Reply
 
Thread Tools Search this Thread
 
Old 31 July 2013, 21:50   #1
Member
 
lukewhiting's Avatar
 
Country: UK - England
Town: swanage
Make: Thundercat
Length: 4m +
Engine: Tohatsu 50
Join Date: Apr 2012
Posts: 968
Best way to measure speed?

On my thundercat I don't have any way to measure the speed apart from the GPS on my phone. However the highest I have ever got it is 36mph?! & when your over taking taking boats with 135hp+ on the back that are clearly trying to keep up, you know your doing a lot more than 36mph more like 50+

Are handheld GPS better than speedo apps on phones? Or what other ways could I find out the speed?
__________________
lukewhiting is offline   Reply With Quote
Old 31 July 2013, 22:00   #2
Member
 
Country: UK - Channel Islands
Town: Jersey
Boat name: Archangel
Make: Ribcraft
Length: 6m +
Engine: ETec 225
MMSI: 235063789
Join Date: Sep 2008
Posts: 1,005
Ask one of your mates to sail alongside you at the same speed. Then compare GPS readouts. If they're the same then I'd say your original GPS reading was accurate.
__________________
www.flickr.com/photos/gj0kyz
GJ0KYZ is offline   Reply With Quote
Old 31 July 2013, 22:02   #3
Member
 
lukewhiting's Avatar
 
Country: UK - England
Town: swanage
Make: Thundercat
Length: 4m +
Engine: Tohatsu 50
Join Date: Apr 2012
Posts: 968
Quote:
Originally Posted by GJ0KYZ View Post
Ask one of your mates to sail alongside you at the same speed. Then compare GPS readouts. If they're the same then I'd say your original GPS reading is accurate and that you would have to ditch your current outboard and buy an Etec to improve your performance.
Etec on a thundercat?! They wouldn't last a minute haha
__________________
lukewhiting is offline   Reply With Quote
Old 31 July 2013, 22:10   #4
Member
 
Country: USA
Town: Seattle
Boat name: Water Dog
Make: Polaris
Length: 4m +
Engine: Yamaha 60hp
Join Date: Apr 2007
Posts: 1,152
At least around here, many charts have measured miles marked on them. E.g. between 2 landmarks. This is all pre-GPS stuff, so you could determine your speed over ground at a given RPM with a stop watch. A reference you'd write down and use for dead reckoning purposes. Currents would need to be accounted for obviously.
__________________
captnjack is offline   Reply With Quote
Old 31 July 2013, 22:37   #5
RIBnet supporter
 
Country: UK - England
Town: Cambridge
Make: Yamaha 380s
Length: 3m +
Engine: 15hp Tohatsu o/b
Join Date: Jul 2013
Posts: 22
I'm new to both RibNet and boating, but I do work in the electronics industry with interests in physics.

GPS devices all work from the same basic principle, though readings could vary - based on the way they attempt to integrate correlated satellite readings in software to a meaningful display (e.g. mean-average, median, peak-hold, etc). Only if the speed were sufficiently constant should all methods read the same, though I'd guess bouncing around on water could have significant impact in the result.

If it were me I would simply borrow a few devices (phones/software or other) and carry them on the boat, comparing readings at given speeds.

As for absolute speed, the relationship between power and speed isn't linear of-course, and there's power-to-weight to consider. Sounds like you're really motoring though, whatever the actual pace


All the best,

Brendan
__________________
Brendan Townsend is offline   Reply With Quote
Old 01 August 2013, 02:42   #6
RIBnet admin team
 
Nos4r2's Avatar
 
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,053
RIBase
Garmin Foretrex of some description. Waterproof, wristwatch type GPS.
__________________
Need spares,consoles,consumables,hire,training or even a new boat?

Please click HERE and HERE and support our Trade Members.

Join up as a Trade member or Supporter HERE
Nos4r2 is offline   Reply With Quote
Old 01 August 2013, 07:11   #7
Member
 
Cookee's Avatar
 
Country: UK - England
Town: Salcombe, Devon, UK
Boat name: BananaShark
Make: BananaShark
Length: 10m +
Engine: 2xYanmar 260 diesels
Join Date: Mar 2003
Posts: 4,225
Try your phone GPS in your car and you'll find it's probably reading ok (the car will read a bit higher - they all do) - It's a disappointment but real speeds are pretty much always slower than you think they are!
__________________
Cookee
Originally Posted by Zippy
When a boat looks that good who needs tubes!!!
Cookee is offline   Reply With Quote
Old 01 August 2013, 08:16   #8
Member
 
lightning's Avatar
 
Country: UK - England
Town: Marple
Make: Zodiac
Length: under 3m
Engine: Tohatsu 9.8
Join Date: Jun 2009
Posts: 648
I have a phone app for speed (speedview pro) and it does work but keeps freezing so I gave up with it.
I bought a cheap GPS device designed for hikers from ebay second hand for £40 (Garmin Gecko I think it is called) which has a speed readout and this works fine.

It doesn't do knots of course, but MPH is OK for me.

