Is it worth getting a log or should I stick with GPS?

Motor_Sailor said:
It's a Sonata. You go fast in one by keeping your head out of the boat and looking around.

Take a GPS if you think you'll need to know where you are, but a speed log is no use racing.
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I tend to agree with that, at least for small yachts and club-level short-course racing, where you don't have a pro or semi-pro crew running target speeds against polars on their race computers.

There are better reasons for a log on offshore racing - are we going faster or slower overall with trim or sailchange tweaks. It's usually pretty obvious though amongst similar boats on short courses.

Speed through the water is nice to have but it's rarely accurate for long, and even if all your GPS's die you can usually guess boatspeed accurately enough for emergency DR, assuming that if offshore you log GPS position hourly or if deepsea every change of watch. Before we had GPS you typically only got a position to within a mile or two once or twice a day at best - sometimes it could be days between sights.
 
My DST800 combined log/sounder is removable and only one hole in the hull. It also has several calibration points, and is much more accurate compared with the ST50 which it replaced.

Without the log you will not know your boat speed. With a log you will know your boat speed, and a much better idea as to what the tidal streams are doing (in conjunction with a GPS). Knowing hull speed is not just a matter of performance racing - it is useful for navigating particularly where there is a time restriction over the tide - either a gate, or perhaps a cross tide passage such as Poole to Cherbourg. It also helps to monitor longer term performances eg. due to fouling.

A GPS cannot replace a log and give the same information. In poor weather my GPS can give some very strange numbers for SOG, and when bouncing around is certainly not more accurate than a log. If the smoothing is increased then the GPS might not leap around quite so much, but the information lag increases.

For occasional use / small boat then perhaps a trailable log a solution?
 
But a log doesn't only show changes to sail trim - slight fluctuations in the windspeed and angle have a greater effect. If you were to spend more than the value of the boat on a suit of sailing instruments and racing computers, then instruments can be some help trimming.

Sonatas don't have limitless sail combinations to evaluate. Basically the full main, genoa and flying the spinnaker are always fastest. If you choose not to, then you have decided to be non competitive.
The only way to learn to sail a Sonata anyway near her handicap, is to sail in a OD fleet. Save your money and use it to get to the Medway for the Nationals at the end of August and get you butt kicked for a week. Nothing will do more for your boatspeed. Full stop. You might also enjoy it.
 
PCUK said:
Obviously no-one bothers with navigation anymore as you can't produce a tidal vector from SOG!
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Why is it obvious, when several people here have said they use a log? Tidal vectors are still taught and used by people for whom constructing them is important for their style of navigation.
 
MissFitz said:
I agree 100% if there's anything to look at - but in the race fleet here all I'm going to see is the fast-disappearing transoms of a clutch of J boats & Prima 38s. So I think a log would probably be useful for fine-tuning the sail settings etc.
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Yes, it can also be very useful when sailing short inshore laps of a club type race - you can build quite a store of knowledge about local tidal effects over time.

I agree with jac, if you don't discipline yourself to cosset the log by removing it after sailing, you tend to end up frustrated with it's performance.
 
Well I had a perfectly good log on my little boat but have removed it filling in the hole in the hull and the hole in the bulkhead. This because I can't bear having anything on the boat that does not work properly. The log was just too fiddly to remove and clean or remove and refit for sailing. I do live in an area of high fouling and warm water so my experience may not reflect your situation but I would always rely on GPS for speed (if I need speed). olewill
 
Ours works for about a week after launching at the beginning of the season, and then needs cleaning. I don't bother. I do understand why people find it useful, but having never had one that works reliably I don't miss it - I'm sometimes interested in how fast I'm travelling in the direction I want to go in, but I've never yet been that interested in how fast I'm going when I'm not going anywhere :). If money were no object I'd replace the paddle wheel log with an ultrasonic speed transducer.
 
Don't newer logs have flaps over the hole allowing them to be deployed and withdrawn with minimal water ingress? I've not seen them let alone tried them. Ours requires pluck and dexterity to deploy which is why it's rarely used. Shame as I find it adds a lot of pleasure to sail tuning.
 
