SC20TR - Bill Roberts

What were the differences [rating wise] between the two boats??? besides Roberts/Roberts...

thommerrill

Eric & Bill,

Great Job! The one (only one picture) picture on the Catsailor website shows you guys "heated-up" - looks like she was running good.

I guess the question "thommerrill" was asking was what was the difference between the two SC20's??

Anyway - Looks like you guys were smoken'. That Asym Spin looked good (looks like a reacher). nice to see a ~ 20 year old boat doing well (no comment on the age of the "crew")

Does anyone else find it ironic that a tired 21year old SC 20 won the Key Largo Steeplechase, and the latest and greatest (M20) by arguably one of the best boat builders on the planet came in dead last on the first leg because of equipment failure? Sure it could, and does happen to any boat during a race…but it’s nice to see that even a old design (admittedly way ahead of it’s time) can, with the proper crew, take on all comers and still end up on top. You have to admit that it gives a glimmer of hope to those without bottomless pockets.

Bill, nothing like backing up your design philosophy on the racecourse.

Congratulations Bill and Eric!

Hopefully someone will post more pictures of the SC 20 in action…

For a decade I have preached the benefits of the Hooter and Bill Roberts was finally convinced by Dave Calvert that this is so.
The Hooter really smoked on the first day, and they would have probably came in sooner than 11th on the second day had it not been for a pitchpole when they hit a sandbar.
Rick

Rick
Did they have a hooter for the first day only? From this picture it looks like it's a normal spinnaker.

Looked like a Hooter from where I was, but who knows for sure. I was pretty busy just being able to get back to the finish line to take down times.
I know Calvert had said that Roberts has finally opened up to the idea of a Hooter.
Personally, I know it works better than spinnakers -- just the world still holds on to monohull theories.
Rick

Hi Seeker,
When we got out in the Atlantic Ocean and put that SC20 in high gear, those eliptical hulls went to work and in an hour when we looked back, all we saw was open ocean, no boats.
Bill

Bill, don’t you think the 38 foot stick and the canvas that comes with it had something to do with your performance on the ocean side? It was pretty darn light most of the day.

Regards,
David Ingram

Hi Rick,
The Calvert spinnaker we used this year in the Steeplechase is not a 'Hooter'. It is a code zero spinnaker (software) plus alot of special Dave Calvert design spin and a little Bill Roberts design spin on sheeting angle. We used this sail for about 2 miles out of 55 miles on the first day of racing.
The SC20 DID NOT PITCHPOLE on the second day of this years Steeplechase Race. The boat did run aground and break the rudder off, then round up and turn over sideways slowly. We sailed the last 2/3rds of the race with one rudder and there were several times that the one remaining rudder was in the air leaving us to steer the boat at 20+ knots with the sails. It was a wild ride home!
Bill

Hi David,
Of course it did, but the winds for the first day of racing were double trapezing with white caps for the first four hours, from start until 1:00pm. Then the winds got lighter by 2:00pm, no traps, and by around 3:00pm to 3:30pm the wind stopped and we paddled in the last mile.
If you want to get into technical issues, 38ft mast etc; the boat we were sailing weighs 550 lbs by Boston Whaler and the class min weight for a SC20 is 450 lbs.
One of Tom Haberman's new ARC22 boats at 450lbs would have gone over the horrizon on us.
Bill

Bill-

Again, Why were the two boats rated differently???

thom

Bill-

Does your "code zero" furl?

thom

Before you poo poo the M20 and the technology it brings to the table at 15 minutes into the race the M20 was in front and pulling away and this was without their spin up, when rest of the leaders were on a double trapped spin reach. I suspect at the pace the M20 slipping away it would have been over the horizon by the time the next boat cleared Angelfish Creek. All boats have problems, and I’ll bet you lunch this type of failure is NOT a recurring theme on the M20.

Speaking of old designs, do you think the Tornado would be a little quicker with 38 foot stick, but I bet she would be handful in anything over 15 knots. What do you think?

