Powering an 18' Super Sport

[Krichbourg]

How well do you think a 115, 4 stroke will perform on my SS? I'm on a motor hunt and I want to do this once. I'm thinking this will be a good mix of power, efficiency and overall use-ability. Mines a '77 and is rated for a 150. Tell me about what you've got and how you like the way it performs. I'm thinking a 4 stroke much bigger than a 115 will be more weight that the boat is designed for and probably more power than I really need anyway. I look forward to hearing what my Brothers in Tin are using and what they think the ideal set up would be. All advise and input is greatly appreciated.

 

[djpeters]

Re: Powering an 18' Super Sport

My 22' SS with an Evinrude 140 will do 35mph wide open (GPS). At 25mph it burns 6gal per hour or 3.3mpg. I know mine is 2-stroke but thats what it does.

Ezmobee has an 18' SS with "about" a 115 hp. outboard (I'll let him explain).

IMHO 115 should be plenty. Our boats are pretty light.

 

[Pugetsound]

Re: Powering an 18' Super Sport

I have a 22 holiday with a 200 OB runs high 40s low 50s WOT. I had 3- 19 ft Glasplys heavy boats 2 with 115 OB. Both would run in the high 40 with trim tabs other was a 120 I/O Ran about 42-45 WOT. The 115 should be plenty of power for the lighter Hull and esp. if its of newer design 4 stroke as the HP is rated at the prop. I have a 50 OB on my 16 SS and it is also very fast I guess high 30- to mid 40s No speed guage but a good guess

 

[ezmobee]

Re: Powering an 18' Super Sport

Ezmobee has an 18' SS with "about" a 115 hp. outboard (I'll let him explain).

Yep. I got a hopped up 90 with 140 carbs on it. They're too big but my mechanic got them tuned pretty well. I assume I'm runnin' somewhere between 90-115 HP.

Looking at these specs http://www.yamaha-motor.com/outboard/products/subcatspecs/63/specs.aspx I'd stick with the 115 (weight). Should be ideal for you.

 

[Pugetsound]

Re: Powering an 18' Super Sport

Sounds good that should do the trick . On newer motors the only difference in HP on some of the larger was carburation and tuning.

 

[barbosam]

Re: Powering an 18' Super Sport

I have a 18' holiday with a 70 hp johnson and although I haven't yet been able to record top speed or calculate fuel milage I estimate that its running at about 30 mph and is IMO very good on gas. I find that the only time it lacks power is when I'm pulling 6 people and one or two tubes, but with 3 people and 1 tube it does great, it's just that once word gets out that I'm putting the boat in the water everyone invites themselves lol and i always end up with a full boat!

I think power wise 115 will be more than enough for great performance and still maintain some fuel economy. My only concern with putting a four stroke 115 on that boat is that it will be much heavier than the two strokes that this boat was designed around. If you go four stroke you might want to consider a 90hp instead as these usually have a smaller (lighter) power head; beyond 90hp is usually a step up to the next largest power head and will be significantly heavier. I think that a 2 stroke 115 would be a better fit. Just do some research and compare the wieght of a modern 4 stroke 115 compared to a 2 stroke 115 (or even 150) of the same vintage as your boat; I think you'll find a huge difference.

 

[Krichbourg]

Re: Powering an 18' Super Sport

Thanks for the input. I actually have done what you have suggested in comparing a 150 2 stroke with a 115 4 stroke. They're close. Your concern is mine as well. There will be times when the boat is loaded to capacity and I want to have enough power to deal with it. Also, current is a factor where I boat. Two strokes are more plentiful and affordable, but I sure would like to have a nice quite fuel efficient 4 stroke. I hope I can eventually find one in my price range. Thanks again for the input.

 

[86 century]

Re: Powering an 18' Super Sport

I have a worked over 200hp merc 2 stroke on my 18' SS. It is way more than I need but the hull has held up fine so far.

 

[Krichbourg]

Re: Powering an 18' Super Sport

I bet that thing will fly! I'm curious about the top speed one could expect from an 18' SS with a 150 hp. I'm guessing close to 50. Faster than I need to go and faster than I could go most days. It gets glassy every now and then but mostly, not.

