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  #1  
Old 04-22-2012, 02:11 PM
erikhaha erikhaha is offline
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Outrigger to beam connection

I have searched this forum and I can seem to find any info about various methods of attachment of a tri outrigger to the main hull.

I am building a 20ft tri based on Gary Dierking's Ulua Proa.

I have increased the main hull dimensions by approximately 30% and the 2 outriggers that I have built are each 16ft in length and based on my calculations each outrigger has a 580lb displacement capacity fully submerged.

I am at the stage that before I can glass the outside of the 1/4" ply ama's I need to design the attachment connection between the main beams and the ama. I am interested in the benefits of a rigid connection versus a connection that will allow for some movement, such as a lashed connection or something in between.

Since this is a relatively small boat and the forces are not that great I have been thinking that a flexible type of connection would be better than a rigid connection, but I am not sure.

Any comments and or experience with either would be appreciated.
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Old 04-23-2012, 06:06 AM
teamvmg teamvmg is offline
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There are 1000s of 16-20ft beach cats sailing, they must have figured out the connection by now, taks a look at some of their solutions.
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Old 04-23-2012, 06:32 AM
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Corley Corley is offline
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I'd scale up the method used on this Ulua in the link, simple and elegant

http://outriggersailingcanoes.blogsp...h-jenkins.html
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Old 04-24-2012, 04:14 PM
erikhaha erikhaha is offline
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Thanks for the responses but the outriggers that I have built have a lot more capacity then the ama's on the Ulua that you refer to.

I specified the displacement in my initial post although not in metric units. So for the people posting here from the UK and anywhere else that use the metric system:

Outrigger displacement = 263kg
Outrigger length = 4.85meters

Since the boat the I am building is a trimaran and not a single outrigger, and the sail area is greater then the proposed area for the Ulua's original design, I believe that I need to re-think the connection of the beam to outrigger.

I am using 3" square x 1/8" thick T6061 Aluminum beams so I can't get the same type of connection as the originally designed Ulua.

Thanks though.
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Old 04-24-2012, 05:06 PM
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Corley Corley is offline
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The method below is very strong I used it on a 18ft off the beach tri the only difference was I built strip plank beams but it was a square section so comparable to what you want to do. Your aluminium beam will have to be long enough to go into nearly the full depth of the float.

If your using a square ally tube this is what I'd suggest. Build into the ama a double bulkhead. Space them so they are a snug fit forward and to the rear of your beam. Tab, fillet and tape the bulkheads into the float hull. Drill a hold through your beam and bulkheads fore and aft, fit a sleeve into the beam and fit a ply doubler where the pin comes through the bulkheads. If the float is intended to demount make the pin accessible by fitting a spinout plastic hatch forward of the beam/bulkhead area. You will want to fit some sort of rubber section or spray skirt at the beam/deck area.
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Old 04-24-2012, 05:28 PM
buzzlymutt buzzlymutt is offline
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we need more information! Are the beams straight,or curved? Overall beam? Planned height of beam from waterline?Demountable ? I feel 1/4' ply is to heavy for displacement of ama.NO NEED TO GLASS! Did you consult this forum before?
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Old 04-24-2012, 11:08 PM
erikhaha erikhaha is offline
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Corley, thanks for the info. Actually that is the same attachment method that I had already planned on using.

I posted here because I wanted to get other opinions as to the pro's and cons of a rigidly attached outrigger to the beam versus a more flexible connection.

Buzzly, why do you think that 1/4" ply is too heavy and that I shouldn't glass them?

Since I will be using this boat in the ocean I do not want to take any chance of salt water entering into the ply. I am glassing the 2 outriggers with 6oz cloth on the outside and 3 coats of epoxy inside.

I am interested in hearing your thoughts.

Attached is a pdf of the design.
Attached Files
File Type: pdf TRIMARAN FINAL-Model.pdf (20.9 KB, 143 views)
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Old 04-27-2012, 04:43 PM
buzzlymutt buzzlymutt is offline
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For the displacement of Ama's 4mm{5/32'}ply would be best.One could even use 1/8" in the compounded/tortured method.Weight is the deciding factor, Glass tape the keel only.No more as this will add to an already overweight hull.Its strong enough already.3 coats of epoxy or untill you have an obviously thick covering,no dry patches.Applied wet on wet,each coat in 1/2 hour intervals,or so.Allow a lot of time for this operation.Good luck
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