Daggerboard position

[AdrianN]

Hi All

I see that all catamarans have both daggerboards positioned in the same position longitudinally (struggling to find the right word....I mean same distance from the bow). I understand that this way I can raise either board without affecting the trim and sail with the leeward board to help fly a hull. But on a cruising boat where I have zero aspiration of flying a hull, would it not make sense to have one board a bit further forward and the other a bit further aft to influence the trim?

 

[Robert Biegler]

I am pretty sure I read, some decades ago, of a cruising cat design that did exactly what you describe, with the board in one hull paced forward of the sail's centre of effort, and the other board aft. Unfortunately, I don't remember the name of either design or designer.

 

[Blueknarr]

Staggered boards on a cruising cat doesn't make performance sence. It would make one tack seriously favorable.
The boards may have been staggered to accommodate interior space limitations.

Staggering on a proa might make sense if a board needed to be moved while shunting.

 

[Robert Biegler]

Staggered boards on a cruising cat doesn't make performance sence. It would make one tack seriously favorable.

How so?

The boards may have been staggered to accommodate interior space limitations.

As I remember it, the stated purpose was to adjust the longitudinal position of the centre of lateral resistance, exactly as AdrianN suggested.

Staggering on a proa might make sense if a board needed to be moved while shunting.

There have been tacking boats designed to adjust the longitudinal position of the centre of lateral resistance. The clearest case are boats with tandem boards, such as Three Cheers, at least one of Bolger's dories, and even Team Philips.

I have seen a cruising boat with three centreboards, one in the bow, two side-by-side in the bilges. The placement of two in the bilges avoided interference with the engine and the possibility of jamming the case with stones, the one in the bow was there to trim the boat.

A catamaran's boards can be placed close to each hull' side instead of the centreline to reduce interference with accommodation. That is likely to help more than longitudinal staggering, which is more useful for adjusting the centre of effort.

 

[Blueknarr]

My response was not as clear as I thought.

One of MY distinction between cruising and performance-racing is
Racing may have multiple. dagger slots while cruisers have only one.

So a cruising cat with boards PERMANENTLY staggered would have different CLRs on each tack.and would behave differently from tact to tack.

So permanently staggering the boards would not be for performance reasons on a cruising cat.

BUT
if the interior layout was different between the hulls - then staggering the boards might be required.

 

[cavalier mk2]

Actually the idea behind cruising cats is not to fly a hull. In that case a board in one hull can be used for both tacks or staggered boards in both hulls can be used to adjust the.CLR. Malcom Tennant did this on occasion.