Propellers and Tachometers

wynkoop

Member III
Silver Maiden made her first run on the new Yanmar 1GM10 today. Her trip from the old marina to the the yard where I did the stuffing box was mostly by sail with a trolling motor to get out of the marina. I did not want to SPRAY salt water all over the engine. That is how bad the stuffing box leaked.

On a 10 minute run from the travel lift to the new marina in calm conditions I was only able to make 3 knots through the water at full throttle. I suspect the 1GM10 does not like the prop that was in use with the Palmer P60.

My understanding on trying to figure out a new prop is that I should make some runs noting speed vs rpm and supply the prop shop with that info and specs on the boat. Easy enough to do, but I have no tach. I also know nothing of how to do a tach on a diesel. I have read about optical tachs. I suspect that is what I have to do, but when I search the interwebs for optical tachs I am finding handheld units. Not very useful when I want to run up and down the bay with the boat.

Can anyone suggest something? I want to in the next few days, while the bottom is CLEAN to run my tests.
 

Keith Parcells

Sustaining Member
Brett,
On a gasoline powered engine, the signal from the spark plug is the source of the tachometer signals and that is converted by the tach into engine rpm. Since there is no spark plug on a diesel, an alternate (no pun intended) signal is from the alternator. That signal can be translated by the tach to rpms. I am not sure which wire terminal from the alternator should be connected to the tach, but once that is done the tach would need to be calibrated using one of the optical techs as a reference. Maybe someone else can weigh in on the proper connection from the alternator to the tach.
 

wynkoop

Member III
Thanks Keith. I will try to look at the alternator next time I am on the boat to see if I can find a legend on the alternator. It is of course damn hard to see the terminal side of the alternator without hanging upside down from the boom with my head lowered into the engine compartment......UGH should have figured this out before I stuck the engine in!
 

markvone

Sustaining Member
Brett,

My alternator (100a Cruising Equipment w/external voltage regulator) has two small wire connections. One is the field connection and the other is the tachometer output. The field is often marked with an 'F' or 'FR' (my 'FR' is so small it looks like a greek letter!). This wire is how an external voltage regulator controls the alternator output vs rpm. I've switched my wires with no damage, except no tach and no alternator output. So look for a small wire (+/- 16 g) terminal on the alternator not marked F or 'FR'. That should be the tach output.

Mark
 

wynkoop

Member III
Hmmmm diving further into the 1GM10 SERVICE manual indicates there should be a Tach Sender someplace on the front of the engine near the flywheel. It looks like I may have an easier time than I thought.....if the sender is fitted.
 

wynkoop

Member III
Well digging into things deeper I find that I do indeed have an electronic tach sender on my 1GM. What I have not discovered yet is how many pulses it makes per revolution. I have found a tach that can be calibrated to your engine, but that requires some info I have not yet sorted.
 

wynkoop

Member III
Further digging through the 1gm10 manual and amazon yields this solution:


I can crank in the number of pulses, which according to the 1gm10 manual will be 97 per revolution and then have a working tach!

I hope this information helps other 1gm10 owners.
 
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