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Grande Mastere Dreade

downwind boat speed

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Ok, this year my goal is to improve my downwid boat speed. I've worked on getting the boat balanced and a neutral helm.   Boat is 20' full keel, non-spin, using a whisker pole, fractional rig.  jib is  non-overlapping.

we have an open class and therefore everyone uses adjustable whisker poles.   what is the optimal length for the whisker pole?   as long as you can extend so the jib is board flat?   or minimize it down to  J length?  what shape of the sail should I be trying to achieve?     is there a formula?  

once I have that figured out, I'll be working on my angles or whichever helpful suggestions that come along.

thanks.

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Given you have a full keel, lets assume you are not talking about planing/surfing, but rather going DDW +/- 20 degrees at hull speed or fraction thereof? 

Best answer is to test: Boat speed vs pole length, vs sheet vs TWA & TWS

If you restrict to TWA = 180 then first guess would be you want to have an adjustable pole long enough to reach from mast a distance equal to hypotenuse of a triangle that is your "J" measurement, or 1.4 X J 

in lighter winds you may benefit from a slightly shorter pole, to allow some curve in sail, though that can be accomplished with sheet relaxation. 

 

 

 

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Folkboats trim their jibs absolutely flat when going ddw. In light air they  reduce wetted area by trimming extremely nose-down (crew sits on the bow in front of the forestay). In more wind you may try anything that extends your waterline length... maybe a neutral fore-and-aft trim but some heel? Don't know your boat but this may be a starting point. 

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Use heel to minimize rudder angle. Go to Cal 20 class site for pics of DW mast fwd. boats.

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Take a look at the formula the Star uses since they are the master of the whisker pole.  A quick check of the J measurement versus the whisker pole length and you could apply that formula to your boat.

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heel to weather.  with a big jib and small main you want the center of effort of the whole shebang (which will be heavily skewed toward the main because its bigger) right over the boat to keep the helm neutral

 

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2 hours ago, some dude said:

heel to weather.  with a big jib and small main you want the center of effort of the whole shebang (which will be heavily skewed toward the main because its bigger) right over the boat to keep the helm neutral

 

Plus, there's more pressure up there. 

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Carefull not to ‘barn door’ the sail, you need a sail shape, ie a little roundness, not completely flat

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many phrf regions allow for up to 1.5 of "J" for whisker pole.......

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Heel to windward to take load/drag off rudder.

Sit forward.

Play with pole lengths during two boat tuning.

Sailing by the lee isn't a bad thing. Good for chasing waves without gybing. It may even produce a little better thrust in some conditions.

Don't forget the main, let the vang right off so the leech opens up a lot.

Do what the winning boat does, use same pole length as them.

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Try this if your rules allow it! Look at the jib sail badge.

You might have a bit of trouble with RRS 54 though.

20792742634_941e987d49.jpg.a642e115b39c809fb3022e1c2d3ca57c.jpg

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PS - it permits much flatter sheeting of the jib if desired with a lot more control over the entire sail shape.

I've never come across it before seeing a Falmouth Sunbeam.

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thanks guys , all good things to work on ...   we do heel to weather to get the main up into the air, sitting forward as not to drag the ass of the boat in the water

(this is an 60's alberg design so some overhang on the back.. ) 

WCB got a specific link for the Star info, I'll do some searches to see what I can find..

Ncik

" Don't forget the main, let the vang right off so the leech opens up a lot. "

that statement goes against everything I've heard and read,  but I do let the outhaul out to max draft..

 

Rogerfal

I might be missing what you are trying to point out, is that the tack attached to the pole?  or the sheet running outside of the shrouds?

if the latter, what the hell do you do at the leeward mark rounding..

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7 hours ago, Grande Mastere Dreade said:

Nick " Don't forget the main, let the vang right off so the leech opens up a lot. "

that statement goes against everything I've heard and read,  but I do let the outhaul out to max draft..

 

Rogerfal

I might be missing what you are trying to point out, is that the tack attached to the pole?  or the sheet running outside of the shrouds?

if the latter, what the hell do you do at the leeward mark rounding..

 

Re the vang for me this is very condition dependent. In the light presumably you don't sail dead downwind instead coming up sufficiently to establish flow over the rig and then as the breeze increases progressively you sail more dead down wind. So to the vang, once sailing on a run let it off enough to let the leech open up so it isn't hooked and maybe a bit more, experiment with it and rely on your feel and observe your performance against other boats. As the breeze builds you will need to tighten the vang progressively otherwise the leech will open to much. I tend to work on feel and what it looks like and when it starts getting a bit sketchy (rolling too much) snug it on a bit.  Another thing to focus on is making sure you spend as much time in the gusts and favourable shift whilst bearing in mind your tactical positioning for the next mark. If you are the driver get one of your crew to help with this.

On the boat in the photo the vang is reasonably eased in about 15kts.

Another thing we can do is to throw the rig forward downwind (not as extreme as the Star but none the less forward of vertical). Exactly why this works I can't explain but suspect it helps to generate flow over the sail plan (please chip in if anybody understands this).

For ref the jib sheets are rigged the same as for upwind. As you observed the tack is poled out. The boats forestay serves little purpose once sailing. There is a tack line cow-hitched to the jib luff wire and then run back to the cockpit with 2:1 guys port and stbd to control how far back the pole is pulled. We tend to set the sheet and play the guy and tack line. It for sure works better than a jib poled out by the clew but to use this method you would need to be racing under SI's or class rules which disable RRS54.

I've never sailed a Star but observe they float their tack off wind and seem to have particularly long poles, both of which must give more control over the sail shape. Loads of good footage of them sailing on the Star Sailors League.

 

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7 hours ago, Grande Mastere Dreade said:

" Don't forget the main, let the vang right off so the leech opens up a lot. "

that statement goes against everything I've heard and read,  but I do let the outhaul out to max draft..

Yep, but it works. Well, it works on dinghies, teams racing, 10 races per day, 40 per day when training, if you didn't open the leech you were left behind. It will depend on the boat of course, so play with it. It shouldn't be obscenely open, but definitely not closed. We called it exhaust and it is a reasonable way of thinking about it. If the exhaust of your car was giving too much back pressure, your engine wouldn't produce as much power.

Slingsby sending it downwind.

 

Stars downwind.

 

 

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GMD

Out there in the future If it's any help just PM me if you want to ask / discuss more.

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21 hours ago, rogerfal said:

 

 

Another thing we can do is to throw the rig forward downwind (not as extreme as the Star but none the less forward of vertical). Exactly why this works I can't explain but suspect it helps to generate flow over the sail plan (please chip in if anybody understands this).

 

 

You guessed it. By having the rig forward of vertical, it allows the wind to flow up and over the sail rather than being a barn door.

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