Friday, December 6, 2013

Own IOM design

After the jif, angel dust rg65s.
An IOM is coming:
This is the first model of the IOM project. The plan is to get the boat on the water in spring and learn about the class. The goal is to attend some international events in the second half of 2015.

About the model,
The hull is designed around a Dave Creed keel finn&bulb, for starters a Creed build rudder will be used.
Jelacic 3D moulded sails will provide the power.

The hull is a low wetted surface design, with a beam of 22,5 cm. Designed with the all popular tumblehome, to reduce the hull area(and weight), but complicate building :(.
It is not a copy of a britpop or fraktal but is designed with a philosophy of it's own.

Chines are soft to reduce drag, the tumblehome is the most extreme around the middle of the boat, lenght-wise, because this is theoretically the part of the hull that provides the most "grip" = reducing leeway.
Also this is the part of the hull where the depression of the waves made by the hull is the deepest so wetted surface area will be reduced when the boat is pressed down-wind(where there is no sinkage and the depression is at its deepest)

The waterline is very narrow at stern, to promote light air performance and shape the waterline into an asymetric wing when heeled, combined with round forward sections this shape should make the hull happy to change direcion.

The finn is quite far forward at midship(centre fo the finn), to insure directional stability in caotic conditions downwind and stable upwind(foil wise).

The above combination should give a boat that feels stable directionally but is happy to manouver when needed.

The hull has lots of reserve volume above the static waterlines, to stay above the waves.
The freeboard goes to a  minimum at stern to reduce hull-weight(also potential windage, but due to the wind gradient i think that there is practically none).
The deck will be flat to make the boat simple. For sheeting an arm servo will be used mounted behind the finn, corrector weights will be placed around the finn-but the final placement s a mater of experimentation.

Tuesday, November 26, 2013


Today there was a lot of wind, gusting to 25 knots, the temp. Was 1 deg. C.
Ice was building..
Fila went good under B rigg, a little bit overpowered up-wind, so tacking was not the easiest in the 10-15 chop.
Down-wind was a blast!
I came in, to adjust the vang and jib twist, grabbed the boat by the mast, somewhere at the lower shroud.
Aaand it broke..
The sails have survived, but a new mast has to be build. And the new rigg has to be setup, this will take the most time.
The plan is to make a new main sail with a shorter foot, to move the ce of the main closer to the mast, for a more balanced helm when sailing down-wind.
The tradeoff will be a slightly higher CE. 
But will be worth, because broaches will be avoided more easily with a nearly neutral helm diown-wind.

Monday, November 25, 2013

Footy design - thoughts

I have been involved in the footy class for good two years now. till today i've build some 10 footys.
In 4 design shapes: Spade(4boats, 9hulls), Karo(4boats, 2depron ,2carbon+1 carbon hull), Duck(a Gary Sanderson design) and a "proto" the newest model.
The participation in two footy goldcups gave me the chance to try other peoples footys, amongst which are the infamous ICE, Steri, Ranger etc.
Alongside with footy and other sail class activities i've been studying naval architecture by myself. Finding resources in books like Principles of yacht design, Elements of yacht design(skene), Ted Brewer books, and all the literature and technical papers i could find on the web.

This is where my thinking stands today:


The advantage in lwl gain by positioning boat diagonally into the measurment box is minor, not worth trying if technical difficulties appear with generall arangement. But if it suits the boats concept then the boat should be as long as possible.


Generally there are two types of boat: a narrow one and a wide one, not many footys are found in between.

Imo a narrow boat should have a beam of 70-100mm, less is to little, as sail carrying ability is reduced. A very narrow boat will suffer in gusty conditions as it will be hammered by the gusts(if the rigg is set for the luls) or left behind in the luls(if the rigg is ment for gusts)

A wide boat, 135-153mm of beam. These boats are very "powerfull", they carry lots of sail, and usually sport a ballast of around 250g or less, because more ballast doesn't seem to improve righting moment enough to beat the added weight/drag.

