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Author Topic:   repower 15sport
chrisb posted 01-29-2001 11:50 AM ET (US)   Profile for chrisb   Send Email to chrisb  
I was given a 1978 15 sport two years ago by my dad. It has a 1990 48 hp johnson manual trim. The hull seems to be in fair condition and dry. The engine idles rough, I'm not very mechanical and have no idea of the prop size and pitch or mounting. It does well with tubes wakeboards or hydrofoils, but cannot pull some of my young and light (40's, 160-210 lbs) peers up on one ski. It also not quit fast enough to be really thrilled when skiing slolam. Every night my wife, three toddlers and I idle around the 225 acre pond, and I weekly measure water samples with a 20 meter hose for the vermont state lay moniter program for clarity,phosphorus and chlorophyll. I know the kids will grow up loving this boat the way I did my dads 68 13 classic. I think I'll need more hp eventually. I want to do the right thing environmentally (there are no four strokes on the 45 camps on the pond maybe I could start the trend) but I worried about the weight. I've heard the light weight honda 50 (200 lbs) is very slow accelerate. The current engine weighs 185 and the boat seems trimmed well but it falls off plane early when decelerating. The 70 four strokes all weigh in at 238+. Are the new feul injected two cycle essentially as clean? Am I missing something? Should I weight 2-5 years and expect the weight to come down on the fours?
A second question I walk around the bimini on the gunwales and sometime dive off but the boat feels like it tips alot. Am I at risk to capsize the thing?
russellbailey posted 01-29-2001 12:42 PM ET (US)     Profile for russellbailey  Send Email to russellbailey     
As far as tipping, unless you are very big you cannot tip it by walking on the gunwales. It will list a bit, but gets very stable as the gunwale gets to the water line. Now maybe if you were leaned up and a big wave hit or something, but still I doubt it. As noted before on the forum, the 15's semi V is deeper and thus the boat rolls up more than a 13 or 17.

For repower, I believe our 1988 70 hp with power trim is about 300 lbs. I would not want any heavier, and lighter would be better. It certainly squats more than it did with the original non-power trim 70. But it's ok.

If you want to get up on one ski, as an adult with a normal size slalom ski, I would not go less than a 70. Our will get us up, but it works hard. Interestingly, I found that the 19" pitch SST prop gets us up better than the 17" aluminum - I think the aluminum must flex enough or lose grip enough on the water to not get us up as fast.

Your boat will fly with a 70 - faster than I care to go. But you'll need it to drag someone out (I say drag and not yank, as I've never seen someone pop up on one ski behind our boat).

eolson posted 01-29-2001 01:19 PM ET (US)     Profile for eolson  Send Email to eolson     
I've got a 1985 Sport 15 with 1985 Johnson 70 power trim. Rebuilt the engine last year.

The biggest person it's managed to pull up on a slalom ski is my wife (~115lbs) on a 63" shaped slalom ski. It cannot pull me up on the same ski (175 lbs) even though it tries for all it's worth. My wife says that it's rather amusing to watch me try - I plow a mountain of water out of the way before finally losing grip on the handle. I either need more power or a bigger ski.

I'm looking for a good slalom for myself right now... I'll let the group know how things work out once (a) I've got the new ski and (b) it's a little warmer around here.

Gainesville, FL

Clark Roberts posted 01-30-2001 07:13 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Eric, a lower pitch prop should do the trick for you! With the right prop you can easily pull a 200 lb. slalom skier from deep water... Clark
Peter posted 01-30-2001 07:38 AM ET (US)     Profile for Peter  Send Email to Peter     
Clark is right, seems that you need to drop down to the next lower pitch prop for skiing. My recollection is that the OMC 3 cylinder 70 has a hard time developing a lot of torque at very low engine rpms. A lower pitch prop would let the 70 get the rpms higher for an equivalent speed and develop more torque to pull you out of the water.
reeltime2 posted 01-30-2001 09:34 AM ET (US)     Profile for reeltime2  Send Email to reeltime2     
I had a 1986 15 S.S. w/ a 60 johnson I was never realy happy with the speed. If I had to repower I would go with the 2 stroke 70 over a 50 4 stroke. The deep v of the 15 needs alot of power to lift that hull out of the water. And if you haul alot of people & gear you will be much better off w/ the 70 just opinion.
chrisb posted 01-30-2001 11:17 PM ET (US)     Profile for chrisb  Send Email to chrisb     
Thanks for convincing me to look for a 70hp. What should be the weight limit for motor, trim, plate and prop for my needs and boat? I quess everyone rules out a four stroke, but is the electronic fuel injection a blessing or a curse? And does anybody's crystal ball think the four strokes will get light enough in the next few years to be worth the wait?
jimh posted 01-31-2001 09:31 AM ET (US)     Profile for jimh  Send Email to jimh     
An ideal engine for a Whaler 15-Sport is the Yamaha 70 HP. This is a 3-cylinder 2-stroke engine.

This engine only weights 230 lbs! As the 15-foot hull is sensitive to weight, this will be an advantage.

The engine has power tilt and trim, which will allow you to trim the boat for best performance.

The down side is the 2-stroke, classic three caburetor engine design. It will smoke, be less fuel efficient, and emit more unburnt fuel and other pollutants.

The upside is the engine is very simple, straightforward, and mechanically refined, so it should run a long time.

This engine is available in either oil-injection or pre-mix fuel/oil versions. You save more money going with the pre-mix model, and gain more simplicity.

This engine has been made by Yamaha since the mid-1980's, and it is a proven design.

Even among 2-stroke engines, its power to weight ratio is a standout.

Of course, it does not fit well with ecology concerns. But then you have to rationalize this by asking: how much fuel are you going to burn in a season?

Last year I probably only ran 40 gallons of gas through the engine on my 15-Sport. When I drive my V-8 Suburban I might use that much gas in one day of towing the boat on the highway on a long trip. I don't feel that the planet or the water will suffer so much that I have to spend $7,000 on a new engine.

And, looking at the total ecological picture, what happens to the old engine? Does it go in a landfill? If I use it until its useful life has been exhausted, perhaps I will actually reduce the net pollutants.


JB posted 01-31-2001 10:20 AM ET (US)     Profile for JB  Send Email to JB     
I second that! I have a 15' GLS with a 70 Yamaha and it's pretty quick. The power tilt is great for launching and getting out of my driveway. I would recommend the oil-injection for simplicity and the fact that any remaining gas at the end of the day goes into my truck and eliminates any questions of stale gas on the next trip.
dtam posted 01-31-2001 08:28 PM ET (US)     Profile for dtam  Send Email to dtam     
I have an '85 15 Super Sport with an '85 70hp Yamaha. It is a fast boat but still has trouble pulling a heavy skier out of the water on one ski.
chrisb posted 02-02-2001 08:30 PM ET (US)     Profile for chrisb  Send Email to chrisb     
thanks for the definitive weigh in on weights and performance. It was hard to let go of the idea of the "latest and greatest" but my main complaint is speed for skiing, and you have convinced me. I'm sure I'll have some prop questions down the road. I want to thank you all for showing me pearls of my 15, I'm so excited a cant wait for the ice to melt.

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