Ballasted Centerboard?

If you don't know about Mighetto ... consider not responding to his post ... he is waiting to take this thread to only he knows where.

 

Having read parts of his contributions, that's good advice. Water world, where's that? If he lives there then, how come these Q & As haven't occurred to him?

http://books.google.com/books?id=Y_...vYd&sig=UVxmp17OIU8livE-GmCR37l0z0Q#PPA269,M1

Pericles

 

Wouldn't a heavy centerboard rip out its case in the case of a knockdown, when it would swing back in?

 

Howdy Mr Dory,

With small boats it usually is not a problem.

With bigger ones it certainly can be - though normally if the case is properly designed the hull attachments are so much stronger than the top of the case that the damage is done higher up - either to the board itself or the case where they make contact.

it actually is quite amazing the forces that a properly designed and built centrecase can absorb with surprisingly little structure.

If the case is glued to both the floor and a bulkhead (either in the middle or the back of the case - plus some sort of web or structural floor at the front they seem to be quite failsafe up to quite big sizes.

But for bigger boats a lockdown mechanism - a pin or screw device or purchase or foam chock - all designed to break in a non serious mode if there is a serious collision can prevent it all falling back in the case.

This should be considered at any rate if there is much weight in the board as it will provide the stability that can help the boat recover from the knockdown.

Best wishes
Michael Storer

 

The case I've described above has metal floors, fore and aft. The forward end of the case also falls on a bulkhead. Being that the case, internal armature of the keel and centerboard are steel, plus the bulkhead and metal floor locations, I have little worry of the board causing damage in the event of a rough strike or grounding. The worst I'd expect is leading edge damage (which I also have a solution for) and pivot pin damage. Both of these aren't that uncommon in larger centerboard boats. The pin I've spec'd is twice the size necessary for the worst task I'd expect it to tolerate, which hopefully will thwart any bent pin issues.

 

When I read of these concerns about the ballasted centre board sliding back into its case, I am reminded of the origins of the beetle and Porsche. The decision to put the engine in the rear led to years of work to make the vehicles handle safely. Development over design is how I have seen it described. Engine in front Herr Porsche!

Thus the discussions about the centre board suggest to me that the sensible step would be to double the hulls for stability and comfort and drop the ballast. On another thread there is JCD voicing his concerns about righting a catamaran. Based upon the fate of Groupama lll, which floated so well upside down that she preserved the lives of all her crew and was recovered, I'd say that multihulls rule! Although, if she'd been a catamaran she would not have capsized in the first place, All that grandstanding, flying two hulls, bloody boy racers in their flash new tri. Mutter, mutter, mutter. In my day, we didn't do things like that! Drive around like lunatics. No respect for other road users. Grumble, grumble, grumble. Grouch, grouch, grouch.

Pericles

 

Pericle's, multihulls have their place, but most have understandable issues with them. I like mutlihulls and monos, having delivered and sailed many over the years, I have my preferences, but I've never seen a mono with a trap door in it's bottom (just in case). When a design has to look seriously at this particular contrivance, it leaves one to wonder (understandable). How would you feel if the next time you boarded an airliner, they made you put on a parachute (just in case)? Better yet, if Boeing made all of its future airliners with automatic parachute deployment devices. Not that it happens all the time mind you (say the wings have a nasty habit of falling off), but enough to force the designers to take serious consideration in it's regard?

 

PAR.

I'm not worried!

I'm a wing walker in my spare time. The times I have put my foot through the doped fabric of the top wing are too numerous to mention. I never wear a parachute and I fallen off eight times already this year.

I am also economical with the truth.

Best wishes,

Perry

 

Have a look at the various open class monohull race boats, 60's, 40's, mini's, etc. They all have escape hatches in the transom, which is perfectly reasonable. The Volvo 70 rule requires one hatch that is useable and above water when the boat is inverted.

With the growing predilection for modern monohull sailing yachts to lose their ballast keels, I would suggest that escape hatches would be a very good idea. Unfortunately folks might think twice about buying them if they knew what the stability characteristics are when inverted and partially flooded.

We have now seen 100's of production multihulls delivered on their own bottoms from South Africa to the Caribbean, with very few (if any) inversions. I would submit that the escape hatches in their bridge decks (not bottoms) are perhaps leftovers from a previous age? Once again a design feature dictated by market pressure rather than necessity. These new multihulls are purchased by neophytes, not experienced people. The experienced monohullers (like you Par) are telling them they must have an escape hatch......maybe

 

Consider a centerboard in the shape of a quarter arch.

Like a quarter of a round faced clock, where the 4.5 feet of leading edge is like one hand pointing at 7, and the other hand pointing at 10 being the 4.5 foot trailing edge.

Now consider the centerboard to be 1200 lbs. of steel, and the case also welded steel.

How should such a centerboard and case be built?

 

I've been looking for a nice cat-ketch to go cruising on, and this is one of the boats I've come across:


Click the picture for details.

1985 Herreshoff 31 Cat Ketch. Fiberglass hull built in Miami with optional 3' shoal draft! Honestly, I'd prefer the 4' draft version but the price is right on this boat. There is an Offshore 33 that I'm also considering which has a slightly deeper draft.

The Freedom 28 and 33 would also fit your description, as they have ~3' draft with their centerboards up. (IIRC)

 

Seafarer24, that Herreshoff is a beauty.

The below the waterline photo showed some sweet underwater lines.

But they didn't describe the centerboard, and i can only assume that, like the hull, it is fiberglass and probable a blade shape rather than steel semi-circle shape.

Am i wrong in thinking that a swinging semi-circle arc shape makes a stronger and more stable board than a swinging blade shape?

How do you feel about that cat-ketch rig in a north-atlantic blow?

 

MCM,

I believe your choice of steel is due to many reasons but durability must certainly be one of them. However boats built in steel need to have programmed into their design an allowance for loss in plate thickness due to rust (which will occur no matter how well kept the boat is), which is dictated by scantlings under "add x % mm per decade of boat life" or something like that. And this is why usually steel boats are built in the 50'+ range...
Also the eletrical systems bonding, and zincs number and positioning will have to be carefully thought of.

Cheers

 

ballasted centreboarders

If you are really serious about centreboaders, light displacement is the way to go. Here are three New Zealand champions from the late 1970's. Note their relatively small rigs and yet these boats were incredibly fast. Ballast was mostly in lead bricks internally with some lead in the board tips; they were daggerboarders actually and not centreboarders.
Farr's One Tonner Jenny H and Whiting's similar sized (approximately 37 foot) Smackwater Jack off Cape Colville - the other being launched (note the easy going low trailer) is Whiting's Half Ton champion Newspaper Taxi, a 30 footer. Now they were real sailing boats and some enlightened person should build them again.