Suitable GPSs for determining speed

[Peter]

There have been a couple of threads on this board lately about knotmeters and other means of determining boat speed through the water. The suggestion has been made to use a GPS to do this. I believe the suggestion means to use a handheld GPS. This is OK while daysailing or even cruising but when racing it is handy to have the speed showing all the time, as happens with a bulkhead mounted speed instrument such as the Horizon SL45. I am thinking that maybe a larger fixed mount GPS receiver might be better as you could mount this so that it could be read from the cockpit and you could have your speed reading showing all the time. My question is, which make and model Fixed-Mount GPS Receivers are being used in this way, and is the speed reading large enough to be read easily when one is at the helm? I'm afraid that many of these would show the speed reading so small that it would not be possible to read them while at the helm. Any suggestions or ideas will be greatly appreciated. Thanks,
Peter S/V Larrikin (CD26)



pkozup@juno.com

[Bill Goldsmith]

Peter,

Regarding your statement, "There have been a couple of threads on this board lately about knotmeters and other means of determining boat speed through the water. The suggestion has been made to use a GPS to do this."

Please note, as I mentioned in my response to Mike's comment below, that GPS does not indicate speed through the water. It indicates speed over ground. Not meaning to be nit-picky, but these can be very different if you have a strong current. My suggestion is that one should ideally have both readings at hand, to get the full picture.

Regarding your question dealing with visibility of the speed readouts on GPS units, note that on the Garmin 176 the size of the readout is user-customizable. There is one setting where you can display the knots in very large numerals that would be visible across the cockpit. The 176 is kind of a hybrid fixed-mount/handheld. Its size puts it large enough to mount it and still see the chart readout, but small enough to hold as well.

I imagine that other models have this feature as well. The Garmin website probably has more detail on which models have the large numeral setting. Other manufacturers may have this feature as well, but I am only familiar with Garmin.

All the best,

Bill Goldsmith
CD27 #173
Second Chance



goldy@bestweb.net

[Ken Coit]

Peter,

My ancient Magellan hand held can be mounted on the pedestal with a simple bracket available from most outlets. I used a couple of cable ties to mount the bracket to the tubing above the compass. You don't need any large display if it is that close and you can take it home or lock it up when you leave.

Only issue is using the GPS as a handhold. It doesn't work.

Ken
S/V Parfait
Raleigh, NC

There have been a couple of threads on this board lately about knotmeters and other means of determining boat speed through the water. The suggestion has been made to use a GPS to do this. I believe the suggestion means to use a handheld GPS. This is OK while daysailing or even cruising but when racing it is handy to have the speed showing all the time, as happens with a bulkhead mounted speed instrument such as the Horizon SL45. I am thinking that maybe a larger fixed mount GPS receiver might be better as you could mount this so that it could be read from the cockpit and you could have your speed reading showing all the time. My question is, which make and model Fixed-Mount GPS Receivers are being used in this way, and is the speed reading large enough to be read easily when one is at the helm? I'm afraid that many of these would show the speed reading so small that it would not be possible to read them while at the helm. Any suggestions or ideas will be greatly appreciated. Thanks,
Peter S/V Larrikin (CD26)

PPparfait@nc.rr.com (u know the drill)

[Hanalei]

Captain Larrikin,

The only way a GPS, of any size, can indicate speed THROUGH the water is if it is tied to another instrument via a link like "Sea Talk(Magellan or Garmin)to a knot log located somewhere else on your vessel. GPS ALWAYS indicates speed over the surface of the Earth.......FWIW....

Dave Stump
Captain Commanding
s/v Hanalei

[Don Carr]

Assuming you are racing the GPS is the perfect tool for determining your optimal VMG to the mark. As mentioned on other posts you will not get through-the-water speed. Better to have 3 knots VMG than 5 knots through-the-water and 2 knot VMG. If, as you say, it is a racing application then VMG to target (mark) is really more useful and GPS does all the calculations for you. IMHO.

p.s.
Maybe Capt Stump might confirm this?



carrds@us.ibm.com

[D. Stump, Hanalei]

Captain Carr,

Think about it, you can not calculate VMG if you don't know your speed THROUGH the water. Again, the GPS would need to be linked to maybe an AutoHelm and a knotmeter to calculate VMG. As an example, if I hook the knotmeter and GPS to my AutoHelm 4000+, it will calculate VMG to a specific mark. But, you still do need a knotmeter!

Hope this helps, but really, all ya MUST know is that you cross the line a long time BEFORE Hanalei!!!!!!!! Your HUMBLE servant......

Dave Stump
Captain Commanding
s/v Hanalei CD-30C
CDSOA #1

[Don Carr]

I respectfully disagree. VMG is simply the rate of movement from my current known position on this planet to a second known position. Follows the shortest distance between two points is a straight line concept. Therefore speed through the water is irrelevant. VMG can be calculated without knowing hull speed. Simply plotting a series of fix plots and deltas over measured time.
I can have a boat speed of zero as indicated by my knotmeter but have
a VMG of 2 or 3 knots simply by current effect. Don't get me wrong, knotmeters are very useful but GPS can be very helpful in determining
the optimal course to a given point without the calculations of set and direction of set. IMHO



carrds@us.ibm.com

[D. Stump, Hanalei]

Captain Carr,

I stand corrected Sir, I was pacing the quarter deck and Killick had not yet served out the morning coffee. Question is, do you know what a Killick is?

