I’m hoping to start soon on my own trimaran design and wanted to have a little discussion regarding the design features that make a multihull tack better - particularly an r/c multihull. I’ve been reading through some old threads and there was mention that some of the latest multihulls (2005) were tacking better than before…so it made me wonder what the difference was.
I am very familiar with modern beach catamaran designs and feel like I have a decent sense about some design features that help a boat tack. Some of these items can negatively affect speed so there are some trade-offs.
[ul]
[li]flatish hull bottoms
[/li][li]daggerboards mounted further rearward on the platform (less turning distance between the rudders and the boards).
[/li][li]crew weight placement during the tack (roll tack - getting the bows out of the water)
[/li][li]sail plan that is efficient at high angles of attack
[/li][li]weight. weight carries through the neutral zone of the tack better (but hurts overall speed)
[/li][/ul]
What features a prevalent in an r/c trimaran to improve tacking ability?
My opinion is you’ve hit on quite a few. If one eliminates any kind of moving ballast, the “roll-tack” idea is lost. A narrow set of beams will (generally) tack faster than a wide beamed boat since the bows of both hulls can cross the wind faster when closer together. Tacking is further complicated by not being “on” the boat so the sense of feeling is lost. Once can only observe and base radio control stick movements based on experience. The right weight can, as you note help carry the boat through the lulls or when tacking, however I would offer the speed gain is minimal (unless grossly overweight) since the majority of recognized classes seem all to be overpowered. I am not sure I have seen any control setups which use a separate channel/winch to control the jib, separate from the main (I am planning on this) which would allow the jib to be backwinded and help push the bows over during a tack. Uni-rigs are a different story, and as you are aware, requires steering skill to be able to hit tacks consistently. While it seems having only a main helps windward performance, giving up that sail area downwind is a real “killer” - but then I used to steer by jib telltales. Downwind I will also grant you a lighter boat can accelerate faster and drive deeper. The rudder/boards distance is a help - but can also make downwind steering rather “twitchy” - which also suggests that a boat with more rocker in the hull will tack faster than a long, minimal rocker that will track better. (I base this on experience/comparison of my old 18 Square NACRA against the COYOTE which had lots of rocker and could tack much, much faster.) On the other hand, the COYOTE had problems with “hobby-horsing” when sailing in waves.
I think you gain in some areas and give up in others. Also depends on the amount of time you want to spend on the radio sticks. While I too, was well versed in big multihull sailing, there was a strange transition - and loss of ‘feel’ of what the boat was doing was the biggest problem trying to relate between the two. Those without multihull experience don’t seem to have issues since they are learning from a distance by eyesight - not feel.
Hi Guys, I totally agree that rocker is a big help in tacking, with a tri though a trade-off is to have rocker in the centre hull and very straight rocker in the armas. If you then include enough diheadral (raise the armas in relation to the center hull) this helps the boat pivot on the main hull when going through the eye of the breeze… The amount of “Diheadral” is relevant to the type of water being sailed in - more for rougher/ bigger waves…
I’m testing a tri I’ve made that has a rudder and centreboard ono each armas but none on the centre hull… So far seems to work well with tacking and when sailing in enough breeze the windward centerboard & rudder clear the water so less drag then…
Cheers
Dave
Hi Dave -
where are you located? Seacats is in the Carolinas, I’m in Minnesota and we have an F-48 in Cleveland, Ohio area. Not much help for you if not in US - but there are others visiting here that may be interested. Thanks, Dick
PS - any chance to get photos posted?
I’m living in Brisbane Austrlia…
Here’s a couple of old pics of version 1 of my 1.5m Tri, Since this one I’ve rebuild a new one from the same moulds but much lighter - down to 4kg from 6.5kg. The new one I hope to get some video and pics of in the next few weeks - I’m setting up a furling screacher on it just to make downwind sailing even more dangerous…
The First pic is of a M40 class tri I’m building - based on a A-Class cat hull scales down. The bottom of the hulls is not yet joined in this pic and the balsa beams are what I’m using to take a female mould off for the cross beams… Final boat will be all carbon and I’m aiming at a sailing weight of 2 kg…
Cheers