How to make a daggerboard breakoff in case of a collision?

Seems like you agree with my statement but misread it. A daggerboard is long parallel to the centerline of the hull and narrow athwatships. In a grounding the impact is usually from the front; along the long span of the foil. Cutting off enough of the long section to make the board break off before causing any damage to the hull would weakin it and make it fail in normal sailing or when recovering a capsize.

 

I reread your statement. I can't see how it could be misread.

None of the "long section" needs to be cut off.
A small notch in the leading edge, elongated horizontally would provide a failure path during a grounding.

The loading on the daggerboard during sailing is primarily from the side.
This would put one side in tension ( and the other in compression ).
The introduced flaw would not significantly weaken the wing during sailing.

I'm wondering if you may be envisioning a much larger flaw than me.
It could be as little as 1 cubic mm of material being removed.

For the record, I do not advocate introducing such a flaw.
But I find the idea intriguing and worthy of discussion.

Capsize recovery is a good point I hadn't considered.
However, I would maintain the small flaw would not cause a failure,
due to it's location.

Thank you Gonzo.

 

The daggerboard is likely to have a chord that is ten times as great as the thickness.Any stress raiser will encourage breaking at it's location but a longitudinal load would have to be enormous to lead to a break,and I doubt it would ever work as hoped.It might be a great deal easier to make a longer slot and to use a piece of polystyrene behind the board as a shock absorber.As ever,it's your boat and your choice and I expect several of us will be interested in reports of the behaviour of the proposed daggerboard.

 

I envision a flaw large enough to make the daggerboard break before it causes any damage to the hull. Otherwise it wouldn't make sense.

 

It would have to be a pretty severe blow.
But then you wouldn't have any centerboard at all.
Capsize recovery would be doubtful on the small boat.
And it may not stay upright long with no board anyway.

I wouldn't encourage it's implementation, but it's a thought provoking idea for applied engineering.

 

In the spirit of keeping it simple, the usual solution is a pivoting board for shallow areas where groundings are common.

 

My 2 pennies . . .

One of the benefits of a center board design, is that it can/will pivot up out of the way in a grounding or object strike. A daggerboard is typically in a rigid trunk, so any forgiveness will have to be in the daggerboard itself. This could be done with the portion of the daggerboard that is exposed below the hull to have a trailing edge hings and either a spring-loaded or break-away mechanism at the leading edge.

This brings back memories of my Sunfish days in instances where the daggerboard was not pulled up quick enough when beaching.

 

Center or daggerboard meaning is little bit confusing for me .

 

Memories of a nosedive?