SC20TR - Bill Roberts

Jake,
The forestay on the SC20 is one foot closer to the mast than on the ARC22 rig plan. Therefore to make a 22 jib work on a 20TR the foot must be shortened one foot and the leech must receive a big undercut, about 8 inches, to clear the mast diamond spreader.
Jake, just to have the history right: The 20TR came out in 1981 and the ARC22 in 1992. The ARC22 uses the same mast and mainsail as the 20TR. The jib on the 20TR is skinnier by one foot because the forestay is one foot closer to the mast than on the 22.
Bill

You're not helping my eye swirling problem but I'm with you now. Thanks!

Thanks Bill/Eric-

I hope to heave my FMS20 back in my hands soon [if Caldwell ever gets through] and was very interested in rigging it. Also thanks dor the clarification Team Cyberspace.

thom

Not exactly Marschassault. The fore triangle of the 20TR is one foot shorter than the 22. Therefore the foot of the jib is one foot shorter than the foot of a 22 jib. This is one foot out of seven feet or about a 14% reduction in jib sail area relative to the 22 jib. The mainsails are the same.
Bill

SC20TR as sailed in Steeplechase

Main = 27 sq. mtr = 290 sq ft.
Jib = about 5 sq.mtr. = 54 sq. mtr.

Only some 90 sq.mtr more than the I-20's on a mast being what ? 6 ft taller ?

What size spinnaker was used on the SC20TR ?

Wouter

Bill,
I guess that’s where I was going…. You get the extra ~12inches on the luff edge. And by lowering your tack corner from the normal position on the SC20 to the 22’s tack corner mount on the spin pole, you increase your luff edge. Doesn’t this increase your foot potential…. even if you’re running a forward-of-the-beam self tacking jib car?

One thing I noticed about your setup is that you run your spin pole in a low position (similar to the ARC22). Is there an optimum spin pole angle of entry for the SC20, or does it depend on what head sail your planning to fly off it? Did this low angle of entry, and having the lower jib tack corner, create any problems for you or is it a non-factor? This winter I’m going to attempt to engineer and mount a spin pole on my SC20TR and I was going to attempt to engineer mine very similar to the ARC22. Any feedback on optimum or desired mounting angles for the spin pole on a SC20TR would be greatly appreciated…!

You know, people can knock the boat (SC20’s), and compare them to or try to refute comparison to….. the new “high $$” boats on the market today….. But on that day, in that boat…. Eric and You were the champions! GREAT JOB! People that have never sailed on a SC20 will never understand how magnificent that boat is and what a pleasure that boat is to sail, thank you!

Bobby

Hi Bobby,
Thank you very much for your praise and confidence in the SC20.
The ARC22 system design has many goals/uses. If you have an old worn out SC20, all hardware and rigging from the 20 is interchangeable to a set of bare 22 hulls. Everything on the 22 is the same as the 20 including centerboards and rudders and gudgens and tramp tracks and trampoline and beams, etc. The 22 hulls are simply 20 hulls with two feet added to the bows to increase the hull fineness ratio and increase the pitch stability. The self tacking jib is an upgrade that can be part of a spinnaker pole set up or without the spin pole simply use a foot tube from the main beam to the jib tack point.
The spin pole set up on my 20 is identical to the one on the 22. The lower pole position leads to a longer luff jib and taller spinnaker. Long luffs are faster. Along the luff of a sail is where the action is; that's where the forward pull is, front third of the sail.
You don't have to engineer anything to put a spin pole on your 20. Just copy the 22 or buy the parts from Aquarius Sails. E mail me if I can help.
Bill

Will Do - Thanks Bill !

I’ll keep you apprised of my progress – Happy Holidays to you and your family!

Bobby - Bill is right, just grab what you need off of Roger's boat! I won't tell if you won't!

Keith,

I have to do something to keep away from those #$%@ Hobbie 20's, they just keep running into me! Need to sail faster... Need to sail faster... Need to sail faster...

Happy Holidays Dude!

Bill,

We are considering adding a spin to our 6.0 over this winter, or more likely summer/fall. Keith (H20) and I have been talking about what size and type of spin to use. From Bobby’s post he is also looking to add a spin to his SC20 TR. Would you share with us the type of spin you used? What were the assumptions behind your choice? Where they big area to run deep or smaller area and longer luff length to run higher and faster or something else?

