Masthead Spinnaker?

Jul 13, 2011
96
Capri 22 MK1 659 Canandaigua Lake
I have a Mark 1 SRWK and I have a asymmetric spinnaker that's a bit too tall that I'd like to use for day sailing. Any thoughts about just moving the spin halyard block to the masthead? Would it require runners?
 
Feb 20, 2011
7,783
Island Packet 35 Tucson, AZ/San Carlos, MX
Any thoughts about just moving the spin halyard block to the masthead?
Not recommended. Lateral loads on unsupported masthead can break your mast.
You could however install a set of hounds at a distance (<18 inches) above the forestay and fly your spin
conservatively.
 
Jul 28, 2016
95
476
I have a asymmetric that was built specific for the Capri 22 standard rig that I would part with. It isn't "new", but it is in serviceable condition for day-sailing/cruising. Drop me a line at delling3@comcast.net if you have interest.
 
Jun 25, 2004
1,108
Corsair F24 Mk1 003 San Francisco Bay, CA
Not recommended. Lateral loads on unsupported masthead can break your mast.
You could however install a set of hounds at a distance (<18 inches) above the forestay and fly your spin
conservatively.
I agree that lateral loads at the unsupported masthead could break the mast. However, I’d be even more conservative in the absence of doing the calculations.

6” above the forestay is more conservative.


... I’d be nerdy conservative unless the mast is WAAAY overspec’d . 18 inches is too long for my comfort if the asymm ever knocks the boat down to 35 degrees of heel, where max righting moment happens (on most boats)

Judy B
 
Feb 16, 2017
164
259
Going to a masthead spinnaker on the standard would not be advisable. The rig is barley large enough as it is. You can lift the halyard up about 15'' MAX. that would be fine.
I have thought about doing the following with my boat before I went BIG!
Raise the standard headstay up 2'-0'' it's not hard, and then lift the spin halyard up 15'' and you're close to the masthead. You will also need to lift the spreaders 1'-0'' and the lowers to follow.
This would greatly help the boat in light air and downwind sailing, the boat is very underpowered downwind. Looking at my avatar you will see a very tall rig with 11'-0'' spin pole, the other boat an S2 7.9 owes me 18 seconds per mile. You can see the size difference between the sails.
All of my headsails and mainsail are standard tall rig sizes.
 
Feb 16, 2017
164
259
I agree that lateral loads at the unsupported masthead could break the mast. However, I’d be even more conservative in the absence of doing the calculations.

6” above the forestay is more conservative.


... I’d be nerdy conservative unless the mast is WAAAY overspec’d . 18 inches is too long for my comfort if the asymm ever knocks the boat down to 35 degrees of heel, where max righting moment happens (on most boats)

Judy B
I have a 37'' taller than normal standard tall rig I have laid it over buried the winches underwater and with a (J70) asymmetrical in 25 knots true!
My spin halyard is 15'' above the jib it won't break! I've tried to break it.
The Factory location of the tall rig spin halyard is 12'' above the jib, so I would say Dr. Judy is not very familiar with the current variations of mast designs from the factory.
 
Jun 25, 2004
1,108
Corsair F24 Mk1 003 San Francisco Bay, CA
I have a 37'' taller than normal standard tall rig
@odj22sailor,
Curious minds want to know:

You said your mast is 37” longer than the TR. What's the mast section? (Manufacturer and section, or Ix and Iy)
Where are the spreaders compared to mast head and where is the spinnaker exit block?
Did you do the engineering, or somebody else?

Judy
 
Jul 13, 2011
96
Capri 22 MK1 659 Canandaigua Lake
OK, upon further review...
Let's say the spinnaker is 28' x 25' x 15'. perimeter = 68'; semi-perimeter = 34'; area = 186.8 sq. ft. (Heron's formula). Round up to 200 sq. ft. because the sides aren't straight.

Wind pressure = .00256 x wind velocity squared. I don't want a chute up over 15mph, so say gusting 30

(How to Calculate Wind Loads From Wind Speeds)

Wind pressure = 30 x 30 x .00256 x 200 = 460# on the entire sail.

Let's say the head gets half the load even though my asymmetric doesn't have big broad shoulders.

There's about 4' of mast above the upper shroud hounds, so the question is: will a 230# lateral load at the masthead kink the mast at the hounds with that 4' lever? Of course, the boat will yield to the pressure by heeling which reduces the length of the lever, so there is an additional safety factor.

Imagine the mast resting on a padded saw horse at the hounds. Now your 230# canary bounces on the end of the mast. Does it hold or break?

I am justifiably humble about my physics chops, so please feel free to point out bad assumptions or blunders.

If this analysis hold up to scrutiny, I'd be tempted to tie the head shackle onto the halyard with a heavy duty cable tie (175# tensile strength). I'd bet that zip tie never breaks. I could also use an under-spec'ed halyard that stretches to cushion any shock loads.
Comments? Criticisms? Concerns? Tales of Woe? Stories of lost love?
 
Feb 16, 2017
164
259
Add this to your equation in 15 tws the boat will not handle a kite with the wind forward of 135 degrees. So with that said the wind will be aft of that. At this point, the backstay will start supporting up the load of the sail. I think all of us that have an understanding of this topic have agreed that going to masthead kites is either not a good idea or not recommended, it's the dynamic loads that we try to account for so going up 12'' to 15'' is not an issue.
I have a true code zero tacked to the end of a 36'' bowsprit with a 65% top girth (of foot length) the LP of the is about 16'-0'' that I use, my concerns are not with any type of side loads it is more "can the shrouds and the structure below decks" handle the load and the backstay handle the loads as well.
This is due to the amount of tension I am using on the luff. Our primary winches are Barient 21 2 speed winch with a 2:1 tack line. we can remove all but 10 -12'' of sag in the luff. That is a lot of load for a Capri 22. The boat is not designed for this, but it sure does haul ass!!!!! We routinely get around the course boat for boat and or beat S2 7.9 and J-24's up to 8 knots of breeze.
I have tried the wire tie they fail every time.
 
Feb 16, 2017
164
259
Oh, forgot to mention your approximate sail area is 350 sf.
ISP=28.0
J=8.1 (8.1x1.80=14.40)
28.0 x 14.40= 403 x .89 =358 sf
Basic calculation for standard spinnakers
 
Jul 18, 2013
34
22
Forgive the resurrection of an old topic...A previous version of the Forum had a front page photo of a short rig with a mast-head symmetrical spinnaker. I don't recall hearing about the demise of that mast.

My low-number C22 SRFK has the spin halyard exit sheave very near the masthead and the halyard is run down to a black plastic bushing just above the forestay. It would be easy to fly a spinnaker from the mast head. And as soon as I can get around to it, I'm rigging a sprit and buying a second hand code zero off some 30 footer.
 
Feb 16, 2017
164
259
Great question, I would not recommend going to a masthead kit with a standard rig using the original OEM mast section. It is 4'-6'' to the masthead. The amount of unsupported mast and the softness of the OEM mast section scares me a lot. I have modified my OEM standard rig to a tall rig but I also moved the shrouds up 6'' and added a set spreaders. I only lifted my Spin halyard up to 1'-0'' above the headstay. I could have gone to the masthead but didn't, only because it's already so close, to the top to begin with.
Now if you have the newer Seldon rig that would most likely not be a problem. That rig is oversized, my modified tall rig weighs about 30 lbs less than the new rigs from Seldon.