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My intention now is to remove the sole roughly 3cm around the opening, grind out any fractured glass from the cracking and lay in many layers of triax and db.   No core is compromised in this area as it is all glass.  I will then replace the floor and let it make a horizontal column to further distribute the sideways load of the board.

 

 

Then I will also attack it in similar fashion from the outside, removing any fractured glass I find and rebuilding.  Glass and more resin are on order!

 

Thanks all for your input.  Martin - that is beautiful work on that trunk.  I'm surprised you have no sole in that area (or was it added later?)   I think the sole would be critical in distributing point loads from the dagger case....

No sole in my boat. None specified and my boat is small with some 1.3 m head room so adding a sole would not really add to comfort.

 

I see Tennant stuck to the same design we rejected back in 1985. There were a number of things we change in the structural engineering. The only things that have broken are things we did not change such as the cross beams.

 

Yes, the sole helps distribute the load but only from one side unless you wrap fibres around the dagger board case and spread them onto the sole.

 

Are you in a hurry? If not, why not spend some time on a bit of proper engineering before slapping on more material?

 

/Martin

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No sole in my boat. None specified and my boat is small with some 1.3 m head room so adding a sole would not really add to comfort.

 

I see Tennant stuck to the same design we rejected back in 1985. There were a number of things we change in the structural engineering. The only things that have broken are things we did not change such as the cross beams.

 

Yes, the sole helps distribute the load but only from one side unless you wrap fibres around the dagger board case and spread them onto the sole.

 

Are you in a hurry? If not, why not spend some time on a bit of proper engineering before slapping on more material?

 

/Martin

 

Not in a hurry - I'm out of the water for at least 4 months for winter   I certainly appreciate your Tennant experience and insights.  Winter will limit my glassing days though as the boat is outside.  So there is some sense of urgency.

 

The sole isn't much - 6mm exterior ply.  I have some 18mm carbon core (similar to Coosa) with which I might replace the ply.  Laying in uni to tie in the sole sounds like a good approach as well.

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So I couldn't help myself and started modelling the board-hull interaction:

Wildfire_hull_section_in_the_making_1.png

Very much work in progress and I can't guarantee the usefullness of the results but the idea is to load it up with some of those finite elephants and hopefully understand better where stresses go.

 

/Martin

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No FEA results yet but I have created an illustration to show the importance of having a healthy separation between upper and lower (boat bottom) supports for the dagger board:

DaggerBoardCaseSupportLoads.png

Figures are from my boat and the support separation in the drawings we bought is roughly 20 cm! The Wildfire design looks better in this respect but I think I would prefer even more separation in the interest of reducing material stress.

 

/Martin

 

PS Only using free and open software this time: LibreOffice on a Linux system.

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Interesting.   I see your point about having a longer daggerboard to potentially take advantage of a higher shelf.

 

Wildfire's shelf is 500mm above the hull exit.

 

I'm thinking some extraordinary event occurred to cause both the dagger to break AND the inner edge of the hull exit to crush.   A hard sideways impact of some sort.

 

I removed the floor in that area and layered up the inner side of the hull over the weekend.  it won;t crush again, at least not in THAT area!  I expect to start grinding on the outside over the next week.   The weather is down to 0 C this morning.   I'm sure that will slow progress for a while....

 

BTW, whether it was an intentional or accidental typo, "finite elephants" is funny either way....

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Fascinating!   I like your style, Brother!

 

The last slide is the most telling for me.  Without the floor, the left image shows a tremendous amount of stress on the hull bottom adjacent.  

 

The right image tells a lot too:   It "feels" like a significant wrap of "Gunstock" (Tennant's term for Uni) running between the hull and the dagger case and then back around and splayed out along the hull/floor would go a long way toward spreading that stress.  Are my non-technical instincts correct?

 

To take that further, it seems like the forces at the leading edge and trailing edge are huge.   The board seems to be trying to tear the boat apart in that area.   And in fact I did have a lengthwise crack both fore and aft in those areas.  The core was not wet, at least not yet.   I DO plan to put further reinforcement in that area.

 

Those cracks are in evidence here:

6bNIoZs.jpg

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