mercruiser 888 with a michigan wheel prop # 031037 (obsolete) Help? please

[higgins48627]

well my original question has gone unanswered
​I don't know if I didn't ask properly or what, maybe I broke some sort of protocol
so I am going to try asking for advice from you professionals out there. many of you may have answered similar questions. I found many forum answers about props and have learned much more then when I started
so let me say when it comes to propellers and the math to calculate I just have no idea
​so......
I spoke with a person at IBOATS sales and they recommended a SOLAS AMITA 3 it is a 15.3inch X 19 pitch new propeller for my old 1972 mercruiser 888.
​was and or is this a viable alternative?
only slightly higher RPM's at WOT I was told.
​I had spun the hub in that old prop, and having replaced the hub once before (6 years ago) I just figured it was time to get a new prop and place the rehubbed michigan wheel prop in reserve
upon receiving the new SOLAS prop and placing it on the outdrive the 15.3 inch hits my trim tab
​the old 15.5 inch did not hit
so what am in missing here
​if the pitch is the same and the diameter is 2 tenths smaller why it the SOLAS hitting my trim tab
​also if someone could please explain what I can expect the new prop compared to my old #031037 michigan wheel prop?
​I cannot place the props side by side as old one is still out getting a new hub
any help would be greatly appreciated



original post below



"hey all
I have a 72 slickcraft SS214 with a mercruiser 888
​dry weight 2500
​plate says 1975 pounds max loading
​as far as I know it has always had a michigan wheel prop on it # 031037
I believe its a 15 1/2" X 19 pitch
this size is no longer available
​would love to get slightly better fuel economy other then slowing down
​I am not pulling skiers or tubes just cruising some of the great lakes and lots of inland lakes here in northern michigan
I am looking for a replacement prop
​does anyone have any recommendations?"

 

[Scott06]

The rake on the blades is more on the new prop end of blades are farther back which is why you're hitting the trim tab. This is pretty common when upgrading to a more modern design. Just grind the trim tab to clearance.

On the rpms not sure why it would increase rpm as it's not much diameter difference, I would suspect the new prop has some cup which would reduce slip and thus drop rpms a little.

 

[higgins48627]

thank you scott06
​to cut down my existing trim tab to allow for 1/4" clearance (top and behind new prop) it would only have about 1" wide tab behind the propeller.

what was explained to me is that every 1 inch in diameter plays out to a 200 rpm difference
​as in 2 " smaller results in 400 higher rpm at WOT
​
​I did contact SOLAS they pointed out an offset anode/ trim tab may work. it appears from phots it may fit nicely behind new propeller, have you had any experience with these offset tabs? sierra part #18-6014 or mercury part # 822777q 1
​do you know what I may expect from the rake difference, as in end results in the water?

 

[Scott06]

You can buy the offset trim tab, but I think cutting the existing one leaving 1" of material will be more or less the same. All this is used for is correcting the torque steer inherent to a singl engine application, so,don't over think it.

Rake increase typically adds more bow lift. http://www.mercuryracing.com/prop-school-part-3-blade-rake/

Bottom line I think the recommended prop is a good replacement

 

[higgins48627]

The offset tab worked great
A little close to the new prop for my liking but it clears
The new propeller worked very well
42 mph via GPS trimmed up with slight chop and no vibration like old mi wheel was giving me
Tach is not working (yet) but didn't seem to be any noticeable diff from 15.5 X 19
So thanks again for the input