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huey42

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"Hello! A Mariner 30E Model 68

"Hello! A Mariner 30E Model 689-S-107165 what year is it ? and what type propeller is good for 300-500lb. alum 15' fishing boat(Elda craft 1978)?
Thanks, Hugh"
 
"An anode in the context of ou

"An anode in the context of outboards usually refers to a small piece of zinc bolted onto the lower unit, somewhere near the propeller. The zinc is intentionally allowed to corrode, thus keeping the outboard itself from corroding.

So yes, it's something you definitely need! Sacrificial anodes need to be replaced if they are more than half eaten away by corrosion - this mostly occurs if you run in salt water. Also, make sure it isn't painted over or it won't do its job. And if it's not there at all, do fit a new one ASAP.

Not sure of your engine, but on some makes and models the adjustable trim tab on the lower unit also doubles as a sacrificial anode."
 
Thanks again your a great help

Thanks again your a great help! I will try and
find one. Hope they still make them for 1985
30 hp mariner? It mite be to old.
 
"I think it should be availabl

"I think it should be available through any number of local or online dealers, either as an original part or an equivalent from another manufacturer. These high-demand parts are usually stocked quite well, and your engine is not that old after all.

Just take your engine serial number to your local Merc dealer or try surfing the parts lookup systems at online dealers (such as this site) to locate the right part and you should find what you're looking for.

Good luck & happy boating!"
 
"I ordered a manual for the mo

"I ordered a manual for the motor and am waiting for it to arrive. All your help, suggestions and advice are greatly appreciated! I need to look for the serial number. MANY, MANY THANKS!"
 
"Umm... that [i]is[/i] the ser

"Umm... that is the serial number: 689-S-107165
wink.gif


By the way, the original question about the prop is a bit more complicated. Someone on the forum with a very similar motor/boat combination might be able to give some suggestions, but mostly it's just a question of testing how your particular rig runs. So there is no 100% "correct" answer as to what is the best prop for a given boat.

As far as I've understood it, here is the basic procedure:

1. Once your motor is set up and tuned properly, load up your boat with the approximate amount of people/weight you expect to have onboard.

2. Run it at full throttle and see what your maximum RPM is. For this, you need a tachometer (tach) - if the boat doesn't have one, you can hook up something called a Tiny-Tach, it's very simple and easy to use.

3. Compare your maximum RPM to the specification in your manual for your engine (usualy about 6000 RPM). The optimum is when you just reach that figure with wide open throttle. That means you're getting the most power out of your engine.

4. If you're achieving significantly less than the specified max RPM, you need a propeller with a lower pitch (shallower "screw angle" of the blades). If you're going a lot over the max RPM figure, that's not good for the engine either, so you need a higher-pitch prop.

Note that the RPM you get (and thus the ideal prop) will vary a lot depending on the weight load you have in your boat. For example, on my 13-footer (pictured), I usually run a 9" pitch prop, but switch to a 6" pitch on fishing trips with 2 people, heavy camping gear, extra fuel etc.

Propeller selection is an endlessly complex topic that can encompass a ton of other factors but for smaller outboards the prop pitch is the most significant variable as I understand it.

There are plenty of decent articles on prop selection you can find by googling, for example this one: http://www.evinrude-parts.com/boat_propeller_selection_article.html

"Prop selector" calculators such as this one may or may not be useful... personally I've yet to get any sensible info out of these but might be worth a try: https://appcenter.mercurymarine.com/propSelector/home.do"
 
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