Hey Everyone,
well I decided to take on a winter project. I have been thinking about building a trimaran from beach cat parts for quite some time. I have an Australian Nacra 16 square that I am looking to use for its parts; hulls as Ama's, mast, sails etc. I came across a c-class catamaran on craigslist out of Vancouver and picked it up from North Vancouver, Canada last weekend. I couldn't pass up the deal, free, and am planning on using one of these hulls for the center hull on the trimaran.
I am sure I will be looking to all of you for more advice as the build progresses, however, have some basic design questions I need opinions on.
a. What is the optimal length to width ratio. The centre hull is 25' long and the two ama's are 17'. I was thinking 16' width, opinions?
b. Anyone have any experience installing bowsprits? Need to know optimal tube thickness and diameters to fly a 300sqft spin on a 29' mast.
c. How would I calculate needed crossbeam diameters and wall thickness? I am also thinking of a internal dolphin striker configuration for the front beam.
Thanks for the help!
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Jay Brown
Nacra 16sq. spin and modified
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Building a beach trimaran....calling all engineers....
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Posted: Aug 15, 2011 - 04:46 PM
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Posted: Aug 15, 2011 - 05:09 PM
Contact adventuretri, he recently finished building a tri using a Nacra 6.0, http://www.thebeachcats.c…ot-3b-carbon-tubing.html.
Turbo
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TurboHobo
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G-Cat 5.0
P16
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Posted: Aug 18, 2011 - 05:57 PM
Does anyone have any ideas what kind of rig I could use for this? The c-class catamarans have 40' high fixed wings these days, so I was thinking of a rig slightly larger than a Nacra 6.0's or a Tornado's. Any ideas? Only things are that it needs to be easy to find and easier on the pocket book. Also, does anyone know crossbeam location ratio's (how much hull needs to be in front of the front beam to prevent pitch-poling?) from a 25' boat?
Thanks for your help...
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Jay Brown
Nacra 16sq. spin and modified
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Posted: Aug 18, 2011 - 11:20 PM
Thats is an ambitious project, but I like it. I would start with A LOT of research and careful planning and draw up specs and where everything will go. Farrier makes awesome tris and I would check out this smaller F-22. http://www.f-boat.com/pages/trimarans/F-22.html Do some more online research to find other homemade tris.
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Alex
Prindle 16 "Shake & Bake"
Portland, Oregon
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Posted: Aug 19, 2011 - 06:30 AM
I would concentrate on the hull layout over the rig. Actually I would recommend refitting a standard rig, Tornado. At 18Ft wide you are going to need to have some significant cross beams. Their location will depend significantly on their affect on overall buoyancy. What are you planning for Beams? How are you planning on determining beam loading?
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See you on the water
2003 Bimare 18HT solo Sailor
Formerly P-19MX solo sailor
Portsmouth RI
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Posted: Aug 19, 2011 - 06:53 PM
Alex and Johno thanks for the replies. I have taken to cutting the bow off of one hull. I have modeled the entry after the vertical bows of the Nacra. Was thinking of inverting bows like the late Infusion, but we will see where the vertical bows take me. The hulls I have are very heavy volume forward of the current crossbeam location on the hulls. I have taken all of the bulkheads forward of the crossbeam location out. I plan on reshaping the hull to accept a bowsprit and improve the hull water entry.
I am thinking the beams will be between 14-16' wide. I figure I can go a little narrower because the boat will have double trapeze. I have checked out some other boats online of similar dimensions and think I can use 4" crossbeams in either carbon or aluminum. The new c-class cat's are 14' wide and use 4" dia carbon. The have a simple dolphin strike set up and I would imagine their compression loads would be significantly higher than mine will be. I am already planning a through hull dolphin striker set up if I choose to go with the tri vs. large cat.
Are there crossbeam ratio's for cats typically? I notice my 16sq is 17' long with a front beam location of 9' from the bows. The current location of the proposed hull cradles on the center hull is 13' from bow with 13' behind it so pretty much dead center of the hull. Although, i would say 65% of the hull volume is forward of the crossbeams.
Thoughts? Another thing I have to ask is how do I determine daggerboard trunk locations?? The current leading edge of the centerboard truck is just after of the current front beam.....
Thanks,
Jay
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Jay Brown
Nacra 16sq. spin and modified
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Posted: Aug 19, 2011 - 07:31 PM
http://thebeachcats.com/pictures/?g2_itemId=81540
started an album to document progress....
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Jay Brown
Nacra 16sq. spin and modified
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Posted: Aug 20, 2011 - 11:21 AM
This guy Isn't kidding. great album catfever, keep it detailed i look forward to following your progress.
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Nacra 6.0 NA
Ogden Dunes, IN
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Posted: Aug 20, 2011 - 10:28 PM
start working out the dimensions and ratios of other popular tris like the farriers, weta, seacarts even the rave foiler and other beach tri projects like the adventure tri and the manshed's project on catsailor.com
mast height to weight and width
beam to length
sail area to weight
mast position to length
dagger center to mast and sail COP
beam diahedral?
float volume and length to main hull volume and length
etc etc etc
trimarans have many more variables than other boats and you want to know what envelope to fit your boat into as if you get any 1 of the variables badly wrong the boat won't perform as expected -
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Posted: Aug 21, 2011 - 11:50 AM
Thank Erice,
I have done many of those calculations actually using the 60' ORMA tri's. But should look at the smaller trimarans. The problem, I think, with using the cruising/racing tri's is that there main hulls have a much larger hull volume due to accomodations etc. With 2-17' ama's and a centre hull of 25' there is no doubt in my mind it will be highly bouyant. I am more so wondering about boat balance bow to stern and how I would calculate the COG on the boat without a rig and sail plan yet?? Thanks to all of you for all the help, I can definitely use as many minds as possible! My goal is a tri with a weight of under 600lbs, a sail plan of 350-400sqft on main and jib plus a roller furling genoa and a bowsprit asym. I figure this boat can push the 30kt mark fairly easily.
