Keel design question

I am building a keel for a new 32' Multimar sailboat. The boat is designed by Carabelli and manufactured here in Brazil. This same type boat is winning more than its share of races. I looked at a few of these racers, measured their solid lead keel and have manufactured a stem using steel plate. You need to trust me that it is a very near copy of the solid lead stem and much stronger. The solid lead keel weighs 1,300 kilos. I have established that I need to manufacture an 800 kilo torpedo to equal the solid lead model. I don't really know what this weight shift is going to do to performance so I have designed a torpedo that will be T'ed to the stem so that I can move it forward or back until the boat is balanced. The plan is to then fix it in place.
I also have been thinking about installing a small hydraulic cylinder inside the torpedo that would allow me to move the torpedo forward and back while under way. I am not a racer but it seems like this ability would be a plus? Would like to hear opinions about this option.
Gerald

 

It will be interesting to compare.
500kg lighter boat, maybe less initial stability?
The bulb may make the keel more efficient, acting as an end plate.
Please let us know how this works out.

 

What is the weight of the total keel? (fin+bulb) It looks like the original allready has some kind of bulb, is this correct?

Moving the bulb has very limited effect on boattrim as the moving distance is small. Not worth the effort, move the tanks and batteries to trim the boat.

 

The lead keel has the following dimensions. Stem is 80 x165 cm a 9 cm cord and tilts back at a 12 degree angle. I can't give you the exact naca number but the nose is mildly rounded and the fattest part of the cord starts 20 cm back from the nose. Add to the bottom of the stem a bulb in the shape of a three dimensional triangle 23 cm wide 20 cm high and 120 cm long. So, the overall height of the keel is 185 cm. No portion of the bulb is in front of the stem. I believe the thinking is that our fisherman aren't very sharp when it comes to marking nets and there is less chance of snagging a net? The overall weight of the lead keel is 1,300 kilos.
The steel stem that I have manufactured has the same dimensions as the lead stem and weighs 130 kilos. I need to add a bulb to this.
The water and fuel tanks are fixed and already cast into the hull. I can move the two 80 amp hr. batteries and that is about it. My motor / gearbox, located under the steps, weighs 30 kilos more than the winning boat.
Gerald

 

A total ballast of 930 Kg. will do for the Multimar 32. The stability of the original (IMS?) however is not verry much RM 48 versus RM 52 for a Mumm 30and RM 65 for an ILC 30. The result will be a lively boat, like the Mumm.

Trim will not be much of a problem, it will raise abouth level, maybe a notch bow up.

My advise is to trade some of the weight saving for a bit more stability. Why not mail Mr. Carrabelli to be sure?

Also make sure you come as close to the NACA section as possible using filler.

Succes with the job!
Arthur

 

Unless I am missing something??? According to my calculations I should have increased the righting moment. I built a wooden model of the solid lead keel and placed the model on an arm on one side of a fulcrum. Then started loading the arm on the other side of fulcrum, until it balanced. Let us assume that I measured everything correctly, using the meat scales across the street in the market and my digital calipers. I calculated that a 800 kilo bulb would equal the righting moment of the 1,300 kilo solid keel. I didn't figure in the weight of the stem so I figure the righting moment is increased or I can reduce the weight of the bulb a slight bit to equal the solid lead keel.
Have called Mr. Carrabelli a couple of times. He keeps answering that little cell phone from all kinds of strange places. My guess is that he is currently up to his elbows in resin and carbon fiber. That is if Brasil One did make it back to Africa? I would like to put this boat in the water in the next six weeks and he wouldn't be available for quite some time.
The shape will be very very close to the keel that I copied. Something that might help some members that have never ripped off a design......... I bought a few packages of shiskabab sp? sticks and lined a meter of them up side by side. Slapped a strip of wood on each side and in effect clamped them together with a few screws. Push the sticks against the shape you want to copy and there you have it.
Gerald

 

Your calculation did't take account for the form stability of the hull. This is more dependent on weight than on centre of gravity. Imagine putting a weight in the middle of the deck of a catamaran high up but increasing stability at smal angles.

Your new keel will have less stability (initial stability) at low heeling angles and more at 90 degree heel. In other words your boat will heel quicker and then hang on better. It will be sailable with a 800 Kg. bulb just a little sporty
in a lot of wind.

I sail an ILC 30 with a 960 Kg. keel 2.00m. steel fin/lead bulb, but with a carbon mast. o.k. with 6 crew on the rail but a little tricky without.

If you don't like the stability maybe you can fill the lower part of the keel with lead later?

P.s. Brazil one is nearly ready to leave, nice job!

Arthur
(Yacht Designer)

 

The lower section of the stem will hold 200 kilos of lead. I might be worth while to pore a 700 kilo bulb and fill the lower section with lead? I get closer to the weight of the winner and reduce the size of the bulb.
Then again it might be worth while to go back to designing and building race cars. That is much easier, they only go around in circles.
Gerald

 

That looks like a good and save plan.
Don't know abouth te cars though, I think I leave the fidling with my Alfa to others.

Arthur