes from the tuning I did yesterday the new stiffer mast looks much better already and the main looks more powerful too - so I hope !!! curious to see some pics of this wing mast when you have it.

atb Gilbert


one of my good family friends who has a boat yard (old school boatyard)

My family friend (sudler lofland) is the guy who looks like Rush limbagh in the beige suit…love his boats and generally has always been a sailor at heart, but really has enjoyed building and refurbishing these old boats. He has the first and last pleasure boats built in this yard…

So the Boat Augusta, yeah I know it a power boat. they don’t have any orginal plans, but that have an original half hull model, about 1 meter long. Its too big for the comb. I though about taping it up and glassing the half hull and then cutting strips from the desired stations and the tracing them and cutting full stations. but I figured it would be too risky. So i’m going to lay up some blue tape top and bottom measure off in 1" increments and begin bending solder wire…

I know this isn’t sailing, but I’m hoping the great knowledge base here might also shed some ideas on duplicating a half hull to a full hull…

Just use a piece of mirror to get the opposite side of the boat. :stuck_out_tongue:

OK, OK - before anyone tries it - it is a joke !

everyone’s a comedian…

FWIW I have ben thinking of every way possible to to get the the mirror image since I know that once I start tracing and flipping the half stations over even in cad I’m going to introduce error in to the mix.

but my plan is to bend the solder and then scan each wire into a PDF and import the PDF into cadd for tracing…

I guess I could lay up a grid on the hull and take measurements and input the data in delft ship…

but I do appreciate he humor dick…as this will be a wee bit frustrating

You need one of these.