Thank you from a Super Cat admirer!

Bobby, I’m with you about those pesky H20 guys; once they get a hold on you they never let go! I have had to repeatedly tell myself “Don’t engage, don’t engage!”

Oh, them 20s are pesky alright! As this year's C-100 displayed, though, a chute may not be enough to get away from us! 'Course, they're still not as pesky as a certain 18 was. Or as pesky as the A-Cats are becoming...

Hi Chris,
The spinnaker style I like, have the most success with, is the tall, long luff sail and it is not max area but it is max luff length. Since most of the forward pull from the spinnaker comes from the front 1/3rd of the sail, max luff length is more important than max area. The max area spinnaker will only sail well deep downwind. When you try to heat it up, sail higher, it overpowers you and you can't hold the boat down in a breeze and it pulls mostly sideways anyway which loads up the daggerboards and makes more drag in the water. The max area spinnaker has a narrow window of successful application. The higher aspect ratio spinnaker will sail well over a wide variety of downwind sailing angles from hot to deep. Unlike the classical spinnaker, the leech of this spinnaker must be flat and quick to twist open and not backwind the mainsail. Remenber that a hooking leech is producing thrust to the rear. When you stand behind your boat in line with the spinnaker leech and the sail is trimmed hot, you should not be able to see the leeward side of the spinnaker. If you can, that spinnaker area is producing thrust to the rear.
The first step to a good spinnaker is the pole. Longer poles are better. They make for longer luff sails and they allow the spinnaker force to lift the bow. Copy the ARC pole support system in general. Select a pelican stricker tube length that puts the pole at whatever height you want it. The pelican stricker tube takes the vertical load from the spinnaker/spinnaker pole and puts it the forestay bridle wires where it goes to ground in the hulls.
Good luck,
Bill

Hopefully not sounding too dense here, but what is a pelican striker? I know what a dolphin striker is, but not a pelican one. I sail a Hobie 20 which only has the dolphin kind. I'm worried that if I go too long on a spin pole, I'll have trouble supporting it and will generate loads that will pull the bows toward each other, causing forestay slack.
David
H20

Bill-

I think a pic says a few words in this case. As can be seen all lines are internal [ie jib luff tensioner, self tacking jib sheet, spin tack line, spin tack luff tensioner for roller furling code zero]. My spin pole was setup for two different types of spins. The pelican striker is shown extending from the bottom. If you are looking for the top of the line engineering then call Tom @ Aquarius Sail. The quality is top notch and his demonstrated experience level is unparralled. Quality first pays off in the long run.

thommerrill
F25c 009 Charisma
ARC22 2234 Widowmaker
FMS 20 57-being refinished

thom

Hi David,
The Pelican stricker is a rigid tube that spans the gap between the apex of the forestay bridle wires and the mid region of the spinnaker pole. In alignment it becomes an extension of the forestay down to the spinnaker pole. It carries the vertical load, compression in this tube, from the spinnaker pole up to the forestay bridle wires where the load then travels down the bridle wires to the hull. This mechanical arrangement of spinnaker pole support and spinnaker load absorbtion has the least impact on hull loading of any spinnaker pole support system I have seen. It also let's you position the pole heightwise anywhere you want it by varying the length of the Pelican Stricker Tube.
Good Sailing,
Bill

On the current Tornado rig, we've got a pole that according to your description, is a pelican striker...but I've heard it called simply a "strut" between the bridles & pole. Unlike the picture shown above, there are a pair of stays attached to the pole where the strut attaches...leading out (athwartships) & down to the forestay bridle tangs on the inner gunwales. From looking at the whole arrangement, I've wondered what the strut actually does for you, since any upward flex at the mid pole point should be resisted by the mid pole stays. Granted these are at a fairly shallow angle compared to the forstay bridle stays, but I can't see them allowing enough flex to load the strut to any level. It all seems kinda redundant...perhaps we can get rid of either the midpole stays or the strut?

Here's a picture of the Marstrom setup:

Mike-

I see the strut you mention but I don't see the pelican striker below or the steel stays that run from the bridal tang to the tip of the spin pole. My pole has four stays as well as the forward trap that wraps around the stays from the main beam to tighten/support/limit movement of the pole at the inetrsection of the bridal strut and pelican striker below.

