RPM question

TinBoats.net

Help Support TinBoats.net:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

PatinIdaho

Well-known member
Joined
Jul 9, 2014
Messages
71
Reaction score
0
Location
Sandpoint Id
Hi. Maybe someone here knows how to convert this cuz I don't!
Looking at a different boat but I do not trust the tach. Seemed to only be reading about 1/2 what it should but I dunno. So
17P prop, 1:6.1 gear ratio and GPS said 31mph at 2000rpm
That seam right?
 
What motor?

Pretty hard to get 30+ mph at 2000rpm. The tach will have setting on the back for alternator 'pulse'. Owners manual will tell you the setting for your engine. I have seen tachs go funny and read wrong even when set right. I don't believe any tach until I verify it against a test tach that is known good.
 
Yeah that tach is probably wrong. Never seen a boat on plane at 2000 RPM. 3000 is barely on plane for most. There are some exceptions but I think the tach is off; which is quite common. There is a pole setting on the back of the tach. Is it possible that the tach was adjusted for a certain motor when new, then re-powered later on with a different motor that requires a different pole setting?

2000 RPM at 31 mph, you would need somewhere in the neighborhood of a 29" pitch (going off of my memory which ain't great nowdays)....
 
Yeah I think its off also. It a 18f Volvo penta i/o Ranger tri hull. Seems to run and work great! I went a head and bought it for 1000 bucks.
Seems like a really good deal!
 

Latest posts

Top