Motor or prop

[familyman]

Just wondering ,got the boat up to full throttle on sunday last at 4300rpm on tacho boat was doing 34 knots on gps.Rig details as follows.
4.6mSportsmancraft half cab
Merc inline 6 115hp
prop 13.25 x 17p
basic canopy with front section open
motor has permatrim foil
Hull is sound ,not chock full of water,no damage to hull bottom

Will have to check whether throttle is fully opening .... maybe a tune up is in order.
cheers jon

[Spaniard_King]

Jon

Top end speed is good

Top end rpm sucks if the tacho is righ and you keep running it above %50 throttle..theres gonna be a big "BANG" shortly

At WOT you need to have 5,500 rpm +

2 strokes don't like being heavily loaded

be careful

Garry

[familyman]

Thats what I have been thinking but I was wondering if the prop size sounds ok?
Cheers jon

[Spaniard_King]

Jon,

Prop size is dependant on rpm.

There certainly looks to be a problem 4.6m + 115 should equal a fast boat with a 17 it should get more rpm than that

Garry

[familyman]

merc inline 6 115hp running premix not autoblend
cheers jon

[Spaniard_King]

Just as an eg

I had a 4.6 m Seafarer with a 70 Evinrude it also had a 13 1/4 x 17 prop and it pulled 5,500 rpm no problem.. cant remember the actual speed but it was fast enough

Garry

[Spaniard_King]

Are you sure the Tacho is reading correctly

Is the Tacho set up for that engine.. there are calibration settings on the back of most tacho's

Garry

[familyman]

Good point,tacho was fitted by the dealer pre purchase so I assume he set it up,will check though.Certainly sounds like motor is going pretty hard at 4300.
cheers jon

[familyman]

Garry just looked at tacho,settings on rear indicate 6p,6c,4p,4c,3p,3c.At the moment it is set for 6p.What the 6p means I have no idea.It is a mercury tacho,also has a calibration screw but I would need to verify actual revs to be able to recalibrate it. [smiley=wut.gif]
cheers jon

[Spaniard_King]

Jon,

ring ya local Merc dealer and ask him what your engine settings are for the tacho

Garry

[Mantaray]

Garry just looked at tacho,settings on rear indicate 6p,6c,4p,4c,3p,3c.At the moment it is set for 6p.What the 6p means I have no idea.It is a mercury tacho,also has a calibration screw but I would need to verify actual revs to be able to recalibrate it. [smiley=wut.gif]
cheers jon

6p has nothing to do with the numbr of cyl but with the alternator poles/crank pulses. a 115 is probably 12 pole 6 pulse but can have a 6 or 4 tach setting?