All-up weight,

I went as low as 300g with spade models, but hit problems with tacking, similar problems have been reported by other builders.
The black KARO weighed above 520g, and is the heaviest footy i sailed beside the ICe(can't remember the weight, but it was above 500), and this karo suffered from unresponsivness, and dynamic sinkage due to the forces of sails. With a different hull a heavy boat might perform.

My conclusion is that it is safe to stick below 500g and above 350g, offcourse the boat should be build as light as possible, and ballast should put the boat up to it's full design weight.


At stem should be as large as possible(7-10cm on boats like SliM, ICE, Steri, Urca and my designs)
at stern it should be 0, or as small as possible to fit the boat in the box with the maximu possible draught.(stern freeboard: 3mm-4cm on my designs and ICE's, urca, steri, duck..)

Hull design details,

The prismatic-coefficient should probably be around 0.6, because this suits an overopowered sailboat.
No speed/angle measurments were made with footys, the only refference could be the internet course, but the conditions are varying and the angles sailed are questionable.
Volume in the front third of the boat is key to downwind performance. Three types of bow are found on footys.
One type has little volume, and a high freeboard, and is designed to be pushed down and cut the water when overpovered downwind(Slim, Karo, Ranger). This type gives stable downwind sailing and is probably just as fast as the moustache found on ices.
Then there is the moustache, seen on ice, awk and bug footys. This bow is pushing the water away from the hull creating lift.
Finally there are footys with lots of volume, these are trying to stay above the water, but usualy don't.
The most effective seems to be the high bow with lesser volume.
The moustache is also succesful on british designs.


Currently i am experimenting with ballasts of 200, 250, 280, 300, 350g, trying to see how they work on different types of hulls, sometimes the all-up weight is to large... bulbs have cg on the same chord lenght of the finn and approximatelly the same shape(something like a naca 64 xx)

It seems that 200-250g work well on wide boats like spade and proto, with the 300g bulb there is already a significant loss in performance upwind, tho the two boats are much more stable when sailing downwind with a heavier bulb. Note: spade was designed for an all-up weight of 380g with a 200g bulb, protos all-up was to be 420 but works best at 375g with a 200g bulb.

The 280g bulb works best on the KARo the 300g bulb can be used for waves and stronger winds, the 350g bulb is to heavy for all of my designs and is waiting for use in a future project.
250and 200g are to light as the 2000sqcm a rigg heels the karo way too much, and tacking in waves is compromised.

Ballast ratios for footys seem to reach from 40% to almost 70% of the all-up weight, light footys are build just as light as the heavier ones, and that is the reason for their lower % of ballast, they simply have less lead.
Generally 50-65% of ballast/all-up weight is a good result.
Two exaples:
Karo, all-up:500g ballsat:280g ratio: 56%(depron boats had a better ratio due to lighter hull)
Spade, all-up:380g ballast 200g ratio:52%
Data fot further comparison here
Note: often it is better to add some weight in order to make the boat more user friendly, e.g. hatches, switches instead of tape.


should be maximized, the theories about lower wetted surface with a shorter finn don't work in the real world, footys are all about POWER a.k.a. sail carrying ability.

Rudder size,

I got good results with 50sqcm and bigger rudders. Some footys use smaller rudders with a very high aspect ratio, and they work well, but if the boat is not perfectly balanced they stall in caotic conditions and the boat loses control.
Karo is sporting a 75sqcm rudder. It's big, bigger than needed but reliable when tacking, waitng at the start etc.
All in all a big rudder does no harm, it reduces leeway, makes handling easier and does not slow the boat down much because of all the sail power available.
Another tip is to have a rudder that is at least 15cm deep(from wl), so when the boat pitch-poles downwind, 2-3cm of the rudder stays in the water and control is not lost.

