Is the centerboard necessary?

[GregH]

It is my understanding that the primary(only?) function of a centerboard is to provide lateral stability- that is, to keep the boat from sliding sideways when sailing anywhere but directly downwind. If this is the case, could it be replaced by increasing the depth of the keel and skeg by an amount equal to, or greater than the surface area of the centerboard? My reason for asking is this: I've just begun building my version of Wm Garden's Tom Cat, and would like to do away with the centerboard. This would provide for a completely unobstructed cockpit, and also allow room for an inboard electric auxiliary drive. Deepening the skeg would also provide room for the aperture for the propeller. I've read of several Catboats that are without centerboard, but could find nothing about their sailing qualities. Obviously, this idea is counter to the overwhelming consensus of sailboat designs, but I thought I'd run it up the flagpole, and see if anyone salutes it.....or shoots it down!

[cs]

Yes you can compensate for the lateral resitstance by keel and skeg. Look at the Weekender for example. It was first designed with a centerboard but after further review it was determined that the keel gave it enough lateral resistance.

But be carefull and take that with a grain of salt. Each boat is different and has different needs. Another thing that a centerboard can do is get heeling resitance down lower to help with righting momement.

Chad

[paladin]

yup...it's done all the time.....you can take any proposed internal ballast and put it outside, build a stub keel outside, increase the lateral plane as much or possibly more with the keel and even change the sail plan..... for instance.... a couple of the plastic catboats with centerboards were built with external "keels" using about 500-1000 pounds of ballast.....the rudder depth was increased.....but....you may need to shorten the boom a couple of feet to rebalance...or you can convert the cat rig to a "Noank Sloop"....lotsa things....talk to the designer if possible or someone really familiar with his work.....

[P.I. Stazzer-Newt]

... Another thing that a centerboard can do is get heeling resitance down lower to help with righting momement.

Chad

Nor strictly true, moving the lateral resistance downwards (all else being the same) will cause the boat to heel more.
But (there's always a but) usually the C.b. is heavy and moving the weight downwards will cause the boat to heel less....

Its never as simple as it looks.

[Larry P.]

greg eliminating the centerboard would greatly affect the windward capabilities of the boat. The surface area below the waterline is not the only consideration, the location of that area of lateral resistance is also important. By lowering the skeg you would be shifting the resistance aft. This could result in a lee helm which is not normally a desired sailing characteristic.

When dealing with below the waterline design elements I would suggest keeping to the builder's design.

[Dan McCosh]

A centerboard is simply an underwater foil that can be lifted out of the way to reduce draft when necessary or desireable. If you don't need it lifted, it could be fixed permanently, and would be a fin keel. You could also design other underwater foils, keels, etc. to do the same job. To keep the performance, or improve it, would take some redesign, but wouldn't be all that hard.

[Joe ( Cold Spring on Hudson )]

Greg obviously I'm new to catboat sailing but I have a LOT of hours under my belt already. Here is my impression of what a large Catboat center board does. #1 yes it provides lateral stability to keep the boat from sliding sideways when sailing. But get this, occasionally I raise the sail in a blow and have not dropped the CB first. When I do that Tidbit will heal over far more without the CB so in my case the CB also acts as sort of a keel. I know I can take on more wind with the CB down.

Additionally in my tidal waters the CB is required to point. Also makes approaching a dock or a mooring much better.

The only thing I wish is I had a little winch to micro adjust CB that would be wonderful.

[Andrew Craig-Bennett]

I would be very reluctant to do away with a centreboard.

Yes, the boat will still sail to windward - sort of. She will make much more leeway and will be a brute to tack. She will no longer dry out as confortably.

As has been said, it is not so much the area of the centreboard as its depth that makes the difference. Which is why modern boats have short, deep, fin keels.

[Thorne]

I believe there are some larger cats that don't have centerboards, but doubt that they point very well -- and are probably significantly wider for their length than your Tom Cat.

As above, stick with the plan, man!

;0 )

Any fooling around with the design can result in poor sailing characteristics, dangerous unbalance in the rig, and/or expensive modifications to sail, mast, and hull. As they say here, "Don't ask me how I know this..."

[Ian McColgin]

The question was not simply dumping the board, but replacing it with keel and deeper skeg and rudder. And adding a motor , batteries, and all.

I'd ask Garden!! It or something such can be done but you're getting such a different boat with different weight and weight distribution that she might turn into a real dog unless the lines are a bit compensated.

Personally, I'd not do it that way, as Tom Cat is about as perfect a set of choises as you can get. You really want a keel boat to desecrate with a motor, maybe a doughdish or something is the ticket.

G'luck

[ken_nyus]

[...] and also allow room for an inboard electric auxiliary drive[...]

Hey Greg,

Just had an electric inboard installed in my 16ft catboat. We went for the first sea trials last week, and if all goes well the boat should be in my slip tomorrow. If you need information on my set up, let me know!

[KAIROS]

Minn Kota has some new electric trolling motors which could be mounted out-of-view on the transom or even on the rudder (providing excellent manuevering, though stressing gudgeons).

I envision making a sliding bracket so that in use the prop is lowered and at the dock the unit is raised so it does not need to be submerged all the time.

Check out this before modifying your design to accomodate an inboard. One of the smaller single prop motos might work well:

http://www.minnkotamotors.com/products/motors/detail.asp?pg=sem

[Boatmik]

I would be very reluctant to do away with a centreboard.

Yes, the boat will still sail to windward - sort of. She will make much more leeway and will be a brute to tack. She will no longer dry out as confortably.

As has been said, it is not so much the area of the centreboard as its depth that makes the difference. Which is why modern boats have short, deep, fin keels.

Good points.

Michael Storer