Heavy loads and a 28hp johnson

[quackaddict1]

Hello all, I have a newly refinished 16ft crestliner aluminum fishing boat and a 28hp Johnson motor to power it. It runs fine with two or three guys and a fishing load, planes fine with proper weight distribution and such.

My question has to deal with the boats second purpose, this rig will double as a portable hunting blind, I will enclose the boat with a hard sided blind and will likely have a heavy (but safe) load to run around with on the lakes we hunt. I have seen a great deal about props and have always wondered if a person should match the prop to the loads, ie having a smaller pitch for heavier loads to prevent motor lugging? Or is this not that big of an issue? I have no idea how many RPM's the motor turns with its current prop, which is from what I know factory original. Our average runs while hunting are probably 2-3 miles and we hunt around 4 days a week. Im not looking to win any speed races, the 28hp is the biggest motor we have had to work with, im more concerned with overall life and maintenance of the motor.

 

[steelespike]

Re: Heavy loads and a 28hp johnson

Can't really make any suggestions without present prop size,max rpm and speed.Prop is usually marked -- X -- ( diameter X pitch).Pitch is the key number.Motor should push that boat easily it does appear to be trimmed in too far but if it pushes best there go too it.It might get on plane slower trimmed out a little but may run faster.Also the antivent plate(just above the prop)should be even with the bottom of the boat and could be higher.
You can get rpm with a tiny tach ,reasonable,easy to install,and fits any 2 cylinder without regard to stator poles.

 

[jay_merrill]

Re: Heavy loads and a 28hp johnson

I agree in regard to the Tiny Tach. Putting one on the motor will enable you to make a decision about prop pitch, while without one, you are just guessing as to what pitch you need. If you buy the Tiny Tach, be sure to specify that it is to be used on a two cycle engine. You can also order the tach with a cable that is the correct length to run from your motor to your steering position. Tiny Tach claims that their product will not work correctly if you splice wire onto the leads to lengthen them.

 

[quackaddict1]

Re: Heavy loads and a 28hp johnson

steelspike, when you say trimmed in to far do you mean so the motor is actually pointing slightly downward? Its on the second to last hole, I need to take it to the lake and mess with that a bit, as it is we only run it to move from one spot to another, though it does seem to put it up on plane OK.

 

[quackaddict1]

Re: Heavy loads and a 28hp johnson

I went out and found the dimensions of the prop, its a 9 1/4 by 11, which from what I have seen is the upper end of the pitches available for this motor. I will have to look into a tach to see what the RPM's are doing, I had been looking into that sort of thing anyways. The vent plate runs about 1-1.25 inches below the bottom of the boat, a jack plate could possibly be needed? My main concern is will using the boat near the load capacity (1145lbs) lug the motor so badly as to create premature failure?

 

[steelespike]

Re: Heavy loads and a 28hp johnson

steelspike, when you say trimmed in to far do you mean so the motor is actually pointing slightly downward? Its on the second to last hole, I need to take it to the lake and mess with that a bit, as it is we only run it to move from one spot to another, though it does seem to put it up on plane OK.

Yes prop appears to be trimmed in to far towards the boat should plane easily but may tend to run too flat or even bow down.Play with it.It would be great if you could get the antivent plate even with the bottom of the boat.You can support the motor on a stick layed on the top of the transom.
Just be sure the clamps have a good grip and it pumps water.My boat has been set up like that since 1965.
Could gain 1 or 2 mph in ideal conditions.

 

[jay_merrill]

Re: Heavy loads and a 28hp johnson

I agree that you should play with motor trim to see if your performance improves, before spending money doing other things. If you decide that you need to lift the motor a bit, a jack plate is certainly a possibility but you may find that having a local welding shop fashion a fixed plate that bolts onto your transom, to be less expensive.

Beyond those two things, prop choice becomes something to look at. I just took a look at prop availability for your motor on www.shop.evinrude.com. Although you didn't state the exact model year of your Johnson, it looks like there are props available for it ranging from 7" of pitch to 13" of pitch. That should give you adequate "room" on either side of your current, 11" pitch prop do fit almost any load range for your boat.

 

[quackaddict1]

Re: Heavy loads and a 28hp johnson

Thanks for the replies guys, I have another hole in the motor mounts that will get me about an inch, I will move the motor up into these holes and make a spacer for the motor to sit on. I will also play around with trim next time out to see what hole works the best. I ordered a tiny tach as well, at the very least I can see what kinds of RPM's the motor is turning and get a better idea of whats going on.

 

[steelespike]

Re: Heavy loads and a 28hp johnson

A tach and gps will really tell you how good your setup is.
Boat looks good.

 

[mickjetblue]

Re: Heavy loads and a 28hp johnson

I'd occasionally check the water temp coming out of the motor, by hand.
If it's hotter when you are running with an increased load, then you are
working it harder. You could be pushing it to premature wear with a heavy load.

Actually, I did that with an older Johnson when I towed a bigger boat that
was having motor trouble. They're good motors, but should not be over loaded.

Good luck!