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Why Tachometer?
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| Northern Exposure |
Posted on 08/31/10 - 12:37 PM
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The 85 Montauk I recently aquired only had a tilt guage (which doesn't seem to work) and a Lowrance X65 with speed and temp sender (which also doesn't work).
I see a lot of discussion about tachometers. I know that on cars the tach helps to not overrev in various gears and damage the engine.
My question is this - on a standard outboard/prop setup, is it possible to over rev and do damage to the engine? Otherwise, what is the need for the tach?
I would like to add some guages to my boat and would consider a tach if I can find one that will work with the old 85 Johnson 90.
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| John Fyke |
Posted on 08/31/10 - 12:43 PM
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The tachometer is a viral key to the engine perpormance. It is the gauge above all gauges. You need and want to know that your engine is performing at factory specs. You can't do without one. The motor needs to be run at certain rpm's especially at wot. Don't blow your motor or decrease performance without one.
John Fyke
Re-Fit or Reef It
1979 15' Sport with Super Sport conversion and 70hp mercury. |
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| Joe Kriz |
Posted on 08/31/10 - 12:47 PM
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The most important gauge is a Tach.
This helps your motor to be within the manufacturers suggested operating range.
It also helps you select the correct prop which you can only do with a Tach.
So, here are my most important gauges.
1. Tach (must have)
2. Voltmeter (must have)
3. Trim & Tilt
4. Hour meter
I recently changed out my all my gauges to the OMC/BRP Tech Series.
http://www.whalercentral.com/images/a...nts_t1.jpg
I would not have installed the Speedometer but I already had a hole in my gauge panel for one.
You can also view the various style of OMC/BRP gauges here although some have been discontinued.
http://www.whalercentral.com/articles...icle_id=43
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| JohnnyCW |
Posted on 08/31/10 - 4:46 PM
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I think the tach can offer useful engine information and my preference is to have one for each engine. However I ran my Outrage just fine for nearly five years without one after the original tach stopped functioning. Since engine was already rigged properly, I eventually found I didn't really have a use for the tach other than wanting it there out of habit.
After having my new etec installed last summer, I've now got a tach again. Other than the first few outings with the new motor, I hardly ever glance at it now that I'm familiar with the engine and it's characteristics.
Edited by JohnnyCW on 08/31/10 - 4:48 PM |
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| CES |
Posted on 08/31/10 - 4:53 PM
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I'm not running a tach on my boat. In fact, I don't even have one installed on the boat.
Tachometers are great if you're trying to find the WOT RPM and for a prop however if you use your boat often and your ear is tuned to how your motor sounds at certain RPMs a tach becomes less necessary. If you don't use your boat enough to developed an"Ear" for your motor, then a tach becomes more important to you as you're basically boating by the numbers.
Edited by CES on 08/31/10 - 4:57 PM
Cliff
1966 13' Sport with a 1993 40hp Yamaha 2 Smoker |
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| Northern Exposure |
Posted on 08/31/10 - 5:50 PM
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Thanking everyone for the feedback.
The gist of my question kind of has a few threads. One - the rig is 25 years old and if nobody had destroyed the Johnson 90 by now without a tach why would I think it would be me to wreck it? The real question involves original equipment. I could see if you were experimenting with props, why a tach would be important to figure out rpms. As for a stock engine/prop however - wouldn't the manufacturer engineers design the prop/engine so that it would not exceed their own specs. - even at top end.
Sorry if I seem ignorant - just curious.
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| ianpatrick |
Posted on 08/31/10 - 6:04 PM
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I have a 150 sport with a tach but no other guages. I sometimes wonder how acurate the tach is anyhow as it sometimes reads 500 with the engine off and I have no idea how they're calibrated. I had a tilt/trim gauge on my old Logic 21' which was helpful but with my 150 sprt, I can feel where the trim should be better than a guage can tell me. Guess it's just easier wth smaller boats. As far as an hour gauge, I wish I had one, but, at the same time I probaly won't get rid of the motor til it's time for the graveyard anyhow. So maybe I don't need it after all!
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| ianpatrick |
Posted on 08/31/10 - 6:08 PM
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BTW, John and Joe, how do we know that our tachs are accurate? I imagine that they, like any piece of equipment can get knocked off kilter. I'm sure that a 500 rpm discrepancy could make for some serious problems. Any thoughts?
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| Joe Kriz |
Posted on 08/31/10 - 6:27 PM
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Northern Exposure wrote:
Thanking everyone for the feedback.
The gist of my question kind of has a few threads. One - the rig is 25 years old and if nobody had destroyed the Johnson 90 by now without a tach why would I think it would be me to wreck it? The real question involves original equipment. I could see if you were experimenting with props, why a tach would be important to figure out rpms. As for a stock engine/prop however - wouldn't the manufacturer engineers design the prop/engine so that it would not exceed their own specs. - even at top end.
