I'm trying to tune my blasting / freerace setup for max lawn-mowing speed on moderately choppy water. Fairly experienced skill level, 80kg.

Conventional wisdom says, move mast base rearward from the mast track centre point to go faster, until you are reaching the limits of control for given windspeed / water conditions.

My most used gear at my local spot is Tabou Rocket Plus 113 (72 wide) with twin cam 7.7 and 8.3 GA sails, 12-22 knt wind range (at a guess), 38cm carbon Z-Fins freerace fin.

I began setting mast base at the middle track setting recommended by Tabou. Since, I've gradually moved it further and further back, to the point the base is now right at the very rear of the track.

My speeds seem have got faster too, but maybe my experience has also improved? Regularly hitting 50 kph now.

However, even with the mast base in this position, the board is still not skipping out of the water on the tail at speed like this Mario K?mpel video @ 6:40


My board 'flies' at full chat fully powered up in a relatively flat position, even though with this setting with the rearward mast base position, only the very back section of the board remains in the water. Is this how it is supposed to be, or is my technique wrong somehow?

Oddly, when I was using the mast base in the recommended middle setting months ago, the board seemed more flighty and sometimes out of control on chop.

In this video with Karo van Tonder, reviewing the Severne Fox 105, she talks about putting the mast base 2cm forward of the mid point for maximum speed.


In this offcial Severne setup video for the Fox, Kurosh Kiani says for maximum speed, he sets the mast base 1cm behind the mid point.


I'm now running my base some 5-6 cm behind the mid point, yet in my mind it still feels that the board is possibly sticking.

So who is right, or is my technique at fault?

Try bigger fin and play around with sail downhaul

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choco said..
Try bigger fin and play around with sail downhaul

This^^^^


mast base position is only one piece of the equation. If you've moved the mast base all the way back and board is still sticking, then you can try bumping boom up and, wait for it..

more downhaul.

You may find that you end up bumping the mast step forward after playing with the two other settings.

bigger fin might also bea consideration, but try the things that don't invole a fresh purchase first.

I was going to suggest too big a fin with too much lift will drive the nose down. a factory fin in a rocket is possibly getting too big for really fast stuff..? So his 38cm (and better quality) fin, is probably ok in around 20kn?
idunno

Subsonic?

Take a look at the slalom tuning videos on windsurf TV they did a few years ago. All the Starboard sailors said they put the mast foot towards the rear of the track. The Fanatic sailors said they put it towards the front. Conclusion - they (brands) put the mast tracks in different places on the board, as different board/fin/sails wouldnt result in a massive difference like that.

50kmh/27 knots is ok for 2 cam sails, but not that fast. So maybe a larger fin for more lift. But as others have said, before splashing out on fins, try other things like raising boom height first. Are you footstraps as far back as they can go?

The Tabou Rocket Plus has a flat rocker profile and not a great deal of rocker at the nose. You wont be the first person to ask about it like this. My Exocet S3 was like this. It was sometimes a bit sticky and the nose caught in chop if not careful, but in the 6 years I sailed it only tailwalked out of control about 3 times. But I used it with Ezzy Lion sails, not the most loose leech and lifty sail on the market.
Mario's board has a shorter plaining flat and wont be as sticky because of it, but harder to control when lit up. As he said at 4:22, his board/fin/sail is too big.

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Mark _australia said..
I was going to suggest too big a fin with too much lift will drive the nose down. a factory fin in a rocket is possibly getting too big for really fast stuff..? So his 38cm (and better quality) fin, is probably ok in around 20kn?
idunno

Subsonic?

Ya could be. Traditionally i find a bigger (quality carbon) fin promotes lift in the whole board, and a smaller one can help settle the nose down if flighty. But you're right, cheap "supplied with" fins can be very hit n miss. A bigger cheaper fin with the wrong design may well hold the nose down.
then theres footstrap position to consider..


nah lets not go too far.

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Subsonic said..

Mark _australia said..
I was going to suggest too big a fin with too much lift will drive the nose down. a factory fin in a rocket is possibly getting too big for really fast stuff..? So his 38cm (and better quality) fin, is probably ok in around 20kn?
idunno

Subsonic?

