Whats wrong GPS or physics?

[jeffstevens763@g]

My ribquest 5.85 90 Suzuki 4 stroke in Oban bay perfect conditions slack water 45 mph running a 14x19 Ali prop same speed 13.5 x 21 stainless steel 5800 rpm two up 50 Lt fuel usual kit GPS & speedo slight difference. For comparison

[Pikey Dave]

Originally Posted by jeffstevens763@g

My ribquest 5.85 90 Suzuki 4 stroke in Oban bay perfect conditions slack water 45 mph running a 14x19 Ali prop same speed 13.5 x 21 stainless steel 5800 rpm two up 50 Lt fuel usual kit GPS & speedo slight difference. For comparison

The trip computer on my Lowrance HDS 9 insists that my top speed is around 73kn [emoji849]

[simonl]

Originally Posted by Pikey Dave

The trip computer on my Lowrance HDS 9 insists that my top speed is around 73kn [emoji849]

On the motorway?

[jeffstevens763@g]

Originally Posted by Pikey Dave

The trip computer on my Lowrance HDS 9 insists that my top speed is around 73kn [emoji849]

With or without bag of sand in bow keeping her on the ogin

[Pikey Dave]

Originally Posted by simonl

On the motorway?

Nope! On a mooring[emoji15]

[rnwright1969]

Originally Posted by simonl

The maths looks fine. Given the updated info that both GPS units were providing the same reading, I share your confusion over the recorded speed!
Over what distance did you record this?

A certain way to prove things would be to time it over a known mile or so. My guess is prop pitch variation, with a caveat that it's just feels too damned fast for the rig you have!

The distance was circa 1800m, from just out from Puffin Dive Centre towards Seil, not the clearest when it comes to satellite coverage but not the most congested area re cliffs and stuff.

It is too fast, hence my separate thread and not on the 'how fast forum', I am trying to see what is wrong rather than justify what I reckon was an unrealistic speed, or maybe it's not?

[rnwright1969]

Originally Posted by jeffstevens763@g

My ribquest 5.85 90 Suzuki 4 stroke in Oban bay perfect conditions slack water 45 mph running a 14x19 Ali prop same speed 13.5 x 21 stainless steel 5800 rpm two up 50 Lt fuel usual kit GPS & speedo slight difference. For comparison

That kinda ties up with my thoughts, you're a bit bigger and heavier but perhaps the ribquest has better thru water characteristics than the avon at top whack, so I would have thought similar ballpark and not massively faster or slower.