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Author Topic:   Speedometer Installation
gnrgunner posted 07-17-2001 12:23 PM ET (US)   Profile for gnrgunner   Send Email to gnrgunner  
I have a 1981 Boston Whaler 13' Sport that I plan on buying and installing a Teleflex 5-35 mph speedometer on. I read in the west marine catalogue that it requires a hole that is 3 3/8" in diameter. What should I use to cut the hole in my dash? (I think I will have just have enough room after the light switch, ignition, and killswitch) Besides cutting the hole, what installation is required, or what does the wire hook up to in order to tell me the speed? Thanks.
hauptjm posted 07-17-2001 12:28 PM ET (US)     Profile for hauptjm    
Holesaw. Fits into your drill.
alan posted 07-17-2001 03:50 PM ET (US)     Profile for alan  Send Email to alan     
IMHO - Speedometers on boats are not that accurate due to wind and water resistance. You might try mounting an inexpensive hand-held GPS. A lot less cutting with a lot more functionality.
Bigshot posted 07-17-2001 03:56 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
You have the room on the lower board next to the switch. You need to hook up a vacuum tube that runs to a pitot tube screwed into the transom. In my opinion it is a waste of $$. They are not very accurate and you are better off with a tach and a hand held GPS. Got a Magellan from Heartland America for $79. Those speedos also will not work with 1 strand of seaweed on it and 13's love to pick up grass.
alan posted 07-17-2001 04:01 PM ET (US)     Profile for alan  Send Email to alan     
IMHO - Speedometers on boats are not that accurate due to wind and water resistance. You might try mounting an inexpensive hand-held GPS. A lot less cutting with a lot more functionality.
glynnw posted 07-17-2001 06:08 PM ET (US)     Profile for glynnw  Send Email to glynnw     
I just installed a teleflex 5-35 speedo on my '70 13, but I suspended the speedo, not cutting a hole until I know it all works. Initial comparison with GPS showed Teleflex reading of 32 mph compared to 30 for the GPS unit.
gnrgunner posted 07-17-2001 06:39 PM ET (US)     Profile for gnrgunner  Send Email to gnrgunner     
Glynw, how much hp do you have on your 13, and how much weight were you carrying when you got the reading of 32 on the Teleflex. I weigh about 170 and using someone else's handheld GPS, i got up to about 34-35 on my 1981 Evinrude 35.
lhg posted 07-17-2001 10:04 PM ET (US)     Profile for lhg    
I have got to say that, with a 13-17 mahogany based Sport model, I would not bother with a conventional Speedo. Instead, I would buy one of the new compact sonar units, like a Lowrance/Eagle X-65, etc, and install the temp sensor and paddle wheel speed option instead, and have it all on one display. These can be more accurate, especially at low speeds, and can be calibrated as necessary by DGPS.

I have the analog speedos on my boats, but since the advent of the sonar speed displays, hardly use the conventional speedo.

Dick posted 07-17-2001 10:19 PM ET (US)     Profile for Dick  Send Email to Dick     
I am running a Raytheon fishfinder with speed and temp. At low speed it is close to my GPS at high speed it is not even close. A standard speedo will be even worse. A GPS, even an inexpensive unit, will give you the most accurate reading.
lhg posted 07-17-2001 10:37 PM ET (US)     Profile for lhg    
Dick -With my Lowrance units, I have found their paddle wheel sensor to be quite accurate at all speeds, once calibrated. They tend to read fast with no offset calibration.

In both instances, I had to put in about 5-10% negative correction. The units allow you to do this in the on-screen software. Part of it depends on what you want to know. I set my displays to show DGPS S.O.G., right next to the paddle wheel water speed. Wind and current can make a considerable difference in SOG, but the water speed will always be accurate. I like to compare both at a given time. Seeing the differences between the two readouts gives the most accurate indication of your boating conditions.

Tom W Clark posted 07-18-2001 03:22 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

I'll be the contrary one here and encourage you to install the speedometer. I like them because they are simple, reliable, inexpensive and can be accurate. Even if they are not accurate, they are precise. I mean that literally; they give the same readings over and over, so while they cannot easily be calibrated, you can learn what the real speed is by comparing the readings to a more reliable source like a GPS and remembering that it, for example, over registers by 2 mph @ cruise speed.

To install, use a hole saw to cut the hole. If you use a drill motor it had best be a 1/2" motor and preferably an angle drill like a Milwaukee "Hole Hawg". A 3 3/8" hole saw requires a lot of torque and a little 3/8" home owners drill won't cut it, so to speak. Better yet, remove the piece to be drilled and use a drill press. Much safer for you and the wood. A hand held drill motor and hole saw can twist your wrist good and "walk" out of the pilot hole and just chew the hell out of you freshly varnished mahogany. I don't mean to scare you, just be careful.

Once the gauge is mounted in the console you simply plug the speedometer hose (pressure, not vacuum from the pitot tube activates the gauge) into the back of the gauge. There is no wiring unless you want to install an instrument light which comes on with the nav lights so you can read it at night.

Mount the pitot tube on the transom and run the hose up and over the transom to the speedometer itself. Very simple.

