UV proof synthetic standing rigging for mast stays.

All the RM math calculators, I could find, are for mono hills, with ballast, and crew weight on the bull warm edge.

 

Great 3/16" dyneema will be much stronger than what I have been using.

Full beam is 16'

From the top of the mast 1000 pound pull would flip the trimaran. If sitting on hard ground.

At the center of sail area, it would probably take 10,000 pounds of force to flip.
3300 at the mast, 3300 at the boom spirit. 3300 at the sail foot.

The 5/32" stainless shrouds take most of the 3300 force, but that 10,000 pound number would be in something crazy like a 40mph wind.

Each ama is 150 pounds
Aka is 50" wide and 500 pounds.
It has a 100 pound steel crash bar frame built into the cabin.
Plus 300 pounds of camping gear,

Total sail area is 210 soft
160 sqft is the main.

It was 4 years ago that I pondered any boat math.

Last year was a new trailer.
Year before was sewing sails.
Year before was adding Sol Cat hulls.

 

I'm surprised by 16 foot beam. Not many boats are wider than they are long.

1/4 inch dyneema is oddly usually cheaper than 3/16. Greater demand for 1/4 makes it easier to find as well. Splices will consume 2 feet each. So add 4 feet to the shroud length. Get an extra couple of yards to practice splicing. I recumend the "brummel" splice. I can do them with just My fingers but a did does help. I have a set of Sampson fids somewhere; I usually find and use able ball point pen. There are plenty of Utube videos.

Multihull RM calculations are a week bit trickier than monohulls. Would you like to be walked thru the process?

 

The sol cat hulls are 20' x 12"
The center aka is 14.5 x 48"
Drafts 6"
Amas are normally drafting 3"


I am interested, in crunching the RM, but I can't seam to wrap my mind around,
What the RM number has to do with how many square ft of sheet I can fly, and still have the mast holding steady?

I tinkered with spreader bars and back stays, numbers a while back and went with 3/16" steel cable.


20 mph with 30 gusts on the main sail only

 

Numbers are more important to engineers than to us run of the mill sailers. We lose if either the rig breaks or our boat is blown over. The engineer loses only if the rig falls over before the boat is blown over. It is the sailer's job to reduce the healing force before capsizing, as it is possible to monitor the angle of heal. We have to trust that the engineering is done correctly because we can't directly observe over straining of the rig until it has already failed. The RM measures how much healing force it takes to capitalize a vessel. It is the engineer's job to ensure that the rig can withstand atleast that much force.

Kind of rambled. Do you understand now

 

Ok I see it is a way to size the rigging to the smallest lightest cable's that will do the job.


At 16' wide with a 28' mast hieght. The solution to this math will probably give me some excessively high tensile strength shrouds.

I am a very beachable trailer sailor, able to dodge hurricanes.

 

Maybe use slightly more than minimal to increase safety factor

Wide boat with short mast, allows wide shroud angles. Wide shroud angles could allow thinner weaker cabling. Only after all the numbers are crunched will anything be known. Until then it's all clueless speculation

 

Did a little destructive testing early on, the weak point was the weld on the mast foot.

This was before I used the black spar and a back stay. The galvanized bar, held the mast up, which focused all the mast force against the mast foot.

Sure I am always ready to learn better ways.
This was an early set up and the boat was single skinned and very flexible. This caused some serious dynamic loading on the mast. Slingshotish, it is now foam cored, and has 4" thick sides.
I had it conventionally Bermuda rigged, but went aft mast, mostly for ease of single handedly, quickly raising the mast. It also allows for more sail area, which is nice on the hot calm August summers.

 

I can't seam to find a RM calculator for a trimaran.



The more I read about it the more complex it gets.

 

You're right quick and dirty mono-centric calculators are useless for tris.

There are members on this forum who are willing to crunch the numbers. Unfortunately, I am neither a naval architect or engineer, so I can't do it for you.

I strongly suggest you start a new thread titled. "Help me calculate my RM" provid the following information:

Trimeran
Full beam is 16'
Each ama is 20'x12", weighs 150 pounds with an at rest draff of 3".
Aka is 14.5'x48" weighs 500 pounds draws 6".
It has a 100 pound steel crash bar frame built into the cabin.
Plus 300 pounds of camping gear,

WHAT is the RM?

HOW strong should the masthead shrouds be if 28' mast.

I wish I could be of greater assistance.

 

Is your boat designed to fly the main hull? Do you know the total buoyancy of the ama(s)?
What is the total weight of the whole boat incl. crew? How far from the centerline of the main hull does the crew sit to windward when sailing in maximum conditions?

 

Maximum Righting Moment for a boat without a deep keel will be less than displacement x max beam / 2. How much less depends on the details of the hull shape(s) and CG height, and requires more detailed calculations. A conservative approachfor sizing rigging might be to use the RM from the formula above.

Edit: The formula above assumes the CG is on the centerplane and close to the waterline. It does not include the effects of crew hiking, etc.

 

By bouyancy are you referring a full submerged or submerged only to a functioning level.?

Probably close to 2000 pounds to fully sink.

The whole boat would be 1000 pounds.

The 200 pound person would be 7 feet from centerline.

The main hull is a 4 degree shallow vee. I had one ama flying once in a 30 mph wind with 210 sqft sail.

My hull speed is 5.5 knots. But it will plane at winds above 20 mph.

Last season I missed all the windy early season sailing. So my memory is faded.

 

Total buoyancy (up to the deck). Is the boat designed to fly the center hull?

 

Doug Lord,

Thanks for stepping up. One of the greatest features of this forum is how there is always someone who knows more than me ready to teach..