Saturday, September 21, 2013

To Cover or Not to Cover?

Cover, obviously....

This boat is a poster child, the upper portion of the enclosure covered for a time, then niether part covered. The lower portion has become barely translucent:


Often the bird dropping are an even larger problem; the vinyl must be cleaned every trip and residue that sits for more than a few days etches a permanent mark.

The covers on the fixed windows (polycarbonate) have cause no additional scratching, have slowed UV damage, cool the cabin, reduce window cleaning, and reduced scratching. Simple enough.

But what to cover the soft windows with? Concerns abound that without some padding or lining the canvas will eat the vinyl whole, perhaps worse than UV sun exposure. Others use plain Sunbrella with success. I've taken a hand full of Sunbrella, rubbed it on Strataglass and seen no damage.

On the right is a weather beaten 16-year old cover, the edging eaten
right off by the sun. Under it is pristine 16-year old Strataglass. The rest of the dodger has been replaced twice and is not as good.Could the skylight have been better protected? No, I don't think so.

On the front windows I have a non-contact cover. It was simpler to build and seemed like a better idea... though I don't know that it was. The front and side windows are already far worse, the result of scratching from rolling and kayaks sliding by.


Would a lined Sunbrella cover be better, as many have suggested, or would it only hold more grit and be more prone to scratching? Would it be like cleaning the glass with a grit-encrusted rag? Always puzzlement. I pretty sure plain Sunbrella is the answer.


Or not to cover....
In very windy anchorages I've been told that covers can flap and scratch the vinyl. No question, if you take Sunbrella and rub it against vinyl, at acts like a fine rubbing compound. Clean cotton, by the way, will not do that and so it can be used for cleaning and polishing, but as a cover it wouldn't last and certainly wouldn't stay clean.

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No universal answer, it seems.





Sunday, September 15, 2013

Sheeting Angle and Keels


rev. 9-18-2013

Cruising cats are not generally weatherly, and the PDQ 32 is no exception. But encouraged by the fact that some fine tuning (transom extensions clean bottom and a weight loss program) has made the speed polars quite attainable, I'm encouraged to move on.

The transoms helped. Less drag equates to higher speeds and higher speed, even a little, means higher lift on the foils. This is critical with low aspect keels, something I learned well in my years of sailing no-keel beach cats; they only point if you keep them moving.

New sails. My genoa sets perfectly (other than the sheeting angle, which we will get to). My main on the other hand, is a bag. But I still want to get a few years more and I'm patient. Jessica's just starting school and I still feel guilty about spending. It will pass. No question, a flatter and faster main will aid pointing, though I wouldn't expect any change off the wind, hence the low priority.

Sheeting angle. A few quick calculation show I use a self-tacker angle of 12 degrees but a genoa angle of 24 degrees. For comparison:
  • Very weatherly keel boats: 7-9 degrees.
  • Cruising monohulls: 9-12 degrees.
  • Dingies: 9-12 degrees.
  • Stiletto 27: 9 degrees.
  • Prindle 18: 12 degrees
While the PDQ doesn't have the best foils,clearly we can do better than 24, which is a reacher angle. But with beach cat rigging (3 shrouds, no back stay), I can't sheet tighter than the shroud.

I will probably add a short run of 1 1/4-inch track between the winches and just outboard (about 2 feet behind where the green tape is, the result of more test sailing) (both winches are the same size). Figuring the space will be tight and the lead may interfere with grinding if not tweaked just so. Most probably I will use the spinnaker sheet as the alternate jib sheet, which will require using a snatch block; I found a compact one from Garhauer that I like. I've got to be certain nothing interferes with normal genoa and spinnaker operation. I suspect a mock-up will be required, to get it right the first time. And more testing.

The track will be out of foot traffic and no new lines are needed. Unless the spinnaker is used, everything can be left in place. If the spinnaker is used, the line transfer should take only a minute, making use of a snatch block on the inner track.

I intend to replace the fixed aft block with another slider, so that both can be adjusted. The cross haul line in the photo is only to hold the snatch block in place during the photo and is not a part of the proposed system.


A side view shows that to get the same lead angle on the higher deck I can be somewhat forward, though any time you move inboard you move aft. The tighter the jib, the greater the risk of hooking the leach into the main up high.



If we were to bring the sheet inside the shrouds, I can go as close as 17 degrees before the cabin top gets in the way. Although 7 degrees sounds minor to the non-sailor, it equates to about 20 degrees of potential pointing, which is huge. We have tested this by barber hauling to an opposing winch (awkward--the line splits the cockpit) (would need to be reset on each tack) and after leeway found about 8-10 degrees course-over-ground improvement, and about an 30% improvement in VMG (velocity made good to windward), which is huge. Additionally is the promise of fewer tacks, which add to that improvement. Yup, gotta do it. We will need to add a short track just between and outboard of the winches with very low profile blocks (to get a good winch lead).

