Yet another prop thread...

[Milehibird]

Yeah I know what you're thinking...."Not another one!" Well, yes. But here's the problem I'm having. The boat takes probably a good 6-7 seconds to get on plane. I bought it just outside Knoxville (~800-900' altitude) and brought it up to Denver (~4500-6000' altitude depending on lake). In TN it was set up with a 4 blade and would run over 60 pretty easy (I think we hit 62 on the test drive). Up here, of course, nowhere near that. I've topped it out at about 4800rpm and about 50mph. Now, the problems. 1. The prop has zero markings on it anywhere so I have no idea what I'm starting with. 2. There isn't any Yamaha dealers within 2 hours of me that I can take it to easily. So, all that being said, anyone have a recommendation for a prop? I figure if I drop 2" pitch from a good sea level prop that would be a good starting point. Boat is in sig (2001 187 DC/1999 Yamaha F175 carb motor).

Thanks,

[STLBassBuster]

A 175 would normally spin a 23-24p 4 blade so drop down to a 21-22P. 3 blade you could try a 22 or 23p.

[MMosher]

23 P Tempest or 23M Yamaha.

[Bruce2]

If you take the prop off pitch maybe stamped on the backside of the hub that goes towards motor.

[Milehibird]

Thanks, I was wondering since I couldn't see anything. Bruce, I'll have to look at that, unfortunately with how small my garage is, the only way to get to the prop is to take the boat out and I don't think about it then. Guess I should remind myself next time I take it out. Also, is there any reason to go to a 3 blade on these hulls? I've heard 4 blades handle better and get on plane quicker. Maybe out of state at lower elevations I could make more use of a 3 blade (where there aren't speed limits on the water).

[MMosher]

Speed limits on lakes? F that.

[spookyg]

good afternoon sir. high altitude is a huge performance robber. if you're at 6000 feet, your 175 loses @ 18% of its output. that makes it effectively a 144 based on the math. there's no way to regain the horsepower without forced induction. you have to fool the engine into turning more rpms. maybe 2 pitches lower. my lake is at 4200 feet and to run the same winter rpms in the summer i will have to drop down 1 inch from a 23 to a 22.

[tomloans]

Prop to pad distance? It sound like the prop is too low. Measure it. There are instructions here on the forum. Do a search. This is the first thing to do before u start spending money and time. Let us know. Also what size is your jack plate?

[Milehibird]

Prop to pad distance? It sound like the prop is too low. Measure it. There are instructions here on the forum. Do a search. This is the first thing to do before u start spending money and time. Let us know. Also what size is your jack plate?

Ok, I tried this. So, first things first, it looks like an 8" Slidemaster jackplate. Now, for prop to pad...either I did something wrong, or you're dead on. To correct myself, the pad would be the lowest part, right below the drain plug, etc. correct? If that's correct, then unless I really screwed up leveling the boat (or my garage is not even remotely close to flat or level), I'm coming up with a P2P of 5", but (and this is the totally unscientific method) looking at it, I don't see how it's a 5" difference. I should be able to tell the difference between 3.5" and 5".

It got on plane quick when I test drove it in TN and drove great. It's just slower since there's less air and thus less power up here. At a lower elevation lake (3900') I could get to about 4900-5000rpm and 53-54mph with 2 people and a lot of tackle (and a heavy driver).

[grout-scout]

Most guys in the higher elevations are running verados because of their superchargers. I bet you need around a 23" prop.

[Milehibird]

Most guys in the higher elevations are running verados because of their superchargers. I bet you need around a 23" prop.

That seems to be the consensus is about a 23" for a 3 blade. But now I'm questioning the P2P on this boat.

[grout-scout]

Nobody knows unless you measured it properly. Everyone here will tell you 3.5", but after trying 5 different props I run most of mine around 4". The only one I can run shallow is a bravo xs and I don't gain anything with it being shallow.

Edit: Crap, I thought I was responding to the guy with a 206. Your 2 screen names are pretty close.

My buddy has a 190 and has to run his prop to pad around 5", anything shallower and it loses speed.

[tomloans]

Prop to pad is always the first adjustment before u start spending money on props. You need a level for the pad {below the drain hole) and the cavitation plate. Then you can properly measure. Once u set this to 4" then go try the same prop again. Watch your water pressure. If your p2p was 5 inches and you set it to 4 inches, your rpm should increase about 400 to 500. I kid you not. But please don't guess or eyeball it. Do it with a level. And watch your water pressure at wot. If the prop is too high your pressure will decrease as you trim up. This means it may be a a little too high. Every 1/4 inch matters at this point. If water pressure is down then drop it 1/4 inch until is goes back to full. Then you have perfection and can properly pick the prop and spend money once. See below

http://www.bbcboards.net/showthread.php?t=62660

[grout-scout]

Actually every single prop runs at different heights, there is no proper prop to pad for every prop made. Some run deeper (fury) and some shallower (bravo); with the temptest being in the middle.

[Milehibird]

So for those familiar with the 187, what should the p2p be? I know everyone says to start at 3.5" for every boat, and others here have said the 18' champs run best deeper. This is for a 2 stroke Yamaha 175 as well, not a mercury (which I've heard different motors also have different p2p requirements).

[LOSTTEXAN]

Can't buy a "properly propped" boat in Knoxville and take it to Colorado without a prop change unless (possibly) it is a Verado.

[tomloans]

Carefully level the bottom of the boat ( below your drain plug ) using your jack upfront and a level. then level your motor using a level on your cavitation plate. then measure the distance from the pad to the floor ( hopefully your floor is even ) and then measure the center of your prop to the floor and subtract. You cannot eyeball this. Do this first then start moving the motor up about 1/4 inch at a time. Take the boat out every 1/4 and see if it improves. 5" seems to me too low with an 8" set back but it is hard to say. Just try moving the engine up and see how it helps your hole shot.

WATCH YOUR water pressure after you get on the pad at speed. If you have plenty of pressure, motor trimmed at speed with a light load ( one person and half tank ) then you can probably take it up another 1/4 inch until you see that when you trim up at speed, you start to lose pressure. Then you have gone too far. the rest of the day keep it trimmed down enough so you have pressure. when home, drop it back down 1/4" and try again until you hold pressure with a light load. If you are running full throttle and trimmed up and water pressure is pegged at max, you are done. This is the best it can get. If your problem continues then you know the altitude is hurting and you need to get down in pitch but you will know much more precisely since you know your motor height is dialed in.

[tomloans]

and incidentally, I would not go to a 3 blade at high altitude if you want to get out of the hole quickly. 4 blade is the way to go.

[tomloans]

also put your throttle control arm ( or foot pedeal )all the way forward and see if your butterfly valve is open all the way. Take the cowling off and see if it is all the way open. If not adjust so it is. Do this in addition to the dialing in your motor height. Just as a precaution in case something happened in the interim during traveling. You never know. You just dont want to start swapping props without checking a few items.

I have seen much after 40 years of boating. lol

[Milehibird]

Thanks for the advice. Honestly, I'm pretty certain it's just the prop since it ran fine in TN. 4000' of extra elevation robs a lot of power, especially from a carbureted engine.
I will definitely check the carburetors and such to make sure they are opening all the way, but again, I don't think there's any issues other than running rich from altitude and the wrong prop.
I plan to stick with a 4 blade for most in-state stuff, but might go for a 3 blade for going to lower elevations.