Lets make it happen!
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Jay Brown
Nacra 16sq. spin and modified
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Posted: Aug 22, 2011 - 01:24 AM
also some very nice design drawings by chris osterlind of lunada designs
http://www.lunadadesign.com/corsica-15r.html
http://www.lunadadesign.c…a-20-beach-trimaran.html
http://www.lunadadesign.c…port-build-underway.html
and a bigger homebuild the L7
http://home.comcast.net/~ritakend/site/
Edited by erice on Aug 22, 2011 - 01:54 AM. -
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Posted: Aug 22, 2011 - 03:40 AM
the seat of the pants engineer in me is concerned about double trapping off a trimaran
has anyone ever done it before?
it may be possible if the floats are as long or longer than the main hull but my experience sailing the weta tri is that short floats are the limit on trimarans. they bury pretty quickly and abruptly and i wouldn't want to be out on trapeze when it happened
the whole idea of a wide tri over a narrow cat is that you get the same righting moment by sitting on the beam of a tri as you do on thw wire of a cat -
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Posted: Aug 22, 2011 - 11:21 PM
I figure double trapping shouldn't be a problem. The ama's are 17' catamaran hulls, plenty of bouyancy and room for the skipper and crew. Also, I agree that the tri has considerably better righting moment than a Cat. My thinking with the extra righting moment and double trap is that I am able to pile on more sail area than a cat of the same length. A tri is a much more stable platform. If the leeward ama is 16' from the windward ama, and the skipper and crew are another 6' from there, that is ALOT of righting moment.
2 rudders or 3?
2 daggers or 3?
Thanks again for all of the posts,
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Jay Brown
Nacra 16sq. spin and modified
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Posted: Aug 23, 2011 - 01:33 AM
keep in mind that beach cat designers generally only design in just over 100% buoyancy into each hull
that is just enough to fly the other hull and rig with a little in reserve
i guess in your case it will depend on how much extra nacra built into the 16sq hulls and how light your c-cat center hull and extra wide beefy beams will be
so cat hulls for trimaran floats generally will not allow the center hull to fly as they simply can not support the weight, they bury the leeward bow and act as a brake
so you should probably only start with a single, deep, rudder
perhaps an oversized nacra shaped rudder to fit into your nacra casting
the adventure tri project got around this by lengthening the nacra 6.0 hulls they used
the added length helps increase the speed before tripping over the leeward bow but also added in more volume/buoyancy to support the extra weight of the center hull
Edited by erice on Aug 23, 2011 - 03:45 AM. -
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Posted: Aug 23, 2011 - 03:44 AM
i would think a rig from an 18-19ft boat would be about right
the best may be an F18 rig as you would have some great sail choices, but that would probably be the most expensive too
something older likely to be cheaper, hobie18, nacra 5.8, prindle 18 or 19
if you are going to base it around the mast ball on your nacra16 you might be best to stick with nacra rigs from the 5.5 upwards to the 6.0
1 way of beefing up your 16sq nacra beams may be to slide some close fitting alloy tubes inside
Edited by erice on Aug 23, 2011 - 03:44 AM. -
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Posted: Aug 23, 2011 - 07:09 AM
Or better yet, use biaxial weave carbon sleeves that come in 4" or 6" diameters (& fit variable diameter tubes) from Fiberglast Corp. in (Ohio?). I've used them in 2" diameter & they"re great. Pete -
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Posted: Aug 23, 2011 - 09:04 PM
Thanks for the replies guys! You guys make some good points regarding the bouyancy issues. I might have to find some 5.8 or 6.0 hulls instead of the shorter hulls. I am thinking the matching rig would work well. I am going to work on the main hull this weekend further. Making foam core bulk head with glass lay-ups. Will shoot some pics at the end of the weekend.
Thanks again
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Jay Brown
Nacra 16sq. spin and modified
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Posted: Aug 27, 2011 - 03:41 PM
New pictures on the technical album. Cut open the bow to allow for easier shaping without wrinkles. Will do the rest of the bulkheads forward of the front beam location tomorrow once the resin is set for these first two. I just used construction foam insulation and covered in sheets of fiberglass with 105/206 West Systems. Next update tomorrow!
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Jay Brown
Nacra 16sq. spin and modified
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Posted: Aug 27, 2011 - 03:47 PM
I have also decided to make the project a modified c-class catamaran rather than the original trimaran idea. The trimaran would have meant breaking up the 16sq., which I have put a lot of money and effort inot modifying it considerably. Plus it's a hell of lot of fun with an 18sq.m main (vs.16sq. on original), and a 19 sq.m chute, all on a 17x8.5' platform.
I am thinking a sail plan slightly larger than a 6.0 or tornado, more the same size as a SC22. I am thinking of 25'loa with a 12.5' beam. Thoughts?
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Jay Brown
Nacra 16sq. spin and modified
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Posted: Aug 27, 2011 - 03:50 PM