An added advantage is that it plots your route. Useful the other week on Loch Sween where we went the wrong way coming back from Tayvallich to Achnamara and got lost....
__________________
lightning is offline   Reply With Quote
Old 01 August 2013, 08:23   #9
Member
 
lukewhiting's Avatar
 
Country: UK - England
Town: swanage
Make: Thundercat
Length: 4m +
Engine: Tohatsu 50
Join Date: Apr 2012
Posts: 968
Ill try borrow a GPS from a mate. I've gone up against zapcats before & have never been beaten by one in top speed so unless they all went 30mph then it's the app that's rubbish
__________________
lukewhiting is offline   Reply With Quote
Old 01 August 2013, 08:30   #10
Member
 
Lee argyle's Avatar
 
Country: UK - England
Town: Porchfield
Boat name: Katie
Make: Stingher
Length: 10m +
Engine: Verado 350 x 2
Join Date: Jan 2011
Posts: 695
My brother-in-law runs a zap cat / 50 tohatsu, running alongside and using my GPS he tops out early 40's - normally I then open my craft up and leave him for dead...........70+
__________________
Lee argyle is offline   Reply With Quote
Old 01 August 2013, 08:40   #11
Member
 
Country: UK - England
Town: Mighty Penryn
Boat name: Little Joe.
Make: Avon Searider
Length: 4m +
Engine: Honda BF50
Join Date: Aug 2005
Posts: 8,872
Little boats always feel fast until a big one goes sailing past. ;-)
__________________
Mollers is offline   Reply With Quote
Old 01 August 2013, 09:33   #12
Member
 
lukewhiting's Avatar
 
Country: UK - England
Town: swanage
Make: Thundercat
Length: 4m +
Engine: Tohatsu 50
Join Date: Apr 2012
Posts: 968
Still think 36mph is reasonable? The second video is the race class that mine is tuned. You can tell its a lot faster than 36mph and more like the one in the video



__________________
lukewhiting is offline   Reply With Quote
Old 01 August 2013, 09:41   #13
Member
 
Country: UK - England
Town: Mighty Penryn
Boat name: Little Joe.
Make: Avon Searider
Length: 4m +
Engine: Honda BF50
Join Date: Aug 2005
Posts: 8,872
Quote:
Originally Posted by lukewhiting View Post
Still think 36mph is reasonable? The second video is the race class that mine is tuned. You can tell its a lot faster than 36mph and more like the one in the video

]
. I'll race ya. :-D Had 47.2knts and climbing with three big blokes and a heap of camping gear coming back from the Scillies at the weekend.
__________________
Mollers is offline   Reply With Quote
Old 01 August 2013, 12:28   #14
Member
 
Cookee's Avatar
 
Country: UK - England
Town: Salcombe, Devon, UK
Boat name: BananaShark
Make: BananaShark
Length: 10m +
Engine: 2xYanmar 260 diesels
Join Date: Mar 2003
Posts: 4,225
Try speedbox, max speed, speedometer or GPS speed amd let them get going for a while, check them against another GPS or a car and you'll be certain that he phone is accurate.

It might have a surf prop on which will focus on acceleration and not top speed - is it running out of revs? You can get something called tiny tach (Tinytach website) or something similar which is useful for setting one of those things up.
__________________
Cookee
Originally Posted by Zippy
When a boat looks that good who needs tubes!!!
Cookee is offline   Reply With Quote
Old 01 August 2013, 13:11   #15
Member
 
lukewhiting's Avatar
 
Country: UK - England
Town: swanage
Make: Thundercat
Length: 4m +
Engine: Tohatsu 50
Join Date: Apr 2012
Posts: 968
Quote:
Originally Posted by Cookee View Post
Try speedbox, max speed, speedometer or GPS speed amd let them get going for a while, check them against another GPS or a car and you'll be certain that he phone is accurate.

It might have a surf prop on which will focus on acceleration and not top speed - is it running out of revs? You can get something called tiny tach (Tinytach website) or something similar which is useful for setting one of those things up.
Just tested it against the car and the phone was 16mph under when I drove at 30mph!! It's not a surf prop but I'm not sure what pitch it is because it came with the boat & all the serial numbers have worn down.

I used to have one of then but I managed to get water in it.

Ill just borrow a GPS & see what happens but either way I'm not too fussed just interested
__________________
lukewhiting is offline   Reply With Quote
Old 01 August 2013, 20:24   #16
Member
 
Country: UK - England
Town: N. Devon
Boat name: (Not Another) Nutkin
Make: Highfield
Length: 6m +
Engine: Outboard, Honda 135
MMSI: 232036183
Join Date: Dec 2008
Posts: 2,015
RIBase
Quote:
Originally Posted by lightning View Post
It doesn't do knots of course, but MPH is OK for me.
...
Have you checked the settings? I use a Venturer and it has a marine setting, lat and long rather than grid and knots
__________________
Andy

Bude Dive Club - www.budediveclub.co.uk
GAFIRS - www.gafirs.org.uk
treerat is offline   Reply With Quote
Old 01 August 2013, 21:09   #17
Member
 
lakelandterrier's Avatar
 
Country: UK - England
Town: Gloucester
Boat name: Lunasea
Make: Ribcraft
Length: 5m +
Engine: Suzi 140
MMSI: 232005050
Join Date: Sep 2007
Posts: 1,978
True speed....borrow a proper old fashioned trailing Walker log & measure v. accurate time over set distance. Might be a bit tricky on a Zapcat, but I'd rate proven low tech over electronic gizmos. And if you can calculate the impact of the drag of the towed log even better.

Not a serious suggestion, but might be an interesting experiment.
__________________
Member of the Macmillan Round the Isle of Wight Club
lakelandterrier is offline   Reply With Quote
Reply

« Sea nav | Top | Wiring »
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




All times are GMT. The time now is 08:04.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.