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Boom height vs Power.

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Created by olskool 4 months ago, 13 Jul 2018
olskool
QLD, 861 posts
13 Jul 2018 4:35AM
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Ok so im off on Windskate tangent again. So on windsurf dropping boom opens leach/ depowers.. Agreed? So why on windskate am i experiencing the opposite???
Use 4.0 Naish Hokua. If i rig boom as per normal i have 'X' amount power. Can pump ok. Now if i drop boom down to bottom of cutout (below my chest) i get MUCH more grunt from each pump. Granted there is more sail above boom so it feels heavier to hold. But definately more useable grunt.
All you vectors n angles gurus.. Whats going on here???

gorgesailor
111 posts
13 Jul 2018 3:22AM
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olskool said..
Ok so im off on Windskate tangent again. So on windsurf dropping boom opens leach/ depowers.. Agreed? So why on windskate am i experiencing the opposite???
Use 4.0 Naish Hokua. If i rig boom as per normal i have 'X' amount power. Can pump ok. Now if i drop boom down to bottom of cutout (below my chest) i get MUCH more grunt from each pump. Granted there is more sail above boom so it feels heavier to hold. But definately more useable grunt.
All you vectors n angles gurus.. Whats going on here???


Dropping boom does not depower the sail - though it may settle the board. The sail power is not affected by boom height IMHO. Given the same outhaul tension the clew position may affect leach tension which could affect power. On the other hand boom height does affect leverage over sail as well as weight distribution to the board which affect planing ability & even waterstart ability - neither of which apply to windskating.... However, I would guess the added area above boom may affect the pumping behavior? .... My best guess.

Mastbender
1794 posts
13 Jul 2018 9:12AM
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Agreed, the boom height shouldn't really effect the power, not considering pumping, but if the booms are low, you'll have less leverage on the rig, but more distance to pump, high booms, more leverage, but less distance to pump.

forceten
427 posts
13 Jul 2018 10:35PM
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I gently disagree with both above posts.


In lighter winds we are better off sliding the boom up as this will generate more lift as well as loosen the outhaul which results in earlier and easier planing.

Opposite : lower the boom, this I do only when severely overpowered, after tightening outhaul.

This 4.0 NAISH sail is from 2003..? Pumping a 4.0 seems a bit unnecessary if its that windy. A newer sail might alleviate the problem entirely.

gorgesailor
111 posts
14 Jul 2018 1:33AM
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forceten said..
I gently disagree with both above posts.


In lighter winds we are better off sliding the boom up as this will generate more lift as well as loosen the outhaul which results in earlier and easier planing.

Opposite : lower the boom, this I do only when severely overpowered, after tightening outhaul.

This 4.0 NAISH sail is from 2003..? Pumping a 4.0 seems a bit unnecessary if its that windy. A newer sail might alleviate the problem entirely.


NO .... you actually don't. Read more carefully.

olskool
QLD, 861 posts
14 Jul 2018 4:30AM
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WINDSKATE. Guys im using this sail in 3-10 kts on windskate. With low boom i FEEL n notice im going faster with each pump, getting more ooomph than with high boom. Granted its a bit heavier in the hands, more sail above boom. I just cant figure why. Seems back to front to what i experience when sailing on the water. Lowering boom slightly decreases power as it loosens leach tension. Normally I use it to finely tune the already set DH n OH setings. eg. Quick fix for flighty n overpowered. Why am i getting different result on windskate? Ive adjusted boom up n down many times. More power down low..Any ideas ???

Subsonic
WA, 1376 posts
14 Jul 2018 7:37AM
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olskool said..
WINDSKATE. Guys im using this sail in 3-10 kts on windskate. With low boom i FEEL n notice im going faster with each pump, getting more ooomph than with high boom. Granted its a bit heavier in the hands, more sail above boom. I just cant figure why. Seems back to front to what i experience when sailing on the water. Lowering boom slightly decreases power as it loosens leach tension. Normally I use it to finely tune the already set DH n OH setings. eg. Quick fix for flighty n overpowered. Why am i getting different result on windskate? Ive adjusted boom up n down many times. More power down low..Any ideas ???




