# UV proof synthetic standing rigging for mast stays.

Discussion in 'Multihulls' started by markstrimaran, Mar 1, 2019.

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### markstrimaranSenior Member

The center hull is built for camping. Sleeping for two, plus a toilet and a large cooler.

It was purpose built for sail trolling at 2 knots, general lake cruising, and be able to stay dry in 30 knot wind/ white caps on the largest lake in Iowa.

We can get some very powerful thunder storms, squalls that pop up out of nowhere, that leave many small boats in dire situations.

I would much rather have the mast fall off then to flip or pitch pole. As it would take a tow truck to right.

Thanks everyone for help and input!!
Some of this ama data will have to wait until I can pump one full of water at 500 gph.

1979 18' sol cat pontoon is not on any cad file for easy volume computation.

They are about 10" wide x 16" tall thru most of the first 10 feet then eventually taper in the front.

2. Joined: May 2009
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Location: Cocoa, Florida

I would suggest you calculate total maximum RM like this:
1-Total weight in lbs times distance from the CB(center of buoyancy) of the lee ama(CB ama = .5 times ama beam)-assume the total weight(minus crew) is on the centerline of the main hull
plus
2-crew weight times crew CG distance from the CB of the lee hull.
=======================
So on this boat Max RM would be total weight in lbs. (minus crew) X 7.58'+ (crewweight in lbs. X distance from lee ama CB) in ft.lbs. This gives max RM with the main hull just flying.
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I wouldn't go less than this or you might find your rig dropping at inopportune times.
As to capsize or pitchpole the skippers skill and judgement are the main factor. When you see a thunderstorm coming reef the rig or drop sail entirely until after it's over.
Whether or not your mast and/or cross arms are strong enough is a question for an engineer and you should invest in one. Anything else is just guessing. The engineer can determine if your mast and cross arms are strong enough for the max RM.
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Can you tell me the maximum sail area and the height of the Center of Effort from the waterline? How deep is your daggerboard? With this info I can tell you the maximum wind pressure you can sail in based on max RM assuming your structure is strong enough. You will be able to provide wind pressure info along with Max RM to an engineer who can then evaluate your structure.
Remember, nothing replaces your judgement as skipper but I think it's great that you are looking into the forces acting on your boat!

Geometric CE
Draw a line from each corner to the center of the opposite surface. The intersection is the Geometric CE which is adequate for this purpose.

Last edited: Mar 6, 2019
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### BlueknarrSenior Member

How will you know that the loads on the rig are excessive and failure is eminent?

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### markstrimaranSenior Member

It's going to happen, when stalled after jibing, and the super power boat wake hits, after coming around a point that changes the vector of the wind.

But then the mast foot is solid welded with a steel insert. Which is riveted and epoxied into the 3x5 aluminum mast.

Making the mast free standing, and bendable, so as force increases so bends the mast. Which is a highly measurable warning indicator. Allowing enouph time to depower. My normal mode is one sail and half reefed in 20+mph and in heavy chop.

When I researched this years ago I used the mast height of a farrier f-22 31' mast to 18' beam ratio and total sail area, and bumped up the beam and lowered the mast slightly, Then shortened the foot.

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### BlueknarrSenior Member

Problem solved. Why all the discussion about shrouds then? How's your mast engineering skills?

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Location: Rhyll Phillip Island Victoria Australia

### trip the light fandangoSenior Member

Your mast is going to snap first if your stays are in good nick and you keep standard or equivalent , so 4mm is heaps of strength in dyneema or whatever you call it there. You're unlikely to go A over T because of your weight in the tinny, but you could submerge the bow, but you have all that floatation. Your issue is no steering in big winds because all your power is too far forward, as you know. There's space for a little, well mainsail/storm sail, that will sit over the rudder which will give you back steering in a high wind and improve the boats action. Waffling on about righting moment when you have an elephant in your room is puzzling, wonderfully academic though. I'm tipping you made your cross beams really quite strong and practical. You threw out convention to get a really fast set up time, I get it ,and it's original thinking, nice to see people are showing interest.

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### markstrimaranSenior Member

Shrouds increase the amount of force the mast can take. They are a safety buffer.

Until I can build a carbon spar.

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### markstrimaranSenior Member

The cross beams are 14 guage steel.

A swing keel board is mounted on the forward cross beam. It can be pivoted in its mount to adjust.

It has slight weather helm.

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### trip the light fandangoSenior Member

Fair enough. I still suspect a future edition will be to increase the length of the spar to improve the sail area for a sort of conventional small mainsail[a reverse set jib with a little and light boom??].. we'll see , anyway, it's an interesting boat.

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### markstrimaranSenior Member

The rear spar is already at max load holding back stay tension.

My biggest obstacle is the mast needs to be more rigid, perhaps a 4 x 6 aluminum. Holding sail shape on the leach in 15 mph wind, currently limits a low drag airfoil needed for faster performance.

The hobie cat 16 mast is just too small. Carbon fiber dreaming, but someday I will maybe find one as salvage.

11. Joined: Apr 2018
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### trip the light fandangoSenior Member

A boomkin could help with the load and create enough space for a small mainsail. The added load of a small main will be much lower than where the mast wants to break at the moment., the top end? Carbon is lighter/stronger so less weight up high is an advantage but having the mast as the weak point isn't such a bad compromise, you can clearly see when you are over doing it. You need more power low and better balance for the tiller it looks like. I just saw the other thread you've posted , I thought this all sounded familiar, ha , cheers.

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### markstrimaranSenior Member

The boomkin, mizzen sail. Would interfere with trolling fishing lines.

Do you think a forward fin keel would equalize sail area balance point? As well as the boomkin?

13. Joined: Apr 2018
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### trip the light fandangoSenior Member

I couldn't answer that, some trimarans start their dagger board forward of the mast but I think it still probably ends up directly below the centre of effort from the mainsail. Could you mount your rod holders on the boomkin..? Because you can make up you own designs with the main issue being speed into the water from the trailer, maybe you could consider two short masts that raise together. either in line down the centre or on each solacat hull, which would have a brace across to the top of both, the middle of which you raise them from , like you do now. You could lower the main load on the sails making it more stable and have a craft that can close haul and manage higher winds... spinnakers or genoas are still feasible in light air..Everything has a compromise .so leave it ...it is a stable platform though.. ha.. cheers.

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