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Old 20 April 2017, 15:08   #1
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Country: USA
Town: Simi Valley
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Prop Upgrade on SR4.7

I have 2011 Searider SR4.7 with a 2015 E-tec 60 on it. Its set up as a center console with leaning post. It currently tops out at 31 MPH with two freedivers w/ spearfishing gear, 24 gallons of fuel, cooler, etc. I'd like to get a little more top speed out of it since I typically go out when the conditions are nice and I am always covering a lot of ground.

Its currently propped with an aluminum 13.5" X 15 pitch. Planes at 16-17 MPH and I can hit the rev limiter at 6200 RPM all day. I'd have no problem justifying the expense for a stainless prop in a different size if it could reasonably score me another 5+ MPH. Any advice on what a max size prop for this setup may be? Is 13.25" x 17 too much?

Attached a couple pics to show the layout if that helps.
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Old 20 April 2017, 15:43   #2
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Country: UK - England
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Make: Ribcraft 4.8 shiny
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Engine: ETec 60. Very shiny
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I run a 4.8m Ribcraft 60HP etec with similar light to medium loads with stainless 17 inch pitch no problem.

If you want 5 knots plus extra the increase in pitch to 17 inch might not get you there. However you will notice the biggest improvement in hole shot to mid range revs.
Very light loads a 19 inch stainless does get that speed.

Speed (and indeed size) isn't everything!
Chuckles
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Old 20 April 2017, 16:52   #3
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Quote:
Originally Posted by congerman View Post
I run a 4.8m Ribcraft 60HP etec with similar light to medium loads with stainless 17 inch pitch no problem.

If you want 5 knots plus extra the increase in pitch to 17 inch might not get you there. However you will notice the biggest improvement in hole shot to mid range revs.
Very light loads a 19 inch stainless does get that speed.

Speed (and indeed size) isn't everything!
Chuckles
Do you think there would be any top end gains? I'm planning to add a t-top at some point in the near future as well, not sure I could get away with a 19 pitch and still get into WOT RPM. I believe the range for my engine is 5500-6000
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Old 20 April 2017, 16:57   #4
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Try a 13x19.

You'll probably find that WOT is too much for rough seas anyways. Should net you a better cruising fuel economy.
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Old 20 April 2017, 19:56   #5
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Country: Australia
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I found that a stainless prop in exactly the same pitch and size as aloy will bring the rpm down by quit a large amount (yes the speed will go up in the same size). By jumping two pitch sizes as people are recommending will end in a large drop in reaching the important max rpm.

With a 13.5 x 15 aluminium on my F70 I achieved a max rpm of 5900, the same in stainless gave me 5400rpm. Im currently running a 13. 3/4 x 13 solas saturn stainless which gives me a max rpm of 6100rpm (200 below engine max). As you can see from these figures its not that easy to just grab a prop two pitches higher and expect to get it right (you may be lucky etec two strokes knock out more power) but even if your supplier does allow exchange postage on these heavy bulky items postage can soon add up if you don't get it right first time. Contact experts or at least fill in there prop selection tables.

Its free to contact experts such as solas propellors who will get you where you want to be in terms of pitch and size, theres also a table you can fill in to find this out on their website.

Im constantly picking free-divers up so constantly in and out of gear near washes and reef, the stainless are harder on the gearbox for this kind of work. I found the prop Im currently using gives me good hole shot for working through surf but also holds speed when working long distances in big swell without having to constantly work the throttle as much as the aloy (it holds grip better).
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Old 20 April 2017, 20:17   #6
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Just had a close look at your setup which looks like you may have a 45lt + smaller 20lt ish tank I would of expected the bigger tank to of been more than enough for a big day out. What range are you getting with the etec as I thought they were better on fuel than my F70 that gives me a burn of at worst 3km per litre and when working with spearo's a full day on about 10-12 lt. Just an observation as you may be able to lighten up the load for a fraction more speed and gain more space.

Also your tubes look very shinny, what are you putting on them

By the way thats an awesome fun looking little setup, you cant beat these small outfits for what we do.

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Old 21 April 2017, 01:08   #7
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Country: Ireland
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I run an etec sixty on a 4.9 m valiant rib. I have owned it for eight years. I have found that the 13.25 x17 Wii prop is my go to prop. I use a fuel burn calculation of 1.3 nm to the liter.(1.5 statute mi!We to liter). My Max rev oon the clock is circa 6200. But I think that these clocks have a habit of reading 200 RPM high. I also have a 13 x19 prop which is fine. But for what i use the boat for it is perfect.. figures based on two men circa twenty six stone and fifty two ltrs of petrol.

Tsm
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Old 21 April 2017, 05:38   #8
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I'm just trying to get my head around the figure of planing at 16 17 mph, you must have quite a different shape hull or a very inefficient prop as mine is up on the plane at 14 to 16 kms.

Comparing different hulls can be tricky as some ride with the tubes clear of the water causing no drag, where my Zodiac has the rear of the tubes in the water even flat out. Some hulls have very deep v for handling rougher water while boats with low or moderate v will perform quite differently.

Is there anyone on here who could lend you a stainless 15 or 17 to see if you still reach max rpm, I feel sure the 17 would get you that speed but will it still get the engine up around its max rpm.

Some people don't realise what harm they may be doing propping engines that rev out to 5000rpm when they should be reaching 6300.
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Old 21 April 2017, 06:10   #9
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Country: Other
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i have a 4.80 rib at similar weight and 2015 etec 60hp
my current prop is 13.25x17 alu
with one freediver + 45 lt fuel 50 lt igloo coller my top speed is 38 mph on smooth sea engine rpm is 5750 on rough sea 36 mph
with 2-3 freediver top speed at wot is 35 mph and
i have a avarage consuption of 0.5 lt / Nm
on plane rpm is 3400 rpm
dont hesitate to switch to 13.25 x17 pitch over all fuel consuption on 20-25 mph is important for maximum milage
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Old 21 April 2017, 07:11   #10
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Country: Ireland
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Before​ Messi g with props you must ensure the engine is at the correct height. The etec likes to run high. I.e.one hole up. If raising the engine be sure to support the engine saddles. Look up a thread "the curse of kerny" for reasons to support saddles.


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