I am getting too stiff in joints to be able to beach start with my board.
I don't remember ever seeing a board with say, 2 fins instead of one, which would be shallower and would allow me to start in shallower water.
Are there such things?
Surfboards have had them for decades.
RRD fireride's have twin fins, don't make anymore but Jez had one on Cocos island last week i think it was a 2010, very nice to ride and good when the tide goes down....
Hifly Madd
I've got two of these. They do let you beachstart in shallower water, and to get away with sailing in shallower water, but its not as different as you would expect. I think you can get away with fins 2/3 of the depth of a single fin for the same amount of lift.
I use weedfins on them all the time as I sail in some weedy areas and its easier to just use the same fins all the time. These also allow you to get away with shallower water.
If you really wanted, it would be possible to convert a board to twin fins.

It's had a hard life. I have had it for a few years now and the deck went soft, and then I replaced the fin boxes too, which is why it looks a bit strange around the finboxes.
"I think you can get away with fins 2/3 of the depth of a single fin for the same amount of lift"
Can anyone else confirm this?