Outrigger Keel Plane Question

As some of you know, I am (trying) to craft an outrigger using cast off Hobie 18 hull and Hobie 16 starboard hull.

Last fall was at point where I was setting up the akas (beams) to set foundations on each hull and so on.

At the outset I knew I would have to be able to adjust the outrigger's distance from the akas or beams, so accommodated that.

Thing is, when I set the boat up, with akas or beams in place, I had to decide if the keel of the outrigger should be on the same plane or even with the keel on the main hull or a bit above it. (Outrigger or ama is to starboard, as the hull asymmetric H-16 starboard hull.)

If the outrigger keel is a bit above, the tramp or deck would be tilted to the starboard on flat surface (water and trailer).

The Hobie 16 outrigger rocker is substantial, so I figured that the hull keel at low point of rocker should be even with the lowest point of the rocker of the H-18 main hull and would likely clear water on starboard tack in decent pressure.

I should add that the Malibu Outrigger plans I have shows its outrigger to be a bit above the main hull (both have similar rocker) but the plans are not specific, as the difference comes via the bracket measurements and hull config...meaning build variations...

I reviewed Gary Dierking's text on building outriggers a few times and did Internet searches and the topic is not covered...

Illustration is below...

Basic question: Should the outrigger keel be on same plane as main hull like a catamaran, or be slightly above...and, if the hull has a rocker like the H-16, does it matter as long as the outrigger keel is close?

 

You need to do a hydostatic calculation based on the weights expected in each hull and compare that to the immersed volume of the hulls to get the hulls to sit flat in the water.
Of course if you don't want it to sit flat you probably ought to set the outrigger to be as low as reasonable since that will keep wave drag on the crossarm to a minimum.
But if you tilt the boat toward the main hull due to the outrigger being lower, you will have to be sitting on the main hull with the seat going the wrong angle for comfort if the main hull is to windward.
But if the outrigger is up level with the mainhull the boat is probably tilted towards the outrigger, reducing the sail force when the outrigger is to leeward.
I guess it depends.

 

Hello Mr. Upchurch, and thanks. I am beginning to think it really does not matter how they sit, if the keels are even at rocker (keel) bottoms...both hulls weigh about same...but H-16 is asymmetric, as you know. Large H-16 rocker and fairly generous on the 18 but not designed to "dig" in or offer lateral resistance.

I figure how the thing sits on the hard or calm water makes little diff once dynamic forces go to work...or trailer it might look funny, unless I adjust bunks to accommodate the diff.

Say, you still have the Tornado hulls?

I wanted them so bad as the one hull would have been the perfect main hull and the akas fit the hull perfect and cut; but I could not locate a trailer, as I mentioned...then the guy in WI emailed me, and here I am, still working on the plan...this spring I go wet. Your hulls would have been perfect for project...

I have read many of your responses here and there and you sure know your stuff. Where'd you learn it all?

Anyway, with the rockers involved, like I said above, am thinking to make them both same distance downward from akas and see what I end up dealing with.

Might as well as just about everything about the project has required crafting from scratch, except for the two hulls. Live and learn. But, that first sail will be fun...thanks again.

 

If there are only two hulls, the setup of the deck makes little difference. The only change will be the angle of the deck to the horizontal.

 

Gonzo, merci.

More I think about it, more I agree.

I have put note on work schedule to make it so the H-16 outrigger or ama lies about 2-4 inches higher than the main hull's lowest point along keel line or rocker radius.

I crafted the connections to use spacers to adjust ama height, so moving it will be a matter of some tedious disassembly and reassembly, but not major PIA.

Should be about right for a start.

I very much appreciate the help I have received here.

Just about every point in project required slow and careful custom crafting, which continues as I type this, but will be worth it, all goes as planned and failures are few.

 

Post photos when you are done. Good luck

 

Not a problem...will post build and first sail...

 

The Tornado was cut up when you let me know it wasn't needed.
To my displeasure, I found the hull was perfect, the deck between the beams had balsa rotted due to poorly built access ports and the main sheet cleat mounting holes punching thru balsa - just a tiny bit.

 

Do you have a mast for it?

 

Gonzo,

I do, but it is jealously guarded.
I'd like to build a tri of about 17' x 15' with enough power to scare myself.
Of course I also have a Hobie 16 rig.

If you need one of the Classic masts there is a guy in town who has at least two, along with numerous hulls, crossbeams, and who knows what else.

If you are interested I might be able to come up with his contact information. I have only talked to him on the phone.

There is another complete boat with a hole in it in east Texas, but it might be impossible to get that contact.

Let me know.

 

I have a NACRA mast looking to get used.

 

Mr. Upchurch. Surely the wife is happier, but now the mowing...

Seriously, as I noted, I miss the opportunity to employ that hull/beam set...and still dream of it.

Would have been a completely different sail and a proper boat...you must do a good bit on a the water.

I get this to be a proper boat, will be taking it out to SF area to see daughter and try to persuade adventurous NY born son in law to sail with the sharks in SF Bay and Tamales Bay and, if interested, may stop down to see you on return trip, with proper storm warnings long before of course.

Tool, have always had a hankerin' to do the Texas 200 and to stop to see a swab (Gouvernail from Anarchy) to trash sail and add a few beer cans to his collection.

Gonzo too, if up to it...Milwaukee area is close to a haunt of mine (Port Washington) be decent trip down by water. Always wanted to see the yacht club there, famous for youth program...I do not deep-six before hand.

Lake Mich is where I learned to sail in 50s and still a fave place to sail.

Again, gentlemen, much appreciate the help...I finished my schedule and plan for the final build stages, save "canvas" work on luff and spray skirts, removable small motor mount and miscellaneous cleats, fittings to add as it goes.

All the best. (Geez, it is 11:30 PM here and 42 degrees...knock on wood.)

Bob Bill

 

Look me up. I sail out of South Shore Yacht Club

 

Deal...and in meantime, I will get hold of the gent just west of Milw who gave me hulls and trailer regarding spars. His Mom's yard is full of stuff and I guess he and his brother are into rebuilding cats.

 

Maybe just herding them . . .