Trimarans with Daggerboard aside the central line...

offset boards

Skip, I have a 24' tri that I have sort of used as a "test" subject, and I added float boards to see what would happen. I have a 19' beam, so they are pretty well "offset". The short story is that you can hardly tell which board/boards are in use. I only have a center rudder, the boat and rudder are very well balanced, and in most conditions the helm is quite light, even with only a single float board down. Of course if your tri flys the main hull, you would need float rudders.
Don't over think control issues, a well designed tri can handle all sorts of odd rig and foil combinations and still be easy to sail.
I do agree with the damage risks, tris have often been sailed with flooded main hulls, but flooding a float can be more critical.
B

 

Thanks all, as I was thinking of freeing the available space inside I was really referring to a cruising boat. I can see the logic about slipping if you fly the main hull but wasn't looking at that.
Yes I have seen the Horstman Tristars have a fixed keel on the amas, but I wasn't sure that they would be the best example given the hull and deck design seems like it would struggle to windward a bit anyhow.
That is interesting that the consensus would prefer the board in the main hull in an accident; I would have thought the boards in the amas could be significantly smaller (not particularly concerned about weight this example) like cat boards, and the surrounding portion of the ama hull could incorporate crushbox, foam and watertight to prevent the float filling etc
I was wondering if it would even work given the layout and it seems like it might be fine judging from your answers. Ta.

 

Indeed, thats what I have learnt on my own... sounds all logically.

HOrstman Tris are great if you look something like a "living room", but the old design of the 60th/70th with fixed short fin keels isnt what I like to sail... too slow, and not enough options to trim (which is fun for me).

 

Interesting... you think one can scale your experiences linearly from small 24ft to bigger 40ft ?

 

A forum fact checking app would be helpful, Tristars have daggers in the amas of course, Ed even had a option to change the angle of attack on some. His layout worked for 20 to 70+ footers.

Harris had some nice tris with centerboards in the amas. For cruising the reefs ama and vaka fins were used on Nicol and shallow Cross tris to protect the hulls in a grounding. Where and how you sail , race-cruise?, should be factored in to your foil choces.

 

The Piver trimarans also had float fins.

 

scale

I went sailing on a cruising 60' cat a couple of weeks ago, it had one dagger in the port hull, and seemed to work just fine. I really don't think scale/size matters at all. I have seen model radio control cats with one board that worked fine also.
Bruce

 

As far as i remember Shuttleworth had made sich a config at first. He said that a cat with one centerboard/ Daggerbord in one hull points 1 degree less only-- less area (50%).

There are some monos with offset daggerboards/centerboards, mainly smaller, bilge ballasted units. Having the board slightly offset opens more, or better possibilities for the interior layout.
In performance no one ever noticed a difference.
Remember the Thames Barges and all those thousands of dutch flatbottoms. Ships with two centerboards , they sail with the leeboard only.

There are also some experimental bilge keelers with spreaded asymmetrical keels
The trick is that the leeward keel delivers more lift, while the windward keel reduces heeling and dampens pitching.
Designer Reinke, known for his very popular steel blue water cruisers with ASY- Twinkeel writes :

Die asymmetrische Profilierung
der ASY- Twinkiele ist jedoch der entscheidende Vorteil dieses zukunftsweisenden Kiel- Systems!
Wie ein Tragflächen- Profil beim Flugzeug erzeugt der in Lee liegende ASY- Kiel einen drastisch höheren "Quertrieb" nach Luv, als das jedes symmetrische Profil je könnte. Der Iuvseitige ASY- Kiel dagegen arbeitet wie im "Rückenflug" bei den gegebenen Anströmwinkeln immer noch mit einer positiven Komponente in Luv- Richtung und, durch die Schrägstellung des Kiels, mit einer aufrichtenden Teilkomponente nach unten. Wir konnten in vielen Jahren evolutionärer Entwicklung in der Praxis erreichen, dass unsere
ASY- Twinkieler mit mehr Höhe am Wind schneller
waren als vergleichbare Mittelkieler!

An advanced unique solution delievers Stöberl under his very fast bilgekeelers w. very little draft. Those boats are pointing very high . His boats are lifting the windward keel out of the water when heeled.
Scroll down for sketches and pix please :
http://www.koriva.de/wp-content/uploads/2013/04/StoeberlSailing_Kimmkielkonzept.pdf

U see, both solutions have offset active wings .

Analog-- there ain't no difference if an aircraft's wings are mounted on top, in the middle, or on the bottom of the fuselage.





pogo

 

"Analog", Well said Pogo.

 

Here's Groucho's offset main hull dagger - and also Sid 650's case being glassed in. Since Groucho goes to windward like a witch, I'm expecting the 6.5m to do the same.