Engine needs replacement. I troll 90% of the time. Can I go underpowered?

[chevegan]

Look I have a 1994 sunbird and the 115 evinrude runs like crap and has failed a leak down test. I seldom care about going over 15mph. Just want to fish and chill out. It's a 17' boat that weighs 1300lbs. Can't I go way smaller with a steeper pitch prob and just relax?? And all the while get better mpg?

 

[Texasmark]

"smaller with a steeper pitched prop?" Wrong direction.

If you drop the HP you need to drop the load on the engine and to do that you reduce pitch. 15 mph isn't on plane or if so, water is barely leaving the back of the transom; big wake, bow up in the air thing...of which you are well aware I'm sure.

Half the HP probably would do that for you and you'd have to play around to get the right prop which would be top end of the mfgr. suggested max operating range. Best bet there is to get with a prop shop and borrow till you get it right. Costs more but in the long run it's cheaper than shotgunning props and hoping for the best.

The Merc 2+2 is a 4 cylinder 2 stroke engine that runs on 2 cylinders at lower rpms which is made for trolling. It's basically 2 alternate firing (180 degrees apart) engines stacked on top of each other with their relationship to each other out by 90 degrees. Makes for a really smooth troller and smooth, quiet running engine. Owners of 4 stroke engines that do a lot of trolling in Northern Climates speak (on here) of crankcase oil accumulating condensation, causing the oil level to rise and subsequent draining and refilling required......google the term and read for yourself. 2 stroke won't have that problem.

Just for grins, the last time I was out I GPS checked the speed at idle and it was 3.5 MPH, calm water, no current, stock engine, no gadgets attached to the engine nor boat.

If you find one in the 115 hp size, like the 2002 I recently purchased on a 17 1/2' Crestliner, you have the best of trolling and when you are ready to get, it'll get. Gearbox would be 2:1 which is (I think) the same as the OMC ratio for that engine so you could run the same prop with a different hub....Merc uses the 15 toothed spline. I know OMC is different but know not the number of teeth.

 

[JimS123]

A friend of mine has a similar boat and a similar usage. He runs a 15 HP Evinrude 2-stroke and it suits him fine. His boat is rated for a 115.

However, in his case there is no current and he can troll up and down and still get back to his dock on time.

You need to realize that a trolling motor may not do the job of one with reasonable HP.

For yours I would suggest a 25 HP minimum, with prop pitched to get WOT at specs.

 

[jimmbo]

You really need a different kind of boat, a Displacement Hull, which cuts thru the water using much less power, instead of a Planing Hull, which is not efficient until on top of the water, planing. At 15 mph a planing hull is at about its worst for inefficiency and even a smaller engine is not going to be an Economy champ at that speed. Only after the Planing Hull is on plane, does fuel economy improve

 

[Scott Danforth]

Can't I go way smaller with a steeper pitch prob and just relax?? And all the while get better mpg?

No, going steeper on pitch while going less hp will simply lug the motor and kill it.

lugging the motor actually burns more fuel

no such thing as fuel economy in a boat unless you have wind blowing in the sails or slaves rowing the oars.

 

[JimS123]

slaves rowing the oars.

I tried that and it worked twice. After than the wife and kids simply refused to comply.

 

[roffey]

I tried that and it worked twice. After than the wife and kids simply refused to comply.

How about the girlfriend? Now that you know the wife and kids wont go you should be golden...

 

[ahicks]

Back to the question at hand, I think I would want at least enough power to get the boat on plane, even if that rarely happened. A 3 cylinder 60-70 horse should do that without a lot of trouble.

 

[roffey]

I would go with as big a motor as your pocket book will allow... several times this summer I had to out run storms and was a few miles from home, the extra horse power was nice to have. Hard to say for sure but I would think anything over a 50hp would her her up on plane?

 

[chevegan]

Shouldn't the correct pitch prop on most 50-70hp motors get me on plane fine since the correct torque would be transferred? And I realized I said steep, my mistake. I'm a car guy and always think lower gearing to transfer torque . Really money is the issue. I don't want to spend 3-4.5k on a second hand 90-115hp especially since I go WOT maybe once out and once back to a fishing spot if I'm not trolling the entire route. 20-30mph is way more than I would need here in Colorado springs. The deeper v hulls are a must with the wind driven waves we get. Plus of course fuel sipping of a smaller motor at idle speeds

 

[roffey]

IMHO, 50-70 would get you on plane... if your happy with it, then its all good. I love being out on the water and any boat will do...

 

[JimS123]

I don't think you can have it both ways. If you buy a cheaper 2-stroke that is good enough to get you on plane, then its performance trolling will be a problem. If you go 4-stroke then you're at a price you don't want to spend.

To meet your cost and usage requirements I think your original idea is the most practical. You WILL need a new prop so the motor doesn't lug.

 

[JimS123]

IMHO, 50-70 would get you on plane... if your happy with it, then its all good. I love being out on the water and any boat will do...

A correctly propped 40 (special prop) would do it. But then again he says he wants to troll. Why is everyone telling him he wants to plane?

 

[roffey]

JimS123 The OP asked..... "Shouldn't the correct pitch prop on most 50-70hp motors get me on plane fine since the correct torque would be transferred?"

If all you want to do is troll than almost any motor would do that.

 

[chevegan]

Thanks, yes 90% trolling. But we do get storms here so getting on plane to get home is the 10% of the time.

 

[82rude]

My brother has a 94 sunbird with a 2003 Yamaha 115 4 stroke on it.Off the top of my head I believe rating is 130hp.If it was me making your choice id stay at around 90 min but because im prejudiced towards etec id go newer Evinrude etec 90 and up preferably 115 H.O.

 

[Texasmark]

Thanks, yes 90% trolling. But we do get storms here so getting on plane to get home is the 10% of the time.

If you ever had a "squall" pop up unexpectedly and didn't make it in before it whacked you, you'd keep your WOT HP. BTDT more than once and didn't like it....but that was back when I couldn't afford to pay attention! Later in life I was able to see it coming and could afford to pay attention and had the equipment to outrun it.....much better!