So I put my math hat on… and started working on some torque and force numbers.
assuming a 600gm lead bulb on the keel @ 20* heel I 'm looking at a torque value of .716 newton meters.
now if I put a 300 gram slug on the upwind side of the hull at the same 20* heel I’m getting .722 newton meters.
the reason for huge benefit of a lower weight, at deck level is that the lever arm is acting in more powerful direction than the angle of the keel. the keel has a larger weight which helps with the forces.
There is no free lunch however. I’ll still need to keep 600 grams int he boat. 300 on each side since I can’t have movable ballast… as the boat heels more, the keel exerts a greater torque better angle, and the deck mounted weight exerts less torque… So. when the boat starts to go with the deck mounted weight, there is a point of no return … it will go over… I’ll need quick thumbs as i think it will act a lot like a catamaran…and a foam block on the mast would help…
Well…id did not sink. enough air got trapped in the bow so when it went over it stayed afloat.
I put the B rig on it and started going down wind… but once I started to round up @#%& started happening fast and my thumbs were not up to the task. it heeled over and then I think the wind caught the hull and it kep going. Iit went turtle immediately and as it filled with water about 8" of the bow kept its head up…enough to drift to shore.
servo’s are apart and drying…I made a foil to go on the rudder to act like a trim tab to get the bow up. but have not fitted it… that might be the next step… once it all gets dried out… my only concern about the rudder mounted trim tab is that if the wind is not enough to keep the tab active and working all it is doing is slowing me down as drag
Sorry, than you leave the ballast in the harbour …
If you have 300g on each side, they will counterbalance each other, regardless of the heel. Ballast on deck level will work with movabale ballast only …
actually the ballast int he corners would not cancel each other since the b at would heel not on the center line of the boat like a typical mono hull. but when it did heel it really did act more like a catamaran it would “fly” the windward side of the boat substantially… so the leeward ballast was not equalizing the windward ballast. Don’t get me wrong it wasn’t helping but it wasn’t hurting as much as you think.
Yes movable ballast is the ideal situation. but can’t do that…so…
orange circle is the internal ballast on one side, the green star is where the internal ballast woudlbe on the other side. and then you have the typical keel/bulb over layed
physics was telling me that at 20* or thereabouts the internal ballast, even with ballast on the leeward side was providing a better righting moment than the keel mounted ballast. the problem is that one you got past the 20* the internal ballast helped less and less, while the keel mounted ballast was doing more to counteract the heel. So much like a catamarat, once it starts to go…Its going over…no amount of hiking out is going to help…
I’m not going to give up yet… since I have a keel made up. I’ll make another bulb but mount it further aft on the keel fin to get more weight aft and maybe that coupled with a T rudder may help the nose dive problem… Or not… only way to find out is to keep trying…
You may have put your math hat on but you needed the geometry glasses too. The biggest difference between your system and the traditional setup is how the torque changes with heel angle. The longer the lever arm, the more torque (righting force) you’ll generate. With a traditional keel, the horizontal distance between the bulb and pivot point increases with heel angle. Your system starts out near the max distance and decreases with heel angle. You lose force just when you need it most.
The wide hull may give you an advantage with a normal keel/bulb vs a narrower hull. The way to take that advantage would be with a shorter keel. Try an 6-8" keel. It may help with the bow diving too.
there is a point about 20*-25* in the case of this boat where the inboard ballast becomes ineffectual and the keel become more effective. I was trying to keep the boat at a heel angle of less than 25* to keep the inboard ballast more effective. But, in the puff it went over…
as the lever arm becomes more parallel to the ground, and the force(gravity) 90* to the lever is the max righting moment.
That’s a tough bit of driving to keep the keel angle in check. I’d rather have the the lever approach parallel with the ground with more wind than leave it.
Here’s another thought for your scow shape. How about building in the little bit of tunnel hull allowed by the rules? It might be enough with your super wide hull.
“3.2.1 In each section of the hull, there will be no point of underwater body below 0.3 cm another point of the same section located closer to the centre line of the hull.”
ok, now I understand. The drawing helped a lot… This idea will not work with a narrow “canoe” like boat like the usual RGs, but may work in this case.
However, it is true what John said. Inboard ballast ist not very effective at high heel angles. Torque will be deacreasing again at very high heel angles. That’s why boats with inboard ballast may capsize.
For my opinion it makes no differenze is you distribute the ballast on both sides (it doubles the lever and halves the effective weight) or to have all ballast in the center (full weight, but half lever)
with hull heeling I tried to put the ballast as close to this point of rotation so the leeward ballast would not have the negative effect on the heel.
My biggets trouble was just trying to control th eboat and the speed it went over, even with the B rig… I’ma going to make a new keel bulb and attach it to the keel a bit further aft to try to move the CG aft and then I also put the foil on the rudder…
I have been toying with the idea of getting away from the “Traditional” skinny boat design. I’ve come up with some lines based on the International Fireball class. It’s sort of a hard chined scow with less bow area. Attached are some 2D views as preliminary thoughts. I understand I may need to adjust for servos and such.
Max beam approx. 175.25mm
deepest part of hull 53.5mm
