carbon fiber wing mast for my cat

[rallard]

I completed construction of my cat Jolie Julie in autumn 2004 and then rigged it with a white spruce lattice/epoxy wing mast. The mast does a fantastic job with the only drawback that it is on the heavy side at 600lbs. for a fairly light cruising cat, Kelsall Suncat 40, 5.0 tons. I am now completing construction of a carbon fiber/ CoreCell replacement wingmast weighting 250lbs. The new mast is stiffer and I therefore replaced the use of spreaders with adjustable double runners as shown on the attached sketch.
The forestay and shrouds are all attached on a single 3-eared stainless steel device at the front of the mast and the runners are attached via traditional vangs and compression tubes directly on the mast at the widest part.
For the runners, rather than attaching each one separately to the adjustment vang, I intend to run a single 10mm dyneema or vectran rope from the upper runner tang, down through a block tied to a 4:1 adjustment vang and back to the lower runner tang. Has anyone experienced any problems using such a single line for both upper and lower runners?

 

[jmolan]

Rallard, Great job on the build. Man that looks like a buitiful boat and rig. The weight saving sounds like it coud be huge. I have often wondered what a CF mast saves in weight over a more traditional Aluminum mast.
I do not see any reason why your set up will not work. If it were me, I would post the question to Brion Toss forum.
Rather than run two length's of line the full length, did you consider a bridle part way down and a single line to the deck? That would eliminate a certain amount of windage anyhow.
Thisis the set up I have for a backstay on a Searunner Trimaran. The tangs are titanium from Colligo, so far it seems to be working great as far as ditributing the load and ease of adjustment.
Good luck on the new mast. How long was the wood mast?What are you doing with it? That is the mast I wanted for my cruiser.

 

[PAR]

Eric . . . tap, tap, tap . . . is this thing on . . .

 

[Eric Sponberg]

I'm here, just getting a cup of coffee.

Rallard, your idea should work and be self-adjusting. That is, you will have the same load at both attachment points on the mast, and the stretch, such as it may be, will be accommodated accordingly.

Looks good.

Eric

 

[Boston]

that was funny Par
you guys are dam dedicated

I do have a question about the carbon fiber though
on the Nemesis airplane in order to get the best strength to weight ratio the builder used a reverse autoclave set up to cure the epoxy
yet this obviously well done mast doesn't look like its sitting in a heated mold
now I could ask the Nemesis builder what the strength gain is and if he used some kind of special epoxy
but Im curious if you guys already considered that and found it to be a negligible improvement for the trouble

thanks
B

 

[Eric Sponberg]

Boston,

Some of the people who have built my masts have autoclaves, others have used vacuum bagged heat cure. The autoclave compresses the laminate more to squeeze out more air and have fewer voids, but we are talking miniscule amounts here. A good vacuum bag laminate may have 2-4% voids, whereas an autoclave laminate may have 0.5% to 1% voids. These processes can use pre-preg carbon or wet-layup carbon, with pre-preg being a more controlled laminate. Resin infusion is yet another technique, which is easy to do in glass, less so in carbon, and this is because you can see the resin migrating with glass, which turns translucent, but wet carbon looks the same as dry carbon, so you can't really tell how well the resin has impregnated the fiber. In all cases, the strength and stiffness properties of the laminates depend on the quality of the molding process, the quality of the materials, and the final fiber-to-resin ratio of the finished laminate. A 70% fiber content by volume is about the best you can achieve, because after than you necessarily have void spots in the laminate.

Yes, there can be differences in mechanical properties by as much as 20% or more, depending on all the circumstances. And generally in aircraft molding, the materials and process costs are an order of magnitude over that which we see in boatbuilding processes.

For me, all this boils down to the fact that I cannot design carbon fiber masts for boats as stock designs. Every boat is different and requires different geometry and dimensions. Much goes into assessing what the final properties will be based on the availability of materials and the skills of the builder and the process that he uses. What works for one builder in the US does not work for another builder in Australia or Africa or England. The mast designs have to be customized to get the most mast, with assured survivability, for the least cost and weight.

Eric

 

[Boston]

when I do my coaster Im going with a CF mast all the way
it will be a two off build
one to sail one for sale
or at least that was the plan till the economy went bust
this bit about a CF mast is the one part I know absolutely nothing about
so thanks for the tip
B

 

[PAR]

Especially cost . . .

 

[Boston]

I guessed about $12,000 pr mast

how close am I

I have a complete shop so I can DIY it
( which if your not careful can just as easily stand for "destroy it yourself" )
and plenty of stuff for the mold laying round
hear rumor Its ok to just vacuum bag it in a cold mold
instead of the autoclave I was planning on having to build
even so I still would have all the crud laying round
so its just cloth and epoxy

hardware would have been similar cost whatever the mast material

 

[rallard]

jmolan, thank you for the info supplied and your interest in the wood mast. I will likely part with the mast after I have completed satisfactorily testing of the new CF mast and have convinced myself that it will not fall apart, which could mean end of next august. If I sell the mast, it would be complete with all wiring, vhf cable, lightning protect wire, 316ss masthead, diamond,etc except for the sail track which I keep for the new mast. The mast is 50' 2" long and attached thumbnails will give you a hint on construction. I'd only want to recover my material/construction costs, which should run anywhere between 4 to 5 $K

 

[rallard]

I'm here, just getting a cup of coffee.

Rallard, your idea should work and be self-adjusting. That is, you will have the same load at both attachment points on the mast, and the stretch, such as it may be, will be accommodated accordingly.

Looks good.

Eric

Eric, your answer is highly comforting and the decision is made, I will rig the mast that way. Thank you.

 

[rallard]

I guessed about $12,000 pr mast

how close am I

I am tempted to get you excited and tell you that you're way too high!

Reality may have a different call. It first greatly depends on the actual size of your "coaster". Then you need to have a pro determine for you the basic construction requirements such as volumes, single skins or sandwich,choice of core and other materials, schedule of lamination...and then you can figure out a meaningful estimate of cost.

 

[Boston]

well I was a custom home builder till the economy went bust
very hands on, not one of those pencil pusher types
so I think I can handle building just about anything

the design is
yes
still a toss up
but if I just keep asking the right questions to the right people
( and this site is definitely the right people )
then the best answers will make themselves self evident

and yes I have a guy in mind who is an accomplished designer and I will definitely be consulting him on the conversion to CF

I went with for rough estimation costs
2.5 ~ 3 rolls pr mast
roll is 50" x 100'
should be aprox enough for a mast on a 39' to 46' vessel
but all is just a guess till I make a few more decisions

thanks for the tips
B

 

[rallard]

Boston, for a 40 foot boat, it can definitely be done for under 10$K . Rolls normally come more with 100 yards or meters than 100 feet. The CF has must unidirectional.
You have the building skill and it is a must; masts are highly dynamically loaded, you will need a lot of knowledge on the building process and on choice of the right materials. Finally, I am a retired pencil pusher. Good luck with the project and I hope it becomes reality. It can be done!

 

[Boston]

oops I meant yards
and I owe you a beer for the pencil pushing crack
send me the address of your fave bar and when your going to be there and Ill call in a brew for you
cheers

and nice to see one of the office boys out in the shop for a change
way to go slacky

B