Boat Speed Indication

[DaveS]

What do you guys use to show your boat speed ?

The NAVMAN 4380 that came with my boat is defunct, and I think that getting it repaired (in common with most micro electronic devices) is not going to be a cost effective option.

Neither do I think that something like the Navman, with it's multi functions, is really necessary for boating on the Broads.

Last Sunday when we were out with the boat, my son plugged in his 'Road Angel' unit (£40 on e-bay ), which normally lives in his 'kit car'. It showed the boat speed very nicely.

I have a redundant Tom Tom 300 (my current car has sat nav built in), so I suppose I could use that as a speed indicator.

So, what else is there that's good, effective, and doesn't cost 'silly money' ?

Dave

[goodall_m1]

Dave

As you need speed over the ground rather than speed through the water

then basically any cheap GPS (or SatNav) would probably do the job on the Broads.

Watch out though for the car ones that speak at you,

an entire day of hearing "Please rejoin the road as soon as possible" might drive you nuts!

Martin

[Antares_9]

There's more stuff than you can shake a stick at Dave but for your purposes the Tom Tom you already have will be as good as anything. I know it is a bone of contention but GPS or even DGPS SOG numbers are not really so accurate at broads speeds and conditions anyway.

[DaveS]

Yes, I suppose the very slow speeds allowed on the broads, do pose a bit of problem in terms of accuracy.

As Martin says, its speed over the ground that's required, as speed through water, when running with the tide/flow, is something different.

Therefore, I guess traditional boat speed measuring devices, could easily see you speeding , as interpreted by the BA rangers, if they measured your speed over a fixed distance, or with radar/laser based equipment.

I wonder how it would 'stand up' in court, if you had a device that accurately measured your speed through the water, but the tide/flow, effectively took your speed over the ground from say a statutory 5mph to 8mph. Would you be expected to accurately know the speed of the flow, at any given time

Dave

[Guest]

I use an indic8tor speed camera thing in the car it will display speed or direction which would be handy. It starts at 2 miles an hour and seams very acurate in the car it has hi vis display and dashboard mountable. It cost about £35 of ebay and is called Indic8tor if you want to search. Just spotted one on ebay £20 bargain.

Jonathan

yes it uses gps

[DaveS]

In summary then Rod, we are required by the statutory laws of the BA, to comply with the regulation speed limits imposed by them. No different to what we are required to do on the road. Fair enough.

However, on the road, we have the means to measure our speed, to a reasonable degree of accuracy, plus or minus any measurement uncertainty. Something that almost every measuring device has, and something that has to be stated on it's calibration certificate, if the device is to be used for a definitive measurement. For example 'speed guns', 'speed camera', breathalyser machines etc.

If the BA are using handheld 'speed guns', and the measurement taken with these devices is to be used in a court of law, the 'guns' will have to be calibrated to UKAS standards, at regular intervals, and have a calibration certificate that gives the 'measurement uncertainty' figures, across it operating range.

If they are measuring speed over a fixed distance versus time, then the timing device, would have to be treated in exactly the same way.

We as boat users on the Broads are required to comply with the statutory speed limits, relative to speed over the ground, but in essence we have no accurate means of measuring our speed. So, we are in fact in a 'catch 22' situation.

Yes, we should, and must watch our wash, if bankside damage is to be kept to a minimum. However, the offence going to court, would surely be one of speeding, and not amount of wash created. After all, how can you specify what, in terms of wash, constitutes an offence, if it can't be measured against a calibated measuring device.

Yes, we can all make a reasonable assessment of our boat speed, but can anyone honestly say that thay can tell the difference between 5mph and 6 mph?

So here we have 'the law', imposing speed limits, which they will punish poeple for exceeding, in the full knowledge that only they, and not the boat user, can measure with any degree of accuracy.

Don't get me wrong, I fully support the imposition of speed limits on the broads, and will always do my best to observe them. However, sometimes the law in this country is 'an ass.

Dave

[DaveS]

I decided not to try and have the NAVMAN 4380 repaired, as I don't think its a cost effective option on a 3 year old piece of micro electronics.

So, today I bought a NASA Clipper Duet, which gives both speed (through the water), and depth, on a 100mm x 100mm LCD display. Showing both parameters at the same time.

I bought the 'in hull' transducer mounting kit for the 'sounder' to avoid drilling holes in the hull.

However, I found that the 'paddle wheel' for the speed, is larger (fatter) than I expected (the unit my son had on his boat was very slimline). The NASA unit is designed to fit through the hull, requiring a 40mm dia hole .

Again, I'm not drilling a 40mm hole in the bottom of my boat . So, I have to devise some means (bracket ?) of mounting it on the transom. Fortunately, the boat has quite a deep engine 'well', with not too much freeboard to deal with.

The 'paddle wheel head, will of course be below the waterline, its just how to support it, without drilling screw holes in the transom, below the waterline.

On the outboard bracket perhaps ?

Dave

[Brian]

Don't get too hooked up on the speed issue as its really down to the amount of wash you create and the the amount of speed in the right place.

The BA crew do have many speed traps about on the rivers. Ive seen many entering Horning.

Its not about getting there as fast as possible.. its about getting there with seeing as much as possible. If you go too fast, you miss the great scenery and the great wildlife that the Norfolk broads has to offer.

