Mac26S mast rake and 150% genoa

[Joe A]

I have to buy a new headstay so I would like to get the mast rake set correctly in the process. The Macgregor 26S manual calls for 3 degrees aft rake. I assume the 3 degrees was meant for the standard sail plan but I have a 150% genoa. I would think that if you change from the standard jib to a 150% genoa that the optimum mast rake angle would change as well. Can anyone off any insight as to how much I should expect the optimum mast rake angle to change? Changing the rake on my boat requires about 1.9 inches of headstay length change for every degree of rake change so I need to ballpark the desired rake before I order the stay. Any help will be greatly appreciated. Also here are a few truths for comment:
1. Raking the mast more aft will increase weather helm.
2. Raking the mast less aft will reduce weather helm.
3. Mast rake should be set by helm feel.

 

[Joe]

Are you sailing with the 150 now? What happens when you roll it up a bit? What if you change to a smaller sail?

Rather than guess at the length, I would opt for more adjustment... One option is to order longer threaded studs. Instead of that, however, you might consider Stay/shroud adjusters. They are pretty common on trailered boats, allowing easy adjustment and quicker set up time.
On my Nacra the adjustment range is 6-7 inches. this allows you to quickly set your rake for daily conditions. Here's an couple of examples that would give you some extra length without guessing at where to cut the wire.

The whole idea is to avoid a mistake in making the stay too long and impractical to shorten a couple inches...

 

[Joe A]

Thanks for your response Joe. Yes I do have the slotted vernier adjusters on my upper and lower side stays and I think I can set the mast rake anywhere I want to and get the proper tension with the new headstay. The problem is that up until now my rig has been so grossly loose that I feel I shouldn't judge by my history. The other problem is there is no way to pin the headstay if the rig is tight. The headstay turnbuckle is not an option with the furler drum partially in the way. When I try to tighten the headstay TB with any tension the headstay cable twists. I plan to install a CS Johnson lever to enable the pinning of the tightened rig. This is the reason I am buying the new headstay (to accommodate the added length of the lever). I'm really just asking if anyone has a feel for what the Mac 26S rake wants to be with a 150 genny.

 

[Joe A]

Just following up. Todd at Blue Water Yachts gave this explanation:
"I wouldn’t expect a big change. The Genoa is larger so it puts more power forward, but the center of effort is farther aft than on the jib, so you usually don’t need to change the mast rake. In either case you want to position the mast so that you have a little bit of weather helm when the boat really loads up. If you have no weather helm, the mast should come aft, if you have too much, it should move forward." Before his explanation I only saw the increase in foresail power. I hadn't considered the center of effort of the genny being farther aft. Now I feel a lot better.

 

[Joe]

Just a side note.... you can use a jib halyard to take strain off forestay while you pin it in desired position.

 

[Freedom77]

Backstay adjuster/tensioner. Simple, cheap, efficient. Allows tension/rake close hauled and looser forestay downwind. Use standard forestay length.