Tach reading

B

BBogey

Petty Officer 2nd Class
Joined
Aug 4, 2001
Messages
140
Little by little I'm getting there? I posted a while back about my coming out of the hole (slow) you folks suggested over propping and to get a tach. After MUCH/MANY problems, (long story) I got my tach. My son and I took it down today and ran it. We ran it "light" compared to how much stuff we would normally have in it.<br /><br />The motor is a 2002 MERC 60HP EFI 4-stroke with a s/s 15" pitch prop. If I trimmed the motor to get MAXIMUM RPM's (which caused the porpise thing) the RPM's were between 5300 and 5400. When running WOT, but smooth across the water, my RPM's were somewhere around 5100. The way "I" read my manual, it appears max RPM at WOT is 5500-6000?<br /><br />Does a s/s 13" prop sound OK?<br /><br />THANKS VERY MUCH for all the help on this little problem I've had!
 
F

Fouled Plug

Ensign
Joined
Jun 29, 2001
Messages
935
Re: Tach reading

In theory, the 2" drop in pitch to a 13" prop will cause you to gain 400 RPM. That would put you in the range you need, but it's a mistake to "lighten" a boat to prop it. Run what you will normally carry as far as fuel/gear/people and prop it to match. If you get the boat in the 5500 RPM range with the 13" and a light load, when you fill it with gear you'll be lugging again. Just my 2 cents worth! :)
 
B

BBogey

Petty Officer 2nd Class
Joined
Aug 4, 2001
Messages
140
Re: Tach reading

I know this will sound stupid...but if I had my boat loaded heavier today, would the RPM's have been even lower??<br /><br />THANKS!
 
J

johnkc

Petty Officer 1st Class
Joined
Dec 12, 2001
Messages
388
Re: Tach reading

bbogey , yes the rpm's should be lower with the heavier load :cool:
 
S

SeaDawg

Chief Petty Officer
Joined
Dec 3, 2001
Messages
418
Re: Tach reading

BBogey, I can't remember if it was your post or not, but I had put a comment out here that I have my boat propped so that with the lightest NORMAL load, it would just hit max RPMs (6000 in your case), with smooth water, no porposing, etc. Everyone's lightest "normal" load is different, and in my case it is just me, my cooler, and my tacklebox (as I fish alone in my boat about 80% of the time). If I always took a fishing pardner, I would prop it based on him being in the boat with me. <br /><br />I would not want to have my son out by himself (very light load)where that he could run the boat at WOT and hold the motor in redline. A kid is a kid and they will do it.<br /><br />Also, you can cure the porposing with a Doel Fin or other aftermarket brand fin that attaches to the cavitation plate. I've ran them for several years, just for the reason you describe.<br /><br />Before I bought the 13 pitch prop, I would try the Doel Fin/Sting Ray, etc. setup, to see if your RPMs will be higher (since you can trim your boat higher). And (as these other guys suggested), load the boat with your lightest "normal" load.<br /><br />Just 2 more cents worth........
 
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