While we certainly must consider rough conditions (the below is based upon semi-protected water observations), the calculations below show the potential benefit of inboard leads. Also interesting is the relatively small change in VMG over a range of angles, thought that simplistic analysis ignores the reduction in the number of tacks required.
 



Keels. Of course, this will be further helped if the keels were optimized. PDQ designed the keels for balance on land, not in the water; nice when dried out, but way too far forward under sail. She loves to weather vane into irons when you're not looking. More area aft might help.

This is a more radical way to add area; a center board that would drop down when needed for leeway and balance. Certainly there is room in the under bunk storage, but I think the added wieght might cost more than the leeway, to say nothing of the complications in construction, operation, and mainatance. This has been done on both cats and monohulls.


PDQ keels are also not very efficient, being low aspect. Several sources suggest that about 5% of the sail area is good for this type and this sort of boat. With about 620 ft^2 of up wind sail area, that would suggest 31 ft^2 or 15.5 ft^2 on each side. Since the existing keels are more like 12.3 ft^2, we are seriously lacking in area. With the factory self-tacking jib, the up wind area is only about 506 ft^2 and the factory keels make perfect sense (12.6 ft^2 suggested). On flat water with a wide lead angle it also works with the large genoa, but when it gets rough, not so much. If I tighten the lead angle to 14 degrees, even more trouble.

The existing keels have a very blunt trailing edge, perhaps 5/8-inch wide. What if we extended this out to a fine edge? that would add about 1 ft^2 per side. What if we add a low angled fence keel for a short distance behind the keel, perhaps 30 inches long? Another 1.8 ft^2; not efficient because low aspect, but thin and very low drag. Both would be simple to do while out for painting and cost very little. No additional draft and nothing to snag on the bottom. I have a chain rode, so keel wraps are a non-issue. This would get the area back into the design pocket.

Note: I did fair the keel, 10/2015. Yup, really helped with balance and VMG. See Good Old Boat Magazine, 2016, for the story.

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The plan? I think the inside genoa leads may appear within a few months--a little more testing and figuring. The new main and keel mods will wait for the next haul-out; I think they will make a fun 1-2 punch. While she will never be a reaching machine like my old Stiletto, I think she will be getting up and down the Bay a good bit quicker than stock, and smoother too; a very fast cruiser for her size. I'll have to calculate new speed polars!

Speed isn't everything. Efficiency means I can also reef earlier without loss, and that makes for easier, safer sailing. 

Friday, September 13, 2013

Reeving

You'd think reeving a block would be second nature to an old sailor, but I'm always forgetting how to reeve a 6-part tackle at 90 degrees. Weave the rope in any other order and you're just throwing money away.



Look Mom... nothing touches!


The problem is friction. For the same reason that you can hold a 2,000-pound load on a winch with 2 fingers by virtue of 3 wraps, a tackle where the line going up rubs against the line going down  will waste energy from the start and virtually lock-up when it gets within 6 block diameters of finished.



I keep this cheat sheet handy for when the davit tackle gets tangled; typically a well meaning guest detaches it and drops it to one side, unknowingly passing the block through the tackle. Oops.

4:1 blocks have a trick too:

Wednesday, September 11, 2013

You would think after 30 years of messing about in boats I would know what basic terms mean. But it seems they mean different things to different folks.






I always assumed "wind" meant the actual wind. The true wind. The first texts I read on catamaran sailing made it quite clear that is what the author believed. Something like this:

Pinching. Probably closer to the wind than Close hauled suggests.
Close hauled. As near the wind as good VMG indicates.
Full and by. Just eased a tick. Full sails. Often better VMG in steep chop or performance multihulls, but depends on the boat.
Close reach. Between close hauled and beam reach, about 67 degrees off the true wind. On fast boats this can be a lot like full-and-by, while slow boats have eased sheets.
Beam reach. True wind on the beam.
Broad reach. True wind about 135 degrees, apparent wind generally on the beam. Still forward of the beam on fast boats.
Deep reach. Deeper than Broad reach. Apparent wind will be on a the beam on a fast boat, perhaps 135 degrees on a cruising boat.
Run. 180 degrees, true and apparent.

I started a discussion on a forum here that resolved nothing. Plenty of references on both sides.






