Tach, volts and prop slip!

[munks]

Hi Folks. I have a couple of problems although playing on the lake today I wonder if there may be some relationship across them in part at least.
Starting at the top, I bought another boat, Fibreglass Buccaneer 560 with a 140hp Evinrude. Engine modle E140TLCUA.
Had it checked over, taken for a test spin at sea, went well. Had a service done to make sure there were no gremlins lurking about.
On way back from service went for short spin on lake seemed to go well although easy enough to break prop free on acceleration. Also noticed fluctuation on taco at times.
Back at lake a few days ago with original prop( S/S 13 x 19 but a bit rough on the edges). Had to be real careful with throttle to get out of the water or motor would break free and rev like mad 6-7000 rpm. Even once planing it would be easy to get it reving out and breaking away(Cavitating).
Thought it might have chewed the bushing out so I talked to a prop repair guy and he said it wouldn't get up on plane at all if the bushing had gone as the most load goes on it as it comes up. Got home swapped it off for a spare ali 13x19 that came with the boat which looks a bit better condition and grabbed the 13 3/8 x 17 off my old boat with it's 90hp erude.
Tried the ali 13x19 today and it was a little more effective than the S/S 13x19, tried the S/S 13 3/8 x 17 and it popped out of the water with a lot less tempering of the throttle than the others but is still prone to cavitation,
So I guess I need a bigger prop, I know fresh water is harder to get up planing on but I am not sure how far to step the prop up.
The next worry is the tach as I don't fully trust it, especially as the charging system doesn't seem to be working as the depth sounder came up with a low voltage warning so I checked the battery back at the ramp and it was only 12.47 volts motor off and didn't go up with the motor running. Also idle speed on the tach reads up around 1100 rpm but it doesn't sound like motor is idling that quick, how many pulses should tach be set for.( motor does sound like it is doing 6-7000 rpm when it breaks free but is a bit louder than the 90hp on the old boat) All 3 blade props)
Cheers Andrew

 

[5150abf]

Re: Tach, volts and prop slip!

Where is the cavitation plate in relation to the bottom of the boat, it is the plate just above the prop and it should be within an inch of the bottom of the hull, use anything straight along the bottom of the hull to check it.

also you said that the rpops were tore up a bit, anything rough on the ede will cause it to cavitate too, the rough part makes air bubbles so take a file and smooth out the edges.

Not sure on your engine which pole it should be set to.

I really think your problem is a set up thing and not a prop problem since it did the same thing with 3 different props.

You are starting your run with the tilt all the way down and working it up as you gain speed yes?

 

[Barnacle_Bill]

Re: Tach, volts and prop slip!

Test your rectifier/regulator for your charging/tach problem.

 

[F_R]

Re: Tach, volts and prop slip!

Do you have that motor jacked up on the transom? Lower it a bit till you arrive at a happy medium, top speed vs. agrivaton.

 

[munks]

Re: Tach, volts and prop slip!

Thanks I'll check that today, I know there is a small amount of space left for it to come down further. On my old boat there is a wedge packer in the mount to get the motor tucked under more for the Hole shot which may help at start but shouldn't change anything once on plane I would think.

 

[munks]

Re: Tach, volts and prop slip!

Just checked and plate is right level with bottom of hull. There is about 3/4 inch left to go down on the transom so should I drop it a little?

 

[F_R]

Re: Tach, volts and prop slip!

You can at least try it. You can always put it back up. Or, you can put up with the ventilation.

 

[munks]

Re: Tach, volts and prop slip!

Well I dropped the motor about half an inch, tested the reg/rect as per instructions in the forum and it came out faulty even though the diode test looked ok. No output on the red wire and by the time I had finished playing the tach had stopped to. Thats been replaced and had the boat out for a short spin on the lake today. Different beast! No prop slip unless over trimmed, tach is as stable as and I don't have to keep trimming the trottle. just set and forget even towing a biscuit around. Drops revs in tight turn but stays hooked up and recovers. I may still need a bigger prop at some stage as I can still wind the revs over 6000 but theres no break free. Also may put wedge block on transom to get better hole shot but will try a bit with a ski first as it gets on plane much better now.
Whats the trade off if the motor gets lowered too far?

 

[metriccrescentwrench]

Re: Tach, volts and prop slip!

Whats the trade off if the motor gets lowered too far?

Mostly the extra drag from more of the lower unit being in the water, resulting in a reduced top speed. On some boats it can contribute to handling problems and chinewalk, but that's mostly on higer performance boats when going in excess of 50 or 60 mph.