Another Mercury Question

[dirtchickn]

I am trying to figure out what the OEM pitch is on my 1998 2 stroke 1998 outboard. Also, I am trying to figure out if changing the pitch will affect the "power" of the prop. I have no concern about "top speed" I want "pushing power." I have it installed on a 26'' Columbia and hate running it at or near full throttle. I guess that really means, can I change the prop and get the same or more push at lower RPM''s?

I have tried the Mercury website, but they only have a prop selector for go fast boats.

Thanks.

Rich

[Yodagwb]

Top end speed loses low end power, low end power loses top end speed. Prop pitch is typically matched to allow the motor to operate at its optium rpms. Why not try taking the prop to a prop shop and talk to the guy, they can typically adjust the cups and pitch 1-2 degrees by repressing it.

If you are running it wide open I would venture to say you are concerned about top end speed

[dirtchickn]

Not necessarily. I just want to move my sailboat at a reasonable speed. I have no choice but to run at full throttle to move on windy days, hence the question about props. I am hoping to figure out a way to get more push at lower rpms. Maybe my logic is wrong, but shouldn''t that be better for the engine?

[RichH]

You want to be able to run at the maximum rpm so that you develop maximum horsepower when needed for ''emergencies'', etc. Running under heavy load at reduced rpm will result in rapid engine wear --- especially the piston wrist-pins and piston rings/cylinder walls. If the hydrostatic clearances in the bearing journals have already become worn you tend to risk ''crashing'' the crankshaft journals against the bearings due to the ''extreme'' cylinder pressure that the oil (pressure) in the bearings have to support. A ''lugging'' engine is prone to ''blow'' head gaskets frequently (and sometimes bending a crankshaft). Running at high load and low rpm is called ''lugging'' ---- Not good for the engine. Look at the "power curve" for your engine: rpm vs. developed horsepower.
F
or long life at your ''normal cruising'' speed try to obtain 75% - 80% of max rpm by adjusting pitch, etc. of the prop --- that will leave an extra 20-25% rpm for ''emergency'' conditions (huge chop, windblown, etc.). If you cant obtain maximum rpm or cant come ''close'' to maximum rpm with your current prop, this indicates that you should consider to ''re-pitch'' the prop so that you can.

A diesel''s ''clearances'' are usually set-up for ~75% of max. rpm to gain maximum service life; running on either side of that value will usually result in shorter service life.
;-)

[Yodagwb]

Two stroke motors are designed to run at high rpm''s, un like 4 stroke. Prolong low rpm operation in a two stroke is not good for it. If you contact merc they can probably tell you what the optium or top rpm operation is, and then if necessary adjust the prop to achieve that target. If your boat is not able to achieve a reasonable operating speed given the proper engine rpm''s your dealing with a under power issue, in which case no prop in the world is going to correct that.

[dirtchickn]

And that''s is unfortunately the problem. I have 8 hp to push 5800 lbs. I get where I want (in and out of the marina) by motorsailiing mostly. I have the advantage (and diasadvantage) of being in a really protected marina. Unfortunately, I cannot ever sail in or out, but by leaving the main up and motoring I catch every last little bit available, hopefully making life easier on the engine. I worry b/c I have really shallow water (the seagulls stand on the bottom)on either side of a 1000 yard channel. Should the motor die, I''m going aground.

I am trying to figure out, short of replacing the outboard, if anything can be done outside of the factory prop to make life better.

[geohan]

If you can''t find a satisfactory fix,have a stern anchor ready to deploy in an instant.