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Go Back   SailNet Community > On Board > Gear & Maintenance > Knotmeter- Clarification needed
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Thread: Knotmeter- Clarification needed Reply to Thread
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Topic Review (Newest First)
12-15-2011 05:05 PM
jackdale
Quote:
Originally Posted by rbraastad View Post
where can i get a wind speed and direction indicator for my san juan 24 thanks anyone
Raymarine, Garmin, Tacktick, B&G, Simrad and other make them. Check your local stores or go online.
12-15-2011 04:23 PM
rbraastad where can i get a wind speed and direction indicator for my san juan 24 thanks anyone
12-22-2009 10:26 AM
ericroline Weed proof, doppler units are now available for a lot of ca$h. I just pull and clean mine before important races. It ties into the ST60 system for VMG calcs.
Do not use petrolium grease on the Oings,,, use silicone grease to prevent from attacking the nitrile Orings..
Interesting experience is that the older DMI paddle wheel is wider than the Raymarine version and works longer between cleanings and works to a slower boat speed.
12-22-2009 09:55 AM
jackdale I pull the knotmeter quite often. Usually it is just to show folks how to do it. Sometimes to clean it.

I agree with Faster; the knotmeter is better for sail trim, if you are into that sort of thing. The GPS uses average speeds over a number of waypoints, the knotmeter is more instantaneous.

In new designs, there is a flap inside the the tube, that prevents a huge amount of water from getting in. It is not prefect, but it does give you peace of mind.
12-22-2009 09:54 AM
CalypsoP35
Remove It Regularly

I have to second Sabreman's comments. We need the knotmeter because it provides the info for the anonometer to give us true wind speed, but even if we didn't need it for that, I find knowing boat speed over water when compared to speed over ground is nice to know so that you know what the current is doing. Also, as someone mentioned the feedback from the knotmeter is much more instantanious than the GPS if you are trying to gage the effects of sail trim on your boat speed.

I remove my impeller everytime I leave the boat and re-insert it everytime I go sailing (assuming I don't forget). It's the only way to keep it clean and functional over any period of time. Fortunately, I have rather easy access to my impeller.

It took me a whole season before I had the nerve to remove the impeller when the boat was in the water. Now, I just do it routinely and wonder why I was so scared to do it before.
12-22-2009 09:32 AM
Faster We do have significant currents (large tides) and I have to say I hate it when someone blocks my line of sight to the knotmeter. For me the through-the-water speed is crucial feedback/data for steering and sailtrim, as much as telltales and waves.

Also since our GPS is a handheld on the pedestal, the knotmeter is a much easier-to-see instrument with a larger readout, esp when steering from the rail.

Still, even though I've done it dozens of times, the old 'swap the plug' in and out always makes me nervous!
12-22-2009 09:14 AM
JohnRPollard
Quote:
Originally Posted by Sabreman View Post
John - I had the same feeling until we raced Gov Cup two years ago. The impeller hadn't been in for 2 years. When I installed it for the race, I saw that it wasn't working, so we used a GPS for the race. GPS SOG lags actual boat speed it really isn't very good at telling what the boat is doing now. On top of that, we used a handheld and at night had to keep turning on the backlight to see what was displayed. This year, we used the knotmeter in conjunction with the GPS and it really helped us to know whether we were he aided or hindered by the current. At times, the current was ~1kt.

I highly recommend slathering Vaseline on the impeller. I read about it here on Sailnet and decided to give it a try this year. We're based on the Yeocomico off the lower Potomac, and marine growth is insane during the hot months. I only had a small bit of slime on the impeller in August after 2 months in the water. After that, there was nothing on it until we hauled in November.

Oh yeah, for racing I'd definitely want it. I've done half a dozen Governor's Cups myself and in a race of that length (or almost any race) those kinds of differences can be significant -- especially when deciding whether to favor the deep water or head for the shallows.

For the family cruising we do, it's rarely an issue. We do pay attention to what little current there is -- by reading the buoys we pass and knowing the tides tables -- but we've never had the need to calculate set and drift. Again, that's a function of our local waters (the same waters the OP will sail on next season.)

But maybe I'll give the vaseline trick a try at our next haul out. Thanks for the suggestion.
12-22-2009 09:11 AM
BubbleheadMd Silicone for the O-ring. That'll provide lubrication and prevent deterioration. Petroleum jelly might eat the rubber.

Petroleum jelly on the impeller itself to keep growth at bay sounds like a great ideal.
12-22-2009 09:09 AM
BubbleheadMd Yeah.......with this new information, I won't even be attempting this until it's good and hot outside.

I have minimal instrumentation and I'm something of a restoral nut so I'd like to have it working.

I think what I'll do is dive on the thru-hull, and lightly insert a shallow, rubber plug with a string attached to it. That way if I encounter any problems removing the red plug (like damaging the interior fitting or something) the exterior plug will already be in place, preventing or slowing water from getting in.

If I encounter no problems, then I can just gently pop the rubber plug out with the egg beater and recover it with the string.

Anyway, that's all months into the future. Thanks for the clarification.
12-22-2009 09:01 AM
Sabreman John - I had the same feeling until we raced Gov Cup two years ago. The impeller hadn't been in for 2 years. When I installed it for the race, I saw that it wasn't working, so we used a GPS for the race. GPS SOG lags actual boat speed it really isn't very good at telling what the boat is doing now. On top of that, we used a handheld and at night had to keep turning on the backlight to see what was displayed. This year, we used the knotmeter in conjunction with the GPS and it really helped us to know whether we were he aided or hindered by the current. At times, the current was ~1kt.

I highly recommend slathering Vaseline on the impeller. I read about it here on Sailnet and decided to give it a try this year. We're based on the Yeocomico off the lower Potomac, and marine growth is insane during the hot months. I only had a small bit of slime on the impeller in August after 2 months in the water. After that, there was nothing on it until we hauled in November.
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