Underpropped and Tach Setting

[steam_mill]

Just got my brand new 17' Cutter on the weekend. It's got a '03 90 hp Classic Merc.<br /><br />I think the motor may be underpropped. At WOT, with a full load (full tank, 4 adults) I turn about 5600 RPM at about 45 MPH.<br /><br />Hole Shot is great and I'm on plane in under 3 seconds. Does it sound like I'm underpropped? I don't plan on travelling at 45 MPH very often anyway.<br /><br />Also, just to confirm, what is the pulse setting for the tach on this motor?<br /><br />Tx.<br /><br />Joe

 

[dilligafda]

Re: Underpropped and Tach Setting

WOT on this motor should be 5000-5500 RPM. The tach should be set on the 6P setting or for a 12 pole alternator. Are you under propped? If you donrun with a full load all the time, yes. I would increase the prop pitch by 1 inch to bring the RPM down to the upper part of the WOT range. <br /><br />Happy boating

 

[steam_mill]

Re: Underpropped and Tach Setting

Since the range for the motor is 5000 to 5500 rpm and I'm turning 5600 rpm, should I just leave it (great hole shot) or should I change prop and keep this one for skiing?<br /><br />Can I do any damage with 100 extra rpm?<br /><br />Joe

 

[dilligafda]

Re: Underpropped and Tach Setting

Check with your dealer, but I'm pretty sure that if there is a failure with the powerhead, they may have a hard time getting the repair covered under warranty. Overspeed damage can include reed chipping/breaking and undo stress on the bearings and other internal engine components. The choice is yours, but I would go 1 inch up on the prop pitch. This will lower the RPM by about 200 and get the engine into the proper RPM range with as little effect to the hole-shot as possible.<br /><br />Happy Boating!