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Mast position on long DW sup foil boards

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Created by AUS126 Two weeks ago, 8 Feb 2024
AUS126
NSW, 192 posts
8 Feb 2024 8:24PM
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On DW boards what is the distance between the board plus foil centre of gravity and the centre of lift of front foil?
I have my centre of lift position about 50 to 75mm forward of centre of gravity position on both my long prone and wing board. In this position I can handle pop up and board stays level when I'm turning.
To my eye, masts on your sup foil boards seem to be maybe 200mm in front of balance point (except for maybe the barracuda). Is this just an illusion because of the narrow tail and the fact they have more volume forward?, or is the seperation between the two getting bigger?
Boards are much more nimble with mast forward but I'm not sure how far I can push it.
Thanks

NordRoi
619 posts
8 Feb 2024 11:57PM
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I think, it depends of the shape. Where you want to paddle...is probably where you want to fly, so you don't have to move your feet after lifting off? Good question. If you have all the weight at the back, a large chunky heavy tail and a super slim nose...further in front would bring you further away from the heavy part...would you feel more nimble?

JonahL
36 posts
9 Feb 2024 3:12AM
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Not sure this answers your question because I don't go by balance point, but my 8'2" has it's total volume center at 48" from tail, expected static CG about 45.5" from tail (nose out of the water, tail pretty much awash) and the center of the boxes are at 33", so just about 12" behind the expected CG while standing on the board. This setup is good with the mast pretty much right in the middle of the box with back foot right on top of the mast

AUS126
NSW, 192 posts
10 Feb 2024 5:26PM
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Maybe I should have asked if boards are balanced tail heavy. I'll pick up a few when I get the chance.

Foilmate
VIC, 22 posts
11 Feb 2024 12:59PM
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The weight will be around the foil boxes with high density foam/ a few layers of carbon, minimal weight at the nose.
So in theory they are 'tail heavy'

Beasho
236 posts
15 Feb 2024 3:11AM
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Measuring from the tail of the board should have gone out of style when Kai Lenny's chopped off the tail of his race board 8 years ago. This is more true with the longer downwind boards.

We are flying aircraft. There is a Center of Gravity (Mass). Essentially it is the balance point of the board. Your feet will straddle this natural Balance point like a seesaw. The Center of Gravity has to be slightly AHEAD of the Center of Lift to be aerodynamically stable. The Center of Lift is ~ the 1/3 Chord point on the foil. This is 1/3 the way back from the leading edge of the foil to the AVERAGE Chord.

Fortunately with Axis gear this corresponds well with the front of the Axis Fuselage.
Key assumptions:
1) Your feet should straddle the Center of Balance of the completed Board making the CG of Person and Board the same
2) The Center of Lift is the 1/3 Chord point of the Airfoil (Front Wing)
3) The CG should be 2" in front of the Center of Lift


AUS126
NSW, 192 posts
15 Feb 2024 7:12AM
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Select to expand quote
'The CG should be 2" in front of the Center of Lift'
Great. That's what I was after. Thanks Beasho and others.

Hwy1North
129 posts
15 Feb 2024 4:53AM
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Select to expand quote
AUS126 said..

'The CG should be 2" in front of the Center of Lift'
Great. That's what I was after. Thanks Beasho and others.



Sounds like maybe you are shaping a new board? Good idea to follow the guidline above and use 16" tracks. I've had a very difficult time finding the right spot on a 6'9" FFB Dagger that I wanted to use for prone and wing (it's way too small for me to sup paddle.) Using the Gofoil V2 mast and a large front wing, the best I can do is as you said, "about 50 to 75mm forward of centre of gravity" due to track placement. This would be fine for sup paddling and winging, but for prone it's all wrong on this board, perhaps not being designed for my weight or usage, or a Gofoil V2. I suspect Beasho may be correct even though it would appear the mast would be too far back if I could move it there... Given the major differences in body types and foil lift spots, the 16" tracks would be very helpfull.

Beasho
236 posts
15 Feb 2024 10:41AM
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I had run these numbers a while ago. But I have the advantage of 2 other board builders in town. They have built 30+ boards, and I am on board number 3. We would argue a lot about these placements. However we have come to a consensus on these measurements and are usually within +/- 1".

That said I did use a 16" set of tracks in my latest build. It is shown in these views. The 16" Chinooks allow for the advanced + fuselage and even more shortening if necessary. The box butts right up against the Center of Gravity, shown as Center of Gravity (CG) drawn on the board.

My set up is using the Advanced model e.g. 40 mm shorter and therefore set 10.5" from CG to Center of Mast shown.




rgmacca
386 posts
3 hours ago , 26 Feb 2024 6:09AM
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Select to expand quote
Beasho said..
Measuring from the tail of the board should have gone out of style when Kai Lenny's chopped off the tail of his race board 8 years ago. This is more true with the longer downwind boards.

We are flying aircraft. There is a Center of Gravity (Mass). Essentially it is the balance point of the board. Your feet will straddle this natural Balance point like a seesaw. The Center of Gravity has to be slightly AHEAD of the Center of Lift to be aerodynamically stable. The Center of Lift is ~ the 1/3 Chord point on the foil. This is 1/3 the way back from the leading edge of the foil to the AVERAGE Chord.

Fortunately with Axis gear this corresponds well with the front of the Axis Fuselage.
Key assumptions:
1) Your feet should straddle the Center of Balance of the completed Board making the CG of Person and Board the same
2) The Center of Lift is the 1/3 Chord point of the Airfoil (Front Wing)
3) The CG should be 2" in front of the Center of Lift



A question on balance point. if I shaped a board and rested the mid point on a broom shaft so that it was balanced like a see saw, would this be the balance point. If I then added a HD foam track block where the MM position would be middle of track (under back foot) would this then alter the balance point. In the past I think where my feet would be and put the tracks under back foot position. So far so good. Thanks.



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"Mast position on long DW sup foil boards" started by AUS126