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  Sport 15: Maximum Rated Horsepower

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Author Topic:   Sport 15: Maximum Rated Horsepower
mhawk153 posted 02-15-2004 02:20 PM ET (US)   Profile for mhawk153   Send Email to mhawk153  
My 1979 SPORT 15 is rated for 70 hp maximum. Is this based on the average weight of a 1979 70 hp motor? I do not want to go any faster than I already can so I will not put a ridiculous amount of power behind me. I am just trying to figure out this rating.
Tom W Clark posted 02-16-2004 11:24 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
mhawk15,

No, the 70 horsepower maximum rating is not (necessarily) based on the "the average weight of a 1979 70 hp motor". It is derived from a very simple formula that all boat manufacturers of outboard powered boats under 20 feet must use to compute the maximum horsepower they can allow.

A manufacturer may choose to assign a lower rating if they feel the need based on their own performance tests, but they cannot exceed the number that the formula yields.

In the case of the classic Sport 15 (and other 15' models including the still in production Alert 15, made by Brunswick Commercial and Government Products, Inc.) the limit was set at 70 horsepower.

Actually, when the Sport 15 was first introduced in 1975, the maximum horsepower rating was set at 75 hp, but that was changed the next year, presumably because it was a bit too much. Having owned a 1979 Striper 15 with a 1979 Johnson 70 hp motor, I cannot imagine wanting any more power than that. At top speed the boat became a little squirrely.

It would seem that the Sport 15 could qualify for an 85 hp maximum rating based on the simple formula described in the Code of Federal Regulations, (33 CFR 183):

(2 x L x W) - 90 = rated horsepower (rounded up to the nearest 5 hp)

where: L=boat length and W=transom width

There have been several good discussions of maximum horsepower ratings here in the Forum. You can search out much information using the search engine of continuousWave.

One good thread where maximum horsepower ratings were discussed is here:

http://continuouswave.com/ubb/Forum8/HTML/000493.html

where2 posted 02-17-2004 01:01 PM ET (US)     Profile for where2  Send Email to where2     
As a good point of reference, the 15' Alert hull Tom speaks of is still in production, and from outward appearances looks like a shiny 1979 15' Sport. The maximum engine weight rating is something like 265lbs or 70hp (I'll have to double check that weight, but it's right around 250). With most of the 4stroke engines weighing in at more than 265lbs for the 70Hp versions, it's something to keep in mind these days. Unfortunately, even the Evinrude E-Tec 70Hp is heavier than the max whaler rates their old style 15' hull for, despite it meeting the horsepower rating.
BQUICK posted 02-17-2004 02:12 PM ET (US)     Profile for BQUICK  Send Email to BQUICK     
A friend had a 15 ft center console with a 90 Merc 6 cyl. With a 2 blade bronze prop it would run 53 mph with 2 aboard. Lots of fun in that boat. Motor wasn't that heavy either.....

Bruce

Bigshot posted 02-17-2004 04:17 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
They can easily handle the weight....been in one with a 115 Ocean Pro.....SCARY!

I think the 60hp Merc 4 stroke or any 60-70hp 2 stroke is perfect for it. Keep it on the light side, she chine walks bad enough with a 250lb 70 on it at 48mph.

mhawk153 posted 02-19-2004 09:02 PM ET (US)     Profile for mhawk153  Send Email to mhawk153     
Bigshot,
ah yes...the chine walk. okay so on the light side, yammie 70-228lb(its got to be a yammie...long story) you say that the omc is more powerful...isnt 70 hp 70hp?
I was considering the 60 4stroke 244 lb....less hp=less chine walk...right? and i checked the yammie 4 is lighter....how much speed do you think i would lose by dropping 10hp?? do the cc's tell you anything about how powerful an engine will be???

Thanx for the help.

Bigshot posted 02-20-2004 10:31 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
The OMC looper inline 3cyl 70hp was one mean 70hp and will almost keep up with a 90 yamaha. No offense to anyone here but the 90 yamaha is more like 80hp and the 70 yamaha more like a strong 60. CC's do make a difference and I do a pepsi challenge any day. I have owned them all.

