Call Out To Those With 170/175 Hulls

[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]

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.

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]

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.

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

[CTsalt12]

Believe my prop is 19 pitch.  It's a quicksilver 2038P19, so I'm guessing p19 is pith of 19.  Gets me right up on plane.  Can't say I ever really try to max out RPMs but definitely will hit 5000.  With a Merc 115 I probably top out around 36, engine is getting a little tired though so I wouldn't place much weight in those numbers

[Brendanpd28]

1976 170. 1988 Evinrude 88 SPL. This is the only data I have right now since I just launched last Sunday.

Prop - 13.5*15
WOT - 35 MPH (GPS Speed) / 5100 RPM

*2 people / 24 gallons of fuel*

[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.

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

I just need to clean and rebuild them. I have a topic on the rebuild thread for the 170's. I am having an issue with it loosing prime after it sits after initial start up. big plume of smoke then runs fine. think the needle is not closing all the way. Have the kits on order, just waiting for them

[boatnamesue]

Well after a long prop search I believe I've found the right one. At least the engine/boat performed a heck of a lot better with it than the 21" pitch prop I've been using. Here's the details for those interested:

'76 Aquasport 170
'98 Yamaha S115TLRW (spec rpm range @ WOT 4500-5500)
Total Test Load: 1850lbs
Test Conditions: Crappy
Test Prop: Quicksilver Renegade 13 x 18 SS Non-vented

RPM.. MPH.. Slip
3500.. 26 .. 13
3900.. 30.. 9
4300.. 34.. 8
4700.. 37.. 8
5100.. 43.. 1
5400.. 45.. 2


The 21" prop I've been using is a Michigan Wheel Apollo SS 13.25 x 21, SS, vented. At 3700 rpms and 31 mph the slip was 15. At WOT rpms of 4700, 40 mph, slip was 14.

The drop down of 3" of pitch to the 18" prop got me an increase of 700 rpms and 5 mph. Kinda anxious to see the performance in perfect conditions. What a difference 3" of pitch can make with performance. My engine was screaming as I've never heard it scream before. And you know 2 strokes can scream!

[hudsport]

i found the best prop for my 1990 174 with 90 hp etec was a  s/s viper 13-7/8 x 15 , boat with a full tank of gas good seas and i get 38 mph at 5400 rpms, good hole shot also. I have a jack plate and trim tabs also.

[CTsalt12]

Hi All,

Reviving a prop thread from the grave.  I'm thinking about making the move from a 3 blade to a 4 blade.  I run a 16 pitch now on my 175 with a 90 HP.  I top out around 35 with an average load, 47 light load/flat water, and about 5200 RPM.  However, my reasons for the switch are not speed related, it's about handling.

I heard from a friend running 4 blade on an 18 Parker that the difference in ride in rough water is very noticeable.  It seems a 4 blade gives more 'grip', more stern lift,  more boat out of the water and allows your bow V to cut the waves as opposed to waves making contact farther in the stern, and a lower planning speed.  Bottom line I'm told it really improves rough water performance. 

Wanted to see if anyone had experience with 4 blades?

[boatnamesue]

Agree w/4 blade planing at lower speed and better hole shot.  You will lose top end speed as result.  Aside from excessive prop slip which will effect forward acceleration, which in turn effects overall hull performance, the number of prop blades does not effect how the hull performs. 

No matter the number of blades, the bow digging in to water decreases rpms with same throttle level position as when bow is not digging in.  Hence using the tilt/trim to adjust bow angle and entry.  Also, the 170 is sensitive to where weight is positioned.  Before considering changing props, experiment with changing bow angle and shifting weight aft or fwd.