After a lot of theoretivcal waffle, first real beef if anyone’s interested.
We now have a strip planked core/plug of Xistera (the bat used to play pelota - to which she bears a more than passing resemblnce from some angles). It’s pretty much symetrical as far as I can see and is not going to need too much sanding and filling.
Displacement is medium - about 510 g. and beam narrower than some (125 mm). Centre of bouyancy and centre of flotation are a long way aft. This gives a ‘long’ bow which hopefully will counteract submarining while giving a finer entry.
Pronounced tumblehome should enable the hull to run efficiently at higher angles of heel than usual while remaining balanced. Hopefully this will increase effective sail-carrying power and make the boat easier to control in gusty conditions.
The very steep run is highly experimental - and a Plan B exists. The idea is a) to help move the centre of bouyancy aft as explained above and b) to move volume into the ends to reduce wave drag at high (Footy) speeds. I hope that at the very low absolute speed of a Footy, the flow won’t separate. If it does, we can use a ventral spine/bustle to straighten the diagonals.
It may work or it may be a very unhappy combination of big boat and very little boat principles. We shall see. By intent (always a dangerous thing for a designer to admit in advance), she is tailored to the internet course - a heavy-weather windward biased ‘brute’.
Looks like a pretty good start Angus.
Maybe “plank” your plug with mylar packing tape and take a glass hull straight over the top??
Brett - you are a genius. I was wondering very much about taking a glass hull off first -in some places round the turn of the bilge the planking is getting pretty doddam thin after fairing and getting the shadows out was always going to be interesting.
But I’d nevr heard of mylar tape - presumably instant finish, instant release.
works pretty well for one offs.
get the tape on as wrinkle free as you can.
coat the “finished” plug with 2 or 3 coats of mould release wax.
Drape your cloth over the hull and smooth down.
apply epoxy and wet out the glass,add a second layer and wet out using as little resin as possible.soak up any excess resin wih a paper towel.
let the epoxy tack off,whilst it is still green trim the glass off at the gunwale with a razer blade or similar then mix up a thin slurry of epoxy and microballons or simlar lightweight filler and paint it all over the hull to fill the cloth weave.
sand when dry,bog again and sand as needed.
Not quite as light as a female moulded hull,but cetainly lighter than your timber one would be.
about 1mm bigger all round than your design calls for ,you will actually notice the small increase in hull volume at this size.so displ may know be 520grams now.
And with a little cleverality you still have the plug (replace the tape) for Plan B.
Thanks for the trouble.
Trouble is I’m used to thnking in terms of building full size boats
Tape will stay on,If it doesn’t you havn’t used enough release wax!!
You could mould an indefinate number of hulls this way.
Yes Angus,your full size building background is showing in the previous threads!!
My experience building little boats has been hard won I assure you.
I think you should just make sure your hull plug is fair and then glass it. Then put a smooth finish on it (doesn’t have to be polished smooth, just no lumps or big scratches). Apply the mold release, then take female hulls off the plug. Thats the method I use to test my designs. Sanding the new hull smooth on the plug is a pain, but then you haven’t gone through the mold making process to produce a gorgeous dud either.
I’ve tried packing tape and plastic wrap as Brett suggested. I have not been able to make these materials lay flat enough against the plug to keep them from printing through to the hull surface. You need to have a light weight lay-up to achieve you target displacement, so the plug should be as fair as the hull surface you want. With these short boats surface irregularities are more pronounced, and I would venture to say, have more effect than on the larger r/c classes or full size boats.
By the way, if you need to make alterations to the basic design I would use a female hull from your original plug mold as a starting point. I’ve “chopped and channelled” M’s and 36/600s, and one of my footy hulls to produce new plugs that are variations (improvements perhaps?) on my initial efforts. This method also preserves your original plug for comparison to later developments.
Good luck however you proceed.