Keel finn,

Due to the low Re footys experience the profile should have a fine entry, the max thickness should be 10-12% of chord, less seems to be risky due to the big leeway angle when accelerating/drifting in light airs.
The planform area on my designs is about 60cm^2(325 size heli rotor blade), this is also the lowest advisable area, less than this does not provide enough sideforce. Leeway increases.
For non chined hulls or hulls with flat sides which provide less "grip" under heel an area of up to 90cm^2 can be used.
A big finn reduces tacking ability, so a boat should have either a small rudder and a small keel finn or both of a bigger area. 
The keel finn shoul be set far aft to move the CE back. The bulb CG must match the LCB of the hull or be set for max 15mm aft of the LCB on the vertical axis(the -15mm option will increase weather helm and reduce nosediving down-wind.

Rigg sizes,

The rigg size is increasing from year to year as the boats are refined.
at the moment the sizes are: A+(light air rigg) 2000-2700sqdm, A 1400-2000sqcm, B 900-1400.
c-rigs are rarely used but generally measure for 500-900sqcm, stormriggs are below 500sqcm.
Going above 75 cm of rigg height above deck rises the CE to high, so that should be a good upper limit for all but the A+ rigg.
The sails should cover as much of the boat lenght as possible, meaning that the whole rigg should not be 20cm wide but more like 50cm wide, this balances the boat better for upwind sailing(it gets more directional stability, and is not as twitchy)
High aspect ratio should be kept if possible!


Most of footys use 9g servos for rudder and sheeting.
For the rudder a 4.5g servo is more than enough, saving 5g of weight.
In the past standard servos were used for the sheet, but there is no need for such a heavy servo, aspecially if the boat is sporting balanced una or swing riggs(a nominal power of 2 kg will do)
With classical riggs a "2.5kg" strong servo should be used.
The above is my experience with a 6.5-7cm long servo arm and direct sheeting.
The Rx should be as light as possible to save weight and space.(weight under 10g is exelent, under 25g is good)
The battery can be a 1s lipo of up to 1000mAh, weight approx.: 26g
Four AAA are also commonly used but are abit heavier.
A on/off switch is welcome, to improve user-friendlyness.

To sum up, the above are just some measurable parameters that work with footy class sailboats.
At the moment i am not sure what is the fastest footy type.
Speed seems to come from the overall package. Such a package can be achived using different approaches:
Like ice(design by Roger Stollery), a relatively heavy and beamy design, which handles downwind with moustaches.
The rigg is a swing, with enough power to overcome the high weight

Or SLiM, a Phil Tyler designed and build narrow boat, of medium diplcement. Going downwind with a narrow cutting bow and a efficient una rigg.
More here

Monday, November 11, 2013

Evolution f5g

Photos of low boom design, on f5g evolution:
The vang is a bicycle spoke and its nut can be rotated inside an aluminum tube for adjustment
the boom can be set at a minimum height of 6mm above the deck before it would hit the keelfinn nut
Sail servo is mounted in the front part of the boat
Project evolution is an exercise in weight distributionin.
The servos(for the optional forward rudder, sail servo), the batteries and Rx are put into the bow, so that the finn can be moved backwards.
The idea behind such weight distribution is to have the bulb on a long arm far aft. The moment of this arm "sinks" the stern and lifts the bow up.
This is a motion found in dinghies like laser, when the helmsman hikes hard on the straps and leans back, this way he accelerates the boat.(by pumping, and trimming the dinghy hull relative to the water surface).

