I've been able to learn about full-size drogues at higher load with 2 tricks. First, pulling them at short scope (actually the best method for emergency steering) gives insight relating to pulling out of a wave face, since a following wave also changes the rode angle. Second, getting a running start at a drogue, hitting it at as much as 7.7 knots (with extended transoms and a clean bottom, that is my best speed) with a non-stretch rode gives some high forces, but I wanted something a little easier to manage and some thing that I could pull continuously at storm-like loading. Like the tandem anchoring trials (coming in 2017 in Practical Sailor), I went to models.
3 times smaller, but faithful in performance characteristics.
From left to right, 1/3rd scale models of Seabrake 24, Delta Drogue 72, and Jimmy Green Marine 60cm Drogue. Sewn from scrap Sunbrella and 1500-pound bull tape. I saw as much as 200 pounds drag out of the mini Seabrake/Delta combination at 7 knots! I later added a mini-Galerider.
(note. These are NOT official copies and any statements should not be taken as such.)
For anchors, I was able to get roughly 8 inches across, I was able to find 2-pound surrogates in the form of a 2-pound Guardian, 2-pound Claw, and a 2-pound Mantus Dingy Anchor (very nice--get one!). But for drogues I was out of luck. So I sat down with a pile of old canvas, a roll of pulling tape, a palm, scissors and tape measure and made my own. Roughly 8 inches in diameter, if towed by a small diameter rode with mating scale chain, they perform just like their big brothers!
- Drag is about 9 times less (expected to vary as the square of diameter)
- speed/drag relationship is consistent (varies with V^2), like the larger versions, but now proven through a larger speed range
- Pulsation behavior is similar (load varies at about the same range and frequency as larger drogues)
- Behavior--yawing and surfacing--is just about identical
And so now I have a set of tiny scale drogues I can test at scale in small craft advisory conditions, as through it were a gale.
The really weird part is that I have already learned some things I that either the manufacturers don't know or are in denial about. Failure patterns--both mechanical and performance--seem to come from pretty basic errors. Not the better manufacturers, though; they seem to know and communicate better.
The early take-aways?
- Anyone can need emergency steering when they hit a log. It is not a black art, but you need the right gear. I tried warps and chain, and it aint' going to work for you. No way.
- Towing warps is not much of a storm strategy. The drag is perhaps 10 times lower than recommended drogues.
- You get what you pay for. So far, the more money, the more stable and rugged the drogue.
- There is a speed limit. All drogues have stability problems over ~ 5 knots in big waves, and my gut at this point is there is no engineering solution. You either carry enough drogue to stay below 5 knots or the risk of the drogue pulling out of a wave face goes up when the waves get steep.
I have one article on drogues in Practical Sailor, with more on the way.