I spent one of the last "holiday" days sailing evolution, with a rigg, in conditions above the riggs range(10-15 knots). Hiding behind a dock, where the wave was relatively small.
The reason for sailing in in a windy but waveless spot was to observe,by eye, the behaviour of the boat under lots/excessive power.
By eye it seemed that upwind the boat would sail just as fast as it would with a well trimmed b rigg, perhaps there was more drift. But i think that the same boat with both riggs would perform identically.
Downwind the boat sails fast, but even at top speed the sails stayed tense, full. Delivering power that was lost because the boat would not accelerate more.
What is this "limit"?
This is a wavemaking drag barrier.
According to mr. Edmond Bruce, author of "design for fast sailing" by AYRS, the wavemaking resistance barrier, displacement boats face when sailing close to hullspeed, is less noticable when Lenght/beam ratio of a slender hull reaches 8. This "barrier", or a steep hill in the wavemaking resistance ploted against speed graph almost disappears when a hull reaches l/b=11.
I will use this post to go back to basics and come up with two ideas for future F5g boats.
Both ideas have been realised in the "big boat" world but have not been pushed to such extremes due to structural and seaworthiness limitations.
The goal is to make a fast boat.
In order to make a fast boat we need a force to move the boat.
Here the rule is simple, the more power(sailarea) a boat has, the faster it will go.
Some will argue that if the sails are more efficient a boat with less sail will sail just as fast as boat with more less efficient sailarea. Wing theory proves that, but in the real world a boat with more sail will be the first to start reacting to wind, if there is little wind. A boat with more sailarea has more tourque powering(moving is perhaps a better term) it through waves. The boat with more sail can take the wind from the boat with less sail etc.
The above are race proven facts that are true most of the time on a race course. But there are some drawbacks of carrying lots of sails.
Since we are talking about model boats that measure less than one metre in lenght, longitudinal stability is an issue. Our models tend to sink the bow, submarine so to say. Footys and IOM boat suffer from this greatly. In f5g i have succesfuly adressed this issue with a foil attached to the rudder, the foil is inverted, so it is pulling the stern into the water.
Yes this foil increases wetted surface and induced drag, but the area of sail i can carry with this rudder is much much bigger. Example: Fila has a5500cm2 a rigg, without the foil it can carry its rigg to about 8-9knots of wind(average wind) with the foil i sailed downwind succesfully in winds of 14-15konts! Evolution can sail with more than 6000cm2 up to 15knots of wind!(it has more bow-volume and a longer keel than fila)
The second issue is transverse stability. With no moving ballasts the most effective combination is a wide hull and a long keel. The combination of both gives the boat a satisfactory counter-heeling moment.
Big sailarea requires a wide hull and/or a hevy bulb. We can fine tune this combination to give good results with the chosen sailarea.
Until now i have never asked myself how wide can a monohull be? The idea of a 750mm 400mm wide F5g scow type yacht is interesting, but hullweight will probably be the downfall of this project.
The problem with wide hulls is that they all make a deep/high wave, causing a lot of distortion over a large area. Despite the consequental high allup weight such a boat could carry lots of sails and putt other f5g boats in shade. Planning potential downwind would be good, but upwind under heel it would not sail past hull speed leaving it just in front of the rest of the fleet.
Without moving ballast i can't see another way around this dragbarrier problem caused by normal displacement hulls of our model boats.
With an aerial canting keel/ballast arm and a narrow hull with a l/b ratio of 11, the boat could reach it's speed potential. The arm extending to windward would keep it right side up sailing upwind.
A rudder foil would keep it from digging in when running. Transverse stability downwind is a challenge. Sailing downwind the arm would be recracted to the middle of the boat so that the CG of the boat be about 10% behind the LCB, this gives good rudder response and keeps the bow from dragging too much. But the ballast would be placed relatively high, on the deck.
A gyro stabilisation for downwind sailing would be needed. Or capsizes would be inevitable unless some lead would be put into the keelfinn, which has to be present anyway(not really, a fore rudder could replace it, but for regata use a fore rudder is one channel to much for my concentration, and it takes away the good feel of a well balanced boat. Just like 4wheel drive takes away the livelyness of a 2wd car)
If only possible, putting led into the keel and having movable ballast at once should be avoided.
Because if you go through all the trouble of making a movable ballast sistem work, then you want all the ballast you have to be active, for maximum efficiency. The lead in the keel would be dead ballast just sitting there to save the boat from capsizing in extreme conditions.
Dispite the above practicallity along with reliability has to have the upper hand and a boat has to be desingned so that it will complete sailing the course when sailing as hard as required with no technical issues or capsize recoveries.
This was a thought about a fast monohull, to sail in a displacement or semidisplacement mode at planning speeds. For the first time i realized that it is almost a waste of time to work on "classic" type keelboats in an open class like F5g where nearly everything is allowed. IF we take a look at iom or marblehead where the rules are much more defined and refined, well that is another story.