Dave

Hi Guys,
For our SC20 Tall Rig rating we used the standard US Sailing numbers and modifications. SC20 Tall Rig 63.5, spin at .96, square top at .995 gets us to 60.6.

According to the results page, the other SC20 registered with SP(spin), TR(extra trapeze), MN(square top), and JU(larger than normal jib). I did not see the other SC20 as they set up at another location. However, I am pretty sure that it was not a tall rig. I don't know why they registered with extra trapeze unless they sail with 3 people. The boat has a home made spin pole with a roller furler sail on the tip. The boat tacks the jib down low and sheets to the tramp with alot of overlap. Even with these modifications added I do not see how they came up with the 59.2 number. I am assuming a mistake somewhere.

As far as the extra sail area helping in the light air, I feel, and was told by Krantz and Leonard on the closest I20 to us that we made most our time and distance when the wind increased to double trap conditions. I'm sure the extra sail didn't hurt in the light stuff, but we were able to drive hard in the double trap conditions.

Who cares what you call our headsail; reacher, hooter, code zero, assymetrical spin? It is a very flat cut sail with an open leech that does not hook when maximally sheeted.

Hope that answers some of the questions.

Eric

Thom, et al,
No, the headsail does not furl. It is launched and doused from a bag on the tramp. It is made of normal spinnaker cloth. I don't think it fits the definition of a "hooter", if there is a definition. I call it an assymetrical spinnaker designed to sail at a relatively close apparent wind angle. It is pretty simple, the faster the boat goes, the closer the apparent wind angle, the flatter the sail needs to be. Feel free to choose whatever name for the headsail you prefer.
Eric

Thom,
I don't know. I never saw the other boat and I do not know what its rating was. It may have been a standard SC20 rather than a tall rig. The standard rig with spinnaker would have been faster than the TR on the second day.
Bill

Thom,
I haven't tried it but it could.
Bill

Hi Dingram,
I'm sure you are right. Marstrom builds excellent products and this failure was the exception not the rule. I'm sure it will not happen again. The technology that the M20 brings to the table is the use of the autoclave to make carbon boat parts which can and does cut the weight of the typical beach cat in half. As far as a breakthrough shape or new design of an important boat part, that is not where the improvement is. The improvement is in the weight redution due to using the autoclave. It takes big dollars to get into the autoclave business. I don't see a US beach cat manufacturer going there because it also at least doubles the price of the boat and we aren't willing to pay that price for our boats. So for a while longer the US built beach cat products are going to be hand laid and vacuum formed fiberglass boats.
Bill

The SEACATS want to host you guys again this year in Columbia SC on May 15-16th 2004. Havent heard back from Haberman for the official answer, but we are already planning this regatta, and would like to have "the Official word" ASAP to continue to gain sponsors. Bill, hope to see you back this year!

David Mosley
www.seacats.org

Would it be a spi using the following definition ?

The girth of the spi at midheight (line from mid luff to mid leech) = 75 % of the foot of the spi sail.

If so than it is a spinnaker or rather asymmetric spinnaker by the definition of the ISAF. If not than it is something else and often it will be a hooter or Genua.

Wouter

The other Supercat was a tall rig -- written right there on his registration form, so he started with the same base PN as the Roberts boat. But the other boat had four modification factors, as opposed to two for the Roberts boat.

Bill,

Is that pole footed jib original equipment for the SC20TR? A friend of mine ordered a set of sails from Aquarius for his SC20TR and got a jib that looked like a hankerchief and was not pole footed. However, I haven't seen his boat in a while and I understand there were some issues with his sails that have since been resolved. The jib might have been part of those issues.

... I thought the "pole-fitted" jib was/is the ARC22 configuration/design. And the SC20 jib was above the junction of the front forstays?? (yes, the SC20 jib is much smaller then the ARC22 jib)

He did get his sails straight through some kind of intervention from Haberman and Roberts, and now uses the "pelican" striker to foot his jib to the spin pole. Very neat system, hope it works better than his old(brand new) sails we used at the Mug last year. The jib sucked in a big way!

