Dagger Boards for a Pahi

[Nigel Signal]

Given the use of cantered dagger boards on catamaran designs by both John Shuttleworth and Chris White I was wondering whether anyone had done the same with a Wharram, or thought about it, in particular on a Pahi? I've attached a couple of images as explanation. Whether we like it or not we do have to sail to weather from time to time and reducing leeway can make a big difference to distance covered. The Pahi hull campared to the Tiki hull appears to have more interior volume and therefore the dagger board case may be less intrusive. It also doesn't have a keel so would be easier to fit a dagger board to? I'm not a designer but I'm guessing that on the 42 it would be somewhere in the worktop in the Galley. Would be interested in what others think of the idea.     

[Big tane]

Daggerboards will take up space inside the hulls. I would recomend incresing the detph of the keel or an centerboard in the middle, as trailer sailors do. Whitch i think would be easyer then redesinig the hulls and the slots for the boards to go down. Onther option is the board on the outside of the hull same as the flying dutchman boards.
Gerry on Big tane.
Toora.

[Andy Best-Dunkley]

I've thought about this but can't warrant doing this to our existing boat. A new build could be a different matter. As far as I understand Boatsmith did something like this on an Ariki 48, but I am not sure if the daggerboard is angled or not. Of course the danger with a daggerboard is if you hit something, then what breaks..? A case on the outside of the hull might be prudent! In our experience you can get a Pahi (42 in our case) to point pretty well even without daggers (we removed the original ones up front). Most other catamaran designs have a more U-shaped hull, so they slip sideways through the water more easily. The deep V of a Wharram grips better.

[Big tane]

Making the keels and rudders bigger would be easy than putting in daggerboards. There is an ytube video tiltled, Basics of sailing a catamaran that will explain a few points. A person i know did have them in his catamaran and broke one. He did not rebuild it and did an dogey repair and then jammed it in permetly. I would go with an swing keel, rather then daggerboards. Placing the swing keel in through the bridgedeck would be easy and no leaks or brakage, as the board will lift up into the casing.
Gerry on big tane.
Toora.

[Éric Bouvéron]

Hi,
Why not put the board outside, as it is seen on some old Dutch boats? The shape may of course be different, but I think it could work fine and the system allows the board to rotate.
Cheers,
Éric

[Nigel Signal]

Hi and thanks for the suggestions. In response; 1) Dagger boards on outside of hull; all the reading I've done suggests it is extremely difficult to provide enough support for the board to stop it move laterally without both adding significant additional weight and creating drag as a result of the support. 2) Dagger boards through the central platform; difficult to support a board that is deep enough to be effective and stop it moving laterally. Some reading suggests the board set up this way draws air and thus disrupts water flow and effectiveness. So the best option appears to be cantered through the hull. This does take up some space but being cantered I suspect minimal shoulder space. Have seen some installations where the space between the hull and board case is used for storage.

Andy, thanks for your thoughts, very interested in your overall impression of the 42. We are looking for a cruising/retirement vessel. I was originally thinking a Tiki 46, and could still head that way, but am thinking the rig on the Pahi will be easier than the schooner rig to manage and the interior layout seems more flexible for a couple. Obviously Ann & Nev had no problems managing their 46. The extra 4 feet seems to make a big difference when comparing the layout plans with the 46 looking much bigger and of course adds to build costs & maintenance costs. The Pahi hull seems wider and therefore more space the have a dagger board case (based on a review of the study plans not building plans).

Cheers 

 

[Soren Carlsen]

What about the issue with the boards up and mooring alongside. The angle of the boards if they follow the outside of the boat?

[Andy Best-Dunkley]

Here is a link to Boatsmith's video which clearly shows the daggerboards fitted to the Ariki https://www.youtube.com/watch?v=_Sxgj0KtedU

(I hope it is ok to give the link here...?)

Another idea that I think would be worth looking into is vortex generators - there was an article in Seapeople no.9

https://drive.google.com/drive/folders/0B_EVsut9cR8OT3otOF94V2JsUDQ (courtesy of Rogerio Martin, great work!) You can also check out this paper http://www.ikarus342000.com/Antivortexp.pdf

One of these days I'll try fitting these to Godzilla. I don't want to have any extra depth with a stub keel, nor a daggerboard to hit rocks - so these might help with upwind ability without adding draft. Personally I don't think putting a daggerboard between the hulls is ever going to work - the lateral forces will be so great if it is large enough that the whole construction would be too massive. Small, Dutch-style lee boards might be worth trying on a small Wharram like Hitia 14 or 17), but again I think on larger sizes the twist force will be very great, leading to a lot of added weight to get strength. Building in a daggerboard as in the Ariki example, the hull construction provides the strength, but this needs to be done at the original building stage.

[Soren Carlsen]

well I think it´s easyer to find that kind of the space on the Ariki that was made by Boatsmith than on a traditional build Pahi42. Don´t you??

[Andy Best-Dunkley]

I suppose the Ariki has a bit more internal space, but anyway, I am not saying that I want to do this, but that here is a good example that shows it IS possible! For example, many (most) builders don't install the Pahi 42's forward daggerboards - if instead one built a more efficient daggerboard in the correct position for CLR it might make more sense, without really loosing a lot of space - IF upwind ability is important to you.