Open Footy Multi?

here is what i sculpted on st. nick’s day. just painted a fair coat on a proto sponson. gonna splash it, make two, make some funky bridgedeckbeams, put them all together into a plug, then start tooling it.
want to do twin rig, like “le hydroplaneur”.
not even done the mono yet, but gotta carve foam when the mood strikes.

You sure do beautiful work, Nigel.

Could you tell us what materials, tools, special techniques you use to carve and finish your molds?

Thanks…Bill H

i find the best, and cheapest is blue, or pink foam. it caves and sands nicely.
uerethane foam is nice to, but i find it to crumbly and messy.
corecell is my favourite. it carves like wood ( some desities feel like wood too)
it stands up to all the chemicals that i’ve ever used.
the composite stuff is all epoxy matrix and reinforcement (e-glass, s-glass, arymid(kevlar), carbon).
there is other resins i use also, but they pertain to other stuff. eg. high heat hetron resin/carbon fiber to make motorcycle exhaust cans, or chemical wash tanks. the polyester stuff i really don’t use, except the hetron(vinylester)
for lay-up, i do by hand, by vacuum-bag, by male/female compression, and resin transfer/infusion(i’m working on a totally clear m/f mould so that the client can watch the matrix infuse through the mould) it should be cool.
my tools are my hands. been hobbying all my life. some techniques i use are widly available, others are trade secrets that you learn when working on top end, one off stuff. always watch the older men pros. they know there s_ _t
(for tino, jacko, and papa mike)

that’s about it

just one question nigel, do you carve your hulls around stations or waterlines?

it’s 420 now.
i sometimes use both. i always have the waterline(WL), and vertical centerline(VCL) on the stations. it is the way i keep them aligned. right now for rapid prototyping, i use the distance measurement between the stations, to cut blocks of foam to that thickness. i then mark the “WL”, and “VCL” on the blocks. then i glue the stations and foam blocks together (station-block-station-block and so on). the two lines are a measument base.
now all that is left, is to block sand the foam until i touch the station in between the foam.
fast and simple.
i am going to do this on a future F100.

cool, thats just how i’ve been doing it! just wondering, you seem to turn them out so quickly, i just wondered if you had a different approach!

Are your stations Balsa?

i use balsa mostly, because it also sands easily. i’ll also use whatever i find that’s suitable, and cheap to make plugs. i don’t go cheap on the materials when i comes time to make the product. the good stuff is just that for a reason. i turn things out quickly because that’s mostly what i do. in fact, i think my production is far too slow. if i had the funds… full time per day…oh man.

anyone tried using diagonals. In the old days of pencil and splines I used to draft hulls largely on the diagonals since they were often nearest to 90 degrees to the skin - and often to the water flow.

If you can cut the angle at the centreline accurately, there is no reason why you shouldn’t use diagonals instead of either waterlines or buttocks.

someone knows their lofting.

eh Angus, i got a question for ya ( or any who know)
in an effort to help the vessel plane down wind, and to help minimize the bow from goin under, is it possible to design the shape of the hull to raise up under way. i read canting keel boats also need fore/aft ballast changes.
i thinking if one puts more bilge curve shape towards the transom, the boat would float transom up, but under way, that new shape would creat downward force, raising the bow.
i’m guessing at this. so i need an expert opinion.

In yacht design ‘know’ is always a very big word!

If we are try to do this seriously, what do you reckon your sailing displacement will be?

there is no displacement. just theorizing stuff
say ya had a one meter that you wanted to “wheely”
cause it submerged a lot down wind.
would changing the shape (the profiled bilge curve) to something like an upside down, pointing aft, foil.
i also have seen that some put a horizontal foil on the rudder.

Take a look at “big brothers” (or sisters)

Bow buoyancy and volume, a short low aspect ratio rig, and the ability to sail faster than wind - not limited by “lead” are all factors that will play into downwind performance. Large sterns add drag and have little if any use, buoyancy toward the rear isn’t needed - in multihulls or in monohulls.

Consider a monohull - upwind or down, when a gust hits the sail areas combine to press the bow down - not the stern. When running downwind, the bows try to dive as the tall rig tries to move forward while hull drag resists thus turning a tall mast into a lever of sorts.

Now back to multihull - MUCH less drag resistance so ability to plane dead downwind is easier to achieve, but with same pitchpole tendencies. In a multihull pitchpole WILL happen as there is no lead underneath trying to maintain stability. On a monohull, the lead tries to resist the mast “lever” and at best a broach happens when stern and rudder leave the water and boat tries to roundup. A bigger stern won’t improve this.

