I recently broke the mast on my Viper 640 monohull, and I'm thinking about putting an ARC-21 rig (mast, boom, and sails) in as a replacement / upgrade. The goal is to fire up the boat with a bigger and more powerful sailplan, and to get 2 trapezes.

I'd also like to put on a MUCH bigger asymenterical spinnaker than the ARC-21 carries.

- Any thoughts?
- Any feedback on how good the ARC-21 rig is?
- Would this kind of rig support a MUCH bigger masthead-rigged spinnaker? I'm worried about what keeps the rig from breaking (going forward) since there is no backstay.
- Suggestions on alternative rigs I should consider?
- Has anyone tried something like this? What kind of issues am I facing?
- How bad an idea is this?

A picture of a Viper 640 is attached ...

Thanks
Jeff

I think your question would be better answered by people familiar with the viper and not the mast.

I think you'ld be better off getting a skiff at that point, cause it's what your going to have.

I don't have the engineering experiance on catamarans to give a definate answer, but I'm sure Bill can. IMHO, you'ld pull the chainplates or shroud ends right out of the boat for starters. An ARC21 rig is pretty darn powerful !
I14 or 49er is in your future

Or if I were you, I'd sell the mono-slug and get a cat. Just having fun with you, I like leaners too.

Jeff

Typically a catamaran rig has no backstay because of the high roach sails used. The mast is held from going forward by swept back side stays. The mast itself is kept from breaking while flying a large spin by maintaining main sheet tension (in effect a backstay of sorts) This feature works very well in catamarans beacause they are able to generate significant apparent wind, and hence keep a large amount of mainsheet tension with correct sail shape while going down wind.

You may want to explore whether you can accomplish this with the semi-planing hull of your boat, or rig some kind of doubler back stay while running the spin. Busted spars are ususally no fun and very expensive.

Good luck

Matt

Hey Jeff,

Before you ask if it can be done….. Ask yourself if it should be done.

I’ve never sailed a Viper 640, but….. By the looks of your picture (if that’s your boat) – she looks like a beautiful machine. My point – If she were a basket case (a total shamble)… ok I could see trying something along the lines of what you are thinking. But she appears to be in great shape – why not keep her “stock” and build up (or buy) something else. I guess I’m a purest when it comes to stuff like that. If the boat were beyond any hope of becoming a “complete” boat again – I could see playing with modifications. You run the risk of taking the boat out of its class – making it un-marketable. Breaking the boat by over powering it. Or simply turning what would seem to be an inexpensive modification - in to a project that would cost more than a stock replacement.
Don’t mean to rag on you – it sounded like a cool idea! If you’re looking for more of a thrill, more power, and a quick way to impress the chicks….. Move to two hulls! Sounds like you’re a closet Cat Dude anyway!

Ballast

Hi Jeff,
The ARC21 mast is the same section and lenght as the old standard SC20. Carrying a mast head spinnaker will require a couple of 1/8th inch Vectran bachstays. Each backstay will require a little 6:1 mechanical advantage pulley system at its lower end so that the leeward backstay can be eased as necessary. With the chute up the main will likely be trimed down the center of the boat. This is proper trim on a chute carrying catamaran. A close reach is likely to be the point of sailing that requires the 'trim out' position for the mainsail.
What does the Viper weigh? It sounds like you are going to soup it up something like an Australian dinghy. Get yourself some agile and quick crew.
Good luck,
Bill

Hi Jeff,

Be careful with the vang loads. Catamarans have a wider traveler and do not use a vang. The mainsheet takes the twist out of the sail. Once you add a vang to the boom it will be loaded in bending, not just compression. There will also be a huge compression on the gooseneck.

What do you plan to do with the mast step?

Sounds like a fun project.

-colin

Go ahead and add some racks, and make it REAL fun.

Check out this Lake Monster we built...

Mike - Yee-Haw! That is too cool. I do think you need a bigger spinnaker though...

As for the 21 rig on the Viper - remember that the 21 rig also is a rotating mast. That would mean for the viper either not letting it rotate, or coming with a mount either on the deck or keel to let it rotate. If it is mounted on the keel as it appears is stock, the boom will be pretty low to the ****. Sounds interesting though! Good luck and keep us posted!

Hi Colin and jeff,
Hopefully the boat won't need a vang. If it will develope enough relative wind velocity, the vector will be far enough forward that a couple of feet of traveller track either side of center will be ample. Idealy this track will be located under the clew of the mainsail. If the boat turns out to be a fast sailing system, the mainsail will always be going to windward and trimmed on or near boat centerline.
Good Luck,
Bill

You are right, I am trying to make the Viper 640 an "old man's" skiff. It has a nice comfortable place for the skipper to sit, and the 185 lb keel gives it some stability.

I share your concern about pulling out the chainplates.