Wiki takes my view; not an authority, perhaps, but I'm hanging my hat there...



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All I can say is that if I make a course reference it is relative to true wind. How my specific boat requires the sails be set is to me of less importance to the story than telling the reader the direction of the waves and the nature of the sailing. That is enough and it is better related by the true wind than some artifact of how fast I'm moving.

Sunday, September 1, 2013

Long Bridles

Rev 10-29-2013

I'm still working my way through this topic--I think many cat sailors are--so this post is a work in progress.

There are 5 conflicting requirements asked of a catamaran mooring bridle and I have yet to hear of a perfect solution. Partial solutions that work, but always prone to some critical flaw.

  1. Turning Leverage. First, cats need a relatively long triangular bridle to keep them into the wind at anchor. If anchored to the center beam they skate all over, with a bridle they are placid. Legs equal to the beam provide sufficient leverage and allow working from either bow, if needed. Longer legs also place less stress on the bridle (basic statics/trigonometry).
  2. Shock Absorption. Actually, this applies to all boats, but more so to cats as they are more inclined to anchor in shallow water. Waves, particularly if breaking or simply steep, impart tremendous energy that the typical all-chain rode cannot absorb. Folks say the catenary absorbs shock, but only true in deep water with several hundred feet out; in a 50-knot squall anchored in 6 feet of water (60-70 feet of rode would be conservative) the rode is so close to straight--within 1 foot-- that chain has no absorptive capacity. What is needed is a nylon bridle long enough to absorb a wave, that is to stretch 2-4 feet. That will require a 30-foot bridle leg. This is even more vital for monhulls, which see severe impacts if a wave strikes the front beam or bridge deck.
  3. Apex of Bridle Must be Off the Bottom. If a very long bridle is used the apex will be on the bottom during slack conditions, subject to chafe. While this is not critically important in the Chesapeake mud bottoms, with rock or shell it would be. Even on the Chesapeake oyster shells eventually take a toll.
  4. Chain Hooks Like to Stay Off the Bottom. Even the the Mantus hook, one of the most resistant to getting flung off, stayed on when I used a short bridle but frequently fell of when I used a long bridle.
  5. One-size-fits-all Would be Nice. What boat has extra room for extra stuff?

In a recent Practical Sailor Magazine one multi-huller suggested using a long bridle, but anchoring the legs far back on deck, to the midships cleats or behind. The bridle then goes through a turning block and forward to the rode. The legs are thus over 30' long for shock absorption, but the legs between the hulls not so long that the apex of the bridle rests on the bottom. Another experienced contributor poo-pooed the practice, citing extra chafe points and rigging. True enough. He was a monohull sailor, of course.



I thought I would try it for a night.  My new Mantus Hook testing bridle is long enough and the wind was gusting over 20 knots. I was protected from waves but not the wind. It kept the bridle off the bottom.
  • The boat rode well, without any jerking or surging.
  • There was certainly movement of the rode through the chocks during the gusts--4-6 inches in the stronger puffs--proof the stretch was working. Webbing chafe gear seems to work, but anything that generates friction also reduces the effectiveness of the side deck portion of the bridle. Additionally, the line could jump out of the chock in rough conditions. A turning block is the right answer, but it must be well placed. For my boat and circumstances it is not needed.
Food for thought. It looked neat and it worked, but with turning blocks there is really too much to set up nightly and there is no go location for a turning block on my boat anyway. For now, it has become my standard method.

Relocating Jacklines

Formerly the jack lines terminated at the forward beam; simple and strong, but cause a tripping hazard. After far to long a wait, after a suggestion by my daughter, we relocated them to the edge of the tram, where combined with a small back-up plate and the natural strength of the hull flange and trampoline track, there is a natural strong point.

The aft end is still anchored to the hard top railings, the spliced end of the dockline cow-hitched around a center point attachment, spreading the load.

The forward end is lashed (many passes of parachute cord adding up to a 5500-pound line) to a 316 SS bolt hanger. The chafe gear is for UV protection.

Less of a trip problem, equal access, easy to re-tension.

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Why rope instead of webbing, as is the conventional wisdom? Though I've discussed this before...
  • UV. We leave them rigged 365 because we believe night comes every day, the water is cold in the winter, single-handers need to stay on the boat, and thunderstorms give little warning.
  • Under foot? We don't worry about stepping on them because they do not run on the deck.
  • Stretch. We like the stretch of nylon dock line because we have a cat and used long tethers. If we were a mono-hull we would use something lower (but not zero) stretch.
And we use 2-arm tethers. One about 84" and the other about 30". Fit them to YOUR boat.