Nissan 9.8 prop dilemma!

It's time to replace the prop on my Nissan 9.8. I am setting up my 14' Jon boat for river fishing here in Virginia. There are some rapids and rocks, so I want a prop that has some get up and go about it that will get me upstream. My choices are on ebay are a 3 and 4 bladed prop. I have no idea which pitch to use.

Tohatsu or Nissan 8 9 8HP Amita 4 H Thrust Alum Prop | eBay

Solas Prop Tohatsu Nissan 8 5'' 7'' Pitch 3 Blade RH 8HP thru 9 8HP 5011 085 07 | eBay

The boat is no speed demon, as it is somewhat heavy, but it's all I can afford to power it with right now.

I also want to protect this prop against rocks this time with some sort of cage or brace to keep it off the rocks.

ANY and ALL suggestions are appreciated!!

Thanks in advance!


jfire

Re: Nissan 9.8 prop dilemma!

What RPM does it turn now, and what prop is on it? Any dealer (including me) can help you with prop selection, but we need to know where to start. It's always a bit of trial and error. The prop guards are available, but they reduce top speed somewhat. You can drop me an email at the office: and we'll be happy to help you.

There are 2 different HT 4-blade props available. That 5 pitch may so shallow as to limit top speed, but it sure will accelerate well at low speeds.

Re: Nissan 9.8 prop dilemma!

Their web site lists a 8.5 X 9 for light loads and a 8.5 X 8 for moderate to heavy loads.

Re: Nissan 9.8 prop dilemma!

There are skeg guards. That offer some protection.
Also there was a post here years ago about smart tabs placed close to the motor helping resist venting and helping to get on plane
as well.These would allow getting the motor as high as possible.
You need to get weight forward possibly to an extreme for quick hole shot and less draught in the stern.
Eliminate as much weight as possible.Go to a 3 gallon tank,a 9.8 will run about 3 hours at wot on 3 gallons.
A styrofoam cooler instead of hard plastic, cans instead of bottles.A relatively light Danforth style anchor.
plastic paddles instead of wood.
A larger bare boat might run higher at speed and plane faster do to the bigger footprint.
If your boat is running close to capacity it may run deeper than the larger boat.

Re: Nissan 9.8 prop dilemma!

You still should determine your current WOT RPM. That will help you dial-in the correct prop. If you need to protect the prop, see For Your Outboards & Stern Drives - Prop Guard propeller guard but keep in mind that prop guards do slow the boat, because of the inherent drag.

Re: Nissan 9.8 prop dilemma!

Thanks for all the replies!
I'm not sure what RPM it's turning or how to determine it.
I know I definitely need a prop guard and plan on purchasing one.

The current 3 blade prop works well, but is chewed up from rocks. Maybe I'll just stick
with the stock prop.

jfire

Re: Nissan 9.8 prop dilemma!

Prop selection is always based on science, but there are so many variables that you must do on-water testing to dial-in the exactly-correct (best) prop. If you do not want to just blindly guess at the correct prop, you need a good tachometer. For a Tohatsu/Nissan 9.8A 4-stroke, you want to get near 6,000 WOT RPM. If you are below 5,000, you are lugging, and not making the motor's full potential. If you go above that, you are over-revving, and the motor's ESG will engage, staggering ignition, to prevent engine damage.

There is no magic wand. You will need to start with a reasonable prop, test it, and go from there. Every boat is different, even seemingly-identical boats, because of the way they are loaded, rigged, and used.

The stock-type 3-blade props tend to be good at speed. The 4-blade HT props are good for slow precision work. Still, actual pitch cannot be reasonably determined without testing.

Re: Nissan 9.8 prop dilemma!

Place an induction Hardline or Tiny Tach in your engine with stardard delivered prop, loaded as usual. Check max rpm achieved at wot and then can go from there selecting a less pitch prop if your current max rpm is way low. Can match a prop pitch that will give middle rpm readings, (5500 rpm) that's between min 5K & max 6K factory rpm parameters for good overall performance. One pitch up or down = 200/300 more or less rpm.

Happy Boating