Technicalities

[persephone]

So,

I began making measurements to figure out if my boat is class legal. There are two items I am concerned about and am looking for clarification.
First, on the mast datum band the rules state the top of the cuddy as the reference point for the top of band 1 "excluding any bead or collar around the partner opening". Does this refer to the molded lip that rolls up from the flat surface of the cuddy top, or does this refer to any sort of gasket or boot to close the hole?
Second, the spinnaker sheave is located so that the "top of the spinnaker sheave shall be no higher than 15 feet 5 inches above mast datum". OK, so what is the 'top' of the sheave. Is it the highest point of the roller itself (the cheek) or is it the saddle that the halyard rides in (a difference of 3/16 or 1/4 inch)?
The reason I am asking these very specific questions is it looks as if my mast does not meet these requirements (spinnaker sheave). I may have to shorten my mast by as much as 9/16ths of an inch. I want to be absolutely positive that my understanding and measurements are exact before I shorten the mast.
Please, no speculation on this. I'm looking for concrete information.
Thanks.

[Phill]

Mast datum does not include the rolled lip the rises above the cuddy top at the mast step hole. So to see that band, if you have that lip, you must look down a bit into the hole. This assumes the rig is at sailing tension.

The haylard sheeve measurement is from the bottom of the sheeve saddle, not to include the cheeks. In other words, if you pull the line 90 degs out from the mast, the measurement would be the bottom edge of the line.

To fix the mast datum, you can simply apply the band a little lower.
This may aggreviate your spinaker halyard sheeve problem. On my first mast, I missread these rules and put the datum band at the top of the rolled lip, then measureed for the halyard and was out of spec. On my sheeve I modified the axle location inside the sheeve housing to get the roller part low enough to make it legal. Remember that the band for boom location Band 2, does not have to be a full 24" above mast datum. Mine is only 21" and my datum band is even with the bottom of the cuddy top opeinig. Loosing 9/16" of mast will not cost you any preformance. As you can see above, my mast is 3" short of max, and Len Fiock, 6 time Nats Champ is 5" short (and 25 lbs overweight). Doesnt seem to hurt his racing.

I would recommend that you sail it the way it is for now, and enjoy it.
If you are going to race it you will eventually want to to fix thsese things. Unless you think you are going to win from the beginning, or are going to Nats or PCC's//ACC's type championships soon, there is no hurry, most local fleets are happy to let you ease into fixing these kinds of things, and can help you with solutions.

phill

[persephone]

I feel a little silly.
I tend to think one dimensionally (so to speak). Of course I hadn't thought to just lower the datum band. But I think with the deck (not the lip) being the ref point and the saddle being the measure point my sheave just makes it.
I am planing on going to the NACR as well as other races, so I'd like to be all legal to start.

Thanks for the information.

[Phill]

Glad to help. My datum band actually tops out just below the cuddy roof, so that I can just see the top of the band from inside the boat. I set it up that way because I use a screw jack to tension my rig and dont want to raise it too high. The only mast measurement that I take all the way to the max is the 20'6"" for band 2 to mast top band.

Wish I could have managed to get to Cape Cod for NAC', but not this year. Have lots of fun, great group of folks in you area.

phill

[seandwyer]

Um...what's a datum band?

[GreenLake]

I think Phill means the band referred to in Section 7.5 of this document:

http://forum.daysailer.org/pdf/dsbylaw3.pdf