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Can't seem to keep foils on my boat.

 

I've got a long thread on boatdesign.net on this one, so no need to hash it out here I suppose.   I am exploring having new daggers CNC'd....

 

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Underengineered and underbuilt foils are far too common.

There is some information on this here.

 

I have enclosed a section that works real well. You can scale thickness a bit to fit your dagger board case. The first coordinate is cord and starts at the trailing edge (1) with zero at the leading edge.

 

Recommended for rudders too.

 

/Martin

prulsY.txt

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But first, I must repair the crushing around the dagger well.  I intend to lay 4 layers of glass on the sole, and then carbon core foam horizontally across the sole to tie into the opposite hull.  Then overlay four layers of cloth to make a horizontal column (and tripping hazard!).

 

Got any better ideas?  Clearly there is a ton of force in this area, and I think there a design or build issue in not having it supported from the back side.  this may have been in the interest of achieving headroom in the cabin....

 

6bNIoZs.jpg

 

6XXE3Ys.jpg

 

zahkfXa.jpg

 

 

KE4LPQx.jpg

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Having wake up coffee, so hope I make sense here.

 

Is it crushing or tension cracking? When going upwind, the base of the leeward board will be pushed against the inside of the hull, so your planned extra support will be a tension member?

Only if you are loading up the windward board upwind will in add significant support?

 

I would think filling in the other side of the case, against the hull, with more support might achieve more?

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Four layers of glass? What kind of glass and why?

 

Here is what we did 30 years ago instead of following Tennant's instructions. This has worked but I (now) understand there are even better ways of reinforcing this area of the hulls.

 

Some years ago there was a very long thread on the renovation of a tri called Timberwolf. Unfortunately all photos are missing now.

 

Having longer boards with the upper support further up in the dagger board case also helps -- less crow-bar like. My dagger boards reach deck even when fully down.

 

/Martin

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If none of the other boats have that horizontal beam then there must be a fix without it. What about just layering in 2000grms of carbon or some equally silly large amount. The area is tiny so any weight gain will be bugger all. That would depend on the floor and bits being sound enough that the problem isn't just transferred to them. 

 

Is there a core in the blade case laminate? Sure it's not that crushing rather then the whole case trying to move sideways?

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Having wake up coffee, so hope I make sense here.

 

Is it crushing or tension cracking? When going upwind, the base of the leeward board will be pushed against the inside of the hull, so your planned extra support will be a tension member?

Only if you are loading up the windward board upwind will in add significant support?

 

I would think filling in the other side of the case, against the hull, with more support might achieve more?

I think it is crush damage, as the damage starts in the middle of the case and radiates out. There is no tension connection between the middle of the board and the case

If it was tension, I would have expected crack to form at the ends and work in.

 

What is key here is understanding what the failure mechanism was:

  • too much flex in the bottom of the hull causing the fibre grass to break?
  • Opening in the base of the hull too large causing point loading of the board onto a part of the case?
  • localised crushing of the core behind the board (unlikely with ply, unless it has got wet and a bit spongy) ?
  • Loading of the lip causing a local shear failure of the edge taping?

Looking at the wear pattern on the antifoul, it looks like the board is loading up the very bottom most point. It might be worth building up with come high density filler above the lip to try and direct the load into the core of the hull, instead of into outermost skin...

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Nice carpet.

 

IMO crushed by the windward board flying a hull, on the angle of death, over waves, doing close to twenty knots.

 

Pull the board up more in these situations. Will also get more positive helm and able to come upwind in gusts rather than the boat veering of downwind and down the mine. Need to reinforce the case with a second shelf half way up or else the case will break next.

 

I do like the idea to lengthen the boards similar to Martin from Sweden and Hooters.

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Thanks Guys.  Below is the drawing showing the shelf etc, and it is built to plan.   The shelf is 12mm ply and supports the upper part of the board.   It has many strands of uni "gunstock" rope around it as well to tie it into the shelf and the side of the hull.   That part seems intact.

 

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.

 

The back side (inner side of the case) appears to be well bonded to the hull at this time, so no changes there.

 

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....

 

o3r4O5u.jpg

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Nice carpet.

 

 

 

Wise Guy!  Yeah, being a finish carpenter by trade, the builder did a few things very nicely.  That "carpet" is that mouse fur stuff - very light, but more inviting for guests I suppose.  Terrapin is a daysailor first and (hopefully) a racer second.

 

Here is a shot facing aft from the head in the starboard hull:  

 

UmeNgG7.jpg

 

He put that green KIWI grip on the floor.   I had to sand it off on the other side, and wow that stuff is tough!

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