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I asked this over at the E-TEC owner's forum, but thought I'd also ask here.

As I've noted in other posts, I have a 2010 E-TEC 30 mounted on a 1969 13-foot Boston Whaler. The engine is a longshaft, and to prepare for its mounting I installed the Kentfab Transdapter to raise and strengthen the Whaler transom.

Delivery documents from the the dealer note a WOT RPM of 5750 for the standard 10.3 x 12 prop (with just the technician aboard). As he handed me the key the dealer said that the "engine really moved the boat along and threw quite a roostertail." When I got home the reason for the latter was pretty obvious: the AV plate was about two inches BELOW the hull line.

The mounting of the 30 only allows you to go one hole up (the top mounting is thumb screws) so I eventually had to order a jack plate and mount the engine on that. I finally have it at a height that seems right for the way the boat is used: almost exclusively on lakes pulling kids on tubes/waterskis, and some fishing.

I should also note that the dealer did not install a tachometer (or a System Check gauge!--telling me it wasn't needed; you might understand why I won't go back to that dealer!). I finally just rectified both, and now see that with the engine higher up the WOT RPM is about 6100/6200. I think it's fairly accurate, since when going downwind the other day with just me aboard testing WOT I hit the RPM limiter when the tach indicated about 6300.

So, question is, what is the right prop for me? On the one hand, it is my understanding that if RPM is too high in range I should increase pitch, but if I need more torque for pulling then I shoud reduce pitch. Is that correct? Maybe the prop I have is fine, I just should be careful for WOT when riding alone?

In response to my post at E-TEC someone recommended the following prop as a possibility: http://www.go2marine.com/search.do?q=2231-101-13

John K.

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Despite what Evinrude's "standard" answer is regarding the optimum RPM, I always try to prop my boats so that the RPMs at WOT are right at the top of the recommended range (6000 in your case) when carrying a light load. This gives you the most flexibility with varying loads and should give you adequate performance out of the hole. Sounds like a 13P might be just the ticket.

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I think the prop you have sounds just about right, based on your description of the intended use. For skiing and tubing, you're going to want the extra pull, and for fishing, you're not going to be running WOT anyway. If you want to squeeze out an extra MPH or two, you could go up in pitch, but I'd be inclined to run what you have for a while and see if you really have that need for speed. One of the nice things about the 13 is the passenger capacity and your current prop will allow you to carry lots of people (or a big cooler and lots of fish!) without strain.

Tim

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The E-TEC 30 has a WOT range of 5000-6000 RPM but its Optimum RPM Range is 5400-5800 so if you are hitting 6300 RPM you are grossly underpropped and need a new propeller.

You should try to get your WOT RPM down to 5800 and that is 500 RPM less than what you are getting now. You will probably have to increase pitch by two inches to achieve this.

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What brand of prop do you have now?

It is well known that the same size prop from two different manufacturers will often lead to different results.

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The prop on the motor is aluminum, and I think it's a stock Evinrude part, but will check to see if there is a manufaturer's ID on it.

And yes, it is my understanding that target RPM is 5800.

Thanks for the input.

John K.

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30 hp is not a lot of hp to pull a skier.You may find that when pulling a skier that the engine's top rpm is around 5800. However you should get a higher pitch prop for normal use. Put the 12" pitch prop on it for tubing and sking and keep the higher pitch prop on it when the kids are racing everybody in sight like I did as a kid. Good luck

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The only identifier on the prop, apart from the size, is #177249, which seems to be a standard Evinrude prop.

30 hp is plenty for my current needs as my kids are still 13 and under, so there's a few years of skiing left with this boat!

John K.

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IMO, a 13P will put you at 5800-5900; a 14P will put you 5400 (5500 if you're lucky). A one-inch change in pitch makes a bigger difference in the lower pitches. Simple math: 1" div by 12" is more than 1" div by 19" (58% more, in fact). Assuming you're reaching 6300 with a very light load, I'd go with the 13P. The 14P will make your boat a DOG. All this assumes you'll be using the same make/model of prop, which may or may not be the best choice.

I'm sure others will disagree.

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Well, I took the chance on the 14p, getting a Solas stainless steel. RPM is now down around 57-5800 indicated on the tach, and top end to about 32 mph. Maybe another second or two to plane, but I couldn't swear by it. Not a dog at all.

John K.

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A rule of thumb is about 200 RPM difference in 1 inch of pitch if using the same or equivalent brand of prop.

Therefore, you moved 2 inches in pitch and your RPM's went down by about 400 RPM which is now in the correct range for your engine.

Glad you got it dialed in.

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This rule of thumb doesn't work so well with lower pitched props. That's they are offered in 1 inch increments. His RPM's actually went down by 500-600 RPM with the 2" change, plus he changed prop brands and went to stainless steel. I still believe his RPMs would have been too low with the same prop in a 14P. 6300 rpm X 12/14 = 5400 rpm. But the fact that the motor probably generates more HP at 5400 vs 6300 means it would squeeze out a few more rpms, maybe 5500. 5600 possibly, but I doubt it because propellers become more efficient (i.e. less slip) as the pitch goes up. Even if it did reach 5600, that would have been a 700 rpm difference for 2 inches of pitch.

Anyway, I'm glad it worked out regardless so you didn't waste money on the new prop.

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There is no brand identifier on the prop I took off, so it was a bit of a crap shoot anyway. When I get the time I'm going to make sure I have an accurate tach (which means, I think, that I have to hook up a laptop to my E-TEC?) and then test again.

John K.

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Ric232,

I am going by what he stated in his first and #10 post...

#1 post stated 6100/6200 RPM WOT
#10 post stated he had 5700/5800 RPM with the new prop

The way I added that up is 400 RPM difference.

So, I am standing by the "Rule of Thumb" which is ABOUT 200 RPM difference with 1 inch of pitch change.
DISCLAIMER: This is only a rough estimate as there are many other variables. However, this gives a starting place on what to expect from a 1 inch change in pitch using the same brand or equivalent style prop.