Ya could be. Traditionally i find a bigger (quality carbon) fin promotes lift in the whole board, and a smaller one can help settle the nose down if flighty. But you're right, cheap "supplied with" fins can be very hit n miss. A bigger cheaper fin with the wrong design may well hold the nose down.
then theres footstrap position to consider..


nah lets not go too far.

I didn't even see he'd listed the fin. Z fins are supposedly quite good, not tried one myself, but 38 shouldn't be too far wrong with a 7.7. Probably a tad small for the 8.3 though? It'll function, but might not generate enough lift to get the board "floating" over the chop. Could be part of the issue?

8.3 might be a bit big for this board to fly it off the fin but 7.7 should be the sweet spot. the 38cm Z fin seems plenty big to me . maybe try moving straps all the way out and back for max lift.

Thanks all - really interesting and useful replies.

I think I'll try changing my boom height a bit. I'm currently running it about shoulder height, but maybe moving up to chin height would generate more lift? Will feel horrible when slogging though. I've tried moving the boom up and down in the past, but was never really convinvced it did anything in my experience, so I just settled on where it felt comfortable. The physics underlying supposedly generating increased lift by moving a boom ~2cm heigher on a 460 cm long sail, which is being held down by a 180cm tall, 80kg rider (me), never really made much sense to me to be honest.

I appreciate the 8.3 sail is probably a bit too big for the fin / board, I'm happy to accept that combo will never be optimal, but as you say the 7.7 should be right at the sweet spot for the rest of my set up.

38cm fin is the stock fin size Tabou supply with the board. The stock G10 fin is okay, noticably more drive than the Z-fin at lower speeds, but it gets rapidly uncontrolable at high speed in chop, and is probably a little draggy at the top end too. Upgrading the fin instantly gave me an extra 1-2 kts top end speed.

My foot straps are all in full race mode, outboard position - but not all the way back. Does moving them backward, say ~2cm really make a big difference?

In terms of downhaul, I fear sometimes I may occasionally have a tendancy to apply slightly too much downhaul, rather than not enough. I'm trying to keep that habit in check at the moment

Speculating here with a bit of bro' physics here, but is it possible that moving the mast base slightly forward could actually increase the lift available from the fin, due to an increase in distance (i.e. leverage) between mast base and fin COE? I understand that one remedy for spin out issues is to move the mast base forward, so following that logic, it would seem that the fin to mast base distance dictates lateral resistance (i.e. also potentially the lift) available from the fin?

Cheers all!

My 2 cents worth with two cam and race sails. To me it's all about control.
I've found the opposite with boom height. Higher boom gives me more early power in marginal winds. Lowering the boom when properly powered up loosens and lightens my board. Maybe it's because a lower boom gives me better control and makes me feel safer . The more downhaul, the faster I go , even though I'm losing power. Because I'm heavy , I'd rather rig bigger , with more downhaul. A under downhauled sail makes everything feel heavier. Also worth playing with the outhaul. For me , less outhaul is usually better because it makes the sail more grunty and more stable . If a nicely tuned rig feels just right , I don't notice it and can use all my concentration on fin pressure , posture and the bumps. There is no right answers. Too many variables. Kit , conditions and rider style. Experimenting is the only way. When trying something new , I do big adjustments so that I definitely feel the difference and then fine tune from there. Then ....there is always the thing..you can tune identically from one day to the next. One day it feels perfect, the next , all wrong. That's why it's important to me to understand what my tuning is doing and adjust on the day. Ratchet downhauls are ace

Footstraps back will help alot with flying. (if you're saying there is another 2cm of holes you can go back?)

Youve got all the right gear and it seems you know what you're doing. But it sounds like the board just isn't sitting on the fin when you go fast.

Having the straps back give you more leverage to load the fin & rail the board, by pressing on your toes on the back foot. This lifts the nose and the Windward rail a little bit, and reduces wetted area alot.

Go for straps right in the back, or one hole from the back if youre over lifting.

Yep. You might be on to something there with the footstraps.

Even though I have mine as tight as they will possibly go, my connection to the board still doesn't feel 100%. According to Guy Crib's Footstraps cheat sheet, for freeride blasting, the straps should be tight, so that only the toes are sticking out the end. I can't get my straps tight enough to do that, which is really odd because I have size 11 feet that are also quite wide. A German review of the Rocket Plus 113 also noted a negative point about the foot straps being difficult to tighten sufficiently. Perhaps mine are just old (4 years), stretched and knackered and probably need replacing?

I've also noticed this weird thing I do with my front foot, in that I tend to twist the heel of the front foot slightly forward from the footstrap and wrap it around the rail of the board. I'm not sure if that could be a cause of the board sticking? I think it's a weird adaptation I've made from the straps possibly being not quite tight enough, so that I wedge my foot into the front strap diagonally. As a result, I think it's possible I'm sometimes using my front foot to drive the board laterally while it is wrapped around the rail, rather than railing the board with only my back foot, pushing directly off the fin?

Thanks again! :)

When trying to get 40 knots on flat water, I was quite frustrated until I got advice from a 50-knot sailor. His main advice was to go against the conventional wisdom, and move the mast base very far forward. That worked very well for me, I picked up 3 knots to get close to 42, and for once was one of the faster guys on the water, instead of being one of the slower guys, as I was used to.

Perhaps moving the mast base forward won't work for you, but sometimes, it's worth going against conventional wisdom to figure out what works best for you. That said, when it comes to doing speed on 8+ m sails, a shoulder-high boom seems very low. If you need to put it this low for control, you might be better off with a smaller sail.

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AoetearoaSailor said..
The physics underlying supposedly generating increased lift by moving a boom ~2cm heigher on a 460 cm long sail, which is being held down by a 180cm tall, 80kg rider (me), never really made much sense to me to be honest.

Okay, as a Physicist I'll give that a go, and in my mind it is all about leverage. The sail has a pressure centre that represents the whole sail area, and this centre is normally positioned just above the highest possible boom setting on the sail. This means that when you are holding on to the boom, the sail can effectively rotate around the boom. The pressure from the sail above the boom is then counteracted by a pressure on the mast-foot. Thus a lower boom will give more downwards pressure on the mast-foot to the board.

Raising the boom by 2cm should then be compared to the distance from the boom to the pressure centre. If the pressure centre is located e.g. 20cm above the boom, then a 2cm movement is a lot (i.e. 10% at the boom clamp and roughly 6.7% at the position of the harness lines, if the clew position is left unchanged). This is best done by trial and error on the water, just move it upwards in steps of 2cm and you will feel the difference. In Formula racing I would often end up with the boom around nose height (when the mast is held upright), but once fully planing in the straps with the sail raked back this feels just right.

Adjusting the downhaul will move the pressure centre, more downhaul moves this downwards and rearwards (in general from an under-downhauled setting).

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AoetearoaSailor said..



My foot straps are all in full race mode, outboard position - but not all the way back. Does moving them backward, say ~2cm really make a big difference?

Speculating here with a bit of bro' physics here, but is it possible that moving the mast base slightly forward could actually increase the lift available from the fin, due to an increase in distance (i.e. leverage) between mast base and fin COE? I understand that one remedy for spin out issues is to move the mast base forward, so following that logic, it would seem that the fin to mast base distance dictates lateral resistance (i.e. also potentially the lift) available from the fin?

Move them back. You have your weight pushing down the board in front of the fin. Unless you are very tall, both front and back straps in the rearmost holes.

Moving the straps forward to stop spin out is a last ditch attempt to cure spin out, after all else has failed in order to take pressure off the fin. If you have a decent fin, you add pressure to it to encourage railing and lift. Moving the mast track forward to solve spin out is because you are moving the COE forward in front of the fin.

If the footstraps are too large, try putting some neoprene between the outer cover and the main strap/plastic strip.

?si=KVr_gYd0CuVMTgEX

See if you can borrow a high-quality fin, of the same size, but with more sweep. Even a (really good) delta fin might give you more pure top-end (MUF make a very fast one, and I hear good things about some of the Aussie customs).

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AoetearoaSailor said..
Thanks all - really interesting and useful replies.

I think I'll try changing my boom height a bit. I'm currently running it about shoulder height, but maybe moving up to chin height would generate more lift? Will feel horrible when slogging though. I've tried moving the boom up and down in the past, but was never really convinvced it did anything in my experience, so I just settled on where it felt comfortable. The physics underlying supposedly generating increased lift by moving a boom ~2cm heigher on a 460 cm long sail, which is being held down by a 180cm tall, 80kg rider (me), never really made much sense to me to be honest.

I appreciate the 8.3 sail is probably a bit too big for the fin / board, I'm happy to accept that combo will never be optimal, but as you say the 7.7 should be right at the sweet spot for the rest of my set up.

38cm fin is the stock fin size Tabou supply with the board. The stock G10 fin is okay, noticably more drive than the Z-fin at lower speeds, but it gets rapidly uncontrolable at high speed in chop, and is probably a little draggy at the top end too. Upgrading the fin instantly gave me an extra 1-2 kts top end speed.

My foot straps are all in full race mode, outboard position - but not all the way back. Does moving them backward, say ~2cm really make a big difference?

In terms of downhaul, I fear sometimes I may occasionally have a tendancy to apply slightly too much downhaul, rather than not enough. I'm trying to keep that habit in check at the moment

Speculating here with a bit of bro' physics here, but is it possible that moving the mast base slightly forward could actually increase the lift available from the fin, due to an increase in distance (i.e. leverage) between mast base and fin COE? I understand that one remedy for spin out issues is to move the mast base forward, so following that logic, it would seem that the fin to mast base distance dictates lateral resistance (i.e. also potentially the lift) available from the fin?

Cheers all!

Re boom height. I think mines about chin height although being short that can mean bottom of the cutout.
I use adjustable harness lines.If it's a patchy day I make them super long to allow easy hooking in subplaning and shorten as necessary as it gets stronger

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SurferKris said..

AoetearoaSailor said..
The physics underlying supposedly generating increased lift by moving a boom ~2cm heigher on a 460 cm long sail, which is being held down by a 180cm tall, 80kg rider (me), never really made much sense to me to be honest.

Okay, as a Physicist I'll give that a go, and in my mind it is all about leverage. The sail has a pressure centre that represents the whole sail area, and this centre is normally positioned just above the highest possible boom setting on the sail. This means that when you are holding on to the boom, the sail can effectively rotate around the boom. The pressure from the sail above the boom is then counteracted by a pressure on the mast-foot. Thus a lower boom will give more downwards pressure on the mast-foot to the board.

Raising the boom by 2cm should then be compared to the distance from the boom to the pressure centre. If the pressure centre is located e.g. 20cm above the boom, then a 2cm movement is a lot (i.e. 10% at the boom clamp and roughly 6.7% at the position of the harness lines, if the clew position is left unchanged). This is best done by trial and error on the water, just move it upwards in steps of 2cm and you will feel the difference. In Formula racing I would often end up with the boom around nose height (when the mast is held upright), but once fully planing in the straps with the sail raked back this feels just right.

Adjusting the downhaul will move the pressure centre, more downhaul moves this downwards and rearwards (in general from an under-downhauled setting).

Brilliant! Thanks so much for that very clear explanation. It makes some degree of sense now - and I now believe in the physics - I might actually feel a difference on the water, ha ha!

@PhilUK "You have your weight pushing down the board in front of the fin" - yep it probably looks that way, particularly with the weird thing I do with my front foot.

It seems like some subtle changes in boom height, footstrap position, stance and maybe also if I think about it - outhaul and harness line length / position - should really get the board flying as it should

As a last resort, I'll look at the fin.

Thanks again everyone...

I ain't a super fast sailor, but I think the fin is the first thing to look at. I have a JP Magic Ride 97 that I could never get to fly off the fin until I picked up a free 28cm free slalom fin a few weeks ago. Now it does.
Even a 30cm weed fin is an improvement on the 32cm fin the board came with.

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SurferKris said..
The sail has a pressure centre that represents the whole sail area, and this centre is normally positioned just above the highest possible boom setting on the sail.

That may be true for most sails (including large formula sails), but I doubt this is true for race sails that have a loose leech down to the boom, and most of the profile below the boom. But your explanation would be just as useful if the pressure center is at or below the boom. When rigged with a similar amount of loose leech, a larger sail with a longer luff length should have a higher pressure center, which would explain why larger sails are often used with higher boom settings (although I've heard from several top sailors that they instead rig their sails so the pressure center remains at the same height, so different size sails feel the same).

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MHSA said..
Footstraps back will help alot with flying. (if you're saying there is another 2cm of holes you can go back?)

Youve got all the right gear and it seems you know what you're doing. But it sounds like the board just isn't sitting on the fin when you go fast.

Having the straps back give you more leverage to load the fin & rail the board, by pressing on your toes on the back foot. This lifts the nose and the Windward rail a little bit, and reduces wetted area alot.

Go for straps right in the back, or one hole from the back if youre over lifting.

Yes, getting the windward rail slightly raised is critical in getting good lift off the fin. You may have to tighten your front footstrap so that your feet aren't set too deeply. This lets you roll your ankles more easily and get your board at the right angle. You will both feel the acceleration and hear the difference when the board gets onto the leeward tail. It might feel a bit loose to start with but you can then regain control with boom height and mast placement to keep the nose down.

^ @Jetlag Agreed! I'm definitely struggling with railing the board effectively. When I get it right, it feels great - the board lifts with this 'skipping stone' feeling. Other times, it can feel like I'm forcing it, and the wetted leeward rail seems to cause more drag.

Cheers!

SKIP ALL THOSE VIDEOS......

The advice is too generic. Every board and fin is a little different, so you have to test it yourself to be really sure (even half a mm of tail kick on 2 of the exact same boards can be one sails nose down and the other nose up... )

Z-fins have a LOT of lift so you want to play around a little with the boom height and mast track to get the nose of the board free. Its counter-intuitive but high lift fins (especially if they are "soft") can actually push the nose down of the board as they are generating lift at the back. To figure that out... you can try strange combos like putting the mast track further forward of middle but then having a really high boom, or the other way: track back and lower boom. Play around with it. What you're looking for is the sweet spot where the board starts to fly and rails itself. Let a bit of outhaul out so your backhand has a lot of pressure to really get it railing.

I like to set my front straps reasonably tight so I can control the angle of the board with my feet... almost arching my foot up in the strap to get it to rail (whereas my back straps are a bit looser so I can go in deep to keep control).

As a novice blaster myself. Here are my tips that jumped me to the next level.

Change board. I jumped on a proper slalom board and was fully lit up pretty quick.

More downhual, at least a pin or two above recomended 2nd hand sail numbers, you need to consider blocks take up room too. Rig up to the look of the sail.

Different sails make a big difference too. I have a mix of 3 and 4 cam and no cam free race sails, they are all beautiful sails in the right conditions.

keep board flat and leward rail if anything, keep sail upright, lean back close the door and hold on!!

Going fast is all about lifting the windward rail. Settings and techniques that help lift your windward rail are
- raise your boom
- move your mast base to the rear of the track
- move footstraps to rear holes
- pull your front foot up in the strap to help raise the rail
- when you have good pressure in your sail, bear away slowly, but maintaining the pressure.
- well designed fins
- full downhaul
- minimum outhaul, i.e full powerful sail just touching your boom.
When you have too much lift, i.e. loosing control, back off one or two of the above until you are on the edge of control.

We usually start lifting off when totally lit. These guys all sail 1 to 2m bigger than us.

Thanks for the tips and advice all. I've worked on moving my boom a whopping 3-6cm upwards from the usual position I was using, depending on sail size and that has really done the trick. The board(s) are all flying now!

Thanks especially to @SurferKris - for the physics explanation: now I understand the theory, I can actually see a real difference out on the water, lol

I have absolutely no idea why two of the fastest guys I know run their booms at the very bottom of the sail cutout, but I guess they must have some secret sauce I don't know about.

Anyway, I'm a happy sailor now! Cheers :)

Footstraps need to be at the back to fly more mate. You should do that first.