View Full Version : Mast foot position to go fast
19th June 2010, 09:43 PM
I keep on moving my mast foot back on my Starboard 160 Formula board and my JP Slalom pro 84 134 litres and it seems the further back you go the faster the board goes is that right?
I seem to be at the limit with the 160 mast foot covering up the hole completely and I seem to be sailing on the fin. I use 70cm stock fin with Naish Slalom 10 meter sail when the free riders are on 7.5 meter sails its great to be overpowered..
Getting the slalom board really going fast seems more of a problem any recommendations?
20th June 2010, 12:57 AM
Sounds like you are free sailing (vs racing), right?
Moving the mast foot back does indeed get you better speed, but you sometimes need
to move it forward (from the fastest position) to regain some control.
If you were racing and going really deep downwind and ultra high upwind, the F-160
would need the mast foot nearly all the way forward, but on free sailing courses (nearer
a beam reach both upwind and down) the board is actually faster with the mast foot
As far as your slalom board, the same applies. Move the mast foot back until the board
is at it's fastest, but move it back forward a cm or 2 if control becomes an issue (tailwalking).
The idea is to have a little wetted surface as possible at full speed, but at some point
control becomes difficult, and you need to increase the wetted surface a tiny bit to get the
best balance between speed and control.
Changing fins can help alot here.
On your formula board you might want to try a smaller 66-68 cm fin as these could be even
faster at your "middle of the road courses". Not good for racing upwind, but betterfor getting max speed.
Hope this helps,
20th June 2010, 03:33 PM
Apparently downhauling a sail a lot reduces the downforce it creates and makes the board ride higher and faster. Can you comment?
I know that with my RAM I certainly got the best speeds when I was breaking my back trying to get an extra cm of downhaul in.
20th June 2010, 09:53 PM
With modern twist off at the top sails, I'm pretty sure more downhaul (which gets you a flatter profile and more twist at the top) will be in all cases faster.
The only caveat is will you have enough low end power to get going?
If you sail in steady winds (and it sounds like you do not there in Hong Kong) trimming your rig for max top end is for sure the way to go, you just need to select a sail size that
will get you to max. speed.
In gusty winds, it's more difficult since you have to have the power to get up to speed so the flatter profile can give you the max. speed.
I do not know if it "reduces downforce", but I am sure that more downhaul gives you a better profile with less overall drag.
Moving the mast foot back also makes the board ride higher, with less wetted surface to reduce the drag even further.
Combine the two, and run right on the edge of losing control, and you will be your fastest.
Also running a smaller fin (one that will spin out at low speeds) and waiting for quite a bit of speed to develop before you really push the fin will reduce the drag even more.
Plus, to go your fastest, you need to sail courses below 100 deg. off the true wind so you really don't need to load the fin much at all.
"Going Deep" can be really scary, but it's where you will be the fastest.
Hope this helps,
23rd June 2010, 05:33 AM
Roger fins are espensive how small a fin can I use on my S/B 160, I weigh 70kilo and use a 10 meter Naish sail, 100% carbon mast and HPL boom?
23rd June 2010, 06:26 AM
Custom formula fins are indeed very expensive.
Older (used) custom fins and stock OEM formula fins are much less expensive.
At 70 Kg. I would think you could go down to around 62 cm safely.
64-66 cm would give you better speed and also most of your upwind capability.
Hope this helps,
23rd June 2010, 10:46 PM
I have the 160, weigh 78 kg and usually keep the mast foot about 2/3 back from the front. I move it about 1/3 back from the front if it is really windy and racing (over 20 knots with an 8.4 or 7.6).
I only use one fin - a Deb R13 70 medium. The custom fins have a much larger wind range than the stock fin. If you aren't racing, then you should go for a much smaller fin as Roger suggests.
However, I have found that in high winds over 20 knots, the water is so rough that I can't get enough speed upwind to benefit from a small fin (larger fin works better). Better Formula racers are better able to keep their upwind speed in rough conditions and could benefit from a smaller fin. Downwind, it's another story, a smaller fin will keep you from getting killed. I have had some hellish crashes racing downwind in 25 knots (1 meter waves) with the 70cm fin.
27th June 2010, 03:08 AM
I'm not on "the team", but I do have quite a few frustrating years under my belt. First, what do you mean by fast? Racing or flat water deep speed reaching are two different things. I believe the width of the board makes a difference with respect to where you place your mast foot. KP suggests placing it just forward of centre so I would assume that this suggestion is in the context of racing slalom boards. I've found that mast foot placement is a compromise. Placing it way back in some circumstances may allow for more speed at the expense of control, planing through lulls and full planing gybes, especially duck gybes since having it more forward keeps the board flatter and planning easier coming out of the gybe. Keeping it just forward of centre as KP suggests helps keep the nose down and stable when blasting through chop and under these circumstances is likely to be faster - a nose bouncing around in chop is going to eat speed. With wider boards like the formulas or Is 150 or 131 moving the mast foot to centre or less allows the board to gybe easier - I'm talking about slalom gybes and not duck gybes. In my opinion the further forward you place the mast foot on these boards the harder it is to initiate the gybe and you lose more speed during the longer drawn out gybe making it tougher to come out fully planing. Not a problem for the pros, but definitely a concern for the rest of us. It is tough to go fast when you aren't in full control, so control should be a primary concern and water conditions, board, fin and sail choice are all variables that need to be considered. Experimentation with mast foot placement will teach you what you want to know or perhaps just confuse you (and me) all the more - it is a balancing act for sure.
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