Semiscale Footy Catboat

[Rick Lindsey]

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)

[ffastffrank]

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.

[Rick Lindsey]

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?)

[Flavio]

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 :-)

Flavio

[Rick Lindsey]

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

[Firstfooty]

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

Cheers,

firstfooty

[AndyT]

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

[AndyT]

Here's some other info that might be of help

[Flavio]

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 :-)

flavio

[Rick Lindsey]

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

Thanks so much!

-Rick