Tach problem?

[Skywalker]

As you might remember, I put an Indigo prop on the boat this season, trying to get my RPMs up. The prop appears to be working well - quiet, smooth, pushing me along nicely. My tach reads around 1400-1500 RPMs at a cruising speed of 5.3-5.5 kts.

My direct drive A 4 matched with this prop should not do this. Tom, at Indigo, sent me an email after he read my post here suggesting that either he was way off with the pitch or my tach is way off. But a T27 with his prop should not go 5 and change knots at 1500 RPMs. Perhaps the gauge is not set for 4 cylinders.

Its an ISSPRO I bought from MMI. The instructions that came with it note an access port where pins can be adjusted for 4 6 or 8 cylinders. My tach, however, does not have this. There is a small port which appears to give access to an adjustment for the needle, to zero her out. There is nothing else.The large hole is for the light. I attached a couple of pics. Maybe one of you has some experience with this. I'm be off to Harbor Freight tomorrow to pick up a diagnostic tach.





By the way, the gauge is two years old and has rusted on the trim like crazy. Disappointing for a marine gauge.

Any thoughts on what I have, what I should do?

Thanks

Chris

[Al Schober]

I bought a laser tach this winter to set the running speed on my snow blower. Very pleased with it. I think I bought it on eBay rather than Harbor Freight. If HF, it would be Centech but my unit has nothing.

[toddster]

Dunno... sounds about right to me.
Looks the same as my tach - I seem to recall something about a jumper to set, but the default position was 4 cyl. ? Dunno, I'd have to check the instruction sheet for sure, which is in a big binder in the nav table, I think, and not at hand at the moment.

Mine has not rusted, but it's a freshwater environment. I have had bad luck with Isspro digital hour meters though. They don't seem to survive the winter in the cockpit. (Don kindly replaced the first one, but the second one failed the next winter.) I really want to like them, since they're a local company, but they gotta work! I would like to eventually get a full set of matching gauges.

As if...

FWIW, here's what I got, with a fresh bottom:

[toddster]

Oh, how were you measuring speed? Could currents be a factor?

[Skywalker]

I was using my gps to measure speed, went in all different directions, in and out of harbor, with current, against current...I am confident that 1500 RPMs is generating in the low 5s in speed.

My instruction sheet that came with the tach describes an access port with pins for 4 6 or 8 cylinders. Obviously, my tach does not have that.

I'll keep playing around.

Chris

[Dave Neptune]

Chris, what RPM"s do you get at WOT? The graph toddster posted follows what I get out of my 35'er very closely. I have often "slow cruised" at around 1500in calm flat seas at about the same speeds of 4.5~5kts. Do you use a vacuum gage?

Just cruised back and forth to Catalina last weekend with the A-4 jib at 2100 (7" of vac) for just over 11 hours. Seas were choppy on the way over at 5.2~5.7 into the waves and very light air and back at 5.5~6.2 with the seas and no wind. Did not use the main to steady the ride "back" and did on the way over.

Dave Neptune

[Skywalker]

WOT is only 1600-1700. I'm pushing her basically as fast as she can go for my 27.

I do not have a vacuum gauge.

That's a long time under power. Obviously a well loved A4! I can't imagine seeing my tach read 2100.

I sent an email to MMI last night, just fishing for info. I called Ken this AM and apparently Don is on the case.

I am wondering if my tach is the correct one. Since I can't set the cylinder, it has me thinking that maybe ISSPRO sent the wrong one to MMI, which I then purchased. It would help explain why my RPMs did not significantly increase last season when I re pitched my old two blade prop.

The good news is the boat is performing well, both under power and sail!

Chris

[Skywalker]

As always, MMI comes through.

Somehow, the wrong tach got on the stock shelves at MMI and I got it! Don contacted ISSPRO this morning, trying to figure out what happened.

I got an email from Stephen in the early afternoon apologizing for the mix up. I new tach will be in the mail tomorrow.

So it appears that my two year effort to chase some RPMs might have been a phantom menace!

And here is more proof that the support from this company and this forum are without equal.

Thanks

Chris

[Skywalker]

I received my new tach from MMI and installed it today. Not a great day to motor around - 20-25 kt winds. Great for sailing, though.

Sitting on the mooring, I briefly revved, out of gear, and the engine quickly shot up to 3000 RPMs without difficulty.

I cruised into a 20+ kt wind at 4.2-4.5 kts at around 1600 RPM. It was mid tide, and running hard on the moon. I pushed the throttle and got up to 1700-1800 RPMs while doing 5.5 kts or so. She seemed to be lugging a bit. Again, it was a hard day to tell.

I still can't imagine getting over 2000 RPMs. I will play with the timing.

From a performance standpoint, motoring into the teeth of the wind with a contrary tide at 4.5 and 1600 seems pretty awesome to me.

I'm trying to figure out the math here. Given my hull speed, displacement, maybe high teens is ok with the Indigo.

What do you think?

Chris