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Hello All

just picked up an ETEC 75 for my 17 foot newport. It came with a 17 pitch SS prop (viper). Prop is kinda big in my opinion. She'll hit 38-39 mph on GPS at about 5,000 rpm. Dealer thinks that is good but gave me the option to switch to a 15 inch prop in a few weeks after engine "loosens up". I don't know what the pitch is.

These engines max at 4,500 to 5,500 rpm - so I am right there. Is it worth it to switch to the smaller prop? I suppose I would pick up some top end but not sure how else it would affect the boat.

Would appreciate any help.

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If you drop down in pitch you will loose top end speed generally but have a better hole shot.

Rules of thumb:
Higher pitch, better top end speed less hole shot
Lower pitch, better hole shot less top end speed

However, with any pitch prop you want to be within the recommended WOT speed like you are already.

Next thing to consider.
How high is your motor mounted?
All the way down? 2nd set of bolts holes? 3rd set of bolts holes?
It helps to know where you engine is mounted now.

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17" and 15" refer to the pitch of the prop. My questions is what is the Diameter of the prop(s) you are referring for?

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I'd like to make sure everyone gets this straight about props.
Please forget about the diameter of a prop.
It means nothing to anyone except the designers and engineers of the props.

We can't buy a prop by diameter.
We buy props by the pitch and brand for a particular motor or gearcase.

Here is just one example of the Viper prop in different pitches.
http://shop.evinrude.com/products/837...3718/Viper

All of the above props are the same diameter but again, who cares about the diameter.
We only have the choice of pitch.

If a 17 pitch prop from one manufacturer doesn't work out, maybe the same size pitch in another brand of prop will.

Again, don't even think about buying a prop by diameter. It really means nothing to most of us except maybe the racer who has props special made for high performance racing.

Sisslechest,
If you drop down to a 15 pitch Viper like you have now, you will gain about 400 RPM's at wide open throttle giving you about 5400 RPM at WOT...

Before doing that though, we still need to know how high your engine is mounted.
If your engine is lower than it should be, then raising the engine might also add 200 or so RPM's.
Let us know.

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Yes Joe I guess you are right Vipers are all the same diameter though, Sisslechest never stated he was for sure heading to another viper but we can assume.

Diameters these days do seem consistent in a specific model line but, some do have different diameters with the same pitch. The BRP/OMC SSTs come to mind in the 17" and 19" pitches.

# 177035 13 3/8" x 17"
# 176572 13 7/8" x 17"
# 177036 13 x 19"
# 176573 13 7/8" x 19"


Also a, 17" pitch BRP designed propeller may not be the same as other manufactures. Stiletto and Turbo props seem to run taller than some others. In other words a 17" BRP" my run like a 15" Stiletto / Turbo. Different prop models can also run better or worse at different mounting heights.

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That's correct Jeff...

We still can't buy a prop by diameter for a particular motor.....
The engineers change the diameter due to many other factors like cupped, double cupped, bow lifting, stern lifting, etc....

Leave the diameter of the prop to the engineers.

Like I mentioned above, 17 pitch props are not all the same.
A person can try different brands of the same pitch props to see what works for them.
When trying a different brand, they may have to go up or down in pitch to get the result they are looking for.

So, again for everyone.... Forget about diameter.... It really means nothing to us.

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Jeff,

You edited your post after I posted.
Those numbers you gave us can't possibly be for the same engine.
Let us know what engines those props are for.
Different years, different gear cases, V4, V6, etc.... all use different props...

If anyone else thinks you have a choice in diameter of the prop, please post it here.
I'll challenge anyone to this.
Find a prop manufacturer. Put in your engine. See what size pitch props are available....
Although the diameter may vary from manufacturer to manufacturer, we still don't have a choice in diameter when choosing a pitch...

I have never see this for any one engine. This is an example:
13 3/8 x 17 pitch
13 1/2 x 17 pitch
13 5/8 x 17 pitch
13 3/4 x 17 pitch
etc....

As you can see from my link above on the Viper...
Even though they may be the same diameter, the diameter could vary for the different pitches.
We have no control of the diameter for any one engine in a certain pitch and brand...
The engineers take care of that for us.