I would go with the 60 4 stroke....you may lose a few mph but she will still be in the low 40's. I would also go with the 60 Mercury 4 stroke being it IS a yamaha with black paint BUT you get EFI for a cheaper price. Your prop and controls will still fit from a Yamaha, might need new cables and tach.

zotcha posted 02-20-2004 04:17 PM ET (US)     Profile for zotcha  Send Email to zotcha     
BigShot, how are ya? My 15' is an '80 with an '81 3 cyl. johnson 70. I'm not sure of the pitch on the SS prop, and am not sure how fast the boat is going. 15 gal. tank under seat and the boat seems to fly. Would the best way to check speed be with a hand held GPS? Motor still seems strong but always wondering when and what to repace with. Would not want to go below 70 hp. and can't really imagine going much more. Any thoughts? Still have not ordered a trailer but my dad will be in Long Boat 3-2--3-9. Seen any Snook?
Bigshot posted 02-23-2004 12:38 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
The 81 is not as lively as the 86-2002. Your engine redlines at 5500 and the newer ones at 6k. I had a 1984 60hp 2 cyl that spun a 19" SST prop and was just as fast as my buds 1983 70hp with a 19" prop. Reason being we both had the same gear ratio, prop pitch and biat. My engine was 60lbs lighter and spun my 19" to 6000rpm vs his 5500. Yes a 60 can be as fast as a 70.....these days even faster. If you have a tach(which you should) you want to be as close to 5500 as possible with light load. I think if you went with the 60 Merc 4 stroke you would not notice much of a difference exceot silent running and twice the fuel mileage.
Bigshot posted 02-23-2004 12:39 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Ps I really don't fish but I have snook in my canal 365 a year.
zotcha posted 02-23-2004 03:26 PM ET (US)     Profile for zotcha  Send Email to zotcha     
BS Guess I have to be more careful. Not sure of redline of engine but trimmed out, light load, flat water, WOT tachs out between 57-5900. May be shopping a new engine sooner than I thought. Still not sure how a '58 Chevy 283 bored .60 over, is considered not to have a redline. Mine is being broken in as we speak, but not back in the boat yet. Check out www.speedskiffs.com home page, and Boats by Name, Fast Forward. Will be in Mt. Dora, Fla. for APBA gathering Mar. 27-29. Maybe there sooner to pick up my trailer for the 15'. Going with Owens and Sons.
Bigshot posted 02-23-2004 03:33 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
A 283 with solid lifters will get valve float before she blows....great engines.

1969?-1985 OMC 70's are 5500 redline. 1986-2002 are 6000. Do not overrev. If you are hitting over 5500 I assume you have a 17" or you had a 19' but it is so worn it is a 16".

Owens makes a nice trailer....never priced them though.

zotcha posted 02-23-2004 03:51 PM ET (US)     Profile for zotcha  Send Email to zotcha     
Interesting. Now you've got me thinking. Will have to get some advice on my prop. I see you say you can get 48+ out of 70 OMC. Have to check with a GPS. I only have a hand held, and I'm not sure I can find someone to come along for reading. Also an additional 180 lbs. To boot, I live on a dirt road awaiting original paving from county. Poured my own driveway, and caught skeg while backing up drive. OH YEAH!!! Definately adds to FEAR FACTOR, as well as the SQUIRREL factor!!! Thanks for the info.
bc posted 03-02-2004 05:07 PM ET (US)     Profile for bc    
In my 15' with a hand held gps I attained 37mph with 2 people and gear. 1984 Johnson 70. My Dad's tri-hull 15' Arrow Glass runs 36mph with a 1976 Evinrude 70. My 15' striper has ptt with Dad's is non-ptt. I think mine is a 17 pitch ss, his 17 ss. Hope this helps.
jimh posted 03-02-2004 10:38 PM ET (US)     Profile for jimh  Send Email to jimh     
[Changed TOPIC; was "max horsepower."]
Bigshot posted 03-03-2004 11:33 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Like I said...86 up have more snot. I ran a 20"SST and had her jacked pretty high. On any given day I could hit 45+.

If your skeg is screwed, buy a skeggard for $99. Great item and looks cool.

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