I've always hated paddle wheel speedometers because they are notoriously inaccurate. They always seem to over register quite a bit (like 15-20%). The ones I've owned did not have any calibration feature. That sounds like the solution to that problem right there.

The other down sides to a paddle wheel speedometer are that they require electrical wiring, cost more money, and if you hit some debris and the paddle wheel itself is damaged it will cost a lot more than replacing a pitot which costs less than $10 and which for the most part won't need replacing anyway because it will simply kick up if it hits something like a log or if the boat is pulled up on the beach. Like I said, pitot speedometer very simple, very reliable.

On the plus side for paddle wheels is the fact that they can measure slow speed of a knot or two which a pitot speedometer cannot. (Pitot Speedometers only begin registering about 8-10 MPH) This is especially good for trolling where you want to measure and control your speed through the water and a GPS merely measures your speed over the bottom.

Whalerdan posted 07-18-2001 07:39 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
I'm with TWC on this as well. K.I.S.S. (Keep It Simple Stupid) and having EVERYTHING in one unit IMO was a bad idea. If one unit goes down you loose everything. We don't design things like that on our aircraft for this very reason.
jimh posted 07-18-2001 08:36 AM ET (US)     Profile for jimh  Send Email to jimh     
Apparently some outboard engines have a PITOT tube built into the lower unit.

On one of my Yamaha 70-HP outboards there is a hose coming out of the lower unit, and I assume this is for a speedometer connection. Is this commonplace on ouboards?

I don't see where the PITOT opening is located on the lower unit, but it must be somewhere! Any hints?

Can you just connect any speedometer to this tubing, or is it calibrated for a particular gauge mechanism?

jimh posted 07-18-2001 08:41 AM ET (US)     Profile for jimh  Send Email to jimh     
Finding a 3 & 3/8th-inch hole saw might be a problem. You may not get one from your local ACE hardware store.

I located one at a power tool specialty store. It was a MILWAUKEE brand.

By the time you buy the arbor and the hole say, you will have spent a large portion of the cost of the tachometer over again!

Whaletosh posted 07-18-2001 09:18 AM ET (US)     Profile for Whaletosh    

It common for there to be a speedo pickup on outboards. All 3 of the Mercuries that I have owned had had this.


I would add my voice to those advocating you forgo the speedometer. By the time you pay for the speedo and the tools to put one in you could get a GPS. If you want a fishfinder you could get a speedo pickup on that as well. Tom w. clark is very much correct in stating that the Teleflex speedo is very reproducable. But then so are GPS and Fishinder speed readings. Plus, the Teleflex model you are thinking of getting will be useless at speeds under 5 MPH. Speed readouts on Fishfinders can be very accurate, my Garmin 240 reads within 1/2 mph of a GPS, from idle to WOT; without any adjustments.

Personnaly, I think you would be much better off with a tach and a GPS and/or speedo equipped fish finder.


gnrgunner posted 07-18-2001 10:32 AM ET (US)     Profile for gnrgunner  Send Email to gnrgunner     
Thanks for all the advice and responses! I guess I have to think about it a little more. I really do not like the idea of drilling into my mahogany and possibly ruining it, but I do sowmewhat agree with what Tom W Clark said in that the analog speedos are consistant and for the most part low mantainence, as well as low cost. As for the tools, my grandfather owns just about every tool out there, so I'll have to ask him about a hole saw. Thanks a lot!
Tom W Clark posted 07-18-2001 11:29 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
OMC introduced the gearcase mounted pitot with the 1982 model year. I had a Montauk with an '82 Johnson 90 and I thought it was one great idea. So simple, so clean, why didn't they think of it sooner? A small hole was found in the leading edge of the gearcase and ran up to a plastic barbed fitting on top of the gear case just in front of the motor's pivot point. You simply stuck the hose onto it instead of drilling holes into your transom and mounting a conventional pitot tube.

Well, it was a great idea that didn't work too well for two reasons. First and foremost, the gear case location meant the if you hit a piece of driftwood or whatever, bits of it would be rammed into the pitot opening. A conventional pitot tube simply flips up out of the way. My gearcase opening suffered this plugging never to be freed again, oh well. The other problem was the plastic barbed fitting on top of the gearcase was very easily broken off. This happened to me as well. I reverted back to a conventional pitot tube and OMC stopped building producing the gearcase mounted pitot, I assume, for the above reasons. Perhaps others have done it better....

Getting back to drilling the hole, I agree that if you don't own the tools and buy them it will cost some $. You could rent them, but borrowing them is even better. Whether gnrgunner should or should not install this speedometer needn't be dependent upon the drilling of the hole. I don't think it's a big deal but then again I have a whole shop full of tools and a set of hole saws. A 3 3/8" size is not hard to find though. Most hardware stores should stock them.

