How much difference would a 70hp to 115hp make

[zosoo7]

I bought my first boat this past summer, and have had it for 1/2 of a season. It is an aluminum 17 Sea Nymph FM170 with a 70 hp Evinrude. It planes out, but it takes a little while and seems like the power is sluggish while it's trying. Would upgrading to a 115hp motor help this? Also, any idea how much difference in speed it make? Right now, it does anywhere from 32 to 35 mph according to the speedometer. Thanks.

 

[tashasdaddy]

Re: How much difference would a 70hp to 115hp make

you are adding 50% more power, it will jump up. speed 45-50, set us correctly.

is the boat rated for the 115hp???

 

[zosoo7]

Re: How much difference would a 70hp to 115hp make

It's rated for 120 hp. Do you think it would help with the planeing? Or is that another issue? Thanks.

 

[jevery]

Re: How much difference would a 70hp to 115hp make

My 17 ft aluminum Crestliner with 115 Merc 4-stroke ran 45 loaded. It will plane much faster.

 

[tashasdaddy]

Re: How much difference would a 70hp to 115hp make

set up correctly it will make a big difference. you presently are below the minimum hp for that boat, to perform. the rule of thumb is minimum is 30% less than rated, that would be an 85 hp minimum.

 

[JB]

Re: How much difference would a 70hp to 115hp make

What daddy said, zosoo

If you used a carbed JohnnyRude 115 60* V4 it would leap out of the water and go like stink. A 4 stroke or DFI 2 stroke would come close.

 

[pine island fred]

Re: How much difference would a 70hp to 115hp make

Your post caught my eye as I figured 70 hp. on an alum. boat should be sufficient. My only experience with alum. was a 14 ft. sears that moved well with 15 hp. Searched on the web and it looks like that boat weighs 1180 lbs. Where does all that weight come from? Could that be with the motor?
My point in commenting is just how much speed do you want? Sound like you are going fast enough but what do I know. Personally I made the mistake of overpowering 2 boats, 50 on a 16 ft. and 115 on an 18. The power is there but I never get the chance to use it. I can have 4 people plus lots of beer on the 16 ft. , be on plane at a comfortable speed and still not go WOT. A 115 if it would be a 4 stroke would be 400 lbs+. Do you want to carry around all that weight? Do you think you would really use all that power. Big motors look neat, you always wonder how it would perform on your boat. Certainally not trying to talk you out of maxing out your boat but try to take a ride in something with a 115 on the same size boat. If you do get the chance, the capt will naturally go WOT and you will be impressed with the speed but think about how comfortable passengers would be. I can tell you right now, the passengers would be smiling and wishing you would slow down at the same time. Only one who enjoys going full bore is the driver, the rest on board are happy when you slow down. I am not preaching, just suggesting you give your 70 hp. motor a chance, maby try to eliminate any excess weight you might be carrying around. regards FRED

 

[Benny1963]

Re: How much difference would a 70hp to 115hp make

the 70 s are strong motors then when you figure the weight diff to 4cyls .
IS YOUR MOTOR RUNNING ON ALL THREE i have run a 16ft cajun with 76 85 evin 4cyl loaded it came up on plane and ran 45 to 47 gps
make sure your motor is running right and that motor height is right
and check wot
good luck as far as overpowering goes everyone has there opinions
im currently running a 150 6cyl on a 17 ft mckeecraft , but tore powerhead up and the best deal i could get was a 175 powerhead so know i will be running a175 crossflow on my mid .it a little heavy but my boat is a mckee
and they have the ability to float larger motors compared to metal boats
good luck bennyb

 

[Silvertip]

Re: How much difference would a 70hp to 115hp make

You have not indicated what the wide open throttle RPM is with an average load. If the engine is not reaching 5500 - 5800 rpm you have one of three situations: 1) Prop with too much pitch, 2) Engine in need of tune up or down on compression, 3) Engine setup is incorrect for the prop and the boat. I have a 17 foot Alumacraft with a 75 Merc and it has no trouble popping the boat on plane and it would run at 40 MPH. My boat is a little lighter than yours but not by much. Call it one less person in the boat. All of this aside, you are marginally powered if the boat can take a 120HP motor.

 

[steelespike]

Re: How much difference would a 70hp to 115hp make

As suggested by Silvertip a solution to better performance could be as simple as setup.Followed by careful prop selection.Max rpm and speed with your prop size will give us an idea where your at.
Your under powered but you could at least get the max from your setup.
cost a lot less than a motor,possibly nothing but time.
Your 70 is about 260 lbs an Etec 90 is 320 lbs a 115 about 370.
other brands probably a little more.Depending on actual displacement.

 

[Mkos1980]

Re: How much difference would a 70hp to 115hp make

We had an 83 Rinker 17FT Fiberglass bowrider which had a Grey 1982 70 Evinrude. It planed very quickly but was not super fast. About 30-35, which was fast enough for us at that time. It was a very strong motor and we never had any problems with it.

 

[zosoo7]

Re: How much difference would a 70hp to 115hp make

Thank you all for your responses. My motor does run at around 5800 RPMS WOT. I'm not really concerned about going any faster, but I'm not very satisfied with it's performance of getting out of the hole. I believe the motor is set up correctly. Would a different prop potentially help/fix this? I don't know the prop size right now, as the boat is away getting new carpet. The boat appears to be built pretty solid which may attribute to it's weight and ability to be rated for 120 hp motor. I've had instances where the water was a little rough and I couldn't couldn't get it on plane even with the 70hp motor. Thanks again.

 

[Holycow]

Re: How much difference would a 70hp to 115hp make

Howdy,
From what I've been reading you might try some of those self adjusting "Smart Tab" things. The cost would be much less than another engine and are made to solve the exact problem you are having. Some one out there who has them might give you better info.. but it sounds good to me.
--Jeff