3 Blade to 4 Blade

[Eddie Payne]

I have a 2008 Z7 with a 175 ProXS. The stock prop is a 24P Tempest Plus. With the boat as level as I can get it I measured prop centerline to floor and pad to floor and am at about 3" below pad which is the height I bought it at. Performance is okay, I can bump 64mph GPS but the chine gets bad.



I bought a 24p Trophy Plus and run it in the summer, better hole shot and overall handling when it is hot here in the south.



Last week I ran the Trophy and with it a 1/2" higher, I got an alarm while making turns, looked like I was loosing water pressure. I lowered it back down and all was good. Max speed was around 60-61. Water temp was 88, air near 100 in Arkansas. I know that has a lot to do with it.



My question is do I need to drop the Tempest down a bit? The hole shot sucks with two people on board with the Tempest.



On the Trophy, do I need to drop down a pitch to a 23 when going from a 3 to 4 blade prop?



Just looking for any thoughts one way or the other.



Thanks.

 

[Bob Bourget2]

Merc props are generally pitch for pitch. What is your water pressure with the tempest?

 

[Eddie Payne]

Bob thanks for that. I want to say between 10-15 psi. I watch it but not as close as I should. One day I will have the Mercmonitor in my boat!

 

[Bob Bourget2]

The correct operating pressure for that motor is 11-14 psi at WOT. I personally like to see a minimum of 15PSI. Keep jacking that motor up, and watch the pressure gauge!!

 

[Eddie Payne]

Bob is it normal to get an alarm while making a high speed turn? I was on Lake Ouachita last week running the Trophy, 3 times I got an alarm while turning at over 55 mph.



It sounds like I am in the range on the water pressure, but will jack it up a 1/4" and see what I get.



I am considering having the Tempest B&B'd this fall and maybe add a little cup to help with the hole shot. The Z7 is notoriously bad with two fat men in it!



Love my motor though.

Thanks.

 

[Bob Bourget2]

It is common to see a loss of water pressure in turns....just be aware that this "phenomenon" can happen, watch your gauges and you'll be good to go.

 

[Eddie Payne]

Thanks for that piece of info.

 

[Jim B]

E5Zero,

I have the same combo as you do. I run mine with the motor 2 3/4" below pad and i run a 24 tempest plus that i have also sent out to DAH propeller to have it blueprinted. I also plugged the top three intake holes per Bob's advice when i first got the boat. I get between 15-20psi wide open out of mine. I can run mine right up to ~67 and change loaded to fish the way its setup now. Chine walk is not really a problem on mine, it did walk a little when i first got it(if i let it do it) but once i got the engine height dialed in and the prop worked it's been a non issue. I have to be loaded really light on gear and fuel and make no wheel corrections to make it walk now.



I have also tried a 24 trophy plus(actually i have tried 3) and i dont think a 24 is enough prop on the trophy. I can easily hit 6k on the tach barely getting to half trim. I have lowered the motor as far as 3 1/2" below pad and it still feels like it never hooks up. I also was not one bit impressed with the holeshot, it was far worse then my tempest until i put a cavitation ring on it then it was ok but not really any better then the tempest. My boat also ran ~6mph slower with the trophy on it vs the tempest i have. Maybe Bob has some input on my situation although i think i know what he is going to tell me....



I have tried every combo of props and motor height i can think of and i keep going back to the worked tempest and 2 3/4". Mine seems pretty dialed in like that.

 

[Eddie Payne]

Jim that is good info. I think we have talked about DAH before. I may get mine done by a guy on Lake Fork. I may jack mine up with the Tempest and see what it does.



For me in the hot weather down here the Trophy does a lot better on hole shots when I am by myself, but put a load in and it is no better than the Tempest. I agree I lost speed as well.