Throttle Cable Adjustment

[sailorboy1]

My Yanmar is suppose to be able to do 3600 rpm according to the manual. But mine only does about 2800 rpm. Now I know the actural speed I would get out of the extra rpms would be minor, but should the throttle cable be adjusted to be able to do it? I mean if I got into a position where it's the engine or the boat, shouldn't it be save the boat not the engine?

[sigmasailor]

Lots of factors can cause your engine not reaching its rated rpm.
Some examples: underwater ship fouled, engine problems, prop problems and yes maybe the throttle cable not properly adjusted.

Can you give us some more info like do you get the rpm's in neutral or in gear, if in gear does the boat manage hull speed. Is the engine producing smoke?

[quartersplash]

It could be that the manufacturers specs are for that engine without the prop and with the pressure of the prop pushing the boat, the max RPMs could be less.

[sailorboy1]

I didn't really notice earlier in the year last year when it was clean. I did notice that the speed was less later as the bottom fouled. In the beginning of the year the boat could do 6.5 kniots at 2700-2800 rpm. whatn the max rpms were. never tried it in neutral as maybe it can do it.

[sigmasailor]

Hmmm, for a 39 ft (as in your profile) 6.5 knots seems a little slow. With a proper setup at full throttle and a clean boat you should expect 7.5-8 knots. That would be unpleasant; 6.5 knots is a better cruising speed at reduced throttle greatly reducing fuel consumption and noise.

Does your engine make smoke when you run it at full throttle? Most likely it can't reach its max. rpm because its fouled. Are you sure you have the correct prop pitch for your engine and boat?

[sailorboy1]

Engine runs great without any smoke etc. Has a MaxiProp that last owner installed.

[daddle]

Two things to check before any conclusion can be reached:

1. Calibrate the tach. Diesel tachs are notoriously inaccurate.

2. Check the RPM in neutral. It should go to the full spec.

[klem]

Originally Posted by daddle

Two things to check before any conclusion can be reached:

1. Calibrate the tach. Diesel tachs are notoriously inaccurate.

2. Check the RPM in neutral. It should go to the full spec.

That is a very good place to start. Once you have done that, you can try seeing whether the throttle lever on the engine will go further than the cable will pull it. That will tell you whether it is a cable issue or something else.

The most likely other problems are an issue with fuel delivery to the engine or a fouled bottom/prop.

[shakey doug]

Hi Don,

We really need to know model of engine also as mentioned wot unloaded rpm ie; high idle.

Cheers Shakey.

[Jim Cate]

Don,
One other factor: the Max Prop, while not a variable pitch prop in the normal sense CAN have its pitch adjusted. Some models require disassembly, others can be done in the water. Point is, you or a previous owner may well have put too much pitch in the prop, and the engine is thus overloaded and unable to reach full RPM.

Cheers,

Jim and Ann s/v Insatiable II lying Broken Bay, NSW, Oz

[S/V Antares]

You should reach at or near max rated rpm in gear regardless of Boat speed. lf not, you are over pitched on the prop, foul bottom etc, Check the throttle cable by putting the lever full throttle ( Engine off) and look at the engine end to be sure the throttle lever on the injecton pump is getting full travel.

[sailorboy1]

Found the setting/adjustment procedure in my Yanmar manual. So in a few months I will give it a try. Of course my tach stopped working end of the last year so I will have to fix that first.

[Chief Engineer]

In a few months????

First disconnect your throttle cable.

This will need two people.

Have a person put the boat in gear while you advance the throttle at the engine.

If you don't have a "catch" or hesitation...the problem is most likely in the cable assembly

[sailorboy1]

Well in the end I think it was nothing wrong with the prop, cable, or hull. I think it was a dirty fuel filter. I did run the tank competely empty last year. With new one (and of course a freshly cleaned hull and prop) the boat did 7.4 knot at 3000 rpm (I fixed the tach) and still had a lot more of throtte cable left.