Sorry if I seem ignorant - just curious.
You have no idea who setup this motor and prop... do you?
Is it setup correctly?
Who knows?
No, there are many posts about buying new motors setup with the wrong prop to begin with from the dealer.
And yes, you can blow up your motor by over revving .....
I certainly don't understand the big deal about people not wanting to have a tach.
Do they dislike tachs for some reason?
I would never be without one regardless of any other opinions.
People without a tach are only guessing at many things like Idle RPM's... Best Cruise RPM's.. WOT RPM's...
What RPM's does your motor idle at? Without a tach no one has any idea....
Good Luck with your decision.
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| joninnj |
Posted on 08/31/10 - 7:08 PM
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Another use for a tach is fine control of your speed. Today I took the late afternoon off to take my son and his freinds wake boarding.
I monitor the speed solely by the tach then compare to the speedo. Boat should run at about 22-23 MPH with a wake boarder. I know exact where it is using the tach. I have always done this even when I slalomed just a few years back. I would tell the driver what RPM I wanted, not MPH...:-)
Someone used the analogy of a car tach... Funny I never look at mine.
A Boat tach is a critical for set up and monitoring proper operation. Joe I totally agree, I would never be without one...
Edited by joninnj on 08/31/10 - 8:15 PM
Jon in NJ
Many other boats and outboards in my boating history
The Whaler is the one I like the best!!! |
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| JohnnyCW |
Posted on 08/31/10 - 9:41 PM
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Once a boat's engine is rigged properly and running an appropriate propeller, calling a tachometer critical is a stretch. I'd rather have one than be without but plenty of motorized vessels operate successfully and safely without a tachometer.
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| MW |
Posted on 09/01/10 - 3:24 AM
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I have limited real estate on my console, I put a "Volt" gauge in, it's the "ONLY" guage that I have. I agree with what "Cliff" said, "You develope an ear for your motor", and as "Ian" said you can "Feel" the sweet spot on the trim pick up speed when it's dialed in. Most Fish Finders now come with a digital volt meter built into them, so it's kind of a useless guage but, it still looks "COOL", and I do use it.
Matt |
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| PaulBW |
Posted on 09/01/10 - 7:08 PM
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As an auto technician I believe a tachometer is a necessary instrument. To some people 6000 rpms might sound fine until a rod sticks through the side of the block. By the way, when I bought my boat it had the same exact depth finder and didn't work. Turned out that the cable had corrosion on the terminals of the plug that plugs in the back. I cleaned it and it works great. Gives me charging voltage, speed, depth and water temperature all at the same time on a four way split screen. Get the tach working first though.
1966 custom 16ft with 1999 Yamaha 90HP |
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| John Fyke |
Posted on 09/01/10 - 7:18 PM
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There is no way of developing an ear to engine performance. Just like a computer on a car. You never know. It's a cheap way of knowing what your motor is doing and possibly a cheap way to repair in the future otherwise.
John Fyke
Re-Fit or Reef It
1979 15' Sport with Super Sport conversion and 70hp mercury. |
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| wldrns1 |
Posted on 09/06/10 - 6:42 AM
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A Tach is essential if you want a good understanding of what's going on. I'll explain:
My 2008 150 Sport came equipped with a 14" Vengeance SS prop. I was concerned to see, at full trim out WOT for top speed, the tach would be pegged over 6k rpms which is the maximum reading of the instrument. This was with just me in the boat.
First step was going for a ride with the local dealer and his equipment to verify accuracy. Yes, I paid for his time. We found I was about +50. Not a significant difference. I had never run my engine with the cover off but needed to for this test. At WOT full trim out, we could hear a clicking sound which the tech explained was the engine protection system rev limiter...not a favorable condition! With the cover on, the clicking cannot be heard. Why the boat came equipped this way is for some other discussion. Moving on to answer your question 'Why Tachometer?'
I ended up purchasing the Vengeance 15", which is an option on current production. WOT is now 5900 and I gained a few mph top speed in the process. With perfect conditions, I'll see just over 39mph.
The 'engine off' reading you see is just a characteristic of the tach itself. Mine's the same. The key on position should drop the needle to Zero prior to engine starting.
One benefit of the original 14 is I have better control of the hull's attitude in heavier chop. I can run with full trim in at a slower speed vs the 15. Effective trim with the 15 requires more speed which can get a little rough. Certainly a finer point but worth mentioning. I guess for best overall hull control, the 14 is the way to go...just stay off the throttle with the tach as your guide, keeping it under 6k. On glass or light chop days though, the 15 sure is fun.
Edited by wldrns1 on 09/06/10 - 7:00 AM |
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