These are close approximations of the maximum righting moment for various configurations of multione. Most of these configurations will be extremely sensitive in pitch when developing this power.My apologies for webtv which will probably not hold the outline form that I will do this in:------------------------------- 1)-Bradfield type foiler with retractable foils: weight approx. 3.3lb; foils develop righting moment therefore maximum is unlimted except by structure.Zero pitch sensitivity.
negatives: waves higher than 6" with periods less than 4’.
2)-Scram type(sliding cross); outside hulls with enough buoyancy to fly main hull; cross extended to leeward.Allup weight 3lbs.Max rm with no ballast:9.15ft.lbs. Pitch sensitivity moderate with movable cross.----------------
3)-Scram type same as 1 except with two pounds ballast on main hull. Allup weight: 5 pounds.Pitch sensitivity : moderate since cross can be moved fore and aft ; max RM:16.65 ft.lb.'s-------------------------
4)-Scram type-cross extended to weather; 2 pounds ballast at max distance to weather of main hull. All up weight 5lb.'s Max RM: 9.66 ;pitch sensitivity LOW
5)-Cat 36" beam,no ballast,3lb.all up weight.Max RM:4.5 ft.lb.s;pitch sensitivity : HIGH--------------------
6)-Cat 36" beam Power Ballast System extended furthest to weather. 2 lb.'s ballast ;5lb. all up weight.Max RM: 12 ft. lb.‘s.;pitch sensitivity:MODERATE if PBS moves fore and aft.------
7)Tri 4’ beam, no ballast, all up weight 3lb.'s; max RM: 6ft. lb.'s ;pitch sensitivity HIGH----------
8) Tri as in 7 but with movable ballast system;2lb.'s ballast; allup weight 5lb.'s; Max RM: 13.5 ft.lb.s; Pitch sensitivity moderate if PBS moves fore and aft.-----------------------------
Top three most powerfull configurations: 1)Foiler,2)SCRAM with hull to leeward+ ballast and 3)Tri with Power Ballast System.-------------------
Most stable in pitch: 1)Foiler, 2)Scram with hull to windward
3) Tie: cat or tri with PBS
Note: that a boat with the SCRAM system can be configured THREE different ways requiring only the addition or removal of weight.
The cat or tri can be configured two different ways requiring the addition or removal of the POWER Ballast System +ballast.
UPDATE: Definition of Pitch Sensitivity: any small multihull that does not use hydrofoils, a t-foil, anti -dive plane or F& A movable ballast system has the highest “pitch sensitivity” because it has the lowest resistence to pitchpole
due to the fact that only the buoyancy forward of the cross arm has any effect on stopping pitching. The amount of buoyancy translated into lift forward compared to the pitching force of the sail is too low.This is a natural design occurence on boats with hull beam to length ratio’s of 10/1 and higher and especially on multihulls scaled down from larger full size boats or multiONES scaled down from F48’s.
Boats with lower pitch sensitivity can carry more sail area than an equal weight boat with high pitch sensitivity.
Tris can be designed with the CB of the outside hull forward of the CG of the boat so that as the main hull flies the boat uses it’s own weight to resist pitchpole. This design feature is not included in the above analysis for the sake of keeping it relatively simple and because if this is not done very carefully a severe pitch up can result when tacking the boat while flying the main hull.
Anti-diving planes set at the right angle of incidence(5 degrees above the level of the waters surface when you push the hull down to the point it would pitchpole if sailing) can help prevent pitchpole especially if coupled with a rudder t-foil.
Power Ballast Systems both of the SCRAM type and the “normal” type can reduce pitch sensitivity if they are controlled properly by the skipper or increase it if not.
Foiler pitch sensitiviy is ZERO because pitchpole is automatically prevented in most conditions and requires no skipper input; a properly designed Bradfield type foiler will have no tendency to pitchpole.
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing