Mast base position (and other things) for maximum blasting SPEED!

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

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.

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!

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.

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.