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Author Topic:   1989 15' GLS Top Speed
Toad2001 posted 01-09-2001 01:16 AM ET (US)   Profile for Toad2001   Send Email to Toad2001  
I am the new owner of a 1989 GLS Sport. Its all original with a 1989 Mariner 40 HP 2 Stroke (4 Cyl). The maximum RPM is 5000. I want to have decent fuel economy, but also want to increase my top end if possible (I haven't checked my speed with a GPS yet). I need a spare prop anyway, just in case. What should I buy?
Also, are these engines any good? Should I keep it until it dies, or trade it on a new Honda 50? (Will the top end speed of a 4 stroke 50 perform better than a 2 stroke 40?)

One last question: The engine is currently mounted as low on the transom as possible. Should I lift it up a bolt hole or two for better performance?

Clark Roberts posted 01-09-2001 06:16 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
I have a 1977 15 (custom center console..see under "cetacea" page 28) with a 4 cyl 40hp Merc, same as your Mariner.. the engine is mounted on a 5" Bob's Machine jack plate , up about 4 inches and swings a 12" pitch yamaha stainless prop... also fitted with Doel-Fin. Top speed is about 36 at WOT and 5700rpm... you should raise your engine and do some testing... and get your rpm up to at least 5500... you will get better accelleration and top speed... but you need to measure the speed (gps is good) so you can compare! The 4 cyl 40-50hp Merc/Mariner engines are, in my opinion, fantastic engines... the smoothest around and I have put over 3000 hrs on one without an overhall.. I have owned probably 20 of these critters.. as with any engine (or other mechanical device) the longivity is dependant on how well it's maintained.. feed it good fuel and oil, keep waterpump impeller current ..use fuel filter... etc...etc... you know all this stuff anyway..
I use my boat as a one or two passenger rig. and the 40 suits my needs perfectly.. A 50hp may be the ideal power for a 15 footer.. With a 40hp you are never going to have a really fast rig, if that's your goal. The 15 will literally fly with a 70hp (max rating) at close to 50mph.. A 50hp four stroker should be fine but remember the added weight... happy Whalin'... clark
Backlash posted 01-09-2001 07:53 AM ET (US)     Profile for Backlash  Send Email to Backlash     
Clark, I can remember my 1989 15 SS with 70hp Johnson hitting an indicated 52mph (speedometer)one dead calm morning on a Florida Keys flat. I agree the 50hp is probably the ideal engine for the 15, the 70hp is IMO too much engine.
JB posted 01-09-2001 10:58 AM ET (US)     Profile for JB  Send Email to JB     
I'm running a Yamaha 70 on a '94 15' GLS and it runs GREAT! I don't have a GPS (yet) or speedometer, but I don't think I can do 50, probably somewhere in the 40's. As I recall from the specs, 42 mph is what is claimed with the max (70) power)...(I'm turning 5200-5300 rpm's)...
Clark Roberts posted 01-09-2001 01:54 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Click on "reference", click on 15', then click on "Clark Roberts comments"... some 15 and 17 observations... happy Whalin'... Clark... Spruce Creek Navy
george nagy posted 01-09-2001 01:59 PM ET (US)     Profile for george nagy  Send Email to george nagy     
I had a 15' with a 70 hp evinrude 2cycle 3cylander. I think that a 3 cylander 60 or 70 hp 2 stroke offers the best power to weight ratio for the 15'. It could pull an adult skier out of the water and move the boat along at a good clip. I would love to get another set up like that some day.
jimh posted 01-09-2001 11:47 PM ET (US)     Profile for jimh  Send Email to jimh     
I have a 50HP Merc 1976 2-stroke. I think the ratings back then were at the powerhead and not the prop, so this might be more like a "40" today.

I had a 15-inch pitch prop, but it seemed too tall. I changed down to a 14-inch pitch and that seems to be about right when lightly loaded. I don't like to rev the old engine too high. I think it tops out around 5400 RPM.

I would like to try a 13-inch pitch, just to see what RPM that would lead to.

All these props are Merc BlackMax 3-blade cupped props, aluminum, about $90 or so.

I agree with Clark on the merits of the old 4-cyclinder Mercury. It runs very smoothly and even trolls at low RPM like a champ.

It does blow some blue smoke, but I plan to keep her running as long as I can. The power, weight, size are just right for the 15-Whaler hull.

I just wish I had power trim!


eolson posted 01-10-2001 07:00 AM ET (US)     Profile for eolson  Send Email to eolson     
Choice of engine depends on intended use.

For some uses, a 70HP might be overkill; however...

My family is a group of fanatical water skiiers. Our 1985 70HP 3-cylinder Johnson is *barely* enough power for us. It'll easily pull up an adult on 2 skis, but doesn't have enough grunt to pull up a 180 pound adult on a slalom. The result - I have to get up on 2 skis and drop one. I'm planning on trying a larger slalom ski this season to see if that'll do the trick.

My personal observed top speed is around 43mph (gps).

Gainesville, FL

Clark Roberts posted 01-10-2001 08:02 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Correction: my post above should have read "swings a 14 inch pitch" Yamaha prop not 12"... oh well, I was close! Jim, your 50 Merc would "light up" with an aftermarket trim/tilt unit (like the CMC).. The 15 hull responds dramatically to trim changes... but like you said, you need to be gentle with a very old engine... happy Whalin'... Clark
matt posted 01-11-2001 10:11 PM ET (US)     Profile for matt  Send Email to matt     
eolson-I had 420 hours on my 85 15' with 70 johnson.before i had it rebuilt last summer,but before the rebuild I pulled a 350lb man on two skis with two adults in the boat without great has a 13x17 prop, if I am reading the stamp right.maybe your motor is tired or the rubber in the prop is needing might check your rpm gauge next time your pulling skiers and see if anything is wrong--matt
JimU posted 01-12-2001 01:17 PM ET (US)     Profile for JimU  Send Email to JimU     
My first Whaler was a spanking new 15 sport with a 70 hp 3 cylinder Evinrude. It was fantastic!!! Some may argue for lower hp but given the hp/weight of the three cylinder 2-strokes, I always opt for MORE POWER if the boat will handle the weight. You don't have to operate at wot. In fact, although my present 16-7 will do 45+ or - with a 90 Yam, I usually cruise at 28-32.

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