Semiscale Footy Catboat

Footy Class General Discussion (Footy)
1

Would this gaff-rigged catboat make a decent sailing footy?

Since I know nothing about designing boats, I figured starting with this little 19’ catboat might help, especially since it’s got the look I want. Would following the scale sailplan yield a reasonable model, or do I need to make adjustments? The changes I’m assuming I’ll need are :

  1. add keel and bulb
  2. lengthen/deepen rudder

Are there others you guys would suggest? Should I scrap the semi-scale idea entirely and go with one of the footy plans (not my preference, but I’d also like my boat to sail)?

I’m obviously not looking to win regattas, but rather have a fun, cute little boat to play with on the lake, and on the off chance that I ever make it to a footy event, be able to “compete” (i.e. lolligag behind the rest around the course)

thanks,
Rick (who will have to hit up graham for his source of dapper little footy-scale sailors, since this boat would definately need one)

2

Lookup posts by “Flavio” from Italy. His boats are real classy looking and he is a Naval architect besides. Also ask for his comments on your ideas.

3

I’ve seen pictures of some of flavio’s boats, and they’re downright dreamy! Unfortunately I don’t have nearly his skill, so I’m planning to stick with a more basic shaped hull (and the first iteration may skip the cabin, but the cabin adds alot of appeal to this boat imho). If he doesn’t chime in I may PM him, thanks for the idea :).

-Rick (who just noticed that if you took the pintail’s lug sail where it lies, and moved it’s mast forward to make it a gaff rig, that it would look remarkably like this cute little boat… I wonder what that would do to it’s sailing characteristics though?)

4

Hi Rick,

yes !

I feel that it is possible to design and build a very pretty semiscale footy based on this nice profile .

Keel and rudder should be enlarged to have “decent” ( most probably quite good ) sailing performances

Beam can be designed not exactly 100% to scale , in order to suit required stability and to have enough room for electronics

Hull could be build in a simple and easy way as a flat bottom skiff ( balsa or light ply )

Cabin can be used as “roof” of a removable waterthight box for receiver batteries and servo.

Most probably she will not be a winner, but without doubt such simple rig and hull shape could become a balanced example between “nice looking” and “decent performances”.

At same time, I have no doubt that no special skills or tools are required

If you ( or somebody else ) are really interested to build this model, I would be happy to make more detailed calculations and drawings.

Let us know :slight_smile:

Flavio

5

Wow, Flavio, that would be awesome! Here’s the other picture I have of this boat, it shows a top view and a funky side view that includes the scale keel (such as it is) and rudder

I was hoping I’d be able to handle something like this if I could avoid compound curves… Maybe some day I’ll be able to build beautiful curvy boats like yours, but this seems like a good place to start!

many thanks,
Rick

6

Rick,

I’m sure there’s no reason why a perfectly nice sailboat couldn’t be worked up from these plans. It would of course suffer the typical cat boat problem of needing a largish rudder to counteract the the totally unbalanced sailplan.

Just make sure you balance the sailplan and the underwater areas correctly and you should be O.K. Besides, Flavio suggests you are on the right lines so it can’t be a total disaster :wink:

Cheers,

firstfooty

7

I built one partly from a george turner hull I also know some one who is in the process of building one 1/6th scale! ~ its a monster but beautiful
If you need any other info just ask

8

Here’s some other info that might be of help

9

Following my previous post, I have done my homeworks starting to crunch numbers in order to design a pretty semiscale catboat footy for Rick ( or everybody else )

I hope it would be interesting to share with you my steps, showing how I will try to finalize the project.

first of all , let’s start writing a basic “wish list”

the model should be :

  • an “almost” scale model based on a benford design cat boat
  • fully compliant to footy class rules
  • pretty ( very pretty )
  • a good sailer, even if not an extreme racer
  • seaworthy enough to sail under a breeze around 10 kts
  • easy to build using balsa or thin plywood

basic design decisions

  • removable fin keel , to suit different wind speed, for easy transportatiton, or for fine tuning of sailing performances
  • the hull should have an “hold space” to insert a removable box ( or something similar ) for easy replacement of electronic stuff
  • the model should be able to use both very advanced and lightweight electronic , or something a bit heavier ( big receiver, hevier servo and so on )

design philosophy
the design of “Brando” ( this is the name ) should be very conservative, and overall dimensions are to be not far from succesful tested models ( cobra, razor, kittywake, bob about - just to mention few of them )

