leong

Andy, I'm not sure I understand your contradiction. But, perhaps, the following will straighten it out: Think of it this way. You're a point on the water moving along due to variable paddling, wind, current, waves and whatever. The GPS has the coordinates of your point (say, east and north) and your velocity vector (say, east_rate and north_rate). The GPS knows when your velocity vector is not pointing to the waypoint. With an arrow (or something) it tells you to turn and stop turning when your velocity vector is pointing towards the waypoint. Note: if the velocity is (east = 3 knots, north = 4 knots) you're moving in the northeast direction at 5 knots.

A reader questioned my analysis saying the conservation of momentum argument applies to accelerating a boat from a standstill, not to steady-state boat speed. Did you ever notice while kayaking when you start the catch you have to pull hard to accelerate the kayak (the blade sort of stands still in the water and you lever past it)? Remember, between each paddle stroke a kayak slows down (it must slow down because of the water drag). Assume it slows down by 0.1mph (my guess, but use another value if you want to). Assume a paddle is in the water 0.5 seconds (my guess, but use another value if you want to). So the stroke has to increase the kayak’s velocity by 0.1 mph in 0.5 seconds. So the average acceleration during the stroke is (0.1/0.5)/3600 = 5.6 * 10exp(-5) [mph/sec squared] Now from a standing start say it takes 15 seconds (my guess, but use another value if you want to) to accelerate the kayak to 5 mph. So the average acceleration at startup is (5/15)/3600 = 9.3 * 10exp(-5) [mph/sec squared] So, using my estimated values, the acceleration while the paddle is in the water is comparable to the startup acceleration. Although the momentum argument is not the whole story, it demonstrates its own energy requirement due to mass. Obviously, additionally drag from increasing weight also slows a kayak down for different reasons. -Leon

With a true Goto function you don't have to perform a new Goto when you stray off the original line. That's because the line is always a straight line from your current position to the waypoint. The GPS will always try to keep you on the current line whether it's the original line or a newly computed line. It knows the location of your variable position and the fixed waypoint. So if you're to the right of the current line just turn a little left until you're back on the line. Remember, the GPS knows your current velocity vector (speed and direction of motion). It has no idea which direction your bow is pointed at. You're just a point on a map to the GPS, including two velocity components (say, east rate and north rate) On my el-cheapo GPS there is an arrow. My job is to adjust my heading accordingly to keep the arrow pointing to the top of the screen.

Yes, indeed.

Stiff boats are faster for pretty much the same reason a well inflated tire is faster. Flex costs energy. But I don't think you'd notice the energy lost on a standard fiberglass boat compared to a stiffer carbon boat. Nevertheless, racers want to save every second.

Andy, As you explained it, the Sight'n go function can't function as a true Goto unless you enter the distance to the waypoint. If not, it can't provide a true Goto function. A standard GPS Goto function continuously draws an imaginary line from your latest position to the stored waypoint. Say you stray from the original Goto-line and drift off a significant distance. What sense would if make to go back to the original line? I’m almost sure that the watch GPS doesn’t have software to remember the old line, anyway. The Sight'n go function seems like just a fancy compass to me. Of course, if you don’t drift sideways it doesn’t make any difference. In a standard GPS there’s a continuously changing line from your latest position to the waypoint. That latest line is the shortest great-circle “line” to the waypoint. The original old line is useless from your new position. Bottom line: I was just pointing out the luxury that a standard GPS’s Goto function eliminates the need for estimating ferry angles. If you don’t care then my point is irrelevant. -Leon

Andy, Some GPSs have compasses. When the compass is on I think that GPS always tries to point your heading vector to the waypoint. It would be like if you could visually see a tree and always paddled towards the tree your course over ground would be a curved path (a pursuit curve) if you drifted sideways. But, I guess that since the watch GPS doesn't know where on the direction line you want to go to it might just be acting like a compass. Perhaps I'm confused. But I don't think the watch GPS will attempt to keep you on the initial straight line to the target. Here's a long post about the pursuit curve and the use of GPS to keep you on the shortest distance path to the waypoint. PS I'll invite Lisa to join this discussion. She has more practical experience with a GPS than anyone I know. In my case, the following quote applies to me (a guy who knows the math of the topic but has limited practical experience). In theory, there is no difference between theory and practice. But, in practice, there is.

