Saturday, December 29, 2018

I Just Want the Boat to STOP!!

I've research all manner of things sailin-related. Drogues and sea anchors, and MOB prevention tools such as tethers and jacklines have featured prominently. Both respond well to engineering analysis.

I often read of a "last chance" line trailed behind the boat. The line described was most often tragically short. Sail magazine described one only 15 feet long. If you fall in head first, angled away from the boat, and the boat is moving at a 5-7 knots, 75 feet is the minimum required distance based on my testing in summer weather. You better have 150 feet if you want any hope of finding it in adverse conditions. They also think that they can either make the boat stop by tripping the rudder (the boat may just tack away and keep sailing--you did not take the time to trim it for heaving to, or bring the rudder back up) or simply haul themselves back to the boat (impossible over about 3 knots). The other thing they always have in common is that they have not TESTED their theory by jumping in. Man, if you have not tested it, don't even report it as an idea. Someone might believe you.

I imagined myself hanging on the said rope at 7 knots, waiting to get tired and let go. I've been towed as a water skier, so it was not hard to imagine. I also tested the speed At which I could hang on to a 3/18-inch floating line, and the speed at which I imagined I could (dressed in foul weather gear and a PFD) haul myself back to the boat. It becomes clear with in moments that what you will pray for is for the boat to STOP. Nothing else. You would give anything to make the boat stop, like dropping an anchor (see where we are going with this?). And as it turns out, that isn't really so hard, at least not with smaller boats.

Basically, it is a parachute with the floating line as the rip cord. You don't need to pull hard, just enough to pull the gear from the storage bag on the deck. The chute and rope stream out, and about 10 seconds later, the chute fills, creating a whole lot of drag. A nylon climbing rope provides the energy absorption, bring the boat to a slow stop (about 1-2 knots, even with the engine at full throttle). All that remains is to pull yourself to the boat, hand over hand, which is not very difficult with the boat nearly dead in the water.

 Yup, I tested it repeatedly, sometimes powering, sometimes under sail, upwind and down. It didn't matter. The success rate was 100%. All I asked of the crew was to keep filming.A seemingly crazy idea that simply works.

I'm not at all surprised. For years, in testing, I would drop drogues and sea anchors off the transom at full speed to create maximum impact force, often using non-stretch rodes and larger boats. Although the strain could be high, nothing ever failed.

Staying on the boat is better. Stay low and clip-in when it gets rough.

[Details are in Practical Sailor Magazine. Obviously, the engineering varies with the weight and speed potential of the boat.]

Friday, December 28, 2018

Tiller Reinforcement

Pretty darn simple, but it's the holiday season.

Because the rudder swings down and into a slot in the hull when the rudder is lifted, the pivot was a counter sunk flat head. A flat head makes a nice wedge, and sure enough, most of the tillers developed splits.

Not a lot of room for thick side plates when the rudder is lifted. 

The solution (after cleaning up, repairing with epoxy, and re-varnishing) was to add 1/8-inch thick side plates, counter sink the bolt on one end, and grind it smooth on the other. No play. No splitting.


Tuesday, December 11, 2018

Actual Anchor Loads

I spent a LOT of time researching this topic, through the literature and by staring at a load cell for hours and hours. I used all sorts of rodes and snubbers, in all weather, on a number of boats.

ABYC (American Boat and Yacht Council) set standards for rodes and deck hardware 50 years ago, based on testing with boats on all-chain rode in open harbors and shallow water (but no breaking waves) and no snubber. In fact, these values are VERY close to what I got testing in similar conditions. This is very much a worst case situation and is something you should NEVER do, but is a good basis for the design of something that cannot fail. I don't think I've ever heard of a system meeting Table 1 requirements that was in good repair failing, outside the eye of a huricane (an even then it isn't the chain that breaks; they either drag or the roller and cleats fail.

Interestingly, every investigator reported 3-5 times less when they measured the strain on their boat (me too). Of course, they wisely anchored in deeper water (lower waves and more catenary), used rope, or used a snubber.

Looking only at the 60 knot row, which is very likely the most you will ever face without some protection from trees or shoreline, we see that the wind load is only about 20-25% of the ABYC load. Waves and snatching make up the rest. If you use a long chain in deep water (at least 20 feet), a long  snubber (35'-50'), or a rope rode, the load will be only 25-30% of the ABYC value.

For larger boats or those around coral and rocks, all chain is nice. Rig a LONG snubber, even if you have to cleat it at the mid-ships or stern cleats to keep the connection off the bottom.
My PDQ came with rope, but I changed to chain and a long snubber after a few years. I liked the increased security, but the main reason was that the windlass handled all-chain better than chain with a splice. 

In my mind, if your anchor is 35 pounds or more, you will be better served by a windlass and all chain, and if it is 15 pounds or less, manual handling and rope makes more sense. At 25 pounds, the decision is up to you, depending on pocketbook, fitness, and sensitivity to weight in the bow. I'd probably go with chain and a winch on a monohull or heavy cat, and manual with rope on a fast multihull.

 With smaller boats and mud bottoms, the rope is a better answer. It is much lighter, gives good shock absorption, and lasts as long or longer, if it is protected from chafe. You see, chain will fail from corrosion in 5-7 years, even if you don't anchor out, whereas nylon can go even longer if oversized a bit. So go oversize for durability and ease of handling. Finally, nylon can actually be too stretchy if over 100 feet are out, and oversize rope reduces this.
My 24-foot, 1700-pound trimaran only calls for 3/8-inch nylon rode, but I like 1/2-inch for better handling, durability, and reduced stretch. I did the same on my Stiletto 27.

I've even gone to a Dyneema bridle to reduce yawing and to reduce the sometimes-excessive stretch of all-nylon rode. Because the bridle does not distort under shifting loads, yawing is reduced.

[Images excerpted from Rigging Modern Anchors.]