View Full Version : How to determine RPM's w/out guages?
As many of you know I just purchased a new boat which I do not believe has any tach or speedo. How do I tell if the boat is running at a "good" RPM level without these guages?
Thanks,
NC
Dodge1
03-24-2003, 04:57 PM
I find it hard to believe that your new boat wouldn’t come with at least a tach but if that’s the case; I’d strongly suggest that you have the dealer add one, before you take delivery.
jim c
03-24-2003, 06:06 PM
I use a mechanical tach most of the time that sets on the crankshaft ans spins along with it . There are electronic ones used for model airplane motors that work well. Check a model airplane catalogue ,should be able to find them.
RANGER
03-24-2003, 06:56 PM
As far as I know there is no way to do that! I would make a STRONG suggestion to have one installed and get the info on your engine to know where your RPMs should be for the best results!
Dodge1,
I guess I don't know if it has a tach or not but I didn't see any on the boat or brochure. It is the 2003 1675 Lund Explorer Tiller. Anyone know if a tach is standard?
Thanks for the response.
NC
GR8WTHUNTER
03-24-2003, 10:43 PM
Sure there is. it is actually kinda easy. If the engine makes a lower pitched "whaaaaar" sound you are not pulling enough r's. When you get that sweet "whiiiing sound you are right on. When you get the "kabam/kachug" sound you went too many r's. Get a tach installed, not that expensive. Rich
just bought 1675 explorer ss thats with side console. it came with tach and full gages, i think it depends on what brand of motor you got but i am sure it will have a least a tach, if not make sure you get one installed
No way that I know of to tell actual RPM without having a tach, but you should be able to tell if your boat is running right at various RPM levels based on how it sounds. First and foremost, it should run smooth at all RPM/throttle levels. No bogs, misses, and no variance (drop off/surges) in RPM when the throttle is kept at the same position. It's not something that lends itself to be easily described. It's more of an experience thing. I've had a 60hp Evinrude, a couple 9.9hp Johnsons, and 90hp Johnson that didn't have tachs. But I could tell whether they were running properly just by the sound. I've owned numerous 2 stroke motocross bikes over the past 25 years. They don't come with a tach, but I can tell when to shift and how they are running based on what my ears are telling me. My point is, any motor, doesn't matter what it's in, you should be able to tell if it's running properly by how it sounds.
Dodge1
03-25-2003, 05:27 AM
Brad, NC’s question was “How do I tell if the boat is running at a "good" RPM level without these guages?” I don’t doubt that your ears are sufficiently attuned to ascertain if an engine is operating properly but I don’t think that you could describe to NC the difference in sound between 4500rpms and 5500rpms, on his new Mercury 60 EFI FourStroke.
Mercury’s recommends a "Max RPM (WOT): 5500-6000" for the 60 EFI FourStroke and the only way NC can ascertain if he’s running within those rpm ranges, is with a tach. Given those parameters, NC goal should be to prop his motor to run as close to 6000 rpms as possible because that will provide him with the best all around performance. Not meaning to beat a dead horse but ears most likely can tell you if a motors running properly but they can’t tell you that it’s running @ 5870 rpms.
There are several other very important reasons for NC to have a tach. The first is to help him properly break in his new motor. The second is to make sure that the prop that came with his new motor isn’t turning absurdly high rpms, don’t laugh at that one because it actually happened to me.
perchjerker
03-25-2003, 05:44 AM
Dont rely on your ear.
http://www.cabelas.com/cabelas/en/templates/product/standard-item.jhtml?id=0015240015383a&navAction=jump&navCount=0&indexId=&podId=0015240&catalogCode=ID&parentId=&parentType=&rid=&_DARGS=%2Fcabelas%2Fen%2Fcommon%2Fcatalog%2Fitem-link.jhtml.2_A&_DAV=%2Fcabelas%2Fen%2Fcontent%2FPod%2F01%2F52%2F4 0%2Fp015240ii01.jpg
Thanks for all of the input. I'm ordering the tach today if my boat does not have one on it already. I appreciate all of the help. I want this rig to run right from the get go.
NC
fshnwalli
03-25-2003, 07:45 AM
Nc
I had a merc years ago with out a tach and wanted to know the rpms went to a local snowmobile shop and they had what is called a tiny tach. you wrapped a wire around the spark plug wire if I remember right and it gave you a readout of rpms plus kept track of hours. Was real reasonable in cost.
Fshnwalli
Perchjerker,
Thanks for the link. I take it this is the tach you would order? If you think so, then I will do it. The dealer said a tach is a tach.
Thanks,
NC
MarkG
03-26-2003, 02:54 PM
You didnt say what motor you bought,but many brands come standard with a tach on their tiller motors that the dealer would install when he rigs the boat.Yamahas for sure. Why dont you call him and ask? If it is not included,just order the one that goes with it and have it installed. The answer to your question is you can't know your RPMs without a tach. On the other hand,a good dealer will know the most appropriate prop for the combination to get you pretty much where you should be,but there are variables that can at times effect it. Get the tach!
cheap tach
03-26-2003, 04:52 PM
Sure there is - while maxed out lower a 1 oz. jig beside the prop until it pickes it up then start your stop watch till 1 minute.kill engine and count the revs. as you slowly unwind. Ive done this many times effectivelly on my trolling motors usually when the wind is blowing me into the rocks.
MarkG
03-27-2003, 12:07 PM
HMMM..interesting idea,,BUT...Then You need to know your lower unit gear ratio so you can then do the calculation from prop RPMs to crankshaft RPMs.
perchjerker
03-27-2003, 12:19 PM
Actually, to be honest, I just saw it in the Cabelas catalog. I have no experience with it. The hour meter feature would be handy. Anytime I had to install a tach I used a Teleflex gauge.
Perchjerker,
Well it's too late:) I ordered it the other day. No biggy, I'm sure it will be just fine and like you said, the hour meter should be useful as well. I just figured it was roughly 1/2 the price of the other ones I saw and since it all seemed the same to me.....
Thanks again,
NC
perchjerker
03-27-2003, 01:06 PM
Im sure it will be fine. Do us a favor and let us know how you like it.
I was thinking about getting one for my kicker.
T-Mac
03-27-2003, 02:06 PM
That boat would not have a factory "pre-rig", thus, no tach from Lund. However, most dealers realize the need for a tach and figure this additional expense (parts AND labor)into the boat package when they quote a package price..on a 40hp and larger (they don't come with props starting at 40hp).
The price of package quoted, depends on what all was included in the price quoted. This is where the confusion arises.
(other examples...prop, spare tire, start battery, transom tie downs, spare tire bracket...etc.)
T-Mac,
Thanks for the info. Everything was listed in the contract. I noticed the tach wasn't and decided to ask the board. With their help (Perchjerker), I decided to order the one from Cabela's and have it installed.
I will certainly let everyone know how it works.
Thanks,
NC