weight estimation
hull 100 gr ( very conservative, could be lighter )
rig 25 gr ( 20gr mast,boom,gaff + 5gr mainsail )
RC 150 gr ( midway between micro receiver and lightweight batteries, and heavy old big receiver with 4 AA )
blades 25 gr ( 20 gr finkeel + 5 gr rudder )
ballast 200 gr ( the “usual” 7 oz fishing sinker )

total displacement 500 gr ( 16.6 0z ) : a very conservative intermediate solution

a very light boat can go down to 450 gr or even less

Main dimensions

overall lenght should be aimed to few millimeters less tha 1’ to take in accound building mistakes : 300 mm

waterline lenght will be around 280 mm considering a sloped transom stern, and an almost plumb vertical bow

max beam will a bit less than maximum allowed ( let say around 140 mm ) to retain typical catboat lenght/beam ratios , as well to have plenty of space for rc

waterline beam will around 120 mm, as good compromise between enough stability and not too much wetted surface
a nice flare of topsides, together with a nice sheer will improve a lot hull aestetic

hull draft will be around 25 mm ( one inch ) assuming a block coefficient 0.55 and displacement not far from 500 gr

hull depth will be close to 60 mm ( at midship ) looking at a “deck underwater” heel angle close to 30 degrees

sail area will be around 900 cm2 ( 140 square inches ), to be increased for light wind condition

keel area will be approx 70 cm2 to have a sail area / keel ratio between 7% and 8% ( the best coefficient used on succesful footy )

All considered, these figure are not far from many existing footy, most probably remarkable differences are :

  • a sloped transom
  • flared topsides ( hull narrower on waterline then deck )
  • a nice sheerline instead of an ugly straight profile

Next time I will try to blend all above mentioned numbers looking at a nice ( and simple ) hull shape and pretty sail plan

stay tuned :slight_smile:

flavio

10

Wow, that sounds great, Flavio! I’ll be eagerly awaiting the next installment :).

Thanks so much!

-Rick

11

Hi Rick,

even if I have been a bit busy today, work on this project is under progress:

I have done a first version of a computer model for the hull, ( see attachment ) in order to match good numbers with a nice shape.

Details are still to be tuned, but we have now a good starting point.

I have been also thinking a lot about building method, and outfitting arrangement

I will do my best to improve the project during next weekend.

( Most probably I will build one of them too… )

have a nice week end !

Flavio

12

Spiking Flavio’s interest is rather like hitting the jackpot isn’t it :slight_smile:

13

Hi Rick, hi Graham…

I have been working on the nice concept of this model during week end, and these are the results :

  • I have done several freehand sketches just for fun, and to plan how to fit rc inside “hold” ( see below )
    One of them is almost a real drawing, two of pdf files are showing freehand cartoons made during long boring phone calls

  • On the computer keyboard I have refined hull shape, adding also rudder, keel and deckhouse to the shell ( as well a tentative gaff mainsail ).

  • Numbers ( displacement, and centers ) are in good agreement with preliminary investigations.

I will show “downlodable” plans of bottom, topsides, deck, and transom soon ( within this week ) so to made possible building a cardboard hull to appreciate a real size 3d hull shape.

Before starting cutting wood, I am still working on longitudinal position of keel and rig, in order to achieve as far as possible - a good longitudinal balance -

Most probably my kitchen table workshop will be busy during next weekend :slight_smile:

have a fair wind …

Flavio

14

You’ve got that right!!! I was hoping for a couple of suggestions (maybe a good keel location, or vague rudder sizing)… Flavio is definately exceeding my expectations by a country mile!

Flavio – Love the cartoons, and the digital boat as well, she sure is pretty! I love how the rudder flows into the curves of the boat.

-Rick

15

Hi Rick,

happy to see that you like my “engineering” effort.

Today I have optimized longitudinal balance, moving a bit to the stern fin keel area, and changing here and there boom and gaff lenght as well mast rake

Longitudinal center of sail area is now a bit ( 12 % of lenght ) forward of lateral plan .

  • This distance is also known as “lead” -

I have satisfied with this number both due to the fact that I used same value on a very pretty ( and very good perfomer ) 10" freesaling catboat model years ago, as well due to the fact that in accordance to a sound theory sail center is above a point " almost" on the center of finkeel side area ( hull and rudder not included )

Hull volumes are also quite balanced due to a quite narrow stern ( in comparison to other catboats- at least ), in order to avoid a bow down trim when the boat is heeled ( according computer ouput , pitch angle should be less than 0.5° at an heel angle around 25° )

All considered, I feel confident that it should be possible to have a balanced model yacht , even if catboat are usually considered poor performers form this point of view.

