Saturday, July 28, 2018

A Coupler That Can Feed Through Fairleeds...

... or rather that is what I need to find. I would like to couple my furler line to webbing, but instead of a swivel as illustrated below, I want a quick disconnect.

From the bow of a sport boat at a boat show.

It needs to glide through fairleads, with  WLL of about 100 pounds. I'm not adverse to machining something, but if I could find a design that would be better. Perhaps I could make something from 3/8-inch alloy rod where the two haves screw together. Not super quick.
Better ideas?

Thursday, July 26, 2018

Dyneema Anchor Bridle

"Bridles are made from nylon, right, to absorb impact?" Well, yes and no.

If the rode is all-chain, yes, at least 30 feet of nylon is required to take the sting out of waves and wind gusts. Since multi-hulls use bridles to reducing yawing anyway, a nylon bridle is an elegant solution.

I usually attach the bridle with a prusik loop, but a knot is fast in light winds and I had misplaced the loop. A knot weakens the line and jams if the wind is over 20 knots (25 knots for a figure 8 knot), so I don't recommend it.

On the other hand, if the rode is nylon, it's easy to have too much stretch, to the point where fore-aft surging is actually increased, This leads to more impact and more yawing, since there is slack in the system. Logically, there is an optimum amount of spring in the system for a given yacht mass and sea state. A chain leader is another non-stretch element. By tuning the amount of chain, other non-stretch leader, and non-stretch bridle, motion can be minimized. 30-40 feet of nylon is good in relatively sheltered areas, and  80-120 feet is the most that is advisable. As much 300 feet is used with sea anchors in storms, but the wave conditions are unlike anything you would anchor in.

The other concern is stretch. A nylon bridle distorts when the load comes more to one side. The more it distorts, the more the boat yaws, and the farther it distorts. With a multi-hull bridle this may increase yawing 10-20 degrees. With a narrow monohull bridle, it may distort to where there is no bridle effect at all. For this reason, non-stretch bridles are better with drogues and sea anchors.

"How about polyester? It is low stretch also?" In fact, I used a polyester double braid bridle on my 34-foot PDQ when I had a nylon rode. It worked very well and was easy to handle. Dyneema works on the F-24 because it is left rigged all the time and Dyneema presents less drag through the waves and weight. It is also very UV resistant and has the best strength/dollar ratio available. It fits the small bow eyes and does not fatigue. Because the rode is recovered from the center hull using the main rode, I never handle it under load. But polyester was better on the PDQ and any application where it might be handled under load, whether by hand or winch.

Always something new.

Thursday, July 12, 2018

Skeg Repair

A nice feature of the Wilderness Systems Aspire kayaks is a retractable skeg. Deployed, the boat tracks arrow straight, but retracted it turns like a (sluggish) white water boat. However, the skeg is somewhat fragile, prone to breaking when dragged on-deck or across rocks when not retracted, and we do tend to forget.

A Factory Replacement for $22.00 would have been one option, and I might have done that had the factory gotten back to me right away, but they took over a week, and by that time I was done.

Additionally, I've been playing with flexible repairs using polyurethane sealant reinforced with Sunbrella canvas. I used this method on the mini-dodger, I've used it for household repairs,  and I used it here. The advantage is a skeg that will give when striking a rock, like a rubber flipper, which makes a lot of sense to me.

 Placing Sunbrella over the crack, after coating with polyurethane sealant. I will add 2 more layers, with sealant between them and over the top.

Locktite PL S30 has proven to make permanent bonds to many plastics, including polyethylene and ABS (what the skeg is made off) so long as the surface is coarse sanded and flame treated. Flame treating is the process of waving a propane torch over the plastic just enough to cause a slight blush, which changes the surface chemistry.

The back corner was broken off. Now there is a nice flexible tip that can't break. It looks a little lump, but the feel and stiffness is like a mud flap.

After that, just laminate as though it was epoxy and fiberglass, alternating layers until the desired thickness is reached. I used 3 layers of cloth; larger pices on the sides and a thicker filler in the center. I trimmed to to size with a razor knife and a grinder. The result is something like a tire side wall, depending on the thickness.

 I wish I'd taken before pictures. I dive into projects too fast sometimes.

I've also used this method to repair leaky ponds, cat carriers, and plastic tanks. What are other good applications for a tough, flexible lamination?