Yes, when the ratio of the delta weight to the starting weight is small the speed percentage change will be correspondingly small. But surprisingly, going from 400 lbs to 404 lbs slows you down by 1% (at least according to my formula). Nevertheless, I think that 1% seems too much. Also, there is less of a glide slowdown with a real big displacement. This website http://www.paddlinglight.com/articles/the-lightweight-secret/ estimates the drag increase for increasing displacement weight is 0114% per ounce. That equates to 0.73% per 4 lbs. Note that my formula doesn't account for drag increase. It's just for inertia due to changes in weight.

To help quantify how increasing weight slows down a kayak use the fact from physics that the momentum of a system must be conserved. During a stroke, the momentum of a kayak and paddler must equal the momentum of the water being pushed back by the paddle. Momentum equals mass (m) times velocity (v). Let m be the total of mass of the paddler and boat, v be the velocity of the kayak, M be the mass of the water being pushed back by the paddle and V be the velocity of the volume of water being pushed. Thus the conservation of momentum equation is m*v = M*V Solving for v v = (M*V)/m Now consider a fixed paddle size and a fixed speed of the paddle moving backward (say at the middle of the stroke). For this case M*V is constant. So increasing m and keeping everything else the same, v decreases; i.e. your kayak doesn’t move as fast. This inverse relationship is more significant than you might think. Even a little extra weight will slow you down. Example: Assume that the combined weight of the paddler and kayak is 175 pounds. Now add 20 pounds more, so the new total weight, W, is 195 pounds. Note that weight is just mass times acceleration due to gravity (W = m* g). If you do the math this heavier kayak (increased displacement) will go about 10% slower if you paddle exactly the same way. Of course you can use a heavier kayak and/or add ballast and/or go off of your diet to get the increased weight and the resulting speed decrease. Ugh! Note 1. Only when the blade is in the water is the kayak being pulled forward. In between, the kayak is slowing down during a coast. So the momentum argument overestimates the total slowdown during a total stroke cycle. Note 2. Various articles like this one https://web.archive.org/web/20170313200355/http://roguepaddler.com/weight.htm make two claims arguing against lightweight kayaks: 1. “Although you expend more effort to propel a heavier load, some of that effort is gained back between strokes when the weight may actually help to keep the kayak moving.” Actually this is only partly true because the increased water drag/displacement of a heavier kayak also slows down the coasting between powered strokes. The increased speed of a lighter kayak during the powered phase of the stroke cycle easily outweighs this glide argument. 2. Heavier kayaks track better. Although this is true (disregarding skegs and rudders) the author’s numerical example of a constant 1-degree tracking penalty of 8 minutes after 8 hours of paddling assumes a constant 1-degree bias. In reality, a kayak that doesn’t track well would tend to zigzag (alternating between 1-degree to the left followed by 1-degree to the right). I computed the actual zigzag penalty in my Mathcad worksheet “Heading Error Penalty”. The correct answer is only 4 seconds, not eight minutes as the author computed for a constant 1-degree bias. For additional information about how a paddle works see Guillemot Kayaks at, http://www.guillemot-kayaks.com/guillemot/information/kayak_design/how_a_paddle_works

It seems that only 5% of people I talk to about GPSs realize the beauty of a GPS is the GOTO. That is, with a GPS, a GOTO a Waypoint can keep you on the proper heading so that your “Course-Over-Ground” is a straight line to the waypoint, regardless of crossing currents or crossing winds. Even if the wind and/or current are variable the GPS can continually provide adjustments to keep you on the right heading angle. So if you’re using your GPS to go to a particular Waypoint, computations of ferry angles or the uses of ranges becomes unnecessary. This is especially useful when you’re paddling in a fog (or in the dark) where ranges aren’t available. Of course, GPSs can fail and one should always be able to use a chart and ranges and a Compass and be able to calculate ferry angles based on estimates of current/wind direction and speed. That said, if the GPS watch doesn’t have a GOTO function then I’d buy a small handheld instead. If it does, the other comments are all reasonable to me. Just my two cents. -Leon

Well this wasn't exactly snorkeling. I was trolling along the Palm beaches and spotted feeding tarpon (about four to five feet long). I just held my camera under water in video mode and this is what I got. Later I hooked one; it pulled me over, I failed a roll and lost my rod and reel (I don't lanyard my equipment to the boat because of sharks)

Thanks Paul. I'll probably visit Seabrook next week near high tide. BTW, the normal maximum ebb at Jupiter Inlet is just about 3 knots.

