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Author Topic:   Repower of 15' Sport
yannvang posted 03-21-2002 02:57 PM ET (US)   Profile for yannvang   Send Email to yannvang  
I have recently acquired a boat that I owned during my childhood, a 15' Sport, 1980 hull. The boat came new with a 60hp Johnson that seemed adequate at the time. I have read many of the prior the posts on the forum and am nearly complete restoring the inside (all new mahogany interior, minor patch work etc... All of the advice really paid off!)

I am now ready to repower the boat (bought it without the engine) and would appreciate any advice on the following: I am planning to repower with a 90hp Merc 2 stroke. My question is, does anyone have experience with this engine on the back of a 15' Sport. I looked at many engines and frankly for the money ($5000 for an '02) this seems to be the best (it weighs the same as the 75hp which is what I originally was looking at). On the Cetacea I saw a great picture of a 15' with a 90hp Merc but it had a Jackplate. Is this a good idea? Any thoughts would greatly be appreciated.

Bigshot posted 03-21-2002 03:53 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Before JB gets on here and chews you out....I would use a jackplate, will help in performance and being you are doing the 90, I guess you are looking for it. Just get a manual one so you can fiddle with engine heights to get max, you'll be glad you did.

The right prop is gonna be your biggest issue. Too much bow lift and you won't be able to trim. Too little cup and holeshot and turning will suffer.

I have seen these with 115 Merc inlines and that was one squirrley SOB. Be careful but also don't get your hopes up too high. With a 70 set up right you will get about 48-50. With a 90 probably 55 or so.

Bass pro shops has them for $4600 and do a search for discount motors or something here and check out those sights. Props can be had for cheap on E-Bay.

Bigshot posted 03-21-2002 03:55 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
On my honeymoon the hotel had a 1978 15' sport with a 115 oceanpro on it. Not 1 stress crack. Have no clue how fast due to being in carribean and could not get more than 4500 rpm's without getting airborne too much.
russellbailey posted 03-21-2002 04:55 PM ET (US)     Profile for russellbailey  Send Email to russellbailey     
For our Striper 15, if I were to repower today I would also get the Merc 90. The Evinrude 70 just does not have the oomph I'd like to yank a slalom skier up, though it will drag one out. And forget about deepwater barefoot starts with the 70 though you can bang yourself up silly trying.

My one concern would be weight. With our Striper, I have a 12 gallon and 6 gallon gas tank in back. With driver plus a passenger in the cushioned rear seat (admittedly kind of far back in the boat), the stern is heavy. Add a passenger in the bow and all is fine. I imagine with a Sport it would be easier to get the weight up front. For that same reason (weight in rear) I'd be hesitant to put a jackplate on.

I can't imagine running it flat out with the 90 - Flipper does and it must really fly. My reason for liking the 90 is the pulling power. And at least in Georgia (where I live) it is fully legal to put whatever power engine you want on the boat. [the only law on powering here is that a manufacturer must include a capacity plate with recommended horsepower]

yannvang posted 03-21-2002 07:07 PM ET (US)     Profile for yannvang  Send Email to yannvang     
Wow! A 115?! I can't imagine that on the back of the 15'. My wife would kill me. I hate to ask a follow-up question on the jackplate, but the dealer I was working with won't answer my questions on this. What type of jackplate would one use for a 90hp Merc? Is there a certain type of "setback" I would be looking for. Thanks again for your help.
bc posted 03-21-2002 09:38 PM ET (US)     Profile for bc    
I personally would stay within the recommended hp rating. In today's world with all the legal / insurance issues you don't need anything that gives them another angle to sue or not paying up claims. For pulling power you can also change the prop pitch.


1981 Striper 15'/Johnson 70

Flipper posted 03-22-2002 12:27 AM ET (US)     Profile for Flipper  Send Email to Flipper     
I am enjoying my 15 with the 90. It's not everyone's ball of wax, but I think it's the most fun to drive and the most versatile rig I could have put together.It planes out quickly with the heaviest of loads, and it handles beautifully-with hydraulic steering.I would recommend the 'no feedback'steering before a jack plate,but the jack plate is the next step towards even better performance.
Bigshot posted 03-22-2002 10:59 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
i run a Vance 6" setback, 4" lift, $135 on E-Bay. Overton's also has a "Highjacker" I think for $139. You can go from there but with only a 90 I see no need for overkill. Believe it or not the plate does not make the boat squat anymore than not using one. Do it! I debated for a while and will never drive without one.
Salty posted 03-22-2002 11:03 AM ET (US)     Profile for Salty  Send Email to Salty     
I had a 1978 15' Sport and re-powered it with a 2-stroke, oil injected 70 HP Yamaha and it performed very well. It had plenty of power, a good hole shot and it wasn't too heavy in the stern. I never pulled any skiers with it to be able to comment on that. The boat always felt well balanced with the 70 on it, which is what it is rated for. It was also great on gas. I was down in Florida with it stopped at a restaurant. The marine police were there and for some reason they had singled out some guy and they were checking out his boat for all the legal requirements. They were giving him a very hard time about some things. These days you never know what they might do if you were over the recommended HP. They do love to get your money.
Bigshot posted 03-22-2002 11:57 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I got pulled over on a maiden voyage in my 76 Montauk with a 115. It was just around dusk and we were about 2 miles from the ramp and in the distance I see a boat coming my way and then the blue light goes on....CG. They pull me over and ask for all the stuff. Registration-nope, running lights-nope, horn-nope, thrwable-nope, lifejackets-yes, fire extinguisher-nope, Have you been drinking-nope(lie), anchor-nope, paddle-nope, flares-nope, can we see in the cooler-nope, driver's license-yes, etc etc. Finally showed him inside the cooler and she contained 2 lifejackets(wanted to keep him guessing). Never asked to see in the platform storage which is where empty beer cans were. Just before he let me long as I belined for the ramp and registered it the next day, he asked what kind of boat it was. I was shocked! Never saw a Montauk? Nope! at lesast we have something in common, the word nope. Stupid greeny from some backwoods area never saw a Montauk, which every marine police and Cg in NJ uses and he is patroling our waterways....geeesh.

Moral is I was totally illegal and he never once mentioned the 115 on the transom.

where2 posted 03-22-2002 01:07 PM ET (US)     Profile for where2  Send Email to where2     
The problem with the 15' hull with a 70Hp OMC and a Slalom skier is the prop. 13-1/4"x19" SS is too much, drop to a 13-1/4"x17" and slalom pulls up fine. Not like a Ski-Nautique with a 351, but way better than it did with the 19" pitch prop. I keep my 17" for skiing, and my 19" for running WOT at 50mph. I could probably put a 13-1/4"x15" on it and pull up 3 slalom skiers, but watch the RPM when you're not dragging anything! It's all in the prop. 70 Hp or 90Hp with the wrong prop will act the same.
russellbailey posted 03-22-2002 03:34 PM ET (US)     Profile for russellbailey  Send Email to russellbailey     
We normally use a 13x17 and are competent but not expert skiers in the 170 lb range. I have a 13x15 we use sometimes - it revs out quickly for cruising but does improve the acceleration for the slalom. We used to use the original 13x19 since it was a nice SST but gave up except for cruising.

Still the acceleration is not what I'd like which is why I'd like a bigger, more torquey engine. Gearing down the prop is kind of like a lower gear in a car - you get more initial force but you also run out of acceleration sooner - not too soon to get a slalom up, but too soon to reach speeds needed to barefoot (at least for me).

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