motor size

[olddawg]

I am brand new here and hope to do this correctly.

I have an older 18 ft Starcraft, probably 70's, Aluminum V-hull. It currently has an 80's 80 hp Mercury on it that is giving me constant problems.

I'm looking to replace it and have something reliable on it.

Capacity plate says 115hp max.
8 persons @ 150lbs
2040lbs total weight

I fish in this and do some tooling around when wifey is in the boat.
I don't see needing to pull skiers, but do need the power to get in the mouth of the Merrimack River if caught out there on a bad day.
Yes, I'm a saltwater fisherman.

Mostly I'm trolling. Up on plane to reach a destination (or run to a spot for wifey), but mostly trolling around, enjoying the time & sunshine. Typically, there's only myself and 1 other on board (it is only 18ft..).

I've seen deals on 60hp 4 strokes and 70hp 2 strokes and I'm thinking either could do the trick.

Would either do what I need?
Which would be better for my uses?

I am currently partial to the new Mercury's, but please do tell me if I should be looking at others.

Thank you in advance. Looking forward to your advise!

 

[tashasdaddy]

Re: motor size

for reasonalbe performance, the rule of thumb is minimum, is 70% of the rated hp. you need atleast 80 hp. the motors when the boat was built were rated at the head, instead of the prop. Newer motors are rated at the prop. so you could probably drop to a 70 hp 2cycle, remember there is a big weight difference, between 2 cycle and 4 cycle.

 

[olddawg]

Re: motor size

Thank you for your response.

I really didn't know if the 60 was too small and this is a good basis to good by.
I see a good buy on a 75hp and under sizing by 5hp will make that big of a difference?
Head to prop measurements.... equals out??

I still wonder if the newer motors are meant to run at troll for any distance.

I also have a 14ft Grumman with a 20hp on her. Trolls all day with no spits and sits up pretty when you ask.
Yes, it has got me through the mouth in some nasty stuff, but it wasn't pretty.... reason for going deeper hulled with a bit more power.

Is the 4 or 2 stroke better for this (not weighing in on the weight difference)?

I hoping not to put a kicker on.... otherwise, I'll just buy a kicker and let this one do it's thing. Run wide open.... It really likes that!

 

[coolguy147]

Re: motor size

2 stroke all the way man!!!!


u could go with a nice new aorund 70-90 fuel injected 2 stroke but i wouldnt go to max cause the newer motors r pretty heavy. or if u wnated to go with a nice 70-90 old 2 stroke aorund era of boat it might match it

 

[JB]

Re: motor size

I mostly agree with TD. You need 80 or more HP for satisfactory performance. I would not take an underpowered boat to sea.

An ETEC 90 is a good candidate, but I would put a 4 stroke on her. . .probably a Suzi or Yammy 115 (they weigh the same as the 90s).

Reason? 4 Strokes troll very well without loading up and are supremely user friendly.

 

[coolguy147]

Re: motor size

making oil!!!!!!

 

[JB]

Re: motor size

making oil!!!!!!

Hahaha Nice try, cool dude. Possible if not operated properly, but better than making smoke and stink.

 

[56 rude]

Re: motor size

Hahaha Nice try, cool dude. Possible if not operated properly, but better than making smoke and stink.

Well that does it!That darn 1982 90 rude has been making me look like a fool for years jb ,barely smokes atall ,trolls all day without a complaint ,why that sneeky no good 2-stoke,lol.It even has the nerve to not smell ,why that no-good

 

[tashasdaddy]

Re: motor size

56 rude, you have one that is tuned to perfection.

 

[56 rude]

Re: motor size

56 rude, you have one that is tuned to perfection.

yes it is ,sometimes i have lots of time on my hands so i play with the toys.ive found since ive gone strictly to syn oils and seafoam the oil or smoke production has almost ,almost dissapeared.now!my 39 evinrude is another story altogether!at about a pint for every gallon theirs no way to make that guy never smoke!

 

[olddawg]

Re: motor size

I've been talking to a few folks now and possible senerios.
Let me ask you.

The merc 80 runs great if run opened up, causes all sorts of problems at low rpms. I have thought of addind a kicker and keeping what I have. The thought of 2 motors just seems redundant to me.
I di own a 20hp Evenrude just loves to troll.
Is this too big to put on my boat as a kicker?
I'm thinking of weight and being off center....

 

[olddawg]

Re: motor size

I've been talking to a few folks now and possible scenarios.
Let me ask you.

The merc 80 runs great if run opened up, causes all sorts of problems at low rpms. I have thought of adding a kicker and keeping what I have. The thought of 2 motors just seems redundant to me.
I do own a 20hp Evenrude just loves to troll.
Is this too big to put on my boat as a kicker?
I'm thinking of weight and being off center....

 

[Tacklewasher]

Re: motor size

I've got a mid-70's 18' Starcraft Super Sport and it's rated for 150hp.

I've got a well set up 1980 115 Evinrude on it and get just shy of 40 mph.

It came with a 1978 70hp Johnson that would get it to 32 or so. Probably could have hit 35 with some work on setup etc. but had the 115 so I sold the 70. Plus the 70 did not have power trim and the 115 did.

I'm surprised yours is rated 115.

I have a mid 80's 10hp Honda 4 stroke for trolling. No way would I troll with the 115. Make too much of a mess and be a pain to troll slow.

How did the 80 perform on the boat?

If I was choosing between a 70 hp Johnyrude vs. and 85hp Johhnyrude, I'd take the 70 as it is a fair bit lighter etc. I'd expect close to the same performance and better economy.

But if the 80 is working as a main motor, I'd pick up a 5-10hp 4 stroke as a kicker. The old Honda's are great motors, run forever and take very little maintenance. Plus they are much nicer for trolling without the cloud of blue. My last little motor was a Johnson 9.9 and while it was a great motor, it always smoked some.

 

[jasonbailey]

Re: motor size

I'm in the middle of an engine upgrade myself. I have a 18.5' fiberglass tri-hull with just over a 6' beam. It had a 1984 75hp Chrysler on it. With 2 adults, 18 gallons of gas, couple of kids and a cooler it would run 37 MPH at WOT. Not too bad I suppose. Currently the boat is at the local Mercury dealer getting repowered with a 90HP two stroke. I would expect with the 90 it should break 40MPH. I looked at the 4 strokes, but the 2 was more in my budget. After enduring many smokey seasons with the Chrysler, I would expect the new 2 stroke to be much much better.

I went with Merc for a couple of reasons. First, it is built in the US. Second, the dealer is the local Whaler dealer and has a good reputation. I looked at the E-Tec's, but did not care for the dealer. The Yamaha dealer was cheaper than the Merc, but I decided to go American.

I would think a 90 on your rig should push it pretty good.