You miss those secret mooring spots

THeres no rush to go anywhere on the Norfolk broads

[Antares_9]

Problem with mounting on the transom (units designed for the purpose apart) is that the disturbed water can easily give false readings. I would look to mount it on the stbd side about 1/3 between the keel and chine level with or very slightly below the hull. But you may well find that the top of the transducer is not designed fo being underwater as it is a through hull.

[Mowjo]

Brian could you please pass that on to the hire company's, turn around days on the Ant are like being on the M25 on a bad day, if they don't get you on the way back they get you on the way out which is worse. Because most are new to the boat they think it steers like car so the bum is swinging all over the place, they chuck them out around 2pm and they have to reach Coltishall in case the pub burns down,

Seriously though I agree with you about speed and wash, I use a handheld GPS for speed, but if conditions are right I do go a bit faster than is legal, but I always watch my wash more than my speed and any more than a ripple off the stern I slow down even if I'm under the limit,, now I have to learn it all agian on the new boat,,,

Frank,,

[Brian]

Brian could you please pass that on to the hire company's, turn around days on the Ant are like being on the M25 on a bad day, if they don't get you on the way back they get you on the way out which is worse. Because most are new to the boat they think it steers like car so the bum is swinging all over the place, they chuck them out around 2pm and they have to reach Coltishall in case the pub burns down,

Seriously though I agree with you about speed and wash, I use a handheld GPS for speed, but if conditions are right I do go a bit faster than is legal, but I always watch my wash more than my speed and any more than a ripple off the stern I slow down even if I'm under the limit,, now I have to learn it all agian on the new boat,,,

Frank,,

mmmm the Hire Craft.. now thats a different kettle of fish Quick lets Go !!! Coltishal by Noon !

[Mowjo]

Oh! and if AJB reads this I never speed, I was just making conversation

[DaveS]

But you may well find that the top of the transducer is not designed fo being underwater as it is a through hull.

I phoned NASA marine today, and asked that question. Apparently, the internal bits of the unit are resin 'potted', and so no problem with being under water.

Dave

[Antares_9]

I phoned NASA marine today, and asked that question. Apparently, the internal bits of the unit are resin 'potted', and so no problem with being under water.

Dave

That’s good then Dave, Nasa kit is surprisingly good especially considering the price and their guys are always ready to help. I recall a factory visit some time ago to write an article on them when they were still embryonic. I was impressed by their attention to detail and enthusiasm, I left with one of their early CRT fishfinder, an export model in a white case (getting back to the sun thing again) for evaluation, I used it with good results for a couple of years.

[Guest]

Sorry to disagree with what appears to be the consensus here, but my experience of simple GPS receivers for use as Boat Speedometers over the past few years is that they are the simplest, cheapest, and most accurate solution.

I've used paddlewheel sensors, both transom mounted on O/B boats, and hull mounted on I/B boats, (with the unfortunate but essential hole). I've found them usually tricky to calibrate (using timed runs at constant speed), inconsistent, and prone to clogging, especially the hull mounted ones, which then require the somewhat stressful technique of withdrawing into the hull, cleaning and reinsertion, without getting too wet from the column of water shooting up into the boat !

By comparison, cheap and cheerful GPS units require no fixed installation, and give a direct reading of the same speed measurement by which the BA enforce it, (speed over ground).

I'm also surprised to constantly see forum comments regarding the "inaccuracy" of GPS units at slow speeds. During their evolution, once they started tracking 12 satellites or more, and after Bill switched off "selective availability" in 2001, I've found them very accurate at all speeds, in the boat, car, cycling, and even walking, (and by that I mean after accurate timing tests over measured distances.)

How I wish I had never drilled that damned 2" hole in my cruiser !!

[jimbo]

Welcome to the forum Strowager

[goodall_m1]

Welcome aboard!

Personally I use my GPS as well, but a periodic "glitch" in the speed is always possible.

Take the "error" factor, say 5 metres (ok it may be less but there often is one), let the first error be to the stern, next fix it moves 10 metres ahead and "whey hey how did I go that fast" because you have moved an extra 10 metres in that instant.

I don't find it a problem when monitoring my speed as usually it is a monentary situation and the next fix brings it back within expected values. It does sometimes make my "max" SOG look a bit fantastic though...

Using GPS is the best that I can come up with for monitoring in an area where it is SOG (speed over Ground) and not STW (Speed through Water) that is the measure. Log impellers etc dont show whether you have a couple of knots of current under you...

But when it comes down to it the aim is to stay under the limit, or reduce speed to stop excessive wash, which ever is the lower.

With a STW measure the two tend to go together, start motoring into an adverse current and your wash is much the same for the same engine setting. But pushing against the tide you will find that your SOG drops (suprise!) and might be tempted to increase the revs, but then the wash goes up. Here it is the wash that dictates my maximum speed, even if it upsets someone who is trying to get to somewhere as fast as possible, and makes them overtake.

The opposite is the the one where I reckon I need the GPS, going down stream at normal revs I could easily find my SOG is too fast, even though my wash is reasonable and its time to throttle back and save some diesel!

(Otherwise it might be a case of watch out for that Heron with a radar gun in its beak!)

Martin