Dave Mosley
www.seacats.org

Marschassault,

And to your point, I thought the Tall Rig SC20 simply had the ARC22 mast and sails. My eyeballs are starting to swirl.

Hi Jake,
The self tacking jibs became standard on all SC products in 1992. The self tacking jibs are smaller in area than the old manual tacking jibs. The self tackers are longer in luff length but shorter in foot measurement relative to the old manual tacking jibs. On the SC20 self tacker the jib luff is 2ft longer than the old standard jib and the foot is about 2.5ft shorter. The jib sheeting point for the self tacker is on the front of the front beam and the manual tacker jib sheeting point was 3ft aft of the front beam on the tramp track. The self tacker jibs on all SC products, 15,17,19,20 are all smaller in area than the old standard tacker jibs on the same boat.
Bill

well done Bill

Bill,
So if I was ordering main and jib for a stock SC20 produced on or after 1992...(self tacking Jib), it would be the same cut as the stock ARC22?

Hi All,

I own the second supercat in question, sail 2032. I have a short rig, oversized jib, square top main, screecher (hooter) and three harnesses. We had three people on our boat. I talked to Rick and he said he would take off the TR but I guess he forgot. It became a non issue when we did not finish.

We set up at Gilberts but we were behind the warehouse. We were working on our boat the entire night before and morning trying to get it back together after we had some damage at the Hirams Haul. We have have been developing the boat to a new sail configuration and did not have enough time to reinforce the hulls before Hirams.

Hope these answers a few questions. you can also go to our website.

Craig

TeamCyberspeed.com

Thom,
According to the registration the other SC20 had an oversize jib and a third set of trap wires and I guess it sailed with three people on board. The oversize jib had the jib tack on the spinnaker pole and sheeted to the old jib trim point about 3ft aft of the main beam on the tramp track. This makes a Genoa type jib something like the old TheMightyHobie18.
This boat received the same corrections for square top mainsail and spinnaker/gennaker as our SC20TR plus he picked up .981 for the genoa jib and .995 for the additional trap wire set. This gets you to 59.2 from 60.6.
Bill

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

Hi Thom,
That is a nice looking Gennaker. Gennakers have been roller furling for years and they are made out of strong, heavy sailcloth/laminate. What does this have to do with spinnakers made out of 3/4oz rip stop material? I'm lost.
Bill

According to North Sails thats a Code 1 furling Asm spin.

thom

Hi Thom,
I think the sailmakers are playing games with sail name/type designations. What weight cloth/laminate is that sail? That is the first time I have seen a triradial sail with crosscut seams also.
Bill

Bill,

Relative to the thread we had several posts ago about superior rudder systems, what happened and why did the Super Cat break a rudder after running aground in the Steeplechase?

Hi Jake,
At the time we ran aground, and we knew we were about to run aground, we had just been hit by a 20+ knot puff and the windward hull was flying high. Eric had the tiller cranked over hard making the boat bare off. The impact with the bottom loaded the rudder blade sideways rather than fore and aft and it simply folded sideways like there was a hinge in the blade along the bottom of the rudder head. The boards and rudders on this boat are all original, 21 years old and built with 1981 construction materials and methods. Todays boards and rudders are much stronger and lighter.
Bill

Bill-

Their info shows both.

thom


[img]http://www.northsails.co.uk/sails/racer/downwind.html[/img] [img]http://na.northsails.com/Racing_Sails/asym__spinnakers.html[/img]

Just to clarify for those of us who do not use this stuff daily:

The "Phi" in Mr. Roberts Euler thin column formula is actually the constant "Pi". This solution applies when the boundary conditions are Moment = 0 on both ends (so make sure the ends really are pin supported in the actual structure).

That was a nice explanation Mr. Roberts.

It is funny to hear people comment that the SC-20 is old. Old like the A-11 Oxcart apparently.

