505 Rig Tuning – Craig Thompson – USA

Here’s an interesting view from Craig Thompson on tuning a 505 rig.

If you spend any time doing boat calibration/setup this weekend, I think it would be worth while to try to verify the consistency of the conventional rake measurement system. My suggestion would be to put your rig at what you think is the base setting of 25′-8″ and then measure your mast rake using the alternate method that Ethan Bixby came up with many years ago:

Without the jib hoisted, attach a tape measure to your jib halyard and hoist it until the zero mark is at the top of the boom black band. Cleat the halyard and swing it forward to the extreme upper forward corner of the bow, where stem, gunwales and deck all meet. Essentially the top forward point on the centerline of the bow. Rig tension does change this measurement slightly, but mast bend does not. Therefore it is much easier to check and relate rakes over a wide range of hulls and rigs.

Measurement range should be as follows:

Mast Rake Mast Rake
Measured Forward Measured Aft
3′ 4″ 25′ 8″
3′ 5″ 25′ 6″
3′ 6″ 25′ 3.5″
3′ 7″ 25′ 2″
3′ 8″ 25′ 1″
3′ 9″ 24′ 11″
3′ 10″ 24′ 8″
3′ 11″ 24′ 6″

My understanding is that when Glaser tuning guide was first developed with the west coast fleet, pretty much everyone was sailing a Larry Tuttle rigged Waterat which made it easy to compare setup. Now more than ever, we have people sailing many different boat types, and I think it would be an overall benefit to the class if we came up with a calibration system that was more repeatable.┬áThe standard calibration method has too many opportunities for error. Transom height, rig tension, how tight you pull the tape measure, mast bend, how high you raise the main halyard when attached to the tape measure can all significantly affect the intended reading of a given mast rake. I can tell you first hand because my old Waterat had a unique transom that was flush with Station 11 and was higher than the Waterat standard. This resulted in a reading that was about 2″ greater using the standard method. The Rondar transom geometry is different from the Waterat as well. In theory, Ethan Bixby’s system should be far more accurate and repeatable.

It would be interesting just to cross reference this alternate mast rake measurement and see how consistent people’s calibration is using the conventional measurement system. I hope you guys have a great weekend of training. I wish I could be there.

Craig Thompson e:iqcraig@gmail.com