20170318

Mast Position

Reconsidered the mast position. The mast position determines many other decisions so we need to get this right.

The center of effort of the sail is 110cm aft of the luff and 90cm aft of the forward end of the mast foot. If we put the mast bulkhead at 120cm, CE will be at 210cm. This increases the size of the bow tank and allows a mast bury of about 36cm.

CLR should now be at 210cm minus a few cm to provide some weather helm. Let us say 205cm. The daggerboard will have a chord of 35cm and run from 187cm to 222cm. The daggerboard case runs between 180cm and 230cm. The extra length allows a robust construction and provides room to shift the position of the board if needed.

The thwart will run from 260cm to 290cm. This leaves 130cm to the aft bulkhead at 390cm. The floorboards should be about 5cm from the bottom.

The aft tank will fit a folded sea chart.

Clarification 26-10-2024

I realize that I have been unclear about the relative positions of CE and CLR.

• CE refers to the center of effort of the sail, calculated from the side view.
  The power on the entire sail is thought to be concentrated at the CE.
• CLR means the center of effort of the hull, more or less the turning point of the boat.
  The CLR for keelboats is traditionally calculated from the side view of the immersed hull, rudder and keel.
  Small boat designer Jim Michalak ignores the rudder and immersed hull, claiming that the big centerboard or leeboard is the pivot point in his shallow draft designs.
• Traditionally, the CE is positioned a few percent of the waterline length forward of the CLR. This is called 'lead'.
  Jim Michalak suggests to put the CE a very small distance behind the CLR to induce a little weather helm.
• I have followed the approach of Jim Michalak, because I believe that Hatseflats with its shallow hull pivoting around its large centerboard is more comparable with Jim Michalaks cruising dinghy designs than with traditional keelboats.
• With the CE at 210cm and the CLR at 205cm, the CE is about 1.5% of the waterline length behind CLR. This should be just enough to induce some weather helm.
  My experience is that Hatseflats is nicely balanced, but quickly turns into the wind if you take your hand off the helm.