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Claude,

For the E-TEC 75 on a Newport you want either a 15" Viper/SST/SSP or a 13" Stiletto Advantage or Turbo 1.

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Sorry,

The numbers I did not mean to post but, Diameter and Pitch I did mean to post when I copied them from another database. Though, those numbers I believe may correspond to the old OMC part numbers.

SST Prop Sizes
13 3/8" x 17"(NS)
13 7/8" x 17"(S)
13 x 19" (NS)
13 7/8" x 19"(S)

The sizes listed above were for the 13 spline SSTs that fit the intermediate gearcase and were available over the years past. One was a swept (s) design and the other in the corresponding pitch was a nonswept (ns). They still can be found used and as NOS at some dealers. While BRP no longer sells the "SST", that does not mean they could / should be discounted in new repower situations.

So, can you go right to a dealer and buy a specific model of propeller from a manufacture in varying diameters in a specific pitch? I would say in most if not all cases, nope.

Can you still source props in the same model, same pitch and varying diameters? I think so, in NOS or used which is where my head was at all along.

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After Digging around though, I did finally find info on Sal A's E-Tec Repower with a 75 on his Montauk which should help Sisslechest a bit. Sal's motor is mounted what looks to be one hole up and he ended up with a 15" Viper though he did not post and final performance numbers.

In that thread also, Tom W Clark commented on Stiletto props to consider (as he did above).

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Gents

Thanks for the very useful information. As a newbie boat owner, I did not realize all these factors need to be considered. Now I know.

I will check the mounting holes and get back to you. I may have the dealer just let me try the 15 pitch Viper and do some testing and comparison of my own.

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To add some clarification to Jeff's posts, the OMC SST model of propeller has been made for several decades. It was the first popular and common recreational stainless steel outboard propeller and it's various designs have stood up very well. It was a propeller ahead of it time.

The older 13-3/8" x 17" and the 13" x 19" sizes are what BRP started calling the non-swept "NS" designs.

The 13-7/8" diameter models have a more modern swept "S" blade design and these SST models are the except same propeller as the Viper models. The Viper is polished, the SST is not. There is no performance difference between them, it is purely cosmetic.

The SST has (sort of) been discontinued with the SSP model taking its place in the older NS design.

SSP stands for Stainless Steel Painted

SST stood for Stainless Steel Teflon (coated) back in the 1970s and 1980s though I think they simply started painting them in the late 1980s. The Teflon was more of a marketing gimmick that anything that actually enhanced performance.

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Jeff,
You are getting close but you are grouping 2 different styles of props together.. The NS and the S. We can't group different styles together in one list.
Separate the 2 prop designs and you still can't choose diameter.
You can only choose pitch.

13 3/8" x 17"(NS)
13 x 19" (NS)
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13 7/8" x 17"(S)
13 7/8" x 19"(S)

We also don't want to group other materials of props together in the same list like Aluminum or Stainless as they may be different diameters.
I think everyone is getting the picture now about diameter. Forget about diameter...
Concern yourself with the pitch and brand.

Sisslechest,
As long as the engine falls within the manufacturers listed WOT with a certain prop, then you are OK.
I had 2 props for my prior 1978 Montauk which is very close to the Newport model.
I had an Evinrude 70hp motor on it.
I also had a 15 pitch and a 17 pitch. Both were OMC aluminum props.
The 15 pitch would give me a better hole shot and the 17 pitch would give me more top end speed. Both fell within the operating range of WOT RPM's...

At the time, a buddy of mine had a 1977 Montauk with the same Evinrude 70hp that I had.
I used the 15 pitch and he used the 17 pitch props and we started a race.
I beat him out of the hole by a long shot...
It took him about a mile or two to finally catch up to me.
So, it depends on what your needs are.
At the time I also water skied so the 15 pitch was my choice for hole shot and the 17 pitch I had as a spare or could be used when I wanted more top end speed for longer runs to fishing grounds.

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Thanks Joe and Everyone Else.

I guess if I switch to the 15, I will get more rpm at WOT, but more than likely no more speed - sounds like a bit less. I am pretty happy with the hole shot as is - compared to my old yamaha 70 anyway.

Claude