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Old 10 June 2016, 10:31   #11
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,614
Also bear in mind the diameter of the prop also affects the RPM......

FWIW, I'm 60Hp, 5m and the difference in literally a tap or two of the trim switch can make or loose 4 knots.

E.G on Monday I had it running at something like 4800 rpm, getting about 20 knts. I trimmed up a tiny amount, didn't move the throttle, and next thing I'm doing 5300rpm, 25 knots and throttled back a bit for a quieter / more economic run!

If you were going with the tide on Etive shouldn't you have been doing about 108 knots?

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Old 10 June 2016, 11:43   #12
Country: UK - Scotland
Town: denny
Boat name: breezy
Make: humber
Length: 5m +
Engine: mariner 115
MMSI: 235913962
Join Date: May 2016
Posts: 636
i remembered to check the prop when i was over at the boat doing some bits an bobs to it and the prop is 12.5 x 19 so the 32 knots i was getting out of it isn't that far off the mark to be honest i was quite happy with this as its fast enough

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Old 11 June 2016, 03:06   #13
Iankristy's Avatar
Country: UK - Scotland
Town: Scotland
Boat name: Skua
Make: Ribcraft
Length: 8m +
Engine: Suzuki df250 4stroke
Join Date: May 2015
Posts: 91
To check speed accurately you need to go in opposite directions and take the average 👍

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