Best regards
-colin pitts

Ho Colin,
Thanks for your suggestions and support. I appreciate your help.
Bill

Bill-

How much larger is an RC30 rudder than a ARC22 in general terms like width, length, chord.

thom

The following comment by Bill is at the same the reason why the strut is the heavy weight solution.

>>This is a stability equation and has to do with 'buckling failures'.

A trick to get around the buckling problem is to induce the buckling failure mode yourself. = PREBEND spinnaker poles. Due to the prebend it can not buckle downwards anymore.

By bending the pole upward you force the failure mode to be directed upward which can be stabilized again by the little wires from the midpole to the bridles. See F18 pole setups. This is lighter (spectra dyneema HT line), cheaper and easier to repair. This has the advantage that also sideways buckling is stabilized which may not be the case with just the strut.

This means that the reason to opt for a strut is only one. Lengthening the luff of the jib. Supportwires to the sides are then still needed to stabilize the pole to the sides or the pole needs to be made stiffer to have sufficient "I" when you want to do it without support wires.

Another trick is to make the angle of the tip support wires relative to the pole as big as possible. The I-20 does this I believe. Here the tip support wires are not lead back to the bridlewires but have their own attachement point forward of the bridle wires.

For cats up and including 20 foot a tube of 40 mm by 2 mm is stiff and strong enough for the all used spinnaker sizes (not hooters). For 18ft and all 16 footers 40 mm by 1.5 mm is by far enough.

I've used 3.55 mtr. by 35 mm by 2 mm for several years and this was on the borderline of buckling WITHOUT midpole support wires. With them I had no problem what so ever not even in windforce 6 (25 knots) although I wished I hadn't pulled the kite then.

40 mm = about 6/10 inch 2 mm = about 1/12 inch

Weight of a 3.75 mtr. by 40 mm by 2 mm pole incl support lines (dyneema) = 2.5 kg = 5/5 lbs

Weight savings on a 3.75 mtr 35 mm by 2 mm pole EXCL strut = 2.5 - 2.2 kg = 0.3 kg = 3/4 lbs. Any guesses what a strut of say 2 ft weights ? Bills 3/4 inch SS strut weights 400 grams = 1 lbs. And than it is not stabilized in horizontal plane.

Two lines of dyneema and prebend in the pole add only grams to whole setup.

The tornado guys are only using the strut to keep the jib area the same to what they had before. It is not a stability device as they still have the lines - wires for that.

Wouter

Hello Thom,
The 30 rudder is 10 inches longer than the 22 rudder. It is also about 1 inch wider on the chord and it is about 1/16th inch thicker at max thickness. For exact measurements call Tom H.
Bill

Hi Wouter,
Prebending the spinnaker pole uses up some of the compression strength of the pole on the compression side. Straight columns can carry more compression load than curved, prebent, columns. If it were not so then the Romans built all those columns at the Parthenon incorrectly. Some spin poles are set up with what appears to be prebend but under load they are straight.
Good Sailing,
Bill

>>>If it were not so then the Romans built all those columns at the Parthenon incorrectly.

Isn't the parthenon build by Greeks ?

Besides I don now of the Parthenon that the construction is crooked on purpose. This is actually the brlliance of the piece. If they used straight lines than the building would not appear straight visually. There is actually no staright line in the contructtion. By incorporations curves and crookedness the architect compensated for the imperfections of the human eye and brain when the object it looks at isn't relatively small and in one plane.

Netherless you are very much right that a prebend pole theoretically has a lowered buckling load. However the by forcing the buckling direction to be upward (by weakening it a little in this direction) one can use lines or wires to stabilize the setup. Of course lines and wires can only provide a pulling force and not a pushing force. Hence the buckling mode of downwar needs to be prevented as that can't be stabilized with support wires to the side.

Of course when a line between the pole and bridle strop is used (Three support wires to the middle of the pole) than the whole system is closed and not prebent is necessary. Even though it is handy to lower the tip of the spi pole.

