Prop question for 95 MA 185

[jackstraw2169]

So I changed my prop to see if I could get better performance and went for a test drive today.

1995 MA 185 with 2004 yamaha F115

I had a 4blade, 17P custom prop, 12.5" diameter. Hole shot was really good in my opinion with top end speed around 38 mph. RPMs at WOT were a little high, around 6200-6400. This was the reason I wanted to change and see if a different prop would bring my RPMs down to around 5800-6000. 

I found a deal on a used 4 blade Solas 19P, 13" diameter prop in near perfect condition and thought that pitch would put me right where I wanted to be and maybe even pick up a few MPH as well. I knew the hole shot would suffer but I didn't expect it to be as bad as it actually was. It was horrible. And to top it off, WOT RPMs dropped to 4800 and only 36 MPH!! So here is my question, why would they drop so drastically? I was thinking it would drop around 400 or maybe 600 tops....but 1400?? And my top end speed dropped a little.....makes no sense to me.

Honestly, I'm really not to worried about it. Just curious. I plan on putting my old prop back on and moving on. I never run at WOT anyway. Anyone need a Solas prop? I have one for sale. 

Thanks in advance for any input.

[Wardolb]

 I don’t really know much about about props but from what i understand you went up 2” in pitch and are running a larger diameter prop. I think that would definitely drop your rpms.

I learned a long time ago you can’t go all half cocked when it comes to prop selection. You can call or email power tech and they’ll help you out.

[jackstraw2169]

Thanks for the reply. I was wanting my RPMs to drop....just not that much. I had a local  prop guy, who carries power tech in his shop, tell me to go to a 19P and I also talked to a power tech rep over the phone who was very helpful and knowledgeable. I guess that's why I'm so surprised how drastic the change was. 

[whichwaysup]

21 hours ago, jackstraw2169 said:

Thanks for the reply. I was wanting my RPMs to drop....just not that much. I had a local  prop guy, who carries power tech in his shop, tell me to go to a 19P and I also talked to a power tech rep over the phone who was very helpful and knowledgeable. I guess that's why I'm so surprised how drastic the change was. 

My 18 MA has a 150 Vmax on it and I'm running a 3 blade 14.5 diameter 19P prop.    You have a 115 with a 4 blade 13" diameter and 19P.   That seems like a lot of prop relative to your HP.   I don't run a 4 blade, but it seems like maybe your prop guy was thinking you were running a 150.  Is that possible? 

[dabear]

3 hours ago, whichwaysup said:

My 18 MA has a 150 Vmax on it and I'm running a 3 blade 14.5 diameter 19P prop.    You have a 115 with a 4 blade 13" diameter and 19P.   That seems like a lot of prop relative to your HP.   I don't run a 4 blade, but it seems like maybe your prop guy was thinking you were running a 150.  Is that possible? 

If everything was the same that would make sense. If the gear ratio on his F 115 isn’t the same as the gear ratio on your 150 VMax that would change everything .  May be worth checking the lower unit ratio than plug all the info into a prop slip calculator . Gigantic difference between a 2.15 ratio and a 1.81  . If nothing else it’s interesting to plug in the numbers . They won’t be the same as real word numbers but will give you a idea how much the ratio will change everything . 

[jackstraw2169]

this is interesting

Old prop

 

New prop