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Mast sizes
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jingebritsen



Joined: 21 Aug 2002
Posts: 3277

PostPosted: Thu Feb 28, 2019 5:12 am    Post subject: Reply with quote

lotsa unanswered suppositions on this last page.

ss59: one points higher AFTER one has gotten up to top speeds. upwind ability is a combo of sail/board/fin/technique. i sail in lots of cross on conditions. need to have extra planing power in following currents in impact zone, yet still survive/thrive outside and on waves. back to kt/technique..... larger sails have their pluses and minuses.

GT:

loop and go is a convenience. threading a base is not a huge deal for most.

luff size issues are mitigated for folks like me that have matching masts. i can put a 430 top on a 460 bottom and get the between issues resolved. have you matching masts? another thing, as sails are becoming more commonly constant curve, having a stouter bottom half makes sails a bit more full down low.

i keep my SDM 400 on hand for storms. down haul the piss out of my smaller sails and do not suffer the leading edge collapse. this can only slightly be avoided by mixing RDM masts..... sail upside wind ranges are greatly enhanced, for me, by using my old 400 SDM.

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coachg



Joined: 10 Sep 2000
Posts: 2672

PostPosted: Thu Feb 28, 2019 9:52 am    Post subject: Reply with quote

GT,

They also make loop & go for the downhaul.

https://www.youtube.com/watch?v=1EQDuiSeCzs

Coachg
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GURGLETROUSERS



Joined: 30 Dec 2009
Posts: 2260

PostPosted: Thu Feb 28, 2019 11:02 am    Post subject: Reply with quote

Thank you, John and Coach,

I didn't realised that tops of same make RDM masts would be interchangeable. At present I'm using a Goya 70% 430, but a different make 60% 400. (Different ferrule diameter.) But I had intended upgrading to the Goya 70% 400 anyway, so that would suit me just fine. (Nice one John!)

I used to have a Pryde loop and go extension with the same two pulleys as in the one shown. But with the general change over to 3 or 4 pulley systems on bigger sails with their greater downhaul loading, I went down that path. But the one you show seems to be a winner. (Another nice one Coach!!)

I can feel that enthusiastic change coming on, and why not? Life can be too full of regrets, if we're not careful!
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grantmac017



Joined: 04 Aug 2016
Posts: 646

PostPosted: Thu Feb 28, 2019 12:54 pm    Post subject: Reply with quote

I don't keep anything rigged. Inserting the mast, clamping the boom and setting boom/extension lengths are at least 90% of my rigging time. Threading the downhaul really doesn't take a minute.
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ss59



Joined: 10 Nov 2016
Posts: 65

PostPosted: Fri Mar 01, 2019 4:20 am    Post subject: Reply with quote

coachg wrote:
GT,

They also make loop & go for the downhaul.

https://www.youtube.com/watch?v=1EQDuiSeCzs

Coachg


There is a newer version of the North XT, the 2.0, which works better for newer sails or sails with a pulley at 90degrees

https://youtu.be/DPbBmVTixlQ

or what I use for smaller sails

https://youtu.be/0gwQnFJhZhg
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GURGLETROUSERS



Joined: 30 Dec 2009
Posts: 2260

PostPosted: Fri Mar 01, 2019 4:35 am    Post subject: Reply with quote

Err, sorry. Quoted wrong sail for 400 mast and 28 cm extension.

Like most; ended up with too much mix and match equipment of different makes - or been sailing too close to our local 'atom box' bag of tricks (nuclear power plant, complete with wisps of steam from various openings and vents!) which is rotting my mind.

I meant my new 2019 Point 7 Spy 5.4 sail with 427 luff. (400 mast + 28 cm extension.) I use an SDM 430 mast in the 6.0 North Session sail. (Prefer that to the RDM in that particular sail.) but it too is a 'silly bugger' luff length of 455 cm, needing up to 30 cm extension. Hence the muddled memory.
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ss59



Joined: 10 Nov 2016
Posts: 65

PostPosted: Fri Mar 01, 2019 12:48 pm    Post subject: Reply with quote

jingebritsen wrote:

ss59: one points higher AFTER one has gotten up to top speeds. upwind ability is a combo of sail/board/fin/technique. i sail in lots of cross on conditions. need to have extra planing power in following currents in impact zone, yet still survive/thrive outside and on waves. back to kt/technique..... larger sails have their pluses and minuses.