Thanks
Jeff

Unfortunately, the Viper 640 class is pretty much dead. It was somebody's "Boat of the Year" in 1997, but the builder went out of business 2 years ago. The molds were sold to a company in Europe, but little / no activity since then. Only about 80 boats were ever sold. There is only one active fleet in Marblehead MA.

So I figure there is no advantage to keeping the boat "class legal".

As far as a shambles goes, the mast is broken, mainsail/jib/spinnaker all were damaged and need repairs, and the mast step was torn loose.

So I figure I'd spend some extra money to make the boat more exciting.

Thanks for your thoughts, and I have the same concern ... lots of cost with the risk of a "hacked" result.

Bill -

I just realized that you must be the designer of the original Supercat boats. Thanks VERY MUCH for your thoughts !!!

The running backstays sound like a good idea. I wish I had put them on the Viper before I broke the mast. It was 20 knots downwind with the spinnaker when it broke, and we were easing the mainsail for control. Probably lost too much leech tension.

The Viper 640 is actually a fairly heavy boat. It is 725 lbs total, with a 185 lb bulb of lead at the bottom of the foil.

I'm actually worried if the ARC-21 rig is large enough. The original Viper mast was 28' vs the ARC-21's 33'. Sail area is 252 sq-ft vs 282 sq-ft on the ARC-21.

But the ARC-22's 38' mast and 380 sq-ft sailplan is probably way too big. So I thought I'd try the ARC-21 rig with a monster masthead spinnaker, and an 18 footer skiff style long spinnaker pole.

Thanks again ...
Jeff

Bill -

The mainsheet traveller idea sounds like a good one, but will be hard to install. I'll try to figure out how ...

Jeff

Mike - That is an awesome boat. Are you still glad that you put all the money and effort into it?

Keith - The rotating mast is definitely an issue. The Viper 640 deck is not strong enough to step the mast, so it has to go down on the keel. I am hoping to talk the ARC-21 folks into selling me a mast with an extra 2-3' of length on the bottom, so that the boom isn't too low.

Thanks for your thoughts ...
Jeff

When I added a spin to my Hobie-18, some advice I got about sailing it in a good blow was "cleat the main, toss the sheet onto the tramp, and take your pitch-pole like a man!" - The truth of it being never release the mainsheet unless the spinsheet has already been blown, or you'll be shopping for a mast...

Maintaining the rotating feature would be interesting.

Well, I'm shopping ;-) that's exactly what I did when I broke it ... ease the main with the spinnaker up in a blow. I liked Bill's suggestion about running backstays, although they are messy and extra crew-work.

I'm planning to keep the rotating feature. It will require cutting away a small amount of the deck around the notch where the old mast went through, to keep the deck out of the way. The mast step should not be a big problem if I attach a small stainless plate to the keel which can accept the bolt for the rotater ball.

Mike -

That is an awesome boat !!!
- How long is it?
- What class was the original hull? Keel?
- How did you attach the racks to the hull?
- It didn't look like there is any bracing on the spinnaker pole. True? I would think that big a kite would break anything that long.

Are you still glad you spent all the money and time? I'm facing alot of the same. My gut tells me its worth it though, cause I love messing around with boats, and I love going fast, but I'm a mono-slug at heart.

Jeff

Hi Jeff,
The max shroud tension is determined by max righting moment. If you don't change max righting moment, you won't change max shroud tension or max chainplate load. If you add trapeze, the extra righting moment goes directly from the trapeze belt/person to the mast/rig/sails and does not go through the standing rigging. That is part of the beauty of the trapeze. The trapeze adds extra compressive loads coming down the mast but it does not add to max shroud tension.
As far as stepping the mast on the deck goes: This is the way to do it. The ARC mast step ball holds the mast base while stepping and unstepping the mast as well as being the mast rotation bearing. Take a piece of your broken mast and make a short column from the old mast step to the underside of the deck at the new mast step. This way when you step the new mast on the deck, the boat won't know the difference and all the loads on the structural system will follow the same paths they always have; no difference.
I don't know exactly where the clew of the mainsail would come to relative to the transom of your boat, but if it is close to the transom, you could beef up/make new and stronger the cross beam that supports the upper rudder pintle and install a mainsail traveller track there.
One of the first things you need to do is make a good estimate of the price of all of these parts. I would estimate you are talking about you spending 10k on parts and sails with you doing all the work. If you are not handy with doing this type work, add another 5k. You know how boat costs are, things could run up to 20k with a few surprise problems.
Good Sailing,
Bill

Hi Keith,
Your problem is that your spinnaker pole is too short and your spinnaker is too vertical. The force vector from the spinnaker is too close to horrizontal and this makes any boat pitchpole. A proper length pole will lay the spinnaker back at the head so that so that the force vector from the spinaker lifts the bows as well as well as pulls the boat forward. A few more feet of pole length makes all the difference in the world in boat behavior with a spinnaker.
Bill