Repower
 

Considering the 2015 115 Mercury 4s for my 1985 20 SF. If anyone has any experience with this motor or setup what are your opinions?

The Tee Top and windshield may hold you back a little, but I would guess you would be in the neighborhood of 30-32 mph WOT with a perfect prop. Probably cruise comfortably at 20-23 mph and get 4 mpg. Unlike the Keys we make a lot of 60-80 mile days when we go bottom fishing off shore because there is very little structure inside of 45' off of Tampa. Good milage helps you use the boat more often. Just sit back and enjoy the VDH ride.

What is the weight of your hull? I would expect mid 30's for a standard gear case, faster for a command thrust Model. Merc performance reports put a command thrust 115 with Enertia prop on a 3300lb scout boat in the mid 40's top speed and best economy of around 6 mpg at cruise. I'm hoping to have some numbers in a week for a command thrust and powertech 14.25x21 pitch prop

Definitely not going for any speed records, distance and fuel economy is what I am after. It's an 85 year model. not sure of the weight. Want to put a platform on the back, 60 gal tank shifted forward, remove the casting deck and put a fish box cooler up front and a livewell type leaning post/rocket launcher.http://cmmarineproducts.com/Product/...0-c8b31cb16eac

The leaning post.

I suspect a slightly higher top speed. But I bet a 17P prop is close to what you want. I run a 15P on a yamaha F100 on a 75 20MA. And hit 33MPH at WOT. I suspect you will do a bit better.

I left my casting deck, but made it shorter so I could slide my console forward, batteries in the console and also put a new 50 gallon tank as far forward as it would go. I also have an aluminum leaning post And a closed transom with fiberglass bracket. My Boat will probably be lighter than yours as i haven't added a livewell or wash down system yet, those are future projects

[IMG]http://picup.su/upload/150418/600_18289_82373.jpg[/IMG]

Looks good. Have you splashed her since the new motor?

Not yet, Just brought the motor home today. Still have to rig it. I floated it with simulated motor/gas/gear weight to make sure she was ok with it and she sat perfectly.

I expect it to be a winner. Lightweight w appropriate displacement to make up for being 4s. Good luck! Look forward to hearing performance nos.

The thing that drew me to it is the shared architecture to the 150. Simple design, big displacement, light weight. I got it mostly rigged today, took a video of the first start up. gonna water test it tomorrow. More to come

Had time to put it in the water for 30 min for the first test run. She did much better than I anticipated for the first run

3 people
30 gallons of gas

Top speed 43.7 mph registered by raymarine gps sog.

Rpm was unknown as i had my tach on the wrong setting but it didn't hit the limiter. It had more in it but I had short distance to work with. No fuel burn numbers yet. we plan to use it for a few hours on Wednesday so I'll have a more detailed report then

Spinning a powertech ras3 14.25x21 pitch. I thought it may have been a little over propped but I think it may be a good match. Will know for sure once I know WOT rpm

I'm liking the sounds of those numbers.

Breaking it in all day today. So far playing with trim on the first full throttle run hit 45.6 mph at 5400 rpm

It sounds like it's going to be a good match for your boat - congrats! How is the hole-shot; does she take a while to wind up? The 2.1L claims 2-stroke like torque. That's probably a bit of an overstatement but I expect the larger displacement will give you good time to plane and good acceleration. I hope so! It's encouraging to see a 4-Stroke manufacturer that is offering tangible improvement in weight at 115 HP.
Please post performance when you can - and your prop info.

45.6 was the best we saw all day. cav plate is to low at cruise and WOT so once I raise the motor up a notch there should be more in it

The motor is super sensitive to trim. I can control the speed plus or minus 4 mph with just a quick flick of the trim switch at wot every time I trimmed up, you could feel the boat surge forward.

It gets up on plane very quickly. I didn't time it but I will next time out. Minimum plane speed was 14 mph.

So far in am very happy with my decision for this motor over the zuke 140

On my Hydrasports I pick up about 4mph by trimming up too. It is fastest a few degrees before it starts cavitating. That’s also my best fuel economy (I guess less motor in the water = less drag). I would bet that raising the motor would make the boat a little less sensitive to trim angle but I don’t think what you are saying is all that abnormal.
What is your prop?

My grady hardly responds to trim at all. I'll have to get used to that.

Prop is a powertech ras3 14.25 x 21 pitch SS 3 blade

Those numbers sound great! That prop is interesting, too. iirc that is PTProp's Rapture clone. Im sure my my 115 tower of power could never spin that prop or any other 14.25 x 21. If that has an excellent holeshot, I think your onto something here. How did your mph @ rpms work out, were you able to manage constant speeds at specific rpms? Where was your anti cav plate relative to keel on these runs?

Comfortable cruise was around 3600rpm running 28-29 mph trimmed out. I'll get a full rpm breakdown next time out. It planes quicker than my grady so to me it feels fast, but that ain't saying much. I'm sure it would be much faster with lower pitch or a 4 blade

On merc performance reports, this motor seemed to perform best with an Enertia prop. I found some threads where my prop was compared to an Enertia on other setups and it was just off the Enertia numbers. So I had an opportunity to pick up this prop used and jumped on it

Constant speeds where easy if you don't mess with trim.

Cav plate iis 2 inches above keel, bracket is 24" setback. It need to go up another hole but the 4 Bolt holes on the motor are just that, holes. The bottoms aren't slotted which means I need a cherry picker to lift it, which is 1.5 hours away in storage so it's not gonna happen any time soon

More to come

I'd forgot you had the bracket, regardless very impressive numbers. I'll guess your motor can still go up a notch or 2. Nice details on report. Were you able to reach max rpm target?

Max rpm for this engine is 6k. Best I could manage was 5600. I'm not the type of guy to take an engine to its max rpm anyway

once I raise the engine up a hole, do you think the rpm will increase at wot?

Anyone in st. Pete with a cherry picker?

Yeah, you should see a bit more rpm if you raise it a notch or 2.
Hopefully you gain as much as 400 rpm so the motor is able to reach max rpms with your regular load. Look forward to more news.

Had it out for 2 hours today. I couldn't set any speed records as it was to rough and windy. I did get some cruise numbers though

On plane in about 2 - 2.5 seconds. This isn't accurate I found it hard to time as with the motor trimmed down to start, and trimming up with throttle the boat stays very flat in the water, hardly any bow rise.

On plane at 3k rpm, 15 mph

3200 rpm - 22.8mph trimmed out
3500 rpm - 24 mph
4000 rpm - 29 mph
4500 rpm - 34 mph
5000 rpm - 39.7 mph
5200 rpm - 41.9 mph

It starts to chine walk going 40 into a headwind And a little chop gets it going

That's as fast as i could take it with conditions. I'm impressed on how it handled it though.

The boat has no tabs by the way. I don't think I'll need them though as I can control it with trim

No fuel numbers as i haven't networked the motor to my a67 through the nmea2000 port yet.

Btw i just noticed there is no anode trim tab behind the prop. there is an anode, just no tab. The only time I've seen this is on twin counter rotating setups

Only lists on plane I've noticed are on Cross winds, but may be because of no tab? I'll have to contact mercury on Monday

Those are good numbers, I am getting similar performance out of my 1994 mercury 150 2.0l with alot more fuel burn of course. This new mercury 115 CT will be on the top of my list when I re power. Thanks for sharing!!

It sounds like this motor has power aplenty and I cant help but think that properly positioned torque tab would benefit tracking. They are surprisingly sensitive.

Hit 46.1 today just me and 39 gallons of gas and some tackle and fishing Rods. Feels good being on the water on a 43 year old boat. Gets a lots of compliments that's for sure