Sailing dead downwind with little more than the windspeed will allow a plane but the fastest you will go is windpeed or perhaps a “touch” faster - but not much. Now in this trim, cracking over to a deep, broad reach and sheeting in with traveller out if so equipped will tighten the leech and will suddenly allow apparant wind to move forward, and the multi will begin to pick up speed - and the apparant wind continues to increase and moves forward - usually well above the true wind. Eventually, the hull will reach it’s maximum speed, but that is caused by drag as a limiting factor (among others - trying to keep it basic here). So for a multihull - or ice/landyacht, tacking/gybing downwind is faster than dead downwind. You must cover more gound, but your velocity made good (VMG) compared to the bottom of pond/lake is so much greater/faster than simply "floating downwind before the breeze. It is why we often comment that a multi/ice/land yacht “CREATES” it’s own wind.

OK - back to your needs - and my opinion is to shift rig back and keep the mast short. Increase bow buoyancy or maybe even add small “wings” to side of bow to help keep bow from diving - kind of like a submarine’s bow planes but not sticking out that far. Finally, consider downwind reaching instead of “floating” for lack of a better word. If you still have pitchpole problems, a few of us have experimented with rudder foils set at a maximum of 3 degrees down angle. In light air/slow sailing it doesn’t seem to affect performance a great deal, but as speed increases so does downward pressure on the foil, which is intended to keep the transom “planted” and reduce pitchpole issues.

Again - take a peek at lines/designs of modern multihulls in the real world and you will seldom see large deep sterns. In fact many trimarans seldom have the float sterns in the water at all !


thanks. so not putting boyantcy in back, but the bow.
so when they say that “this multi has more flare in the bows, to help reduce pitch poling”. where is this Flare?
is it below, or above the WL.?
what is big brothers?

Dick’s comments are fine for a multihull or very light displacement monohull. It’s very difficult to see how you getca Footy below about 210 g. with electrics. Scaled up, this equivalent to an old fashioned C&C 28. It will surf readily and plane occasionally. A scale open 60 is about 50-60 grams in comparison as I remember it (I did calculate it much earlier in the thread).

Playing around with the profile will have minor benefits but will almost certainly cause a lot of drag. The best trick is to flatten the underside of the bow and making the profile a bit steeper than you usually would.

Trouble with foils is that the lift is proportional to the square of the absolute speed in other words, if you go twice as fast you get 4 times the lift, 3 times as fast 9 times the lift… because a Footy is unlikely to do more than about 0.7 m/sec this does restrict things a lot. Probably not worth doing.

I have seen a French ‘super Footy’ that looks lique an overweight squid with an apple-pip shaped hiull and big, thick canard wings forward. Because they are thick these foils add pure bouyancy high up. The boat will slow a lot if it gets over-powered but hopefully will not go out of control. But remember that with any forward foil that it must never be able to go to a negative angle of attack - otherwise it will tend to bury the bow.

If you have a very light structure, reducing draft may be a good idea. this means that the centre of drag is higher and the ripping couple smaller.

Hope this helps.


Ah, i’m seeing the light.

oh this has nothing to do with my 350g disp. footy hull.

just daydreaming about stuff

i was thinking about something in my past.
someone had made a hull, and was showing me, when a naval engineer walked by and said to my buddy. "that will make the trasom go down an plow through the water.
i was thinking about this past event and figured, hmmm transom down…bow up? would a small amount of this help keep from pitch-polin?
didn’t know, so i asked yawl

forgot the thanks…thanks.

nigel, you might think about boats like ex-playstation-cheyenne/Orange 2 both had soaring bows that were flared, adding reserve bouyancy up there. or sea-kayaks where they cannot afford to dive the bow, large large amounts of flared reserve bouancy in the bows. i know i am just agreeing ith what others have said, but you also ought to think about adding a very flat “planing surface” in the stern. my father and i were just talking about this last night. most of the fast boats in the world have a rocking forward motion, i.e. they dive until the reserve bouyance stops them, then they rock back until the flat aft surface stops them. very short, forward-oriented sliding.
just some thoughts!:stuck_out_tongue:

First part of Barrett’s contribution, I agree totally. Was going to put more or less the same thing on just after your last post but got ditracted.

On the second part: interesting that. After sailing my father’s Hustler 30 (Holman & Pye Half ton circa 1970) for a long time I have always tended to have a slight kink in the profile aft. The Hustler was rather like an S&S 34 without the bustle with a narrow, tapering V-stern and quite a steep run aft, but very clean diagonals.

She tended to surf slightly later than the opposition but when she did she would set off like a rocket and stay on the semi-plane. There was obviously a discontinuity in the drag curve and we hypothesised that it was the result of a hydraulic jump caused by a rapid change in volume.

The same principle with a considerably wider, flatter stern seemed to work quite well on our Spring Onion and Solution half tonners.

Is that what you meant about ‘rocking’?

“Rocking” may work well with monohulls with lead keels to “dampen” the motion, but not on a multihull. The last thing you want on an 18 foot long boat is the top of the mast (31 ffeet in the air) moving forward, then rearward. Everytime the mast moves backward, the airflow on sails is lost, drive is lost and all must be reattached as the sail rocks forward once again. One of the problems associated with a Hobie 14/16 with the “bananna” shaped hulls. Lost of sail drive when “hobby-horsing”