HELP w/1998 Mariner 50 4 stroke Big Foot Lower Unit

[snooks2005]

Re: HELP w/1998 Mariner 50 4 stroke Big Foot Lower Unit

yeah everybody seems to be out of ideas what tuneups would you suggest?

 

[BillP]

Re: HELP w/1998 Mariner 50 4 stroke Big Foot Lower Unit

Two suggestions...reduce the prop diameter and use a 4 blade prop on jackplates...pitch way up if you are mostly running with the jackplate up. Put a Doelfin on it. The Doelfin let me get approx 5 mph faster just by letting me trim higher...expecially so if you are using a 3 blade. Don't forget the low water pickup and presure gage when getting this high.

 

[snooks2005]

Re: HELP w/1998 Mariner 50 4 stroke Big Foot Lower Unit

BillP.....I have already tried the smallest diameter 4 bladed prop that power tech makes which is a 12 3/4 x 12 pitch. So what you are saying is to have the diameter of this prop reduced?

 

[BillP]

Re: HELP w/1998 Mariner 50 4 stroke Big Foot Lower Unit

You need less diameter and lots more pitch to make approx 6000 at full throttle while jacked up. If you can't find a stock 4 blade look for a 3 and size for around maybe 18 pitch. This stuff is really trial and error. Math only gets you to the starting gate. <br /><br />Your 3 blade may be much better if you try the Doelfin...I would do that before anything else. The one I added made a whopping big difference at top end. It reduced cavitation/ventillation a huge amount when trimmed up. You have another 400 rpms to play with...presuming the max is 6000? I currently have a Mariner 50 4s with 2:0 gearcase and the max is 6000...3 blade propped at 5600 on a 20' pontoon.<br /><br />I ran in a hardcore flats boat that was pitched at 27 (yes 27)on a 4 blade. This one had a 175 Merc and all the go fast goodies for shallow running. It literally screwed through soft bottom in ankle deep water at 45mph with 2 up...it ran 65 in clean water. It was a 20 "Crossover" (650lbs kevlar)and made in your neck of the woods.