Design Considerations for rougher water?

So I have decided to modify my “fun boat” design a little bit. Adding 10mm to the freeboard throughout the whole length on the account that I will be sailing on a medium sized river that feeds into the bay it is fairly choppy due to wind as well as boat activity. While I am taking time to make these modifiations, is there anything else I should consider for rougher water? I used to sail my Star 30" in the same river and it had a hard time on even the lightest of chop. Thanks for the help.
Andrew Miller

  1. At the bow, a narrow, fine entry at the waterline and plenty of flare at the sheer, so she pierces the waves and gets plenty added bouyancy as she plunges.

  2. Low aspect rig, so the center of effort isn’t moving around as much, and you aren’t working the rudder as much to compensate.

  3. If a bulb, a short, fat one to reduce the pitching moment as far as possible.



I love a ketch rig for strong wind. Low center of effort and you can easily reduce sail and keep it balanced with various sail combinations. There aren’t any ketch racing classes though. Too bad.

I don’t know, is it good to have a bigger rudder with a low aspect rig so the long boom doesn’t cause weather helm in a big puff down wind? Now that I think of it, a big rudder moves your over-all center of lateral plane aft which I guess is another way to reduce helm.

I had a really good Ketch model once and it was a total screamer downwind in a big puff. Never pitchpoled once. Now I’m into class racing.

I think I have most of those covered. I am staying with a slopp rig and am trying out the twin foil system, with a fore and aft rudder, so Im not sure if rudder size would relate or not. Thanks for the input, hopefully she sails well, although it is still a little ways off.
Andrew Miller

Is the rudder system going to be fully functional, or just the aft rudder moving?

They will both be functional but the front one will oly turn a fraction of the aft one and in the opposite direction. SO it will not have collective capabilities.

you might want to make the aft rudder a little deeper than what would look neccasary if the rough water is caused by the wind. If its just rough water but no strong wind than a rudder thats a little longer than normal would produce more turning force.

Well since the whole boat is being modeled after a CBTF boat the rudders are inherently longer to counter act the sideways motion that the canted keel will no longer work against. The boat is about 43" and the rudders are about 8"-9". Im guessing that will be plenty but let m if you think otherwise.
Andrew Miller

8"-9" deep right? I said longer referring to the fore and aft axis and deep meaning up/down. sorry for any confusion. If they are 8-9 inches deep, that should be fine.

Ohh my bad I see what you are saying. Umm I was planning on making them identical maybe about 3/4"-1" long. Keeping in mind that the aft rudder will be considerably farther forward than a standard single rudder.

that should be long enough than. Have you considered actually making a system that would allow you to use the “collective” steering? some radios can reverse servos and other things like that that would make it possible. The collective would help with leeway in rough water

I thought about it, but as of right Im woring with what I have and all I have are 2 Channel radios at this point, but the future may hold collective steering for this or another boat.

Be prepared to put on a single, rear rudder with much more area. Past experience has shown that neither dual rudders nor very narrow deep rudders work very well at model boat scale particularly in high wind and chop.

using 2 channel radios, it is possible to make a boat with “collective” steering.
Its not exactly easy to explain, but you would use 2 transmitters and recievers, and a servo for each of the foils and if you wanted you could use a separate winch for each sail. One transmitter would control the forward foil and the jib, while the other transmitter would control the mainsail and the rear foil. I am currently installing a system like this to control a heavily modified EC-12 that is carrying a 150% genoa. One transmitter will control the sail winches that are used to for the genoa, while the other transmitter will control the rudder and sail arm for the main. The only problem here is that you have to use 2 frequencies for one boat.