Whatever happened to ultrasonic logs? They were going to take over the world, but it doesn't seem to have happened. Too expensive? Accuracy issues? Reliability issues? Fouling issues?
 
JumbleDuck said:
Whatever happened to ultrasonic logs? They were going to take over the world, but it doesn't seem to have happened. Too expensive? Accuracy issues? Reliability issues? Fouling issues?
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I've been wondering about a Pitot tube version. If I've got my calculations right then a 500mBar differential sensor would be good for speeds up to 19kn. If the sensor where connected with copper tubes then fouling aught not to be a problem. It would be possible to fit into the standard through hull. I haven't given any thought to sea-water compatibility, slamming, air under the hull or the effect of air pockets in the tubes. Maybe next winter if I run out of real work.

Of course a handy sailing physicist to help hone the method would be a bonus;)

John
 
JohnGC said:
I've been wondering about a Pitot tube version. If I've got my calculations right then a 500mBar differential sensor would be good for speeds up to 19kn. If the sensor where connected with copper tubes then fouling aught not to be a problem. It would be possible to fit into the standard through hull. I haven't given any thought to sea-water compatibility, slamming, air under the hull or the effect of air pockets in the tubes. Maybe next winter if I run out of real work.

Of course a handy sailing physicist to help hone the method would be a bonus;)
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Leeway could be an issue, as slip in aircraft is a pain for a standard pitot tube. A pot pitot is far less affected, though, and could be mounted on the leading edge of the keel. Could be a nightmare for fouling, though.
 
JumbleDuck said:
Leeway could be an issue, as slip in aircraft is a pain for a standard pitot tube. A pot pitot is far less affected, though, and could be mounted on the leading edge of the keel. Could be a nightmare for fouling, though.
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Am I right to think the pot pitot shields the apertures from flow in an unwanted direction? The description/image I found looks as though the pot opening faces forwards, pressure builds up inside and is applied/reflected to a rearward facing aperture inside the pot.
 
I seem to recall pitot style logs were tried in the 60's ?

I imagine they're even more susceptible to flotsam and wee beasties than paddlewheel jobs.

On another boat I had a Smiths paddlewheel log and it was never accurate ( I tried calibrating it over a measured mile a few times ) and it was always getting jammed by little residents.

I find the GPS plotter much better for daysailing, but like Jumbleduck back it up with a towed log when crossing the Channel or going west.

I had high hopes for ultrasonic logs too - rather than holes in the hull - but maybe they suffer from boundary layer flow, or simply getting antifouled over ?!

I always wonder why modern towed logs like a 21st Century Stowe aren't available.
 
Ruffles said:
Don't newer logs have flaps over the hole allowing them to be deployed and withdrawn with minimal water ingress? I've not seen them let alone tried them. Ours requires pluck and dexterity to deploy which is why it's rarely used. Shame as I find it adds a lot of pleasure to sail tuning.
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I have had logs with and without flaps. With a decent set-up and the transducer in a watertight box, cleaning a log should not be too much hassle. The paddle wheel on my old Navico log was always getting fouled with weed, and I became just as accustomed to clearing it. My current Raymarine one seldom pick up weed due to its different design, and I can often go months without giving it attention other than a little silicon grease smeared over it. The flap helps a lot.

If you enjoy sailing, a log can add much to the pleasure, and makes beating easier, as well as being useful when motoring to check on performance. If you just want to go from A-B, then a GPS will serve as well.
 
Thanks Raymarine flap type through hull reduces water ingress to less than a cupfull. It's possible to get away with a similar amount with a NASA type one as long as you're well organised and have the blanking cap to hand. I'm always a bit concerned about cross threading it.
johnalison said:
I have had logs with and without flaps. With a decent set-up and the transducer in a watertight box, cleaning a log should not be too much hassle. The paddle wheel on my old Navico log was always getting fouled with weed, and I became just as accustomed to clearing it. My current Raymarine one seldom pick up weed due to its different design, and I can often go months without giving it attention other than a little silicon grease smeared over it. The flap helps a lot.

If you enjoy sailing, a log can add much to the pleasure, and makes beating easier, as well as being useful when motoring to check on performance. If you just want to go from A-B, then a GPS will serve as well.
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