Does underpowering a boat cause problems?

[ward cleaver]

I have a 14' Fiberform and the 40hp Johnson needs work. So I am wondering what problems if any I will create by powering it with my 1963 18hp Evinrude. I just want to go fishing on some of the larger lakes around here, not pull any water skiers. I could use some advice from some experienced boaters on this.

 

[paultjohnson]

Re: Does underpowering a boat cause problems?

Ya might not be able too get on plane, but....Ya should be able to troll like a sumbch...

 

[metriccrescentwrench]

Re: Does underpowering a boat cause problems?

Well, you'll be limited to going slow, and slow isn't any fun. Plus, your ability to make a dash for safety in case of impending bad weather will be limited. Other than that, give it a try, it won't hurt anything (though you might find that the 18 is overpropped for that big of a boat, but you won't know that 'till you get on the water).

 

[JB]

Re: Does underpowering a boat cause problems?

I don't know if you would call them problems, Ward.

If the 18 won't plane your boat you will have to go slow and burn a huge amount of fuel.

If she will plane your boat you will save on fuel and have more money to spend on lures.

My guess is that it will plane, though you may need to go to a "short" pitch prop.

Good luck.

 

[ward cleaver]

Re: Does underpowering a boat cause problems?

I was actually mostly wondering about fuel consumption and load on the 18. So apparently I need to try to get on plane if I'm going more than a minute or two to a new spot in order to save fuel. That makes sense. And it won't hurt the 18 although I may not have the best prop for the job?

 

[JB]

Re: Does underpowering a boat cause problems?

Well, that isn't exactly true, Ward. Two strokes don't like to be run at full throttle unless they can get to optimum operating rpm. That requires the correct prop for the job at hand. Too little rpm is called "lugging" and can damage the engine.

Borrow a mini-tachometer and find out what rpm she turns when running wide open. If she will get over about 4500rpm (if I am wrong here, someone please correct me) you will be fine. Otherwise, take your facts and numbers to the Prop Forum and get advice about a substitute prop.

 

[ward cleaver]

Re: Does underpowering a boat cause problems?

Unfortunately none of my friends have a tach that I can borrow. How about this: if it planes it's not lugging. I assume this to be true because once it planes the load on the outboard is greatly reduced. Further, how about this: it's ok to motor along at a moderate speed (not planing) at less than WOT? But if it is shuddering etc under these conditions it probably is lugging.

 

[JB]

Re: Does underpowering a boat cause problems?

Yup. You got it.

 

[saumon]

Re: Does underpowering a boat cause problems?

Unfortunately none of my friends have a tach that I can borrow. How about this: if it planes it's not lugging. I assume this to be true because once it planes the load on the outboard is greatly reduced. Further, how about this: it's ok to motor along at a moderate speed (not planing) at less than WOT? But if it is shuddering etc under these conditions it probably is lugging.

Not exactly. Yes, you could ?step out the hole? and being on place with a reduced load but still lugging the engine. If you don't have the right prop, at startup when at WOT, as an example, you could be at 3500 rpm then at 4000 rpm when on plane and you're lugging it. It need to run at least over 5000 rpm.

You'll be able to cruise and run anyways, you'll just shorten the engine life...

 

[ward cleaver]

Re: Does underpowering a boat cause problems?

Since this is suppose to be a temporary solution until I can get a bigger outboard, I doubt I will put more than 5 (maybe 10) hours with this setup. And maybe I can clear out the soot/carbon deposits with some fuel stabilizer?

I looked for a low cost tach and the tiny-tach looks interesting. Any recommendations one way or the other on that?

Thanks for your help. It's times like this when I miss my Dad. He seemed to know everything about just about everything.

 

[saumon]

Re: Does underpowering a boat cause problems?

For a short period like that, you don't need to worry at all. Put it on the back and have fun. And yes, Tiny-tach is the preferred brand if you need a portable or add-on tach.

 

[ward cleaver]

Re: Does underpowering a boat cause problems?

Thing about the Tiny-tach is the non-replaceable battery. So it dies after 5 years. Sounds dumb to me.

I'm looking at the non-contact tachs. Anyone know if I'll be able to use that out on the water?

 

[ward cleaver]

Re: Does underpowering a boat cause problems?

My wife and I took the Fiberform out on the lake today - powered by the 18hp Evinrude. Unfortunately we were only able to get up to 8mph. The motor didnt shudder (very much) and sounded like it was running pretty good. It wasnt until we were on our way home that I realized I should have adjusted the trim to drive down the stern and raise the bow in an effort to get er on plane. So we decided its worth one more try. I hope that works. Otherwise I dont think this setup is going to work. Seems like we used a lot of gas for only one circuit around the lake.

 

[Home Cookin']

Re: Does underpowering a boat cause problems?

I grew up with an 18 evinrude on a 13' whaler. Learned to ski with it. Whole family went for boat rides and fishing in the bay. I was, however, a whole lot smaller!
I gues alone it would go about 20-25 mph

 

[Silver Eagle]

Re: Does underpowering a boat cause problems?

When I had my 320 hp I/O I always reved it up and kept the bow low .It got on plane much easier that way, trim the prop forward puts the nose down .You don't want the bow up,your wasting power and speed.With it up your pushing the water not cutting it.