There is nothing wrong with having an analog speedometer in addition to a fishfinder with a paddlewheel speed sensor and a GPS. In fact I think this is the preferred route. I have had all these on a couple of my boats, though I have now stopped paying the extra 50 or 60 bucks for the optional speed/temp sensors because of their inaccuracy. But like I said earlier, if they can be calibrated (can the temp be calibrated too?) then I might reconsider.

glynnw posted 07-18-2001 12:10 PM ET (US)     Profile for glynnw  Send Email to glynnw     
gnrgunner - I have a 2002 Merc 25 2 cycle enigine, so 30 mph is about all I can get. Frankly, 30 is fast enough to entertain me in a boat this small.
Landlocked posted 07-22-2001 10:59 PM ET (US)     Profile for Landlocked  Send Email to Landlocked     
Installed a lighted "Lido" series speedometer and tach this weekend. Have had a GPS unit for a while but just wanted a guage cluster.... Can't say I needed it - at least the speedometer but having both balances out the console. If nothing else - the speedo lets you maintain your optimum cruising speed at a glance - and its right there under the wheel. May be off a mile or two/hr but its always the same amount "off". Who cares whether your going 30 or 31.5 as long as your not trying to navigate by (dead reckoning)

AS far as installation - the bigest pain for me was getting the darn steering wheel off. There are no holes for a standard Wheel puller and the legs of the gear puller I had were too short... Tried all kinds of things chain, nylon webbing etc to give the puller something to hook to. Finally gave up and used a hammer. Worked. Just use a center punch on the bolt and give it a bunch of solid bumps while pulling back on the wheel.
(loosen the nut on the inside of the console a little to give the wheel more play.

As far as wiring - The speedo is just a tube like others said. The light is electrical but simple. Run a line to your negative buss and a hot wire to a switch on the panel. You'll want the light to be controlled by a switch. If you have a lighted tach, you can just use a jumper from the speedo like you would on a house switch when carrying the circuit on. Use 16guage Anchor wire. The tach has the circuit for the light, a wire to the ignition switch, and a wire to the sender from the motor. Sender is Gray for Johnson.

Cutting the holes is really no big deal. I purchased a 3 1/2 in hole saw at Home Depot - $12.00, already had the arbor but its only like $9 more if you need it. Mark your hole. Keep a firm grip on the drill and go slow till its in about a 1/4 inch then speed up. I cut through 1/2 inch mahogony and 3/4 inch plywood + the fiberglass with a cheap black and decker drill. If you take the wheel off, you probably won't need an angle drill. IF you have a handle that will screw into the side of your drill, use it to help control the drill against the torqe.

If you haven't checked out the Lido's do so. The stainless bezel looks really good with the stainless wheel

Landlocked posted 07-22-2001 11:03 PM ET (US)     Profile for Landlocked  Send Email to Landlocked     
Oh yea, the Lido calls for a 3 13/32 hole (87mm) the standard 3 1/2 hole-saw H. Depot carries is only 2mm bigger. Made no difference just used a little marine calk around the unit and under the bezel.


SuburbanBoy posted 07-22-2001 11:38 PM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
The comment Tom W Clark made about slow speed accuracy is right on. If you are an avid troller, the actual water speed is very important. (I have heard that there are downrigger suspended speed sensors, useful for "at the lure" speed measurements. These take into consideration turning effects and underwater currents.) Also, if you are serious about water sports (skiing etc.) you will want to consider some of the specialty speedos available for that application. I use a console mounted GPS w/fishfinder and trolling speedo (Garmin 168). Just remember to measure twice and cut once. Good luck.


Pbob posted 05-29-2003 12:57 PM ET (US)     Profile for Pbob  Send Email to Pbob     
I have suspected this problem with at least two older Q'silver speedos here. I also gave one of these to my father and he thinks the same thing. Seems like I can't make my boat go as fast as I used to and the RPM is the same, boat feels the same, etc., just that gage reads around 5mph slower than it used to. Probably closer to 10 mph on my older boat (15+ years ago). These are the Bourdon-Tube type, with the water hose connecting between the pitot tube or a nipple on the outboard lower unit. I do agree with the one who said he likes them because they are consistent and simple, but maybe not so consistent over the long term. But at least, it can be a relative reading for immediate performance indication, as when changing trim angle or shifting load within the boat. Also, the analog needle is easier to detect when it is moving as you are driving the boat. Please respond with any comments, questions or suggestions. Another good way to cut the dash mounting hole is to use a divider (compass) to scribe a perfect-sized circle onto a plywood template and then spindle (barrel) sand this template, checking it for fit around the speedo. Don't forget that there is a small tit on the rim of the bezel to keep the speedo from turning in the hole. Nick this out with a hacksaw blade or pocketknife. When you are happy with the template, fasten it to dash in desired spot and use a router with a following-type bit to cut out the hole. If the template has been made large enough, you can clamp it. If it is too cramped in the mounting location, you can use 2-faced tape or small brads to hold it down.
I might just have to go and buy a fish graph with paddle wheel speedo, but it's too bad the water pressure speedos seem to go bad with age. Did anybody tell you how to adjust them?
kgregg posted 05-29-2003 03:34 PM ET (US)     Profile for kgregg  Send Email to kgregg     
gnrgunner, DON'T cut that hole! Please give some thought to Garmin Etrex handheld GPS. $95 something from Amazon. Another $30 or so at local boat shop gets you spiffy plastic GPS holder that screws to top of center console. Kevin

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