How hard can ya run 'er?

[waterinthefuel]

I have my trusty 1993 Johnson 28 and it's hardly ever missed a lick since bought new in 1995. My question is this.....the speed (or rpm) that I had been running my boat at cruise yielded me a decent cruise speed. Since I don't have a tach, I just go by "feel." Well, one day I decided to increase the RPM a bit, how much, I don't know. But after I pushed down a tad harder on the throttle the front of the boat came down a bit and the ride got smoother and faster. A small increase in power yielded a fairly decent increase in speed. I know I was on plane before, but maybe I wasn't going fast enough for my Stingray ventilation plate thingy to actually work.

So.....since I have no tach and showering down on it even from that increased cruise speed yields enough "umph" to knock over coffee thermoses in the bottom of the boat....am I hurting it running it that hard? My dad says no and that those little engines were bulletproof. I want it to last me a long time, as it already has and runs and looks new. I just don't want to harm my engine running from non-productive fishing hole to non-productive fishing hole.

I've GPS'ed it and my old cruise speed was 15, new is 20, wide open is 27. Hey, don't laugh, I only have 28 ponies!

 

[1730V]

Re: How hard can ya run 'er?

Your dad is right, they are bulletproof. But. You can probably get your boat to plane better at a better attitude if you make some minor adjustments.

Run the engine one hole lower on the trim, if you can. Your engine has a trim pin that runs side to side in the mounting bracket. Move some weight forward. Such as putting a longer hose on your gas tank.

I'm not a fan of hydofoils. They add a lot of drag and can cause quirky handling. If I were you, I'd try the rig out without it. You can always bolt it back on.

 

[waterinthefuel]

Re: How hard can ya run 'er?

It's funny you say to move weight forward, as the last time I asked a question (not this one) about my boat I was told to maximize the speed I needed to move as much weight back as I can and trim the motor up. This boat is a stick steer, so I sit way up front.

Not sure if that would affect your answer.

And you are right about the hydrofoil. I did not used to have one. But it seemed that when I did it picked up the back of the boat and made it run flatter.

For those of you not familiar with a 28, it's just a 30hp powerhead de-tuned slightly with a non-flow thru hub. It also doesn't have oil injection.

 

[1730V]

Re: How hard can ya run 'er?

My answer was pretty generic not knowing your set up. You're right, the 28 does not have the flo-thru hub so moving it up is a trial by error process.

You can only run so flat until you start to dig the bow in. That can be scary.

I think I'd still paly around with it without the foil. They do cause quite a bit of drag.

 

[wbeaton]

Re: How hard can ya run 'er?

I don't understand your problem. Running at WOT is not what I'd call running the engine hard unless you are over-reving the engine, which you probably aren't since you didn't mention your prop. I assume it just has the standard all-purpose prop OMC puts on those motors. If your WOT speed is 27mph then 20mph is probably a fine cruising speed. I normally run my motors at WOT unless I'm trolling. The purpose of cruising is more about economy than engine life.

 

[Silvertip]

Re: How hard can ya run 'er?

Ahhhh - the old "economy" vs "speed" thing rears its head again. Although the engine burns less fuel at cruise than it does wide open, to get where you are going at cruise speed requires that you run for a longer period of time to get where you are going so there is very little difference in the amount of fuel burned. Run it wide open unless you are not in a hurry to get anywhere. Constant slow speed operation without a periodic high speed run causes a two stroke to develop carbon build up.

 

[dajohnson53]

Re: How hard can ya run 'er?

...

I've GPS'ed it and my old cruise speed was 15, new is 20, wide open is 27. Hey, don't laugh, I only have 28 ponies!

First, if you're running at ~20 mph and your top end is 27, you're most likely well within a normal cruising RPMs for a 2 stroke. It's very common to cruise at about 70-80% of wide open. So don't worry about that, it's what the engine was designed for.

Second, for fun, take your GPS and a couple of full tanks of gas and compare MILEAGE (MPG) going your old speed vs. your new sweet spot (i.e. ~15 vs. ~20). Heck for fun, do another test at wide open. You'll need to do something like a 30 minute trial at each speed, measuring distance and fuel used. This would be easy with a GPS and a full tank, or an accurate dipping stick for your tanks.

I have a very strong suspicion that you are not only going faster and smoother at your new sweet spot, but your MPG is probably quite a bit better. I know that my best MPG is at about 75-80% of wide open. I burn gas faster, but I get much further.

Good luck, I'd be interested in hearing what you find out.

 

[waterinthefuel]

Re: How hard can ya run 'er?

Fantastic idea, it may be a while before I have enough time to do all three trials, but your idea is really good!

 

[steelespike]

Re: How hard can ya run 'er?

Your speed is pretty good.But a stock 18 is good for 27 under ideal conditions.
Of course your speed depends on what type boat your running.If you are indeed sitting way up front you may want to consider moving back to at least the first seat ahead of the stern seat.It will make it easier to get the bow free of the water.It also may feel smoother for you.Less vertical movement than at the bow.For speed you want as little in the water as possible.For now lose the fin.and work on fine tuning your setup.Raise the motor vertically 1/4 in. at a time until just before venting becomes a problem.Be sure clamps have a good grip and that it pumps water.If you can gain an inch you might get 2 mph or more
On my 18ft Crestliner bare bones utility(275lb hull weight) w a 50 rude tiller when I want to really go I move the tank back to the transom and I slide back against the transom.It really lightens things up.Bow really rears on hole shot but its kind of fun.It still lays a little flat but if I trim out one more hole she bounces.I may try a wedge and see if it works with half a notch.
Sure not the best setup for rough running.