Anyways the Prebend lowers the buckling load but adding the support lines increases the buckling loads again. So much so that the new setup how as much higher buckling load. You loose a little but that is corrected out over by winning alot. End result is a big net gain.

>>Some spin poles are set up with what appears to be prebend but under load they are straight.

Yes this could be the case. I haven't looked at it like this. On the boats I sailed this wasn't noticeable.

Wouter

Mike-
Thom,

I think there's some confusion here...What I call a strut, I thin some call a pelican striker. I've always thought a dolphin striker points down toward the water while a pelican striker points upwards...is this wrong?
Anyhow, the Tornado runs stays from bridle tangs to the mid pole at bottom end of strut. In the picture I showed, these stays are the light brown vectran line below the bridle stays (stainless). There is only one other pair of pole stays, from the bow tips to the end of the pole (again using vectran). There is no stay from the main beam.

Parthenon--built by Greeks, a temple with surrounding columns, non-straight for aesthetic rather than engineering reasons
Pantheon--a dome built by Romans in Rome

Both are remarkable feats and facinating to study and see; neither have anything to do with sailing or spinnaker poles

Wouter,

This is what I was wondering...why is the strut necessary on the Tornado even with the jib luff below the bridle & down to the pole? The mid point of the pole cannot move upwards and side to side appreciably because of the vectran stays attached there and down to the bridle tangs on the inner gunwales. What does this strut get you other than redundancy? Is the concern the midpole will bend upwards when loaded by the jib luff tension...because of the very slight stretch of the vectran stays? Or, is the angle from the pole to the bridle tangs not sufficient to handle the loading?

Mike.

Mike-

As I said above when Bill gave his view " I stand corrected" but Wouter says the opposite. All I know is mi boat is in the pic. It works and I really don't know which is which...

thom

Mike and Thom,
A strut is a beam which carries a load along its axis. It has nothing to do with up, down, front,rear or sideways. In the catamaran industry a Pelican stricker is a strut that extends upward like on the front beam of a big ocean going cat and is associated with the forestay. A dolphin stricker is a strut that extends downward under the main beam of many beach cats or downward under a spinnaker pole. If some class wants to call a strut a jack rabbit, so what. Let it go. It is time to move on.
Bill

Mike,

What I found was that a spinnaker pole cna easily be made strong enough to resist the spinnaker loads on normal sized beach cats. No strut is required. However there can be advantages using such a strut.

-1- If the strut is loaded up then the bridles can be taken higher which reduced the toe in bending moments in the hulls.

-2- It keeps the luff of the jib straight without alot of jib tension. Remember that tension in the forestay keeps the luff straight and no such tension is present between the bridle strop and pole. You don't want to load up the jib luff to much as that curves the leeach and may pull the draft to far forward.

-3- When the vectran / Wire support line run very horizontal then these line do not stabilize the pole in upward or downward direction. Today many try to get the pole as low as possible. Prebend can take care of this though.

-4- If the luff of the jib is tensioned than it will put a significant load on the pole which is far greater than the forces required to stabilize it in the vertical plane. Maybe the support wires run vertical enough to stabilize the pole but they will hardly ever run vertical enough to take the luff tension of the jib.

-5- A spi pole needs to kept up by at least one element. As all the support wires run downward it means the one element is required to pull it up. Often this is a ring or wires going down from the bridle strop to the pole. With an elongated jib luff this could be a wire also but why not have the advantage of at least point 2 and 4 as well ? In same cases it may pay to have point 1 too. If you are going to have an element there then why not use it to the max.

That is the reason why I use it. I made my boat wider and didn't want to load the boat up more so I raise my bridle strop and keep the angle to the hulls constant. In order to get the jib area in and keep the pole up I opted for a strut. I think I will load it up to medium level. I don't want to end up with a heavy thick road because of buckling considerations.

I don't know why the Tornado guys did it. I hear they changed nothing to the bridle height so I guess the answer must be found somewhere in points 2 to 5

Is it necessary ? I don't think it is. It can be done in other ways at well. May it be the msot attractive option ? That is likely.

