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 Post subject: Another cause of leeway
PostPosted: Tue Apr 04, 2017 7:37 pm 
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Standard wind drag causes us leeway, a push by the wind away from our goal like in this picture:
Image

But some contact with boat designers (book and forum) made me aware of another contributor to leeway: a shallow surface water current driven by the wind if it has enough speed, fetch, and duration. The only antidote is deep daggerboards (turbofins?) and rudders.

They are skeptical of the shallow skeg approach, and in fact I was puzzled by lack of upwind progress of a boat with even less fin depth than my Hobie (but plenty of fin area). It would shoot upwind on rails at protected sites, but an exposed site would not allow progress even tho the wake and bubble trail did not indicate excessive wind leeway or wave pushing. It was a wind created current doing the stealth push.

So bottom line that I take for Hobie yaks is to keep those fins long, vertical and use the sailing rudder in strong beating to windward or don't expect much progress. I gather a couple models can also use a daggerboard. I thought the problem was just physical action of big waves, but could tell it was more than that in above incident.

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PostPosted: Wed Apr 05, 2017 10:53 am 
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A slow steady pedal action will help you gain upwind performance at a higher angle. Especially with an inflatable.

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PostPosted: Wed Apr 05, 2017 3:19 pm 
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When not in a hurry I will beat against a firm wind in these modes:

Protected water -> close hauled without pedaling
Lively water -> bear off to close reach without pedaling (otherwise waves break momentum, halt apparent wind, lose steerage)
Aggressive water -> very close hauled with pedaling

What's new to me is considering not only waves but current to comprise aggressiveness. I will look for signs of this special non-tidal downwind current around channel markers on today's i12s excursion.

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PostPosted: Wed Apr 05, 2017 6:37 pm 
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I think about it more in terms of boatspeed. In light breeze with boatspeed low (about the same speed I could pedal/paddle), I can improve pointing by 20 degrees or more by human power. When the sailplan is working so that the boat is moving faster than I can "help" it, I'll take the lower course unless there is an obstruction I can pass if I assist. A lot is experience in your conditions and your boat. A lot also is how fit you are and how much of a hurry you are in.

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PostPosted: Thu Apr 06, 2017 1:01 am 
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daft wrote:
The only antidote is deep daggerboards (turbofins?) and rudders.

Thanks, but I think I threw things off track with above statement. I am not looking for any antidote for Hobie kayaks unless some person self sabotages, like not keeping fins down when sailing (like most customer youtubes sailing non-Islanders with feet still) or doesn't consider longer turbo fins and sailing rudder.

Knowledge is power. Awareness of wind driven water currents can lead to other responses than brute pedaling. In my case it happens when I finally clear the last buoys of a boat channel after an upwind slog thru boat traffic. Now I understand why I can't look at my wake or bubbles on the water, see that it projects easily clear of the buoy and then merrily depart on my first pure sailing tack. The wake or bubble trail is drifting with the current and can run me into the buoy.

I had never noticed such a thing with my background of weak tidal currents and deep daggerboards. But now I recall returning from many snorkle outings with ripping offshore winds, and the offshore current would fight my return. The particles in the water would stream outward vs the bottom. What recently highlighted the issue was a shallow/wide fin craft couldn't even get away from a shorebreaking inferno beach which a deep/narrow daggerboard craft could do easily. Oh, I remember that Venice floods when winds funnel the Adriatic up onto it.

I can't relate to folks wanting to pedal - I want to savor pure sailing, not go from A to B faster or do redundant exercise which I already have to do onshore. I do appreciate Hobie pedals which allow me to use maze like harbors where beach launches aren't available, or return when the wind poops out. But when the pedals can stop, it is like flipping a switch and saying ahhhh. Same thing when the motor shuts off on a big sailboat - I have spent many motorsailing days with the captain seeking that darn incremental angle.

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PostPosted: Sat Apr 08, 2017 7:59 am 
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daft wrote:
Standard wind drag causes leeway...

But some contact with boat designers (book and forum) made me aware of another contributor to leeway: a shallow surface water current driven by the wind if it has enough speed, fetch, and duration.


Surface water current? If the wind has sufficient speed, fetch and duration, you will get waves/chop. That will definitely slow you in a little light boat and provide opportunity for more leeway. Your other scenario when in protected waters has also eliminated fetch so you "shoot upwind".

Seriously, I don't think you need concern yourself about a surface water current causing leeway. :mrgreen: If it helps you, though, by all means, invent more reasons why you can't go to weather.

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PostPosted: Sat Apr 08, 2017 2:13 pm 
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tpdavis473 wrote:
Surface water current? If the wind has sufficient speed, fetch and duration, you will get waves/chop. That will definitely slow you in a little light boat and provide opportunity for more leeway. Your other scenario when in protected waters has also eliminated fetch so you "shoot upwind".

Seriously, I don't think you need concern yourself about a surface water current causing leeway. :mrgreen: If it helps you, though, by all means, invent more reasons why you can't go to weather.

Here's what the widely acclaimed god of boat design, Philip Bolger, said on p 36 of "Boats with an Open Mind":

Quote:
Keels like this hold on to windward quite well unless the wind has blown hard enough and long enough, over a big stretch of water, to start the surface water drifting.

Over and over he makes this point about shallow keels, which isn't controversial among boat designers I encountered in a forum where my admiration for a beachable twin shallow keel boat was laughed at as something that would sail backwards in above conditions (compared to a thin deep keel).

You talk about waves and chop doing this, but I factored that out of my experiment. My long thin daggerboard boat could easily pull away from an eternally wind lashed deepwater beach with 2000 mile fetch, while my other boat with equal fin area (2 half length fins) couldn't. More than that the problem boat could point well enough, but I realize you have to look at wake to see your real progress. The huge red flag was the wake showed a nice angle upwind but never made progress! It handled wave push fine, but the wake (and fins) was being pushed by a surface current.

One snorkling experience alone should have shown me the possibility of this when 40+ kts offshore winds suddenly turned my snorkle into a whistle and ripped the top 10 or so inches into a streaming offshore river. Not a rip current since no incoming waves. No windwaves could form with the super short fetch, but the current was enough to almost negate my powerful fins and I had to windmill my hands into the deeper water to get back to shore. And like I said earlier I have snorkled another site hundreds of times with onshore waves and around 15-25kt offshore winds. The long return is always tiresome with a shallow slow offshore current of particles streaming by. If tired I sometimes just kicked at a speed to hold my place over the bottom til each wave ratcheted me closer. Sometimes maybe a rip current, but I think normally windblown in spite of tiny fetch.

And it's not just Venice but other places that get rising water from storm wind surges. It may be calm locally, but surface water is blown in from hundreds of miles away.

There may be a further reason I am subconsciously reluctant to pedal while sailing. I pedaled too hard during early experiments which enlarged the soft slot where the drive axle seats into on my inflatable. The drive would pop out all the time until I saw the enlargement in the forward (thrust) location. I have patched this with glued spacers, but it is progressing and now I started wrapping the axle with electrical tape (much better than other tapes because grippiness keeps the levers from slipping). Nobody else seems to have this problem, but I may only have so many pedal strokes until it is unfixable. Recently I went well out to sea when a rogue set of waves blacked out the horizon. Just the effort to quickly align bow into the waves caused the drive to pop out on one side, and conditions were too iffy for me to correct that on the go.

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