DN boom

I am making an aluminum boom for my DN. Other booms I've seen have alot of ability to adjust the blocks. Why is this? It seems that because the blocks on the hull are not adjustable you would set the blocks on the boom to them and be done. What am I missing?

boom adjustments

I have adjustments on both. You could do it with only one and many serious racers do. I use the adjustments on the deck of the hull to match my mast when I move it back and forth and I use the adjustments on the boom for fine tuning and getting my set up correct. I haven't used a different boom position in a few years.

block adjustment on boom

To tune a DN for max. performance, the sailors move the mast fore and aft on the deck as much as four or five inches. Mast moves forward, compression from head stay increases, mast bends more, sail flattens more. And vice versa when mast moves aft. Also changing the position of the cup on the bottom of the mast changes the rotation and essentially changes the fore and aft position of the mast. Because the boom moves fore and aft with the mast, the relationship between the boom pulleys and deck pulleys change. It is necessary to be able to move the pulleys on the boom or on the deck, and some skippers move both. This is the very basic explanation.

The only mast-rotation contro

The only mast-rotation control is via the boom. If you move the boom blocks forward of the deck blocks, then as you sheet in (utlimately when the blocks "interlock" as the boom is sheeted to the deck) the boom will pull back on the mast track and cause the mast to "de-rotate". Conversely, moving the blocks aft on the boom will cause the boom to push on the mast, increasing rotation. Also note that the relative positions of the block on the tiller-post and the forward boom block has the same effect.

Aerodynamically, a more rotated mast generates more lift and drag, and it useful for accelerating (ex. at the start of a race). De-rotating reduces lift and drag, and is desirable to allow the boat to achive top-speed on good ice): http://www.tspeer.com/Wingmasts/teardropPaper.htm

In general, most DN sailors these days seem to favor somewhere between a neutral position or a bit of pull. A few favor quite hard pulling to really derotate the mast at high speed.


Geoff S.
DN US-5156/Laser 145234/Renegade 510