Thanks again guys. I'm going up to Seabrook in a week or two to arrive about an hour before high tide. One more question. I'm not worried about paddling against a 3 knot current going through the inlet. But does a big tide race form? Going against a 3-knot current in a tide race is above my pay grade. I did just that going through the Jupiter Inlet in Florida when I capsized and failed a roll. Luckily, I was close to shore at the mouth of the inlet and and landed on a nice soft beach.

Thanks guys. I've done Essex bay and Plum Island so many times I just want to try something new. As you know, Essex Bay marches go dry at or near low tide. Is it feasible inside the Seabrook bridge near low tide, especially if you want to poke around the marshes?

What's it like to paddle the Marsh at Seabrook (anything interesting to see)? Is it worth a one hour drive (for me)? Anything to be aware of going out to the ocean and any good landing spots on the ocean side? My usual paddling is out Manchester Harbor (35 minute drive) or Lanes Cove (45 minutes) or circumnavigate Cape Ann from Gloucester HS. -Leon

Are those dowels holding the two halves together that slide into holes to accommodate the tapering of the hull? If so, wouldn't a hard push break them apart?

The nomenclature problem also applies to "boats". Is a 10' recreational kayak used on a lake the same as a sea kayak used on the same lake. Too bad there isn't a unique name for more advanced kayaks. End of my rant. It's not a big problem in the scheme of things.

I hear you mate. It's a big nomenclature problem in this sport. Unfortunately, the word kayaker is used for novices who paddle fat bathtub-looking kayaks as well as experienced people who can paddle long and skinny sea kayaks in rough water. I wonder if technical mountain climbers would mind being called hill strollers? Our sport needs a more unique terminology. Any ideas?

A footbar permits leg drive with your feet/knees close together. It's also easier on your feet. That’s also true with a foam block against the bulkhead, but it’s a hassle to change to different lengths. Be sure that your kayak has a big enough cockpit and high enough deck to allow you to adopt a leg position like with a surf ski. Besides the Onno, here’s a footbar with steering pedals I just found: https://shop.expeditionkayaks.com/collections/kayak-accesories/products/the-big-foot-kayak-foot-plate-system The nicest thing about my Epic 18X is that the cockpit is big enough for leg drive but still allows for leg bracing for rolling.

When I don't use a wing this is my paddle of choice. http://www.epickayaks.com/product/product/epic-active-touring-paddle

Nick, I agree with everything said, except I think it’s a bad idea to remove the emergency strap. It’s a belt and suspenders backup if the grab loop rips off. I have a snap dragon model with the emergency strap and, although it’s not recommended, it’s much easier using it than the grab loop. Just a little force* to the right (or left) moves it off the side of the coaming and the spray skirt practically falls off by itself. The force on the side to stretch the spray skirt x inches is much less than the force from the front. Think of pulling on the side of an elastic band stretched between two points vs. pulling (or pushing) perpendicular to the elastic band.

Ugh, cut a rectangle through the gel-coat/carbon-fiber and push the stern eye out through the bottom. I don't know what the eye is fastened to. Probably some reinforced section. I assume the stern eye looks like this ->http://www.go2marine.com/product/78277F/sea-dog-stern-eye-with-adjustable-finish-nuts.html . I doubt that the rectangular flange on the bottom is just seated up against the bottom of the thin top deck (it's an 18' boat that weighs only 38 lbs.). The repair job for that is doable, but not for me (especially working with carbon cloth). So far the stern eye is just wiggling a little and I try and avoid any force on it. But it anchors the rear deck lines so there's always some horizontal force on it. Anyway, before tackling such a big job I'll wait until it breaks loose itself (hopefully, not while someone is doing a T-rescue on me; note to self: practice and practice rolls

I may have to do that. I'll measure the span.

Excellent, Cathy. They they even have squirrels wearing little pink work clothes. Thanks, -Leon

The hard part will be to seat a socket on an unseen nut over 4 feet away. I think I need something like an endoscope with a remotely controlled wrench. I guess it will be cheaper to buy a new kayak. I'll probably wait until the eye comes out and install something from the outside (a watertight toggle bolt?).