I guess it depends on the spin size [615, 742, or 450 sq ft furling code zero] for the boat regarding all the stays [2 from main beam, two from bridal tang to forward tip plus forward tramp].

thom

We rigged a P19 up with a pole this summer. Since the boat was old... he was using a Nacra Bridle foil to resist the bows towing in. He had lenghened his forestay to use the nacra bridle foil. The MX jib luff extended well below the original bridle wire intersection and was tacked onto the foil. Essentially duplicating the strut used on the Marstrom tornado to lower the jib tack. We rigged the pole below the foil, and tried to induce the proper amount of prebend into the spin pole using the bow bridles.... Oops.. the loads needed to bend the pole (at this angle)simply towed in the bows (despite the bow foil). The solution was the pelican striker that was used by Bill on the Supercat pole (below the strut). The pelican striker allowed us to prebend the pole the proper amount without transfering the loads to the bows. The bow bridle serves to keep the tip centered and slightly load the pole up.

The Tornado gets away without a pelican striker because the pole is carried quite a bit higher then we could on the P19. The class spec is that the jib tack cannot extend below 50 centimeters of the intersection of the bridle. Essentially this carries the pole at a fairly high angle and the Tornado bows can handle the loads.

If you are going to maximize your luff length by lowering the pole as much as you can... well you have to compensate somewhere.

Take Care
Mark

Tornado Sailor,
The strut is the mid pole tube located 'below' the spin pole that carries the wire that runs the length of the spin pole. This strut carries the vertical load induced by the luff tension of the spinnaker. (The Tornado does not have this for reasons I will discuss later.) This vertical load travels up the strut and passes around the spin pole in the collar and then on up the Pelican Stricker Tube where it is handed off to the forestay bridle wires. This is the vertical load carrying system on ARC boats. By simply varying the length of the Pelican Stricker tube, the spin pole height at the tip can be set anywhere desired, like low for a longer luff spinnaker.
Now we have to handle the horrizontal forces from the spinnaker. A set of 'whisker wires' connecting the end of the spin pole to the bows of the boat or forestay chainplates near the bows will control and carry the spin pole side loads. Now all spinnaker generated forces are taken care of and we can put the pole at any height position desired.
The Tornado does not have the strut and wire below the spin pole. Therefore the vertical loads and the horrizontal loads from the spinnaker must both be carried by the 'whisker wires' connecting the ends of the spin pole to the bows. Since these 'whisker wires' on the Tornado also carry the vertical spinnaker generated loads, another constraint enters the picture. To keep from overloading the spin pole in axial compression, the included angle between the spin pole and whisker wire when looking at this geometry from the side view must be 10 degrees or greater. This sets the min height of the spin pole above the bows for the Tornado. This 10 degree angle is the same minimum angle as is used on diamond wires relative to the axis of the mast. This sets diamond spreader arm length.
Now there is more to this system. The spin pole can be made of a significantly smaller diameter tube if the spin pole is stableized at its mid length point. The stability equation for tall slender columns in axial compression says that the moment of inertia required for the tube to be stable is directly related to the unsupported length of the tube. Therefore if we can stop the tube, spin pole, from moving at mid point, we can use a smaller diameter tube for the spin pole. That is why the spin pole on the ARC boats and Tornado are stabilized at mid point both vertically and side to side.
Good Sailing,
Bill

Hi Folks.
What's the origen of the name Pelican striker.

I assumed that since the Dolphin striker would smack the fish on the tops of their heads... AND
Since the pelican would probably sit a bit taller... then next highest strut pointing down would be the pelican striker.

Why isn't the spin pole strut called a pelican striker?

Hmm. I will go get another beer
Mark

Hi Mark,
The strut on the spinnaker pole extends downward from the spin pole which is about at deck level at pole mid point. It is very close to a Dolphin striker, just not quite as deep. It could encounter/strike a fish or Dolphin.
The Pelican striker extends up from the spinnaker pole to the intersection of the forestay bridle wires. It could possibly encounter/stricke a bird or Pelican.
A litle corney but maybe it makes sense.
Bill

Hello Bill-

I stand corrected...I thought it was the opposite. I thought the strut was on top...you learn something every day.

thom

Bill,

I'm sorry to say this but you're confusing alot of people for no good reason.