Wouter

Marstrom Tornado's are built with some millimeters toe-out, so when you crank the main sheet, the pressure on the forestay straightens the hulls. I think it was 7 mm, but I'm not quite sure.

Marstrom used to have som PDF's on their web site from Multihulls Magazine about their building process, but it looks like they are removed on the new site.

I have never seen a Tornado with any kind of dolphin striker or compression strut on the bowsprit. When the 'sport' rig was introduced, one of the big issues was that no rebuilding was neccesary. You could just add the neccesary equipment and go. (Nevermind all the old non-Marstrøm platforms that could not take the strain of the bigger sail area).

I was the one claiming the Tornado DOESN'T have a dolphinstriker.

It has a strut between the pole and bridle strop as seen on all Tornado's with the new rig.

Can anybody understand now how much confusion it causes by calling this element a Dolphinstriker or Pelicanstriker ?


Wouter

I am wondering -- has anybody EVER hit a dolphin or a pelican with any part of their boat?

I don't know about hitting a dolphin, but during the H-20 Continentals in September, one of the boats straddled a massive sodden log, maybe two feet in diameter, floating just above the surface like a tropical ice burg and caught it with their dolphin striker. It bent the stainless rod parallel with the tramp. Ouch

Hi Rolf,
If the spinnaker pole is stalilized at a mid length point, the jib tack for example, then the effective length of the pole is half the actual pole length and a smaller and lighter weight tube can be used.
If a strut tube is put in place between the jib tack at the spin pole and the intersection of the forestay bridle wires, two important options open up. One is that the forestay bridle wires can be made longer, a taller bridle, which reduces the toe-in loads on the hulls. Second the jib tack can be set at whatever height above the hull deck is desired. Longer luff sails produce more forward thrust and make the boat go faster.
If a strut, vertically downward, is installed on the underside of the pole immediately under the vertical strut connecting the top of the pole to the forestay bridle, and this strut has a tension wire connecting the lower end of the strut to the ends of the pole, then it is possible to lower the outer/forward end of the spin pole which allows a longer luff spinnaker. Again longer luff sails produce more forward thrust and make the boat go faster. The arrangement I have tried to describe here is a lower spinnaker pole and the pole can be straight under load and longer luff jibs and spinnakers can be used.
I have no idea why the Tornado class did what they did. That is their business.
Bill

Yes Mary!

I was swarmed by a pod of good sized dolphins a few years back on an old hobie 18. They are right along side us, zooming past and darting directly across the bows with only inches to spare. We were moving at about 8 kts. At one point, one of them seemed to enjoy matching our speed while swimming between the hulls just in front of the main beam. What a site! At some point, another one thump against us somewhere along the port hull. An amazing day!

I've also hit a seal on that same boat. We were in a good breeze, boat has moving 15 kts easy. My rookie crew was mumbling something while facing forwards...I could not make out the words over the sound of the wind. Moments later...THUMP! "What was that?!" I asked..."The SEAL!" came the reply...."Didn't you hear my warning you??"

Ahh, that piece of rigging is not about any kind of compression on the Tornado (I'm refering to the Tornado, altough the discussion is a bit broader..).

The small cylinder going from the bridle intersection and down to the pole is to restrict the maximum luff length of the jib with downhaul applied in a measureable way. As per the Tornado class rules.

Lowering the tip of the pole could be handy trough a dolphin striker, but hitting waves would be a consern. Also, most classes has a max luff length of spi's as well (The Tornado also has a rule about minimum height of tip above deck).

I think the names dolphin striker and pelican striker are much more memorable than 'compression strut'

Mary,

Dolphins get hit by dolphin strikers all the time. You might have seen some of the ones that have been hit; they have a hole on top of the highest portion of their body.
GARY

Be careful, Gary, you might start a new mariners' myth.

When I sailed the Hobie 18 I always tried to find the pod of dolphin which had the highest number of the ones that had already been punched by a dolphin striker. Then my chances of hooking-up with one was the greatest.

