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Old Jun 23, 2011, 07:42 AM
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RGinCanada's Avatar
Guelph, ON
Joined Sep 2004
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Build Log
Gaff-rigged catboat "Dynamite"

It was suggested I mention the build log for "Dynamite" in this forum.

It is a 12" gaff-rigged catboat. If all goes as planned, it should sail in 4-6" of water. I guess we'll see
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Old Jun 23, 2011, 10:39 AM
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looks nice.....can a cat boat sail into the wind as well as a sloop?..just curious.....
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Old Jun 23, 2011, 12:25 PM
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With me at the controls, they would be about equal...

(of course that means absolutely nothing... I'm a terrible sailor!)
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Old Jun 23, 2011, 12:57 PM
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A catboat should be the equal of a sloop going to windward. Where a cat has trouble is on a broad reach or a run. W/o the jib to offset the lever arm of the mainsail boom, the cat has a strong weather helm. This means that the skipper has to hold the rudder hard over to sail a straight line, and a large rudder deflection always slows the boat. The weather helm can be reduced substantially, however, by raising the centerboard part way (true for both cats and sloops). So, a knowledgeable skipper of a cat could probably beat a inexperienced sloop skipper on all points of sailing :-)
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Old Jun 23, 2011, 02:12 PM
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I am pretty much a landlubber. All the plans show the centerboard as in 'Option A'. Is this the 'fully deployed' state, or is 'Option B'?

(I should mention the centerboard is drilled along the periphery of the curve, and there is a matching pin/hole in the centerboard trunk to lock the depth. If 'Option B' is valid, how is the centerboard kept in place?)
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Old Jun 24, 2011, 07:44 AM
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United States, MD, Severna Park
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A. On B, that shark fin on the board usually sticks up through the centerboard trunk in the boat. Judging by the size, there's probably a series of holes along it's trailing edge where a pin goes to hold it in the spot you want. Put the pin in the top-most hole and sit it down on the pin and the board will be in the position of option A.

Most production boats now will use a line to raise and lower the centerboard.

A centerboard on a small boat is to give it lateral resistance (keep it from sailing sideways) because small boat's tend to be very shallow an fairly flat bottomed with very little lateral resistance without one. It typically has nothing to do ballast and if there is weight in the board, it so it'll lower when you want it down, and not float back up into the trunk.
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Old Jun 24, 2011, 08:10 AM
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JerryTodd,

Thanks for that info. I had planned on fabricating the centerboard from brass for the added weight. From your comments, I guess plywood will do just as well. (or does the whole wind and water don't scale thing come into play here, and I'll need the added weight down low?)

I am planning on increasing the surface area of the centerboard by roughly 50% as a starting point.
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Old Jun 24, 2011, 08:36 AM
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For a sailing model you'll want something more like a dagger-board. You can make it removable and whatever length you need. It should probably be at least as long as the mast on your gaff rig. You probably wont need much weight to sit her where you want her in the water, so you'll need a deeper fin to get more righting-effect from the weight you have.

A little open boat like that will get knocked down a lot in gusts, and if you leave her open she take on water and sink. You should think about hiding some buoyancy inside and/or making the hull watertight.
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Old Jun 24, 2011, 09:05 AM
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Hmmm.....

This boat is intended to sail in a fountain-type pond maybe 6" deep, so matching the height of the mast isn't an option.

I plan on buttoning up everything forward of the cockpit, and filling the voids elsewhere with foam. For now, I'll leave the centerboard as a stub, finish the hull to the point where I can work out my weight budget, and then see what my options are.

I'm guessing that a small 800maH lipo, a micro servo for the rudder, and a standard servo for the sail will be all the electronics I need.
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Old Jun 24, 2011, 12:03 PM
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Lookin Good RG !
I am learning from this.
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Old Jul 22, 2011, 04:03 PM
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Parker, Colorado
Joined Sep 2008
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Any updates RG? Now that our titanic friend left i need entertainment!
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Old Jul 22, 2011, 08:34 PM
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Guelph, ON
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I recut the frames, and installed the bottom and sheer plank. Then I tried to install the closing plank. There is a lot of twist near the bow, and the plywood I chose just won't lay down.

I'm picking up some thinner plywood this weekend, and will hopefully make some progress.

In the meantime, I have another build on the go...
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Old Jul 22, 2011, 09:38 PM
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Great! Im interested in a simple catboat for my father, I have an RG and would like to sail with him. What plans did you use?
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Old Jul 23, 2011, 06:15 AM
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Basic plans are available in Dynamite Payson's Boat Modeling book, and the full set (for the real thing) are available for $40.00 at www.instantboats.com

I've tweaked the plans a little to make it R/C.
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