A pelican striker is the thing BELOW the spi pole. It's name is derived from a similar setup on old schooner rigs which have such a device to stabilize their jib poles and that is BELOW the bowsprit as well.

The thing on top the spinnaker pole is the Strut.

And really Bill, pelican strikers on spinnaker poles are NOT necessary and only make things complicated and heavy. Look at the I-20's and Tornado. NOBODY Is using pelican strikers anymore. Even the boats slugging it out in the Worrell do fine without one. If they hold up than why should other (regatta) boats have them ?

Stop reinventing definitions that are already in place.

Okay my flame suit is on and now anyone can tell me who I as a European pantsie don't know diddly [censored]. Considering you all pretty much sailing European boats by now makes your flaming pretty rediculous. Not Bill, not you.

Wouter

Hi Wouter,
Actually they are all struts. If a structural member carries a load parallel to the member, it is a strut.
In the US struts that extend above deckline are called Pelican Strikers and struts that extend below deckline are called Dolphin Strikers. Sorry to have upset you so much over nothing important.
Bill

Thom,
Yes, the sail could be furled. But to do so will greatly shorten the life of the spinnaker cloth. The initial turns of cloth will be very very tight about the luff tape and this will wade and twist and stretch the light weight spinnaker cloth. The bottom spool is going to make several turns before the top rotor ever makes the first turn, OUCH!!! I don't need to ruin a good spinnaker just to roller furl it.
Bill

Wrong Bill-

That hasn't been my experience with my roller furling spin. I don't the other guys on the Fboat list with furling code zeros have experienced that either. If they have they haven't mentioned it. I believe they got theirs from Elliott Pattison while I got my from GM Sails of Austrailia. If you would like to see an example of Elliot Pattison furling code Zero go to Mike Leneman's Multimarine.com site and select the "Products" button and go to the bottom of the page. Or you can go to the Farrier Marine site and look at the F33 update for 12/2/2003 and see the furling North Masthead spin pictured"
thom

Wouter,

I am not sure about this. A strut over the spinaker pole (whatever the name) doesn't seem to be unnecessary, complicated or heavy.

If you want to extend the jib foot down to the spinaker pole, just add a vertical strut and it's done. The strut will also reduce the free length of the pole, so it will serve two structural purposes. Seems quite simple, light and efficient to me.

You can avoid the strut if the jib foot is fixed to the bridles instead of the pole, but then the foot is higher and you loose sail area exactly where it generates more power (luff) and less heel (low). Not a smart move.

You can avoid the strut by lowering the bridles so that they attach the hulls to the spinaker pole, but then they wil partially submerge when the boat heels (more drag). Also, not a smart alternative.

If my memory is correct, all the maxi cats use one of those bridles, as most cruising cats do. Am I missing something here? Could you please detail your point of view?

Thanks,
Luiz

Bill,

I think I could have worded that more politely, my appologies. I've just reread my post and although I stand by the content, I think I did you wrong on the presentation. I will blame the 10 cups of coffee for that but also present my appologies to you.

Regards,

Wouter

Hi Luiz,
"If you want to extend the jib foot down to the spinaker pole, just add a vertical strut and it's done. The strut will also reduce the free length of the pole, so it will serve two structural purposes. Seems quite simple, light and efficient to me".

You are 'right on' again; you understand correctly.
The equation for 'max allowable load' in a tall slender column is: P = Phi**2 x E x I / L**2 . This is a stability equation and has to do with 'buckling failures'. The import thing to notice here is that the moment of inertia, I, is in the numerator and the the unsupported length, L, is in denominator. For spinnaker pole schemes without support at the pole mid point, L is the total length of the pole. If the pole is stabalized at pole midpoint so that it can't move vertically and it can't move sideways, then the L term in the equation is L/2 which is then squared. This makes the denominator 1/4 as large as it is for the unsupported pole and therefore the I term in the numerator can be 1/4th as large, a much smaller diameter pole, and lighter weight also.
On the SC20 at first I used a 3/4inch diameter SS thin walled tube 2ft long to connect the mid pole point to the apex of the forestay bridle wires. This short tube buckled and I had to go up to a 1 inch diameter SS tube. The system really works and my spinnaker pole is much lighter weight than others of similiar length.
Bill