Daggerboard location on 9' fiberglass sailing Dinghy

Here is a still from a YouTube video from SV Florence and their 9 foot Spindrift nesting dinghy. The boat has an interesting mast step and air boxes as well.
Did you decide on a sailing rig?
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You could move the mast step and supports later on to balance out Center of Effort (CE), or different sail sizes or shape. The placement and weight of crew will also change the way the boat handles. It will be very tender so you will always be moving up the high side and fore and aft to balance it out.
These peanut shell prams had a lateen sail.

Folk *vastly* exaggerate the importance of mast and daggerboard position on small boats. As well as all matters of trim as mentioned above, you can also alter the balance by larger and smaller rudders and centreboards. Mast and board slot are a long way back for a small boat, but not I suggest, outrageously so. There are more extreme racers. A lot depends on how you visualise using the sail. If it will be mostly used for a relaxing drift downwind with two or three folk on board it probably doesn't matter a damn. My only concern is that if you will be sailing it on your own, and want to be able to sail against the wind then the mast and centreboard position will rather tend to force you to sit further back in the boat than would be ideal. Its good if the centreboard is a bit forward of the place you want to sit.

With the boat in this state moving the centreboard slot isn't that big a deal, and I think in your place I would do it. As for where to put it. Well, as I say its not very critical, but figure sailing on your own you probably want to be near the centre of the boat front to back. So the centreboard needs to be a bit further forward so its not clouting your knees. Maybe the back of the slot 12in to 18in forward of the middle?

Indeed, in a small sailboat without ballast and sailing with little heel ... the question of Balance when fitting sails and hull is practically dissolved.

And, on the contrary, a deep hull deep in the water and quite heeled can produce a large turning/Yaw moment, which must be compensated by moving the sails forward.

That is why the masts used to be around 30-40% LWL, that is: the rig so to speak loads its shoulder on what was called the Leeward Wave at the bow.

If you were to set the hull in water as it will be with crew and gear weight, rudder and keel you could push the hull sideways from a single point to ≈ approximate its center of resistance. Same with sails center of effect with a piece of cardboard cut to shape to approximate balanced on a single point.

Hi @ocad, how is your restoration progressing?

I bought a Davidson 9 in good condition a two months ago. I can share some photos and measurements if you might find them helpful.

Yours looks to be very different from mine, are you certain it is a Davidson 9?

@throoder , it would be great to see a couple pictures of your Davidson 9 boat with a few dimensions related to the rig. Please and thanks!

It looks to me that this boat started out as a rowboat, and someone decided to try to make it into a sailboat, but moved on before completing the project.

The problem I see here is the mast will step right in the best spot for the skipper to sit. And the dagger board slot seems to be closer to the stern than the bow.

My guess is that the builder intended a fractional sloop for the boat's rig. Even then there is a good bet he got it wrong.

I think a single sail rig of one sort or other will work with the slot and mast partner where they are.

But the skipper is likely going to have to sit either next to the mast or on the bottom of the boat, under the thwart.

It will probably be better to move the slot forward of the thwart and to put the mast forward of it. Then a mast partner plank can be secured at gunwale height to hold the mast up.