high thrust prop

SkiDad

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Jul 18, 2010
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If we switch to a high thrust prop on a pontoon will it got faster or slower than a standard prop ?

try to help our neighbor with a new prop and he doesn't get all the rpm with a 14x11 but it's running well other wise. 12-15 mph depending on the load. 60 HP bigfoot on a 22" pontoon
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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depends.....what is your WOT RPM now? you state he doesnt get all the RPM, which means he is over-propped now or too deep.

is your prop depth correct?
 

SkiDad

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It’s not my boat. But last tirne we were out it got around 4600-4800. I’m not sure it’s over propped because it accelerates very quickly but I know it should hitting at least 5000 or so. How do I tell if the engine is too deep on a pontoon.
 

WesNewell

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Jan 3, 2018
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497
wot rpm should be 5500-600 rpm. AT wot, waterline should be no higher than the splash plate for a pontoon.That's the top plate, not the av plate. Having the water line even with the av plate is ideal, but with pontoons, that may leave it sucking air in choppy water. You can find the recommended prop here if you know the specs on the toon.
https://www.mercurymarine.com/en/us/propellers/selector/#!/step-one
 

Sea Rider

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Sep 20, 2008
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If water flow at speed skims right over the uuper small plate motor will produce side, back or even over transom water splashes which will slow combo down. Best top prop thrust is achievedt right under small plate with motor trimed to 90 deg and deck weight evenly distributed.

Will need to drop at least 2 pitches from current one to pull wot revs much higher...

Click image for larger version  Name:	WF through UWDP.JPG Views:	1 Size:	83.1 KB ID:	10745096

BTW, this setting works spot on for any newer motor having at least 4 inches heights between upper and lower plates.

Happy Boating
 

ahicks

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Sep 16, 2013
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If we switch to a high thrust prop on a pontoon will it got faster or slower than a standard prop ?

try to help our neighbor with a new prop and he doesn't get all the rpm with a 14x11 but it's running well other wise. 12-15 mph depending on the load. 60 HP bigfoot on a 22" pontoon

First, there's no such thing as a "standard" prop. Even when talking the "right" prop, there's different strokes for different folks.

A "high thrust" prop will generally sacrifice top speed to gain more "bite" (traction?) on the water (that's the whole idea behind the "Bigfoot" option). You would do that to increase low speed maneuverability, or possibly when pulling/towing (a tube for instance).

My questions are, will the new owner ever be pulling anything? Is there an interest in attaining the most top speed available? If no, the prop he has now may be just fine.

And last, if this Merc is a 4 stroke, my experience is they sound a lot less "busy" at 5k than they do at max suggested rpm, and there's very little difference in speed between that available at 5k vs. 5.6k. -Al
 

SkiDad

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We are going with them tonight. I’ll check out the height. I know the prop is all chewed up so we are definitely going with another 14x11. He does what another 2 Mph and I think it’s possible with a undamaged prop.
 

SkiDad

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sorry for the long delay. We got a chance to change the prop on the neighbors pontoon boat. Went from a 14x11 Mecury to a 14x11 Solas prop.

on the same day the top speeds were
Mercury - 14 mph @ 4800
Solas - 15 mph @ 4800

I was hoping the solas would get the RPMs up a little but no dice. I looked at the linkage on the engine and it seems that it goes fully open when they push the throttle all the way forward (I checked while we stopped to swim)

is this just the nature of the boat they have ? - i would have like to see 5500 rpm but maybe it's just too heavy of a craft. The engine height seems good as well. I don't think they want to go any lower in pitch.
 

JLesko

Cadet
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Jul 10, 2019
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15
Between those two props is very little difference. Call Turning Point and speak to Phil. Tell him what you have and the boat info. I had a 112 on a 19 foot center console running a 13.75 x 17. The boat would only run up to 4300 rpm. Top speed was 30 mph, but took forever to get on step. I went to a 14 x 13 prop he recommended. I now plane within 5 seconds. Rpm’s jumped to 5800. A little high, but I am just mindful of the throttle...The trade off was losing 6 mph on the top speed. It is a heavy boat and I don’t usually go over 22mph and 5000 rpm, so the prop he recommended worked great. You may have to try a few different ones to find a good compromise between speed and power...
 

QBhoy

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Mar 10, 2016
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Hi
the big foot usually has a high thrust prop. In fact it’s specifically designed for high thrust low end power. Even the gearbox is different from the normal equivalent. The result of which is just as you describe. Strong pick up low down. Down side is they usually don’t shine in the top end of things.
 

SkiDad

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Jul 18, 2010
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from what I can tell neither the mercury black max or solas prop i bought were the high thrust versions. I didn't get the high thrust b/c I figured it would loose speed. from what I can tell the gear case is 2.3:1 so at my numbers I'm getting 30% slip - which seems really high to me.

i got Solas Rubex 9411-140-11
 
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