Next time I will make a first evaluation of stability : heel angle versus wind speed, in order to increase/ decrease sail area, and/or ballast weight

Meantime I have started to select a straight and dry plank of balsa

… see you later

flavio

this a refined version of lateral profile ( deckhouse has been changed a bit too )

16

Today I have done basic calculations about stability performances.

In other words, it means a lot of number chomping to check if :

1 ) we have too much sail area ( or not enough ballast weight ) -overpowered boat

2 ) we have too much ballast ( or not enough sail area ) - underpowered boat

Usually it would be advisable to modify both parameters ( canvas and lead ) in order to have a nice balance.
In this case, I feel that it would be nice to avoid a too big mainsail in order to save a “semiscale” look.

To put it simple , optimization will be based on a proper calculation of ballast weight instead of changing sail area

There are a lot of good solutions, depending on your average weather condition, so as first conservative approach I have designed a boat that will sail in a comfortable manner up to 10 kts, and capable to witstand something more.

I have used specialized naval architecture softwares, as well several homemade excel spreadsheets, in order to plot the diagram below

calculations are based on following data :

boat displacement 480 gr ( 17.3 oz )
sail area 860 cm2 ( 133 sq inches )
deck underwater heel angle is close to 24° - 26 °

Diagram most important informations are that :

heel angle at 10 kts is 20°
wind speed when deck becomes wet is 12 knots ( more or less )
Most probably storm rig should be used when wind is over 15 kts

These numbers are good enough to start now thinking about building method…

fair wind to everybody :slight_smile:

flavio

17

Hi Flavio,

Do your computer programs and calculations offer any help or predictions with nosediving and submarining when on a run (a very common Footy trait), and how to alleviate this tendency?

I like the aesthetics of your catboat so far. Would you go so far as to say it’s a catboat Sharpie?

Regards,
Bill Nielsen
Oakland Park (Ft. Lauderdale), FL USA

18

Hi Bill,

two or three things about downwind nightmares :

1 - broadly speaking

I feel confident that this model should be able to sail safely downwind without troubles up to 15 knots of true wind speed ( and much more using storm rig ).

a -because gaff rig is lower in comparison to a modern rig ahving same area ( and in turn capsizing lever is reduced )

b -because due to this old style sheer bow freeboard is almost double than deck height above water at midship

c -because bow sections are v-shaped adding dynamic lift to the bow

2 - calculations

it is possible to make calculations aimed to assess pitch angle to wind speed relationship, even if this calculation are based on many assumptions, the results are that Brando should have a nose down angle between 8° and 9° sailing at approx 1.5 knots under a 15 knots breeze

Enclosed computer pictures show the situation better than many words

Calculation are not able to show if the boat is still under control, but the rudder is still 70% underwater, and triangular shaped old fashion skeg should improve directional stability.

Conclusions :

computer simulations are not able to give a perfect assesment of downwind performances, but number are reliable enough to support our hopes to be far form the danger of unwanted underwater scuba sailing

But the proof of the pie is in the eating… ( isn’t it ? )

Flavio

PS …yes this model is definitely a sharpie catboat.

19

One good new : I have started to convert balsa into sawdust

One bad new : I have problems to download digital pictures about building progress ( frankly speaking, I have lost the connecting cable )

Awaiting better pictures I have attached below a freehand sketch showing most interesting points :

1 _ Footy Control Unit ( patent pending :slight_smile: )

This time I have started building starting from inside.
All electronic stuff has been installed on almost square ( 105 mm x 95 ) < 4" x 4" > plywood block.

Servos are screwed to the block, batteries and receiver are held in place using “office quality” rubberbands, on the lower part

As first approach I used an old and heavy Hitec receiver ( 30 gr ) and 4 AA Nicad batteries.

If needed, future “upgrading” improvements to rx and batteries are easy simple and quickly

FCU will be stowed inside deckhouse, with the ply plank almost at same deck level

2 - Hull
Hull has been divided into three compartments : fwd and aft there are two enclosed spaces ( to be filled with ping pong balls or foam if needed )

Center space is between two transverse bulkheads, and is big enough to store the abovementioned advanced “FCU”

Fin keel can be inserted ( an removed ) into a purposely designed socket on the bottom of the hold.

3 - Materials

  • topsides, deck, and bottom 1/16" ( 1.5 mm ) balsa
  • stern transom two layers of balsa
  • fin keel “socket” thin ply
  • bulkeheads 1.5 mm balsa ( again )

Even if I am still far for launching, “true” wooden hull shape looks nice and very “classic”

More soon !

Flavio

20

ok, now I have been able to found the cable to connect my digital camera to computer.

These are first images of hull and removable FCU ( footy control unit )

Flavio