Tach Is Down Have Questions On New Spare Prop Pitch

[thedukeryan]

I spun the hub on my stainless 3 blade 14x19 prop so while it is being repaired I am using a Aluminum 4 blade 14x21. The guy at the marina assured me that 4 blade 21 pitch aluminum will be comparable to my 14x19 3 blade steel. With that said my tach went out on me so I have no idea what my RPM's are at. I took it out yesterday and the boat ran great with the new prop. My only concern is that the different pitch, blades etc may cause a problem. Another thing I will note is that it seems like I am getting better performance out of the new 4 blade. Could be my imagination but it seems like I am getting higher cruising speeds and acceleration. Any info advice would be greatly appreciated.

 

[hwsiii]

Re: Tach Is Down Have Questions On New Spare Prop Pitch

The 4 blade 21" pitch might be comparable a little to your 3 blade 19" pitch depending on what SS prop you have. A 4 blade normally increases hole shot and acceleration all the way to WOT, it is also smoother because the 4th blade helps to reduce vibration, cruising speed increases because of the increase in blade surface area and less prop slip and many other good things. Theoretically you lost a lot of RPM because of the increase to a 21" pitch, but your SS probably had a theoretical 20" pitch and then you lost RPM to the 4th blade, my guess is you probably lost about 500 RPM. But you will only be running it a short time so you should be fine.



H

 

[thedukeryan]

Re: Tach Is Down Have Questions On New Spare Prop Pitch

Thanks for the post... I guess my new question is if I drop in RPM's but notice more speed, better acceleration and smoother ride wouldn't this be considered a good thing? My logic is that if the engine is running at a lower RPM but the boat is performing better I would be better off keeping this one full time and the three blade as a spare. I'm really enjoying the difference in the 4 blade but don't wanna leave it on if it is gonna damage something. Another question is am I gonna burn more gas with the 3 or 4 blade or is it gonna be comparable? Thanks for the help

 

[muchco]

Re: Tach Is Down Have Questions On New Spare Prop Pitch

You should really repair the tach issue as if you have an outboard which I am just assuming it's not a good thing to be lugging the motor. If you were indeed at max RPM with the 3 blade prop and you suspect that your dropped 500 rpm that would be bad. With out the tach you will never know, best get it working to be sure.

 

[hwsiii]

Re: Tach Is Down Have Questions On New Spare Prop Pitch

Once you get a working tach let me know what the RPM are and we will know how much it is lugging your engine. It is always best to be able to run your motor at the maximum recommended RPM and NOT the lowest RPM. Boat motors are running under much more strain than a car engine at all times. Think of it as a truck driving uphill all the time with no lower gears to take the strain off the engine. My opinion is if you had the correct 19" pitch on there you are lugging your engine at this time, but theoretically all you need to do is get a smaller pitch 4 blade prop and you will have even more hole shot and acceleration. We will find that out when you get your tach working and with the right 4 blade prop you will inrease your mileage and cruise as well.


H

 

[thedukeryan]

Re: Tach Is Down Have Questions On New Spare Prop Pitch

Will try to get a new tach this week and update. If the tach is good but the wiring is bad can someone tell me what the tach wires connect to? Im hoping the tach is bad and just needs replaced.

 

[hwsiii]

Re: Tach Is Down Have Questions On New Spare Prop Pitch

Ryan, try turning the switch on the back of the tach back and forth a few times, some of the time that will get it working again because the electrial contacts become corroded and usually it is a grey wire. But make sure you turn it back to where it was initially.


H