I am widening my Nacra NA 5.8 to 11.5 feet.

I have already added a squaretop w/boom and a carbon sprit and F18 chute. Boat will be setup as a very fast and hectic singlehander. i'm 6'5" and 220, the width should make it manageable.


Here's the question.

I have two options:

A. Fabricate a new bow foil which is 3.5 feet wider than stock. Run the pole on top of it. i have fabricated a stainless "triangle" on which the cable for foil prebend rests atop, and the pole passes through.

B. epoxy a stainless sleeve onto the carbon pole. Place a 2x2 T6 beam between the beams on the center line. Then run a cable from the back beam to the end of the (lengthened) dolphin striker rod. then run cable from DS rod to stainless sleeve where forestay attaches. Then run anther cable from DS post through spreader under forestay to end of pole for pole prebend.
- i would replicate the system seen on the GC32 catamarans.


the boat wont be in big seas, and i want to keep the jib tack low enough to continue to use the NA jib, so i have no proble with the pole siting lower than would be normal, hence the elaborate setup. I think that if i go with option B, i wont need to drill holes in the front of the hull either, and can manage pole side movement with the existing forward tangs, since all upward force will be managed by the under-stay.


thoughts?

http://www.thedailysail.com/files/imagecache/Article_image/article_images/GC32AustriaCup070_620.jpg

http://www.sailweb.co.uk/media/2013/05/5105-1-1000.jpg

Option A sounds like a simpler and possibly more reliable solution to me.

It also seems to me that the typical beach cat spin pole may be a bit undersized to deal with the loadings being placed on it in the configuration for option B.

That is a concern, namely, the arrangement in option B would place large compression loads on the CF pole, something CF isn't particularly spectacular at handling.

or is it torsion CF struggles with? i always get those mixed up.

In any event i could always run an aluminum tube from the front beam to the forestay, hook all my wires to that, and slide the CF tube inside.....

i'm just really not crazy about fabricating a 112 inch long bow foil. haha

You might considering a system similar to what the supercats use. Seems much easier to make at home. You would have to modify your jib some, but not much. You may be able to see some of it here.

Basically you made your bridles wires as you would in a non-NA rig. Use a SS rod goes below your forestay to a ring around the spin pole. A pair of cables locate that ring to either side using the bridle tangs.

http://www.thebeachcats.com/classifieds/catamarans-for-sale/p13103.html

Yeah i would, but because i am setting it up to single hand, i really need a furler, which wont work with that configuration.

seems like a large job and a fair amount of cash needed (new extrusions, new tramp, etc)

why not just buy a 18square, super cat 20, mystere 6.0xl or other wider boat?

Well, i have the 5.8 and its ready to go, besides 18 square masts can't support a jib, much less a chute.

I need a new tramp anyways, the old one is tearing apart. I have a ton of sailboat parts in my inventory. everything from cabling to spreaders to you name it. I also have a metal fabrication shop. Everything from welders to mills.

take out the cost of the tramp (i have to buy one anyways) and all the parts and pieces i already have, and this will cost me 350 bucks.

The idea is to do it in such a way that everything (except the added boom) can be removed and the boat can be set up as a stock 5.8 again.

all sounds like great reasons to me. especially, "I also have a metal fabrication shop"

take lots of picks, I would love to see them

Where do you sail?

I am accumulating the parts and pieces and finalizing the design in sketchup. should be underway in the next week or so. Maybe a build thread would be in order... hmmmm

It looks like the aluminum sprit idea will save a fair amount of weight vs. the bowfoil, and what weight it does have will be further aft. I do think it is prudent to use an aluminum extrusion rather than rely on the carbon tube, 6 pounds or so is a small price to pay for piece of mind...

The boat is in Muskegon, MI.

Then you should have plenty of time to get this sorted out. At the rate we're going, ice probably won't be off the lake until June.
It's been a long time since I've seen the big lakes ice up like this.


Quite the winter we're having!

First update:

I was able to gather all of my supplies and inventory together. I have enough blocks and cleats to hold me for the next decade i think. I also gathered together all of the rigging i had leftover from an E-scow project several summers ago. I will be using that for the spinpole support. the workshop was adequately messy, so i decided to get started.