If you decide to use the “tape method”, I use plastic packaging tape to cover my foam plugs. Consider putting it on at an angle to the plug itself, since it can then take on a compound bend. In theory, you will “cold-mold” the plug using tape instead of thin wood veneer or ply. Unlike wood, you must overlap the tape by a few mm so that no epoxy leaks through and sticks to your hull. It will leave a very faint line where overlap takes place, but so small it is of no worry.
In the attached photo - I used a brown colored packaging tape (used to seal cartons for shipping) and you can see the overlap, and a couple of places where I wanted to double-up. It is over a foam hull plug, and there was probably a dent in the foam, so adding two pieces of tape eliminated having to fill and sand. Another foam “plug” is on the left (the other half of a vertically split hull) . Because of the shape of the hull, I had to apply the tape at the aforementioned angle.
How about using iron-on plastic (mono-kote) like the airplane guys use to cover there planes? Large sheet, easy to put on, no wrinkles, high gloss finish.
Tbarjohn, Glad to see a fellow Illinoisan participating in the forum.
Dick has shown us a very nice tape job with tidy overlaps on a multihull plug with long lines and subtle curves. But, while probably the best example of the technique I’ve seen documented its not really applicable to the Footy’s extreme compound curves and transitions.
I also doubt that that multihull was laid up entirely with sheathing glass as we do with the Footy. Those lap joints will print through with any lay-up, the trick then is to have enough resin to be able to sand them out after the cure. The problem for Footies is that applying more resin to facilitate sanding out the print through means more weight in the initial hull (which may mean the finished hull will be too heavy in relation to the overall displacement target) as well as the risk of sanding through if you are too vigorous in removing the excess resin.
Larger, longer hulls can carry a few extra ounces in the lay-up because of the greater displacement volume and longitudinal dispersal of those ounces. The Footy does not have those factors working in its favor.
Obviously the Footy hull has to be built light to get as much weight in the bulb as possible. Going to the effort to create a round bilge hull says to me that the builder is after something more than a one-off hard chine boat. Even if the eventual goal isn’t going into production with the design Angus has come this far already so why go quick and dirty to finish the job? It is very possible to have a gem of a design but create a half-assed hull that doesn’t do the design justice or illustrate the reasons for going to the effort in the first place. Then its very possible that the designer will move on with changes before really knowing what he or she was working with in the first place.
I don’t know whether this thing is going to work or not. It is bristling with ‘innovative’ features on the basis that if you know nothing about model yachts the right thing to do is to go extreme in the first place so that you don’t end up ‘knowing’ exactly the same things as everyone also thinks they know just out of habit!
I’ve bought a standard kit as a trial horse with which I can swap the rig and some of the appendage innovations as a control - but added uncertainties like a hull that is overweight or unfair would just make the whole process impossible.
I was suggesting the tape method to build a hull that needed finishing on the exterior - and as a one (or two off). To use it as a mould (female) from which to make other hulls could still be done, albeit wiith the small ridges of tape overlap - but keep in mind, we aren’t laying up 3mm plywood or veneers - but very thin tape to act as a mould release - not as a mould by itself.
My assumption was that one a layer of cloth was laid up, fill and fairing would take place on the exterior of the hull. The concept or idea is not intended to make a mould for production building of hulls. If (on a larger boat) one sprayed the inside of the glass hull with gel coat, I would guess there would be enough thickness to allow any small lines to be removed. I find it much easier to finish the outside of a hull, rather than the inside of a female mould - if for access reasons alone. Otherwise, one could use the outside of the wood that is cut away for cross section (shadow) templates, and layup the strips and fill, sand then polish the inside of a female “plug” to allow layups directly inside a wooden mould.
It really depends on how many hulls you want to make and how necessary a gloss finish on outside of hulls will be - and - if small lines from the thickness of the tape will really influence any design ideas or performance issues. I have a suspicion that primer and paint (if used) will more than handle the filling of the tape lines.