As usual, "it depends", but it's pretty basic trigonometry...
As I mentioned earlier, matching your VMG sailing DDW by broad reaching at an angle of 45 degrees from DDW will be very difficult to achieve on most displacement hulled sailboats, sportboats flying sprit sails are of course best suited to this tactic...
As the graph above shows, if you're making 4 knots DDW, in heading up 45 degrees to a broad reach you're gonna have to sustain 5.7 knots to break even. VERY unlikely boats like yours and mine will see such an improvement in boatspeed by such a change in course, without resorting to making a drastic change in the sail being carried, such as setting an asymetrical, or similar... As a glance at the graph indicates, only in very light airs, or at speeds significantly below hull speed, are sufficient increases in boat speed by broad reaching likely to pay off...
On the Hallberg-Rassy sailing wing & wing that I pictured above, we were effortlessly making hull speed and above sailing DDW. No way would we have made broad reaching pay off with that boat, in that situation... Not to mention, the route we were sailing from the Mona Passage, between the DR and Turks and Caicos, and then thru the Mayaguana Passage and on up Exuma Sound, it just would have been an incredible PITA to manage with a shorthanded crew, and a freakin' aluminum pole that felt like it weighed 200 pounds, and having to use docklines as guys, etc...

More importantly, sailing DDW allowed us to sail a course close to the Silver Bank, and stay clear of the busy shipping route between the DR and T & C, jibing downwind would have involved criss-crossing that route repeatedly... No thank you, dealing with the nightly squalls was action enough for me...
Or course, simply plugging in your destination waypoint to your GPS, and monitoring the change in VMG on different headings, makes this all very simple to determine in real time...
Now, the larger question is, why is this thread still in "General Discussion"? Shouldn't it be moved to "Seamanship & Navigation", where fewer people might be likely to notice it?

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