Michael Storer Boat Design

PD RACER FAQ

Weather and lee helm on scows - helm balance

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Sometimes scows and some multihulls require that the centreboard or leeboard be moved a bit further forward compared to a conventional monohull.

The reason is that most of the resistance of the vessel comes from the most deeply immersed part of the hull/hulls - which is the leeward side.  This unbalanced resistance tends to make the boat want to bear away so the board/s need to be moved forward to create an opposing moment in the opposite direction.

I was "reasonably" sure the position of the sail and centreboard would be OK and we had some latitude to change the mast position if there were problems.  However it ended up being a moot point - the PD Racer hull just doesn't like being heeled - because of the straight sides any heel just makes the corners of either or both of the bow and stern transom dig in slowing the boat badly.  So the boat is never heeled enough to move the drag centre to leeward as Bob was suggesting.



Bob Wrote:  Thank you for your letter.  I didn't know if you had any experience with straight sided scows. I learned to sail in one. And that ones designer put the leeboard where it would > usually go in a pointed skiff. It would not sail upwind at all until the board was moved forward.

Hi Bob,

I learned to sail in something quite similar by the sound – though with a centreboard - if you took A PDR, cut it down to a minimum hulldepth scow with 3' 6" beam and 40sq ft of sail you would have a Northbridge Junior.  Hullweight was about 45lbs

Here is a pic of a modern one - it has started to sprout most of the expensive trappings of a conventional racing dinghy.

Mine was quite a crude instrument - for example had a big rubber band as a boom vang - a particularly silly idea - didn't work very well – a bit of rope is much more effective:-)

A decade and a half later I spent a couple of seasons sailing an International Moth around - 11ft with 10ft wings, 85sq ft and a hullweight of 60lbs (it was heavy by the then standard of 40lbs).

Bob: BTW. On multis don't they move the mast further aft as well as the board?

Exactly.  It doesn't matter where the centreboard/Leeboard is in a boat - the rig just has to be sorta in the right place in relation to it.  The "sorta" is where the experience comes in - as you so rightly point out.

We'll have our boats in the water in a week and a bit - so ... proof of the pudding ...

And just be aware that I have never been wrong before ;-)

Best Regards
Michael Storer.




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