Think of the rig as a lever, with the mast base being the fulcrum and the boom being the "lifting" point.

Bump the boom up and you (the sailor) have more leverage on the mast, but you get less movement/swing at the tip of your mast end.

bump the boom down and you have less leverage on the mast, but more swing at the mast tip when you pump because youve moved the "lifting point" closer to the fulcrum. Keep in mind theres a sail attached to your lever.

Pumping on a windskate is about direct speed increase, youre not trying to get the board to climb onto its bow wave, so you can feel the full effects of a lower boom.

Ian K
NSW, 2721 posts
14 Jul 2018 9:58AM
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Subsonic said..


Bump the boom up and you (the sailor) have more leverage on the mast, but you get less movement/swing at the tip of your mast end.




More leverage on the mast? Well the tension in your arms might be less but your leverage on the mast all boils down to how far you have your mass outboard. If your boom's high you may not be able to get your mass out as far. Lower your boom if overpowered, albeit with more tension in your arms and harness lines.

forceten
427 posts
14 Jul 2018 9:03AM
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I'm using the sail for a purpose it wasn't designed for. I don't understand why I dont understand

Beam me up Scotty

olskool
QLD, 861 posts
14 Jul 2018 2:26PM
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Subsonic, Copy that! Ok my arms are set length. So with the boom down low, when i pump im actually moving the mast tip thru a bigger arc than with boom rigged high. Makes sense. Its about 20cm lower than id ever rig.
But makes a huge difference to the power generated.... Chalk n cheese.

olskool
QLD, 861 posts
14 Jul 2018 2:36PM
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forceten said..
I'm using the sail for a purpose it wasn't designed for. I don't understand why I dont understand

Beam me up Scotty


Pull ya head out of your freckle! A wsurf sail is a wsurf sail.....Same principle works whether its on a skatey, raceboard, or slalom kit.
Just a lesson in Physics n Geometry dude....
Dont worry yourself, go back to sleep.
Leave the carpark carvin to me.

forceten
427 posts
14 Jul 2018 8:52PM
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olskool said..


forceten said..
I'm using the sail for a purpose it wasn't designed for. I don't understand why I dont understand

Beam me up Scotty




Pull ya head out of your freckle! A wsurf sail is a wsurf sail.....Same principle works whether its on a skatey, raceboard, or slalom kit.
Just a lesson in Physics n Geometry dude....
Dont worry yourself, go back to sleep.
Leave the carpark carvin to me.



The laws of physics , they apply to a board on water the same as a skateboard on a hard surface ? Resistance or cohesion the same ::hydrodynamics and all those fluid equations vs the lateral forces on those little wheels ?

Rather on the rude high scale side, one insult would suffice .

oh dear I left out a smiley face

boardsurfr
685 posts
14 Jul 2018 9:42PM
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Moving the boom higher lets you put more of your weight in the harness even is the power in the sail is not great. In marginal planing conditions, that can help to get planing faster (without pumping), and to stay on the plane in lulls.

If I have to pump a lot, or want to be able to move the sail around better (e.g. doing freestyle), I find a lower boom position works better for me. The angles (more sideways than up) just seem better.

That said, formula and slalom sailors on large gear supposedly use a high boom, and pump a lot to get going, in marginal conditions.

Select to expand quote
olskool said..
So on windsurf dropping boom opens leach/ depowers.. Agreed?


No. I've never heard or read that dropping the boom opens the leech (as opposed to using the lower grommet on sails that have 2 grommets, which definitely opens the leech). The point usually made about dropping the boom lower is to gain control. But don't take my word for it, check what Andrea Cucchi and Vincent Langer (PWA sailors and multiple national and world champions) say in Tricktionary 3:






LeeD
298 posts
15 Jul 2018 12:37AM
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On windskate, your wheels don't slide sideways like your fin does windsurfing.

olskool
QLD, 861 posts
15 Jul 2018 4:25AM
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LeeD, exactly. So all energy goes to forward movement. But thats not what im talking about. Pumping power is. Dropping the boom by about 10inches enables the rig to travel thru MORE air for each given pump. Got nothing to do with planing or schlogging n very little to do with leach tension as i previously thought. Its all about the geometry of windsurf rig. Subsonic explained it. SPOT ON...
As for all the replies about planing. Wake up, did you read the question?
Go try it on a WINDSKATE n you too can go where few others have been! Where else can a 4.0m sail be used in 3-8 kts wind to reach speeds of 15-17kts?
Mr Sulo, we seem to have a problem......

