Many people are worried about what happens when a vertical drop dagger board hits the bottom at speed. Surely it will get damaged?!?
My experience is different – there is little damage on even fast boats and the dagger board is much more efficient because of the smaller slot.
I’m with Kai Mei on the dagger board being better than a pivoting board. It does offer a lot less drag and is much easier to fabricate and less prone to leaks and jamming. It also weakens the hull less.
Dagger boards and cases are also very easy to fabricate.
And no moving parts to jam, leak or break is nice too.
My BETH Sailing Canoe has a dagger board and is about the same weight as our PD Racers. But when it hits a rock or sandbar it can be going 3 or 4 times faster than a PD Racer will ever get to. This is not uncommon as I sail it on the lower reaches of the Murray River which has more than a few shallow spots and limestone outcrops. I also have a tendency to go exploring which does put protuberances at a higher than normal risk.
The energy involved varies with the square of the speed – so the energy trying to break things on the canoe will be 3 squared = 9 times greater than a puddle duck will ever see.
Over 10 years of use I have had to repair the centreboard two times – simply planing the trailing edge off the board and gluing a new one on and planing down to the original profile.
The case has never been damaged (always ensure it has good bonding area to the bottom of the boat by having a transverse frame glued to the back of the centreboard case. Something I do with all my designs.
The centreboard damage in both cases didn’t affect the day’s sailing either.
As far as the daggerboards on the OzRacers goes – I took one of our two up the Mooloola River and did prang with a mudbar/sandbar several times as I navigated the unknown stretch – the boat stops with no drama and no damage. Three times I hit a rock shelf (well I wasn’t aware it went right across the river so I hit it in three different places!)and it resulted in a small ding in the centreboard leading tip (which no-one else would be able to notice) and a small ding in the trailing edge where the board exits the hull.
So I wouldn’t worry about getting tooooooo technical with protecting damage from hitting things.
Most of the racing boats in Australia have dagger boards. Some just use a piece of garden hose threaded down the back of the dagger case and held with a single boatnail at top and bottom. The nail is only put through the back face of the hose – not through both front and back.
Tho’ most people don’t bother at all.
However if sailing a very great deal in water that quickly and repeatedly ranges between shallow and deep a pivoting board can be reassuring but not essential.
Best Regards
Michael