boom sweeper

Editor

Administrator
Staff member
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carlsbad
boom-sweeper.jpg


The IRC rating offices have seen a growing number of instances and inquiries about additional cloth set under the boom, known by various names including lazy sweeper, deck sweeper, mainsail skirt, water sail.

In response to this, the IRC Technical Committee has issued IRC Notice 2021/02 which explains that this cloth is defined as a sail and explains how to measure the additional area so it can be accounted for in the rig factor.

Read it.

 

ryley

Super Anarchist
5,381
583
Boston, MA
weird.. it looks like they're just changing the size of the sail area polygons and basically counting *all* of the area under the boom as sail area.

 

Zonker

Super Anarchist
8,887
4,800
Canada
That is what they are doing. It's now a sail, albeit an inefficient one. But rating the area like it's an efficient sail.

So you take a ratings hit > benefit.

 

Glenoid

New member
Quite simply, this bit of rag constitutes an end plate to the airfoil, damming slippage between the deck and under the boom, hopefully cleaning up airflow for a greater section of the main.  That's what all those cute little wingtips on virtually every airliner are doing nowadays: limiting wasted end-slippage of attached flow on the foil. Amazing it took so long to appear on a boom.

 
Quite simply, this bit of rag constitutes an end plate to the airfoil, damming slippage between the deck and under the boom, hopefully cleaning up airflow for a greater section of the main.  That's what all those cute little wingtips on virtually every airliner are doing nowadays: limiting wasted end-slippage of attached flow on the foil. Amazing it took so long to appear on a boom.
This (decksweeper) makes a noticeable difference when we changed to this on the F18 cats. Much more power, even in the lighter stuff.

When I asked Pete Melvin what he would do to make my boat more efficient and faster (Lumbo 32 co-designed by his office) the first thing he said without hesitation was to add a decksweeper to the boom. Interesting to see it's starting to happen on monohull keelboats. I predict we'll see more in the near future.

 

12 metre

Super Anarchist
3,745
612
English Bay
Quite simply, this bit of rag constitutes an end plate to the airfoil, damming slippage between the deck and under the boom, hopefully cleaning up airflow for a greater section of the main.  That's what all those cute little wingtips on virtually every airliner are doing nowadays: limiting wasted end-slippage of attached flow on the foil. Amazing it took so long to appear on a boom.
Agreed.

As you say, I believe the main advantage is end plate effect.

Any attempts to include it in the sail area calcs - even as inefficient sail area effectively bans it. 

Or at least anyone would be silly to have one if it was included.

 

PaulK

Super Anarchist
Quite simply, this bit of rag constitutes an end plate to the airfoil, damming slippage between the deck and under the boom, hopefully cleaning up airflow for a greater section of the main.  That's what all those cute little wingtips on virtually every airliner are doing nowadays: limiting wasted end-slippage of attached flow on the foil. Amazing it took so long to appear on a boom.
If they're going to ding you for it and you still want to see the instruments, not block the crew and get the end-plate effect, why not go for a Park Avenue Boom?

image.jpeg

 
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