Basher
15 posts
18 Jul 2018 6:13PM
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It's perhaps important to ask what effect changing boom height has on sail power, but also what effect boom height has on sailor stance. Stance is the more important thing here: For example, if you have a high boom then you tend to hang off it more, meaning more of your weight goes down the mast to the mast foot and you have less body weight on the tail of the board. A high boom therefore can help early planing. We often lower the boom in windy weather or if over-powered because that increases body weight on the tail of the board, plus having the boom in front of you gives you more muscle control over the rig. Changing boom height means the boom sits at a different angle on the mast, effectively changing the outhaul tension, so in that sense, boom height has an effect on the outhaul setting of the sail - with a knock-on effect to sail fullness or lower leach tension. But does boom height effect leverage over the rig? I'd say not much. Most people just set their boom height to where it feels comfortable.

forceten
427 posts
19 Jul 2018 9:08PM
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Think ? He actually read its a skateboard ?

bc
QLD, 629 posts
20 Jul 2018 10:27AM
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just a thought but dropping the boom by 10 " is a lot , so with boom lower the mast can now "whip" more as you pump making the pumps more effective

olskool
QLD, 861 posts
21 Jul 2018 5:17AM
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bc said..
just a thought but dropping the boom by 10 " is a lot , so with boom lower the mast can now "whip" more as you pump making the pumps more effective



Exactly what im feeling. Im 6'2" n boom at bottom of cutout SERIOUSLY has more grunt. Its lower than my sternum. Stumbled across it setting up for kids windskate. Sounds odd i know but it means i can use a smaller lighter sail.(more manouverable) Pump it until apparent wind is effectively powering sail.

olskool
QLD, 861 posts
21 Jul 2018 5:21AM
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forceten said..
Think ? He actually read its a skateboard ?


Yeah, what he said!!!

forceten
427 posts
21 Jul 2018 8:48AM
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olskool said..

bc said..
just a thought but dropping the boom by 10 " is a lot , so with boom lower the mast can now "whip" more as you pump making the pumps more effective




Exactly what im feeling. Im 6'2" n boom at bottom of cutout SERIOUSLY has more grunt. Its lower than my sternum. Stumbled across it setting up for kids windskate. Sounds odd i know but it means i can use a smaller lighter sail.(more manouverable) Pump it until apparent wind is effectively powering sail.


10 inches would be enormous, think below the reinforced mast zone.
Froma normal height I doubt 10"would even be feasible

olskool
QLD, 861 posts
21 Jul 2018 9:04PM
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Forceten, not sure what sails you use. But every sail i have has a cutout well over 35cm(14") in length. Pretty sure the mast reinforcing would extend past ANY CUTOUT for a sail to be used with that length mast. Like ive said at 6'2" i have my boom high about 5-10cm from top of just about every cutout. So 10" is easily obtainable.
Watchu smokin boy?

Wing 11
WA, 90 posts
2 Sep 2018 3:56PM
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boom height has affect on sail power.

low boom looser leech =less power=more control
high boom stifer leech=more power=less control

If two clews which is just 2cm difference make change on leech,boom height(+/- 35cm) has more imact to leech.
This is pure geometry stuff.
put boom max up,make more tension to leech parts of sail ,thus more powerful..
(but this is so minor influence on leech,biggiest sail power/depower makes downhaul ..)

Try explain with hobby trifoiler sail,you see how high is boom attached to the mast,that position put more tension to leech area.
Imagine now if this boom stay horizontal,leech will not has tension any more,pure geometry...
so putting boom up, make sail more powerful=easy to catapult
(the same way like sailboat control leech with boom vang...)

trifoiler

peterowensbabs
NSW, 75 posts
3 Sep 2018 7:52PM
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forceten said..
I'm using the sail for a purpose it wasn't designed for. I don't understand why I dont understand

Beam me up Scotty


Easy tiger, why so snotty?



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