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Stress failure around a hydofoil kiteboards' Center of Gravity

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Stress failure around a hydofoil kiteboards' Center of Gravity

Postby lightandfrost » Wed Sep 11, 2019 2:15 pm

A hydrofoil kite boards' center of gravity(CofG) is a point normally forward of the mast between the front foot strap or preferred forward foot position and the point of mast installation. Riders pivot around this CofG when riding by changes in fore and aft foot pressure. The CofG position is a function of the installed fuselage angle on the mast. Lowering the installed fuselage angle on the mast so the nose of the fuselage is deeper in the water moves the CofG forward. Raising the fuselage angle on the mast so the nose of the fuselage is shallower in the water moves the CofG toward the rear.

Light and Frost(L&F) has now seen six(6) commercial kite boards all race types and two(2) of our kite boards built for onshore wind wave riding, begin to crack forward of the mast box or mast installation position near the boards' CofG. There appears to be allot of stress induced by this constant change in foot pressure around the CofG which in turn puts stress on the boards' hull bottom forward of the mast. In the race boards mentioned above, all were of carbon fiber and foam construction. The carbon fiber crystallized and lateral cracks began to form across the hull bottom of the board. When these race boards were opened, no stringer was found, as the board relied on the false assumption that foam thickness and the use of carbon fiber would provide the necessary strength. In our surfboards made with fiberglass, foam and stringers, the fiberglass actually buckled and the foam cracked, but the stringer did not break. Originally L&F considered these cracks found in their two(2) boards were just the result of the high stress put on the hull as the board beat its way out thru multiple lines of breaking wave and white water as we do not in general ride flat water. But when these same cracks were seen in race boards used in flat water riding, a trend seemed to be forming.

L&F are now reinforcing the hull bottom of all our hydrofoil kite boards with four(4) layers of 200 weight glass from the front foot strap rear plugs to just aft of the mast installation area. Since reinforcing this area, no further failures have been seen. Readers note that L&F is only interested in riding extremely rough water in and out thru multiple lines of breaking waves in mostly onshore wind conditions. Hence our equipment is designed for strength not speed. L&F has no interest in riding flat water or high speed racing therefore weight is of lesser significance. In the pictures provided below the white area of the green board is where the fiber buckled from the foam and was then repaired and reinforced. The second picture is a board L&F reinforced prior to use.

The mast attachment area is not covered here. L&F have two(2) methods, neither of which have failed.
Board IMG_20190810_124803.jpg
Board IMG_20190910_155841.jpg

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Re: Stress failure around a hydofoil kiteboards' Center of Gravity

Postby jumptheshark » Wed Sep 11, 2019 2:28 pm


You gotta stop this third person bullshit.

It seriously erodes credibility.

As to your point..... Well yeah, the stress is highest at the front edge of the plate or tuttle box. This is pretty well understood.
These users thanked the author jumptheshark for the post (total 3):
TomW (Wed Sep 11, 2019 3:26 pm) • faklord (Wed Sep 11, 2019 4:07 pm) • evan (Wed Sep 11, 2019 5:32 pm)
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