A posted a picture of the mast prebend. Let me know if it looks like to much
http://phatom364.blogspot.com/

That looks like a massive amount of prebend to me, assuming the backstay is slack. It could be the photo though.

No it's alot, I can't get rid of it. the forestay is to length, the side stay are tension to 40, no backstay to speak of. I'm going to remeasure the forestay, but I had it odd the boat when I measured and added I think 2' for the deck plate.

See if it straightens some if you slacken the uppers. Check the bend by holding the main halyard against the mast by the boom and look what kind of gap you see up the mast.

I would disconnect the backstay and then work on the rig. You would be suprised how much a "slack" backstay can bend the mast.

David
#397 - Mallorca

Check the position of the mast butt on the cabin sole. It HAS to be 1" back from the angle down in the floor. This has a huge impact on mast prebend/rig tune-every 1/2" back in mast butt position pushes the top of the untensioned rig forward about two feet-so when the rig is tightened, the headstay will have way too much sag, and the mast will have way too much prebend.

Also-check that your lowers are also at 40 (I'm sure they are, but just in case...)

That backstay thing worked great for me. I was re-tuning this summer several times and I took the back stay adjuster off first and the last time I took the backstay off all the way during the tuning process. I increased boatspeed and seemed to get much better shape out of my Harrstick main.

Velocity Girl
#278
HHSA

Steve,....what do you mean 1" back of the angle? I have an '86 model and I hace am oval sleeve that fits into the mast extrusion
I do not have a choice for the position on the sole deck

Taras
Hull #532
BreakAaway
_)

The oval you refer to that the mast fits into must be set so the front of the mast is 1 inch back from the forward edge of the molded step the mast sits on. If it is not, you need to move it. Some are mounted with screws so the plate can be loosened and moved. Others require you to redrill the mounting holes.

"The oval you refer to that the mast fits into must be set so the front of the mast is 1 inch back from the forward edge of the molded step the mast sits on. If it is not, you need to move it. Some are mounted with screws so the plate can be loosened and moved. Others require you to redrill the mounting holes."

Can someone please elaborate on this.I thought I saw pics on this topic on this board somewhere. I want to check mine, as I'm trying to re-tune her now that the deck rebuild is almost complete.

Are you sure about that Steve? Is the fulcrum not the headstay attachment up at the hounds?

Not to my understanding-with the mast butt max forward and headstay at class max (rig tune slack) my mast sits hard against the back of the partners, and my headstay is completely loose. So on my boat at least, the fulcrum is where the mast passes through the deck.

But-I think my numbers are off. I did the calc's a long time ago. I think the rig moves fore and aft at the hounds about 8" for every inch of movement on the cabin floor (sorry for the exxageration-I'm not an engineer). Still a significant difference though , as rig tension settings and headstay sag are dramatically impacted by fore and aft position of the hounds.

I know this from experience-my mast butt was frozen about 1 1/2" aft of the class measured position for the first several years that I had the boat. My rig had HUGE prebend and my boat was slow until I fixed the butt position (with a lot of effort) during the off season several years ago.

My headstay adjustment was off, At let out 3/4 inch that help alot.

Rob - Sorry I don't have any pics of this. When you pull your mast you'll see an oval that is screwed to the deck. The mast extrusion fits snug over this oval and prevents the mast base from moving. You should be able draw a line 1 inch back from the forward edge of the molded step the mast sits on. Measure the thickness of the mast extrusion and draw another line behind it. This is where the front of the oval that is screwed to the deck should be positioned. Once everything is reassembled, the distance from the forward edge of the mast to the forward edge of the molded step should be 1 inch for best class legal rig tuning.

Letting out the headstay 3/4" would increase the pre bend in the lower section.
It seems your backstay is too short and holding back the tip of the mast - On FW we had to add a 3" toggle to get enough slack - we always keep the sag in the backstay 3-4" and very rarely tension it below 15 knots.

With that much sag in the backstay don't you have trouble with the top main batten foully on the backstay? I all ready have that problem in light air. I'll have to measure the backstay when I winterize, but it seem a lot of the bend was in the top 1/3 of the mast. Easing the headstay reduced that bend.

With the amount of slack we have it's very easy to flip the backstay around the batten in the tack - besides our latest main does not have a full top batten.

I think my mast step is too far back.


http://img218.imageshack.us/my.php?image=dscn0472ap9.jpg

Yup!

What affect does my aft stepped mast have on sailability?

Will this be something I should move up on my priority list? Or no

I have constant 15 mph trades, would this help me in depowering the main with the backstay since its already bent back some? Or Is it just innefficient?.

It will start depowering the main earlier and will impact light air sailing. Most sailmakers have their designs setup for the optimal sail shape starting with the rig in the correct position. With 15 kt trade winds shouldn't even need to start the backstay tension.

Since you need to pull the mast to adjust the base position, if you are not doing racing, you can wait until a convenient time when you pull the stick. Otherwise if you are racing, you are taking a performance hit.

It being that far back is also effecting the center of effort but I cannot remember if this is creating more weather helm or less. Not enough coffee yet.

David
#397

[This message has been edited by dbows (edited 09-26-2008).]

it works like a windsurfer, mast aft and you turn into the wind, mast forward and you turn away from the wind. I moved the mast step from 2" off to the recommended 1" off the step, it made a significant difference in performance and increased weatherhelm.

I measured mine the other day and it is 1 1/4"
Is it worth the effort of advancing it the 1/4"?