 My prediction is that this weight distribution will improve reaching and running speed.
upwind the boat will be "stiff", unhappy to go over the waves, hopefully this won't produce a boat with a heavy bow, that slams into waves.
Tacking will be snappy, but the boat won't have much momentum to punch throught the waves when pointing directly into the wind.

evolution tasted the water for the first time today, no leaks,weighed down to he desired 1600g displ
With 1600g this boat is looking to be on the light side.(most national class boats weight 1700-2000g)
the coil behind the mast ramm represents the weight of the rigg(165g), the two battery packs are the finn and bulb(800g)

Monday, November 4, 2013


Karo, my second own design footy survived it's first season.
It posted a good result(7th) at the goldcup, and was the basis for classic rigg development.
It is also my first panel build boat ever, and my first boat intended for easy building(karo is winner of the richardson trophy, an award for simplicity and promotion of fun).
now the black boat was refurbished into it's original/optimised form:
the new 285g bulb seems to work best with the 1500sqcm a rigg

the paint is tired, the hooks for a classic rigg remain on the boat also a new balsa bumper is in place
all up
This is KARO's final shape, it will remain like this.
It's a competitive boat, that is oriented for windy days. I am looking forward to sail her at some future footy regatas.

a complete set of pdf plans will be free to download soon.

Tuesday, October 22, 2013

proto footy update

The unarigg was moved 2cm forward, now the boat has better helm balance at bigger angles of heel, and is stable while nosediving downwind.
The 200g ballast is a good choice for this hull. but a 250g bullb will be introduced, because bigger riggs(more than 1500cm2) will also be used on this boat.
I also tried it with the 350g bulb of of a KARo, but that was too much, the boat didn't want to heel, and with no grip from the chine leeway increased. Responsivnes was also compromised.
Today the wind went from 2-3 knots to some 7-8, A+ to A rigg conditions.
Autum is in full swing, later the wind blew the leaves away, luckly
The light conditions were just to demanding for my Iphone today
downwind is now stable, this boat does lose more speed than a KARO does when nosediving
reaching is good, even when overpowered.
More conclusions will be drawn when i get a chance to sail against a KARO, or other footys..
here are a couple clips:
and with the 350g bulb:

Saturday, October 19, 2013

jif update

the jif 65 is comming along nicely the deck was glued on and the hull was laminated.
ready for deck and lamination

the aft par of deck structure
the deck was glued on with thick CA glue, it is a 2x 80 g7m2 glass laminate
the hull was laminated with 1x 50g/m2 + 2x 20g/m2 glass and is now sanded awaiting 2k paint
i am not happy with the weight increase, 72g is what 3layers of wood varnish on the inside, the deck and the lamination have brought so far.

the deck looks like this, the two holes in the back are as by plan, the forward ones will provide acees for gluing the shrouds and the fore stay to the bottom of the boat and for adjusment of the mast post( a 5% variation of CE is posible. with blocks the mast can be mowed forward and backward, rake wil be adjusted up to 5 degrees backwards)

Now the mission is to build a thin(3mm thick) finn and a rudder.
After that two riggs will be build a swing and a classic.

Friday, October 11, 2013

new footy prototype

Yesterday a new design went waterbourne,
It is a fat design, made out of 4 3mm depron panels for easy building.
It is placed longitudinaly and nose down into the box, 153mm wide at stern and has a 32cm lwl.
The bulb is 200g, total weight is 380g. The updated KARo a rigg is used.
The goal for this boat was to create a light weight(sub400g) boat, which is beamy, with lots of volume, so it can go over the waves(no through them like KARo does), i decided to go for the 4 panels so i can modify the hull quickly, and so that some one will decide to build it cause it is a 4h project if u already have a rigg.
templates follow.
It goes quite good already. I will shift the rigg forward tho for a more neutral helm when heeled(the 12% lead of CE to CLR is not enough, there is some weather helm, too much for my liking. The hull is very stable obviously(lots of volume is shifted forward so the entrance angle is quite bad but that doesn't seem to affect speed.
Upwind the chine bites, and the boat is shaky over the little waves, i don't like that..  ..but it seems faster upwind than a karo. Downwind it has a problem.. is so light that it gets thrown over it's bow and onto its side, it takes too long to get to the old course again..   ..a possible solution to that is a longer rudder. But when not heavily overpowered it goes well.
Tomorrow it will be in the water again with the changes. There are also some leaks that have to be fixed.
After i am happy with the balance upwind and downwind is solved this proto will be taken apart for templates.