 

[ezmobee]

Re: Powering an 18' Super Sport

I get 40 in mine. 50 should be no sweat for a 150.

 

[Krichbourg]

Re: Powering an 18' Super Sport

So who holds the SS speed record? I've gone 70 years ago on a guys jet boat. It was glass that day but 70 on the water is still scary, for me anyway.
Let's say two similar boats are going 35. One is doing it with a 115 and the other with a 150. How big a difference in fuel usage would you guess?

 

[Starman8]

Re: Powering an 18' Super Sport

My 79 18SS has the Merc 115hp inline 6 and weighs about 285 pounds. Never water tested yet, but she sounds like an HD, and will be fast enough. Merc's these days at 115hp Optimax are inline 3 and weigh closer to 400.

The older 4 strokes are heavier than the newer ones, the Merc 115 4S weighs a tad over 400 pounds. I had a 2000 90HP Merc 4S on my other Star, and it weighed 400 pounds and pushed the 19 footer 38mph.

As much as I loved the 4S I wouldn't hang one on my 30 year old SS.

If I had a newer boat, would probably jump to Yamaha 4S as they build them with higher HP than Merc.

 

[Huron Angler]

Re: Powering an 18' Super Sport

So who holds the SS speed record?

That would be either our buddy 86Century w/ his 200hp 18' SS at 50+ mph...or SSchefer with his "Frankenmerc" 185? hp that pushes his 18' Monark(Canadian Starcraft) 50+ mph.

Both are faster than I need to go, but sure look like fun

 

[sschefer]

Re: Powering an 18' Super Sport

The FrankenMerc weighed in at around 400lbs and pushed the MonArk Legend 1800FS over 50mph. The new owner had a problem with something clogging up the cooling system on his first day out. I suspect he picked up a plastic garbage bag or something similar. It wasn't his fault except that he wasn't watching the water pressure gauge.

Consequently he overheated it and fried #2. I'm fixing it for free just because I know the guy saved for a long time for this boat. I've just about got it ready to put back on later this week. He did say he had no problem getting to 50 mph before #2 siezed.

 

[Pugetsound]

Re: Powering an 18' Super Sport

My 22 Holiday will go 50 but wont run it that high. with my 200 hp Johnson 21 pitch prop.

 

[86 century]

Re: Powering an 18' Super Sport

The fastest I have seen on the gps is 55.4. That was running with the wind the other direction 10min later only went 54.6.
This was done with a 19p ss three blade turbo at well over 6000rpm.

I don't know how much fuel your 115 will burn. My merc loves its fuel will run though 37gal in just over an hour running it hard or cruising she doesn't seam to care where the throttle is.

 

[Pugetsound]

Re: Powering an 18' Super Sport

ULP !! Was that 37 Gal for 1 hour or did you hit the wrong key????

 

[barato2]

Re: Powering an 18' Super Sport

As much as I loved the 4S I wouldn't hang one on my 30 year old SS.
i understand where you're coming from re the weight, but IMHO, a big alum resonance chamber would benefit lots from relative quiet of a 4 stroke...?

 

[MichaelP]

Re: Powering an 18' Super Sport

The fastest I have seen on the gps is 55.4. That was running with the wind the other direction 10min later only went 54.6.
This was done with a 19p ss three blade turbo at well over 6000rpm.

I don't know how much fuel your 115 will burn. My merc loves its fuel will run though 37gal in just over an hour running it hard or cruising she doesn't seam to care where the throttle is.

37 Gal/hr...Holy carp!!! Must have a bilge pump pushing fuel for ya. Hope you meant 3.7 gal/hr.

 

[Pugetsound]

Re: Powering an 18' Super Sport

The fastest I have seen on the gps is 55.4. That was running with the wind the other direction 10min later only went 54.6.
This was done with a 19p ss three blade turbo at well over 6000rpm.

I don't know how much fuel your 115 will burn. My merc loves its fuel will run though 37gal in just over an hour running it hard or cruising she doesn't seam to care where the throttle is.

37 gal an HOUR?????? must have ment 3.7 gal hour????