Getting some air

[Justwin]

Unless Porter boats are very light, it's not likely you'll want a 21" pitch on a 140hp engine on a 6.5mtr. 19ish max I would have thought.


True it very much depends on the weight factor and I suppose we have another 10 horse, but on our 6.5m Tornado (which actually measures 6.7) with a 150 Mariner Optimax, we are getting exactly 52mph @ 5200 RPM with a 21 Laser s/s prop, 2 up. The engine won't acutually rev anymore even if the prop wasn't in the water although the manufacturer claims 5250 - 5750. (Actually got 56.7mph on the gps last night although I think that was helped but the healthy tide in Strangford Lough - N.I.)

[Mark Halliday]

My co-owner claims 40kts, 2 up in a flat sea, with the current prop. The engine is limited at 5700rpm. I have not had a chance to try to beat this yet, however the ST40 said Max Speed = 38.1 last Saterday, 3 adults, 4 kids. With that lot on board I was watching the waves not the GPS for verification. I should imagine that it was a bit high.

[jwalker]

Originally Posted by Justwin

..but on our 6.5m Tornado (which actually measures 6.7) with a 150 Mariner Optimax, we are getting exactly 52mph @ 5200 RPM with a 21 Laser s/s prop, 2 up.

What gearbox ratio does your engine have? At 1.87 that's only about 6% slip. I'd check the speedo.

[Mark Halliday]

Originally Posted by jwalker

What gearbox ratio does your engine have? At 1.87 that's only about 6% slip. I'd check the speedo.

The book says 13:26!!!! which in my money is 1:2. (I presume it is 13 teeth to 26 teeth)

The speedo impeller is about 14" forward of the transom and suffers from the "squirt effect" when landing. Max speed is recorded as an instantaneous reading, and the current speed is averaged over 20 seconds. In truth I we did not do more than 32kts.
Oh yeah, and the fish we caught was at least thaaaaaaatttt big .

EDIT-
JW - I just noticed you were not talking to me. Sorry.
1 point. Are Statute miles the same as US miles? I presume Smart Gauges work in US measurements.

[Justwin]

It would be the rev counter I'd be more suspicious of - speed was ground speed off the GPS.

[Matt]

Including anything up to an extra 6 knots from a favourable tidal flow.