Aquasport Mechanicals - things that need a wrench, screwdriver or multimeter > Props

Call Out To Those With 170/175 Hulls

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boatnamesue:
For those who are operating a 170 or 175 model, I'd like to learn what hp engine you have but more specifically what prop pitch you're using (and meeting top end of engine spec rpm range).

I have a Yamaha 115hp 2 stroke with a 21" pitch.  It's the prop that came with boat/motor when I purchased from previous owner.  The spec rpm range at WOT for my engine is 4500-5500.  At WOT I can top out at 4700 rpms and 41mph.  I had the opportunity to trial my friends yamaha K series 17" prop.  The results were:

* Far better hole shot, but rpms were 4800-5000 as boat leveled out.  With my 21" the boat levels out round 3200.

* At WOT top rpms were 5700 and 41mph (same max speed as my 21")

* Cruising speed of 30-32 mph and 4600 rpms.  With my 21", I can maintain the same cruising speed with 3600-3700 rpms.

So needless to say the 17" pitch is too low for my boat.  I recon a 18" or 19" pitch will be a perfect fit.  But I'd like to hear from y'all running a similar hull as mine and learn if you've found a particular prop that hits the sweet spot for your boat.

wingtime:
Your over propped.  You want o be able to hit the max WOT RPM with a light load.  Also check to see where your cavitation plate is riding on a plane. Too low and that will cost ya some speed and RPMS.  Your lugging your motor with your current prop.

boatnamesue:

--- Quote from: wingtime on June 01, 2017, 10:39:32 PM ---Your over propped.  You want o be able to hit the max WOT RPM with a light load.  Also check to see where your cavitation plate is riding on a plane. Too low and that will cost ya some speed and RPMS.  Your lugging your motor with your current prop.

--- End quote ---

Yes, you are correct.  Knowing this is the reason why I started this thread.  I'm hoping to learn what prop pitch others are using that operate the same or similar hull. 

My AV plate is level with the bottom of hull.  You make a valid point to raise the engine.  I've entertained this idea of raising engine up by one notch, which puts the AV plate 3/4" above the bottom of hull.  However, even if I made this adjustment it would not result in an increase of 800 rpms.  Maybe a few hundred at most.  But the issue is a over propped boat as you mentioned.  Thus I need to fix the issue causing the low rpms, which is prop related. 

minionsram:
115 evinrude. upper most hole my cav plate is at top of water, no cav except in tight turns. Im running a 13*19 Factory prop. jumps out hole great and planes out quick. my rpms are at 5000-5200 at wot. best speed was 42 with just me the gear and half a tank of fuel. I am having an issue with my carbs right now though. oh and the prop has one bent flight on it.

boatnamesue:

--- Quote from: minionsram on June 01, 2017, 11:19:56 PM ---115 evinrude. upper most hole my cav plate is at top of water, no cav except in tight turns. Im running a 13*19 Factory prop. jumps out hole great and planes out quick. my rpms are at 5000-5200 at wot. best speed was 42 with just me the gear and half a tank of fuel. I am having an issue with my carbs right now though. oh and the prop has one bent flight on it.

--- End quote ---

Right on, thanks for the response.  What's your carb issue?  I service my own carbs, might be able to help.

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