The first thing i decided to do was to build the bracket which will attach to the end of the dolphin striker bolt. The DS bolt will go through it. The rear section of the understay will attach to the back of it, and angle upwards to the rear crossmember and the aft end of the spinnaker tube. Then the front section of the understay will attach to the front of the bracket. (or understay backbone) two cables will attach here. One will lead directly under the jib, furler and forestay, and the other will lead through a spreader extending down from under the forestay, and forwards to attach at the tip of the pole, underneath the spinnaker. My earlier post has pictures of a similar design.

Right. so i had to make the bracket. The first thing i did was to determine the target distance for the bracket to protrude underneath the front crossbeam, assuming it would be immediately above the DS strap. (putting it below would require drilling a 9/16 hole through a 1.5 inch aluminum strap. too risky) The objective was to maximize the distance down to increase the amount of vertical downward pull on the forestay, while minimizing the extent to which it would protrude under the beam, to avoid hitting many waves. Taking into account the deflection rates of the selected spinnaker pole, i plotted the curve of force vs. angle of shroud, and decided on 10 1/2 inches depth of DS strap, and roughly 10 inches down for the understay backbone.

Having arrived at that measurement, i was able to plot the triangle created by extending the rear understay to the rear beam from the DS backbone. I then determined the angle to be approximately 8.5 degrees.


I took 2 pieces of 1x1/2 inch steel bar from my inventory. I bent one of them to the 8.5 degree i needed. This way, i can use the old staymaster adjustable shroud i have in inventory. I the took the second piece, made it shorter than the first and placed it on top, so the angled section extended aft of the stacked part. Then i welded them together all the way around. I grinded the weld filets smooth, and drilled a 9/16 hole in the center (for the DS bolt) and holes in the front and back for the fore and aft sections of the understay.

Then i painted it.

Then the truck from ALRO steel showed up. I recieved my raw materials for the new crossbeams.

I recived 1 24 foot 4" x .125 wall aluminum tube, a 24 foot 2 inch tube for the spinpole, an aluminum strap for the DS, and some other odds and ends i'll get to later. Total cost was 345 dollars delivered to my garage.

Not wanting to waste time, i dug in immediately, and cut the 4 inch tube to size, which happens to be 11 1/2 feet long.

I then removed the front beam, so that i could use it as a template for drilling all the many holes i would have to drill.

After i removed it, i brought everything down into the basement shop and began measuring, and remeasuring, and then measuring again. First up was the center DS hole. I was careful to us several gradations of bit size to ensure a clean centered hole. I was able to maintain a tolerance of <1/16 in.

I then moved to the DS strap. I retained the fitting from the old tube which is basically three bolts welded to a stainless plate. It was alot easier to use this kind of an arrangement as the alternative would be to make up three compression tubes, and have 3 through bolts on either side.

After alot of drilling i was able to get the new strap mounted, and cut to size. The objective was to have the end of the strap be exactly 12 1/4 inches from the end of the tube to ensure a proper fit on the hull, my tolerance was <1/16 of and inch again. With a sigh of relief i moved on to the bolt eyes.

In order for the understay arrangemnt to work i needed side to side support for the pole to have the whole thing work sans bridle foil. I got 2 grade 9 bolts and 2 screw on eyes, and attached them at both ends of the pole, just above the DS strap. the eyes have a breaking strength of 3800 lbs, so i should be good.

Finally, i pulled everything off, and build compression tubes for the DS bolt, amd the two pole shroud support eyes. Getting the compression tube for the DS centered on a 9/16 hole, 6 feet down a 4 inch tibe was.... interesting....swearing was involved.

After that i put the whole thing back together, tensioned the DS to put prebend in the tube, and the front crossmember is done!

Note- i selected a DS bolt with 180,000 PSI tensile strength, 2.4 times stronger than stock, which should handle additional loading from the design.


That's all for now. I'm having a party on saturday, and will be enlisting the attendees to help me install the finished cross member.

lookin good!

Making progress. Got to the point of doing a full mock fitting using lines instead of cables, and a board as a spreader. Still a lot of details to finish that's for sure, but everything has fitted together exactly as planned. No surprises.....yet.

More pics

The spin pole appears to extend to the rear beam...is that temporary?

Looks like the DS rod goes through the pole, seems it might see some interesting loading.