Tuning the mast on a DS II

[rkennedy]

My sails were pretty beat so I bought new north sails.
I went to the tuning guide at the north site and by the second paragraph I was already confused.

MAST RAKE AND SHROUD TENSION
To measure the aft rake of your mast, hoist a tape measure on your main halyard and hold it tight at the intersection of the transom and rear deck. This measurement, without your jib up and your rig set “snug” (no play in any shroud or forestay), should be 24 11” to 25’ 1”. Then hoist your jib and pull the rig forward through either a magic box, a block and tackle, or using the forestay (as a bow and arrow effect) until you achieve a 25’1” to 25’2” measurement at the transom. With this rig tension (approximately 150 lbs on the shrouds) the leeward shroud should not go slack until the wind velocity is approximately 10 mph. This may require more rig tension than you are used to carrying, but this tension is important in keeping the jib luff sag down to a minimum for maximum speed and pointing capability.

My 1st question is when measuring from the top of the mast to the transom rear deck do they mean the bottom of the transom where the floor meets the transom?
Or the top of the transom. I measured my mast from the top of the mast to the top of the transom and it was 25'1",
If the measurement is supposed to be to the bottom of the transom then wouldn't the DSII have less distance because of the elevated floor? Or does the bailer equal things out?

[GreenLake]

The top of the transom, and it looks like your measurement matches the range they give, so you are fine.

Another way to confirm whether your rake is set correctly is to sail the boat and notice whether you have to pull hard on the tiller going upwind (too much weather helm) or whether you don't feel any pull even as wind pipes up (too little weather helm). You should not need more than 5° rudder deflection to keep your boat from rounding up.

Given your measurement, I would expect your boat to be pretty balanced.

Many jibs nowadays contain a luff wire or equivalent bit of Dyneema that can take over the tension provided by the forestay. That allows you to fine tune the luff tension (and sag) with the jib halyard. You may want to rig a simple halyard tensioner.

Here's a pretty crude 2:1 tensioner (blue line) that pulls on a loop fixed to the jib halyard.


(Click on image to enlarge)

I use a single block with a simple hook which makes the tensioner easy to connect after raising the mast.

[rkennedy]

Thanks Greenlake.
To use that halyard tensioner do you have to have the wire in the jib ?
I assume that if you are going up wind and pulling on the tiller more that 5 degrees then you would use the tensioner to move the mast forward?

Thanks

[GreenLake]

The jib is the second I got from the same sailmaker (now retired). The first one had an actual wire, but for the second he switched out the wire against Dyneema rope which is just as strong as wire of the same diameter, but much lighter. So, in that sense, yes it has a luff "wire".

There are two independent things to tension on a jib: one is the tension in the "wire" from which the luff is suspended, which determines the "sag" and with it the shape of the luff. The other the tension in the cloth itself, this determines things like folds in the cloth.

On jibs without integral luff wire, the cloth tension is set by the halyard and the "wire" is the forestay which on our boats cannot be adjusted in tension underway. On jibs with a luff wire, the sag of the jib is controlled by the halyard. There's a separate "tack line" that you could rig to pull on the bottom forward corner of the sail cloth (just like a Cunningham for the main). Pulling on that would straighten the cloth independent of the tension in the "wire".

Now, many people don't actually bother with two completely independent controls. A common technique is to use a lashing (several wraps of thin stuff) to tie the cringle in the bottom of the cloth to the eye on the wire that gets connected to the stem fitting. In effect you fix the relative length of the (stretched) cloth to the length of the luff wire. As you tension the latter, you also tension the cloth. As your sail ages, you can adjust the length of the lashing as needed to give better results.

That's the setup my sailmaker suggested and what I have rigged on my boat.

As the wind increases, the pressure on the jib increases and it has a tendency to sag more. That's the moment when I add tension to the jib. And in principle the reverse if the wind slackens again. For the initial tension I look to see whether there are any "scallops" in the luff of the jib, that is when the luff isn't straight between adjacent connections to the forestay.

Tensioning the jib halyard will probably affect mast rake to some degree, but that's not the reason you do it. It's best to think of mast rake as essentially fixed: even if the jib halyard has some influence over it, you don't actually use that to control mast rake.

(Btw, cranking a vang or a really tight main sheet would also affect mast rake a bit, by pulling backwards. Again you would not use either to affect rake, but to primarily cause other changes).

With the boat properly set up, if I really have to yank on the tiller, I know I'm overpowered and drop the mainsheet a bit or put in a reef.

[rkennedy]

Thank you for the detailed explanation.

On a Hank-on Jib without a luff wire you would probably not want to pull on the jib halyard so hard that it moves the mast forward because,
you will end up with a vertical crease running up the luff, and you may take some years off the jibs life if you stretch the luff out?
I am always curious about halyard tension, I know I have over done it when I see those vertical creases.
I would like to know what indicators people use to tension their halyards, main and Jib?

I know you said your sail maker is retired but I was wondering who it was?

[GreenLake]

Jib halyard tension shouldn't be used to "move the mast", but to make sure the jib is set properly.

If you get vertical creases, you've overdone it. However, if your jib has a luff wire (or Dyneema rope equivalent) you might get creases if your lashing at the tack is too tight.

If you have no integral "wire", then forestay sag will have to be controlled by forestay tension; however, that is not readily adjustable under way, hence the jibs with integral "wire". If yours isn't done that way, time to upgrade.

For some of your other questions, you might want to take an idle hour or two and read the older posts here on the forum. It's amazing what you can find out.