What does mast rake angle actually do?

I've been wondering about this for a while as I have been experimenting. Does it just help stop the nose from going under in a touchdown, or does it help with in flight stability? I've been experimenting with various shims on my starboard freeride 150, from no shim up to a 2degree shim (total angle of approx 3.5degrees). I can't say I've noticed much difference in flight. The board has quite a bit of up curve at the nose, so I've never had an issue during touchdown even with no shim, the board always bounces up fine.

the foil mast fits better in the box with less angle on it, so I've kinda settled on a .5degree shim at the moment (mainly because my other shims have snapped). But wondering if I'm not suffering from nose dives if there is any advantage to more rake?

im mainly using small foils (starboard SLR 560 front wing is my fav at the moment), trying to break 28knots. Have the footstraps all the way back and mast foot all the way back, but still feels a bit back foot heavy, so wondering if more rake would help this at all.

any thoughts appreciated.

Select to expand quote

aeroegnr said..
I'm much less familiar with the flight effects but when it's really choppy, adding 1deg or so (up to 1.5) of nose up rake takes my board from incredibly difficult and scary to navigate over the chop to a lot more forgiving. I don't want to be in heavy chop with a 95cm wide board with zero rake because it's really hard to keep the nose from digging on the upwind or on a reach.

But the extra rake does affect takeoff and takes more power and aft pressure to lift, so if it's light wind I don't rake it at all.

What board are you using? Some of the newer boards: hydro, phantom, etc are really flat, so I can see how it would help with those.

If you've got the starboard evo mast (and a lot of the other brands foil sets have it as well), then there's a better than average chance there's already a decent amount of rake built in, but at the mast/fuse join as opposed to shimmed mast rake. Much less shim angle required (maybe none?) if that's the case. Idea behind it all is to stop heavy touch downs that can send you over the front.

I did try shimming out for a period of time with the iq foil (so no inbuilt angle). I found it counter productive. It actually just threw everything out of kilter and I had more touchdowns than usual amongst other issues. But it was on course race gear, and i didn't get too invested in retuning everything. There was too much wrong and the easy fix was ditch the shim. Probably a different scenario for foil slalom.

Select to expand quote

shaneNZ said..

starboard freeride 150............

Have the footstraps all the way back and mast foot all the way back, but still feels a bit back foot heavy, so wondering if more rake would help this at all.

any thoughts appreciated.

I'm struggling to understand why boards need any shimming to alter the mast rake. Brands, just put the box in the correct position and make your masts at the correct angle in the first place. For maximum strength, the mast head should be a perfect fit in the box. Why should you have to adjust the rake and make in a less perfect fit for better performance. If you are PWA standard, then adjusting for fine tuning is acceptable but on freeride kit its nonsense.
A local here had a Tabou freeride foil board and AFS freeride foil (v1), and there wasnt enough rake in the mast and the board sailed nose down. But he mixed brands. I have the same foil (albeit v2) in a AHD board and it was fine. He shimmed the mast and it now works. iirc I compared the rake of the foils and it was the same.

Another lad had a Starboard Freefoil 150 foilboard and a Starboard Supercrusier foil, both new and bought together, as recommended by Starboard on their website. He couldnt get it on the foil without a big gust, I was watching him on his first session on the kit, he was really struggling. The boards box/footstrap/mast track/foil fuselage combination did not work. He told me he complained to Starboard, they told him to buy a longer fuselage and took their recommendation off their website. Either the board or foil wasnt built to spec, or they hadnt tested the combination. Really bad customer support if you ask me, he had spent a lot of money as was told to spend more.
He put that foil in his Tabou RocketWide and as the footstrap plugs were further back it was ok. I dont know if he ended up changing the foil setup so he could use the board.

Important to distinguish between two moments:

-Before take off, more rake = less angle of attack, meaning that it is harder to pass the 'hump' to get onto the foil in marginal wind conditions for your setup, especially in choppy conditions (feels like the board is 'sucking you down').

-In flight, more rake = higher nose trim > better in choppy/wavy conditions, including going into the jibe (less likely to stick the nose in the back of the wave), and easier to recover from touch down. Note that the behavior of the foil itself (i.e. angle of attack of the wings, and delta between them) is unaffected by the rake once in flight. However, more rake does move the front wing slightly further back compared to your front foot position making the foil feel a bit more 'back footed', hence the feeling of more control especially on a reach. Conversely, for up/down wind course racing, you want all the lift you can get from the foil, so you'd normally want less rake than would be ideal on a reaching course.

Hi,

I have a different take on shimming. What it does is it alters not only the ratio of angles between the board, water flow and the front wing, but also the angle between the water flow and the back wing. The latter is the crucial bit.

The best way to think about it is to visualize this as an airplane. If I want the airplane to rise, I need to set the back wing (stabilizer) angle of attack so that that the rear edge of the back wing is higher that the fromt edge, e.g. like this: / (exaggerated example). What this does is it sucks the back wing down, and this changes the Angle of attack of the front wing to this: \ which of course results in a huge push up of the nose.

To make a long story short, shimming is crucial, and even airplanes have adjustable stabilizer angles. Otherwise you need to keep pushing at the back of the board to get up but maybe your balance requires you to be a bit more up front; or in airplanes - you would always have the controls pulled out all the way to your stomach. It is a way to set up a different static trim for the conditions and all other adjustments start from there. Think of it as a third (or fourth) leg which can apply a bit of pressure where you want it constantly.

Low wind - big shim
High winds - low or no shim

From my experience the les rake you have the more power you have in the foil, and the faster the take offs, but you lose a bit of stability in reaching and touch downs are harder.

For the iq foil settup im using iusually run 2 deg of rake. If its chopy, wavy and high wind i have gone up to 3.5 deg and it is noticabely more control and easier.

When you are up on the foil it only interacts with the water, so doesn't really change with mast rake adjustments. All you are doing is lifting or lowering the nose of the board relative to the rear end. When sitting on the water the board sets the attitude, then the foil will be similarly adjusted nose up or down with mast rake changes.