I completely agree with what you say. h=However, if you imagine pointing very high, at higher board speeds the apparent wind moves closer to the nose of the board ultimately causing a stall or the need to turn off the wind slightly. At slower speeds, the apparent wind is less of an issue and therefore a higher pointing angle can be achieved. I have always thought that is why sailing dinghies can outpoint me - because they are slow. By the same logic, I can point higher in a lot of wind because my speed relative to the wind speed is less pronounced and therefore the apparent wind is less of an issue?? I genuinely dont know the answer but that seems to make some logical sense to me
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DanWeiss



Joined: 24 Jun 2008
Posts: 2272
Location: Connecticut, USA

PostPosted: Mon Mar 04, 2019 10:56 am    Post subject: Reply with quote

ss59 wrote:


I completely agree with what you say. h=However, if you imagine pointing very high, at higher board speeds the apparent wind moves closer to the nose of the board ultimately causing a stall or the need to turn off the wind slightly. At slower speeds, the apparent wind is less of an issue and therefore a higher pointing angle can be achieved. I have always thought that is why sailing dinghies can outpoint me - because they are slow. By the same logic, I can point higher in a lot of wind because my speed relative to the wind speed is less pronounced and therefore the apparent wind is less of an issue?? I genuinely dont know the answer but that seems to make some logical sense to me


Apparent wind moving forward does not cause stall, just a change in the L/D ratio. A sail stalls when the apparent wind is too far aft for the sail's sheeting angle. We often call this oversheeting.

You are describing Velocity Made Good aka VMG. Each boat/board has an ideal VMG related to their relative position to the mark. Slalom boards VMG in a narrower range than almost any other sailing craft because the slalom market rarely exceed 45 degrees from each other. FW boards likely have the largest or nearly the largest VMG angles of any planing hull. Conversely, they don't beam reach very well when setup to race WL courses.

Racing a keelboat for a 1-mile beat upwind is tough for any windsurfer in non-planing conditions because not only can the keelboat point higher for longer and at a more constant speed the windsurfer is much more sensitive to velocity changes and looses gauge in each transition from puff to lull and back. The only advantage for a windsurfer is the ability to tack and return to speed quickly, but at the loss of ground upwind. The keelboat will continue upwind progress throughout its tack even though it comes around more slowly. Yet this inertia requires time to create through the building of speed after a tack, so keelboats rarely tack on small changes in wind direction to follow or cover the windsurfer.

A dinghy may be outpointing you not because they are slow but because their lifting foils are so much larger and generate comparative L/D ratios at low speed through the water. The dinghy's comparatively large sail area continues to generate lift to drive the foils in light winds whereas even a Raceboard must be pumped upwind to keep up.

Every craft has its limit before loosing lift by pointing too high. Most of that derives from the sail's ability to be tuned for stability but the limit also derives from the amount of drag created by the hull and blades in the water.

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GURGLETROUSERS



Joined: 30 Dec 2009
Posts: 2260

PostPosted: Sat Mar 09, 2019 3:49 am    Post subject: Reply with quote

As you say Dan, a dinghy with a large centreboard, (and a yacht with a large keel), can outpoint a longboard in sub planing conditions. It always struck me that they have their centreboards (keels for yachts) near to the middle, front to back, of the hull, relatively near to beneath the mast base. The adjustable side to side rudder is the only trailing foil.

I wonder if that large rigid fin of the longboard was somehow steerable (by back foot on a swivel ) it would allow the board, in sub planing winds, to point higher without stalling the hull and sail drive?

The fin once snapped on my earlier racing longboard (Bic Be-Bop) leaving me having to sail back in on a cross/off day, using one foot either side (front and back) of the centreboard, to scissor the hull. The amazing thing was how sharp and reactive it was, and the incredible angle it shoot off into the wind for as long as I could keep balanced before it hurled me off. (Practice helped get it back in.) But it made me think that a small foot steerable rudder at the back, instead of a rigid fixed fin, would show a dinghy a thing or two in sub planing winds!

But then, a longboard not optimised for proper planing would be an abomination, which no self respecting windsurfer would be seen dead on! (Starboard can keep their Serenity!)
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