SC 20 Mainsail Block Holes & Mast Rotation

[Kevin Keller]

I haven't been able to go sailing lately on my boat but I saw the question on the SC 19 sail clew. I am wondering about mine also but for slightly different reasons.

As you might know, I upgraded my sail rig to that of a ARC 22 design (mast being the original standard mast for the 20 but with the auto-rotating base). I have a pretty flat sail now. So if I want to put some curve into it I put the mainsheet blocks in the aft holes. The problem with doing this is that my mast rotates past the 90 degree point or close to it. (0 degrees being forward and 90 degrees pointing to the main beam end). Doing this makes the sail go flat then instead of curved, kind of defeating the point.

Even when I go to the farthest forward position the mast still seems to over rotate. I think it has been mentioned in earlier posts about increasing shroud tension and it will prevent the rotation. Mine are pretty tight and it doesn't seem to change it much. If I think about how it is designed, it doesn't seem like it would help prevent the rotation either. Maybe I am misunderstanding how it works.

I do sail in in some high winds at times but it seems like the boat is just not moving as fast as it should be, it feels like it is being held back. I have had our commodore out on the boat in some windy conditions and he says his Miracle 20 would be going faster in those conditions, which he has proven.

I have wanted to call you guys regarding this but haven't had the time (I'm out of the country right now). Have you any ideas?

[Matt Haberman]

Kevin,

The logic still applies on your 20 with the ARC-22 rig as was described in the other post.

Keep in mind that the dolphin striker post is floating on your 20 and as the rig powers up, it causes the shrouds to get looser and allow for more mast rotation. The rig will need to be pretty tight when sitting on the beach w/ no sails up to compensate for this. I would suggest that the mast should only rotate about 60 degrees (pointing towards the daggerboard trunk) when sitting on the beach. When sailing this will limit the mast rotation closer to 90 degrees.

Hope that helps.

[Kevin Keller]

Hi Matt,

Thanks for the reply.

When you say the mast pointing at the daggerboard trunk I assume you mean the aft edge of the mast? To me when you say pointing, it would be the front of the mast doing the pointing.

I am wondering what prevents the mast from rotating past the 60 degree position while on the beach, is it the aft edge(sail track) of the mast hitting the shroud? So when you are powered up and the lee shroud is loose the mast will be allowed to rotate past this point?

To have the shrouds that tight, so as to have the lee shroud tight under wind, sounds pretty dang tight... too tight almost?

Do you ever want the mast rotating 90 degrees? over 90 degrees?

It seems the mainsheet position on the mainsail clew also controls the rotation, yes?

Do you use the mainsheet position to control the twist in the upper part of the sail, the draft at the lower part, or the rotation?

Trying to make this thing faster. Thanks for your answers.

Kevin

[Matt Haberman]

Hi Kevin,

When you say the mast pointing at the daggerboard trunk I assume you mean the aft edge of the mast?

YES

I am wondering what prevents the mast from rotating past the 60 degree position while on the beach, is it the aft edge(sail track) of the mast hitting the shroud? So when you are powered up and the lee shroud is loose the mast will be allowed to rotate past this point?

Yes as the mast rotates the shrouds wrap around the mast and prevent it from rotating.

Do you ever want the mast rotating 90 degrees? over 90 degrees?

90 degrees is probably far enough on the 20.....

It seems the mainsheet position on the mainsail clew also controls the rotation, yes?

Yes, on the boomless rig it is the combination of mainsheet position and shroud tension.

Do you use the mainsheet position to control the twist in the upper part of the sail, the draft at the lower part, or the rotation?

Mainsheet position will control rotation which will in turn impact the draft in the sail. Mainsheet Tension combined with traveler position on the other hand will impact both draft and twist.

[Kevin Keller]

Matt,

Thanks for the reply.

I want to ask you a little more about the shroud tension. Mine is pretty tight, difficult to close the lever locks. How tight is yours? I am afraid of putting a permanent curve in my hulls (over time). As is I usually release one of the levers when I am done sailing for the day. When you are sailing is your leeward shroud tight? in high and low winds?

I do have synthetic shrouds which I imagine stretch a little but as one stretches the other would probably shrink.

Being a pilot, it seems that having the mast at 90 degrees degrees would be an inefficient airfoil shape for higher winds. It would seem more appropriate as a leading edge slat on a jet's wing for lower speeds and higher lift. Does the ARC 22's have spreaders which bend the mast? and not need the rotation so much?

You need to bring your honey to Hawaii and stay with me for free. You can show me the proper way to sail this boat.

Thanks,

Kevin

PS... I'm serious about the offer, you or Tom.

[Rhiannon]

This seems to be an interesting conversation, and I don't like to butt in, but I have to ask what is probably a naive question.

My boat has a mast rotation control on the boom, aside from the occasional bonk on the head, what is the advantage of going boomless? Is it Weight?

John

[Matt Haberman]

This seems to be an interesting conversation, and I don't like to butt in, but I have to ask what is probably a naive question.

My boat has a mast rotation control on the boom, aside from the occasional bonk on the head, what is the advantage of going boomless? Is it Weight?

John

John, The other big thing is simplicity. You don't have to worry about adjusting the rotator for upwind and then downwind. You just set your mainsheet block position on the clew for a given wind condition and then forget about it.

[Matt Haberman]

I want to ask you a little more about the shroud tension. Mine is pretty tight, difficult to close the lever locks. How tight is yours? I am afraid of putting a permanent curve in my hulls (over time). As is I usually release one of the levers when I am done sailing for the day. When you are sailing is your leeward shroud tight? in high and low winds?

Kevin, I would say that our levers close about 1/2 way very easily and then it takes some force to close them. Considering the age of the boat it probably is not a bad idea to leave one open when the boat will be sitting unused for days at a time. Our leeward shroud does get loose compared to the windward one, but it isn't "flopping around loose". In fact from a distance it still looks tight and you don't realize it is loose unless you go and push on it with your hand at which point it will move a little.

I do have synthetic shrouds which I imagine stretch a little but as one stretches the other would probably shrink.

I am not sure about the shrinking part, but I am certain that the synthetic shrouds are stretching more then the Stainless ones when under load.

Being a pilot, it seems that having the mast at 90 degrees degrees would be an inefficient airfoil shape for higher winds. It would seem more appropriate as a leading edge slat on a jet's wing for lower speeds and higher lift. Does the ARC 22's have spreaders which bend the mast? and not need the rotation so much?

Correct, 90 degrees of rotation would be used for very light wind conditions, as the wind comes up you will rotate less. The mast on the ARC22 is pre-bent with the spreaders, but I am not sure about it needing less rotation.....