Once the protruding end of that dolphin stiker would snag in the animal's scar-hole, the boat can really fly. The dolphin's tremendous power allows him to actually lift the boat some and this gets you right into planing mode where he can then scoot you along at tremendous speeds.

I miss the striker on that boat so much! The Mystere that I sail on now, has a flat bottomed striker so I have to actually hook onto their fold between their beak and skull with the trailing edge of the striker's bar. Much more difficult to engage this hook-up and also more difficult to maintain it for any good distance.

Those days of riding the "seahorses" are sorely missed!

GARY

Gary you have been to sea too long...

Gary,

This scar hole thing is a myth, this is actually a hole through which the dolphin "breathes", because of this boats like the mystere are actually faster, the sudden rush of speed you are describing when on a Hobie 18 is due mainly to the initial panic of the dolphin as you block its airway, but this speed cannot be maintained as the dolphin soon passes out.

Hooking the fold does not panic the dolphin quite as much but allows you to ride for longer maintaining a higher overall speed.

I have had trouble tacking and gybing when using the dolphin striker does anyone know how to get them to turn?

dangle a fish from the end of your tiller extension when you want to tack or gybe.

has always worked for me.

Personally, I feel that harnessing the pelicans with my striker is more effective. It might not be as fast as the dolphins, however, the pelicans provide more lift in my bows, and I avoid that nasty habit of dolphins to dive. Pelicans aren't very intelligent either, so they work for peanuts :P

Hmmm. I take a different approach when I sail. I try my best to hook up with mermaids...

Keith, dare I ask what a mermaid striker looks like?

Mary - Some things might be better left to musings and imagination after a few rations of rum!

Not too much of the rations, though. That might have been what got the mariners of old thinking romantically about manatees...

SOMEONE SAY MANATEE!??!

(Here's George, the friendly manatee that visited us in Bahia-Honda)

I'm sure someone can correct me (in the legal sense - there's no hope for the rest), but aren't we NOT allowed to mess with manatees?

You are right. However, in this case, we are not sure this is a manatee. I think it is a rock with a dog head stuck onto it, and Rick thinks it is a watermelon with the back half of a pig sticking out of it. If it is a manatee, it appears to be giving birth to an alien.

it was a manatee.

We were docked in Bahia-Honda state park... we were sittin around, and we heard this loud yell in the direction of one of the cigarette boats that was docked. Alot of people were heading over to the boat after a while, so we checked it out.

The guy with the hose owned the boat, apparently he was hosing the salt off his watercamaro, turned aft and saw the sea-cow propped up on the swim deck staring up at him, licking the fresh water rolling off the stern. He drank fresh water out of the hose for about an hour straight. The park ranger came out and said that its unusual for them to venture that far south from the everglades, and the big guy was probably in desperate need of some fresh water. The whole time a ranger was there, and the manatee seemed to enjoy the crowd... after he had his fill, he went back underwater and left.

Now that we've completely hijakced this thread from the dolphin/pelican striker debate...

I'm glad you said that was a water hose. I was afraid it was the hose end of a beer-bong from the party going on! Maybe that's what the manatee was really looking for.

Manatees seem to migrate much further than anybody ever thought. There is the sometimes mentioned one dubbed Chessie that was first found at the mouth of the Chesapeake. He was tagged, and supposedly theyfound that he was making a yearly trek from Florida up the coast to the Bay and points much further north, only to return to Florida for the winter. Just like the rest of the snowbirds. I'm not sure if they're still tracking him or what.

I once had a seagull crash into the tip of the mainsail about 2 feet from the top while sailing with GARY on his Mystere off of Anacapa Island. I suspect he got surprized by either our speed or possibly our tip vortex. I just heard the thud, looked up, and saw him sliding off behind the main, with one "arm" still wrapped around the leach to windward! I couldn't see how he faired after that as the main was in the way.....never saw him again.

Alan Thompson
I20 - San Diego