Dave Stump
Captain Commanding
Hanalei

[BIll Goldsmith]

I agree with Don that the GPS gives you instantaneously calculated VMG results, but using only the GPS, you get the result, but not the "why." For instance, if you have a VMG of 3.5 knots toward a mark, is that because you're sailing at 5 knots while bucking a 1.5 knot current? Or are you sailing at 3.5 knots in slack water? You'll be able to make these judgments with both gps and knotmeter data whether you have a nifty electronic setup, or whether you just set them up next to each other the low tech way like me.

If racing, you're going to want to know the current to plan the next tack (I defer to racers here for strategy, etc., not my specialty). And if just cruising or daysailing you'll still want to know the current so you can at least mentally judge its set and drift, and when to break out the wine for the last tack into port!!

Bill Goldsmith
CD27 #173
Second Chance

I respectfully disagree. VMG is simply the rate of movement from my current known position on this planet to a second known position. Follows the shortest distance between two points is a straight line concept. Therefore speed through the water is irrelevant. VMG can be calculated without knowing hull speed. Simply plotting a series of fix plots and deltas over measured time.
I can have a boat speed of zero as indicated by my knotmeter but have
a VMG of 2 or 3 knots simply by current effect. Don't get me wrong, knotmeters are very useful but GPS can be very helpful in determining
the optimal course to a given point without the calculations of set and direction of set. IMHO

goldy@bestweb.net

[Mark Yashinsky]

or killock - A heavy stone used on small vessels as a substitute for an anchor; also a small anchor. Or are you calling your admiral, merely a leading seaman??? For your continued health, I hope you are refering to the anchor.

[Don Carr]

Thank you for the information. I hadn't a clue.

[Nautical Traditions Offic]

Captains Commanding,

The Killick was the seaman assigned to take care of the Captain! He served his food, assisted him with his uniform, and generally took care of the "Old Man"! So, yes, you could say that he was the sailor that "anchored" the Captain.....this is fun....your most HUMBLE servant.....

Dave Stump
Captain Commanding
s/v Hanalei CD-30C
CDSOA #1
Nautical Traditions Officer
CDSOA, Inc.

[Bruce Bett]

The Capitan is a scholar who knows his books well! The following is from the Oxford English Dictionary, with which there can be no dispute. And so we know what a killick is and something of the whims of modern authors.

A glass of wine with you both and later perhaps some toasted cheese.

Bruce Bett
Sostenuto
CD 25 #496

a. A heavy stone used on small vessels as a substitute for an anchor; also a small anchor. to come to a killick: to come to anchor (obs.). up killick: to weigh anchor.

1630 WINTHROP New Eng. (1825) I. 40 The wind overblew so much at N.W. as they were forced to come to a killock at twenty fathom. 1632 T. MORTON New Eng. Canaan (1883) 262 The inconstant windes shiftinge at night did force the kellecke home, and billedge the boat. 1643 R. WILLIAMS Key Lang. Amer. 111 Kunnosnep, a Killick, or Anchor. 1670 NARBOROUGH Jrnl. in Acc. Sev. Late Voy. I. (1711) 107 Instead of Anchors, they have modern Crab-claws, or Kellocks. 1758 Ann. Reg. 292/1 They sent out another float, with killicks and ropes. 1768 J. BYRON Narr. Paragonia (ed. 2) 82 We hove up our..Kellick, which we had made to serve in the room of our grapnel. 1837-40 HALIBURTON Clockm. viii. (1862) 29, I shall up killoch and off to-morrow to the Tree mont. 1840 R. H. DANA Bef. Mast xiv. 32 We usually keep anchored by a small kedge, or keeleg. 1883 Times 18 May 7 With some bits of wood and a large stone..[is] fashioned a very good kedge or killick. 1897 R. KIPLING Capt. Cour. 63 Dad says next one [anchor] he loses..he'll give him the kelleg.



b. A leading seaman's badge, bearing the symbol of an anchor; hence, a leading seaman. Also attrib. or as adj., leading, chief. colloq.

1915 ‘BARTIMEUS’ Tall Ship iii. 62 He paid for the misplaced generosity of his well-wisher with his ‘Killick’. (footnote) Anchor. The distinctive badge of a leading rating. 1920 Unreality II. iii. 115 Picked up my killick. Ibid. iv. 126 The sight-setter raised his brows at the red worsted anchor adorning Bill's sleeve. ‘Killick, eh!’ he ejaculated. 1925 FRASER & GIBBONS Soldier & Sailor Words 135 Killick.., the lower deck term for the Petty Officers' Anchor arm badge. 1930 G. WELLS Naval Customs 91 Killick,..a slang term for a ‘leading seaman’. 1945 ‘TACKLINE’ Holiday Sailor xiv. 143 Been in barracks for a matter of six months. Killick then, o' course. 1949 PARTRIDGE Dict. Slang Add. 1092/2 Killick-scribe, a Leading Writer.

or killock - A heavy stone used on small vessels as a substitute for an anchor; also a small anchor. Or are you calling your admiral, merely a leading seaman??? For your continued health, I hope you are refering to the anchor.

bettb@macomb.cc.mi.us

[D. Stump, Hanalei]

Captain Bett,

I forget, what is the US Navy enlisted rating that displays an anchor? Machinist Mate, or what? I seem to remember we called them "anchor clankers" when I was in the countrys' service back in '63!

Hanalei

[Neil Gordon]

>>...what is the US Navy enlisted rating that displays an anchor?<<

That would be the Boatswain's Mate. Machinist Mates have a propeller on their rating badge.


Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167



neil@nrgordon.com