Thursday, October 10, 2013

Funky funk plane!

A week ago a great deal was made. I managed to buy a slope soarer plane:
It screams 80's! and it is about 30 years old, vintage stuff.
Some people would put it on the shelf, but i will fly it. It's a slope soarer and slope soaring is super enjoyable + there is a perfect hill for soaring only 10 min of driving away from where i live and another one is 20 minutes away, the hk bixler i use as FPV is not that good at slope soaring but it can do it.
I am not sure what model this plane is? neither was the previous owner, but i know that it was built from a kit as it has a "q.c. passed" stamp in the fuselage.
 It is masively built the fuselage is 5mm balsa, the wings are foam balsa sandwich laminated together in the middle, it also has air brakes.
The control lines are made of stainless steel wires, and are 3mm thick(heavy duty)
no servos came with the plane, it has space for standard servos, tho 12grammers will be used.
the transparent cabin is missing.
Some repairs will be made, oracover re-glued, and servos instaled.
It will fly again!

Jif 65 build

Because i have no will to continiue with the angeldust rg65, i decided to build myself a jif65 wich will be equipped with my design rigg, and will be used for comparison to new designs.
The jif65 is a classic rg65, ment for easy building, but results from some regattas show that it can perform if executed well.
The hull seems to have a low prismatic coefficient, a relatively deep v and is quite beamy for a canoe style boat.
planks are 2mm balsa, bulkheads are 3mm balsa as suggested by the plans
Todays progress was good, managed to get all the templates cut out, and build the hull.
The front two bulkheads also have holes cut in them to save weight. The hull with no servos now weighs 76g which is ok according to some build logs on the web.
Not sure why this pic is downside up, but here are the servos. Fresh from hobby king this servo ripps pants with only 60g of weight and lots of torque. the rudder servo is a corona something 9g servo for rudder. The servos are set on a (50g carbon/1mm balsa/ 50g carbon) sandwich wich is supported in the middle and weighs a mere 7g, the finn box has a 3mm wide slot and is made of the same sandwich, the green stuff is some very stiff foam found in baumax.
That's it for now, by the weekend i hope to have the hull glassed and the deck bonded.

Saturday, October 5, 2013

Last race, no wind, offseason, national champion etc.

Today the last race of our national champ series took part at Koseze pond. The picture below sums up the whole race:
It was like that almost all the time. Damn drifters :(
Dispite the lack of wind i had a good time, just chatting and debating about prototypes present at the race.

The race went allright for me, finishing most of the races in second place, behind the best light air boat:
prototype one, nothing that special about the boat, just anice looking setup, only thing i would change is the bulb
it caries a boom with a sort of trolley setup, creating an overlap of sails, like a genoa does on real boats.
The above prototype was in the water, but not racing. It is here to stay so we will have a chance to get to know more about it next season.

prototype no. two, a almost 2000g very heavy wingsail boat, the wing has direct control from a 180deg servo, the flap is also trimable
Great props are to be given for inovation, but an about 3000cmsq wing can't cope with fila or #93 and their 5000something sqcm riggs, also i think that fat profiles with no camber don't realy work in low wind conditions(up to 3-4m/s) where renolds numbers for 30cm chord are below 50000.
The winged prototype was also special under the waterline, carying this bending keel with a winged bulb
proto number three, a wingmasted swing rigg, the sails were somewat to stiff
under powered, far a boat as hevy as fila, but a great idea, with a food box hatch wich must be nice to use compared to my patches
underwater a classic setup is to be found, carbon everything, and a half profile bulb
will be great to se this boat sailing in winds, when the rigg functions as it should
the mast from above, carbontube, two wire cut stirodur halves wraped in dacron
a KARO being build by one of the guys
it was a good day i was second in the race, a good margin behind #93 but also barely touchable by the rest of the fleet.
I am also the national champion of 2013, with two wins and two second places on the scoreboard
the two medals(silver second place in the race, and gold for national champ)